Help with BMS

[toddcarpenter]

Hi there. I had a bad headway bms so I decided to upgrade the 48v pack to a 60v pack. I ordered 2 bms from Mr. Ping. I wired them up as instructed and I let it charge for 12 hours yesterday and it only got to 70v. The charger goes on then off quickly so it takes forever to charge. I took it for a ride today and it stopped at 64v at only 3.5 amp hours on 10ah cells. When I got home one cell registered over 4 volts and another registered 2.7v. All of the rest registered 3.35 volts consistently. I have already changed out 2 cells that didn't match yesterday morning. I think the bms is not managing the cell voltages appropriately and is killing my cells. When I go down the white pins the wires are plugged in correctly and the voltage numbers are correct at the pins on the board. However when I measure the individual cells, there is one cell that the bms, when hooked up, is draining quickly and the cell reads 1.8v when the bms is hooked up and reads 3.8v when the bms is unhooked. That is the cell that was over 4v when I got home from the ride. I think the bms is reading that cell wrong. I tried the other bms and they both do the same thing. Any thoughts? What is the best bms to get for a 60v headway? I ordered more cells so I can upgrade my other 48v to a 60v, but I have to get this bms thing figured out first? Any help would be greatly appreciated.

 

[dogman dan]

Very confusing to me. At first I just thought, ok your pack is out of balance and we know it can take days and days for the slow ping bms to balance it.

But reading again, you have one cell that is the problem and the others are all ok? This one cell is fine till you hook up the bms, when it immediately drians to 1.8v, or does it take awhile? But the same cell is also overcharged to 4.0v at times? It all sounds very weird when you type it out in a few sentences and just confuses me at this point. Which cell is it? is it the one that provides power to the bms? Weird to get two defect bms that have the same defect. Or did I misunderstand that too?

Looking at your list of bikes, you may know a lot more about batteries than I do. But my starting point would be to put some break in cycles on the new cells, then manually balance the cells. Do some safe short rides with no bms and see how the cells behave all by themselves. Do they stay balanced? With short rides they should. Then if the pack behaves normal, you can add the bms and be able to say, AH HA, this effect must be caused by the bms. Some of your wierd effects could be just caused by a hard to detect problem in the wiring of the pack.

 

[dnmun]

sounds like you wired up the BMS wrong. if it is 4V after you exhausted the pack, that is a bad sign. you may want to recheck your measurement.

 

[toddcarpenter]

I'm individually charging the cells now to ensure they are all the same. I double checked my wiring and the sense wires go up in voltage appropriately when probing in the pins of the connector that attaches to the bms. I'll hook up the big charger and see if that one high voltage cell spikes immediately without the bms to see if it's just a cell with low resistance if that's possible? I'm kinda stumped too. The thing is that the pack was balanced and after hooking up the ping bms then it got way out of balance. The cell that it immediately starts to drain is in the middle of the pack in series. That's the weird thing. I would love to try out a different bms. Any recommendations?

 

[toddcarpenter]

With a clear head, fully scratched from yesterdays weirdness with the pack. I took out the crazy cell and replaced it because when I would put my probes on it the voltage would jump around a lot and not settle like the other cells do. I think the bms just wasn't able to sense that cell correctly. After replacing it, the bms did not try to immediately drain the new cell. They all seem happy now. Time will tell of course lol. I should let you know that I originally thought that I had a bad headway bms like others have had and that's why I decided to upgrade this to the 60v from a 48v pack that I used just fine last year. I think that after winter, I had a bad cell and not a bad bms. Sheesh. Oh well, I've learned a ton about building packs now that I've had to perform multiple surgeries on one. Thanks for the help guys!!

I have to update my list of bikes now and shoot some pictures for you guys. I built a KMX trike with a 5306. It's wicked. No pedaling required with the 60v up a 23% grade lol. A 5306 and a 20inch rim is a torque monster. The only problem is finding enough traction to make it up my gravel driveway.

 

[999zip999]

One time I had a broken wire going into one of the bms pins going into the plug that plugs into the bms it read 1.5v or .09v and the next cell read 6.0v. The rest read 3.8v fix the pin, fixed the problem. All are 3.8v. The other time the pins inside the 8 pin connector had to be push in then hot glued to hold in place on the split pack white plug it to read .09v and 6.0v. till glued. Hey where can I get a good 8 pin connector ?

 

[scoot]

deleted post

 

[999zip999]

So it's one bad cell after the winter ? Because of storage ?

 

[texaspyro]

Hey where can I get a good 8 pin connector ?

DB9... even has a pin to spare. Also available in 15, 25, 37, 50 pin... and then some.

