# what is the minimal full function BMS for Li



## dtbaker (Jan 5, 2008)

trying to put together a minimal but full function BMS for a Li system.... Does adding a 'volt-blocher' per cell do the job, or would I need other stuff for appropriate protection?

I don't really care about sophisticated display, output, etc. I just would want the pack protected from over/under voltage and temp warnings right?

so.... whats the minimal setup and cost for 'doing it right' without going overboard?


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## JRP3 (Mar 7, 2008)

Jack Rickard would tell you the minimal setup is no BMS  I'd like for him to be right but I'll probably be going with volt blochers, though I'm considering a setup where the shunts are outside the vehicle and only connected when charging. Don't know if this would be practical, but I am a bit nervous about possible shunt problems causing a vehicle fire.


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## dtbaker (Jan 5, 2008)

I would agree that the volt-blochers at a minimum would be what I would consider just to have a better feeling about cell balancing during charge. I have not read close enough whether they handle over/under or thermal monitoring as well since it seems that IF out of balance, cells can get pretty hot during charge or discharge, correct?


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## JRP3 (Mar 7, 2008)

I think the high and low voltage outputs should signal imbalance before a temperature difference shows up and the shunt should bleed off the extra charge on overvoltage during charging.


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## JRP3 (Mar 7, 2008)

I would add a fuse to each one for added protection.


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## MN Driver (Sep 29, 2009)

JRP3 said:


> Jack Rickard would tell you the minimal setup is no BMS  I'd like for him to be right but I'll probably be going with volt blochers, though I'm considering a setup where the shunts are outside the vehicle and only connected when charging. Don't know if this would be practical, but I am a bit nervous about possible shunt problems causing a vehicle fire.


If you charge your battery like Jack Rickard your batteries[theoretically] will never reach the shunt voltage and therefore the heat problem in the shunts would never be a problem unless you were going to be throwing enough total energy in a cell to destroy it anyway.

Basically he in essence aims to keep all voltages below the max safe voltage once balanced initially and has a low current final charge phase where he ends charging at about 1 amp and then stops and resumes charging a few times. In the end he probably isn't getting the maximum possible range out of a pack, but he isn't as concerned over range as most of everyone else is, he has a pretty good range compared to many people with his pack/vehicle combo it seems.

The problem with Jack Rickards charging process is if one cell rapidly starts to fail in an unexpected manner, such as suddenly having a reduced capacity or high internal resistence(which I have run into personally with consumer electronics using LiIon cells and have no reason to think that LiFePO4 is immune, because I don't think it is), the cell will rapidly go over voltage and destroy it. Whether or not the high voltage that occurs causes the spewing of toxic smoke or starts the cell(followed by the pack and car) on fire is something different. I think with Jack Rickards plan, the least that should be there is some sort of monitor to trigger the pack to stop charging shall one cell suddenly have a voltage jump, but based on his dual parallel pack design and Brusa charger, he has it set up so that if one of the strings raises in voltage to a certain level over the other one it will terminate the charge and he can investigate, so essentially he has a way of knowing there is an issue. If he didn't check it this way, I'd think he was setting a cell or a few up for failure.

With a shunt, the idea is that you reach the final resting voltage and start bleeding your current that would normally go into the cells once they are full and you will be as charged as you possibly can be based on the final voltage you choose which seems that the most comes from 3.6v from SE cells, 3.7v from TS cells from what I've been reading here in the forums. ...but if you were thinking of setting your cells that you wanted to have max out at 3.7 volts, then if you set the charger to terminate at 3.65 volts or so multiplied by the number of cells then if you have a well balanced pack and shunts set at 3.7, then you might not get much shunting at all. I'm not sure of the 3.65 volts setting though, it would take some experimentation to find out the exact point to where you would minimize shunting(therefore less shunt heat) for the maximum charge and range. An oversized pack for the range you are using or during shorter trips between charges you could use such a plan for less shunting. I plan to have a pack that can take me 100 miles for when I need it but have a typical 60 miles between charges so I'd have the room to pretty much have shunts be the failsafe, of course implementing their high voltage cutoff, which making sure the voltage stays in range is the most important feature of a BMS.


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## dimitri (May 16, 2008)

Its funny and ironic that I was also obsessed about shunting/balancing before I got my cells and we had this discussion thread with AndyH where he was trying to convince me that LVC protection is more important than HVC and I didn't believe him at first....

Well now that I have 3000 miles on my LFP pack, I can say balancing is good, but not nearly as important as LVC. Sure, we all plan for 80% DoD, but there will be one time when you will get 100% DoD for whatever the reason, life is funny that way.... and LVC will really save your ass.

Latest version of VoltBlochers has both LVC and HVC and balancing, so that is all you really need, but I can't stress enough how important it is to have a cell level voltage display like PakTrakr.

