Lifepo4 Battery not charging

[sharkfan12]

I have a 24v 20ah lifepo4 battery for an electric bike. I bought the battery off ebay complete with BMS. It charged the first time i got it overnight, when i woke up the charger had changed from red led to green led.

However I needed to change the charging plug to fit in my housing, in the process i have gotten the polarity wrong and have been trying to charge my BMS with reverse polarity. After trying to find out why it was not charging with the new plug i have realised the mistake. after reversing the polarity of the charging plug, the BMS does still not want to charge. The battery pack has a voltage of 24.1v currently and the charger is putting out 29 volts or so, so the charger is Ok and the battery still discharges ok.

So i bought a new BMS off bmsbattery.com, however one of the chips on the new BMS gets very hot. when i connect the flat 8 wire plug (for the cells). tried askiung manufacturer for help, but they are no help.

Any ideas anyone??
i would really like the get some charge back into my new battery so its doesn't stay discharged for too long.

Thanks

 

[dogman dan]

If nothing else, put some charge into the battery by bypassing the bms. Just stop before the light turns green, and or monitor the charge very closely at the single cell level to make sure you don't go over 3.8v on any of the cells. With the bms removed, you can probe with a voltmeter at the bms plug to get individual cell voltages.

However, your new bms may be working how it should. As the batteries reach the top of charge, the higest ones will start discharging through the bms while the rest keep charging. This results in heat, so your bms could be acting normal. The fets are the chips expected to get a bit hot.

Or it could be frying, wich happens. Pingbattery.com sells a suitable bms, which may not be more reliable but at least comes with pings much better CS. You have to email him and ask, he doesn't usually have the parts on the regular website.

 

[dnmun]

you need to get a voltmeter.

you need one to diagnose whether the battery is already dead, and to prevent such mistakes from happening to begin with.

a voltmeter is $3 at harbor freight vs a $200 battery. those BMS from bmsbattery are junk. your battery may now be junk too.

too bad you have no pictures or any info about who made the battery or the BMS that is ruined. we might have been able to help.

 

[sharkfan12]

I didn't have a voltmeter at the time. However I assumed red was positive and black was negative, like everything else. But obviously not.

Anyway, the battery seems ok. 24.1v output and each cell is approx 3v.

I'll post some pictures when I get a chance.

Any similar priced bms's available that are not "junk"?

Thanks

 

[dogman dan]

24v, and 3v is pretty much discharged. 3.7v is charged for lifepo4.

Have you tried charging without the bms?

Man if I had a new charger for every time I did that, mixing up the + and - . I can do it even with the help of a voltmeter.
Actually, I do have a new charger for every time, they just weren't free.

 

[sharkfan12]

Ahuh!! Major breakthough people.

I connected the charger directly to the battery. Still got a green light on the charger.

Hmm. So i connected my ammeter on the positive side when connected to the battery..... No current being delivered to the battery. However the charger still has an output if 29v. So im guessing there is something wrong with the charger detecting a battery and delivering current to it.

I have connected an old scooter charger to the battery and is charging so far. However it is very slow at only 450mA.

So it looks like im up for a new charger unless somebody tells me otherwise. Any good budget ones out there? Preferably one that uses red wire for the positive!!

 

[dogman dan]

Well that's sure a new one for me. Usually a charger either has a broken wire or plug, will display green but no voltage is seen on the plug. Or it simply fries, and no longer puts out voltage at all. Sounds like your old charger is stuck on the mode where it just barely trickles into the battery at constant voltage.

It would charge the battery, in a month or two. Great news, chargers are cheap. Well cheap in the US...

 

[wallypedal]

I just worked on a similar problem to yours. The battery was 36v from e-bikekit in the metal case, with a switch and fuse, and 3 prong connector.
Internally, the 3 prong only has the two outside wires connected. It would not charge. I connected another working charger directly bypassing the whole fuse and switch setup, and it charged just fine. So next we will wire up the original matching charger doing the same bypass (we changed connector types), and will report back here. Just wanted to mention the possibility that anything else that the juice goes through on the way to bmps and battery should be suspect too.

 

[dnmun]

wally, did you check the fuse in the charging plug end of the ebikekit.com battery? there is a small 3A fuse inside the cover.

we still have no idea what kinda battery this guy has, no pictures or any way to advise, just guesses, which is useless. actually worse than useless because alotta newbies think all the advice is meaningful, but is often a waste of time and either doesn't solve the problem or can make it worse.

 

[dogman dan]

Yeah, newbs need a dogman is meaningless warning when they register. :lol: My check the plug advice is spot on a few times though. Anything more than that, I have nothing to contribute but bla bla bla.

 

[sharkfan12]

Dogman isn't meaningless. In fact you've been the only helpful one on here.

