Problem with SunThing BMS?

[Boomerpilot]

Have a new 48V20Ah liFepo4 from Sun thing. Had one good 20 mile ride with everything normal. Next ride( after battery charged) made it about 5 miles when motor cut out. Seemed as if could reset battery( BMS?) by unplugging connection to controller from battery( battery would act strong but then cut out shortly again). Recharged overnite and had same experience again. Battery read 51 V when cutting out. Battery only reading 55V when fully charged. Got a new quality charger but seems to make no differance. I opened the battery so could see the BMS which has led lights. While recharging eventually saw lights gradually mostly illuminate and at one point measured 58 V from battery. However left on charger overnite and next day, no LEDs lit and battery back to 55 Volts.

Measured individual cells and mostly 3.47 V with two lowest at 3.35 V.

I am quite a newby, but based on what I have learned on this great forum I am thinking the BMS is bad. Some reason it is not allowing battery to fully charge? I also think it is cutting out battery prematurely when in use for some reason? But why with battery still showing 51 V?

Prior had a 36 V lead acid. When I reinstall this the bike performs as it used to, so don't think a controller/motor problem.
Bike is a conversion using a ebike kit controller (20amp) and 500W motor. Controller literature says ok for 48 V.

Any thoughts or help appreciated

 

[dnmun]

what made you think the BMS is bad? you said it worked when it hit the LVC and it even was able to charge it up to 58v with the leds lit. so what is broken?

can you take a picture of the BMS so we can see what it looks like and show you how to test it?

do you know if the charger is working or if there is a burned fuse?

 

[Boomerpilot]

Really seems to only charge battery to 55 V. Only one time while keeping a close eye on things did I see all the lights lit and the 58 V, but later while still on charger , no LEDs lit and only 55 V. All wires from BMS appear good.

I don't really know anything for sure beyond the chargers say it it fully charged ie green lights. But when I measure battery it is at 55 V. Then after 5 miles of light use the battery is cutting out, where I measured it was down to 51 V. The battery should have far more capacity than this in my mind.

Sunthing charger measured 60 v output, Quality charger from Electric rider measures 58.5 V, so believe chargers are fine.

 

[Boomerpilot]

BMS pic

 

[dnmun]

use VGA on your camera.

did the BMS do anything that would make you think it is the reason the battery is not charging?

did the charging mosfet get hot or did something happen to it to make you think it is bad since it was obviously working.

can you verify that there is voltage on the battery side of the charger plug?

 

[dnmun]

post up a picture of the other side too. measure the cell voltage for all 16 cells right there on the BMS where those numbers B1-B16 are printed.

for the first channel put the black probe of the voltmeter on the B- spot and the red probe on the B1, then for #2, B1-B2, and so on, for all of them and post them up here. use the 20V DC scale and measure to .01V.

 

[Boomerpilot]

Measure cell voltages while on charger or off charger?

 

[dnmun]

you can measure them while charging but it sounds like there is no current going into the battery. that was why i asked if you can measure any voltage on the battery side of the charging plug.

 

[Boomerpilot]

I was able to confirm charging voltage on battery side of charging plug. Right at this minute have all but two leds lite and battery at 56.7 v. If the battery keeps gaining voltage, is it normal for it to drop back to 55 V when it stays on charger? When I measure this 55 V the lights are not lit, but charger light is green and has been on charger for 48 hours.