You think you know how well your cells are doing, but unless you see the voltage of each cell under load, you don't know squat and you will eventually kill at least one cell. You can argue that one cell replacement is cheaper than buying a PakTrakr, but you have been warned 

Why do I feel that we have discussed all this a million times? Searching older threads can do wonders....


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## MN Driver (Sep 29, 2009)

Although if not for every cell, but for a general idea of pack temperature, I'd like to know how warm those cells are. That way when I end up doing a 3C run to test top speed or showing off the car to someone for the first time, or maybe even take it for a few laps on the track someday just for fun, I can monitor the battery to make sure I'm not getting too hot, granted the external temp at the top of the case is likely going to be cooler than inside but at least it should give a general idea of where things could end up.

Has anyone considered a thermal fuse used in some way or another to protect their pack? It's something I've considered for the ebike I'm designing since I'll be running it overspec but for a large scale car pack, would an 3C draw bring up a temp issue that would warrant this? I think it would if the 3C draw lasted for a minute or more without some form or active cooling. I could be wrong, but has anyone done a long heavy draw on the cells and checked?


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## JRP3 (Mar 7, 2008)

dimitri said:


> Latest version of VoltBlochers has both LVC and HVC and balancing, so that is all you really need, but I can't stress enough how important it is to have a cell level voltage display like PakTrakr.


Can you really watch the display for each of your cells as you're driving?


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## Amberwolf (May 29, 2009)

This is hardly a part of a minimal BMS, but:

I think what I'd want is a colored-dot display that just showed green for cells above a setpoint, amber for cells below that setpoint, and red for cells below safe LVC. Preferably the shape of the display would reflect the physical positions of the cells within the vehicle, to make it easier to find the cells later to troubleshoot the problem, without having to use a separate reference. 

The voltage reading would be displayed in amber or red to help remind you where on the curve the voltage is--if it dips below LVC an amber display would change to red at that point. 

I'd prefer but wouldn't require a way to touch a dot and have it bring up the actual voltage reading for that cell, so you could watch it while you did testing, on-road or in-shop. 

If the dot display was small enough (as it should be) then I'd have it so a touch on the area of the display brought up a "zoomed" view of those few cells that were under the fingertouch, whcih would each then be large enough to touch a single cell display accurately, to bring up the cell voltage reading.


Another thing I'd like to add to it is a thermal sensor (several, actually) for each cell, which would light up an additional blue dot for that cell on the same dot display if any of them went over the setpoint temperature. Touching the cell when that is active will bring up the temperature reading (in blue). 

If it also has a voltage problem, it could be set to autotoggle between temp and voltage every second and a half or so, swapping colors as needed, until you touch the display again at which point it "locks" to whichever one you touched. Touching again goes back to toggling, double touching/tapping goes back to just the dot display.


If there is enough dashboard screen real estate, I'd prefer to leave the dot display up all the time, and place these readings individually next to it. The cell being displayed would have a brighter dot than all the others.
________
Sex_Dirty


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## tomofreno (Mar 3, 2009)

Dimitri,

So you have your own design shunt regulators and paktrakers on each cell as well? How did you interface your LCV signal to your controller? I have a different controller, but maybe it will help me. Right now I just plan to have the LCV signal light up my "Check Engine" light.


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## tomofreno (Mar 3, 2009)

Hi Dan,

I am in the final days of conversion and am using Voltblochers (vb). I also have adhered a thermal fuse to the back of each board with permatex gasket compound. This permits me to easily cut one off and replace it, withstands 600F, and adheres well to the board. These are daisy chained together and are connected to 12V during charging (connected to the N.O. contact of the "charger relay" which disconnects 12V from other things during charging). They are in series with a DPST relay that cuts both phases of the 240VAC to the charger if a fuse opens. They also drive another relay that connects pin 2 (hot reg) to pin 1 (+5V) on the Manzanita PFC30 regbus input. This also shuts the charger down. The thermal fuses open at 200F, hot, but well below the combustion point for any materials in the battery boxes.

The vb's shunt about 0.7A at 3.6V, with the standard 1.5 Ohm resistor, that's a bit less than 3/4W power dissipation in the resistor. The transistor probably contributes a similar amount. I tested one at this current and the resistor felt slightly warm.

I am using a PFC30 charger. The HCV signal from a vb drives a mosfet-based relay connected between pins 1&2 on the regbus input to the charger. An HCV signal turns on the relay and shuts down the charger and starts the charger's timer. When the signal shuts off the charger resumes charging. The timer is reset every time a vb HCV signal is sent after a period of no signal, so the charger cycles on/off until it reaches the pre-set pack voltage, at which point it shuts off. If the HCV remains on long enough for the timer to time out, the charger also shuts off. I will have to experiment with this, but hope to set this time short enough so that a cell driven up to 3.6V would put out a HCV signal long enough to time out and shut off the charger. I have set the HCV level to 3.50V and will set the pack voltage setpoint on the charger to 124V, or 3.44V/cell. I expect that normally the cells should be balanced well enough that the pack reaches 124V and the charger shuts off with no or few cells hitting 3.5V. 

