I would like to build a battery pack using 4 x 26650 cells in series (14.8v) to power a cordless drill. Now I was going to use TrustFire 5000mah protected cells from Manafont. They seem to be a pretty decent cell.
My number 1 issue is that the cells will not fit into the original battery pack case, so I want to make my own pack by creating a mold, then placing the 4 cells that have been soldered together in series into the mold then pouring resin into the mold to create a solid battery pack.
The thing I am worried about is the heat dissipation, as the solid resin pack will tend to insulate the the batteries and retain heat. I am still not 100% sure what the discharge current will be, but as an estimate say max of 5 amps (probably less but adding a safety factor). Charging will be done much less at around 1 amp.
What are your thoughts? how hot is the pack likely to get with a constant discharge of up to 5amps? is this going to be dangerous?
Well at the moment the drill uses shitty 1300mah nicad sub c cells connected in series. Obviously I will be using a lithium hobby charger to charge the pack not the original one supplied with the drill.
You still should consider using IMR cells + BMS instead.
And you’d need 5 of them to replace original 18V NiCad pack, not 4. (5 * 3.7V = 18.5V, way closer to 18V than 4*3.7=14.8V).
Currently its a 14.4v pack running 12 x 1.2v Nicads, so 4 x 3.7 li-ion running 14.8v should be ok. Definitely happy to consider IMR but they will need to be protected as running in series - Not familiar with the term BMS?
Hmm, with IMR + BMS the price is getting pretty up there. I spotted this on the website and thought it didnt look too bad.
14.8v 4Ah max 10A discharge…
yeh, thats what I am worried about… because the original cells are only 1300mah I thought it couldn’t draw too much current, but like you said its that initial inrush that will make the protection circuit kick in…
Use A123 LiFePO4 cells. They are what DeWalt used (until they switched to Samsung). They can supply over 200 amps! They are nominally 3.2V per cell and have a VERY flat discharge curve. They are also MUCH safer and less temperamental than LiCo cells.
