Ping Battery Sense Wire Woes

[themadhatter106]

It seems like I am always fixing the sense wires on my split ping pack. The main problem I have been having is mechanical breakage. I have had the wires break right at the cells on two occasions. I have had the wires break at the bend where they come out of the pack about 3 or 4 times. I have also had the wires break off on the back of the JST connector a couple times. Additionally I have had the wires break where I had to solder two wires together. It wasn't the solder joint that broke but it seems to be that the wire before the joint simply flexed and snapped off even though I used shrink tubing to help stop flexing.

Its a real shame too because my BMS is cutting out just because of a broken wire even though the battery is not in danger of being damaged. When this happens on the road there is really no good way to fix it besides stripping the wires with a pocket knife. Then twisting them and taping them with electrical tape but that usually fails after the first few bumps. Its times like these when I wish I had a BMS bypass switch.

Now I am trying double shrink tubing on solder joints and hot glue on the back ends of the JST connectors as well as hot glue to stabilize the wires where they come out of the pack.

Has anyone else had problems with the sense wires?

I am annoyed enough by all these wire failures that what I am thinking of doing is just replacing all of these weak wires for something more beefy, probably 22g since that is the thickest stuff that the data sheet says these JST-SM connectors will take.

 

[Tench]

It sounds like you know the solution, do it once and do it right!

 

[DAND214]

It sounds like the battery is bouncing around. The wires are flexing too much and breaking the joints.

You can replace the wires, but if they are still flopping around they will still have problems.

Dan

 

[dnmun]

this is a common problem for the ping packs since the sense wires are so thin and the tiny strands break at the edge of the solder because that is where the flexing takes place and leads to the metal fatigue and failure.

you have to do like ping does on his initial build and use hot glue or adhesive to attach the wire to the cells so it cannot flex at the soldered connection and break off. the glue acts as stress relief.

that was what i liked about the bestechpower BMSs. the sense wires are larger and the strands are larger inside the wire so they have less chance of breaking from metal fatigue.

but the sense wires should always be glued down in the pack like ping does, for any battery pack.

 

[999zip999]

Yes the wires are very small and with small movement are pull they can break and even break under the wire coating or insulation. I use a cheap hot glue to hold the split pack plug. Why cheap hot glue ? Because it holds good enough and can be removed if needed . Good hot gule you might need a heat gun.
With so many problems and fixes is best to redo and put some tape or cheap hot glue, then leave some slack for movement.
In an oil field they put a half circle in the pipe.

 

[amberwolf]

Wherever any wire can flex, and is not firmly fixed, you're going to get bending and eventual fatigue. Thicker wires will help, but if it can move even the tiniest bit (like a little loop of wire not fastened down right at the cell) then it can bend until the metal fatigues and fractures and breaks.

It's worse the more solid the wires are; the more strands, and the thinner the strands are, the better it flexes. When solder wicks up the wire then it breaks at the wick/wire joint, usually. Often breaks right at the soldered connection if it didnt' wick up the wire.

Fixing the wires to the object they're soldered to will help with that.

Larger wires will help, too.

Tying down all the wires everywhere so they can't move will help. But if there is a place where a wire will cross a boundary between parts of the bike that move relative to each other, the larger the loop of wire is that crosses that boundary, the better off you may be. Less length to flex means more stretch and flex on any one point of that loop, more length (up to a point) can put less stress on any one point.

 

[dogman dan]

By now, it's pretty clear that you have too much movement, and there is too much damage to all your wires. So replacement time is here for all of them, using some higher strand count wire, perhaps thicker too, if thicker will work with the tiny jst plugs.

You gotta stop letting those things flop around too!!!!! Eventually you will damage the pouches too.