It takes about 0.1V drop across the shunt transistor to get much current flow, so the max shunt current should be around 3/4A, and power dissipation should be small even when a cell does get somewhat out of balance. If something goes way out of wack and a board gets hot, the thermal fuses should shut the charger down.

This of course does not charge the pack all the way to the max (for SkyEnergy cells) 3.6V/cell or 130V. But the difference in stored energy is only (3.6-3.44)*36*180 = 1037Wh, or about 3 or 4 miles out of an expected 55 - 65 mile range. I reduce the risk of overcharging my cells, plus, I drive down about a 200 ft change in elevation over about 3/4 mile when I leave my house and expect regen (HPGC AC50 motor) to suppy part of this on the drop. Speed limit is 25mph, so say I get 100A regen (total guess) and go 25 mph, then it takes about .75/25 = 0.03 hr to get down the hill so I would get 124V*100A*0.03hr = 372Wh, this will still keep me safely under the 3.6V/cell max, and I don't expect I'll get 100A regen all the way down.

I think this gives a fairly safe system for relatively low cost, but of course with any system you can imagine scenarios where it could fail (for example a thermal fuse fails to open). I would like to be able to read out cell voltage and temperature on the dash, and may upgrade to something better someday, as I expect new and improved bms will be coming out over the next couple years. If you want a turn-key system I would wait a while and see what becomes available. On the one hand I like systems with lots of redundacy and operational checks, on the other I like something simple with immunity from efi, and reduced risk of a chip failure. 

Tom


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## JRP3 (Mar 7, 2008)

I like your setup but if your HCV is set at 3.5 volts and shuts the charger off at 3.5 how would a cell ever get to 3.6 volts? Once it drops down and signals the charger to come back on wouldn't it shut it down again as soon as it or another cell hits 3.5 again? Also, pictures and part numbers of everything


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## dimitri (May 16, 2008)

JRP3 said:


> Can you really watch the display for each of your cells as you're driving?


Yes, Paktrakr has display mode called "All Bats", shows a bar graph with each vertical line representing individual cell. As you accelerate, you see those lines drop lower, but the bad ones drop deeper than usual and you immediately spot them.


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## dimitri (May 16, 2008)

tomofreno said:


> Dimitri,
> 
> So you have your own design shunt regulators and paktrakers on each cell as well? How did you interface your LCV signal to your controller? I have a different controller, but maybe it will help me. Right now I just plan to have the LCV signal light up my "Check Engine" light.


I wired my LVC to a FET, which drives the buzzer and small relay. Buzzer is under the dash and its quite annoying, can't ignore it 

Relay has 5k resistor across NC pair and wired in series with throttle pot, so normally NC shorts this extra resistor, but when LVC occurs, relay opens and effectively cuts throttle in half, reducing the load on the pack.

This works with Soliton1 since it has 0-5V throttle input, so extra resistor creates additional voltage divider, reducing throttle voltage. If you have Curtis with 0-5K input, then you would add resistor in parallel to the pot, to reduce total resistance as seen by controller.

Hope this makes sense.


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## tomofreno (Mar 3, 2009)

> ...but if your HCV is set at 3.5 volts and shuts the charger off at 3.5 how would a cell ever get to 3.6 volts?


 I don't want a cell to get to 3.6V, so I have room for regen. But one might, depending on how fast cell voltage climbs with charge input at that high of cell voltage, how fast the charger shuts off, and how many repetitions it has to go through before the pre-set pack voltage is reached. I expect all of this will take some careful monitoring and tweeking during the first several charges to get it working acceptably. I'll post some photos and part numbers on my build thread - but only after I test and see if everything works!

Tom


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## JRP3 (Mar 7, 2008)

tomofreno said:


> I don't want a cell to get to 3.6V, so I have room for regen. But one might, depending on how fast cell voltage climbs with charge input at that high of cell voltage, how fast the charger shuts off, and how many repetitions it has to go through before the pre-set pack voltage is reached.


I would assume that the HVC signal is instantaneous and immediately shuts the charger off at 3.5 volts, no? I understand you don't want a cell to get to 3.6 volts, I just don't understand how the shunts could ever come into play at 3.6 volts if the charger is always shut off at 3.5 volts?


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## tomofreno (Mar 3, 2009)

> ...you see those lines drop lower, but the bad ones drop deeper than usual and you immediately spot them.


 Cool!