Individual cells while on charger
3.52
3.55
3.57
3.53
3.38
3.55
3.54
3.63
3.64
3.56
3.42
3.54
3.49
3.54
3.56
3.52

 

[dnmun]

i think you will find that the leds turn on when the cell voltage for that channel reaches 3.60V.

that means the cell has charged up enuff that the shunt transistor is turned on and the charging current will bypass that cell and it will go through the shunt resistor, the 2512 surface mount resistors there with the 820 printed on them. that means 82 ohms, (82 times 10^0 is 82 ohms).

when the battery is first charging up there is a large variation in the state of charge of all these cells. some of them will fill up with charge before the others. if the charging current is above (3.9V/83ohms) 47mA then the cell will climb above the 3.90V upper limit for charging, called HVC for high voltage cutoff.

your pack may have gone to HVC and that turns off the charging mosfet so the battery is then disconnected from the charger to prevent it from overcharging.

when the charger is turned off, the pack voltage drops rapidly because it does not have the charger voltage pushing against the resistance of the battery to the charging, so the voltage drops quickly.

you can put a watt meter shunt leg in series with the negative charging lead and monitor the charging current. they are cheap on ebay $12.57 i think is my cheapest buy.

http://www.ebay.com/sch/i.html?_sacat=0&_from=R40&_nkw=60V+100A+watt+meter&_sop=15

if you find that the charger turns off and stays off, it may have a type of latching output that the king pan lipo chargers had.

edit: i also noticed there is a switch on the edge and i bet if you turn it off the battery will stop charging and it will not have a voltage on the output. that allows you to turn the battery off when you connect it to the controller so it doesn't spark. i think.

 

[Boomerpilot]

Dnmun you are way above my knowledge level.

Worse case if the battery will only charge to 55V I still don't get why the extreme short range on the bike with the cut off at 51 v. I thought the low voltage cut off was in the 40 V range generally?

What about bypassing the BMS when using the battery, wouldn't this allow me to get some function out of the darn thing?

 

[Jason27]

Have you tried contacting sun thing about the problem? Is there a warranty?

 

[Boomerpilot]

No I haven't but previous emails while ordering were frustrating,and with the 8 wk delivery to get it and my having open endthe pack I am not hopeful about any warrenty

 

[dnmun]

Dnmun you are way above my knowledge level.

Worse case if the battery will only charge to 55V I still don't get why the extreme short range on the bike with the cut off at 51 v. I thought the low voltage cut off was in the 40 V range generally?

What about bypassing the BMS when using the battery, wouldn't this allow me to get some function out of the darn thing?

i was under the impression you were charging the battery now. is there no current flowing into the battery and charging it up?

 

[Boomerpilot]

Yes, I am charging and there is normal voltage coming out of the charger, but the battery seems to not reach charger voltage . Maybe gets to 56.7 V on charger when leds lit and 55V when not lit ( even though still on charger). When off charger for any length of time battery reads 55 V.

With your 3.6 V comment are you saying this BMS will limit the full voltage to 16 x that or 57.6V theoretically?

 

[dnmun]

no, it will not limit it.

so what was the problem? i thought you said it would not charge?

 

[Boomerpilot]

Is it not adnormal for this battery to only charge to 55 or 56 V.? Also the problem is I can only go 5 miles on it before it cuts out

 

[dogman dan]

I think your first ride of 20 miles severely unbalanced the battery, which had not been allowed to "break in" , or in other words, get fully charged and balanced. It's normal for the lifepo4 pouch cells to need a few gentle discharges and long recharges to perk up and take a full charge. 51v cutoff seems to me to be shouting that the pack wasn't drained, but one cell group was low enough to pop the bms shutoff on the second ride.

I don't think you wrecked the pack, but it did not like it and may need a long time on the charger to fully charge, and a few more gentle cycles might help it take a charge better. I think your bms is just fine.

Edit, re reading the posts above, you might have one or two fully charged cells shutting off the charger early. You do need a charger that will allow a restart of the charge when the bms brings that one about to overcharge cell back down. Then the charger will charge all the cells for a time, shut off, restart, shut off, etc. Till all the cells are up, and you see about 58v pack voltage. The 55v charge is definitely not done, as shown by not all the led's lit. All lit, it's balanced and charged as much as it will take that day.

But you could also just be having an issue with the charger, if it will not put out 58v. The sunthing charger is pretty cheese. What voltage is your new charger putting out? Is it 55v? You say that now with the new charger you never see any led's light up? New charger not high enough voltage?

