Safety check, BMS and 18650's

[Rednecktek]

Ssssoooo... not sure if this is the right place or not but I figure it's gotta be close. I've got a weird one for y'all.

I picked up a cheapie "40w" bluetooth party speaker at Home Depot in Guam the other day for our BBQ's here on the ship. It charges via USB and inside (because I HAD to tear it open) appears to be a pair of 18650's in parallel for it's advertised "Up to 3 hours" of run time.

I also have a Milwakee 24v tool battery with a busted case that I'm pulling from service, they can just use the other 6 we have. As I understand it, most tool battery packs are a set of 18650's connected up for whatever voltage the pack is.

I'm wondering if I can take the cells out of the Milwakee battery, rewire them in parallel, and parallel them up with the 2 18650's in the speaker to massively increase the run time of the speaker (our BBQ's are WAY longer than "Up To 3 Hours") without setting anything on fire.

I realize I won't have optimum balancing and all the stuff that a BMS provides, I can deal with that. What I'm wondering is will it catch fire or explode or produce VX Nerve gas if I try to do it?

Trying to buy a BMS isn't really much of an option and I am trying to keep it to parts on hand. The ship can't just run into town to the local Radio Shack and getting stuff sent to Guam is difficult at best.

So, Tl;Dr: If I repurpose old cells from a tool battery and parallel them up with the speaker batteries without some kind of BMS, will I sink the ship?

 

[sunshine_eggo]

Ssssoooo... not sure if this is the right place or not but I figure it's gotta be close. I've got a weird one for y'all.

Should be in the Uncommon section as these are NCA cells. I reported to request a move.

I picked up a cheapie "40w" bluetooth party speaker at Home Depot in Guam the other day for our BBQ's here on the ship. It charges via USB and inside (because I HAD to tear it open) appears to be a pair of 18650's in parallel for it's advertised "Up to 3 hours" of run time.

I also have a Milwakee 24v tool battery with a busted case that I'm pulling from service, they can just use the other 6 we have. As I understand it, most tool battery packs are a set of 18650's connected up for whatever voltage the pack is.

My understanding as well. My DeWalt batteries are 2P5S for 20V/4Ah

I'm wondering if I can take the cells out of the Milwakee battery, rewire them in parallel, and parallel them up with the 2 18650's in the speaker to massively increase the run time of the speaker (our BBQ's are WAY longer than "Up To 3 Hours") without setting anything on fire.

Yes. Once the cells are completely separated, let sit for at least 48h. Hopefully, all cell voltage will be about the same. Do not use any cells that are less than 3.0V.

I realize I won't have optimum balancing and all the stuff that a BMS provides, I can deal with that. What I'm wondering is will it catch fire or explode or produce VX Nerve gas if I try to do it?

Balance only pertains to cells in series. If you're 1SXP, all cells are implicitly "balanced" as they are at the same voltage due to the parallel connection. No BMS needed.

This chemistry (NCA) actually has a strong voltage to SoC correlation, so same voltage cells at rest are at the same SoC.

So, Tl;Dr: If I repurpose old cells from a tool battery and parallel them up with the speaker batteries without some kind of BMS, will I sink the ship?

Assuming you're just planning a 1SXP battery bank, not likely.