 

[Spacey]

I have just had nearly the same exact problem. I have a 16 cell 12ah 48v Headway cell pack. Having bought 2 x BMSbattery.com BMS's....... I hooked up the first one all correct and the bike initially started but then pulsed on and off really fast about 2 to 3 times a second as if the BMS was shutting off and on constantly.

After cursing this and blaming it on the BMS I exchanged it for the 2nd BMS from the same company. This time it worked fine and was nice to see the cell LED's on the BMS reacting when charging. Anyhow......I took the bike for a test and whilst trying a steepish hill the whole thing just stopped dead. Again I cursed what I thought was the BMS cycled home and took it off.

After a straight charge without the BMS and a few short test rides I thought all was well (but I did notice that the top of cell 8 was getting very hot on charging)......until my cycle anAlyst that I had just bought decided to turn off randomly. Every ime I powered up the bike the cycle analyst would turn on for about a second before turning off......so I thought that I'd better check to pack voltage.....29volts???

Cursing even more I hen check each cell, the first four are 3.7 and the next three are 3.4 .......but the last cell read -1.2v Negative voltage? I then realized that I had tightened the screw head on that Headway cell so hard that the top of the Cell had been spinning around inside itself. But why would the cell be reading Negative voltages?

So maybe my first BMS was not broken but was protecting or trying to protect the pack? the second one must have been working as well.

BMS's are really confusing to me, in fact they do my head in lol. I have ordered a replacement Cell. Any advice would be appreciated.

 

[toddcarpenter]

I feel your pain. How was your bms wired?

 

[dnmun]

you twisted off the electrode so it is no longer connected internally. the individual electrodes are spot welded to the underside of the cap you twisted off.

 

[Spacey]

I feel your pain. How was your bms wired?

The First negative was a thick wire directly to the BMS and then the BMS wires went to each Negative with the last wire on the BMS going to the Positive on the last cell.

Looks like the Cell is buggered lol.

 

[dogman dan]

connections to the sensing wires can lead to wierd stuff. I just had a bit of trouble with some new lipos that just arrived. It seemed that a few of them were having trouble charging. All kinds of weird readings were showing on the charger. first one cell would plummet voltage, then suddenly the next cell would show double the voltage. It turned out the issue was a bad jst plug on the sense wires. Swaped out the sense wire for a different one, and everything returned to normal.

Given the way we depend on our bms's, it shows how dependent we are on sensing wires and plugs that work right. A wiring problem could easily result in the bms allowing a cell to get ruined.

 

[texaspyro]

Given the way we depend on our bms's, it shows how dependent we are on sensing wires and plugs that work right. A wiring problem could easily result in the bms allowing a cell to get ruined.

A VERY good reason for having an intelligent BMS that monitors all the cell voltages.

A bad sense wire usually shows up as a cell with very low voltage next to a cell with around twice the normal cell voltage. Any BMS worth the name will scream bloody murder when it sees cells below LVC and/or above HVC.

And oh, yeah... JST connects just plain suck for balance connectors. And not just normal, everyday suckage. We're talking big green donkey size suckage. They were never meant to be mated/unmated more than a very few times. Also unmating them usually involves pulling on the wires to get them apart... a sure way to cause a broken connection. If you are messing with your JSTs every time you charge, your pack WILL wind up toast.

 

[toddcarpenter]

I still want to know what the best bms is for the money?

 

[jdcburg]

From what I understand, a BMS only works to keep cells from getting overcharged or over-discharged. I have an 8 cell (24V) 20ah TS pack, so for my money the best bms is a Celllog 8M ($15) and a balancing charger. I use a Turnigy Accucel 8150 , $42 + s&h from Hobbyking, but there are others. The Celllog has an adjustable HV and LV alarm that can be rigged up to a louder alarm, flashing LED or a cutoff. It can monitor up to 8 cells so you'd need 2 for a 36-48V system. AFAIC, running w/o a Celllog or other monitor is like driving your car w/o a gas gauge. There are threads here describing how to hook up a LVC or HVC using the Celllog, but I just watch it more carefully when I know I'm near the limit. The balancing charger should be able to balance your pack(s) on the high end. The Accucel needs a power supply that you can buy or make if you have an old computer PS. The Celllog and Accucel both use the JST connectors but I use pigtails on them that I run to mid-wire connectors so I'm never connecting/disconnecting at the device - jd

 

[999zip999]

That's my point about the sense wires. I had a bad one in 16 pin to the bms and have a split pack with a ping 8 pin white connector. Junk the pins moved and had to be glued after good contact. And my BMC 600 had a white three wire bullet connector pure JUNK! Please fix these simply problems. The bad wire in the 16 conn. was my fault.confest.