> I wired my LVC to a FET, which drives the buzzer and small relay. Buzzer is under the dash and its quite annoying, can't ignore it
> 
> Relay has 5k resistor across NC pair and wired in series with throttle pot, so normally NC shorts this extra resistor, but when LVC occurs, relay opens and effectively cuts throttle in half, reducing the load on the pack.


 Nice Dimitri! Have a part number/source for the buzzer? I assume you meant 5k to 0 for the Curtis. I'm not sure I want to have the controller cut power too much automatically, as I may be pulling out across the path of a semi, but a tad decrease would alert me. Seems the buzzer and light would suffice though.

Tom


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## JRP3 (Mar 7, 2008)

tomofreno said:


> I assume you meant 5k to 0 for the Curtis.


Isn't Curtis, and most controllers, set for 0-5K throttle?


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## tomofreno (Mar 3, 2009)

> I would assume that the HVC signal is instantaneous and immediately shuts the charger off at 3.5 volts, no?


 I expect the signal is, but it probably takes x msecs for the charger current to shut down. If this continues through tens of cycles because one cell is at significantly higher voltage than the others, it might get to higher voltage than 3.5V. As you say though, it should shut off the charger and keep it off until it relaxes to a lower voltage, then shut the charger off shortly after it comes back on and drives the cell back up to 3.5V. If this cell is significantly higher voltage than the rest, then this should continue until the cell remains at 3.5V long enough for the timer to time out and shut off the charger, or the pack reaches 124V and shuts off the charger.

Tom


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## tomofreno (Mar 3, 2009)

> Isn't Curtis, and most controllers, set for 0-5K throttle?


 Yes, I got confused.


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## Amberwolf (May 29, 2009)

JRP3 said:


> I understand you don't want a cell to get to 3.6 volts, I just don't understand how the shunts could ever come into play at 3.6 volts if the charger is always shut off at 3.5 volts?


Assuming the shunts are always attached to the cells, then they'd come into play during regen if it ever got above 3.6.
________
FoxxxySara


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## dimitri (May 16, 2008)

Amberwolf said:


> Assuming the shunts are always attached to the cells, then they'd come into play during regen if it ever got above 3.6.


You better hope this never happens  , regen would overrun shunts instantly....but its highly unlikely to ever happen since Tom is playing safe and undercharges his pack as it is.

Tom, if you shut off the chager when first cell signals HVC, then you will never have balancing phase. HVC should signal the charger to slow down, not stop. Stop should occur in the charger when max pack voltage is reached. Forcing charger shutoff should only happen if the thermal fuse blows, indicating overheating shunt.

Although in your case of significant undercharge, I'm not sure balancing even makes sense at all, as long as initial balance is done during the build.


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## dimitri (May 16, 2008)

tomofreno said:


> I expect the signal is, but it probably takes x msecs for the charger current to shut down. If this continues through tens of cycles because one cell is at significantly higher voltage than the others, it might get to higher voltage than 3.5V. As you say though, it should shut off the charger and keep it off until it relaxes to a lower voltage, then shut the charger off shortly after it comes back on and drives the cell back up to 3.5V. If this cell is significantly higher voltage than the rest, then this should continue until the cell remains at 3.5V long enough for the timer to time out and shut off the charger, or the pack reaches 124V and shuts off the charger.
> 
> Tom


This situation describes severe imbalance in the pack, it doesn't really happen in real life as long as initial balance was done. LFP cells drift out of balance very very little with each cycle. Voltage differences between cells are usually less than 0.1V, especially since you are planning to stop charging at 3.5V. Voltage difference becomes a little more apparent at the end , like at 3.7-3.8V , at which point your charger should be at 1-2 amps. This is where shunts come on and help level out those little differences between cells.


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## tomofreno (Mar 3, 2009)

> You better hope this never happens
> 
> 
> 
> ...


 Yes, I am hoping to avoid that scenario the dumb way, by leaving enough capacity in the pack to safely absorb any regen without overcharging. This requires I don't ever go down too large a hill with the pack near full charge, something I would like to not have to keep in mind. I recently found a second pot on the Curtis controller schematic labeled "brk". I am thinking this may be a pot that can be used to control electric braking. If I can verify this with HPGC or Curtis, I may be able to use a relay driven by an HCV signal to short this pot to stop regen. Now I am thinking maybe I should use two relays in parallel for both this and the HCV signal to the charger in case one fails. At least with the charger I have the thermal fuses, with regen there is nothing. How are you planning to handle this JRP3?

Tom


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## JRP3 (Mar 7, 2008)

In my driving I don't see that as a likely scenario and was just planning to leave some room in the pack the same as you. It may be necessary to only charge to 3.45 or so to be safe. Another possibility would be to just turn on the heater or the A/C to bleed off some charge, it probably wouldn't take much. I suppose you could hook up a relay to do that automatically on a HCV signal.


