# Capacitor Banks



## Tesseract (Sep 27, 2008)

TexomaEV said:


> 4. Capacitor Bank, I've only just started testing with this, but so far the results look good. What I'm proposing, is build up a large capacitor bank for the pack voltage you are using, place it between the controller and traction pack. For the most part, paralleled onto your traction pack, as close to the pack as possible....


This is not a half-bad idea, but you want the capacitor bank to be as close as possible to the *controller*, not the battery pack. This will give you two benefits for free: it will cut down on the noise radiated from the battery pack to controller wiring run and the inductance of said wiring will assist the capacitor bank in smoothing out the current pulses to boot.


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## TexomaEV (Jul 26, 2007)

*Re: Personal Experience with Prismatic LiFePO4 Cells*



Tesseract said:


> This is not a half-bad idea, but you want the capacitor bank to be as close as possible to the *controller*, not the battery pack. This will give you two benefits for free: it will cut down on the noise radiated from the battery pack to controller wiring run and the inductance of said wiring will assist the capacitor bank in smoothing out the current pulses to boot.


I'll try that. Currently in the E-Barstool Trike, that I've been playing around with capacitors on, the batteries and controller are just inches away from each other.


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## TexomaEV (Jul 26, 2007)

*Re: Personal Experience with Prismatic LiFePO4 Cells*



Tesseract said:


> This is not a half-bad idea, but you want the capacitor bank to be as close as possible to the *controller*, not the battery pack. This will give you two benefits for free: it will cut down on the noise radiated from the battery pack to controller wiring run and the inductance of said wiring will assist the capacitor bank in smoothing out the current pulses to boot.


Here's a photo of the "Flux Capacitor" we just installed. It is a bank of 40ea, 1100uF, 200vdc capacitors, all wired in parallel. It is then paralleled onto the traction pack. We couldn't find room for it closer to the controller. Why 40 capacitors? I just picked that number, because there are 40ea LiFePO4 cells in this hybrid traction pack.


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## JRP3 (Mar 7, 2008)

*Re: Personal Experience with Prismatic LiFePO4 Cells*

What's the approximate cost of building the original "flux capacitor" and which exact brand caps were used, where did you get them? Also, Beeps/Cloud says "When using the recommended Monitoring Systems we offer a 3 year Warranty." Do you know what specific system they are talking about and is it a full battery management system or just a battery monitoring system?


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## TexomaEV (Jul 26, 2007)

*Re: Personal Experience with Prismatic LiFePO4 Cells*



JRP3 said:


> What's the approximate cost of building the original "flux capacitor" and which exact brand caps were used, where did you get them? Also, Beeps/Cloud says "When using the recommended Monitoring Systems we offer a 3 year Warranty." Do you know what specific system they are talking about and is it a full battery management system or just a battery monitoring system?


I built this capacitor bank out of aprox $85 worth a capacitors and copper tubing. Not fancy, but it helped develop a device that could help others, I hope that others will try it, and help determine how large it needs to be to maximize it's ability to help, yet not over do it, keeping down the cost if there shows to be a peak, where something bigger doesn't help any more. 

These particular capacitors were just some that I found on Ebay. They are 1100uF, 200vdc capacitors made by Mepco/Electra. Main thing is find as large a capacitance you can afford, and make sure they can handle well above the fresh charge out voltage of your pack. Then parallel them up, and connect it up to your pack. You'd want to use something like a 1K 25watt resistor to precharge the bank to your pack's voltage, BEFORE connecting the "Flux Capacitor" otherwise you'll have a very nice but scary fireball.

I believe Beepscom/Cloud is selling the "BEQ1" regulators by www.hotjuiceelectric.com, but the units I'm testing as well, from LL Labs would work as well for warranty issues. Best advice though would be to talk with them for sure. The main thing is the cells have to be individually regulated on the charge cycle, be it individual regulators, or something built into the charger. My personal preference is individual cell regulators, as I don't like an umbilical cord coming from the charger with multiple voltages and grounds going all over the pack, waiting for a short circuit to happen. Then use something like a PakTrakr to monitor the individual cells, or the unit being designed by www.Evie-Systems.com

More photos of the "Flux Capacitor" are at: www.flickr.com/mbarkley


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## TexomaEV (Jul 26, 2007)

*Re: Personal Experience with Prismatic LiFePO4 Cells*



Bowser330 said:


> I wish i had the skills you do Texoma...just to mention, I am from Texas originally...have since moved to southern california...
> 
> I am very hopeful for you and excited about the results of the flux capacitor bank...
> 
> I feel a hybrid pack deep cycle batteries that charge a capacitor bank is the best way to go for a long range ev with the short spurt energy of caps, Plus the absorption of maximum amps from regen...


Thanks for the kind words, My ultimate goal is to help fellow EV'rs improve on what they already have or plan to build. Here is an excerpt from the driver of the pickup before and after the capacitor bank:

" I have to admit, I had a little doubt that the capacitors would make any felt difference. I figured if anything they would only just lenghten the life of the batteries (and would be hard to measure that performance) . I used a large stereo capacitor to try to help stiffen up my DC/DC converter output. I gave up on that capacitor and went for a full time 12 volt deep cycle battery for that because even the capacitor didn't help that DC/DC converter. So you could see why I had started out with some doubt. 

I drove the truck before we put the "flux capacitors" in. We did some more changes to the truck so it needed a test drive. We limited our selves to 90 amp draw for this drive because we don't have the lithium connections that we wanted on the batteries yet. The truck did ok, I was comparing it to how my Fiero drives (I know not a fair comparision but thats what I had to compare it to). The amperage fluxuated a lot while trying to maintain a speed, slight adjustments on the throttle made big amp swings. We only averaged about 45 MPH and probably top speed was 50 MPH. We got back to Mike's place with the truck after about 6 miles. We checked the batteries and connections and did some more modifications. 

The big modification was adding the "flux capacitor" to the pack. Mike's work on the capacitors bank was impressive, just look at his Flickr site! Once we got the capacitors mounted we charged up the capacitor bank. It took a while for it to get up to voltage using the pre-charge resistors. We got it up to 100 or so volts and to fill it up the rest of the way I took the big terminal connection and just hit the battery terminal; a BIG spark later we had a fully loaded capacitor bank (DON'T TOUCH THE CAPACITORS NOW). Mike and I jumped into the truck and took off for our second drive. We didn't plug in the truck because we were working on it. So it still had the previous 6 miles on the pack and it wasn't fully charged in the first place because no regulators yet. But we went on our 2nd test drive of the day. Got through Mike's neighborhood and got onto a 55 MPH road heading out of town. Once I started accelerating on that road, I could already feel a difference. I was getting better acceleration. We accelerated up to 45 MPH (speed limit at that spot) and was able to maintaine that speed with very little amp fluxuations (the previous run we only made it to say 35 or 40 MPH at that time). When the speed limit went up to 55 MPH, we acclerated more and still felt like it had plenty of power. We were abe to get faster, smooth out the amp fluxuations, felt like more power and was able to still do all of this while keeping our 90 amp limit we set. I was blown away on being able to feel a difference. I got a whole new level of an EV grin on the 2nd drive. We went further down the road and turned around at a gas station. Mike waved at the owner of the gas station and we headed back. About the last 1/2 mile we started to loose a little power. We were able to coast the rest of the way to Mike's neighborhood. We drove through his neighborood back to Mike's place and Mike checked the controller and the aluminum plate. It was pretty warm, so the controller was probably cutting back the power so it wouldn't warm up any further. So that would probably be something to look at, a big heat sink on the controller. But over all, I was very impressed with the capacitors. I was actually able to feel and see a difference on the performance of the truck. Of course its not going to turn the truck into a high milage vehicle but it will help with acceleration and probably the longevity of the battery pack (no matter the type of battery). I am convinced to try a capacitor bank on my own EV now. " - NTEAA Member


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## JRP3 (Mar 7, 2008)

*Re: Personal Experience with Prismatic LiFePO4 Cells*

Am I correct in assuming that if one had a 3300uf 200vdc cap you could use 1 third as many for the same result? How did you come up with the 1100uf size for your pack?


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## Bowser330 (Jun 15, 2008)

...cost?...


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## TexomaEV (Jul 26, 2007)

*Re: Personal Experience with Prismatic LiFePO4 Cells*



JRP3 said:


> Am I correct in assuming that if one had a 3300uf 200vdc cap you could use 1 third as many for the same result? How did you come up with the 1100uf size for your pack?


At this point in the capacitor bank experiments, we don't know how large we can go and still see improved results. But the larger your capacitors are in capacitance, will certainly make it easier to put together a nice large bank with less components.

Nothing magic about the 1100uF size, it was what I found cheap on Ebay, that was rated for 200vdc, which was above my pack's charge out voltage. 

I'm building another bank the same size as the first, and will install it on the opposite side of the pickup, keeping the look of the hybrid pack symmetrical,
along with seeing if there is anymore improvement by doubling the size of the overall capacitor bank.


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## Bowser330 (Jun 15, 2008)

*Re: Personal Experience with Prismatic LiFePO4 Cells*

can't wait to hear the results of the double cap pack...

have you thought about trying to see how much regen energy you can store into the flux capacitor pack?


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## TexomaEV (Jul 26, 2007)

*Re: Personal Experience with Prismatic LiFePO4 Cells*



Bowser330 said:


> can't wait to hear the results of the double cap pack...
> 
> have you thought about trying to see how much regen energy you can store into the flux capacitor pack?


Regen would be interesting, but this vehicle is DC based, without regen.

You asked earlier about cost. The current capacitor bank, once all the screws, lockwashers, copper busbar tubing, capacitors, and gorilla tape, came together it all probably came up to no more than $85.


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## dimitri (May 16, 2008)

*Re: Personal Experience with Prismatic LiFePO4 Cells*

Here is an interesting site about building large capacitors bank

http://www.myelectricengine.com/projects/mpdthruster/capacitorbank/capacitorbank.html


I am still struggling to understand actual real benefits of using capacitor bank. Caps are on battery side of the controller, right? So motor still gets its energy in PWM pulses. Caps only smooth out battery current, not motor current. So what is the real benefit? Is it a fact that current drawn from battery in pulses has adverse effect on the battery? Are there any studies or theories to that effect? Does it effect all battery chemistries?

Somehow this whole thing smells like snake oil, I'd like to see actual formulas and graphs that show how caps effect the current pulses, how big does it have to be to actually have meaningful effect, etc. I know I can understand it if someone explains, I am just not smart enough to come up with it on my own. Obviously there are reasons that controllers are filled with caps and having more of them is probably better, but I'd like to know the physics behind it, can someone put it in layman terms? 

TexomaEV, please don't get it wrong, I love the info you share, I just need something more than a "feeling" of improvement, I need actual math and physics behind it. I think that we should be able to calculate optimal size of the cap based on formulas, not just experimenting until it "feels" right.

I know that caps don't store that much enegry, their only benefit is to discharge it super fast, so the benefit has to do with frequency of PWM pulses and ability of the caps to fill in the space between the pulses, am I on the right track here?

Thanks


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## Bowser330 (Jun 15, 2008)

*Re: Personal Experience with Prismatic LiFePO4 Cells*

One of the benefits I think is great is that you dont over task your batteries with high amperage pulses (if you have a cap bank) which will throw your batteries out of indentical charge cycles....so its easier and safer to charge your pack and your pack will last many more charge cycles...

of course i make the above claim relying on texoma's pending test results.


​


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## Zemmo (Sep 13, 2007)

*Re: Personal Experience with Prismatic LiFePO4 Cells*

I'm the one who helped install the caps and did the driving. That message was what I sent to our EAA chapter, I didn't think to send it here on DIY. Thanks for doing that TexomaEV.

I don't know about the formulas to be able to prove why it did what it did. But one proof is the 90 amp draw that we limited our selves too. With out the capacitors, the amps draw was a little harder to keep constant. Also the top speed achieved was lower without the caps. The 2nd drive without recharging but with the caps installed, I was able to keep the amp draw more constant and archived a few more MPH on the same 90 amps on the same road.

Of course this wasn't my own vehicle, so it was all new handling and feeling. But comparing drive 1 to drive 2, there was a difference. That was just the initial test. More tests need to be done to figure out several thing. Like adding a second set of the capacitor bank. 

I was convinced enough to buy a larger (quite a bit larger) capacitor bank for my own EV. So I can see and feel the differences in an EV I drive every day (including the freezing rain we have today). I have more data readout capabilities on my car (and performance history) than the Ranger (which has no performance history at all) so I can get better data. I also have access to an accelerometer so I can test acceleration performance before and after. I already have performance statistics of my car so hopefully I can get a better in depth info about the use of them.


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## ulnpiper (Sep 24, 2008)

*Re: Personal Experience with Prismatic LiFePO4 Cells*

If I understand the capacitor storage formulas correctly, the energy stored in the capacitors you tested was about 0.1375 Kwh

Assuming your battery pack is ~150volts

(1100uf)*40 caps = 44 farads
Joules = (44*150*150/2) = 495,000
Kwh = 495,000/3,600,000 = 0.1375 Kwh

http://en.wikipedia.org/wiki/Capacitance
http://en.wikipedia.org/wiki/Kilowatt_hour

Not enough to carry you too far. It'll be interesting to see if the effects are also beneficial for extending battery capacity by smoothing the current surges, as well as appearing to give more 'power on demand'.
-gary


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## dimitri (May 16, 2008)

*Re: Personal Experience with Prismatic LiFePO4 Cells*



> (1100uf)*40 caps = 44 farads


I thought "u" stands for "micro" , not "milli". In which case you are off by 1000 times, it would be 0.044 farads and subsequently 0.1375 watt/hours, not Kwh. This makes more sense, because according to your calcs you could drive a light vehicle half a mile using $80 cap bank, I wish it was that good


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## ClintK (Apr 27, 2008)

*Re: Personal Experience with Prismatic LiFePO4 Cells*

(Please correct me if I'm wrong...)

Wouldn't the benefit of capacitors be that it helps against voltage sag? If you connect a series of batteries charged to say 150 Volts to a pack of 200 Volt capacitors... the capacitors will charge to 150 Volts.

Without capacitors, when the driver hits the gas the controller pulls a high discharge from the batteries. The batteries can't handle huge discharges so they sag to say 120 Volts.

With capacitors, when the driver hits the gas the controller pulls a high discharge from the batteries & capacitors. Capacitors have no issue delivering all the power you want to pull. They in effect lesson the voltage sag because they supply some power. I would imagine at the worst of the voltage sag the capacitor's voltage and the batteries' voltage would be identical (say 130 Volts).

