Are you still working on the car?
Or when are you going out to try a few things?
I will make it direct connection to the charger tomorrow to bring the voltage up. I have reached out to the battery manufacturer to find out what the low voltage cut off and top of charge settings are, so I have a clear idea of what that’s supposed to look like. Once those two are done I’ll connect everything as it’s supposed to be and see if it works. I will let you know what unfolds.
Thank you,
Greetings, I made up a cable to go from the charger directly to the battery today and plugged it in. It ran for a few minutes and then indicated that it had a full charge. The problem is it only measures 79.6 volts. Does this indicate a problem with the charger? I would expect a full charge would be somewhere between 84 and 87.6 volts. Needless to say nothing powered up in the car. 72 volt or 12 volt subsystem. Thoughts?
Did your builder get back to you with parameters or suggestions on what is going on with this custom pack?
Was this a charger supplied/suggested by your battery builder?
I agree. 79.6 is still really low. This is based on a guess that you have a 24 cell Lifepo4 pack(Y/N?). You should be more up around 84~85v.
If all cells were perfectly balanced, right now you are only around 3.31 per cell. From what I can tell from your last status screenshot, at least one cell is higher or lower by 0.36v. Did that change with the charge cycle? Did Balance turn itself ON?
These are all questions you should ask of your builder. Also find out if there is a page on the app to view cell status. (like this)
Needless to say nothing powered up in the car. 72 volt or 12 volt subsystem.
If your battery is still wired up to the car, monitor the app again. Does DisMos stay ON? Also- Monitor the volts on the battery posts. Does it remain active/high? or does it still drop low (close to zero)? You need to have a stable power supply first.
We should probably check again if you have the B+ and B- cables hooked up to this battery. First look sounds like you originally did it correct. DON’T simply flip your cables around just to check. Getting it wrong would probably upset some sensitive components.
I think I am getting a bit thick in my advanced years. I realized this morning I needed to register the app to get full access to it functions. I now have access to the information you asked about and quite a bit more. I took photos of everything and am passing it along. There is definitely an imbalance in the cells. Not sure yet how to correct that.
It appears that DisMos stays on. Battery post voltage still at around 78.2. In other words, it seems stable.
I verified the connections for B+ and B-. All good.
Regarding the ignition interlock: on most GEMs, the Delta-Q charger uses a low-voltage signal (not full B+) to trigger the interlock circuit and prevent driving while charging. When you’re replacing it with a “dumb” 72V charger that lacks this feature, you’ll need to simulate that interlock logic manually.
Yes, you can use an SPST switch to bridge B+ to the interlock wire, but with caution:
- Verify Voltage: Before connecting 72V directly, check what voltage the interlock circuit is actually expecting. In many GEMs, the interlock expects 12V or 48V — not the full 72V pack voltage. Feeding it 72V directly could fry something.
- Safe Option — Use a Relay: A safer and cleaner approach would be to use a 72V coil relay:
- Connect the relay coil across B+ and B- (your main pack).
- Let the relay’s normally open contacts bridge 12V (from an accessory or DC-DC converter) to the interlock input when the pack is “live.”
- That way, the interlock engages only when pack voltage is present, and you isolate the full 72V from sensitive control wiring.
- Optional Switch for Manual Control:
- If you want manual control (say, for service mode), you can wire a switch in series with the relay coil to disable the interlock intentionally when needed.
- No Temp Sensor? Be aware that LiFePO4 batteries don’t like charging below freezing. Since your charger lacks a temp sensor, you may want to add a low-temp cutout switch or at least monitor temps manually in colder seasons.
Thank you very much. I was not aware of the voltage difference anticipated for the end. Interlock. I’ll see if I can find a relay and put that in place.
Hey dneiil,
What is your background?
How well do you know Gem cars? Specifically → this car is a '05.
I believe this thinking is incorrect. But WTH, Now you are going to make me go out and check the output of the closest DQ to see exactly what is coming out on that green wire.
- No Temp Sensor? Be aware that LiFePO4 batteries don’t like charging below freezing
This is usually taken care of by the BMS. I don’t know who set this battery up, but the Chg Low Temp Protect is set to -10c. That sounds a bit cold.
Then again- Kim has not actually stated what cells are in this Custom Pack from China. (I took a guess that it might be Lifepo4).
@khay5020 Has your builder/supplier checked back with you to answer your concerns?
- Do you know what chemistry these cells are?
Some of these parameter settings are wayyy off for Lifepo4.
Cell Hi Protect 3.75
Cell Low Protect 2.3v
Both sound like they are over the edges of where I’d want to run.
What does the pack housing consist of on this battery? Does it allow for easy access to the internal works?
The imbalance between 23 and 24 looks like a loose or bad connection. If you try to power up the car again while watching those two cells(or running another charge cycle), I bet the difference gets worse.
There is definitely an imbalance in the cells. Not sure yet how to correct that.
Balance should be keeping this in line. It looks like it is not running, or set to come on when cells are above 3300 mv. (3.3v).
The high cell is 3.4, which should have triggered it. Possibly, more cells should be above the threshold. Try setting the Balance Voltage at 3.2 and see if Balance goes active.
Concern: How does this BMS balance? If it is active, it should transfer power from the High cell to the Low cell.
If this is a passive Balance system, it will simply dump the power from the high cells into a resistor bank. It will continue this until the entire pack reaches balance range of the lowest cell. (It takes a long time).