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## brainzel (Jun 15, 2009)

dimitri said:


> (...)HVC should signal the charger to slow down, not stop. Stop should occur in the charger when max pack voltage is reached. Forcing charger shutoff should only happen if the thermal fuse blows, indicating overheating shunt.(...)


Dimitri, how did you connected the Zivan NG3 to this?
I read my manual, but I haven't read about a signal input to slow down the charge process.


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## dimitri (May 16, 2008)

brainzel said:


> Dimitri, how did you connected the Zivan NG3 to this?
> I read my manual, but I haven't read about a signal input to slow down the charge process.


You don't really need HVC feedback with Zivan NG3 since its programmed to slow down on its own, based on pack voltage. Assuming the pack is balanced, when voltage gets to 3.6V per cell Zivan will slow down, so by the time first cell starts shunting at 3.8V the charger is already at low current anyway.

I did connect HVC to thermal sensor input on Zivan ( its not documented in the manual, it took time to research and test on my own ). When charger senses over temp condition on the thermal probe input it stops raising current, waiting for battery to cool down, this was designed for Lead Acid packs originally. However, I found this functionality is quite useless and not worth the trouble with LFP pack, since charger is always in the safe low current zone by the time voltage gets to HVC levels.

Hope this helps.


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## tomofreno (Mar 3, 2009)

> Voltage difference becomes a little more apparent at the end , like at 3.7-3.8V


 A bit confusing...The full charge voltage in the SkyEnergy cell spec is 3.6V. Full charge in the Thundersky cell spec is 4.2V. So I think you are talking about TS cells when you say the end is 3.8V?

Tom


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## dimitri (May 16, 2008)

tomofreno said:


> A bit confusing...The full charge voltage in the SkyEnergy cell spec is 3.6V. Full charge in the Thundersky cell spec is 4.2V. So I think you are talking about TS cells when you say the end is 3.8V?
> 
> Tom


Yes I am referring to TS cells since this is what I have, but I am confused by the difference between TS and SE specs. Same chemistry cells should have very similar voltage specs. I suspect that Chinese translation is playing a role here  . I think there is a difference between terms "full charge" and "max safe charge voltage", but people seem to mix them in discussions. Maybe I am wrong....

Those who have used both TS and SE cells may be able to clear this myth once and for all. Maybe EV Components can chime in here?


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## tomofreno (Mar 3, 2009)

> Another possibility would be to just turn on the heater or the A/C to bleed off some charge, it probably wouldn't take much.


 Yes, of course that is assuming you know that one or more cells are at or close to full charge. I agree it is pretty safe to just undercharge initially, and that is what I intend to do. I would like to "idiot proof" things as much as possible though, so anyone can charge the car, or get in it and go with no knowledge of how it works - even if they top of the charge in a Walmart parking lot and then drop 1000ft in elevation braking all the way (I live in a mountainous area).

I did verify there is a braking potentiometer input to pins 17, 18, and 27 on the controller. This is for use with the brake pedal on a vehicle to vary regen current. I also spoke with HPGC. They program the controller for "moderate" regen, and do not use this pot. They are working on a system where they will use this pot to vary regen current. This will interface with the controller through a CAN bus to limit regen based on cell voltages. The controller will be the main module for a bms. I'm not sure what they have planned for control during charging. Sounds like it could be a very nice system though. He said check back in about 4 weeks. Btw, they have a new website in case you didn't know: HPEVS.com


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## JRP3 (Mar 7, 2008)

dimitri said:


> Yes I am referring to TS cells since this is what I have, but I am confused by the difference between TS and SE specs. Same chemistry cells should have very similar voltage specs. I suspect that Chinese translation is playing a role here  . I think there is a difference between terms "full charge" and "max safe charge voltage", but people seem to mix them in discussions. Maybe I am wrong....
> 
> Those who have used both TS and SE cells may be able to clear this myth once and for all. Maybe EV Components can chime in here?


I think it's been discussed before that the SE cells are not exactly the same as the TS cells and use the "Aleees" powder. Jack Rickard has used both TS and SE and says the SE cells have a narrower voltage range and overvolt above 3.6 where the TS cells can go to 3.8. I think he feels that all the usable energy is below 3.45 and doesn't go above that with the SE cells.


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## MN Driver (Sep 29, 2009)

JRP3 said:


> Jack Rickard has used both TS and SE and says the SE cells have a narrower voltage range and overvolt above 3.6 where the TS cells can go to 3.8. I think he feels that all the usable energy is below 3.45 and doesn't go above that with the SE cells.


