Low cost battery supply.

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robca
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Re: Low cost battery supply.

Post by robca » Wed Jan 06, 2016 11:54 pm

Chinese battery makers believe that the higher the number they can print on the label, the better.

The highest you can get (for real) is below 4000mAh, with most of the reliable, branded 18650 in the 3000-3500mAh range

Most of the no-name cheap Chinese batteries are, like Andy says, 800 to 2000mAh. Rarely you'll find anything higher

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martinayotte
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Re: Low cost battery supply.

Post by martinayotte » Wed Jan 06, 2016 11:59 pm

So, the white ones I've shown, GTR branded, labelled at 10000mAh, is probably still below 4000mAh ?

It is some kind of scandal like Volkwagen scandal ... :evil:

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mrburnette
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Re: Low cost battery supply.

Post by mrburnette » Thu Jan 07, 2016 12:55 am

martinayotte wrote:So, the white ones I've shown, GTR branded, labelled at 10000mAh, is probably still below 4000mAh ?

It is some kind of scandal like Volkwagen scandal ... :evil:
More like truth in advertising - or, lack thereof!

I suspect that the unsupported numbers are coming from a complete misunderstanding of "mA/hour"; that is, the low internal Z of the battery probably does support 10A+ of instaneous current until the battery over heats or the $1 VOM smokes on the 20A scale! My guess is that a cheap meter and cheap test leads would top at about 10A.

To put the above into perspective, AWG "0" gauge wire is 0.1002 Ohm/1K foot @25C: so, a 3.6V Li-ion cell would pump approximately 36A through 304.8 Meters of 0 gauge wire... of course, that single cell is probably going to be the weak link in our 2 component short...

From: http://www.buchmann.ca/chap9-page3.asp
The internal resistance of a naked Li-ion cell, for example, measures 50mOhm at 25°C (77°F). If the temperature increases, the internal resistance decreases. At 40°C (104°F), the internal resistance drops to about 43mOhm and at 60°C (140°F) to 40mOhm. While the battery performs better when exposed to heat, prolonged exposure to elevated temperatures is harmful. Most batteries deliver a momentary performance boost when heated.
Thermal runaway.

Ray

zmemw16
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Re: Low cost battery supply.

Post by zmemw16 » Thu Jan 07, 2016 1:49 am

easy the easter bunny, harvey and certain low flying porcines persuing fraud inquires :D
srp

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martinayotte
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Re: Low cost battery supply.

Post by martinayotte » Thu Jan 07, 2016 2:05 am

Thanks Ray,

But all those becoming much technical ...
I like technicals when it digital, but never really digested them when analog.
At school in early 198x, I was saying "5V is a civilized voltage"

So, for those 18650 batteries, I will play with them ... Fear of ignite fire came back ... :-(

mrbwa1
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Re: Low cost battery supply.

Post by mrbwa1 » Thu Jan 07, 2016 4:26 pm

I haven't looked much into the 18650 cells but have a range of LiPo packs for quadcopters.... Do the 18650s have a C rating on them?

At least in the Hobby world, the C ratings don't tend to get over-inflated too much. Some of the packs even list a peak/burst and an average C rating as some setups can easily overdraw a battery and cause a brownout to the Flight controller (usually resulting in BAD things like a mangled pile of parts).

I would likely be more tempted to power projects from Quadcopter batteries since I know them pretty well and have all the equipment for easily charging packs (not to mention a pile of spare batteries laying around).

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ahull
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Re: Low cost battery supply.

Post by ahull » Thu Jan 07, 2016 4:43 pm

mrbwa1 wrote:I haven't looked much into the 18650 cells but have a range of LiPo packs for quadcopters.... Do the 18650s have a C rating on them?

At least in the Hobby world, the C ratings don't tend to get over-inflated too much. Some of the packs even list a peak/burst and an average C rating as some setups can easily overdraw a battery and cause a brownout to the Flight controller (usually resulting in BAD things like a mangled pile of parts).

