Help! Battery 36v lithium

[Stevo55]

Please could someone explain this to me in simple language. My new battery pack is fully charged and showing 40v ish. If I leave overnight it shows about 2v and won’t take any more charge through the charging port.
if I reverse charge through the main power feed after 10mins it’s showing full power again. I’ve done this a couple of times now obvs making sure nothing gets warm and it happens just the same way ‍
Wat could be the cause of this and what am I doing sort it out ?

 

[Stevo55]

Wat am I doing to sort it out I meant to write. It’s obviously achieving something but I can work out what. There’s no reset button on the battery I can see btw

 

[cyclebuddy]

A new 36v battery should charge to between 41.5 and 42v when properly/fully charged. Some BMS's shut down/sleep the battery when full... if that happens, just a small spurious surface voltage is sometimes measurable.

If asleep, the common way to wake it up is to hold the power button down for several seconds (up to maybe 30 seconds).

Generally, you shouldn't be reverse charging a lithium battery - the BMS is there to protect the cells.

 

[Nealh]

Reverse charging via the discharge port simply bypasses the bms protetction, the BMS doesn't support same port charge/discharge. One will likely end up with an unbalanced cell pack and cause damage to components.

40ish volts isn't a very accurate reading and should be 41.5v - 42v for a good balanced pack, before reverse charging (a bad practice ) , did you try and ascertain what the 10 cell groups indivdually read voltage wise ?

 

[Nealh]

Looking at that bms , it to me apears not to use balance features and is a simple board that simply looks after lvc and hvc. To check the 10 x 3p cell groups the bms board would need removing to access the cells ends to probe.
With reverse charging without manually monitoring voltages, one has no idea if any cell has gone way above 4.2v .

 

[Nealh]

A little knowledge is dangerous if you have little idea of what is going on with the pack by reverse charging. You certainly risk a fire occurring , it my not occur at charging or straight away but a short within cells could occur anytime when one isn't aware of it.

 

[Stevo55]

Wow thanks for the responses. Ye agreed , it prob isn’t the best idea. After YouTubing for hrs I’m guessing what I’m doin is switching the overload / overcharge transistor into a different position rendering the battery pack useable again. Not sure why it’s switching the current off in the 1st place. The output is 41.6v and holding ! I’m going to leave it unplugged for a few days to see if it’s a battery fault or something on the bike making the safety feature kick in. What I don’t understand is the battery wasn’t low on voltage and it wasn’t being charged so why would it switch in the first place.

 

[Stevo55]

Looking at that bms , it to me apears not to use balance features and is a simple board that simply looks after lvc and hvc. To check the 10 x 3p cell groups the bms board would need removing to access the cells ends to probe.
With reverse charging without manually monitoring voltages, one has no idea if any cell has gone way above 4.2v .

I think it’s 5x 6 not 10x3
If it’s 41.6 should be ok
Each cell seemed to measure 4.1 v without disconnecting which I seriously don’t want to do.

 

[Stevo55]

A new 36v battery should charge to between 41.5 and 42v when properly/fully charged. Some BMS's shut down/sleep the battery when full... if that happens, just a small spurious surface voltage is sometimes measurable.

If asleep, the common way to wake it up is to hold the power button down for several seconds (up to maybe 30 seconds).

Generally, you shouldn't be reverse charging a lithium battery - the BMS is there to protect the cells.

i hope it’s this , it would make me very happy ( apart from wasting hrs for no reason ) I will find out in the morning I guess

 

[Nealh]

The battery is 36v /10s so is 10 x 3p groups, it only looks like 5 x 6 because of the buss connections.

 

[Bikes4two]

I think it’s 5x 6 not 10x3
If it’s 41.6 should be ok
Each cell seemed to measure 4.1 v without disconnecting which I seriously don’t want to do.

I'm thinking you're not clear on describing battery configurations.(let alone tinkering!). Do be careful!

If it is a 36v battery then you have 10 cells in series and if it's 10x3 (or 10s x 3p) then there's a further 2 cells in parallel with the first cell. Each cell has a nominal voltage of 37v hence ten in series gives you a nominal 36v battery.

