How do you repair broken tabs on ping battery?

[azisme]

I'm in a little over my head on this one. I have a 48V 10Ah Ping battery that has a weak cell. It was reading 3.32 volts when the remaining cells were reading around 3.58 volts. So I decided to take the battery apart to isolate the cell and purchase a replacement from Ping. In my gentle as a bull in a china shop fashion, I managed to break off not one, but five tabs from the pouches in the process off opening up the battery. I wasn't too worried until I realized that the remaining portion of the tabs are not solderable. It appears that solderable extensions to the tabs are mechanically fastened onto the stubs on the pouches. See the photos:

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Does anyone know how to attach the stubs to a solderable material?

To add to my dilemma, I now can't seem to locate which cell is the trouble cell. I left the battery on the BMS for a couple of days since I last used the battery. The BMS may have rebalanced the cells as they are all reading around 3.25 volts now. However I don’t recall the BMS balancing the bad cell before. I had to isolate it and charge it individually. Is it likely that all I had was a broken tab to begin with? I sure don’t want to have to tear this thing apart again once it’s back together so I would like to be certain. How do I test them?

 

[dogman dan]

I seem to remember a post where a similar problem was solved by crimping some copper strip onto the tab, but I think there was a lot more tab left in that case. That doesn't look like much to work with. that post may have been in the duct tape batttery thread. Test by voltmeter on the bms leads, or where they attach, each cell group should be a higher voltage and subtrraction can give the voltage of the cell group.

 

[Link]

I think you CAN solder to them, but it's really hard. Like I had to get the broken one on my pack pretty hot and covered with flux before it would bond properly. Took me a few tries. I dunno, though. Mine wasn't broken quite that near to the packaging.

Other than that, all I can think of is very carefully opening up the sealed part of the pouch holding the lead and sandwiching the lead back in there. Use some electrically conductive glue or something to hold it together.

Worst comes to worst, Ping can probably sell you individual cells for around $10 each, I'm guessing.

 

[azisme]

dogman- electricridefl posted in the duct tape thread how he repaired his with a homemade crimp.He did not specify any further. His was broken at least as close as mine. I am waiting on a reply to a pm to see what he used. In the mean time, I think I will wander the hardware department to see if I can find something. As I sated, I did test the cells. The big surprise was they were all almost identical voltages. I guess a broken tab may have been my problem to begin with.

Link- I will give it another shot soldering. I didn't use flux so maybe that will do the trick. If I can get the solder to take at all I think I will use that along with some type of mechnical fastening for extra strength. Electrically conductive glue? Hmm, I will have to do some research.

I already emailed Ping before I tore into the battery. He quoted me $8 each plus $20 shipping for 4 cells. I wanted to identify and remove the bad cell(s) first to see how many I really needed. My plan was to order 4 and have 2 or 3 as backups, but it's looking like I may have to order 5 and have whatever I can salvage as backups. The other four tabs are not broken as far down, but they are missing the easily solderable portion.

 

[fechter]

That looks tough.

From what I can tell, if a pouch gets torn or punctured it's pretty much toast.

You appear to have a tiny bit of metal sticking up from the plastic, so it may be possible to solder to it if you can avoid melting too much of the plastic in the process. Clamping below the site with some kind of heat sink may prevent melting beyond the heat sink.

Then it would be a matter of tinning both sides and placing the two parts slightly overlapping and heat again to reflow them together. Sounds tricky. On the other hand, they are useless anyway, so you have little risk in attempting it.

New cells sound like a good idea.

 

[buzzfirst]

Maybe someone with a tab welder could attach a new one. At your risk of course! It seems like there is enough there for that.

 

[azisme]

I ended up ordering 5 cells from Ping. I soldered them to the other cells on the battery without much problem. I did not try to solder any of the broken tabs; someday I will get to it. I then soldered the wires back on from the BMS and plugged in the BMS connector. As soon as I plugged in the connector I noticed a faint burning smell and one of the resisters was getting warm rapidly. The connector was locked in so it took me 10 seconds or so to get it unplugged. By that time one resistor was very hot, had a burnt smell, and had a superficial brown burn mark on it. I ended up discovering that I had inadvertently swapped two of the brown wires which ended up feeding 12+ volts to that resister when it is designed for 3+ volts. My bad.

Now when I try to charge the battery, the cells that are fed by that portion of the BMS are unregulated and reach dangerous voltage levels in just a few minutes. The BMS does seem to equalize the cells when left alone for several hours though. Is the BMS worth trying to repair?

I ended up mailing Ping for a price for a new controller ($47 plus shipping), along with pricing for some new battery options. My intent now is to repair my current battery (which is too small for my needs) to full operating state and then selling on eBay (with full disclosure). I will now post a new thread to ask some questions about what battery size I should get.