Jack Rickards recent blog post said that he was planning to stop at 3.5 volts, he says that for a very long duration the pack was hanging at 3.46 volts during a 75 amp charge from his bench supply before it started rising and then once past 3.5 it rose quickly up to 3.59, once it reached 3.59 a 75 amp charge to the 180ah cell caused the cell to hop to 3.76 volts, which was over the max recommended voltage. On discharge he says that 3.0105 volts turned to 2.9161 in 5 minutes and another 5 it was 2.540, then 1.85 volts after another 5. So basically what he says in his jackricard.blogspot.com blog is that he plans to run 3 volts to 3.5 volts because outside that range the flat discharge curve is anything but flat and from his charge it will skyrocket and plummet qiuckly. For how he disagrees with a BMS shunting system I think he has it planned well.

For max range though if you wanted to use shunts to top off cells to reach 3.55 or even if you wanted the 3.6 you would need to have dropped a decent amount of amperage before passing the 3.5 volts mark where the curve is no longer flat.


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## MN Driver (Sep 29, 2009)

tomofreno said:


> I did verify there is a braking potentiometer input to pins 17, 18, and 27 on the controller. This is for use with the brake pedal on a vehicle to vary regen current. I also spoke with HPGC. They program the controller for "moderate" regen, and do not use this pot. They are working on a system where they will use this pot to vary regen current. This will interface with the controller through a CAN bus to limit regen based on cell voltages. The controller will be the main module for a bms. I'm not sure what they have planned for control during charging. Sounds like it could be a very nice system though. He said check back in about 4 weeks. Btw, they have a new website in case you didn't know: HPEVS.com


This paragraph makes me very happy, thank you very much for this information and the new link, I could never find anything at the high performance golf carts site regarding this motor at all, glad to see there is a site that actually shows a picture of what I'm looking to get. I'm looking forward to getting an AC50 or whatever comes along that may be an improved version of this.

The only thing I don't like about the controller set to a 'moderate' level is that I want to be able to actively control regen. I want to be able to control regen like how it's done in the second half of this page. http://www.metricmind.com/ac_honda/throttle.htm He uses a pot attached to the shifter that slides up and down so it will default to 0% regen, which works for me because I use coasting quite a bit in my driving up to 100% which when I brake and don't want to spend awhile for 'moderate' regen to happen and would rather be pulling about 150 amps of regen rather than 60 amps or so, I want to be able to pull it. In my current gasoline car, if I'm approaching a stop sign on a 55mph highway, I will plan it out so I coast down to about 25-30mph before applying the brakes. With regen I would like to coast down to about 40mph and then apply a heavy amount of regen as to get where I'm going quicker and also recover more of the power that I would have wasted braking from 30mph to zero.

I read through the Tesla motors debate about no regen, a switch for regen or a standard regen where it would regen a little more than compression braking from a gasser and apply more with brakes. My situation is a little different, in the winter, my brakes are the safety way to stop, regen is a bad idea for two primary reasons. Number 1, if my pack isn't warm the internal resistence is likely to push my voltage too high and I still don't want to put -any- charge into a pack below freezing, I want that disabled unless the pack is warm. Also if I'm braking in snow or ice, I'm more likely to lock my brakes with regen, I don't want anything interfering with my control to the ground when things are slippery. I think manual regen is best, I will be the only one driving the car, if someone elses drives it, they will drive a manual and I'll probably just tell them to not touch it and all will be well as-is.


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## Amberwolf (May 29, 2009)

MN Driver said:


> Number 1, if my pack isn't warm the internal resistence is likely to push my voltage too high and I still don't want to put -any- charge into a pack below freezing, I want that disabled unless the pack is warm.


What if you design something that siphons the regen power to a pack heater, until it has reached the minimal temperature needed?
________
Katelyne


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## tomofreno (Mar 3, 2009)

> Jack Rickards recent blog post...


 Thanks! I read through his blog. Good data, especially since I have the SE180Ah cells. Based on this I think I will set my charger voltage to 125V or 3.472V/cell, and leave the HVC at 3.5V. If the charger voltage is at the 3.444V/cell I planned, I'll be somewhere on the flat part of Jack's curve, and may shut off the charger prematurely.

If you are interested in the AC50 you might give HPGC a call. They told me several weeks ago they were working with another supplier on a higher voltage controller for their motors. I don't know how that has worked out. They also mentioned today that they will be adding more to their new website soon.

Tom


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## tomofreno (Mar 3, 2009)

> Tom, if you shut off the chager when first cell signals HVC, then you will never have balancing phase. HVC should signal the charger to slow down, not stop.


