Any update on your project? How are the cells behaving under high C loads.? Mine continue to be in perfect balance....Are you sure you are isolating voltage drop across your wiring and measuring directly on cell terminal? Either way, 100-150mV slump for a .4C test on the Frey 100Ah cell doesn't seem bad to me. According to the EVE 280 charts posted by RCinFLA, a similar .4C test would slump around 70-80mV.
In my case, I have moved forward with my build as I am satisfied with my tests. In the end, I paid for a 60Ah cell, and I believe that is what I got. If you look at my second test above, you can see I was able to pull about 62Ah at this high discharge. Am I going to loose some energy to heat? Yes. Will the cells survive these high C-rates as long as I remove the heat? I think so. Would an EVE storage cell survive these high C-rates? I doubt it.
From what I have seen, this is a complex topic with not-so-simple answers. I will leave it to the those who have more experience. When RCinFLA said "0.260v drop due to R_ionic is not too bad for 3C discharge rate", that was enough for me to move forward.
Any update on your project? How are the cells behaving under high C loads.? Mine continue to be in perfect balance....
Thank you. It has been long journey.I am looking forward to your load test results. Please do post a summary here.
What kind of C rates are you anticipating for your build? I assume this is for a motor - so some big inductive loads. I'm surprised you are not using a mechanical rely type BMS....
MP
Well you are working with higher voltages than me ( i'm 12 volts) so a FET based system may work for you.Thank you. It has been long journey.
I will definitely post my load tests here.
I expect C rates up to 3C. This will be powering a walk behind tractor using a 3 phase induction motor through a Curtis controller. HPEVs AC-9:
https://www.hpevs.com/ac--electric-motor-for-motorcycles-ac-9-03-27.htm
I also have concerns about the mosfet based BMS. I do have an easy out should I have issues. The Curtis controller uses a contactor before the drive. I can change things around fairly easily and power only this contactor through the BMS. The only thing I don't like about this option is the inability to use the BMS to estimate SOC.
I am hoping that an AC induction motor run via a curtis controller might be a different beast? I can control max motor currents via settings in the controller.My understanding is that issues with a FET BMSs can arise from inductive loads (motors) where the initial start-up current can be 4x - 5x the sustained load and close to a dead-short if the motor stalls.
I was thinking the same thing, but then cell #16 was the limiting factor on discharge...? CuriousThat cell #9 is the one to watch. Perhaps some slightly higher internal resistance and some higher self-discharge? Overall, seems like a minor issue however.
That could very well be the case. I don't know enough to comment. The start-up surge current i was describing i know occurs with series wound motors...I am hoping that an AC induction motor run via a curtis controller might be a different beast? I can control max motor currents via settings in the controller.
Likely cell #16 just has slightly less capacity. 100mv deviation down at 2.6v , 2.7v is not a lot capacity difference. You are always going to be limited by your lowest capacity cell. Seems OK to me.I was thinking the same thing, but then cell #16 was the limiting factor on discharge...? Curious
Thanks, application will be a walk behind tractor that can run a variety of implements:Awesome work! Congrats and thanks to shared.
Is I missed the function of this battery and those HPEV motor?
Nice! Really cool and useful tool.Thanks, application will be a walk behind tractor that can run a variety of implements: