something not charging

[pauldo]

I have a 12s 5p lifepo4 pack.
I charge through this bms http://www.aliexpress.com/snapshot/6290240442.html?orderId=64171138909262
The charger is http://www.aliexpress.com/snapshot/6486119718.html?orderId=65738565059262 it has 43.1 volts at the pin by my multimeter.
When the batteries get to 3.3 volts each x 12 39.6 volts the battery charger turns from red to green and the voltage stays at 39.6.
What is happening,
Why does the charger turn off
Thankyou

 

[Nobuo]

Are You able to try a charge without bms?

 

[pauldo]

Not at the moment

 

[Gregory]

When the batteries get to 3.3 volts each x 12 39.6 volts the battery charger turns from red to green and the voltage stays at 39.6.

So you measured each of the 12 strings of cells and they were ALL at exactly 3.3V when the charger shuts off? Are the cells old?

Also I'd personally be looking to increase the charger voltage to 43.8V.

 

[pauldo]

When the batteries get to 3.3 volts each x 12 39.6 volts the battery charger turns from red to green and the voltage stays at 39.6.

So you measured each of the 12 strings of cells and they were ALL at exactly 3.3V when the charger shuts off? Are the cells old?
no
Also I'd personally be looking to increase the charger voltage to 43.8V.

It is already at 43.1 by my multimeter

 

[friendly1uk]

I believe your calculating the 3.3v not measuring it. Please clarify this already asked question.

 

[dogman dan]

Yes, I suspect on or more cells is charging much higher, and the bms is shutting off the charge while it discharges the high cells trying to balance the pack.

It sounds, with the limited info we now have, like your pack is simply out of balance. It could also be compounded by an inaccurate voltmeter. But even if that is the case, measuring individual cells should show which cell is way different, even if it's off by half a volt.

A damaged worn out cell will fill too fast since it has no capacity left, and the pack will be perpetually out of balance. So it's still possible your battery has sections that are done for.

 

[dnmun]

post up a picture of the BMS so we can show you where to measure the voltages on the BMS at the base of the sense wire plug.

 

[pauldo]

Does this bms balance, http://www.aliexpress.com/snapshot/6290240442.html?orderId=64171138909262.
I have 12s 5p. lifepo4
It seems to turn off when 1 cell gets to 3.65, the other cells are from 3.4 to 3.55.
When the top cell goes down to 3.5, the others are 3.25 to 3.4, the bms chargers again till 1 cell gets to 3.65.
Can i drain individual cells through the bms and how do i do it.
Thankyou
Paul

 

[dogman dan]

It just needs to go through that cycle many times to completely balance.

You could use one of the manual methods to drain just those highest charge cells to hurry the process up. My favorite way is a 12v turn signal light bulb. I solder two wires to the bulb to make a one cell discharger. Contact those two wires to the terminals of the cell you need to discharge, if you have access to those. If you can unplug the bms, you can use that plug to access the wires you need to tap.

But I'd just try letting the bms do it first. If the charger won't restart on it's own, you need to let the battery sit an hour or so, then plug it back in to restart the charge.

 

[Ykick]

Does this bms balance, http://www.aliexpress.com/snapshot/6290240442.html?orderId=64171138909262.
I have 12s 5p. lifepo4
It seems to turn off when 1 cell gets to 3.65, the other cells are from 3.4 to 3.55.
When the top cell goes down to 3.5, the others are 3.25 to 3.4, the bms chargers again till 1 cell gets to 3.65.
Can i drain individual cells through the bms and how do i do it.
Thankyou
Paul

I looked and looked at the spec info and NO mention of balance or equilibrium function, current, etc. PCB hidden under the metal cover further clouds identifying if this BMS/PCM can balance cells. Based on my experiences buying BMS/PCM (and other techie gear) from China, if it doesn't mention if it performs some function, it probably doesn't. I'd say NO balance but I could be wrong...

And to be that "grumpy old guy" I will add - most of these BMS/PCM "balance" functions seem really weak when used on 5, 10, 15, 20Ah cells and/or series strings. 84mA is considered fairly high on many BMS but my experience is that can be painfully slow to achieve any meaningful balance and then if you have a charger or PS that doesn't turn back on after a balance drain, forget it.

As advised, use lightbulbs or maybe old heater elements to drain. Or, when you gain more experience and get up to speed try charging low single cells up rather than draining high single cells down. That's pretty much how I handle balancing if needed. However, I've had a good run of cells lately and nothing ever seems to need balancing = WINNING!!!

 

[pauldo]

Contact those two wires to the terminals of the cell you need to discharge, if you have access to those. If you can unplug the bms, you can use that plug to access the wires you need to tap.

I cannot get to the individual cells,how do i discharge through the bms,do i use the 2 sense wires that i detect the high voltage.
Thankyou
Paul

 

[dnmun]

that BMS does not have an HVC of 3.65V so your voltmeter is inaccurate. you have to measure the voltage while it is charging. measure the voltage on the BMS where the sense wire plugs are soldered to the pcb.

 

[pauldo]

Ok i have another meter that say's 3.68v while charging.
Anyway it does not seem to be balancing,it only turns off and on and the other cells do not catch up.
How do i manually discharge
dogman dan wrote:
Contact those two wires to the terminals of the cell you need to discharge, if you have access to those. If you can unplug the bms, you can use that plug to access the wires you need to tap.
I cannot get to the individual cells,how do i discharge through the bms,do i use the 2 sense wires that i detect the high voltage.
Thankyou
Paul

 

[dogman dan]

Yeah, you can tap those sense wires of the high cell, connecting a 12v turn signal bulb for a few min to bring it down some.

Sounds like your pack is balancing, if the charger is going on and off. It just takes forever sometimes if it's very out of balance.

Seriously, it could take weeks on the charger if really out of whack.

 

[dnmun]

your voltmeter should read 3.90V when it turns off the charger. if it turns off at 3.68V then your voltmeter is inaccurate.