 

[Stevo55]

The battery is 36v /10s so is 10 x 3p groups, it only looks like 5 x 6 because of the buss connections.

 

[Stevo55]

Yes , It was the bus connections that made me think that , I figured there was 3 in parallel and three in series on each bus , that’s what it looks like but as it’s clear to see I ain’t no expert ! Ask me a plumbing question
So it looks like it’s going into a sleep mode and not waking up ! And I’m waking it by reverse charging it which I haven’t done again incidentally. Why wouldn’t it be waking up ? Is there a work around , I read somewhere of a push button which I could manage to fit i guess.

 

[Stevo55]

Hilarious

 

[Stevo55]

Update
There’s 41.4 across b- & b+
3.2 across p- & p+
no continuity across b- & p-
If I short b- & p- there is 41.4 across p+ & p-
Any help is much appreciated.

 

[Nealh]

B- & + is correct as it is simply taking th volatge from the the series connected battery pack.
P- & P+ is the pack voltage to the controller one should see the same voltage as this this is the discharge voltage , 3.2v indicates the BMS is faulty and is not switched on. Usually a blown discharge fuse would indicate 0v, the 3.2v is just a residual voltage so the discharge P circuit has a fault.

B- & P- use different circuits and will use a mosfet or other for switching.

The BMS is an unsual one as it all B+/-, C+/- & P+/ - connections are made to it, most generic and other BMS only take B-, C- & P- connections with any power + needed taken from a tiny balance wire connection.

Your BMS doesn't use balance, instead it proably uses a simple rudmentry resistor circuit to cease cell group charging oncc it hits the required voltage and doesn't balance voltage via draining excess away and then charging again.
One can only assume the board is faulty and reverse charging is not the answer.
Go over the board minutely with a mag glass and check all components to see if any damage (heat) can be seen , diodes, resistors or the mosfets may show damage by discolouration or lown missing parts.

 

[Stevo55]

B- & + is correct as it is simply taking th volatge from the the series connected battery pack.
P- & P+ is the pack voltage to the controller one should see the same voltage as this this is the discharge voltage , 3.2v indicates the BMS is faulty and is not switched on. Usually a blown discharge fuse would indicate 0v, the 3.2v is just a residual voltage so the discharge P circuit has a fault.

B- & P- use different circuits and will use a mosfet or other for switching.

The BMS is an unsual one as it all B+/-, C+/- & P+/ - connections are made to it, most generic and other BMS only take B-, C- & P- connections with any power + needed taken from a tiny balance wire connection.

Your BMS doesn't use balance, instead it proably uses a simple rudmentry resistor circuit to cease cell group charging oncc it hits the required voltage and doesn't balance voltage via draining excess away and then charging again.
One can only assume the board is faulty and reverse charging is not the answer.
Go over the board minutely with a mag glass and check all components to see if any damage (heat) can be seen , diodes, resistors or the mosfets may show damage by discolouration or lown missing parts.

Thanks very much for info , and advice. I’ve had a propper look round the board with magnifier and can’t see any damage / heat or swelling at all.

 

[Stevo55]

Looks like it’s a cheap bms just seen the same one on eBay for 8.99
Do people repair them or do u just get a different bms? What’s a decent quality 10s 36v bms ?

 

[Nealh]

Buy a new one, most wiil be different to that one but will have balance wires to solder, £10 - £20. Not the daly ones they are a bit iffy.
I use ann power on aliexp.

 

[guerney]

Not the daly ones they are a bit iffy.
I use ann power on aliexp.

Might be too early to say, but did your Ann Power BMS prove more reliable than Daly? I see Vruzend sell the same brand:

10S 36V 40A BMS lithium-ion battery BMS

10S 36V 40A BMS This bms is for a Lithium-ion battery. Not suitable for a LiFePO4 battery Specifications Voltage: 36V Brand Name: ANN Size: L108*W60*T11mm Nominal Capacity: 10-50Ah Weight: 0.1KG Model Number: 10M40AFK Type: Li-ion battery BMS Application: Lithium ion battery pack is_customized...

vruzend.co.uk

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