# please welcome me with open arms?



## Woodsmith (Jun 5, 2008)

Hey, welcome!

Have you thought about selling the Porsche to a collector and using the money to EV a kit version?

You can have any combination you want but it is down to budget. DC is cheaper then AC and there are more 'off the shelf' components.

Low voltage means high current means bigger cables and connections (check the price on big cables).

High voltage means lower current, smaller cables and better efficiency due to less heat and I^2R losses.


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## IanJames (Apr 23, 2010)

You do realize there is no "kit" version of a 911 or 912... thanks for the input


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## piotrsko (Dec 9, 2007)

actually a VW bug conversion kit would probably fit with the possible exception of the transmission adapter. about the same weight, and size. I recall we used to put a bunch of squareback stuff on PMP's because it was cheaper than porsche stuff.

You don't have a lot of trunk.

Lot of terrifyingly smart people here on the site, but it is like pilots, ask 10 of them a question and you will get 25 different "correct" answers.

Your money. GROK it all over and decide what compromises YOU'll have to make to do YOUR thing. Headaches can be temporarily fixed by liberal applications of your favorite drinking medication. 

ask SPECIFIC questions like "How much WH per mile do I need?" "How far/fast can I go with floodies?" expect a hundred different answers as to why their method is the best.


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## EVfun (Mar 14, 2010)

None of the choices you have outlined are "right" or "wrong." They are just options to choose from based on your budget and requirements. 

There is no reason to be hung up on 144 volt systems. A pack voltage between 120 volts and 156 volts is pretty common because there are a number of motor controllers available in that voltage range. It is also a range that most all DC series motors can handle. These no longer really limit your options because programable higher voltage controllers are readily available now.

I recommend a DC drive using a series wound motor. Since this is the most common combination for conversions you can get the most good advice and see comparable examples.

I recommend you visit the EV Photo Album to get some ideas and see what has been done.


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## IanJames (Apr 23, 2010)

Thanks, this helps.

Tell me, what is the main difference in power between a 120v and a 144v system. Aside from the 1,000 to 2,000 dollars saved on lithium batteries, what is the actual power difference? Is it off-the-line or range?


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## benz18725 (Apr 8, 2010)

Amp hours has a direct relationship to range. Voltage is more or less the amount of torque, therefore acceleration and top speed. 

A 144v system will have better acceleration and "power" than that of 120v, but the range depends on the Ah of your batteries chosen. To compare range, you may want to compare pack capacities in kWh. This is simply (amp hour rating)x(total voltage). Higher is better, of course.

Correct me if I'm wrong on any of this.


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## Woodsmith (Jun 5, 2008)

IanJames said:


> You do realize there is no "kit" version of a 911 or 912... thanks for the input


Yeah, I checked before saying it and said it a bit tongue in cheek hence the  smilie.


It just seems such a good car as it was that it may rate as one I wouldn't convert if it was mine.

However, good on you for wanting to convert.


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## Tesseract (Sep 27, 2008)

benz18725 said:


> Amp hours has a direct relationship to range. Voltage is more or less the amount of torque, therefore acceleration and top speed.
> 
> A 144v system will have better acceleration and "power" than that of 120v, but the range depends on the Ah of your batteries chosen. To compare range, you may want to compare pack capacities in kWh. This is simply (amp hour rating)x(total voltage). Higher is better, of course.
> 
> Correct me if I'm wrong on any of this.


Ok, since you asked for it 

More amp-hours (Ah) equals more range _if_ the pack voltage is equal. That is to say, a 200Ah/144V pack won't have any more range than a 100Ah/288V pack. 

And torque is proportional to current, while speed (rpm) is proportional to voltage. These relationships hold true for all motors, AC or DC, btw.

Carry on


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## Qer (May 7, 2008)

IanJames said:


> a) It will be a city car. But we have hills in Vancouver. And I have a lead foot.


Hills + lead foot -> loads of Ampere. I think it's safe to say that a typical shoebox controller won't make you satisfied. A couple of hundred amps might be enough to get you uphill, it might also be enough to do some tire screeching on flat ground, but I'd bet it won't be enough to do both.