I wouldn't think the capacitors would actually drain to 0 before the batteries start being tapped. I'm predicting that the capacitor voltage is always the same as the batteries (never higher than max charge, never lower than worst sag). Can you guys test this?

Of course I'm just pulling all this out of my ... so again, please correct me if I'm wrong.


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## TexomaEV (Jul 26, 2007)

Zemmo, thanks for stepping in here. These guys are really full of great questions, and rightfully so. I'm just glad you were there to do the testing, as an unbiased driver. I value your perspective, and know you are honestly giving your account of the event, stating it as straight as possible, just as you always do. 

I'm working on that second capacitor bank, it'll be a bit more slow going, with me having to go back to work now, but I really would like to get it done, for show-n-tell at the NTEAA meeting on Saturday. I hope you also have your capacitors in by then, and maybe have it built up as well.


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## Zemmo (Sep 13, 2007)

*Re: Personal Experience with Prismatic LiFePO4 Cells*

The capacitors will only go up to the voltage of the battery pack. So even through the caps are capable of couple hundred volts, they will only go to pack voltage. The caps will give off their stored energy very quickly but they won't sag lower than pack voltage. Once the draw balances out, the caps will re-collect their energy from the battery pack. So the caps dump their energy load during the peak demand and refill during the low demand (kind of like net metering). So the batteries don't hit the high amp load. We all know that this is an Amp game.

FYI, if you do attempt to do this, you have to be sure that the charging voltage is within the capacitors normal voltage rating. If you have regen you have to take any spikes from that into consideration.


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## reddwarf2956 (Dec 1, 2008)

*Re: Personal Experience with Prismatic LiFePO4 Cells*



Zemmo said:


> The capacitors will only go up to the voltage of the battery pack. So even through the caps are capable of couple hundred volts, they will only go to pack voltage. The caps will give off their stored energy very quickly but they won't sag lower than pack voltage. Once the draw balances out, the caps will re-collect their energy from the battery pack. So the caps dump their energy load during the peak demand and refill during the low demand (kind of like net metering). So the batteries don't hit the high amp load. We all know that this is an Amp game.
> 
> FYI, if you do attempt to do this, you have to be sure that the charging voltage is within the capacitors normal voltage rating. If you have regen you have to take any spikes from that into consideration.



I will add an example as to show how these caps work. Your computer uses a AC to DC voltage regulator. What it does is first run AC 110 V power into a transformer which drops the Volt down to 12 or 5 in old machines and even lower in newer ones then the AC Voltage is ran into a Bridge rectifier which make the AC sine wave in to one which the voltage is never negative (or positive if mis-wired). There is were the caps come in in play. The shape of the waves in a mathematical sence is a sine wave function within absolute value function. So, the voltage goes from some thing a little more than 12 V to 0 V back to a little more than 12 V 120 times a second. The caps do the job of filling in the holes and cuting down the peaks as to make the ending voltage a flat 12 V.

What Zemmo stated is correct for how the caps work for the voltage sag, but there is another benifit that comes from the current and power. Remember, your motor is a coil of wire, so voltage lead current in it. In a cap, current follows the voltage and so you can end up with a matching the current and voltage at the same time to have a better power output. This explains the boost of power Zemmo felt in the 2nd dirve.

The mismatch of power because of a coil or cap in a circuit is called power factor. The best power factor is 1 and that only happens in an all resistor load.

One thing I am wondering about is the controller, it got a bit hot at the end of the trip. I wonder if the owners manual states not to put caps in parallel as they may cause the controller to over heat? Or, something else it might say?

JN


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## JRP3 (Mar 7, 2008)

*Re: Personal Experience with Prismatic LiFePO4 Cells*



reddwarf2956 said:


> One thing I am wondering about is the controller, it got a bit hot at the end of the trip. I wonder if the owners manual states not to put caps in parallel as they may cause the controller to over heat? Or, something else it might say?
> 
> JN


Why would that happen? The caps can't put any more power into the controller than the batteries can produce, they should just smooth out the momentary voltage sag from the batteries, right?


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## reddwarf2956 (Dec 1, 2008)

*Re: Personal Experience with Prismatic LiFePO4 Cells*



JRP3 said:


> Why would that happen? The caps can't put any more power into the controller than the batteries can produce, they should just smooth out the momentary voltage sag from the batteries, right?


Remember that most controllers are connected by wire to the motor with no caps in between, so the designer of the controller plans on the voltage sag in the design. He would expect the voltage sag and a max current and so the power. Now by adding the caps, this change the sag and the current to be come at the same time which means the the power is higher which make things which have higher resistance and heat up. Well that is my concern. If the engineer is good, he would design the controller to have caps to be added and not need to worry and would even suggest adding them like has been done.

The caps act as a reserve bank of power at time of voltage sag. This means the power has on charging been placed there. Now as the batteries sag, it take the total power of both the batteries and the caps and uses it in both to go into the controller and motor to run things. Either alone use less power.

JN


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## reddwarf2956 (Dec 1, 2008)

*Re: Personal Experience with Prismatic LiFePO4 Cells*



reddwarf2956 said:


> Remember that most controllers are connected by wire to the motor with no caps in between, so the designer of the controller plans on the voltage sag in the design. He would expect the voltage sag and a max current and so the power. Now by adding the caps, this change the sag and the current to be come at the same time which means the the power is higher which make things which have higher resistance and heat up. Well that is my concern. If the engineer is good, he would design the controller to have caps to be added and not need to worry and would even suggest adding them like has been done.
> 
> The caps act as a reserve bank of power at time of voltage sag. This means the power has on charging been placed there. Now as the batteries sag, it take the total power of both the batteries and the caps and uses it in both to go into the controller and motor to run things. Either alone use less power.
> 
> JN



TexomaEV,
Thinking about this answer, got me thinking maybe the controllers Amp limit is being mislead or misread. Where is the points where the amps are measured and how quick is the measurements for the controller? The caps can of course pull more than 90 amps in a short amount of time be for the controller figures that out. Or, the reading is of the batteries and not the cap and batteries.


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## JRP3 (Mar 7, 2008)

*Re: Personal Experience with Prismatic LiFePO4 Cells*



reddwarf2956 said:


> Remember that most controllers are connected by wire to the motor with no caps in between, so the designer of the controller plans on the voltage sag in the design.


I think any decent controller is built with some headroom since a fully charged pack right off the charger will be higher than nominal. A 72 volt controller is built to handle more than 78 volts for example. Besides the caps voltage will start to drop soon after the batteries start to sag unless it is a huge capacitor bank, which is not something we are dealing with.


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## Zemmo (Sep 13, 2007)

*Re: Personal Experience with Prismatic LiFePO4 Cells*

Most people have to put a big aluminum heat sink on the back of the controllers to keep them cool. Mine has a big old heat sink on it; John's Corbin has a water cooled aluminum block; Mike's got several computer aluminum heat sink and fans. The Ranger only has a thin aluminum mount plate, the plate is part of the mounting bracket. We don't have very much data on the Ranger running, so we don't know if it normally gets warm or not. As Mike even said, we don't even know if it has the thermal paste under it to make sure it has good heat transfer. So it will just be something else to look at, but I think it wouldn't hurt to have a heat sink of some sort on the bottom side of the mount plate.


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## TexomaEV (Jul 26, 2007)

*Re: Personal Experience with Prismatic LiFePO4 Cells*

I'll be evaluating the space under the aluminum mounting plate to see if I can add a much thicker piece of aluminum to the area where the controller is mounted. Worse case, I'll put an aluminum piece the size of the controller, between the controller and the aluminum mounting plate, with lots of heat sink compound on both sides of the additional aluminum plate. 

The current sensor is on the battery side of the controller, right at the B- input terminal of the controller.


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## reggiewatson (Jan 4, 2009)

*Re: Personal Experience with Prismatic LiFePO4 Cells*

My 11 year old son suggested the other day that we add "a stack of them capacitors" "with a button you can push when you want the extra power". I think he wanted something similar to a NOX system. I know this may be a little off subject but do you think it's possible?


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## Zemmo (Sep 13, 2007)

We should probably start a new thread about the Caps since this one is about Prismatic LiFePO4 cells. 

The caps would be more beneficial by having the caps connected full time. The power difference I felt wasn't a feeling like NOX (the throw into the seat feeling). It was just better acceleration as if I used more amps. If you didn't have the caps connected full time, the moment you tried to use them, they would first have to fill up and thats putting more drain on the batteries and the batteries would already be under draw from driving. So they should really be connected full time so they are always full and ready to go.


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## dimitri (May 16, 2008)

*Re: Personal Experience with Prismatic LiFePO4 Cells*

Yea, separate thread for caps would be great, maybe admin can merge cap related posts into a new thread so we don't lose what's already here.

After reading all the remarks here and much research I feel that a lot of people don't realize how much energy is actually stored in cap bank. I think there is this "magic" feeling surrounding the subject, the name "flux capacitor" certainly helps, gotta love Back To The Future movies 

The reality is that $80 cap bank mentioned here stores enough energy to propel the car for whooping 10 milliseconds ( approx guesstimate ). This is more than enough to smooth out PWM pulses and maybe have some positive effect on battteries long term , but lets face it, its not going to help you burn rubber unless you multiply the capacity by a 1000 times.

Not bashing anyone, just trying to clear up confusion. I think its a great addition to any EV, we just need to keep focus on real numbers.


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## Zemmo (Sep 13, 2007)

*Re: Personal Experience with Prismatic LiFePO4 Cells*

Yes we need more time for testing. Mike is currently putting together another capacitor bank to run in parallel with the existing one. I am expecting my order any day now to build mine for my car. The cap banks Mike has been building is 44,000 mfd each so he will soon have a total of 88,000 mfd (two banks). The one I am building is 300,000 mfd (or 0.3 Farad). If the price of the Ultra Caps weren't so expensive we would all be using those but for now, and for the price we can build these smaller cap banks.

We are experimenting by doing, we don't know the formulas for like calculating the Amp Hour storage or performance. But once we get more info on what happens we will post it. Any EE's out there, please jump in and help with formulas or what to expect or reasons why.


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## JRP3 (Mar 7, 2008)

*Re: Personal Experience with Prismatic LiFePO4 Cells*



Zemmo said:


> We are experimenting by doing, we don't know the formulas for like calculating the Amp Hour storage or performance. But once we get more info on what happens we will post it. Any EE's out there, please jump in and help with formulas or what to expect or reasons why.


This might help:


> 1 Farad is 1 Ampere second per Volt. 1 F = 1 As/V.
> 1 Ah = 3600 As
> 3600 As / 12V = 300 As/V = 300F


http://www.physicsforums.com/showthread.php?t=256751


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## TexomaEV (Jul 26, 2007)

*Re: Personal Experience with Prismatic LiFePO4 Cells*

I just requested that the threads in this topic about capacitor banks, be pulled out into a new thread, so that others can read about our discussions. Many are probably not seeing them, being listed here under the LiFePO4 topic.

By the way, the second capacitor bank is put together, and just needs installed on the hybrid traction pack in the pickup. I'll probably wait until after our NTEAA meeting to install, as I want to bring it to the meeting for show and tell. Maybe charge it up on someone's EV, and do some spot welding.


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## TexomaEV (Jul 26, 2007)

*Re: Personal Experience with Prismatic LiFePO4 Cells*



reggiewatson said:


> My 11 year old son suggested the other day that we add "a stack of them capacitors" "with a button you can push when you want the extra power". I think he wanted something similar to a NOX system. I know this may be a little off subject but do you think it's possible?


Reggie, for a "Turbo Boost" for what you might call "Passing Gear" you can install a contactor that you can turn on, between the output of your controller and the motor, that switches in a 6 or 12volt battery pack that can discharge the peak current that the motor is using from the controller.

Effectively, you are boosting the output of the controller voltage to the motor, instantly, yet still maintaining the pulsing input to the motor from the controller.

Key, is to find a battery or paralled setup that can handle the current discharge of your controller's maximum output.

Others are already doing this on small scale EV's such as Scooters. It would take some work, but could be done in an EV.

OK, back to capacitors............. lol


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## reggiewatson (Jan 4, 2009)

*Re: Personal Experience with Prismatic LiFePO4 Cells*

Thanks Texomaev.
When do you think your new thread on capacitors will be posted?

Reggie


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## TexomaEV (Jul 26, 2007)

*Re: Personal Experience with Prismatic LiFePO4 Cells*



reggiewatson said:


> Thanks Texomaev.
> When do you think your new thread on capacitors will be posted?
> 
> Reggie


I've not received a response as of yet from the forum owner. Hopefully soon.


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## TexomaEV (Jul 26, 2007)

Thanks for setting up the new topic on "Capacitor Banks" and moving the old threads over to it. 

If it doesn't get to bad,

"weather = cold, TexomaEV = stay inside where warm" 

I'll install the second bank of capacitors. I might also get to pick up some of the LiFePO4 regulators from LL Labs at our monthly NTEAA meeting, and install them along with the new studs/nuts from www.evie-systems.com 

I can't wait to get a FULL charge on the hybrid traction pack, and see how it all works with each other, IE: AGM, LiFePO4, & Capacitor Bank 

Zemmo, plans to show off his "Texas Sized" capacitor bank at the meeting. I think he's a relative of "Tim the Toolman" Taylor........ He'll have to post a photo of his newly built capacitor bank, if he's not done so already, in a thread here.


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## Zemmo (Sep 13, 2007)

I got my capacitors in and have the bank built and ready to put into the car. Unfortunately it doesn't fit where I want to put it. I am thinking I will have to re-locate my 12 volt battery and put the cap bank in its place. I have a quick video of the bank on my youtube site.

http://www.youtube.com/user/ElectricFormula

I calculated my cap bank at 300,000 mfd but I was wrong, since it they are wired in series and parallel the capacitance is 1/2. So in the video I said 300,000 mfd but it really is 150,000 mfd. I will update the video so it has the correct stats some time. Thats still a big cap bank, its about 3 1/2 times larger than the first cap bank we tested. Hopefully this weekend I can get some testing done even if the cap bank is sitting in the passenger seat.


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## Tesseract (Sep 27, 2008)

*Re: Personal Experience with Prismatic LiFePO4 Cells*



JRP3 said:


> Am I correct in assuming that if one had a 3300uf 200vdc cap you could use 1 third as many for the same result? How did you come up with the 1100uf size for your pack?


I know you asked this awhile ago but this thread appears to have been severed or orphaned or something so I missed it.

In short, no, the amount of capacitance is not the only factor here; the Equivalent Series Resistance (ESR) is arguably even more important. An 1100uF electrolytic and a 3300uF one will likely have similar ESR and it is this parameter that determines the current capability of a capacitor. So, 3x 1100uF is much better than 1x 3300uF, from a current rating standpoint.