 

[dogman dan]

Get the 20 ah. Less stress on each cell.

 

[HighTekBikes]

I am confused about what kind of cells are used in the Ping battery. From reading past posts, I thought they were prismatic, which to me means hard square shape. Is this a relatively new pack? Did Ping change the cell type recently? The picture shows polymer cells (soft pouch). For many years polymer meant LiCo (cobalt). Now I understand they are putting LiFePO4 into the polymer bags. That must be what Ping is using, right? Putting duct tape around delicate polymer pouches sounds strange as it would be very vulnerable to physical damage. I must be missing something, can someone enlighten me? Thanks.

 

[dogman dan]

Prismatic cells, whatever the chemistry, are the foil pouches. Often several are paralelled and put in some kind of plastic case. So the hard square shape you are familiar with often has foil pouches inside. On a post of a PSI cell dissasembled, it looked to me like several smaller cells in the 10 ah round cell were rolled up around each other inside the tube, Apparently some sort of flat sheet is the best way to make lifepo4 work, which is then put in a pouch, or rolled up in round cells.

The ping batteries are lifepo4 pouches, version 1, 5 ah pouches recomended for 1c discharge rate. version 2 that started selling late last summer, is 4 ah pouches recomended for up to 2 c discharge rates. Untill I see results from a 2 c test, I still consider both types a 1 c battery.

Because they are only wrapped in some duct tape, some kind of box, enclosure, or something must be used to protect the pack. I took an aluminum cookie sheet and by cutting the corners, was able to form a very tight box around 5 sides of mine, and then put it into the bag that came with a WE kit. Later, I found a perfect metal toolbox to bolt to the rear rack, and put the pack, cookie sheet and all in that. If you don't protect these pingbatteries, or the 18650 round cell duct tape packs well, you risk physical damage to the cells if the bike simply falls off the kickstand. It's a pain to have to fabricate a box, but for saving 3-400 bucks it can be worth it. I found the cookie sheet trick perfect, since the pack can rattle around in the box a little bit, but nothing will rub a hole in the duct tape. The cookie sheet is folded around the pack in a very tight fit, so there is no rubbing between it and the duct tape. This first layer stays on the pack at all times, and I can put the battery on another bike by using the bag if I want to.

Somebody needs to find a source of a metal box or a strudy plastc box that perfectly fits pings 36v 20 ah and 48v 20 ah packs. I found my toolbox at a garage sale, it's possibly 50 years old. Most of the stuff in wallmart that is the right sise is too flimsy.

 

[monster]

wandering the hardware department seems to be my main hobby

 

[monster]

azisme you could try sliding a wire in next to where the tab ripped off. a paper clip could be used to clamp it. i wouldn't solder it because you don't know what the temperature spec is on the ping cells. you could try cutting some of the pouch away to reveal more of the tab. if you do puncture the cell you might be able to glue it closed again.

 

[liveforphysics]

You need aluminum solder flux, a razor blade, a heat sink, and a very hot iron to fix that cell.

I've had crashes that ripped the tabs clean off of lipo packs. You can fix them.

Trim away about 1-2mm into the plastic with the razor to expose enough of the tab. Heat sink each side of the tab as it passes through the plastic. A bar of aluminum on each side clamping does the trick. Maybe could get away with an ice cube too, but it would be more messy.

The trick is to be fast. For fast you need a very hot iron. I use an 85w iron with a chisel tip. Tin your tip with aluminum solder. Zinc flux paste can enable regular solder to work as well. Regular solder does not bond to aluminum without either of those items to help it, so you are kinda fighting an impossible battle without them.

When the tab is heat sinked, hit the tab with the iron as hot as it gets, and apply as much pressure against the tip as possible with the solder on the other side of the tab to quickly transfer heat into the tab. After about 2 seconds, the solder should melt and tin the tip of the tab. Now the hard part is over, and you can easily solder it to anything. The trick is in having the right flux and solder to get it tinned.

They sell kits with special solders and pastes for making LiPo packs. You are basically doing the same thing by fixing your aluminum tabbed LiFePO4 cell.

Best Wishes,
-Luke

 

[azisme]

Luke, thanks for the great info. I ended up buying new cells to replace the ones with broken tabs, but of course in the process I hooked up a BMS wire wrong and burned up part of the BMS. I just recieved a replacement BMS and will be hooking that up tomorrow, so hopefully all will be well. I will save my old cells as a backup though and try your method sometime when I have less going on.

 

[liveforphysics]

Cool. Glad I could help.

When you eventually give it a try, you can search RC forums for "lipo tab repair", and you will see hundreds of guides for doing the exact sort of repair you need.

Sticking batteries in 5lbs devices wizzing around in the sky at 100-300mph results in lots of tabs getting sheered off batteries.