Problem with 36V 15Ah LifePo4 pack not charging completely

N

nukezero

10 kW
Joined
Jul 2, 2013
Messages
560
Location
Los Angeles, CA
So we got this new 36V 15Ah LifePo4 pack from Sunthing28 on ebay. The charger puts out 45.2V. The problem is that the charger is shutting down at around 39.5V. We can only get a range of about 5 miles before the battery hits LVC. After one hour of charging, the battery goes back up to 39V. The battery pack has been cycled for 3 days now with the same result.

The pack is supposed to be capable of being charged up to 44V+ according to sunthing28. We tried a different charger that puts out 42V, and that charger also shuts down after 39V.

At first we suspect that the battery has no BMS, but why would the chargers shutdown early if a BMS doesn't exist? The charger should just continue to charge the pack for as long as it can up to 44V no ? Sunthing28 says the bms is inside the pack, but we can't know for sure until we tear the pack open.

Second, is it possible that perhaps one cell is disconnected or not secured to the BMS properly? Therefore, the BMS is shutting down the charger early resulting in the other cells not getting their full charge?


Thanks for the help!
 
dnmun said:
the pack is unbalanced. you need to put it on the charger and measure the cell voltages while charging. list the cell voltages here. #1 at the bottom and #12 at the top.
Click to expand...

okay. we left the pack on the charger overnight for 2-3 days straight, 16 hours total. Each day, the battery pack was completely discharged to LVC.

So you're saying that it needs to be cycled like 10-15 times to get it to completely balance? How would we balance the pack even if we found out one or two cells were below voltage?
 
Dis charging to LVC why ? You are triing to fill the low cells and your lvc discharge befor the pack is balance up setting the balance of the pack. You need to leave the pack on the charger a light discharge and leave on the charger for the bms to balance the pack. Please DO NOT discharge the pack to lvc. You need to charge and balance the pack. Discharging the pack to lvc expose the pack to a greater unbalance.
Lvc should not be the rule.
 
Got it guys! So that explains why the first time, the charger was turning on and off when it was at 39V or something on the first day of full charging. It wasn't doing that the past couple days.

Will have it tried out and let y'all know.
 
how can you measure the cell voltages? The BMS is tucked inside hidden away in the battery pack. We'd have to rip apart the battery pack with the heat-shrunk blue wrappings.
 
nukezero said:
Got it guys! So that explains why the first time, the charger was turning on and off when it was at 39V or something on the first day of full charging. It wasn't doing that the past couple days.

Will have it tried out and let y'all know.
Click to expand...

Sounds like the charger was balancing the cells. Have you left the pack on the charger for 18 hours straight without un-pluging it? Also, can you meter all the batteries and post the voltages of each cells after a full charge of 18 hours?

Post some pictures to let us see what you have.

:D
 
nukezero said:
how can you measure the cell voltages? The BMS is tucked inside hidden away in the battery pack. We'd have to rip apart the battery pack with the heat-shrunk blue wrappings.
Click to expand...

so why is that a problem? your battery is dead! you have to fix it. or throw it away like everyone else who is afraid to do anything.
 
I think its not dead. You just kept driving it further out of balance by discharging it to 100%, before you ever got it fully balanced in the first place.

Follow the advice I have given many times for a new pack, or an old pack that has been sitting for a long time. Let it charge 24-7. Don't discharge it much more than around the block, till it starts to look like it's fully charging and balancing. Try not to discharge it to 100% in the future, unless you must. When you do, give it extra time on the charger to get balanced again. Typically, discharges less than 80% deep won't unbalance the pack near as much.

If it won't start charging to the voltage of either charger you are using after a week, then I'd start cutting into the battery to access those wires and follow Dnmun's instructions. It's possible one of the small wires is disconnected and causing a problem. It's not like you can send that thing back to china, so it's trash can or try to fix it.

Once you have access to the wiring, you can use various methods to hurry up the bms balancing the pack. It can take two weeks to let the bms balance a very unbalanced pack.

If Dnmun is right, and you have a dead cell in the pack, then you must open the pack to determine which is good and which is truly dead and taking no charge at all. Then you can try to get sunthing to send you some new cells. Chances are, you won't get them. But you can buy cells from Ping. Maybe sunthing would credit you for that cost.