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## Tesseract (Sep 27, 2008)

Zemmo said:


> ...I calculated my cap bank at 300,000 mfd but I was wrong, since it they are wired in series and parallel the capacitance is 1/2. So in the video I said 300,000 mfd but it really is 150,000 mfd. ...


It is critically important that you put a resistor in parallel with each capacitor when connected in series to force voltage sharing between them. The resistor must be low enough in value to pass the maximum leakage current of any one capacitor. For example, if the leakage is 2mA (typical for a large can-style electrolytic) and the voltage is 150VDC then the resistor needs to be 7.5k or less (and rated for 10W or higher). Failure to do this will result in the capacitors with the lowest leakage current being exposed to the highest voltage and vice versa.


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## JRP3 (Mar 7, 2008)

*Re: Personal Experience with Prismatic LiFePO4 Cells*



Tesseract said:


> In short, no, the amount of capacitance is not the only factor here; the Equivalent Series Resistance (ESR) is arguably even more important. An 1100uF electrolytic and a 3300uF one will likely have similar ESR and it is this parameter that determines the current capability of a capacitor. So, 3x 1100uF is much better than 1x 3300uF, from a current rating standpoint.


Thanks for the clarification. Is the ESR something that is printed on the cap, or can be calculated, or does it have to be tested in the real world?


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## Tesseract (Sep 27, 2008)

*Re: Personal Experience with Prismatic LiFePO4 Cells*



JRP3 said:


> Thanks for the clarification. Is the ESR something that is printed on the cap, or can be calculated, or does it have to be tested in the real world?


For this type of capacitor (e.g. - screw-terminal) the ESR is always specified in the datasheet. Here's where the news gets really bad, though... ESR is dependent on: frequency, temperature, voltage, the phase of the moon (just kidding) and the capacitor's age. ESR gradually increases over the capacitor's lifetime as the electrolyte inside evaporates and end of life is when the ESR has doubled. Unfortunately, not only do you need to know the initial ESR spec for this to be useful, you also need a special meter to measure the ESR because a regular capacitance meter probably won't indicate anything is amiss.


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## Zemmo (Sep 13, 2007)

Tesseract said:


> It is critically important that you put a resistor in parallel with each capacitor when connected in series to force voltage sharing between them. The resistor must be low enough in value to pass the maximum leakage current of any one capacitor. For example, if the leakage is 2mA (typical for a large can-style electrolytic) and the voltage is 150VDC then the resistor needs to be 7.5k or less (and rated for 10W or higher). Failure to do this will result in the capacitors with the lowest leakage current being exposed to the highest voltage and vice versa.


This is very interesting to learn about this. Does the voltage used in your calculation based on the battery voltage or capacitor rated voltage or even possible max usage voltage (like when on a charger). My pack voltage is 120 volts nominal. It is usually at 128 volts when charged (old batteries). When being charged the voltage gets up to 148 volts. So which voltage would you use. Why do we need a resistor on each capacitor? They are wired in parallel so wouldn't you only need 1 on each parrallel set (so 2 resistors total)? Being that my bank is wired in series and parallel, wouldn't the bank balance the caps in parallel?

Mike put together five 35 volt 68,000 uf caps in one series and they were used on my car for the first test. After a week of usage, I check the voltage between each cap and they were all within 1.5 volts of each other. So they were doing pretty good in keeping balance with each other.


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## TexomaEV (Jul 26, 2007)

Zemmo said:


> Mike put together five 35 volt 68,000 uf caps in one series and they were used on my car for the first test. After a week of usage, I check the voltage between each cap and they were all within 1.5 volts of each other. So they were doing pretty good in keeping balance with each other.


When I built that little test pack, I wanted to see just about what a worse case could be. Therefore, it's 5ea low voltage (35vdc) caps in series, using, get this, galvanized tin/sheet metal as the interconnecting busbars. Jared experienced over a week, voltage readings across each capacitor, being much more close to each other than I ever expected.

I'm also going to be very interested in the results of his "Texas" sized capacitor bank, compared to my packs, using the smaller capacitors, after the discussion of ESR with smaller capacitors -vs- large ones. Jared get that thing installed, glue it to the roof of the car if you have to....... lol


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## mattW (Sep 14, 2007)

I think the peak effect would be when the energy stored in the capacitors is more than can be discharged in a single acceleration period with the maximum voltage sag of the batteries. Then the caps would charge back up to the battery voltage in time for the next acceleration burst. 

Working out the actually current they could put out is more complex because the more amps the batteries give out, the faster they would sag and so the more amps the capacitors would give out, which means the batteries would give out less and sag less...  Has anyone got a graph of the voltage across their batteries during hard acceleration?


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## Tesseract (Sep 27, 2008)

Zemmo said:


> This is very interesting to learn about this. Does the voltage used in your calculation based on the battery voltage or capacitor rated voltage or even possible max usage voltage (like when on a charger).


Yeah, I wasn't clear about that, was I? The voltage is per series-connected capacitor. If you have 2 in series then each cap should get half the pack voltage and therefore can be rated for half the maximum voltage expected. And, as you noted, the maximum voltage depends on whether the capacitors ever see the charging voltage (on the battery pack side of the contactor) or just the pack voltage when driving (on the controller side of the contactor - which is the location I recommend*). 




Zemmo said:


> Why do we need a resistor on each capacitor? They are wired in parallel so wouldn't you only need 1 on each parrallel set (so 2 resistors total)? Being that my bank is wired in series and parallel, wouldn't the bank balance the caps in parallel?


Technically speaking, you don't need a resistor across each capacitor - one resistor across each parallel set of capacitors (then connected in series with the other parallel sets) will work, it's just that you might need an awfully big resistor to balance out the worst case difference in leakage currents between the parallel sets!

Practically speaking, since it is the difference in leakage current between capacitors in series, it is reasonable, if not absolutely prudent, to rely on statistics a little bit here. That is, the more capacitors in parallel the more likely the total leakage current will be the same as another set of the same type and number of capacitors in parallel. What you cannot count on, though, is that the paralleled capacitors will age at the same rate, and DC leakage current, just like ESR, increases over time and at a faster rate at higher temperatures. So, if you want to minimize the size of the balancing resistors you really need to measure the leakage current of each parallel set by applying the expected voltage each set will see and after they are charged up inserting a DMM to measure the leakage current in mA. Repeat the process for each set and take the difference between the highest leakage set and the lowest - that is the current the resistor across each set will need to pass to ensure balance _at that moment in time_. As the capacitors age that current will undoubtedly change, but probably not much (statistically speaking). Finally, the balancing resistors will also discharge the bank when disconnected from the pack - a very important safety measure (and should be used even if you don't have to connect capacitors in series).

* - Obviously, if there are resistors across the capacitors they will constantly drain the battery pack, which is the first good reason to place the bank after the _contactor_. The second good reason is that the whole point of the bank is to smooth out the current pulses the controller draws in operation, and that means the inductance between the capacitors and the controller needs to be as low as possible. In other words, as close to the controller as practical. Yes, there are capacitors inside the controller that perform this function but, at least in the Kelly I dismantled, they are rated for only 20% of the maximum ripple current possible (relying on statistics - maximum ripple occurs when the duty cycle is 50% and maximum current is being drawn from the motor, so it is reasonable to reduce the ripple current rating on the supposition that this condition will occur very infrequently and for only brief periods when it does).


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## ulnpiper (Sep 24, 2008)

Tesseract said:


> (on the controller side of the contactor - which is the location I recommend*).


But with a large bank of capacitors storing a considerable amount of energy, I think it would be best to have a way to isolate it. I agree with the reasons for putting it as close to the controller as possible. However, how will you be able to safely work on the high voltage side, and 'off' on the ignition key will not mean off for the 'juice'.

Does that mean you need a second set of contactors for the capacitor pack(s)?

-gary


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## JRP3 (Mar 7, 2008)

Tesseract said:


> * - Obviously, if there are resistors across the capacitors they will constantly drain the battery pack, which is the first good reason to place the bank after the controller. The second good reason is that the whole point of the bank is to smooth out the current pulses the controller draws in operation, and that means the inductance between the capacitors and the controller needs to be as low as possible.


Don't you mean after the contactor, before the controller? So it would be batteries->contactor->caps->controller->motor?


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## Tesseract (Sep 27, 2008)

ulnpiper said:


> But with a large bank of capacitors storing a considerable amount of energy, I think it would be best to have a way to isolate it. I agree with the reasons for putting it as close to the controller as possible. However, how will you be able to safely work on the high voltage side, and 'off' on the ignition key will not mean off for the 'juice'...


How about just putting a resistor across the capacitor bank? That's standard practice whenever you have more than a few joules of energy storage, especially at higher than 48V.


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## Tesseract (Sep 27, 2008)

JRP3 said:


> Don't you mean after the contactor, before the controller? So it would be batteries->contactor->caps->controller->motor?


Oops. Absolutely correct... Thanks for pointing that out before someone hung a bunch of caps on the output of their controller (oy! what a disaster that would be!)

(corrected the original)


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## reddwarf2956 (Dec 1, 2008)

JRP3 said:


> Don't you mean after the contactor, before the controller? So it would be batteries->contactor->caps->controller->motor?


How do we figure out the size of the bank to do the most "work"? I realize the job of the caps is to fill out the voltage sag, so I do not mean the w = 1/2*C*V^2. And, the talk has lead to placement of resistors and where to put the caps. Maybe a good figure or drawing to show what you are thinking?

On seeing how quick the caps can discharge, what safety precautions can be integrated into the circuit?

JN


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## Tesseract (Sep 27, 2008)

reddwarf2956 said:


> How do we figure out the size of the bank to do the most "work"? I realize the job of the caps is to fill out the voltage sag, so I do not mean the w = 1/2*C*V^2.


Actually, you do mean that equation... 

Unfortunately, it's a moot point because you can't reduce the peak current from the battery pack by only hanging a bunch of capacitors across it - you need a huge inductor in series with the capacitors as well to "isolate" the battery pack from the controller when a huge amount of current is demanded. 

The only practically application for a capacitor bank is to smooth out the high frequency ripple current from the controller, and for this task the RMS ripple current rating of the capacitor(s) used is most important. Divide the max motor current in half for the worst case ripple current.

*Adding a few capacitors to help take up some of the burden of smoothing out the ripple current is a "not half bad idea"; attempting to add enough capacitance to absorb the current peaks from accelerating is a "full bad idea".*


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## Zemmo (Sep 13, 2007)

This is some great discussions! I'm learning a lot. I wasn't feeling very well after I got back from our EAA meeting yesterday so didn't get anything done. Today I felt even worst and slept most of the day away. I am finally up and about now. But no time to install my bank. It looks like my bank won't fit where my 12 volt battery is at either. So I will have to get creative as to where to mount my bank. The bank will be very close to my controller so thats where it will be installed. As a permanate installation it does sound like a contactor would be a good idea. But I am worried the suddent draw once the contactor connected would weld it shut. How would you slowly charge the capacitor bank up and give it a main connection to the controller? So when I am ready to do the permanate installation I could use the help on the design. But for testing I think we will be ok so we can find out for sure if it is worth doing.

Once I get this installed onto my car, I can make runs with and without the capacitors. I have logging capability to record voltage drops and amperage usage. I also have access to an accelerometer where I can get performance measurements. So I will be able to see 0-60 improvments if any. I will have all of this data shortly after I get it installed.

I do think that this resister is a good idea to install even when testing. Could you tell me exactly which one to get to install. Let me know what info you need to calculate the resistor. Thanks for the help.


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## Zemmo (Sep 13, 2007)

I actually took out my 12 volt battery and attempted to install the bank in its place while getting a mounting point for the 12 volt battery. I was able to get a spot for the 12 volt battery and get the caps in the cubby hole but no good mounts for either one in that configuration. If I made the cap bank a little bit smaller I would be able to keep the 12 volt battery in its current location and the cap bank will fit vertically into the very corner. But before I start tearing apart the cap bank I want to do some tests. So I got a plastic tub that the cap bank will fit into. I will just put it in my passenger seat and hook it directly to the battery pack (happens to be closer). I will run a few tests to see and measure the differences. I can change the bar configuration and remove a set of capacitors (bar change only) to see how smaller cap bank differers from the larger bank. I need to get some wires long enough to get to the two battery terminals and should be able to do some tests shortly.


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## rmay635703 (Oct 23, 2008)

http://www.sell.com/2H7ZP Too bad that one wasn't a higher voltage
http://www.hobbyengineering.com/CatPSSUPER.html
http://www.tecategroup.com/ultracapacitors/maxwellboostcaps.php

I am wondering what effects a real supercap might have on performance as you would be entering the equivalent of a small battery with a very high amperage output.

Anyway a little off topic but potentially a money saver, for those of you who are packrats like me or know of a unlimited source of broken old computer related items and audio related items.

You can easily find 200v capacitors in the 400uf on up area in old computer powersupplies, in old monitors and obviously in the power supply section of any old audio equipment.

Just unsolder what you want and best of all its free and you are practicing the 2nd R Reuse.

Good previous thread
http://www.diyelectriccar.com/forum...the-largest-storage-supercapacitor-18576.html


Cheers
Ryan


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## ulnpiper (Sep 24, 2008)

Or you can get 10.0F at 2.5v here...
http://parts.digikey.com/1/parts/90541-cap-10-0f-2-5v-al-type-gold-rad-eec-a0el106.html

So 100 of them in series ~=250v = $581.86


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## Zemmo (Sep 13, 2007)

The ultra capacitors would be nice but because of the price, they don't usually fit into our budgets. Thats why I am testing the computer grade caps, they are cheaper but 
not as large of capacitance. The problem with using the stereo capacitors is you need so many of them in series and the capacitance drops by a lot (divided by the number of capacitors in series). So if you put 10 of those 6 Farad stereo capacitors in series, once you got it up to voltage it would only be 0.6 Farad. Plus one long series has the problem of getting out of balance between each other.

I got my caps installed onto my pack tonight. It took over 30 minutes for the pack to get to voltage with the charge resistor. Even though it took a really long time to get to voltage, there was no spark when making the permanent connection. Even though it was late and getting cold, I couldn't wait to go for a drive. I went around the neighborhood and didn't feel any differences. So I jumped onto a faster road and drove around. Still didn't feel any differences. So then I drove around for 15 mile trip and couldn't really feel any differences. So I guess I am going to have to wait and do my dailly drive to see if there is any differences.


