I’m building a new battery pack for our BlueROV2 using 21700 cells I found that that have some really nice characteristics for the price. (I’ve used these with great success in 48v ebike packs.)
A 4s6p rack of these cells gives 28 Ah for $120. That’s an all-day battery for us. (With a longer tube, we could even fit 4 more cells and bring it over 32 Ah.)
Problem is, the 21700 cells won’t fit in the stock 3 inch enclosure in an efficient way. To keep costs down, I’m thinking about permenantly sealing the pack in a piece of 3.5 or 4 inch schedule 80 PVC.
I’d run the power cables through one of the end caps, secure the battery pack inside the tube. Then glue the end caps on with PVC cement.
I’ll use a waterproof connector to attach the battery tube to the electronics enclosure or charger. (I’ve got several spare Subconn connectors laying around.)
This site puts the collapse pressure of 4" schedule 80 higher than 300 psi. Water pressure at 100m is about 160 psi. I could install a stainless service port for vacuum tests.
The permanently sealed battery enclosure appeals to me. The end caps are far too easy to knock out in the stock configuration, especially when lowering it over the side of the boat. Also, saltwater always drips into the tube during battery swaps offshore.
Am i overlooking any glaring reason why this wouldn’t work?