parallel board malfunction?

[RVD]

so, i was getting my charger set up to charge 3x4s 5ah turnigy lipos. i usually use a parallel charging board. it's a cheap board that i got from hobbyking last year. i don't use it that often but have been using it for the past few weeks and it seemed to work well. it's a 6x4s parallel charging board.

however, this morning i was setting up my first 3 (of 6) 4s lipos when i ran into an issue.

i plugged in the 3 charging leads first (as usual) and then i plugged in 1 of the balance plugs. i then plugged in the 2nd balance plug when i felt the board get hot and heard a sizzle and smelled some burning. i immediately pulled out the 2nd balance plug and saw that the 1st balance plug had burned out (and detached from the board).

any ideas? just a bad balance board? did i do something stupid again?

i know that i didn't do anything really dumb like have the charging leads plugged in serial and then try to plug in the balance leads in parallel, etc. these were just 3 individual 4s packs plugged into the parallel board.

a few other points of interest that i don't think have anything to do with this but might?

1) the batteries were slightly warm since i had just ridden into work - usually i let them cool off for an hour or so

2) i plugged in the charger first and then started plugging into the parallel board. however, the charger was not started of course. i was going to start the charging after getting everything plugged in.

3) the charger is a cheap 50w imax b6. it's slow but i feel it's fairly safe and it plugs into the ac wall for relatively safe and easy charging at work (where i don't want a fire and where i can't babysit this thing charging). it takes around 6 hours or so to charge and i'm fine with that since i have all day at work.

so any idea what happened here? i'll probably take the 4s pack out of my circulation.

 

[dogman dan]

You did something stupid. I've fried two of those things the same way, both of them in the first week or so. It's really easy to screw up, with so many wires and plugs

You've connected packs in parallel at the board with the balance wires, while they were still in series at the mains. Or so I thought, since you say you didn't. without a picture of what you did, I can't say how it happened. But you definitely shorted a pack at the balance plug somehow.

 

[RVD]

hey dogman, thanks for the thoughts.

really puzzling. I have done a lot of stupid things in my day including trying to hook up balance plugs in parallel while the mains were in series. The first time I did that was about 4 years ago and I was puzzled but I know now to look out for that. Although to be honest, I made that mistake about a month ago and smacked myself in the head so I have been very cognizant of that. I know I didn't do that for sure.

My only guess is that maybe the parallel board malfunctioned in some way?

anyway, i'll charge without a parallel board and just use my parallel harnesses. the board might be fried a bit anyway and something might be shorted out as a result.

 

[dogman dan]

It's a mystery what you did. But it must have somehow been a short of course.

What were you plugging in at the time? The mains or the balance leads?

Was it the very first time the board was used? If so, maybe it just had a short built in.

This kind of problem with paralleling balance leads led me to just stop doing it. I just manually balance each pack now, using a light bulb or an RC charger to single cell charge or discharge. The way I run my packs, I need to balance about 4 times a year. I just don't push em so hard at the end of the discharge they unbalance themselves.

 

[RVD]

i have been using this board for about a month without any problems.

i plugged in the main charging leads first (3 batteries) and then started plugging in the balance leads. the first balance lead was fine. the second balance lead is when i started to hear it clicking and burning so i immediately pulled it out of the connector. in that short second, the first balance lead had already burned off.

usually i do it this way...3 charging leads and then 3 balance leads and then 3 more charging leads (from my second pack) and then 3 more balance leads. then i parallel balance charge 6 batteries (the charger charges them to 4.2v/each).

oh well, i guess it's just an unsolved mystery.

 

[dogman dan]

IMO, you did something different that time. The board wouldn't have spontaneously changed its circuits.

My best guess, something to do with plugging into the wrong balance plug socket. Like you had a 6s plug, then used the wrong socket, choosing the 7s plug on the board. Something like that created a short. One of those balance plugs was not plugged in the same as the others.

I found those things tricky to use, and always made a mistake in a week or two. It's part of why I took to never using paralleling gear on my balance plugs. Sure, lots of plugs to check voltage on, but I learned to do it quick with my cellog 8.

When I balance a pack, I just charge or discharge the one cell that needs it. In the end, it's been tons quicker than waiting for a balancer to discharge 10 ah worth of perfectly balanced cells, to let one 5 ah cell out of 28 cells charge a bit more. (a 14s 10 ah setup) Far quicker to just charge the one low cell by hand.

 

[RVD]

i finally brought the bad battery home last night and did some analysis. this is battery #1 so the one that i plugged in first...it was fine when i plugged it in. when i plugged in the 2nd battery, it started to spark, etc. so i pulled #2 only to notice that #1 also came out with the burned balance plugs.

i analyzed battery 1 and it's a 4 cell. when looking at voltage it says that cell 1 is 0.3v and cell 2 is 7.9v. cells 3 and 4 are fine (roughly 3.9v each).

so my guess is that maybe somehow cells 1 and 2 got merged?

 

[DanGT86]

Get that pack out of the house! Who knows if its bad cells or balance leads melted together but either way you don't want it anywhere you would't put a fire.

I'm thinking the packs may have been very imbalanced when you paralleled them through the balance leads. The voltage difference caused the higher one to charge the lower one at an unregulated current that was too much for the balance board to handle.

So your connections could have been correct just not for those particular packs at that time.

 

[dogman dan]

I think you have some melty wires on that pack now, a result of the KFF, not the cause.

Open the top, check cell voltage at the tabs, repair the damage if possible. If a tab vaporized, you may have to convert that pack into a 5s.

If you really do have a cell at 0v, that cell is safe. But if you really charged a cell to 7v, then it's toast. To make it safe, discharge that cell. Once no electrons live inside the pouch, it's not going to catch fire. But you gotta get that cell out of the circuit to be safe.

What I'm trying to say is, you can safely leave a dead, discharged cell in the pack, but you must bypass the bad cells, by moving the discharge wire to a good cell.

 

[RVD]

ok cool. it's stored in an ammo can right now (ventilated can). i'll probably just toss it. it's a 4s pack so i'd be salvaging it to a 3s pack at best and simply not really worth my while.

i don't know if one cell really got to 0 and another got overcharged to 7+ volts but that is what the voltage reader (reads from the balance tabs) is showing.