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## david85 (Nov 12, 2007)

Just got here. Going to *try* and follow the technical stuff, but most of its over my head


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## TexomaEV (Jul 26, 2007)

Zemmo said:


> I got my caps installed onto my pack tonight. It took over 30 minutes for the pack to get to voltage with the charge resistor. Even though it took a really long time to get to voltage, there was no spark when making the permanent connection. Even though it was late and getting cold, I couldn't wait to go for a drive. I went around the neighborhood and didn't feel any differences. So I jumped onto a faster road and drove around. Still didn't feel any differences. So then I drove around for 15 mile trip and couldn't really feel any differences. So I guess I am going to have to wait and do my dailly drive to see if there is any differences.


I wonder if it's the large caps, vs, the many smaller units I have all in parallel, or if it's the weirdness of the hybrid battery pack? Other variables as well, how cold were the Pb/acid batts? It was darn cold up here in Okieville last night. I hope you at least see an extra mile or two in range difference tomorrow. Or your resting voltage is higher after the typical drive. 

We need an EKG machine for EV's, something with an umbilical cord of sensors you can connect to everything and log data..... lol


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## Tesseract (Sep 27, 2008)

Zemmo said:


> ... I went around the neighborhood and didn't feel any differences. So I jumped onto a faster road and drove around. Still didn't feel any differences. So then I drove around for 15 mile trip and couldn't really feel any differences. So I guess I am going to have to wait and do my dailly drive to see if there is any differences.


There won't be any difference for the reasons I outlined in post #51 of this thread.

Furthermore, the capacitors need to be connected together in a particular fashion to equalize the current sharing among them and minimize the stray inductance. TexomaEV happened to get the layout mostly right in his setup, probably by dumb luck, but mostly right all the same...  




rmay635703 said:


> ...You can easily find 200v capacitors in the 400uf on up area in old computer powersupplies, in old monitors and obviously in the power supply section of any old audio equipment.


Indeed you can, but how are you going to connect them together? Make your own pc board, perhaps? Well, keep in mind you are wanting to smooth out ripple currents in the 100-400A range and the caps in a pc power supply *might* be able to handle 2A each and then you need to use really wide, like ridiculously wide, traces on the board to carry that amount of current.

Controlling 50-150kW of power is not a trivial task. Physics is fighting you tooth and nail the entire way. Not to discourage anyone, but even EEs that don't specialize in power electronics don't bother trying to do this kind of design by themselves.


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## TexomaEV (Jul 26, 2007)

"" Furthermore, the capacitors need to be connected together in a particular fashion to equalize the current sharing among them and minimize the stray inductance. TexomaEV happened to get the layout mostly right in his setup, probably by dumb luck, but mostly right all the same... ""

Thanks, I think? ............. lol


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## Zemmo (Sep 13, 2007)

Yes, it is colder out now compared to summer but I am comparing winter performance and mileage. As of this mornings drive, I did not see any difference (mileage or performance). Of course I have only done 1/2 of my drive thus far (so only a short trip). But no changes just yet, I will leave it hooked up for a few weeks of testing.

I did notice that the DVM I had connected to the caps showed slightly different readouts compared to my digital voltage display in the dash. At rest the voltage is a little higher and under load the voltage is a little lower. I am only talking about 1 to 1.5 volts but interesting to know.

The caps have been keeping pretty good balance between each other. I don't have a resistor yet to try and balance them so this is just self balancing from the parallel banks. At rest they are within 1/2 volt of each other, when charging they seemed to drift a little further apart and had almost 1 volt difference. It is a little hard to test under load differences because I am driving. I need to get two more DVM and have them connected at all times to monitor it really well.

I wouldn't mind trying to get a hold of a shunt and meter to watch the amperage going in and out of the caps, it would just add one more piece of data. It would probably be hard data to capture since it would happen so quickly. My equipment is only able to capture data every second, I am afraid that wouldn't be fast enough to see whats happening.

Another thing I noticed while driving is the cap bank sags in voltage before the batteries do and to a larger extent than the batteries and then they balance out to the 1 to 1.5 volts described above. I need to try to rig up multiple cameras and merge the videos together so you can see all readouts all at the same time. Unfortunately I don't have enough equipment to be able to do that. But I will try and do the things that I can.


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## Zemmo (Sep 13, 2007)

TexomaEV said:


> I wonder if it's the large caps, vs, the many smaller units I have all in parallel, or if it's the weirdness of the hybrid battery pack? Other variables as well, how cold were the Pb/acid batts? It was darn cold up here in Okieville last night. I hope you at least see an extra mile or two in range difference tomorrow. Or your resting voltage is higher after the typical drive.
> 
> We need an EKG machine for EV's, something with an umbilical cord of sensors you can connect to everything and log data..... lol


It would be easy enough to change out the cap bank with another one. So we could try your bank in my car. That would show us two different banks in size and configuration. I'll test this one for a while and later some time we can meet up and swap banks.


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## ElectriCar (Jun 15, 2008)

I'm still trying to figure out how y'all have this thing connected and where the ripple is you're trying to filter out. I was trained in electronics and worked in the field with power supplies, building and repairing for nearly 20 years so I'm very familiar with their operation. Though this application is different, the physics is the same. 

I assumed you would connect them in parallel with the battery pack. My thinking is they would discharge as needed upon accel and recharge as the pack rejuvenates after a sag. 

The larger the cap pack, the larger the discharge ability thus decreasing the sag or furnishing more current to the controller, depending on the needs of the controller.

Please clarify the connection on the vehicle where you noticed the difference. I find it hard to believe with such a small cap bank though that there would be any appreciable difference in performance. 

I just read where Maxwell is selling a 16V parallel bank of (3) 3000F Boostcaps to the city of Chicago. They're using them to start diesel engines on their transit buses on very cold days when the batteries don't want to cooperate. They said that during starting most of the power would come from the cap bank. So what would that come to? 150A for 3-5 seconds? That would really help you accelerate!


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## Tesseract (Sep 27, 2008)

ElectriCar said:


> I'm still trying to figure out how y'all have this thing connected and where the ripple is you're trying to filter out....


Series dc traction motor controllers are essentially a buck converter - the ripple on the input (battery) side is the result of the switch chopping the supply voltage (and current) at duty cycle D to deliver an average voltage to the motor (Vin * D). But batteries, wiring and interconnects all have non-zero resistance and inductance, so this chopping inevitable creates ripple. Just 0.1 ohm of combined resistance and reactance results in 50V of ripple if the input current consists of 500A pulses of current. Connecting a bunch of low-ESR capacitors across the input terminals right at the controller can smooth this ripple out by, in effect, turning the inductive/resistive impedance of the batteries and wiring into a low-Q LC filter of sorts.


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## reddwarf2956 (Dec 1, 2008)

Tesseract said:


> Series dc traction motor controllers are essentially a buck converter - the ripple on the input (battery) side is the result of the switch chopping the supply voltage (and current) at duty cycle D to deliver an average voltage to the motor (Vin * D). But batteries, wiring and interconnects all have non-zero resistance and inductance, so this chopping inevitable creates ripple. Just 0.1 ohm of combined resistance and reactance results in 50V of ripple if the input current consists of 500A pulses of current. Connecting a bunch of low-ESR capacitors across the input terminals right at the controller can smooth this ripple out by, in effect, turning the inductive/resistive impedance of the batteries and wiring into a low-Q LC filter of sorts.


You say that a 50 V ripple will occur with 500 Amps, what will it be for just 100 A? And, to a question that was asked, does the Volts matter? If there is voltage regulator for a 144V pack,(does a 78144 exist?), would it be useful?

My guess is higher volts means lower amps to have the same power delivered, so lower amps leads to lower ripple. But, this implies that a Cap bank can act as a way to reduce the number of batteries by lowering the ripple also. The higher the battery pack voltage, with a similar mass car and gearing, the smaller the need for the caps bank, but the higher cost for the batteries. Correct?


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## Zemmo (Sep 13, 2007)

I got a little update on the cap bank. I drove up to my friends place in McKinney which is 32 miles round trip. I didn't see/feel any acceleration performance different (at least not feelable difference). I found one of my motor mounts broken while trying to find locations to put the caps. So I won't be doing the accelerometer tests until I get that motor mount fixed. I am sure it has been broken for a while, I put a band-aid fix on it for now. Anyways back to the actual update, I got a little over 10 percent increase in my mileage on that drive to my friends place and back. But on my way back it was late at night so hardly anyone was on the street and all of the lights were flashing yellow. So I got to do some good hypermiling. So if you figure if there was traffic and lights were running I would have gotten a little under 10 percent increase. So that is a good sign that I am getting better mileage. I'll have to do a few more long trips to found out more on improvements. So that is the update so far.


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## TexomaEV (Jul 26, 2007)

This is still good news. At least you didn't decrease the range by 10%....lol

And if it helps with the longevity of the batteries, controller, even better. 

My brother dropped off some more copper tubing, if you want to come up, and replace the aluminum busbars with copper you're welcome to do so. 

I hope you can get that mount welded/repaired easily.


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## Zemmo (Sep 13, 2007)

So far the aluminum bars are working out good. They don't get hot or even warm and they are really flat and make good contact onto each capacitor. Thats one thing I worry about on the copper pipe, its not perfectly flat and not making a good contact.

Have you finished making any more capacitor banks? Maybe I could try one in my car to see if there is a difference on different types of capacitors.


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## TexomaEV (Jul 26, 2007)

Zemmo said:


> So far the aluminum bars are working out good. They don't get hot or even warm and they are really flat and make good contact onto each capacitor. Thats one thing I worry about on the copper pipe, its not perfectly flat and not making a good contact.
> 
> Have you finished making any more capacitor banks? Maybe I could try one in my car to see if there is a difference on different types of capacitors.


I've got a way to make them perfectly flat now. The hydraulic press at work does wonders. I've only completed the second set for the Ford Ranger. I've been focusing on installing the LiFePO4 regulators, and aluminum studs in the batteries for now. That's why I was hoping to tease you up here for some copper, maybe you'd feel sorry for me, and help with the installation of these regulators, replacement busbars, aluminum studs, etc.......... lol

I'm wondering if the copper gives up the energy (current), better than aluminum, since copper is 40% better than aluminum, or is it, aluminum is only 40% as conductive as copper...... Seems like you have to have 3 times the thickness of Aluminum to match the conductivity of copper, I think. Someone here will know the specifics.


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## Zemmo (Sep 13, 2007)

Is there any reason why the capacitor bank would help the charging process? I just took my battery measurements, I have been logging them down every week since putting on the desulfators 4 months ago. Tonights readings are higher than normal, almost across every battery (even my weak batteries). After two months with the desulfators, I haven't see much change on my batteries, they have been pretty constant. But what ever reason my packs voltage is higher than average. The only change I have done on the battery side is the capacitor bank but I didn't expect any battery voltage changes. Could the cap bank have some sort of effect on the charging?


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## reddwarf2956 (Dec 1, 2008)

Zemmo said:


> So far the aluminum bars are working out good. They don't get hot or even warm and they are really flat and make good contact onto each capacitor. Thats one thing I worry about on the copper pipe, its not perfectly flat and not making a good contact.
> 
> Have you finished making any more capacitor banks? Maybe I could try one in my car to see if there is a difference on different types of capacitors.


Zemmo,
I am wondering if this might be why you are not seeing a increase power, but better mpc, miles per charge?

http://en.wikipedia.org/wiki/Voltage_regulator#DC_voltage_stabilizers

What I am thinking is that you are already seeing a boost by the zeners, so the caps only hold the current for later use.

Where is the break in the support?

JN


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## JRP3 (Mar 7, 2008)

Zemmo said:


> Could the cap bank have some sort of effect on the charging?


Wouldn't the caps just hold the higher charge voltage a little longer and bleed it back into the batteries? I'd imagine after sitting a while the pack would drop down to normal.


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## Zemmo (Sep 13, 2007)

I have been taking my Zener regulators on and off of batteries. I have been trying to get some of the batteries to a higher voltage. Once the battery starts hitting 7.8 volts when charging, I put the Zener regulator back onto that battery. But my Zener regulators are designed to slow down the charging process on that battery.

The caps don't store more volts to use later. The charger raises the voltage of the batteries and the capacitors(for my pack its 148 volts when charging). Once the charger shuts off the battery's voltage goes back down to its normal voltage (128.1 volts after 6 hours). As the battery voltage drops when the charger is off so does the capcitors voltage. The caps stay right around the voltage of the pack. They won't store the charging voltage (148 volts) and use that later, they balance out between each other. The cap banks we are using don't store that much current. Especially at the amperage our cars use it up at. Our cap banks is mostly used for smoothing and filtering. The UltraCaps or SuperCaps can store the current, but those are thousands of dollars.


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## Zemmo (Sep 13, 2007)

JRP3 said:


> Wouldn't the caps just hold the higher charge voltage a little longer and bleed it back into the batteries? I'd imagine after sitting a while the pack would drop down to normal.


I guess it could be doing that. I will check it in the morning before I leave for work and see if there is any significant differences.


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## Zemmo (Sep 13, 2007)

I checked my voltages this morning and they were back to about normal averages. Each just a little higher in voltage, about 0.01 to 0.02. But that is an interesting effect on the batteries with caps in parallel. They hold their surface charge longer, at least I'm guessing you could call it the surface charge. So I guess that will be something else that I will get to watch for. If I have to wait that long every time, that means I won't be able to drive the car one whole day out of the week just to be able to get these readings.


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## Zemmo (Sep 13, 2007)

Todays drive still showed a 10% increase. I had to run home and back to work so I had double the miles today. It is too hard to see the increase on short runs. Todays drive was only 18 miles but it still showed that increase. I must be using less amps on the drive but it must be a small amount because it doesn't seem different. Just FYI, the 10% is about 4 to 5 miles.


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## JRP3 (Mar 7, 2008)

10% is quite a large improvement. If that holds up I'd say that's a worthwhile addition to your setup.


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## TexomaEV (Jul 26, 2007)

Zemmo said:


> Todays drive still showed a 10% increase. I had to run home and back to work so I had double the miles today. It is too hard to see the increase on short runs. Todays drive was only 18 miles but it still showed that increase. I must be using less amps on the drive but it must be a small amount because it doesn't seem different. Just FYI, the 10% is about 4 to 5 miles.


Still, 10% is nothing to sneeze at. What does one gain with regen? Isn't it about the same as around 10%. Plus the hopeful other advantages, I think was well worth the investment in the capacitor bank.


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## Zemmo (Sep 13, 2007)

Yeah that is quite a bit. I actually want to do a long drive, to max out the miles of the battery and see how many miles I get. The drive last weekend was 32 miles. This weekend I am planning on going to Dallas which would be a 50 mile trip. So that should give it a really good test. I am getting mid to high 40's on my MPC, since the colder temperatures and before installing the cap bank, I was averaging low 40's on the MPC. I think actually driving that long distance should be the best test on the mileage.