I would likely be more tempted to power projects from Quadcopter batteries since I know them pretty well and have all the equipment for easily charging packs (not to mention a pile of spare batteries laying around).
You typically can't get away with messing with C ratings (and yes, most 18650 cells from known sources will list the C rating). If you were to overstate the C rating in the ebay listing, then when the customer tried to discharge or charge based on the over inflated rating, bad things would happen pretty quickly.

Lying about the capacity is much easier to get away with. The C rating depends on chemistry, physical size and construction. The pouch cells typically used in RC models often have higher discharge ratings than similar sized 18650 cells but this is not always the case.

Either type can be used for relatively low current applications, but if you are using them in a demanding role, I suggest you use cells from a known manufacturer, rather than "BangoodWhizbangLoadsaSmokeUltraFlame 10,0000mAh best price" cells from the less reputable corners of the interwebz.

This little tool might help if you are building an STM32 controlled portable spot welder, or whatever.

Another source of used high capacity 18650 cells (assuming you don't have a ready source of old laptop batteries) are scrap LiPo power tools and power tool batteries. More and more of these are heading for recycling, or appearing as "spares or repair" on ebay. The same caveats apply to them as to laptop batteries. Probably most of the cells are good, but your mileage may vary, and watch out for the sharp bits when dismantling them. :D Also check they are LiPo and not NiMH or NiCd
- Andy Hull -

enif
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Re: Low cost battery supply.

Post by enif » Thu Jan 07, 2016 7:23 pm

Having followed this discussion with interest, here is the link to the 18650 batteries which I now use regularly (after a lot of disappointments with cheap "UltraFire", "TrustFire", etc):

http://www.aliexpress.com/item/10Pcs-in ... 13083.html

I have bought at least 50 of these PKCELLs and always tested the capacity of each cell individually 4.2V -> 3.0V @0.5A. So far, I never had any cell below the nominal 2200mAh, most range between 2250 and 2350mAh. I usually buy when they have a 30% or higher sale (for which I never had to wait more than a week to happen), so the price I paid was always between $19 and $22 per lot of 10.

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ahull
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Re: Low cost battery supply.

Post by ahull » Thu Jan 07, 2016 10:35 pm

enif wrote:Having followed this discussion with interest, here is the link to the 18650 batteries which I now use regularly (after a lot of disappointments with cheap "UltraFire", "TrustFire", etc):

http://www.aliexpress.com/item/10Pcs-in ... 13083.html

I have bought at least 50 of these PKCELLs and always tested the capacity of each cell individually 4.2V -> 3.0V @0.5A. So far, I never had any cell below the nominal 2200mAh, most range between 2250 and 2350mAh. I usually buy when they have a 30% or higher sale (for which I never had to wait more than a week to happen), so the price I paid was always between $19 and $22 per lot of 10.
Those look like the sort of thing you find in laptop batteries. Generally if the cell states a reasonable capacity, (2000 to 2600 mAh) there is a good chance that the seller is being honest.

If the cells have that utilitarian look, with no fancy packaging or weasel words stamped on them, they are probably from a production line that is supplying in large volume, and they are worth a punt.

At $2-$2.50 per cell, shipped (depending on quantity), those ones you linked to are pretty good value too. As with most things, half the battle is finding a reliable supplier.
- Andy Hull -

mrbwa1
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Re: Low cost battery supply.

Post by mrbwa1 » Fri Jan 08, 2016 4:50 pm

Thanks for the extra info @ahull!

I just am not that familiar with the 18650 cells. I would imagine their Current ratings are in line with the intended use: Laptop batteries. and I agree about charge/discharge rates. The accepted rule for 3S Hobby Lipo packs is 1S (Charge a 2700Mah pack at 2.7A), however I usually charge them at a lower rate, especially the first time when I have to discover what the true capacity is. I suppose I should get busy and build a battery temp probe so I can feel a little better about that 1S rate (it's not like it's hard since I have all the parts laying around...

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