 Yes, I would like to be able to have the Manzanita cut back to low current with an HVC signal, but as far as I can tell this isn't how it works. The "hotreg" input (pin2 pulled up to 5V by connection to pin1) shuts the charger down until this signal goes away, at this point it resumes charging at full current. Rich at Manzanita says this is what he wants, in order to more quickly charge. The way I understand it, his "regs" shunt while the charger is running full current, until they get hot, then they shut down charging until they are cooler, then resume at full current. It is not specifically designed for a HVC signal. I'm not sure how this will work out. When the charger comes back on at full, say 30A, it will drive a high cell immediately to HVC, and shut off again, giving a current surge through the cells, and through the shunt of the high cell. I suppose the cells will equalize this way through multiple repetitions as long as they aren't too far out of balance. I had the impression the charger cut back to low current when the timer was activated by the HVC signal, but it now appears this is not the case. I'm still investigating.

Tom


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## MN Driver (Sep 29, 2009)

tomofreno said:


> Thanks! I read through his blog. Good data, especially since I have the SE180Ah cells. Based on this I think I will set my charger voltage to 125V or 3.472V/cell, and leave the HVC at 3.5V. If the charger voltage is at the 3.444V/cell I planned, I'll be somewhere on the flat part of Jack's curve, and may shut off the charger prematurely.
> 
> If you are interested in the AC50 you might give HPGC a call. They told me several weeks ago they were working with another supplier on a higher voltage controller for their motors. I don't know how that has worked out. They also mentioned today that they will be adding more to their new website soon.
> 
> Tom


These 2 amps or so that these shunts can handle seem small for the 180+ Ah cell sizes especially if using a small number of cells, like if using a number somewhere in the 30's or less. The charging current that we need to drop to accomodate the low amperage shunts seems to me that it could add an hour or so of extra time to the charge for a good full charge balance. I haven't gathered any sort of consensus to what people usually like to use as their final charging amperage before terminating their charge when using these shunts, C/20 would be 9 amps for 180Ah or 10 amps for 200Ah. Can a shunt that would let the voltage of a cell ride well beyond it's standard shunting voltage at 2 amps be able to effectively shunt when being charged with 10 amps of current? I feel like it would be a serious guess and check to calculate the voltage that the shunts will really end up blocking at when pushing high amps.

I don't know what to think about the higher voltage controllers at this point, I like the idea of using a smaller total count of cells due to the extra plastic casing that takes up extra space and more cells requires more BMS shunts and more initial work to balance. The main reason of why I want a controller that can support higher than the max of the 1238's 130 volts is so that I could add more 200Ah(or 180Ah) cells once I have assembled the car if I find that I can't get the goal of 100 miles. I'm still wondering if the Honda Insight Gen 1 could do 100 miles with 22,400 Wh or not, I would have to get better than 224Wh/mile to reach it theoretically with 100% DoD, or 112 miles if the car accomplishes 200 Wh/mile. I'm looking for a 100% DoD of 100 miles to be my goal but don't really need to drive more than 60-70 but it's a goal so I can achieve longer pack life. It's a car that weighs 1800 lbs. including it's engine and hybrid pack in the back. I'm sure without the pack and the engine that getting it to 1500 pounds wouldn't be hard, add around 500 pounds of batteries, controller, and electric gear brings it to 2000 lbs, it has good aerodynamics, is 200Wh/mile possible?

One other important detail, I'm still about 2 years(maybe more) from when I will be starting my conversion so I'll get to see what HPGC and LiFePO4 manufacturers will produce and what the cost of the batteries will end up coming down to.



Amberwolf said:


> What if you design something that siphons the regen power to a pack heater, until it has reached the minimal temperature needed?


I would want all of the regen power to go straight to the heater in that case because I have experienced how quickly I can cause a Lithium Ion cell to lose capacity and have internal resistence go permanently through the roof by charging it at -10f for a few hours. I don't know if I can trust the 'below zero' ratings of that Thunder Sky puts on their cells for charging or not, but the internal resistence that comes with discharging and charging them when cold makes me want to shelter them as much as possible. My plan is to build cell boxes that are well insulated and heated before charging and while parked at home and then when I park at work the goal is that they don't reach freezing, I would probably use a pack run cell heater that I could put on a timer to turn on an hour before leaving work that would raise keep the batteries around 50 degrees so they have an easier life when I drive off. In warmer weather I would lose the insulation and have the enclosed box run with a blower to keep things reasonably cool.


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## tomofreno (Mar 3, 2009)

> Can a shunt that would let the voltage of a cell ride well beyond it's standard shunting voltage at 2 amps be able to effectively shunt when being charged with 10 amps of current?


 The clear message from Jack, Dimitri, and others is that the cells don't get that far out of balance in normal usage, so you don't need large shunt current, and you don't want to shunt while the charger is supplying large current because the shunts will overheat. I haven't heard anyone talk about large time, like an hour, added to charging to equalize. With regard to initial imbalance, my cells arrived charged to 3.27 or 3.28V as measured by my cheapo two decimal place dvm, so they are likely within less than 0.05V of each other, and that seems to be what others experienced. 