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## ElectriCar (Jun 15, 2008)

Zemmo you are aware of the incredible difference temperatures make in mileage from a lead pack aren't you? Are the temps being noted in your trips? I don't know what type pack you have but just wondering what if any affect the temps may have on your data.

For me, a trip in the 30F range versus a trip in the mid 40's or so is a world of difference in mileage for me. Keep updating though. If the data continues to come in good, I'm all in!


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## david85 (Nov 12, 2007)

I have no doupt that Zemmo knows that temp affects battery performance. Keeping a log of the conditions of each trip might help isolate that variable, but I think he already knows that too.


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## Zemmo (Sep 13, 2007)

I actually haven't been tracking any temp changes. I haven't really seen that much of a mileage swing from temp changes. But then again in Texas, it is generally warmer. When I have been driving around temps have been around 45 to about 70 in general. Just today it was 49 degrees when I ran the dog and was 54 for the high. This weekends drive, when I left at noon it was 58 and when I got back at 1 in the morning it was 41. On that drive back when it was the coldest, I got my best mileage but thats when I got to do really good hypermiling.


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## ElectriCar (Jun 15, 2008)

My mileage was great when we had some hi 60's in December. However when we went to the 30's shortly after, mine died at 28 miles, and that wasn't continuous driving nor highway. However I did have my 2kw heat on some and was all at night but I have LED lights all but head lights. At the time of death, I had only driven it a few times and didn't have my PakTrakr installed yet. Just basing it on my warm driving mileage experience...


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## reddwarf2956 (Dec 1, 2008)

Zemmo said:


> I checked my voltages this morning and they were back to about normal averages. Each just a little higher in voltage, about 0.01 to 0.02. But that is an interesting effect on the batteries with caps in parallel. They hold their surface charge longer, at least I'm guessing you could call it the surface charge. So I guess that will be something else that I will get to watch for. If I have to wait that long every time, that means I won't be able to drive the car one whole day out of the week just to be able to get these readings.


I think I missed something here. What was the effect? Why can you not drive the car for a day per week? What was the reason for the wait?

Also, could the desulfators be doing anything?

JN


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## Zemmo (Sep 13, 2007)

Usually after 6 to 12 hours of my batteries off the charger they would level to their state of charge. This last time I took the measurement it was high at 12 hours (after done charging). So I waited till the next morning to check the voltage and then I got close to their normal level state of charge. So now I will have to wait 24 hours for the batteries to level out to get a consistent reading. So if I got out Saturday night and plug it in that night, 12 hours later the charger shuts off and then another 24 hours after that to let the batteries level out. So that would blow my Sunday which is when I normally check the batteries. I am just trying to keep consistent, I wouldn't want to show those higher voltages on my spreadsheet because it would be overly inflated readouts.

The desulfators have already done their thing two months ago. The voltages raised up during the first two months and then leveled off. They haven't gained any further on their SOC after those two months. Whats happening now is with the caps in parralell, it is keeping the surface charger longer. The desulfators only run in mili amps so they aren't enough of a draw to burn off the surface charge. I am sure it helps but not enough to speed up the balance.


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## Zemmo (Sep 13, 2007)

ElectriCar said:


> My mileage was great when we had some hi 60's in December. However when we went to the 30's shortly after, mine died at 28 miles, and that wasn't continuous driving nor highway. However I did have my 2kw heat on some and was all at night but I have LED lights all but head lights. At the time of death, I had only driven it a few times and didn't have my PakTrakr installed yet. Just basing it on my warm driving mileage experience...


I'm warm blooded my self and I have hardly run my heater this winter, probably 2 or 3 times. It draws about 8 amps when running from the traction pack. I already converted all of the lights to LEDs except for the headlights but those all run on the 12 volt side and it has its own 12 volt deep cycle battery that is not part of the traction pack, plus no DC-DC converter. It has a 12 volt charger which charges it up when the car charges up. So my 12 volt side of the car has no draw on my traction pack. The 33 Ah deep cycle has done well on my car.


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## Zemmo (Sep 13, 2007)

I just wanted to share a little experiment I did this morning. I drive by amp readouts a lot. I tend to pick a number based on speed and terrain and try to maintain that amp draw. I've made every day a game on how low I can get my amps down to and also that Curling game (you know the one on ice and brushes) and guess where I can let go of the throttle and time myself to the stop light without hitting my brakes. Anyways, I thought that I would try driving by feeling only. I turned off all of my gauges and just drove without know my amp draw. I gotta tell you it was driving me nuts not knowing what I was drawing. I don't know how anyone could have an EV and not have an amp gauge. Anyway, I expected it to be lower than normal since I couldn't see my amp draws, I figured I would have a tendency to over draw on amps. But just judging by the feeling of the car, I arrived at work at the same DOD. It was nice to know that my driving habits don't change even when I can't see my amp draw.

Back to the main subject, I checked the balance of the capacitor bank and it is still staying in balance of each other by 1 volt. I think it helps keep it in balance by having so many caps in parallel (2 of them in series for the voltage and 5 of those series in parallel for capacitance). So it seems to have them in a series/parallel configuration keeps in balance well enough for usage. But for the simplicity, I think getting caps in the proper voltage and just run them all in parallel is the best bet. Thats what Mike has done on his battery banks and what was in the EV Ranger. I used my charge resistor to lower the voltage of the higher caps so they are balanced now. I will see if it will keep it balanced from usage or if they will drift apart.


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## ElectriCar (Jun 15, 2008)

Any new data to report? New leads on supercaps? Just bumping...


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## Zemmo (Sep 13, 2007)

I won't be able to do any accelerometer tests until I fix my motor mount. I found the strap that wraps around my motor was broke. It added extra support to the motor. I put a band-aid fix on it for now and still drive it as an every day car. I put 2 pipe bands on it and had them cross over the top of the existing strap. For daily driving it has work out fine. But I don't think those pipe bands were designed to take WOT forces. I really just need to take my car out of commission for a few days and have a shop make a new beefier strap or fix and reinforce the old one. After Saturday is a good time for me to do that.

I don't know if Mike has done any other changes to the Ranger EV yet, I know he was working on building the 2nd cap bank to put into the truck. Once he is done the truck will have 88,000 mfd, when I drove it, it only had 44,000 mfd.

I've had my caps on my car for almost two weeks now and have had time to reflect on what I saw and felt. I think a lot of what I was seeing was learning to drive a new EV. The first time I drove it without the caps, I was find out how to shift it (to tach gauge) and in unfamiliar territory. The second time I already knew how to drive and when to shift so things went smoother. But we did get a higher MPH while pulling 90 amps. I think the best test is the accelerometer test for performance, but I will have to get my motor mounts fixed on my car before doing that. Maybe we could do that test on the Truck. I would have to schedule that with them and the guy with the accelerometer.


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## ElectriCar (Jun 15, 2008)

Yea, just yesterday I had to loosen my motor mount and turn it. As the pack has gotten broken in it is apparently allowing more amps out to create more torque. 

It seems to have gotten stronger lately even as temps have dropped! I raised the hood to show someone and noticed the motor/tranny had twisted about to about the 11 o'clock position!

Now it will kick up a little gravel when I step on it even with 2600 lbs on the rear wheels!


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## Zemmo (Sep 13, 2007)

I did my drive to Dallas today. A cold front came in and made it really cold today. It was 33 degrees, not sure what the wind shield was but that 33 degrees was cold when you're just standing out there talking about the Fieros. It was 26.4 miles there, recharged for just shy of 3 hours, and drove back which was 26.5 miles. I ended up using 54% to go to Dallas which at that percentage is a calculated 48.9 miles per charge (mpc). For the trip back, I ended up using 64%, which calculates out to 41.4 calculated mpc. If you average them out for a round trip, that would be 45.15 mpc. So thats still roughtly 10% improvement from what I was getting before (which was 41 mpc in the cold). That was a good long range test, almost 53 miles in one day. It was cold, had some pretty good hills (in Dallas, its flat out where I live), and a good variety of real world driving and still had positive results.

I now have two weeks before my next event with the Fiero. So now is a good time to take out that motor mount and see about getting it fixed or a new one made. On the way back I stopped by a friends place and checked how his motor was mounted in his Fiero. I may try making a mount like his, it looks very solid.

I'll have to try to convince Mike to let me try one of his capacitor banks just to see if there is any differences in different makes, models and sizes of capacitors.


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## JRP3 (Mar 7, 2008)

Would it ever be possible to take a 20 mile round trip with the caps, then disconnect them and recharge and take the same trip a few hours later the same day? Might give more exact comparison.


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## Zemmo (Sep 13, 2007)

Yeah that would be an easy test to do. I will do that in the next few day. I'll see about getting a route that will give some variable terrain. Probably do the two tests at night so I can eliminate traffic differences.


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## GTWCMT (Jan 22, 2009)

This has been good reading. some ooh's ahh and some lol's

here is what I think:
-noticable difference; well as the cp pack alters the current flow from the batteries, this would be effective on bat packs that may be older and smooth them out. also with LA and LIPO there may be some differences.

- the 10%; this could be factrs like wind direction and drag at the different temps and directions of travel. it would need to be carried out over a longer period of time to see if it really works.

-Delivery; The caps would take out the sags and the highs as well, so you're getting a flat line in current draw. I did notice your estimate on the Cap pack was discharging. If I remember correctly this is roughtly the same rate that the controller is plusing the motor.

In summery - it would seem that havent a smoother delivery in the current draw gives a better range that foot control.
Maybe a step up/boost cap and dropping back on the batteries would show some benefit (less weight to pull / higher volts less amp draw)


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## hidbulb (Jan 26, 2009)

wooh...thanks guys for posting a great information!It looks like I'm learning each post...


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## Zemmo (Sep 13, 2007)

Unfortunetly the weather hasn't been very forgiving down here. Raining, misting, freezing rain, etc. But this weather is suppose to break today and hopefully I can perform the first tests on the same route with and without caps.


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## 1clue (Jul 21, 2008)

This has been a really interesting discussion.

It seems the tone has changed dramatically from beginning to end, and I for one am not a real wizard at electronics.

I would like to say some things here, and hopefully somebody who knows more can verify it or correct it.

It seems that the way you guys are wiring your caps in, the bank can only filter out the short term changes in your battery pack. For example, noise from the controller, like radio-frequency noise and, say, shocks from the road causing the motor to momentarily draw a whole lot more amps.

Here's what I know about batteries and caps:

A capacitor's state of charge can be read directly from voltage. A discharged cap reads zero volts, the fully charged one reads its maximum voltage. A battery stays at approximately the same voltage for its entire cycle, and starts dropping as the battery gets very close to empty -- still not zero, just lower. Moreover, each type of battery (PbA, LiPo, etc) has different characteristics.

A capacitor can charge or discharge very rapidly, meaning also at a very high current compared to a battery of the same specs. A battery has fairly specific conditions under which it can charge or discharge without damage.

All that taken together, I'm going to submit a couple theories:

First, the situation you guys are using these capacitor banks for use a tiny fraction of the energy actually stored in the caps. Your battery voltage varies only a slight bit, so your capacitor energy stays more or less constant. The more "resistance" (substitute impedance if you know what that is) between the battery and the cap you have, the more energy can be used from the capacitor bank, and the smoother the ride the batteries have. This type of filter you guys are making is necessary, but I would think a good controller would have that already built in. More the better, to a point.

Second, some of you were evidently thinking of the cap bank as a separate power supply. I know this is possible because there are threads on this site and even a white paper regarding a capacitor-only drag racer.

Let's say we have a hypothetical car with regenerative braking and a regular battery and a huge capacitor bank.

In my mind, in order to have that sort of capacitor bank (UltraCap Bank, for example, let's say UCB for short) you would need a very good BMS (battery management system) and a completely separate CMS (capacitor management system) each going into a single well-filtered motor controller.

The BMS would need to do the normal things a BMS does, in addition to preventing huge amounts of current from rushing back into the battery during regen.

The CMS would need to charge and discharge the caps within the limits of the capacitors, AND have a mechanism to adjust voltage of the capacitor bank to the voltage at the front of the controller. In other words, it would be something like a DC-DC converter.

Each controller would be responsible for limiting current being supplied by that system to the "power bus" and by that means protecting its energy source or charging it as appropriate. If the voltage gets too high, both start charging their supply within the limits of the storage system. If it gets low, they supply voltage as they are able.

Not being an electrical engineer, I have no idea how viable this idea is. I'm a computer guy, so it seems pretty logical to me. I would like to hear from one of the experts on how well that would all work.

Thanks.


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## ElectriCar (Jun 15, 2008)

Don't think you need anything to charge the caps as they will be charged with the battery charger. However IF they're connected on the opposite side of the contactor from the batteries, when energized the caps will draw a chunk of power immediately. A precharge resistor should take care of that. Don't know if this will impact the contacts longevity but I suspect it will degrade the contacts over time, particularly without the resistor.


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## 1clue (Jul 21, 2008)

Regarding charging the capacitor bank in the later half of my post, I was thinking in terms of regenerative braking and a massive ultra cap bank to be used as a charge for several seconds.

In that event, I would think that in order to use the full capability of the capacitor bank, you would need to have some sort of DC-DC converter so that you could get energy into it and out of it no matter which side is higher. Two of them, in fact, one for each direction unless somebody could come up with a bidirectional converter.

In other words, if you are half charged on the cap bank and you hit the brakes, the DC-DC converter would dump energy into the cap and keep charging it right on up to the max safe level your controller thinks is good. And when you take off, you would dump that energy back into the motor controller, and when the cap bank gets lower than the battery bank you could DC-DC convert it up again to continue using the charge.

Not sure that the results would be worth the expense, just trying to reconcile a capacitor bank with a battery bank, and the both of them to a single motor controller. Actually, I'm pretty sure that what I described is not really feasible, just a hypothetical idea about what it would take.


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## GTWCMT (Jan 22, 2009)

I see where you going. What you mean is that you use the motor as a gen, if you have it unregulated (there by getting the most out of the regen) and then topping off the drive caps. From what I know you dont get a geret deal back from regen.

A step up would be a on-off drive drive and gen system, it wouldnt make it a smooth, but you would get back a lot more of the output power back. convertional controllers wouldnt work with it.
its worth just looking at a cap as a fast charge and discharge battery.


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## Zemmo (Sep 13, 2007)

The DC to DC for the cap bank does sound more ideal. It would be able to use more of the energy in the caps instead of only the top little bit. The caps I got in my car match the sag of my battery pack. Any good controller would have some small caps to help filter some of the pulses but it would be hard to get any large capacitance in the controller. I think adding the larger caps helps filter it even further. 