Edit, you might try the original charger again, maybe it will cycle on and off and allow a full balance and charge.

It is fairly normal for a lifepo4 pack to charge to 58-60v, depending on the charger used, then the bms is supposed to discharge it some, to 3.6v per cell or thereabouts. Dropping overnight, off the charger below 3.4v on any cell is not good. It could be happening because of a weak cell group, or it's possible the bms is not working right. If the bms, you'd expect to see one led that will not go off overnight.

 

[DAND214]

AS dogman said, leave it on the charger for a day or two. Don't disconect it because the green light is on. the BMS will turn the chaarger off and on as the cells ablance. Use the charger that came with the pack.

It seems to be that most newbies do what causes this problem. BUY a new LiFePo pack and run it till the BMS hits LVC which causes a big inbalance of the cells. This is most common on the low cost packs.

Dan

 

[999zip999]

Do not run till LVC if running down to LVC the battery is unbalanced and would need long time on charger. Just short rides and long time on charger. Don't test battery for LVC.

 

[Boomerpilot]

Thanks guys, sun thing charger puts out 60V. Electric Rider metal better quality charger puts out 58.8V. I can determine the charger voltage is reaching the battery. Think both chargers are fine.

Solid 2 days on charger and battery reads 56.5 V when immediately removed from charger. All LEDs seem to be lit.Maybe making some progress, as prior was only 54.9 and most lights not lit.

I like dogmans theory that I unbalanced the pack with the first ride. Frustrating though as a newbe that the technology is so fragile and not user friendly. Interesting that my wife has an off the shelf Prodeco with a lithium battery thAt has worked flawlessly for a number of cycles, without any careful break in, me not any better.

Not a fan of the Sunthing battery setup by the way, that requires opening the pack to see the BMS and the leds so you have a clue about charging. All you have is the charger light shows green so I think an average user thinks "well it is charged up",
But apparently this is not the whole story by any means with this battery.

 

[Boomerpilot]

Dogman, another question; all BMS LEDs are lit now as I said and battery at 56.2 V immediately after disconnect charger.

Is it normal now for them to stay lit as long as battery stays connected to charger? If I disconnect from charger are they supposed to gradually go out?

So just stay on charger for days or a week and see if Voltage comes up?

 

[DAND214]

Thanks guys, sun thing charger puts out 60V. Electric Rider metal better quality charger puts out 58.8V. I can determine the charger voltage is reaching the battery. Think both chargers are fine.

Solid 2 days on charger and battery reads 56.5 V when immediately removed from charger. All LEDs seem to be lit.Maybe making some progress, as prior was only 54.9 and most lights not lit.

I like dogmans theory that I unbalanced the pack with the first ride. Frustrating though as a newbe that the technology is so fragile and not user friendly. Interesting that my wife has an off the shelf Prodeco with a lithium battery thAt has worked flawlessly for a number of cycles, without any careful break in, me not any better.

Not a fan of the Sunthing battery setup by the way, that requires opening the pack to see the BMS and the leds so you have a clue about charging. All you have is the charger light shows green so I think an average user thinks "well it is charged up",
But apparently this is not the whole story by any means with this battery.

You might let him know about it.
It won'thelp you with the BMS being hidden. But might help future buyers and help him to know about your concern.

As for your current problem, don't quit charging it.
There has been others wuth this same thing happning (sun_thing, etc). Kept it them on the charger for a couple days and it was better than better.


Dan

 

[999zip999]

Sunthing dosn't put in as much Love as Ping or Cellman does.

 

[dnmun]

you don't have to leave the BMS inside the battery. even if you have to extend the sense wire cable, you can have it located where you wish and just run the B- cable to the battery. the BMS could be next to the controller and have 2' long sense wires. but you could not use the ping signalab in that case. but the others with a separate sense wire B0 at the bottom of #1. then that would work.