> I'm still about 2 years(maybe more) from when I will be starting my conversion


 At the current rate of change in this industry that is an eon. Things will be very different then as far as available components, and you will likely be able to just buy a well-made ev for not a lot more than you could do a conversion.

Tom


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## MN Driver (Sep 29, 2009)

I don't think that it will become that close in price for a ready-made drive it off the lot EV. The Nissan Leaf EV is the only vehicle where they plan to sell you an electric car for the same rough price as a standard car with a gas engine except they don't sell you the battery pack with it, you pay a lease for the pack which in the end you would pay more because that is how marketing and sales works. I'd prefer to avoid a car that will rust out on me because that is the demise to the body of car that I choose therefore my choice is to use a lighter aluminum car that won't rust so the automakers won't win on that part, the rest of the vehicle I put together myself where if there is a problem, I can service it without digging into my pockets to have some dealership tear apart and replace a full battery for a few bad cells or however else they want to gouge me. At this point I've seen this dream car body and it comes at a price of about $5k right now. If the battery costs come down 20% in the next 2 years I'll put $8,000 of LiFePO4 or whatever better battery may come along into the car, $4500 for the controller/motor combo I'm looking at, the roughly $3k of other accessories required for a conversion including a BMS system, heater, vacuum pump, etc. I'd be thrilled to find a sub $15k production 2 seater electric car out there that can get 100 miles, but the only way to do it is to find a used production EV out there that could get 100 miles, but it isn't out there. I don't think in two years there will be anything out there that fit my needs yet so a conversion in two years will likely be the only way to get what I want. If I get proven wrong then I will still be satisfied but we shall see. Moore's law says that technology of transistors doubles every two years but even Andy Grove, former CEO of Intel said that electric car technology isn't making it's strides at that pace yet. It's clear the automotive manufacturing industry isn't that motivated to put enough money into development to make the advances that quickly and the battery manufacturers are now just getting money to do it. The advances are coming wicked quick but not quite at the pace to where it's within reach just yet. Once the money starts moving where it should the advances will come but it's just not happening yet. GM isn't making an electric car, it's close but it isn't an electric car, they already scrapped the electric car that made 100 miles with little problem and they are producing a steel version that gives 40, it's a step backwards to leave room for future growth. I'm not convinced GM is in it for the best interests of the EV buying public. ...but if I could get a used one for $10k a number of years down the road and they have proven themselves, I'd be all for it.


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## dimitri (May 16, 2008)

tomofreno said:


> Yes, I would like to be able to have the Manzanita cut back to low current with an HVC signal, but as far as I can tell this isn't how it works. The "hotreg" input (pin2 pulled up to 5V by connection to pin1) shuts the charger down until this signal goes away, at this point it resumes charging at full current. Rich at Manzanita says this is what he wants, in order to more quickly charge. The way I understand it, his "regs" shunt while the charger is running full current, until they get hot, then they shut down charging until they are cooler, then resume at full current. It is not specifically designed for a HVC signal. I'm not sure how this will work out. When the charger comes back on at full, say 30A, it will drive a high cell immediately to HVC, and shut off again, giving a current surge through the cells, and through the shunt of the high cell. I suppose the cells will equalize this way through multiple repetitions as long as they aren't too far out of balance. I had the impression the charger cut back to low current when the timer was activated by the HVC signal, but it now appears this is not the case. I'm still investigating.
> 
> Tom


If this is the case, then you can forget about shunting/balancing, especially if you are planning to undercharge your cells anyway. Balancing is only effective in very small increments at the end of full charge, as an insurance that it won't get off balance over long time. But if you are undercharging and your charger is pushing 30 amps, then might as well stop when first cell hits HVC and be done with it. You really don't need balancing in this situation.

Just to show how much balancing is actually going on, my pack is balancing at 1.5amps for about 20 minutes, which means 0.5 ah on 160 ah cells, which means 0.3% of total charge. 

During that 20 min time, most cells ( I'd say 36 out of 40 ) start shunting within 5 minutes of each other. Few cells which are catching up happen to be same cells which feed PakTrakr, which makes them go off balance just a little bit due to few milliamps taken by PakTrakr.

Where I am going with this is that balancing is not all that important as long as you have HVC controlling the charger and not let it overrun any one cell at any time. If you simply rely on charger sensing total pack voltage, not cell level HVC, then eventually you will overcharge one or more cells, even if it happens 6 months down the road.

Hope this makses sense...


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## JRP3 (Mar 7, 2008)

dimitri said:


> If you simply rely on charger sensing total pack voltage, not cell level HVC, then eventually you will overcharge one or more cells, even if it happens 6 months down the road.


Sounds as if that would depend on how high you are charging. If you continuously under charge the entire pack you would avoid overcharging any cell, unless they go out of balance. This does not seem to be happening on cells that are all under the same demand, i.e. not powering a paktracker or other device.


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