The weather down here hasn't cooperated at all. We are getting freezing rain right now. They are saying tomorrow is the last day of it, or at least what the weather guy says.


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## 1clue (Jul 21, 2008)

Ideal, yes, assuming that you have an infinite supply of money. Which I don't.

The problem I see is that the DC-DC controller would probably need to be able to pass all the current used by the motor controller. Actually, both ways if you want to charge it. So just guessing, the capacitor bank's "CMS" like I used in my example would cost about twice what your motor controller would. And you still need a motor controller.


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## DIYguy (Sep 18, 2008)

I think I can get a bunch of caps rated at 23,000 uF -10 +75, 50 VDC - 75 surge. They are mounted in parallel groups of 5. Could I build a decent cap bank with these if I series up say....4 to get 200 volt strings and then paralleled them? Pic below. They have Al bus bars on top.


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## ElectriCar (Jun 15, 2008)

DIYguy said:


> I think I can get a bunch of caps rated at 23,000 uF -10 +75, 50 VDC - 75 surge. They are mounted in parallel groups of 5. Could I build a decent cap bank with these if I series up say....4 to get 200 volt strings and then paralleled them? Pic below. They have Al bus bars on top.


If my training from 27 years ago serves me right, 3 series sets of 5 connected in parallel using the nominal C=23000uf would yield a bank C=38,[email protected], 225V surge.

Formula: C in parallel=C1+C2+C3 Therefore each row=115,000uf @ 50V

C1---C2---C3---C4---C5 
+
C6---C7---C8---C9---C10 
+
C11--C12--C13--C14--C15

C in series=1/(1/C1+1/C2+1/C3)

V in series=V1+V2+V3

So if you have 30 of these, you can combine two of these in parallel and have a bank rated 76,666uf @ 150V.

Jeez, that's a lot of work to make that happen!


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## Zemmo (Sep 13, 2007)

I thought that when you put the capacitors in series that they drop by N number of capacitors. So 23,000 uf divide by 5 would only be 4600 uf but it would be at 250 volts. I am no expert but that was my understanding of what happens with capacitors in series, voltage goes up but capacitance goes down. My bank is 2 in series and then 5 of those in parallel.


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## ElectriCar (Jun 15, 2008)

Zemmo said:


> I thought that when you put the capacitors in series that they drop by N number of capacitors. So 23,000 uf divide by 5 would only be 4600 uf but it would be at 250 volts. I am no expert but that was my understanding of what happens with capacitors in series, voltage goes up but capacitance goes down. My bank is 2 in series and then 5 of those in parallel.


I see your confusion. My dashed lines was intended to show them beside each other in parallel. Sorry bout that. C1-C5 are parallel, just like his photo shows. 5 in parallel = 115000uf @ 50V. 

Now make three of those.

Then series them. 115,000/3=38333uf @ 150V (50+50+50)

I'm pretty sure of that.


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## reddwarf2956 (Dec 1, 2008)

DIYguy said:


> They have Al bus bars on top.


I am a bit worried about your Al bus bars having holes in them. You might want to measure the temp at these points to make sure they don't act like fuses.  You are trying to put a large number of electrons across these smaller spots which is causing resistance. The whole idea of bus bars is low resistance which means that you might have some problems.


JN


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## DIYguy (Sep 18, 2008)

Thanks guys for the information, I am not an electrical type... although I know the basics. I did think that capacitance dropped and voltage added when series connected. That's a good point about the holes also...never thought about that. They were mount holes. These units were used on a 650 amp weld power supply....so, perhaps not too far off. But thank you, I will be sure to watch this. I could "TIG" weld up the holes...or even scab a piece of Al to bridge. Sounds like a have something that may work though. 

Should I test these first, if so, what would be a good way to do that? Charge them one at a time or a bank and see if they each hold charge maybe?

Thanks again.

Gary
BTW, I'm planning on running a 180 Volt battery pack, so, I should probably shoot for a 200 volt cap capacity? ...or do u think the surge capacity will cover me?


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## ElectriCar (Jun 15, 2008)

DIYguy said:


> Thanks guys for the information, I am not an electrical type... although I know the basics. I did think that capacitance dropped and voltage added when series connected. That's a good point about the holes also...never thought about that. They were mount holes. These units were used on a 650 amp weld power supply....so, perhaps not too far off. But thank you, I will be sure to watch this. I could "TIG" weld up the holes...or even scab a piece of Al to bridge. Sounds like a have something that may work though.
> 
> Should I test these first, if so, what would be a good way to do that? Charge them one at a time or a bank and see if they each hold charge maybe?
> 
> ...


An FYI from when I worked on them, it used to be the life time of these things was around 10 years. They do last longer however but they degrade over time until they don't function properly. That said you may want to find a meter to test their capacitance values before use. 

Fluke is one brand I know that has a C tester on some of their multimeters. The Fluke 87 has one but don't know the range it will read to.


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## DIYguy (Sep 18, 2008)

ElectriCar said:


> An FYI from when I worked on them, it used to be the life time of these things was around 10 years. They do last longer however but they degrade over time until they don't function properly. That said you may want to find a meter to test their capacitance values before use.
> 
> Fluke is one brand I know that has a C tester on some of their multimeters. The Fluke 87 has one but don't know the range it will read to.


Thanks ElectriCar, for that. I will be sure to test them if/when I go fwd. Lots of other stuff to do first though!  (my wife is starting to think I am becoming a junk collector! lol  ))


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## Voltswagen (Nov 13, 2008)

Zemmo
Any updates to report on your capacitor bank?


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## Zemmo (Sep 13, 2007)

Unfortunately, I have two problems. I drive my EV in the rain. Well I have two batteries that became very weak. I noticed it when doing my weekly battery checks but I didn't know what the problem was. Two weeks later I found out it was my battery desulfator. Water got into the case and fried that desulfator and then created a short in that battery. So it constantly drained that battery. It was on there for two weeks before I took off that bad desulfator. So far those batteries aren't recovering. So that would throw off any test that I would do because it is weak batteries. The range is only about 10 miles now without murdering those batteries. Those two weak battery are at 6 volts after those 10 miles which is about 60% DOD. While the other batteries are around high 6.20's or low 6.30's which is about 15% DOD. So those two batteries will throw off any test that I would do. The other problem is my motor mount is still broke. My band-aid fix is still holding but I am just doing my normal accleration. I think a hard acceleration would break those pipe bands.

I know Mike finished the second bank for the Ranger EV. But the Ranger doesn't have the guages that I have and doesn't have access to an accelerometer. So he can only go by the feeling which he says the accleration feels strong. But only going by feeling doesn't prove anything. This weekend the owner of the Ranger got it back so Mike no longer has it to do tests. Maybe we can talk the owner into doing some tests some time. Once I figure out what to do about those weak batteries I can resume testing and have something to show for it.


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## Fsldgr (Feb 15, 2009)

*Re: Personal Experience with Prismatic LiFePO4 Cells*

I am getting ready to install Maxwell Ultracapacitors (Ucaps) in my vehicle (http://www.evalbum.com/1967) and have been trying to find all of the calculations needed to estimate performance. I will not be installing in parallel with the batt pack but rather engaging the Ucaps only for acceleration and hill climbing and then disengaging for recharging which will be done with an on board Honda EU2000i gas generator. So far, what I have been able to find on estimating useful power from a Ucap bank is as follows.

The calculation for Capacitance is dividing the capacitance by the number of cells used. Take the result and multiply by the square of the voltage and divide that result by 2. In my case I am using 1500 Farad Ucaps at 2.7 Volts each. I will have 46 Ucaps to get t 124 volts. So ....

1500/46=32.6 = Capacitance
(32.6 x (124 x 124))/2 = 250,628 Joules
1 Joule = 1 volt x 1 Amp x 1 second

Here is a reference for Maxwell

http://www.maxwell.com/pdf/uc/General_Sizing-1007236.pdf

So if I use 75% of the energy in my pack I should be able to draw 120 volts at 50 amps for 30 seconds (a slow acceleration) which should save the batts a lot of grief. The voltage drop will leave me with about 80 volts at the end of the draw. 

I know this is quite different from what is being discussed here but I am hoping it will add to the discussion.

The Honda generator will be able to completely recharge the Ucap bank in about 2 minutes. We have a double shaft motor and may add a pulley to drive an alternator/generator during braking to to to capture some of that energy and throw it at the Ucaps. I am planning on producing 120AC to send to the charger with the alternator/generator on the second shaft and need to find out how to do that and with what components. (Any help will be most appreciated)) 

The nice thing about the Ucaps for regen is that they will suck up every electron you throw at them. 

TFB


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## Voltswagen (Nov 13, 2008)

Hello Tom and welcome to DIY.
We are a community of EE's, Not EE's, Old Wrench Guys (like me) and even some Smarter Than EE's (or so they think).
You'll find this a great place to bounce new ideas off other builders and maybe gain some knowledge from the experience of others. 
I know I have.
We're kinda the leading edge of a movement that Detroit wishes would just go away. But we will not go quietly into the night. We will continue to build our EV's and show them to the world embarassing and exposing Detroit at every turn. I for one am proud to be a member of this community. OK I'll get off my soapbox now and let the conversation continue.
Roy


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## Fsldgr (Feb 15, 2009)

Roy,

Thank you. I am looking forward to learning from the community and making the best EV that I can. I am hoping to get the Ucaps up and running by the end of April and will post reports on performance as soon as I have any data.

Tom


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## GTWCMT (Jan 22, 2009)

Fsldgr One od the most simple ways to get a regen switching unit to you use a solinoid (spelling) to the break switch that allows full swtich on and draw with the brake is pressed.
You will find them on older cars that trigger the starter, with the lower vlotage atthed also to the brake switch, you will need a resistor or some sort, which Im sure that someone will be able to tell you what you need for your gen.


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## HDS (Aug 11, 2008)

Hi Fsldgr:
I like the concept of the ultra capacitors for starting purposes, helping to take the burden of the large starting currents off of the battery pack. It seems to me, for this to work effectively, the voltage of the capacitors must be higher than the batteries or at least higher than the battery voltage if the battery voltage sags during starting. Let's say at this point the caps are "exhaling" electrons. But they will only discharge for the time period that the capacitor voltage exceeds the battery voltage. As soon as they are equal, they will stop discharging. 

In order for them to help on the next startup they have to "inhale" electrons. That means that the voltage of the battery pack (or another source) must be higher than the capacitor voltage in order for the caps to charge up. If the charge that is charging them up comes from the battery pack than I think that you really do not gain anything; the power came from the batteries anyway.

If I understand "Pulse Width Modulation" correctly, the controller pulses the DC motor, the motor coils will experience a collapsing magnetic field as each pulse shuts off, this inductive reactance is fed by diodes back through the motor coil which increases performance. As I recall from Voc School, the remedy for inductive reactance is capacitance. I think that adding a large amount of capacitance at this point might compromise this effect.

I wonder if it might be a better idea to charge them only with sources other than the batteries like household a/c which will work for the first start-up; and after that regenerative braking for subsequent starts. Also, it is normal for batteries fresh off the charger to have say 148 volts for a 120 volt pack. Controllers are designed for this. If the capacitors can be charged to this voltage level with regenerative braking, than they will be ready to discharge as soon as connected for starting.

We have to be mindful of the fact that caps can carry their dangerous levels of voltage for a long time after charging. If we put a resistor across them it will discharge this voltage but if it is in parallel with the battery pack, it will also drain the battery pack. 

Keep the ideas flowing, this is good stuff.
HDS


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## Voltswagen (Nov 13, 2008)

HDS
That is exactly Tom's idea: to charge the caps with an onboard small generator seperate from the batteries.
On another note if wired parallel to the battery pack the capacitors should 
smooth out the voltage sag under acceleration thereby extending battery life.
And you are correct the capacitors wired to the pack would have no more total voltage than the pack itself but the capacitor bank discharge would be much faster than the pack alone. Kinda like a shot of NOS. Think about the primary job of a capacitor....starting voltage only.


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## ElectriCar (Jun 15, 2008)

Voltswagen said:


> HDS
> That is exactly Tom's idea: to charge the caps with an onboard small generator seperate from the batteries.
> On another note if wired parallel to the battery pack the capacitors should
> smooth out the voltage sag under acceleration thereby extending battery life.
> And you are correct the capacitors wired to the pack would have no more total voltage than the pack itself but the capacitor bank discharge would be much faster than the pack alone. Kinda like a shot of NOS. Think about the primary job of a capacitor....starting voltage only.


What's the reasoning for dragging along a generator, disconnecting and reconnecting the caps into the circuit? Why not tie them parallel to the pack. They will discharge much faster than the pack is capable thereby MAINTAINING the pack voltage by dumping the required amperage and preventing or minimizing battery sag provided there is enough capacity. I can't see why one would want to bother with all the other "contraptionment" or am I missing something?


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## Voltswagen (Nov 13, 2008)

Electricar
Tom's idea for a small onboard generator would charge the caps beyond pack voltage. Lets say to 200v on a 120v pack. Then under acceleration
the caps would momentarily discharge more power which the controller should be able to handle. Once discharged the generator would automatically kick on and replenish the caps to the higher voltage and then shut off.
It is more complicated than just wiring the caps in parallel with the pack
but a greater effeciency could be gained.
We need Zemmo and friends to bring us more data on their parallel caps setup. And I'm still thinking about the drawbacks posted by HDS.
We're just trading ideas.
Zemmo believes he gained 10% in range with his caps and for an $85.00 investment it becomes intriguing.


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## Fsldgr (Feb 15, 2009)

I did not want to tie the Ucaps to the battery pack because I did not want the Ucaps recharging off the batteries. I want a hybrid vehicle using batteries for cruising and another power source for the acceleration, hill climbing, and any other big power draws. Being able to get some energy from regen and an on board generator would also increase my range dramatically. 

Although I am extremely interested in retrieving energy from braking, I am even more interested in grabbing energy from coasting downhill or coasting into stop lights (Hypermiling). There are instances in my driving where I see a green light half a mile away, know that it will change before I reach it, and can begin to coast into it allowing the generator to help brake the car while pumping energy back into the Ucaps. I also have a few hills with a stop sign or light at the bottom that are between .3 and .8 miles where I could also do some coasting with the generator engaged and grab a lot of energy for the Ucaps.