Lead acids are good for serious Amps and don't require BMS but they suck at range and low temperature. Lithium don't like brutal discharges (except A123 and some other special kinds, but they come with a serious price tag) and requires careful handling but on the other hand gives much more range and weight less.

A bad charger can kill off a pack rather quick no matter chemistry, a good charger might be pricey but pays off in the long run. Going for a cheap charger or a controller that can't limit battery current and using Lithium will get rather expensive pretty quick, Lithium is rather non-forgiving to abuse but treated correctly they'll run much longer than lead acid.



IanJames said:


> b) do I need to be fixated on the 144v system?


Depends on your controller. Most modern, microcontrolled controllers have a much wider Voltage span than old, Analogue controllers. The Soliton 1 (which is partly my creation so I'm a tad biased here  ) can handle anything from 9-342 Volt in and can be configured in any relevant way to avoid motor- or battery abuse.


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## Guest (Apr 24, 2010)

benz18725 said:


> Amp hours has a direct relationship to range. Voltage is more or less the amount of torque, therefore acceleration and top speed.
> 
> A 144v system will have better acceleration and "power" than that of 120v, but the range depends on the Ah of your batteries chosen. To compare range, you may want to compare pack capacities in kWh. This is simply (amp hour rating)x(total voltage). Higher is better, of course.
> 
> Correct me if I'm wrong on any of this.



Well I can tell you first hand about this but at a different voltage. I built my Ghia with a 72 volt system. Thought it was decent and was able to get a top speed of about 65 mph with that. I kept that for awhile and then decided to make the jump to 96 volts which is the next logical step up. Since the Ghia is limited in space and I have 6 volt batteries in the car I was limited pretty much to a max of 16 batteries which in series is 96 volts. Heavy as hell now and running 96 volts and using a controller that can dish out 700 amps ( not that the floodies can live long at that output ) but I usually never see those high currents. The car now accelerates like it has a stock 1600 vw engine and gets to freeway speeds nicely and my top speed is now 85 plus. The plus being if I ride it a bit longer it will go faster. But that is pushing the limits of the battery pack. So I went from a top speed of 65 to 85 and the acceleration was exceptionally better from 72 to 96 and I'd expect that the difference would be even better if I could go to 120 or even 144 or even 156. Because the higher voltages will allow me to actually use the amperage for acceleration better without killing off the batteries. So my next logical step now is to go to 156 volts (the limit of my controller) and go with lithium. I'd go 200 Ah only because I want the range. I think I can fit enough into my little car to get that. Weight would still be less than what I currently have now. 

By the way, welcome and I agree with the other guys that it is usually requirements that dictate what you need or want along with budget. It can also be dictated by the size of vehicle your converting. The Ghia and the 914 are small cars but you can put in a decent pack of batteries. Yes, a VW adaptor plate will fit the 914. I think that you can even fit a large 11" motor in there too. 9" would be perfect. A Warp9 would do. Rebirthauto.com has an excellent adaptor plate setup for a good price. The quality is top notch. I have one. 

AC is fine if you can afford the motor/adaptor/controller setup. Many you can buy as a kit are expensive and not overly powerful. They work but I'd want better. So I decided to go with DC. The regen thing would be nice but all in all it is really not needed. The biggest thing regen can do for you is to help you stop your heavy vehicle. With lithium you lighten the load by quite a bit. Be sure you have a minimum of disk brakes up front to help stop your vehicle. Drums work but can be anemic. I have drums all around on my Ghia at this time and that extra 1,020 lbs of lead is noticeable when stopping. 

You picked a very good car and a fun one too. Have you ever driven one? I have and they are great. A street legal go kart. How fun is that. 

