Upgrading a DPV Battery

Hi Guys, thanks for the add.

Im hoping for some advice on a project Im doing. I want to upgrade the duration of the battery on my Dive Scooter for a long cave project Im on. At present it is powered by Li Ion cells running at 25.2V 512Whr. If Ive done the sums right then 7S13P, built with 3400mA cells will give me a shade over 1750 Whrs. Or in other words slightly more than 3 times the duration.

This I think will work in terms of physically fitting it in the unit without adding any significant mass. 4550g total. At present 4160g This is further complicated because an under water vehicle is reliant on being neutrally buoyant. I think the 500g increase in mass will be offset by a slight reduction in volume. I can also remove/add a small amount of ballast if need be.

Ive allowed a small volume for a BMS.

This will obviously need field testing and Im hopeful that I may actually end up positively buoyant and could therefore add further cells.

Ive been looking at Panasonic cells, which I will spot weld together using Ni strips.

Do Any of you experts see any obvious flaws before I spend a lump on cells?

Any advice gratefully received.

Cheers

Simon H (UK)

13p great I slit would use high quality cells. And gaskets on pos side. Make sure all cells are of same voltage and batch before assemble. Lots of threads on blue tooth BMS.

Thanks, when you say gaskets do you mean the small cardboard disks? Such as https://www.ebay.co.uk/itm/200x-18650-Battery-Insulator-Insulation-Ring-Adhesive-Cardboard-Paper-CG-/162965161639

Cheers

Yes as some manufacturers use a palstic separater and can melt. Plus the whole can is neg.

Again thanks.

Im about to order my cells.

Panasonic NCR 3400mAh/6A Rechargeable Flat Top 18650 Battery

Are these considered a reasonable cell?

If you don't mind me asking does my math add up?

7s13P

7x3.6= 25.2 Nominal V
13x3400= 44200mAh
44200/25.2=1754Whr

Simon

what exact cell are you talking about who you buying yourselves from ? Nikon ? I think that's where most of the people in Europe buy them from new cells

Thats a panasonic NCR18650B, they seem to review ok here? from techdelivered.co.uk £10 a pair.

TBH Im not well up on this tech only really started researching because of this project, from what I have gathered, stay away from chinese stuff and recycled, This is a critical piece of equipment so not going to skimp for a few quid . Am finding it interesting though. Every days a school day

S

Just looked on Nkon bit better price there, thanks

Wh is calculated Ah x Voltage. Real life Ah would be little lower value, let us say 3,3Ah. 3,3x13=42,9Ah x 25,2V = 1081Wh. How much current does it consume during dive or what is the wattage of the motor? This is important before making cell choice.