Trying to find good batteries from a good source, where'd you get yours and what are they?


#1

I need to get some batteries, as the ones I am using now do not belong to me. They are the LFP26650E 3.2V 3300mAh PTM. I found them here but I wanted to see what other people were using (and what vendor they went with), or if anyone was using anything better... I was told the recommended ones on the site (Trustfire 26650) are not what is being used right now so I don't want to get them if everyone's already using better batteries :)

Thanks in advance for any advice anyone can offer me

Cheers


#2

Hi Anthony:

Yes, here at OROV we have been playing with unprotected LiFePO cells since January. During our field testing in January in the Sea of Cortez, the Trustfire cells did not tolerate exposure to sea water well. Since occasional leaks are a fact of life in the field, we're trying to find a battery solution that is more robust. LiFePO cells are more rugged than LiCo or LiMnNi, though they have a somewhat lower capacity. They also have a lower voltage, but the ROV runs fine on 9.6 V. The bare 26650 cells are a little shorter than the protected Trustfire cells, so we've been adding a small disc that contains an embedded polyfuse for short-circuit protection of the battery pack.

In short, the cells you list should work, but with a couple of caveats:

1.) They are not protected, so it's up to you to keep them safe from undervoltage, overvoltage, and overcurrent situations. Make sure that your charger will properly work with the lower voltage of LiFePO batteries.

2.) You're probably going to need to add a spacer of some sort to make up the extra room in the battery tubes. The cells you show are flat-topped, and you need to be careful that all the cells make good electrical contact.

-W


#3

Hey Walt! Thanks for this reply! I borrowed Matthews batteries in Tahoe and they seem to work well enough (they're the ones I figured I'd go with). Being that the batteries aren't so cheap, I want to make sure I buy the right ones the first time around. I added a spring to the opposite side of the battery tube per Matthews recommendation as to address the issue of the physical size of these particular batteries. Sounds like we're still working to find the "best" solution, so I'll just keep up-to-date with the changes and go with the ones I am borrowing.

Additional question: You said you're using a "small disc that contains an embedded polyfuse"? Is there any documentation regarding this? And is this something I should look into? Is water leaking inside causing short circuits and if it is do the batteries die? (sorry for the rookie questions I appreciate your reply)


#4

Hi Anthony:

No documentation yet, though I think we're closing in on a design that we like. Having a polyfuse in the battery packs will protect against a number of short-circuit conditions, though not all of them. If a battery tube floods with salt water, there's not a whole lot you can do to keep the batteries from shorting out. That's why we like the LiFePO chemistry- it's a lot more tolerant of this kind of abuse than other Lithium chemistries.

-W