Pete


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## Guest (Apr 24, 2010)

I hope this will help IanJames. I am running 144Volts FLA and an advance DC and Curtis controller. There are some killer hills here in the Ozarks. The 144volt setup works satisfactorily. Tesseract. I have toyed with the idea of getting rid of three of the eight volt batteries shaving 189lbs of the weight off the car and dropping the voltage to 120V. This would cause more current draw on a 6% grade at 120v than 144v even with the 189lb weight loss. Yes? Therefore shortening the range? IanJames There are some here that are running 12 volt batteries and I guess happy with such. My first pack was 12X12. about 900lbs. vs. the 1134lbs. for the 18 eight volts I now run. The 8volt are a compromise between 12volt and 6volt. The 12volt are lighter but with less ah and 6volt with much more ah but way to heavy for my conversation. Its a Fiat X19. You said you have a lead foot. Well not all the lead is in my batteries. Some of it is in my foot too. The 12volt didn’t last very long or go very far under those conditions. The only time a heavy foot comes in handy with a EV is if it is a amp sucking monster and you only have to go a quarter mile. If you don’t already have or haven’t read Build Your Own Electric Vehicle by Bob Brant do so. It is over ten years old but still has useful information. There is a newer edition but someone else here will have to give you the name.


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## IanJames (Apr 23, 2010)

okay NOW we're getting somewhere! Thanks guys!! I'm particularly interested in the downside to Lithium. Very interesting. I'm starting to think I need to find a way to fit 18 8v batteries in the little monster...

First of all - the car is a 912. Not a 914.
And there are disc brakes front and back. 

Okay so now I'll get a little more specific:

Acceleration.

And the question of weight. 18 batteries adds about 1100 pounds of weight. The car is listed at (dry weight) 2100 lbs and a max permissible weight of 2870. My my guess, the engine is about 150 lbs (conservatively) so that about equals the engine weight I will have removed. The gas tank (full) is about another 130 lbs. So I'm 180 lbs OVER the max. (correct me if I'm wrong on the stats...)

Am I in trouble here? 

Plus me (175 lbs) and the occasional lite-weight passenger, what kind of acceleration should I expect? 

The original car had a 0-60 time of 11.5 seconds. (remember this was a 912, not a 911) What should I expect from 144v using the 8v batteries?

I was planning on a Curtis 1230 controller.

Jump in!!


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## IanJames (Apr 23, 2010)

PS - thanks for the info on the Ghia. That is a very relatable car to the 912.


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## EVfun (Mar 14, 2010)

You have to decide how much power you "need." Roughly, one kilowatt of pack and controller potential will get you one horsepower. By that I mean, a 144 volt pack used with a 500 amp controller will get you about 72 horsepower (144 times 500 equals 72000 watts which is 72 kilowatts.)

The general rule of thumb given by Tesseract is correct, increasing voltage moves the motors power band into a higher rpm range while increasing amperage increases the motors maximum torque. 

Range is a function of how much battery power is onboard. Pack voltage times the pack amp-hour rating will give you pack watt hours. Watt-hours divided by 1000 will give you kilowatt hours. 

That is 2 bits of information sound nearly the same but are very different. Kilowatts indicates the horsepower you will have and kilowatt hours will indicates the maximum range you have.


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## IanJames (Apr 23, 2010)

Thanks EVFun - Helpful, but That's the stuff that makes my brain hurt. I've never been good at math... 

PPS - Gottdi:
How much range are you no getting?


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## Tesseract (Sep 27, 2008)

notmrwizard said:


> ...Tesseract. I have toyed with the idea of getting rid of three of the eight volt batteries shaving 189lbs of the weight off the car and dropping the voltage to 120V. This would cause more current draw on a 6% grade at 120v than 144v even with the 189lb weight loss. Yes? Therefore shortening the range?...


Yes, more current draw; yes, you'll be shortening the range not only because there will be less batteries, but also because you'll be drawing a higher average current from the ones that are left (which makes the Peukert effect worse). This, of course, assumes that you can meet your speed goals with the lower pack voltage


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## IanJames (Apr 23, 2010)

Oops - typo man strikes again...

GOTTDI: How much range are you getting with your current setup? (are the weights similar to my 912 - 2100 dry/2800 laden?

And TESSERACT - your controller sure LOOKS cool. I'd have to consider it simply because of the cool factor! What does it offer over and above a Curtis?