From what I understand, Zemmo is using his Caps to smooth out his acceleration and balance his batteries. Apparently this does not add energy to his system but rather make using his available energy more efficiently. If that is so, then beside having a bank of Ucaps for what I just referred to, I will add the small caps to do what Zemmo is working on with his setup. However I have a set of BattEQ battery equalizers that use capacitors to shuffle energy between and among the batteries in my string to keep them balanced. I am still testing this and will post when I have any data to support any conclusions. So I might already be doing something similar to what Zemmo is doing with his caps.

Tom


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## the gas wizard (Apr 19, 2008)

so is the idea to have a huge reserve of amps to dump into the motor from a cap pack rather than pulling from the main pack all the time? i am really keen to try one of these setups on my car! any input would help heaps!

thanks


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## Fsldgr (Feb 15, 2009)

Assume the the system Ucap bank is 120 Volts and that the Amp draw from the bank on acceleration is 50 Amps the following table shows the number of seconds of acceleration for each size of Ultracapacitor. The sizes is in Farads and each one is at 2.7 Volts. To get to 120 Volts, 44 Ucaps would be required.

Cap Size..........650..........1500..........3000
Seconds............13............30.............60

At 168 volts and a 50 Amp draw, a 3000F bank of Ucaps could provide up to four 15 second bursts before recharging is needed. At the end of the fourth burst the Ucap bank would be down to 95 Volts. *More theory* .... with a 168V 3000F bank and braking regen it could be possible to go up to six city blocks (all with stop signs) with one bank and no draw on the battery pack at all. One 50 Amp acceleration, coast, brake, stop , and start all over until the bank is down to 90 Volts or so. *Of course, I have yet to test all of this in real world conditions which I hope to have done before the end of May*.

At an Amp draw of 100 Amps for the same pack of Ucaps the number of second would be cut in half. In either case, the voltage drop would leave the pack at ~76 Volts with 25% of the energy still in the caps. The higher the system voltage, the more the Ucaps, the longer the acceleration time.

Now the bad news. Ultracapacitors are expensive, very expensive! Maxwell also sells a tiny PC board that fits onto the cells to keep them balanced. Another expense but well worth it. I saw a sale of Maxwell 650F caps on eBay. Ten of them would cost $240 USD + shipping + the balancers. So for a bank of 650F at 120 Volts the total cost could be as high as $2,000 USD. A bank of 1500F at 120 Volts would be around $3,000 USD from the same eBay site.

My controller can handle up to 168 Volts so I will eventually increase my Ucap bank size to that level. This all assumes that the theory and calculations are correct.

The big thing to remember is that the Ucaps need to be recharged after each use. I am electing to use a gasoline generator as part of my setup so I am not totally divorcing myself from the BIg Oil curse. The Honda EU2000i will put out 1,600 watts (using 1 gallon of gas at full tilt for four hours) so I will be able to recharge the 120V bank in about 2 minutes. With regen it could be even faster if I can find the right setup.

So .... here is a question. *Can a battery pack be discharged in series and then charged in parallel? If I were to wire the pack in series with + and - leads going to the controller and another parallel wiring setup on the same pack but with the parallel terminal leads going to a charger, would it work?* I will assume that batt packs and Ucap banks work the same way. Then I could flip a switch that would change the configuration from discharge to charge. If this were possible I could route the regen charging current directly to the Ucaps without using a charger since Ucaps grab energy as fast as you throw it at them. The only other thing necessary in the circuit would be an automatic shutoff as soon as the Ucap bank reached its top voltage level.


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## ElectriCar (Jun 15, 2008)

Fsldgr said:


> Assume the the system Ucap bank is 120 Volts and that the Amp draw from the bank on acceleration is 50 Amps the following table shows the number of seconds of acceleration for each size of Ultracapacitor. The sizes is in Farads and each one is at 2.7 Volts. To get to 120 Volts, 44 Ucaps would be required.
> 
> Cap Size..........650..........1500..........3000
> Seconds............13............30.............60
> ...


You mention a 50A draw from a stop so I was just curious what type vehicle you're doing this on. My S10 truck draws over 450A from a dead stop. I pulled 458 today from a stop starting in 2nd gear and that wasn't a hard acceleration. Normal accel is around 250-350A with an Advance 9" motor pulling a 4200lb truck when using 1st gear.


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## Fsldgr (Feb 15, 2009)

Using PakTrakr on my 1974 VW I read 45 Amps on a slow acceleration ... a very gentle slooooow acceleration. I need to check that because I thought it was a bit low. I will be installing an Ammeter to get a *second opinion* The numbers I used here are mathematical calculations for illustration purposes. I have not been able to install my Ucaps yet so I haven't checked the real world conditions yet. 

I have no real data yet so I cannot make any absolute conclusions. As soon as I am hooked up and ready to roll with the Ucaps I will post hard data here.

Thanks for the comments

You are pulling 4,100 lbs while the VW is less than 2,500 so Amp draw should be lower for me but I will check nevertheless.
Nice looking truck!!

Tom


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## ElectriCar (Jun 15, 2008)

Oh yea, I'm reading motor amps so don't know what that translates to in pack amps.


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## reddwarf2956 (Dec 1, 2008)

*Fsldgr*,

Take a look at:

http://www.metricmind.com/ac_honda/main2.htm

on the left side, you will see an Ultracap link for this AC powered car.

John Nicholson


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## Fsldgr (Feb 15, 2009)

John,
Thanks for the link but I read Victor's page before I ever started building mine. He gave me the idea for using the Ucaps although I will trying a different application.

Tom


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## DIYguy (Sep 18, 2008)

Hey Zemmo ... any updates? What are the conclusions here, if any?

Thanks


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## Zemmo (Sep 13, 2007)

I was having a problem with batteries so I took the capacitors out while trying to find the problem. I eventually found two bad batteries. I left the capacitors out and eventually let a friend use them for a little while in his vehicle. I am getting those capacitors back here shortly but I have found another two bad batteries just last week. My pack is just on its last leg. I guess thats just what happens to a 7 year old pack. But anyways, I don't have the proper testing tools to be able to confirm either way that the capacitors help the controller or batteries.


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## ElectriCar (Jun 15, 2008)

So any updates???????? 

I Just bought 10 1000uf 200V electrolytic caps and am using the buss bars from a 225Amp breaker panel to tie them together. The aluminum buss measures 3/16 x 1.25" approximately. 

An engineer came up with the number somehow of 16000uf. He said the Curtis 1231 had about 6000uf inside so I should add at least 10000. Don't know how long before I can get it all wired up though. 

He said he did this on a vehicle with weak batteries and doubled the mileage. Newer batteries wouldn't notice as much improvement I think he said due to lower internal resistance thus lower voltage drop to begin with.

Also he recommended multiple smaller caps versus fewer large ones as several smaller ones could pass more current than fewer larger ones.


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## JRP3 (Mar 7, 2008)

Double the mileage? From 1 mile to 2? Caps won't store that much energy.


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## Fsldgr (Feb 15, 2009)

I have had a few delays so my caps are not installed yet. It looks like we will be all set to go by the end of the month. I will post as soon as we are up and running.


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## ElectriCar (Jun 15, 2008)

JRP3 said:


> Double the mileage? From 1 mile to 2? Caps won't store that much energy.


No, not stored at all. Again, and I'm going by my old memory and what I know about electricity when I say this. The caps function is to charge during the off period of the cycle and discharge when the control turns on. Let me expound on this.

When the control turns on, there's a HUGE inrush of current from the pack. Current passing through the batteries and cables = voltage. This voltage, known as voltage drop is wasted energy. Any voltage drop created on the batteries or cables doesn't make it to the control. Voltage drop is a part of the cause of battery "sag".

Ie, if you have 2 six volt bulbs and wire them in series on a 12V battery, each bulb will read 6 volts across it. If you think of voltage on one of the lamps as this voltage drop, the remaining 6V is applied to the 2nd lamp, our motor for this explanation. The sum adds up to equal the supply voltage on the pack.

The caps charge and discharge with each cycle, 10000 or how many cycles your control operates at per second. What happens is the charged caps discharge during the on time and supply some of the current. That lowers the demand from the pack. Less current from the pack lowers the voltage drop, which is wasted energy. 

So with less wasted energy in the form of voltage drop, there's more available to drive the vehicle. My contact said that older batteries have higher internal resistance. So for a given current, the drop will be higher due to higher resistance in those batteries leaving less for actual driving.

Hope this helps.


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## JRP3 (Mar 7, 2008)

The controller has caps in it that are already at pack voltage through the precharge resistor, where is this inrush of voltage coming from?


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## ElectriCar (Jun 15, 2008)

The inrush comes in when the transistors turn on and stops when they turn off. When they turn off the capacitors recharge.


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## JRP3 (Mar 7, 2008)

I could be mistaken but I'm not sure it really works the way you describe. How would having more caps before the controller behave any differently than the caps in the controller other than keeping the pack voltage a little "stiffer" longer? I can see slightly better performance, I just don't see anywhere near a doubling of range or much range extension at all.


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## ElectriCar (Jun 15, 2008)

JRP3 said:


> I could be mistaken but I'm not sure it really works the way you describe. How would having more caps before the controller behave any differently than the caps in the controller other than keeping the pack voltage a little "stiffer" longer? I can see slightly better performance, I just don't see anywhere near a doubling of range or much range extension at all.


I asked him the same thing. Said the total needed to do the job was 16000uf. So I'm adding 10K more to total that much.

Re the range doubling. He said it was on an ev with old batteries. Granted doubling is a lot. Maybe he said it gave it 50% more but I thought he said doubled it...

Regardless of what he claims, I'm doing it. I've always been one to prove something or nothing. I just generally don't lend credence to skepticism. There's always someone who says it can't be done and always someone just as determined to prove it can. I'm somewhere in the middle.


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## Fsldgr (Feb 15, 2009)

I agree. I would like to know if it made any difference at all. It could be well worth the slight expense and work.

"Those who say it cannot be done should not interrupt the one who is doing it. " 
Chinese proverb


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## JRP3 (Mar 7, 2008)

There is good evidence that a cap bank can be helpful. I'm not saying you shouldn't try it, I'm just saying the claimed potential benefits sound far fetched. I'm quite happy to have you try and then post your results


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## Crash_AF (Sep 18, 2009)

Any updates to this experiment?

Later,
Joe


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## Zemmo (Sep 13, 2007)

I just received my cap bank back just this week. But I don't have a steady platform to go by any more. My battery pack just needs to be replaced. I drove my car yesterday to work and on the way home I was getting my low voltage alarms a lot. Round trip is only 10 miles, it is now barely making that. I have priced out a new pack, just need to take the time to do the swap. Once I get a new battery pack and get it broken in again I'll have a steady platform to go by on performance info.


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## TexomaEV (Jul 26, 2007)

I just recently installed a small bank in the E-Celica.

I did install this capacitor bank as close to the controller as I could, here's an installation photo:

www.flickr.com/photos/mbarkley/3954645044/

Zemmo, when you get your traction pack replaced and start logging results with your current capacitor bank, maybe you could run some tests with a capacitor bank made with these smaller caps that I have to see if there's a difference regarding Large (Texas sized) -vs- Smaller Capacitors........


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## JRP3 (Mar 7, 2008)

Have you noticed a performance difference? Do you have pics of the assembly process?


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## TexomaEV (Jul 26, 2007)

JRP3 said:


> Have you noticed a performance difference? Do you have pics of the assembly process?


Here's a photo that might help explain how I build them, and what from:

www.flickr.com/photos/mbarkley/3973549388/in/set-72157622233348554/

I've noticed a shorter charge time so far once I plugin at the end of the day after a typical commute. Not very scientific as I can't always swear I drive the same speed or number of stop/go lights with this though. 

Somehow, I need to figure out a rock solid measurement of differences if any.


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## ElectriCar (Jun 15, 2008)

Got mine built but not quite finished. I'm using bus bars from a 225 Amp breaker box we removed. It's aluminum but will be fine. I'll post photos if I get the chance. My camera cable is AWOL so I can't load them on the PC now. I'm going to wrap the buss in red and black shrink wrap since the cap terminals are only abour a quarter inch apart, then assemble it and install. Can't wait to get it done.


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## ElectriCar (Jun 15, 2008)

Zemmo said:


> I just received my cap bank back just this week. But I don't have a steady platform to go by any more. My battery pack just needs to be replaced. I drove my car yesterday to work and on the way home I was getting my low voltage alarms a lot. Round trip is only 10 miles, it is now barely making that. I have priced out a new pack, just need to take the time to do the swap. Once I get a new battery pack and get it broken in again I'll have a steady platform to go by on performance info.


So is the bank installed on this vehicle? I understand that old batteries benefit the most from caps due to their high internal resistance. A guy told me he got a huge bump in mileage with such a pack.


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## JRP3 (Mar 7, 2008)

Where does the energy come from? Old batteries give less range because they don't hold as much energy, I still don't see how caps will change that.


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## ElectriCar (Jun 15, 2008)

Do you know how a controller works? I'll explain how I think the caps works as best as I know how. 

For low power needs, the control switches the power on then back off. One on/off event is one cycle. Say during that cycle the control switches on for 10% of the cycle time and is off 90% of the cycle. One cycle time may be a millisecond, not real sure. 

What happens is that during the 90% time period the caps charge up and are ready to discharge when the next on event happens. Lets say without the caps the pack discharges at 300 amps. If you have 300 amps through the pack, you create voltage drop across the pack (sag). You may for example have 150V pack voltage on your volt meter at rest. When you draw 300 amps off it you may only have 135 at the controller whereas the pack voltage drop plus the cable voltage drop makes up the other 15V. 

Now you install the cap bank. Caps store voltage correct? So they're sitting there now charged up to 150V. When the controller turns on, the caps will discharge AND the pack will discharge as well to feed the controller. The caps power will make the pack discharge now at a lower amperage for example at 275 versus 300. That creates less losses in the battery in the form of voltage drop. Voltage drop btw is power that is wasted on the way to the controller, power that doesn't move the vehicle. It's the same thing going on when the controller heats up. That heat was made in the controller due to internal resistance and is wasted energy.

Because the caps in play reduces the voltage drop and wasted energy, it leaves more energy to power the vehicle. 

Old batteries have higher internal resistance. Power = amps x volts. Amps x resistance = volts. Higher amps = higher voltage drop in the pack. So an old pack for a given amp draw (current pulled from the pack) will result in higher voltage drop and less voltage reaching the controller. Less drop in the pack due to the caps = more voltage reaching the controller. Once again, with the caps in place the amp draw off the pack is reduced and less voltage is wasted leaving more to power the motor.


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## dimitri (May 16, 2008)

> One cycle time may be a millisecond, not real sure.


Although your understanding of the process is correct, that quote above is the key. Its all about timing. You really need to understand how long capacitor is able to supply current in comparison of the pulse cycle.

