Lifepo4 Top balance problem and Voltage Problem

Joel007799

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I dont know what bms i have, its the One that came with the cells. But i dont think it does much for the cells. Im connecting the positive and negative directly to the battery so i dont know how this bms can cut of the battery. I belive its just a shit bms that is balancing the cells a little bit. I know that some bms you connect your cells thru the bms but that is not the case with my bms.
So i think i need to check on the cells myself anyways. Or do i need to buy a bms that i connect the cells thru?
 

MisterSandals

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Im connecting the positive and negative directly to the battery so i dont know how this bms can cut of the battery.
Okay so you are bypassing the BMS. This is not terrible but just know that you are responsible for keeping the battery and cell level voltages in their safe ranges.
Keep an eye on things, particularly wire and connection temps until you are certain your setup is semi-safe.
I know that some bms you connect your cells thru the bms but that is not the case with my bms.
If you completely bypass your BMS for charging and most day to day battery uses, the chances of you destroying cells is very high. Exceeding the 3.65V and 2.5V limits is often very bad for cells.
The BMS is a cell protector, balancing is pretty much a novelty item as the balance current is often in the millivolt range, less than 1/1000th of what your charge current would be for example.
 

Joel007799

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Okay so you are bypassing the BMS. This is not terrible but just know that you are responsible for keeping the battery and cell level voltages in their safe ranges.
Keep an eye on things, particularly wire and connection temps until you are certain your setup is semi-safe.

If you completely bypass your BMS for charging and most day to day battery uses, the chances of you destroying cells is very high. Exceeding the 3.65V and 2.5V limits is often very bad for cells.
The BMS is a cell protector, balancing is pretty much a novelty item as the balance current is often in the millivolt range, less than 1/1000th of what your charge current would be for example.
I do have a volt meter for the voltage of the battery but maybe i should invest i 4 more so i can have 1 on every cell. But as we talked about before. My cells in serie as they att now ther volt is 13,85V and the Cell that is the higest V is at 3,58V. So if i dont charge over 13.8 i should be good for overcharging?
 

Ampster

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So if i dont charge over 13.8 i should be good for overcharging?
The risk to your pack is if the other cells drift down then that one cell that went to 3.58 becomes a runner and goes above a safe voltage. The pack voltage would never go above your setting but that cell could be ruined.
 

MisterSandals

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You REALLY need to run everything thru the BMS with the exception of the starter (which pulls more amps than a BMS would allow).
It’s really not possible for a human to manage continual charging and discharging of a vehicle battery without overcharging or discharging at some point. You will kill your battery or at least a cell or two.
Heck, your battery might even kill your alternator if there isn’t proper regulation of amps an LiFePO4 battery is capable of pulling.
 

Joel007799

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You REALLY need to run everything thru the BMS with the exception of the starter (which pulls more amps than a BMS would allow).
It’s really not possible for a human to manage continual charging and discharging of a vehicle battery without overcharging or discharging at some point. You will kill your battery or at least a cell or two.
Heck, your battery might even kill your alternator if there isn’t proper regulation of amps an LiFePO4 battery is capable of pulling.
Yeah, im going to run the battery with the bms but the alternator will stop charging when the battery goes up to 13.8V and will have the voltmeter right next to the steringwheel so i will se if the battery goes under. And i did order 4 more voltmeters so that i can easy check if some cell is under 2.5 or if a cell is over 3,65. I know that its possible that the alternator vill charge more that the alternator can handle becouse the cells can pull more then the alternator can handle. But my alternator is rated to 100A so if it will overcharge and burn out i will swap it to a higer amp alternator.
 

Joel007799

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The risk to your pack is if the other cells drift down then that one cell that went to 3.58 becomes a runner and goes above a safe voltage. The pack voltage would never go above your setting but that cell could be ruined.
Yeah i have thougt about that to. But i belive that the cell that is higer then the others will also discharge faster then the other cells. and i did order 1 voltmeter/cell so i will see if one cell goes higher then the others. I will run the bms but i tought that it could be good to se all the cells voltages and the pack voltage so i can stop charging or discharging the bank a bit if some cell is high.
 

MisterSandals

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And i did order 4 more voltmeters
why not get a 4S battery monitor? Does your battery have balance leads?

This one has audible alarms when your set limits are reached (saved me a few times before i settled on a BMS):

 

Joel007799

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why not get a 4S battery monitor? Does your battery have balance leads?

This one has audible alarms when your set limits are reached (saved me a few times before i settled on a BMS):

My battery does not have balance leads (I think).

That might be a good idea. Then if One cell is to high or low that thing Will alarm me.
 

MisterSandals

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My battery does not have balance leads (I think).
You will have to make them:
I bought this. Cut one connector off, added ring terminals (2nd link).


 

Joel007799

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Looks like a balancer. He has been mighty resistive to accepting that he needs a BMS.
I Will get a bms of its necessary But that bms must handle the start current apms and that bms needs to work and not overheat when i use my apmlifyers and draws 100 of amps for some time.
 

Ampster

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I Will get a bms of its necessary But that bms must handle the start current apms and that bms needs to work and not overheat when i use my apmlifyers and draws 100 of amps for some time.
You can always be the BMS. I would just rather spend my time on my hobbies than constantly checking my battery voltage.
It is high current that can cause weaker cells to sag so your high current needs could be solved by a bigger pack with lots of cells in parallel or a high current BMS. Among the high current BMSs are ones using a separate contactor and current shunt.. That way the current does not have to flow through the BMS. All EVs use that design. You have a lot of choices.
 

sunshine_eggo

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You can always be the BMS. I would just rather spend my time on my hobbies than constantly checking my battery voltage.
It is high current that can cause weaker cells to sag so your high current needs could be solved by a bigger pack with lots of cells in parallel or a high current BMS. Among the high current BMSs are ones using a separate contactor and current shunt.. That way the current does not have to flow through the BMS. All EVs use that design. You have a lot of choices.

My personal experience is that a Human BMS has a 100% chance of failure at some point.
 

Joel007799

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Looks like a balancer. He has been mighty resistive to accepting that he needs a BMS.
I did connect a elictrical fan to the battery today.
Before i started the test the cells where:
Cell1: 3,39
Cell2: 3,57
Cell3: 3,35
Cell4: 3,39

After 10min when connected to the fan the cells where:

Cell1: 3,35
Cell2: 3,38
Cell3: 3,32
Cell4 3,35

And when i connected the fan cell 2 dropt from 3,57 to 3,42 in like 1min. And after 5min all cells did go down in voltage pretty ecual. No cell did go faster down in volt then the others after a few minutes. So that was good news. I Will go out and measure them again after 1-2hours when they have setteled down.
 
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