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## toddshotrods (Feb 10, 2009)

IanJames said:


> ...And TESSERACT - your controller sure LOOKS cool. I'd have to consider it simply because of the cool factor! What does it offer over and above a Curtis?


Ha! That's like asking what the space shuttle has over the Wright Bros. first successful bird! 

Sorry, coudln't resist!


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## Guest (Apr 24, 2010)

IanJames when you build you can do better than a Curtis. The only reason I have one is it was what was recommended and the selection was smaller in 1999. Then after the first one blew up EVA gave me a pretty good deal on the second one. I am hoping to upgrade this year if I don’t decide to sell everything first.


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## DONEAL (Sep 10, 2008)

Web page for ev porshe
http://www.evporsche.com/


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## IanJames (Apr 23, 2010)

Thanks DONEAL. I've seen those guys. They are doing conversions on much newer 911's. But there are some interesting photos of the engine compartments that are helpful. I'd really like to meet someone who as done a 912. I sort of have, but they are in Germany. http://www.classic-ecars.de/


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## DONEAL (Sep 10, 2008)

Yes, good pictures, here is another page for adapter plates, not sure if it will work for an 911 or not.
*Web page http://www.ecosmotors.com/parts.html*
*High-performance Adapter Kit
*Connects ADC or Netgain motors to stock VW/Porsche transmission
Patented flywheel allows the use of a stock clutch
Includes starter block-off plate and mounting hardware
Recommended for 120V+ high-performance vehicles


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## IanJames (Apr 23, 2010)

here's a new idea! I found a fellow in Germany who has converted the exact same car and has shared some info. Can you help me decode this?

"...we now use 20 Optima batteries 12V / 55Ah. wired to parallel pairs with 12V / 110Ah, whitch then are wired to a series of 10 pairs, so, 120V / 110Ah. The difference to the 15 US 8V batteries is a slightly lower tension when fully charged, but the tension of the Optimas is much more stable ofer discharging. The range of our car is about 95Km, going still relaively strong with battery tension down to about 112V..."

Have any of you had experience with this sort of creative wiring?
Insights? Opinion?


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## EVfun (Mar 14, 2010)

He has a 59 mile range. The battery pack consists of 2 Optima batteries wired together parallel (+ to +, - to -) and then these buddy pairs are wired in series for a 120 volt pack. 

When he is talking about "tension" I believe it is s reference to the pack being more "stiff", meaning less voltage sag under load. It is not desirable to drag a lead acid cell under 1.75 volts (so 10.5 volts for a 12v battery, 7 volts for an 8 volt battery.) It tends to shorten cycle life. In short, he find this to be a more powerful pack.

I don't recommend buddy pairs with lead acid batteries. It's controversial, but I don't find it to be a terribly reliable combination. In practice, lead acid doesn't always share as good as theory would suggest. 

You have found a good source for information about motor choice. Either he has it right or he can say what isn't a good choice.


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## IanJames (Apr 23, 2010)

Thanks, you answered my questions about the wiring. It is all greek to me!! What I do understand is weight v. power. 

Can anyone help with the weight to power calculation? I'm trying to determine if the 144v system which requires more weight in batteries will actually give me more power and range than a lighter load of batteries and 120v? 

Here is the last correspondence:

"We also use the ADC FB1 4001, our 912 accelarates in about 10sec from 0 to 70Km/h, from 70 to 100Km/h then takes about another 10sec. The Optima pack weighs about 400Kg, the complete car about 1250Kg. The 18x8V pack will weigh about 550Kg, so it may be, You will not get much better accelleration than with 120V system. The addittional 150Kg batteries will reduce the range when You have to climb hills, and You don`t get back the energy when going down the hill again. If You have many hills where You live (no, I never have been to Vancouver), You should provide regenarative braking (the Zapi controller brakes when releasing the "gas pedal" and brakes harder when steping on the brake pedal), to our experience the range gain is about 10% to 15% in flat areas, much more when climbing hills (range can be only 50% when You have to climb a lot).

