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21700 batteries

Product Support Batteries and Chargers
#1

So I have been researching battery options. I see a lot of cool ideas on the forums about battery holders a couple of you are building and other things about charging and all that GREAT INFO !!!

However the one thing I haven’t seen is any mention of the 21700 cells … they seem to have a higher Mah rating and a little cheaper to get ahold of. I guess what I am asking is other than the physical size ( obviously the 21700 is bigger) are / would there be a down size to building a pack with these cells to get a longer run time ?

#2

Maybe no one has tried it yet?

Just keep in mind that most 18650 (and I guess 21700) are rated for lower currents. Our 18650 cells are the INR18650-30Q which can handle bursts up to 20A. We use a 4s6p configuration with allows the ROV to draw up to 120A without damaging the battery.

So I advise you to take a good look at the datasheets before moving on, and then let us know how how it goes!

#3

William,

Thank you for your response and for the data on the batteries you use. I have looked at the data, and researched the forum. I found one other person / post talking about these 21700 batteries. And the only downfall I can see is the size difference. However the specs allow for a lot of benefit to use these … you can get them in 5000mah ( and bigger) which is a significant increase over the 3000mah in the 18650 along with more run time, they seem to be more cost effective as well. I have seen these if you build a 4s6p config the same as yours using the the 21700 that should give you well over the peak amps you currently get … correct ? is that a bad thing to have that available power ?

Any advice anyone can give me would be greatly appreciated… I am looking at building this as a sealed unit … so I wont have to open the enclosure to swap batteries , in theory you would just quick release the battery and place on another one … kinda like a battery pack for a cordless drill of sorts …

#4

I made a battery pack out of 21700 cells. The main disadvantage is that they don’t fit efficiently into the 3 inch battery tube that comes with the ROV. They had lots of power and a nice boost in capacity, though. I think my cells were 4800 mah, and the pack had about 30 Ah in a 4s7p configuration.

I mounted them in a 4 inch pvc tube, which required some extensive modifications to fit under the BlueROV. But otherwise it was great. I went with 18650 cells for my next battery pack, though. Makes for a much more streamlined ROV.

#5

I’m using The Samsung INR21700-50E. Very happy with quality and performance, though I run relatively low loads (a 4S2P 10 Ah giving me a full day). With a cheap battery spot welder (under $200) there’s enormous flexibility in how you can configure them is a tight space.

#6

Yeh I was looking at making like a flat sealed pack, with custom flat sealed “box” to mount under a 3inch tube on my custom rov … that is good info to know that running a 4s2p works I was wondering how many parallels I would need . I am gonna do some research in building a pressure vessel for it.