Greetings,
I ordered a Lifepo4 battery pack, 72 volts, 120 amp hours. It contains 24 cells according to the BMS. The only information I received from the builder is as follows: “The charging voltage for lithium iron phosphate batteries is between 3.3-3.4…It is impossible to charge to 3.65.” Not very helpful to be sure. It is my understanding the individual cells need to have a charge between 3.4 and 3.65 volts to be considered optimally charged. Any idea why the builder might telling me something very different?
The pack housing is an aluminum box with a removable top fastened with screws. I can probably open it. Beyond the connections for 23 and 24, what do I need to identify? Any special precautions I should take?
I can attempt to power up the car and/or run another charge cycle and record the changes in 23 & 24 first thing tomorrow.
I will try setting the Balance Voltage at 3.2 and see if Balance goes active. What setting should I observe to confirm whether or not the Balance goes active?
It is impossible to charge to 3.65.
I would then ask your tech why the Cell Hi Protect is set to 3.750?
If for some reason your charger goes wild, or that it is not set properly, These BMS settings have potential to allow the pack to go all the way up to 90v.
On the bottom end, Also point out why the Low protect is 2.300?
If you still have a line of communication to a tech, send him a screen shot of your cellV page and ask him for instructions on how this happened on a new pack (with zero cycles) and best to proceed.
One Setting that I’d like to explore is Balanced Method (currently set to Static Equilibrium). What other options are available?
if Balance goes active. What setting should I observe to confirm whether or not the Balance goes active?
On you status page, It appears Balance is greyed out. I’m assuming that means it is not active. I assume that will be more dominant on that screen, and a close watch on the High/Low cells to see if the Diff Volt number goes to a smaller number.
===
I’d also like to point out that this BMS has been logging the faults (Operation History).
Explore that page a bit more. It is showing you why the battery has been faulting when you are not watching.
From the single page you shared, you have a couple cells reporting issues. On event 4 → Cell 23 went undervolt,
but then Event 10 → Total pack Undervolt went to 35.95???
This means every cell went to 1.49???
Then Event 11 saw a total pack overvolt at 90.71v !!!
This is highly unlikely for a battery that has not even been able to light up the car yet.
Ask your builder for help/suggestions on this. It sure sounds like a loose connection or a glitchy BMS. I hesitate to offer advice on someone else’s battery without knowing exactly what it is. Opening this battery will probably will void any warranty and a last result if the builder bails out on you.
Thanks very much for your input. I will follow up on your suggestions with the builder and see what I can learn. Enjoy your weekend!.
We get no weekends here. Feel free to report back when you get news/
On the battery Balance Method, the options are “Static Equilibrium” and “Charge Balance”. Does that mean anything to you? Is one preferable over the other.
Thanks,
In your previous reply you asked me to contact the builder and, “send him a screen shot of my cellV page and ask him for instructions on how this happened on a new pack (with zero cycles) and best to proceed.”
Please forgive my confusion:
-
I don’t understand “my cellV page”
-
what do you mean by “how this happened” ? To what are you referring specifically when you state “this”?
Send him/them the page that shows all the cells individual voltages.
Then also the Operation History page(s).
That should get him started.
First look at this shows there are two wild cells.
***The following is pure speculation from some of the data you submitted. ***
Basically, it looks like you have a cell (23) that is close to dead. When you try to connect the car, the cell drops below the Low Voltage parameter and the BMS shuts off the whole battery. (it is doing it’s job)
You also have a cell that is High(24). When you plug in to charge, this cell trips the Cell overvolt and the BMS again shuts off the battery to protect the cells. Cell 22 is also quite high.
The rest of the pack is sitting at 3.26v per cell which is about
50% according to the LiFePo4 standard SOC chart.
However - Where my scenario (above) sorta falls apart when looking at your data logs. It seems Cell 1 (or the whole pack?) went overvolt at one time. That might have been a weird logging error.
Usually, the BMS will take care of this on it’s own, but something is holding back the Balance function. I’d have to study the system to possibly figure it out, but first person to ask would be the guys that know the pack.
Unless they are jackwagons.
This why I wanted you to watch the battery status and run it through some tests and see for yourself. It might provide some useful info.
Thank you for your insights. I sent copies of all the pages from the app, that I sent you last night, on to the builder. I also asked him the questions that you posed.
I plugged in the battery charger for a few minutes this afternoon to see what effect, if any it had on the state of charge. In the short time that I had it plugged in, I didn’t see any changes even in the tents of volts. I did however experience a fairly noisy beep while it was plugged in. I’m assuming this is some type of charging alarm of sorts?
I will get back with you as soon as I hear from the builder. I too hope he is not a jack wagon.
Thanks again,
Kim Hayes
20055 N 11875 E
Mount Pleasant, UT 84647
801-599-5519
I suggest a bad balance lead between 23 and 24. Unplug bms and measure volts at the plug.
Yes, your guy is a jack wagon.
I think you missed the part where I wanted you to observe cell voltage directly.
You can also watch the status of the Charge FETs to see if it goes off.
If the car is still hooked to this pack, Try flipping the Master Sw to ON and see if the low cell takes a dive and trips the LowV Protect and shuts down the output.
Hopefully others can learn from your mistake. 
you guys are on the right track. the problem is 23 and 24. either a bad lead, bad bms or wayyyyy out of balance. balance on static will help but if this is a passive balance bms(probably) it will take a very long time to balance.