True 3.7v 5500 or 6000 MaH Li-Ion 25500 or 32600

jhcolman · May 9, 2011

Hi All

Looking for a true 5500 or 6000 MaH 3.7 volt Li-On. Protected. Ideally 6000 MaH at 0c. That stays close to 3.7v until capacity close to exhausted and then rapidly drops. Good to high quality. With tabs (or capable of taking tabs). So looking fir nirvana, but will settle for bliss.

Almost bought an AGM Battery,but price is now $150 per cell!!! Ouch!!

Goal: to assemble into a 4 pack, in series and parallel, to get 12000 MaH and 7.4 volts. Must fit into a cylinder that that us a tad wider than 32600s. I will post cylinder size. It readily fits 4 standard D bats, and with an insert can fit 5 standard C bats. There is sufficien play (in diameter and length) to fit a pack. Wish to set up the pack so that it is not wired, but is an insert that will fit between the contact springs at the + and - poles.

LED array has max 8.4 volts.

Would appreciate any help re sources for the bats and design of the pack.

Thanks

Jhcolman

fivemega · May 10, 2011

jhcolman said:
Goal: to assemble into a 4 pack, in series and parallel, to get 12000 MaH and 7.4 volts. Must fit into a cylinder that that us a tad wider than 32600s. LED array has max 8.4 volts.

Even if you use highest capacity (2900mAh) 18650 cells, you need 2S/4P (2 serial, 4 parallel) set up in Elephant II. This is much wider body than you think and you will get nominal
7.4 V / 11.6 mAh

BTW, MAh means Mega Ampere hour but I think you meant mAh.

Norm · May 10, 2011

Go to edit post / Advanced and click the no icon button below the icons.
Norm

Aquassey · Jun 2, 2014

Please forgive noobie ignorance.

Is a 6000 mAh 3.7V li-ion battery (32650) a safe substitute for the original equipment 5500 mAh battery? Application is a Bigblue LED divelight. Bought the 6000s after a frustrating search for an equivalent.
Reliability is of utmost importance.

vicv · Jun 2, 2014

besides size and capacity your requirements really are not possible. No Li-ion cells will work at 3.7v for most of the time then drop quickly. That's not how the chemistry works. You'll need nickel chemistry for that and it won't be 3.7V

StorminMatt · Jun 2, 2014

vicv said:
besides size and capacity your requirements really are not possible. No Li-ion cells will work at 3.7v for most of the time then drop quickly. That's not how the chemistry works. You'll need nickel chemistry for that and it won't be 3.7V

The closest thing you are going to find to what you want is LiFePO4. It maintains a voltage at least as well (if not better) than nickel chemistry. But even here, you get 3.2V (and NOT 3.7V). Unfortunately, 3.7V chemistries are just not good at holding a voltage. It starts high and drops as the battery is discharged.

With all of this said, you might consider one of the Feilong 32600/32650 batteries if you want a high capacity Li-Ion cells. They are available as a 5000mAH LiFePO4 32650, a 6000mAH LiCo 32650 (Inthink protected is available), and a 5000mAH LiCo 32600.

vicv · Jun 2, 2014

From my testing lifepo4 cells continually drop in voltage as well as 3.7v chemistries. I'm not sure where that rumor came from that they hold a steady voltage

StorminMatt said:
The closest thing you are going to find to what you want is LiFePO4. It maintains a voltage at least as well (if not better) than nickel chemistry. But even here, you get 3.2V (and NOT 3.7V). Unfortunately, 3.7V chemistries are just not good at holding a voltage. It starts high and drops as the battery is discharged.

With all of this said, you might consider one of the Feilong 32600/32650 batteries if you want a high capacity Li-Ion cells. They are available as a 5000mAH LiFePO4 32650, a 6000mAH LiCo 32650 (Inthink protected is available), and a 5000mAH LiCo 32600.

HKJ · Jun 2, 2014

vicv said:
From my testing lifepo4 cells continually drop in voltage as well as 3.7v chemistries. I'm not sure where that rumor came from that they hold a steady voltage

Probably from this kind of discharge test:

UltraFire%20BRC32600%204000mAh%203.0V%20(Green-white)-Capacity.png

vicv · Jun 2, 2014

That's pretty good. Maybe mine aren't very good. I have some Samsung 18650 that I got from a new drill battery pack. All of them continually drop voltage as they discharge and they're definitely lifepo4 cells

StorminMatt · Jun 3, 2014

vicv said:
That's pretty good. Maybe mine aren't very good. I have some Samsung 18650 that I got from a new drill battery pack. All of them continually drop voltage as they discharge and they're definitely lifepo4 cells

Are you positive that they're LiFePO4? LiFePO4 starts out at a out 3.6V, drops almost immediately down to 3.2V, and remains around there (maybe dropping off tenth or so of a volt) until the battery is dead. At that point, voltage drops off a cliff. If these batteries have the more steady drop in voltage during discharge, they are probably IMR (lithium manganese oxide) and NOT IFR (LiFePO4).

vicv · Jun 3, 2014

Definitely lifepo4. The battery pack is a nano phosphate pack. I looked up the cells online by the number on the side. And after being charged to 3.6v they steady at 3.35 or so within the hour. At a 1A discharge over the first minute they drop to about 3.05-3.10v stay there for around 2 minutes then steadily drop

StorminMatt · Jun 3, 2014

It could be that one or more of the cells are damaged.

vicv · Jun 3, 2014

All twelve of them from a brand new pack straight from Dewalt? This wasn't an eBay buy. I got it from work thinking they were a123 cells. Dewalt had just changed to the Samsung cells

Conte · Jun 5, 2014

18650's are below the Lifepo4 sweet spot in my opinion.
It's just voltage sag cause they are so small. The bigger lifepo4's will hold their voltage better. Especially the lower cap ones designed for higher output.

Conte · Jun 5, 2014

You guys realize of course the OP is from 2011.
Aquasseys post was a bump with a new inquiry.

Aquassey said:
Please forgive noobie ignorance.

Is a 6000 mAh 3.7V li-ion battery (32650) a safe substitute for the original equipment 5500 mAh battery? Application is a Bigblue LED divelight. Bought the 6000s after a frustrating search for an equivalent.
Reliability is of utmost importance.

If the OEM battery was a 32650 Li-ion, then I see no reason you can't use a 32650 6000mah.
It'll be the same size the voltage, you'll jsut get more run time.

The question is, is it a quality cell that is actually giving you 6000 ?

Since you bought them already, make sure you test them thoroughly. Make sure they give you the performance you need before you have to rely one them.

StorminMatt · Jun 5, 2014

Conte said:
18650's are below the Lifepo4 sweet spot in my opinion.
It's just voltage sag cause they are so small. The bigger lifepo4's will hold their voltage better. Especially the lower cap ones designed for higher output.

LiFePO4 18650s aren't too bad at holding their voltage. But they are DEFINITELY below the 'sweet spot' of LiFePO4 in terms of capacity. Larger cells (like 26650s and 32650s) have much better capacity in relation to that of LiCo cells of the same size.

Aquassey · Jun 6, 2014

Conte said:
If the OEM battery was a 32650 Li-ion, then I see no reason you can't use a 32650 6000mah. It'll be the same size the voltage, you'll jsut get more run time. The question is, is it a quality cell that is actually giving you 6000 ?Since you bought them already, make sure you test them thoroughly. Make sure they give you the performance you need before you have to rely one them.

Appreciate the guidance, Conte. Will wring the batteries out, before I trust them in a cave.

True 3.7v 5500 or 6000 MaH Li-Ion 25500 or 32600

jhcolman

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