Lithium Ion Battery Rebuild

[SF0059]

So the wife loves having a cordless stick vac for quick pickups. Our Hoover Linx's battery went on the Fritz, so she got a Dyson V6 on Black Friday last year. While I'm not a big fan of these toy vacuums, she likes them so I don't fight her on it. Part of the reason I didn't just replace the Hoover's battery is because it cost $60+... not worth it for a vac that you can get for $80 on sale. So I decided to fix it myself. I took apart the battery pack. As suspected, it was 5 18650s in series for 20v nominal voltage. The batteries were Sanyos and all were reading a discharged state of 3.2v except one that was 2.6v. That was my culprit. After a little research I found that the Sanyos were UR18650W2 with a relatively low 1500mAh and 15A discharge. I picked up 5 Samsung 20Q 18650s with 2000mAh and 15A discharge for $3.50/ea. I almost picked up the 30Qs which are 3000mAh with a 15A discharge, but those were $7/ea. which defeats the purpose of a "cheap rebuild". Tonight I popped out the old batts and soldered in the new ones. Worked like a charm! I know that you really shouldn't solder on 18650s because of the potential for heat damage, but I moved quickly and I think it should be alright. I'm working on creating a low voltage/high amperage battery welder from a microwave transformer, but that project isn't done yet. So solder it was. I don't have pics of the after, but here is the battery sled disassembled as a before. Just an encouragement, pretty much anyone can replace 18650 battery pack cells. Just be careful not to short and vent them!

 

[E150GT]

cool. I wouldnt have thought to do that

 

[901Memphis]

You can also get cells with tabs already installed for building packs

 

[SZR48207]

Nice work. I used to work in a battery store while in college and spent many days rebuilding these battery packs with a spot welder. This is back when NiCD 18V DeWalt was the king of cordless tools so we would have companies drop them off by the box full for rebuild.

 

[sleddriver]

I have some of my own to rebuild...when time permits. Next time I'll order cells with tabs.

 

[901Memphis]

Here is a link to the Tenergy 2600 mAh. You can order them with or without tabs so be sure to select the option in the menu. They seem to be the most popular so they are reliable and solid but not expensive. http://www.batteryjunction.com/tenergy-18650-tab-2600.html You can get Panasonic ncr18650b cells with tabs which are 3400 mah but they are faked often so buyer beware.

 

[SF0059]

Originally Posted By: 901Memphis

Here is a link to the Tenergy 2600 mAh. You can order them with or without tabs so be sure to select the option in the menu. They seem to be the most popular so they are reliable and solid but not expensive. http://www.batteryjunction.com/tenergy-18650-tab-2600.html You can get Panasonic ncr18650b cells with tabs which are 3400 mah but they are faked often so buyer beware.

The Tenergy batteries are rated at a 2C (8 amp) discharge rate and Panasonics are more like 5 amps. The Tenergy also sketches me out because the published discharge rate uses charging nominclature (1C, 2C, 3C, etc). Since the stock batteries were 15 amps I decided to stick with something similar since it is a pretty high current application. High draw on low amp batteries can lead to cell damage, premature failure and, in the worst case, meltdown/venting on non-protected cells. The vacuum's cell pack is run in series which increases the voltage, keeps the operating mAh and amp ratings of the individual batteries the same. The two highest mAh/amperage batteries available right now that would have been safe to run in this application are the LG HG2 at 3000 mAh/20 amps and the Samsung 30Q at 3000 mAh/tested stable at 20 amps with a 15 amp rating. Would have used one of those, but tried to keep this on the cheap.

 

[kc8adu]

tenergy cells are not high quality. and i do not see balance/sensing taps on that pack. all is well till 1 cell drifts or even was at a lower state of charge when assembled.then its all downhill. no wonder it failed. li-mn are supposedly somewhat self balancing but you have to overcharge the others to catch up. like many consumer grade packs its a poor design.

 

[Y_K]

Originally Posted By: 901Memphis

You can get Panasonic ncr18650b cells with tabs which are 3400 mah but they are faked often so buyer beware.

At the current state, any battery claiming over 2500 is a fake of sorts. 2100 to 2500 max

 

[Zeus33]

Originally Posted By: Y_K

Originally Posted By: 901Memphis

You can get Panasonic ncr18650b cells with tabs which are 3400 mah but they are faked often so buyer beware.

At the current state, any battery claiming over 2500 is a fake of sorts. 2100 to 2500 max

Incorrect. I own plenty of the mentioned 3400 mah Panasonics and have seen my charger put more than 3000 mah charge into them. Here is a link confirming the same. The tester does extensive testing on batteries and chargers. Panasonic green 3400 mah 18650 testing

 

[Y_K]

I said 'of sorts'. High density ones require BMS, otherwise you may become a subject of one of those fiery stories. No need for a famous Internet tester

 

[kc8adu]

ncrb's are a lousy choice for a power tool pack. the ncrb and ga are nice for flashlights and other low demand stuff. lg has a 3500 now but it too is for lower demand stuff. OP did fine with his cell choice.25r would have been a good choice too as would he2/he4.