Keep us advised how this turns out. If sunthing will not make good on a dead cell he sent you, we need to know about it.
 
i asked the sunthing guy to send me samples to test and they never even repied. i offered to pay for them and told them i wanted to know if they could provide pouches for repairs but never heard a word from them at all.

yesterday there was another guy who burned up the mosfets on his sunthing BMS but he also disappeared when we asked him to provide some info and pictures. nothing you can do when people don't wanna help.
 
I know you really like a reply, but sometimes people just take our info, fix it themselves and vanish. I always think first about the hundreds of other guys who will also read this thread and learn from it. So I don't mind repeating the same thing over and over.

But as you know, I'm an electronics moron. I'm only good for advice like, "try charging it longer" or, "look for a broken plug".

So we really appreciate it when you try to help folks diagnose a bms or battery problem.
 
Nukezero has been helping me out and I thank him. Rather than continue to impose on him to relay my story I’ll try to keep everyone updated.
I have an A2B Metro that lost its built in controller last year.
http://endless-sphere.com/forums/viewtopic.php?f=6&t=45907
I have been using an external Lyen 12fet controller since then and with the oem frame battery.
I vacillated between rebuilding the battery pack with more Li ion or going to Lipo (72V 11A) as Eadamine did.
http://endless-sphere.com/forums/viewtopic.php?f=6&t=43482
I lust for the speed but the added maintenance and safety concerns pushed me back to the Li ion.
The frame pack has finally lost its capacity, when new I could ride 18~20 miles, now it’s good for @ 8 miles. So I decided to get a Lifpo brick to keep me rolling until I receive and rebuilt the frame pack.
http://www.ebay.com/itm/2013-36v-15ah-LiFePO4-Battery-5A-Charger-BMS-For-Ebike-Kits-Powerful-By-Express-/141043892242?pt=US_Rechargeable_Batteries&hash=item20d6df0012
The Lyen controller had the LVC set to 31V, I never expected to bottom out the brick within 4 miles of riding….but I did.
So maybe I have hurt the pack, such is life! I will take all the suggestions to heart and at present will do a ‘light discharge’ followed by a charge cycle. Will do this several times over the following days and report back.
I was hoping that the 35/15A Lifpo brick would give me the same range as the oem 36/11A Li ion.
I do know that the added weight over the rear wheel changes the handling enough that I won’t be keeping this setup once I rebuild the frame pack, but for the time being I would sure like to be able to ride more than 4 miles.

wj
 
is this a lipo pack or lifepo4 pack? he said lifepo4. if it had a BMS that caused it to cut out there is nothing wrong with the pack. it just has to be balanced but we need info.

all you have to do is put the battery on the charger and record the cell voltages while it is charging and post them up here so we can tell you what to do.
 
dnmun said:
is this a lipo pack or lifepo4 pack? he said lifepo4. if it had a BMS that caused it to cut out there is nothing wrong with the pack. it just has to be balanced but we need info.

all you have to do is put the battery on the charger and record the cell voltages while it is charging and post them up here so we can tell you what to do.
Click to expand...

It's a LifePo4 pack from sunthing28. Not a LiPo.
 
dnmun said:
so this is two different people with different batteries or is the same battery? nobody has a voltmeter to measure cell voltages?
Click to expand...


I sold the battery immediately after receiving it to the wymjymn. This is one battery, two people trying to figure it out. :)

I received the battery, checked the battery and charger, hooked it up for a minute to make sure it worked. Battery was showing something like 38/39V. Then I shipped it to him the next day.

Thanks
 
Good charger voltage 45 volts I would leave on charger for 5 hrs. and see if it comes up. It could take days as the bms bleeds the high cells down slowly as it gets the high cell down the charger will charge all 12 cells to the first one hit's 3.8v or so. And the bleeding process starts again solwly then the charger kicks in till one cell ( S ) hit's 3.8v repeat, repeat. Till all fill up.
If no progress then you must cut it open to get at the sense wires or bms to check voltage and follow Dnmum if he can help.
 
don't cut the battery pack open, just cut the plastic sleeve that is on the BMS lengthwise on the backside from one end to the other in the middle so you can fold it back over the BMS later.

that BMS is the same as the hi current signalab without the leds. you measure the first cell voltage between B- spot and the first pin on the sense wire plug, where the pins are soldered to the BMS. put the black probe on one pin and the red probe on the next higher pin, measure to .01V using the 20V scale and post them up so we can tell you what to do next.
 
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