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Why doesn't a li-ion battery take load?

Posted: Nov 30 2019 2:59am
by azad
Hi,

I've been using a 36V motor that draws ~13A current at peak. I initally used a set of three lead-acid (12V 12A) batteries in series. They had sufficient power to easily pull not only my weight but also payload of 10kg more. They gave me a speed of 35km/h at full speed. I have now replaced them with a set of Li-ion batteries (10 x 12.8A + 10x 12.8A = ~26A) however, I am worse off than the lead-acid batteries. They can't even provide enough power with the same motor to carry my weight at 15km/h. Without the load (i.e. running the bike without riding on it), battery current indicator stay full at full throttle but when I put weight on it, battery instantly drops to lowest mark on the indicator.

Can anybody tell what is going on and how can I get the power from the batteries?

Thanks,

Re: Why doesn't a li-ion battery take load?

Posted: Nov 30 2019 3:02am
by john61ct
Do you mean Ah where you've used amps by mistake?

If so, maybe you got ripped off, sold crappy packs. New or used, which cells used? Link?

Have you checked cell voltages?

What charger?

Re: Why doesn't a li-ion battery take load?

Posted: Nov 30 2019 3:44am
by azad
john61ct wrote:
Nov 30 2019 3:02am
Do you mean Ah where you've used amps by mistake?

If so, maybe you got ripped off, sold crappy packs. New or used, which cells used? Link?

Have you checked cell voltages?

What charger?
Yes it is Ampere hour.

Yes the voltage are 4.3 at full charge. I am using 2x2A 36V chargers to charge each 10 battery set separately.

Re: Why doesn't a li-ion battery take load?

Posted: Nov 30 2019 10:30am
by HK12K
Oh my. :cry:

I can't easily find test results for those cells, or even any published specs, but at a claimed 12,800mAh I suspect they have exceedingly low amp ratings. They're probably 5amp continuous discharge cells which would explain why they sag to the point of uselessness when any real load is applied.

The fact that they're ultrafires, or any chinese rewrap for that matter, doesn't help. You cannot trust the claims of chinese battery re-wrappers or the batteries they sell. They blatantly lie and inflate their advertised specs as a rule, and what is actually under the wrapper can literally change at any time. Not worth it.

Also, it's really easy to damage cells when soldering. If you heat soaked them, or any lion for that matter, it's very easy to internally damage them. So even if they were appropriate for the task at hand they might have ended up damaged during assembly.

Tl;dr: Buy better batteries and use a spot welder and nickel strips for assembly.

Re: Why doesn't a li-ion battery take load?

Posted: Nov 30 2019 10:46am
by kcuf
lesson learned junk cells

never buy cells with fire in name

Re: Why doesn't a li-ion battery take load?

Posted: Nov 30 2019 10:52am
by HK12K
Also, fwiw, if you're charging to 4.3v per cell you are dangerously overcharging them. 4.2v MAX. 4.1v for best cycle life and range.

Re: Why doesn't a li-ion battery take load?

Posted: Nov 30 2019 11:49am
by docw009
Where's the BMS? You've already got these cells overcharged at 4.3 volts per cell. That's a potential fire in the making. Not kidding. You need the BMS.
Image

The yellow Ultrafires are used for vaping and flashlights. They are probably 1.0-1.2 AH cells. Can't run an ebike. Sold on ebay by liars. There is no such thing as a 9800 mah cell,
https://www.ebay.com/itm/16X-Flat-Top-1 ... 0008.m2219

Re: Why doesn't a li-ion battery take load?

Posted: Nov 30 2019 11:57am
by NCC1941
Yeah, your problem here is that you built a pack out of scam cells. There's no way they're 12800mAh, and as you've discovered, they can't handle any real load. And as others have already mentioned, you're risking a fire with your charging behavior.

I would suggest that you poke around and do a lot more research before making your next purchase. Lithium ion batteries are a mature technology. If a cell's specs look way too good to be true, that's because they are.

Re: Why doesn't a li-ion battery take load?