I can't recall from top of my head, but I did some math on this subject and determined that typical bank of caps such as those shown in this thread will only supply curent for miniscule percentage of the time compared to the pulse time, which basically makes them almost useless.

Yes, the physics are right and there is no negative effect, but in reality there is almost no positive effect either. So, if caps are cheap or free and you want to play with stuff, sure, go for it, but if you spend even close amount of money on them compared to the cost of one additional battery, then battery will always win.


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## ElectriCar (Jun 15, 2008)

I'm going to try it but I've got only maybe 200 charges on my pack. I have 10 10000uf caps. I decided to go with 10 smaller units due to faster time constants of smaller caps. I hope to have them fully assembled and installed within two weeks or sooner time permitting. I certainly don't expect a massive improvement but anything helps. 

One thing trying something will do is eliminate a lot of conjecture and speculation. Cost is only about $100 for caps and wiring. 

And your comparison to adding a battery, you have to charge a battery every time it discharges from the wall and it's another 75 pounds of lead to haul uphill. If the caps add 5% or 2% what one battery would add to my range, it would be free range as the caps are preventing the waste of energy you already paid for. The battery requires more $ to use again.

I haven't a clue if I'll notice a difference but it can't hurt. If I don't notice any difference I may add another 100000uf bank and try again unless I learn something otherwise.


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## Tesseract (Sep 27, 2008)

dimitri said:


> Although your understanding of the process is correct, that quote above is the key. Its all about timing. You really need to understand how long capacitor is able to supply current in comparison of the pulse cycle.


Yep - dimitri's correct. You will get zilcho effect on range with caps.

The only benefit I see is reduced noise emissions from the controller, and even that would be better accomplished with a couple of good ~1uF film capacitors.

The basic equation you use is: C*dV = I*t

dV is the difference in voltage across the cap between charged and "discharged" (e.g. - ripple if in a power supply circuit)

So, let's say we allow 10V of "ripple", or droop and the controller is drawing 100A from the battery pack. If you want to sustain that amp draw for 1 measly second you will need 10F (as in Farads) of capacitance.

A capacitor is considered fully charged after time 5RC, so precharging this bank with a 680 ohm resistor will take 9.44 hours.


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## dimitri (May 16, 2008)

ElectriCar said:


> I haven't a clue if I'll notice a difference but it can't hurt. If I don't notice any difference I may add another 100000uf bank and try again unless I learn something otherwise.


Please don't take my words as an attempt to discourage you from trying and learning, but don't say it can't hurt, you already admitted to hurting your wallet out of $100 

The process you are trying is not new, long time ago people learned how to describe it in mathematical formulas. It would take no money and less time it takes you to assemble the cap bank to read few pages of the book and calculate exactly what the outcome will be before you spend a dime on it. Then you will see that, yes, there is positive effect and its improving your EV by say 0.0001% or maybe even 100 times better 0.01% or maybe even 1000 time better, say 0.1% , woohoo! You just saved yourself $100 

You see, super caps are measured in 100s of Farads and what you make is measured in fractions of one Farad, so the result would be also measured in fractions of 0.01 % , so why bother?

I am all for learning things hard way sometimes ( see my 100 amp charger thread  ) , but at least you have to have a sense of measurable result, otherwise why bother?

Sorry, I mean no disrespect to anyone, afterall we all have our specialties, some are better mechanics and some are better EEs , but any intelligent person is expected to listen and learn from other peope instead of trying to prove the world wrong, but that's just my opinion.

I'd be the first to admit I was wrong when you show measurable results of your experiments


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## ElectriCar (Jun 15, 2008)

Tesseract said:


> Yep - dimitri's correct. You will get zilcho effect on range with caps.
> 
> The only benefit I see is reduced noise emissions from the controller, and even that would be better accomplished with a couple of good ~1uF film capacitors.
> 
> ...


I think you misunderstand what I'm trying to accomplish. As far as ripple, I'm not concerned with that. There is no ripple from a battery, only sag due to Vd and possibly chemical reaction limitations or what have you. On a scope you will see apparent ripple but that's just the sag, unlike ripple from a rectified AC source. However it acts the same I suppose. I'm not trying to get Vcontroller to maintain a higher level however, I'm trying to reduce Vd across the pack.

As far as your time constant goes, I'm not using any resistors. The only resistance is in the cables and cap leads. The pack resistance I think is irrelevant for the RC time constant because whatever voltage comes out of the pack is headed to the controller and the only difference is Vd of the cables. I'm using parallel 1/0, equivalent to a 4/0 cable so resistance is low there, way less than 1 ohm. 

Now if you were on the same page with me, you say Zilch. Have you tried it? According to calculations years ago, the helicopter could not fly. And I've heard the same thing about the bumble bee. It shouldn't fly either. But they both do. So in both instances something was missing from the calculations obviously.

I've read about one person on this board who tried it with a small increase in range. I spoke to another guy, an EE who repairs Curtis controllers who also tried it after his own calculations and said he increased range on very old batteries. 

I certainly don't know but I'm open minded and willing to try it. I've always been that way. We can speculate and calculate til the crows come home but until it's tested who knows. If everyone trusted their calculations completely the helicopter may have never been invented. There must be some balance between theory and reality. Trying something will merge the two.


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## ElectriCar (Jun 15, 2008)

dimitri said:


> Please don't take my words as an attempt to discourage you from trying and learning, but don't say it can't hurt, you already admitted to hurting your wallet out of $100
> 
> The process you are trying is not new, long time ago people learned how to describe it in mathematical formulas. It would take no money and less time it takes you to assemble the cap bank to read few pages of the book and calculate exactly what the outcome will be before you spend a dime on it. Then you will see that, yes, there is positive effect and its improving your EV by say 0.0001% or maybe even 100 times better 0.01% or maybe even 1000 time better, say 0.1% , woohoo! You just saved yourself $100
> 
> ...


I'm no EE but did study capacitors in school so I understand the concept I presented earlier of how it SHOULD work. But my efforts are not blind as you seem to think, and I'm not offended by your comments at all as I don't think you know where I'm coming from. My efforts are based on efforts and calculations of others and their results. No I wouldn't spend $100 for a moon shot without some reasonable expectation of success based on what I've learned somewhere.


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## dimitri (May 16, 2008)

> I certainly don't know but I'm open minded and willing to try it. I've always been that way. We can speculate and calculate til the crows come home but until it's tested who knows. If everyone trusted their calculations completely the helicopter may have never been invented. There must be some balance between theory and reality. Trying something will merge the two.


I am 100% with you on this one, but we'd have to agree on a way to measure results. How do you propose to measure results of increased range? We all know that range in EV is an elusive bastard, minor fluctuations of your right foot may skew results, I'm not even talking about randomness of traffic patterns. Clearly you don't expect more than 1-2% improvement, so how can you measure such small differences?

As for what other people say, don't forget "placebo effect". After you put an effort into something you are inclined to feel results, especially if you expected small improvements which are hard to measure. If you spend $100 and you "feel" improvement, that's worth the money even if it can't be measured in miles or volts


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## major (Apr 4, 2008)

Hi guys,

I've done some work with capacitors across the battery. And Tess is right. If your time constants are on the order of seconds, it takes a lot of farads. I used ultracaps. 

Nothing wrong with forging ahead with experiments. I hope you convince yourselves and others of the value. I have a large quantity of large electrolytics, new old stock, I'd like to sell off. 

And Tesseract,

I charge up 10 F capacitors in like 8 seconds.  Well, about 70% of the total energy. First charge out of the box takes about 15 minutes with a current source.

Regards,

major


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## Tesseract (Sep 27, 2008)

ElectriCar said:


> I think you misunderstand what I'm trying to accomplish. As far as ripple, I'm not concerned with that. There is no ripple from a battery


No, I didn't misunderstand you at all. I mentioned ripple not only because it is the most common use of that equation but because there is quite a bit of ripple on the battery cables going to the controller - after all, the motor controller draws current from the batteries in sharp pulses at its switching frequency (1.5khz to 20khz). Thus, the current waveform on the battery cables is a square wave with a varying duty cycle. The voltage waveform is a triangle wave whose peak-to-peak value depends not only on the total capacitance present, but often to an even greater extent on the total impedance of the batteries, cables and the actual _capacitors_ (their "ESR").




ElectriCar said:


> I'm not trying to get Vcontroller to maintain a higher level however, I'm trying to reduce Vd across the pack.


External capacitors will help with _that_, sure. 




ElectriCar said:


> As far as your time constant goes, I'm not using any resistors.


On which side of the main contactor are these additional capacitors going to be located: the controller side or the battery pack side? If on the battery pack side then disregard my mentioning of precharge. If on the controller side, though, then consider what I mentioned very carefully. 




ElectriCar said:


> Have you tried it?


Nope, I haven't tried it. Don't need to touch a red-hot burner on the stove to know it will burn the crap out of me, either.




ElectriCar said:


> According to calculations years ago, the helicopter could not fly. And I've heard the same thing about the bumble bee. It shouldn't fly either. But they both do. So in both instances something was missing from the calculations obviously.


Let's see... you are essentially arguing that just because some seriously complicated aerodynamics problems weren't solve until relatively recently that one should be equally skeptical of the rather basic equation that describes the behavior of a capacitor?

Shall we attempt to overthrow Ohm's Law next?


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## Tesseract (Sep 27, 2008)

major said:


> ...
> I charge up 10 F capacitors in like 8 seconds.  Well, about 70% of the total energy. ...


Not with a 5W 680 ohm resistor you don't! 

(I picked that value, btw, because I seem to recall that's what Logisystems recommends for the precharge resistor for its controllers).


8 seconds, 10F, approx. 1 RC... so a 0.8 ohm resistor, huh? *That* would certainly be spectacular.


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## 280z1975 (Oct 2, 2008)

ok, since this thread is getting a bit more tech than I can handle can someone point me to a website (or book) to read up on these EE concepts, abbreviation and ideas. I'm understanding the basic argument, just not the finer points. ... ok, I'm back to lurking (with a slightly confused look )


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## major (Apr 4, 2008)

Tesseract said:


> 8 seconds, 10F, approx. 1 RC... so a 0.8 ohm resistor, huh? *That* would certainly be spectacular.


No resistor. Just the ESR and short cables. From a current source. Peaks in the range of 160kW.


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## dimitri (May 16, 2008)

major said:


> No resistor. Just the ESR and short cables. From a current source. Peaks in the range of 160kW.


WOW, how do you close the circuit?


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## major (Apr 4, 2008)

dimitri said:


> WOW, how do you close the circuit?


The motor inverter is directly connected to the cap bank. In this case, there are no batteries. You can see half the cap bank in this picture. 

http://www.diyelectriccar.com/forums/showthread.php?t=25994&highlight=ultracapacitor+candy


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## JRP3 (Mar 7, 2008)

ElectriCar said:


> Do you know how a controller works?


Not enough to build one, but yes. I just think you've taken one individual's anecdotal experience and run with it in the face of reality. Others who know more than me concur. Have fun with it, but don't be even a little surprised when there is little or no range improvement.


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## Tesseract (Sep 27, 2008)

ElectriCar said:


> ...
> Old batteries have higher internal resistance. Power = amps x volts. Amps x resistance = volts. Higher amps = higher voltage drop in the pack.


So far, so good...



ElectriCar said:


> So an old pack for a given amp draw (current pulled from the pack) will result in higher voltage drop and less voltage reaching the controller. Less drop in the pack due to the caps = more voltage reaching the controller. Once again, with the caps in place the amp draw off the pack is reduced and less voltage is wasted leaving more to power the motor.


Things get sort of murky here, though. The capacitor bank MAY reduce the equivalent series resistance of the battery pack as seen by the controller - that depends on many different factors, though. For example, are these older (surplus) electrolytics, especially "computer grade" 85C rated Coke can sized electrolytics? If so, they are undoubtedly well past their prime and might have 1 ohm of ESR each (whereas a brand new cap of the same size/voltage rating might have an ESR of 0.1 ohm). 

Then there is the inductance of the wiring between the battery pack, cap bank and controller - it's not much, to be sure, but when you are dealing with current pulses in the 100's of amps even a few uH are significant. This is where I could see a cap bank providing the most benefit, along with being able to counteract the sag from the delay in electrochemical reactions inside the battery to produce a sudden increase in current (on the 10's of milliseconds scale maximum, though, since the amount of capacitance needed quickly becomes impractical).

As for reducing the amount of current drawn from the battery pack, though, this is where things really get dicey. It is actually reasonable you could use enough capacitance to both reduce the apparent internal resistance of the batteries as seen by the controller and mitigate the effects of the time lag inherent in all electrochemical reactions. This would reduce the amount of instantaneous sag in pack voltage when a sudden increase in current is demanded by the controller. However, we are talking about time scales in the 10ms range, not the several seconds or more range. In other words, for that brief period of time the average current draw from the battery pack will be reduced, because the pack won't be allowed to sag as much.

Now, whether that amounts to anything is a whole 'nother story, and why I said things get murky at this point. I don't think it is worth the effort to test, but if you are going to test it you need to be very careful to ensure the runs are as identical as possible - I'd consider any test that involves driving on actual streets as invalid because it would be impossible to ensure equivalency between runs.


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## ElectriCar (Jun 15, 2008)

dimitri said:


> I am 100% with you on this one, but we'd have to agree on a way to measure results. How do you propose to measure results of increased range? We all know that range in EV is an elusive bastard, minor fluctuations of your right foot may skew results, I'm not even talking about randomness of traffic patterns. Clearly you don't expect more than 1-2% improvement, so how can you measure such small differences?
> 
> As for what other people say, don't forget "placebo effect". After you put an effort into something you are inclined to feel results, especially if you expected small improvements which are hard to measure. If you spend $100 and you "feel" improvement, that's worth the money even if it can't be measured in miles or volts


I may try do some testing with the vehicle stationary. I did that to compare power consumption at a given speed with various gears. I found that whether in 2nd gear or 5th gear at a given speed, the power consumption was nearly identical. I did it on the road on flat stretches at first then duplicated in in the shop. The difference wasn't significant enough to justify cranking my engine to twice the average IC engine rpm for a given speed.

I did that because some said at around 5000 rpm the FB1 motor was most efficient. However that puts a lot of stress on the tranny versus half that rpm. There may be a slight difference but IMO it's not worth the wear on the tranny for a slight gain.


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## Sparrow159 (Mar 30, 2010)

This looks like a great project. I'm hoping it could help me get more amps out of my sagging LiPO4 pack. But the date of this thread is 2009. There's no updates. Just curious how many others have done this and what are their results? What were your results with the double cap pack?

Thanks for being a pioneer.


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