If You have a look on our website, the photos show the Optima setup. Before we started conversion of our 912 to LiFePo batteries, we thought about fitting one additional pair of 55Ah Optimas to 132V / 110Ah, this will give to our experience) abillity of spinning wheels when going off (slightly). With the 120V Optima system You have spinning wheels on the wet street and You are able to drift the 912 around 2nd and 3rd gear curves."

All input is GREATLY appreciated!!!!


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## DavidDymaxion (Dec 1, 2008)

IanJames: I'm converting a 911. You can see a few details on my website, http://ExplodingDinosaurs.com .

The 912/911 is a great choice for an EV. They are light, pretty good aero, are designed to be a bit tail heavy (as often happens with conversion EVs), have great brakes, a strong tranny, and lots of aftermarket support.

I'm converting my 911 for about the price of a racing rebuild on the motor. Small wonder there are kits to put Chevy and Mazda rotaries in these cars! You need a deep love of oil if you own a gasser 911. Mine held something like 15 quarts of oil. There was a remote oil reservoir, remote oil filter, separate oil cooler (some cars had a 2nd one in the front fender!), meters of oil line, motor mating surfaces at the center, top and bottom of each pushrod tube, cylinder top and bottom, valve cover gasket, front cover, rear oil seal... Several of these places leaked on mine... The underside rear meter of the car was coated with 1 to 10 mm of varnished oil... It took forever to get it off the car and tranny. I pity the poor soul that has to clean the old motor. 

I think I could get 11 batteries (Optima Blue Tops) up front, at floor level. I think I could get 10 batteries at floor level in the rear, with an 11 inch motor. A 13 incher would be tight, maybe couldn't fit the batteries. I could get three batteries above the smuggler's compartment, and 4 to 6 above the motor, so you could get as many as 28 Optimas in spacewise. Obviously you'd be over GVWR.

I don't recall seeing a dollar budget -- how much are you willing to spend?

It's hard to find a high power DC regen setup. Kelly has some controllers for sepex motors. If you want high power and regen, you'll need to do something custom, or go with expensive AC (like http://www.ACpropulsion.com ).

A quick and dirty power estimate:

(max controller amps * battery pack voltage) / 2

The /2 takes car of voltage sag and inefficiences, and gives you power in kW at the flywheel. Equate directly to hp, and that gives you approximate rwhp after driveline losses. This is very rough, but gives you a quick ballpark number. If you want real power out of the car, forget this 144 Volt stuff and go high voltage (240 to 336 Volts) and run a Zilla 2k.

Your clutch won't even be up to the kinds of torque an electric motor can produce, I'd suggest you get a grabbier racing clutch, and/or a stronger pressure plate. I got a Kennedy Engineering Products pressure plate. It triples the clamping force, and saves several pounds of geared, rotating weight.


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## IanJames (Apr 23, 2010)

Cool project David Dymaxian! My project is less ambitious than yours but I totally appreciate you jumping in. Here's the difference as I see it. I'm doing a 1967 Porsche 912. The 912 was originally a poor-man's 911. All the look with the performance of a slightly beefier VW!

It will be a daily driver. I have a lead foot, yes. But I don't expect performance any greater than the original. 0-60 was about 12 seconds. If I can get that with a little fun off the the line I'll be happy. The next question is range. I'd be overjoyed with 75 miles.

Here's what we were planning: 
9" ADC double shaft motor
Curtis 1231 controller

I NEED HELP WITH BATTERIES!! I'm having a hard time finding the budget for Lithium.
I haven't removed my engine and gas tank, so I'm not sure just how many 8v batteries I can fit. It seems to be the right choice if not going lithium. 

How big are the Optima Blue tops? The US battery 8v size I'm hoping to use is: 
L: 10 1/4" (260mm) W: 7 1/8 (181mm) H:11 1/4" (286mm)
I need to fit 18 to assemble 144v

Jump in!


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## DavidDymaxion (Dec 1, 2008)

Thanks for the kudos, it certainly has been great fun, and the car even moves, too!









I think it's of enough general interest I thought I'd answer here, too. The Optima Blue Tops are a little bit smaller:
http://www.optimabatteries.com/optima_products/bluetop/specs.php

I like that they have the terminals on the top, and have the marine wing nut terminals (handy for regulators).