And with the Australian dollar eqaul to 1.06 US dollars, its not just the US that can get cheap chargers
Anybody have any suggestions for a good charger for around 40-50 bucks?

I was thinking of the alloy case 130w one off bmsBattery.com

 

[999zip999]

How is the bms ?

 

[dnmun]

i agree with dogman, if there is voltage on the charger plug then the charger works.

 

[wallypedal]

wally, did you check the fuse in the charging plug end of the ebikekit.com battery? there is a small 3A fuse inside the cover.

we still have no idea what kinda battery this guy has, no pictures or any way to advise, just guesses, which is useless. actually worse than useless because alotta newbies think all the advice is meaningful, but is often a waste of time and either doesn't solve the problem or can make it worse.

The fuse is a solid white colored thing, and shows good continuity when I tested it. On things getting worse, yep. There are so many potential ways of screwing this stuff up. On this and other forums, I finally realized that the ability to type and get on a forum does not establish any real expertise credentials!! That goes for me and the bunch of "legend in their own mind" experts out there as well

 

[sharkfan12]

How is the bms ?

Just reconnected the battery to the bms, then tried the temp charger again. Success!! The batter was getting about 350mA. Out of the 450mA last night with the charger directly on the battery, i have come to the very sophisticated conclusion that the bms uses 100mA. And that my charger is stuffed

 

[999zip999]

Dogman, I thank you for your advise. And to add to that my bah, bah, bah. How about a pic of the battery.

 

[sharkfan12]

Dogman, I thank you for your advise. And to add to that my bah, bah, bah. How about a pic of the battery.

Not much to see on my battery. just a gaffa taped box with 2 wires and cell balancing leads

 

[dogman dan]

The charger could be stuck on the green light on mode I suppose. It could show voltage, but never kick on to supply more than a trickle of current. The usual failure is easier to diagnose, obviously disconnected wire at the plug, or stinking charger that shows no voltage out at all.

 

[leonardo]

I have encountered the same problems listed here. The charger started charging for about five seconds. Then it switched off again.
I took the following steps:
-checked if the charger was still ok: measured the output of the charger. It was still about 43 volts.Okay.
-checked the voltage of the battery output: 30 volts. It is a 36V 7Ah battery, 12 cells. If cells go below 2 volts they must to be regarded dead in the water. So I guessed the battery was okay.
-I opened up the battery and bypassed the BMS system, connecting the charger directly to the battery.

Now the charger did not switch off. Now, charging LiFePO4 batteries unbalanced (without BMS) can be dangerous, so I checked the batteries every 15 minutes on heat production and measured the voltage too. It started at 30 volts. By now it is 34 volts. So it is charging again!

I do not know yet if the BMS is dead. When the battery is charged I will connect the charger to the BMS again and see what happens.

Thanks to all guys of this thread. You were very helpful.

 

[dnmun]

did you measure the individual cell voltages?

when you charge without a BMS there is nothing to prevent some cells from being overcharged and ruined.

the reason your charger was shutting off before was because there was one cell that was so high it shut off charging.

now that you have charged without the BMS to protect it, that cell is now most likely dead and the pack is ruined.

but of course you think it is ok because it is charging. whatta waste.

 

[999zip999]

Leonardo, The voltage at cell level, do not let one cell go above 3.8v maybe 3.7v when charging.

 

[leonardo]

Dnmun, 999zip999, thanks for your replies.
You both are very right in your concerns.
I have checked each cell seperately and they were all between 3,50 and 3.60 volts. Non of them was ruined.
The charger that came with the battery shutted down at 43 volts automatically. (12 cell battery) That means nothing when one cell is ruined, I do realise that.

Now, when the battery was full again, I reconnected the BMS again. Measuring the voltage outage from the BMS it was only 35 volts, while the battery itself measured about 42 volts! All cells are healthy. Is the BMS dead? What is happening here?

 

[dnmun]

i assume the output FETs are turned off? no current flows?

see if you can find a loose connection in the sense wire bundle from the cells to the BMS. measure the cell voltage on the BMS where the sense wire plugs in. verify that the voltages appear on the BMS, do you have a picture of the BMS?

if it is only about 3.6 for the high cell then that implies that the BMS was not shutting off because it detected one cell above the HVC, but that it cannot see the voltages of the cells. which means either loose connector or broken trace on the BMS.

so see if you can find where the voltages are missing on the BMS.

 

[leonardo]

Dnmun, you are right, no current flows at all.
The BMS is a double layer thing. A big cooling plate is preventing me to see anything of it. I will try to disassemble it and upload a picture.
I did not think of a loose wire or loose connector. I will try that one first. Thanks again for your thoughts.

 

[999zip999]

Make sure the sense wire's are all pluged in.