New accumulators for the electric wheelchair

[DanielDv]

Hello friends, maybe this doesn't belong here but I don't know who to turn to and I think there are experts here who will see what it is about. I apologize in advance for my bad English (Thank you for your understanding). I installed two new Leaftron LTH12-90 Lithium batteries (12V/90Ah) in my electric wheelchair and I have a problem with the wheelchair turning itself off four times a day. I have downloaded the OverkillSolar app following the advice here and am attaching the error messages. I am also attaching the technical data of the batteries I use. Can someone please explain to me what I should focus on or what to change in the BMS settings? Despite the shutdown, these batteries are fantastic. However, I am afraid of damaging them. Thank you all very much for your understanding and advice and tips
Daniel

OverkillSolar:

Datasheet battery:

 

[chrisski]

Daniel,

Your batteries are shutting off because of overtemp at 65° C. I would not adjust settings for that. In fact, the spreadsheet gives a 60° C discharge temperature, so the temp already appears set too high.

I have no good advice to help you out. I would instead look to find a way to cool the batteries down and keep them from getting that hot. Venting and a fan in the battery box is one method. Also possible, the wires are way too skinny, but this ought to heat wires up, not the battery.

Unfortunately, finding ways to cool the batteries are much easier said than done.
=====
What type of batteries did these replace?

 

[mikefitz]

Hi, as sugested your batteries are overheating during discharge. There appears to be only one temperature reported by the BMS and this is the temperature of the battery cells or the temperature of the internal battery control electrics.
It may be under high power requirements, the control ( battery protection circuits, BMS) are overheating.
Is it possible to get screen capture with the Overkill app during use whilst the battery is working and a further capture as soon as possible after battery shutdown.
I understand most motors are 24 volt with a maximum current in the region of 50 amps and normal current in the region of 10 amps. This is well within the specification of the battery.
It's possible the battery is faulty, ( or rather the BMS is faulty) .

Mike

 

[DanielDv]

Daniel,

Your batteries are shutting off because of overtemp at 65° C. I would not adjust settings for that. In fact, the spreadsheet gives a 60° C discharge temperature, so the temp already appears set too high.

I have no good advice to help you out. I would instead look to find a way to cool the batteries down and keep them from getting that hot. Venting and a fan in the battery box is one method. Also possible, the wires are way too skinny, but this ought to heat wires up, not the battery.

Unfortunately, finding ways to cool the batteries are much easier said than done.
=====
What type of batteries did these replace?

Thanks Chriss for your reply, originally 2 x 74 Ah gel Traction batteries were installed. You are certainly right because even the previous batteries overheated problems, the cart automatically slowed down as much as possible But it was not a big problem because the cart continued to work without interruption. I already have the cooling solution promised so thank you for pushing me forward to speed it up

 

[DanielDv]

Hi, as sugested your batteries are overheating during discharge. There appears to be only one temperature reported by the BMS and this is the temperature of the battery cells or the temperature of the internal battery control electrics.
It may be under high power requirements, the control ( battery protection circuits, BMS) are overheating.
Is it possible to get screen capture with the Overkill app during use whilst the battery is working and a further capture as soon as possible after battery shutdown.
I understand most motors are 24 volt with a maximum current in the region of 50 amps and normal current in the region of 10 amps. This is well within the specification of the battery.
It's possible the battery is faulty, ( or rather the BMS is faulty) .

Mike

Hi Mike, This seems to be the problem you mention. Yesterday I tested the truck in intense heat when the asphalt was 50 degrees Celsius and the batteries were about 10 cm above it, no error appeared, but when charging at night, one battery only charges to 60%. I tried reconnecting to the charger but the situation did not change, the weaker battery started to charge but disconnected after a while.
For the time being, I have borrowed the batteries to test how they will behave with my electric wheelchair. So I will try to arrange for them to replace only the one problematic battery and I will try to test again. I am attaching the screenshots below.

PS: Battery number 1 has errors are they serious?

 

[chrisski]

I believe both batteries are at the same SOC because the voltage is the same. The BMS just needs to cycle enough to be accurate.

My Overkill BMS spent two years before both read accurately. There is a setting to reset the other to 100 percent, but I don’t know how to do that.

For overvoltage, the cells can be balanced. Because a nut had come loose, I was getting one cell not matching the others. I tightened the nut and set the Overkill to always balance above 3.4 volts and left the batteries for 5 days, and the cells were balanced. After they were balanced, I returned the settings to only balance above 3.4 volts when charging.

 

[mikefitz]

Battery number 1 has errors are they serious

Not serious but may prevent the battery pair from reaching the same state of charge.
What is happening is that, under charge, one cell is reaching protection voltage limit and preventing further charging. The battery will still function under load.
This is common with new batteries and it takes some time for the balancing process to get the cells balanced.
If the batteries are connected is series for a 24 volt application, then each should be charged with a 12v charger to 'full',
before connecting in series. Even then its possible they may become unequally charged, after a time, where a 24 volt charger is used.
I guess you are using a 24 volt charger, it could be the charge voltage setting is too high, do you have any details of the charger specification?

If the problem only occurs in charging then modifying the charge voltage to a lower value, ( if possible), may help. Lithium batteries in series, each with its own BMS, need to behave is a similar way. Since they will not be identical, after a time or even when first used, one of the batteries is 'weaker' than the other and this effects charging and discharge.
To prevent this either charge each separately with a 12v charger at intervals or fit a 'mid point balance' device.

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If radiant heat from the road surface is an issue then simple reflective shields under the batteries bay help. If you can use the Overkill app when mobile the temperature recorded could help the discussion.

 

[DanielDv]

Thank you very much, friends, for your willingness and time. I really appreciate that you took care of me and helped me, this way I avoided confusion and frustration. The initial error apparently occurred in what Mike writes. I called my service center and the technicians confirmed that they didn't really charge the batteries but installed them right out of the box. They also don't have experience with it and they installed it for me to test. So the first step will be to replace them with new batteries that will be charged to 100% each separately and then we will see how they behave. You guys are the best.

 

[DanielDv]

Ahoj přátelé, mám nové baterie a chci se zeptat na nějaké drobnosti. K čemu slouží spodní tlačítko „Reset“ v solární aplikaci Overkill? Používal jsem to u prvních baterií a kapacita baterie se vždy měnila např. ze 100% na 70%. Mohu ji nyní beztrestně používat? Nic nepokazím?

 

[robbob2112]

Thank you very much, friends, for your willingness and time. I really appreciate that you took care of me and helped me, this way I avoided confusion and frustration. The initial error apparently occurred in what Mike writes. I called my service center and the technicians confirmed that they didn't really charge the batteries but installed them right out of the box. They also don't have experience with it and they installed it for me to test. So the first step will be to replace them with new batteries that will be charged to 100% each separately and then we will see how they behave. You guys are the best.

If they are in series they will drift apart over time due to tiny differences in internal resistance. The only way to keep them in sync is to use an equalizer like the one linked ealier.

 

[DanielDv]

Elektrický vozík zřejmě nemá ekvalizér a baterie má každá svůj vlastní BMS modul, ale myslíte, že budu potřebovat ekvalizér? Pokud ano, který byste chtěli? Děkuji za odpověď

 

[DanielDv]

Mohu použít tento Balancer:

Vyvažovač baterie DEWIN​