If you do flooded batteries it's easiest to hose the acid off of them, so plan ahead for that with drain holes. Something nice about the Optimas is they are truly sealed batteries (under normal operating conditions, anyway), so they don't spit acid.

You don't have a "slighty beefier" VW, you have a "much beefier" VW! The Porsche tranny and brakes are much tougher. The Porsche is much more stable, too. You can even "fix" that oversteer thing with battery placement. 


IanJames said:


> Cool project David Dymaxian! My project is less ambitious than yours but I totally appreciate you jumping in. Here's the difference as I see it. I'm doing a 1967 Porsche 912. The 912 was originally a poor-man's 911. All the look with the performance of a slightly beefier VW!
> 
> It will be a daily driver. I have a lead foot, yes. But I don't expect performance any greater than the original. 0-60 was about 12 seconds. If I can get that with a little fun off the the line I'll be happy. The next question is range. I'd be overjoyed with 75 miles.
> 
> ...


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## IanJames (Apr 23, 2010)

Which model of "blue tops" have you used?


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## DavidDymaxion (Dec 1, 2008)

Optima Blue Top D34M


IanJames said:


> Which model of "blue tops" have you used?


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## TX_Dj (Jul 25, 2008)

EVfun said:


> I don't recommend buddy pairs with lead acid batteries. It's controversial, but I don't find it to be a terribly reliable combination. In practice, lead acid doesn't always share as good as theory would suggest.


To expand on this a bit- Any time you put two batteries in parallel, regardless of capacity, the stronger one will discharge into the weaker one. This is desirable in some situations, and it causes the buddy pairs (or parallel strings) to "equalize" very well with each other when they are new and well-equalized to start with.

But, if one cell develops a problem between pairs or strings, it can quickly cause a thermal runaway condition inside that battery or worse.

The same can happen in series, but typically the issue only manifests while charging or discharging, rather than spontaneously while your car is sitting unattended in the office parking lot.

Example: This year I replaced the batteries in my cordless mower. On battery was still good and strong, and charges out to 97% capacity. The other has a cell issue, and during discharge got very hot. After discharge, this pair (in series) had the stronger battery in the mid 12's and the weaker battery in the upper 10's. If these two batteries were wired in parallel, the stronger battery would be discharging without any current limitation into the weaker battery, going over it's 0.2C max charge rating. The battery would get hotter and hotter until it vented or until it caught fire.

In my racing scooter, I run two strings of high-rate 12v AGMs @ 36v/6Ah each through a fast switching dual-diode. This allows the batteries to share the load, minimizing voltage sag and peukert effect, without putting the batteries at risk of discharging into each other.

I am not a fan of paralleling any batteries in buddy pairs or strings. And my buddy, who is a retired EE specialist (I.e. when large company's R&D teams couldn't solve issues in their designs in months, they'd consult with him and he'd solve the issue in hours/days/weeks by himself) agrees- he's the one that spec'd the diode package I use in the scooter.

That'll be $0.02, please.


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## DavidDymaxion (Dec 1, 2008)

My parallel strings batteries very quickly get out of balance, unless they get a few shots of hundreds of Amps of regen. When I put on buddy pair wires the balance stays much better, though they still slowly drift out of balance and need regulators. No catastrophes so far, but they are only about 9 months old and haven't been used much.


TX_Dj said:


> To expand on this a bit- Any time you put two batteries in parallel, regardless of capacity, the stronger one will discharge into the weaker one. This is desirable in some situations, and it causes the buddy pairs (or parallel strings) to "equalize" very well with each other when they are new and well-equalized to start with.
> 
> But, if one cell develops a problem between pairs or strings, it can quickly cause a thermal runaway condition inside that battery or worse.
> 
> ...


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## IanJames (Apr 23, 2010)

really great info. Now here's yet ANOTHER idea... Supercapacitors. Here is a note from a fellow from Xaviartechnologies.com 

"...Maxwell capacitor modules. They can store much more energy than a battery, charge faster, and can cycle a million+ times. Two 75volt modules is 150volts; as opposed to (12) 12 volt batteries. It takes up less room and less weight means more miles per charge. "

At a quick glance I love this idea. It looks to cost about 10k for two 75v boxes. BUT is there anyone here with realworld experience? Range, power? I'm not entirely sold on Lithium. I have them in my vintage Vespa scooter conversion and they are not the magical solution they appear to be. 

Anyone? (and in keeping with the tone of this thread, please keep things in layman's terms? - IE, 0-60 acceleration, range in miles, hilly terrain etc) 

THANKS!


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## Guest (Apr 29, 2010)

> I have them in my vintage Vespa scooter conversion and they are not the magical solution they appear to be.


Not all lithium batteries are the same. I'd not judge the ones being used for EV's to the ones you find in these bikes/scooters. 

Pete


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## IanJames (Apr 23, 2010)

I'm sorry I mentioned the scooter... 

Supercapacitor anyone? Maybe you gigantic brains (and I mean that sincerely and in a positive way!!) can decode this into something that gives me some idea of real world usage: 

http://www.maxwell.com/ultracapacitors/datasheets/DATASHEET_BMOD0094_1012179.pdf


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## Guest (Apr 29, 2010)

I'd work with what is truly available and tried and true. Floodies, AGM, NiCad, NiMH, and any variation of such and Lithium. No one is going to be the saving grace, but a combination of all. 

Pete


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## Guest (Apr 29, 2010)

Supercaps will find there place.


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## IanJames (Apr 23, 2010)

Isn't this cool - from the ARGONNE NATIONAL LAB:

Charging Ahead: Taking PHEVs Farther on a Single Battery Charge


Ultracapacitors will dramatically boost the power of lithium-ion batteries, enabling plug-in vehicles to travel much further on a single charge.
Every six months, we’re reminded to change the batteries in our household appliances: smoke alarms, flashlights and radios. But what if you had to change the battery in your plugin hybrid electric vehicle (PHEV) just as often?

Fortunately, researchers at Argonne may have found a way to exponentially increase the calendar and cycle lifetimes of lithium-ion batteries. Electric double-layer capacitors— typically referred to as ultracapacitors—have an energy density thousands of times greater than conventional capacitors and a power density hundreds of times greater than lithium-ion batteries.

In an electric vehicle drivetrain, energy density provides sustained speed, while power density facilitates acceleration. “Energy density is what allows you to run a marathon; power density is what enables you to sprint,” said Ted Bohn, an automotive engineer in Argonne’s Center for Transportation Research.

“Ultracapacitors aren’t of much use just by themselves,” he added, “but when you couple them with lithium batteries, they dramatically boost the performance of the entire vehicle.”

When an electric vehicle merely needs to maintain a particular speed, it requires little of the battery’s power density. However, when the car needs to accelerate from a standstill to a cruising velocity, today’s lithium-ion batteries must strain to provide the necessary “oomph.”

“Ultracapacitors give an electric vehicle the initial boost it needs to get going,” Bohn said.

A PHEV or pure electric vehicle needs a battery with sufficient power density to accelerate the vehicle quickly. A vehicle that uses an energy-dense battery that lacks sufficient power density will fail prematurely, possibly in a matter of months if driven aggressively. By using the same potentially lower cost energy-dense battery, in combination with ultracapacitors, the vehicle will have sufficient performance and the batteries should last 10 years or more.

Today’s hybrid cars recharge their batteries by transforming kinetic energy from the wheels into potential electrical energy as the driver brakes. Conventional lithium-ion batteries, however, absorb this energy slowly and inefficiently. By contrast, ultracapacitors, because of their immense internal surface area, sort of soaking up reclaimed energy like a sponge.

“By integrating the entire system,” Bohn said, “we can drive down the cost. When we can put these various electronic elements together, we’ll transform an $8,000 battery into a $4,000 allelectric drivetrain system.”

Funding for this project was provided by the U.S. Department of Energy’s Vehicle Technologies Program under Lee Slezak.

March 2010


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