Posted: Nov 30 2019 12:16pm
by HK12K
docw009 wrote:
Nov 30 2019 11:49am
Where's the BMS? You've already got these cells overcharged at 4.3 volts per cell. That's a potential fire in the making. Not kidding. You need the BMS.
Image

The yellow Ultrafires are used for vaping and flashlights. They are probably 1.0-1.2 AH cells. Can't run an ebike. Sold on ebay by liars. There is no such thing as a 9800 mah cell,
https://www.ebay.com/itm/16X-Flat-Top-1 ... 0008.m2219
Ultrafires, Trustfires, etc are a big NOPE in the vaping community as well. MAYBE good for a flashlight, but even then there are way better options for a myriad of reasons. These are labeled as 12,800mAh too. It's an absolutely absurd lie, but that alone is telling. Usually the higher the mah, the lower the continuous discharge rating. There are probably flashlights that could send these things into thermal runaway.

Re: Why doesn't a li-ion battery take load?

Posted: Nov 30 2019 12:58pm
by Voltron
There's a nice YouTube vid of a guy cutting ripoff cells open, and inside was a tiny lithium battery wired in to make voltage... Packed in with enough ballast to make it about the right weight.

Re: Why doesn't a li-ion battery take load?

Posted: Nov 30 2019 2:22pm
by Voltron
I'd wager it would need about 4 or 5 in parallel to not sag too much.
And have you actually metered the amp draw during acceleration? I was surprised to find my 20 amp rated controller was pulling close to 40 amps briefly during pullouts.

Re: Why doesn't a li-ion battery take load?

Posted: Nov 30 2019 2:58pm
by socrace
Measure each cell voltage individually while motor is running to find possible bad cell (diff voltage across the bad one).

Re: Why doesn't a li-ion battery take load?

Posted: Nov 30 2019 3:02pm
by rockstar195
F A K E ___C E L L S ! ! ! ! !

Get real authentic ones....gotta pay to play.

Re: Why doesn't a li-ion battery take load?

Posted: Dec 01 2019 12:37am
by amberwolf
socrace wrote:
Nov 30 2019 2:58pm
Measure each cell voltage individually while motor is running to find possible bad cell (diff voltage across the bad one).
In this case, they are *all* bad cells. :/

Re: Why doesn't a li-ion battery take load?

Posted: Dec 01 2019 11:07pm
by dustNbone
Yeah I agree, can't think of a single application where it would be safe to deploy those cells. They could be literally anything, would be interesting to chop one open and see what they're actually composed of.

Re: Why doesn't a li-ion battery take load?

Posted: Dec 02 2019 7:54pm
by E-HP
dustNbone wrote:
Dec 01 2019 11:07pm
Yeah I agree, can't think of a single application where it would be safe to deploy those cells. They could be literally anything, would be interesting to chop one open and see what they're actually composed of.
I have a bunch of those UltraFire cells that I used to power some motion sensor lights that I have in my hallway. In the beginning, they would last a couple of weeks, about the same as a couple of Samsung cells that I have. I rotate through them, so after about a year, they probably have a dozen charge cycles each. The UltraFires are down to about a week between charges, so the capacity has dropped by half, while the Samsung cells still last a couple of weeks. Of course the imaginary capacity of the UltraFires, on paper, is way more than the Samsungs. I'm relatively OK with using them for this application, or in my cheap flashlights, but not on anything that draws a significant amount of current.

Re: Why doesn't a li-ion battery take load?

Posted: Dec 02 2019 10:23pm
by amberwolf
https://lygte-info.dk/info/batteryDisas ... %20UK.html

Just one of a bunch of places you can find disassembly pics showing what's actually in some of these cells.

As that site shows, some of them are obviously ripped out of old battery packs and reshrunk with covers over the ripped off spotwelds (and corrosion). Some might be "new" cells, but don't have the protection stuff in them that their wrappers claim (and obviously can't have the capacity they claim). Etc., etc.

Some detailed testing of some of those cells:
https://lygte-info.dk/review/batteries2 ... %20UK.html

https://lygte-info.dk/review/batteries2 ... %20UK.html

They're old stuff, but the *Fire brands aren't any different now than they were then. ;)

Re: Why doesn't a li-ion battery take load?

Posted: Dec 03 2019 5:08am
by d8veh
As already said, you can't believe anything about the specification of any cells with "fire" in the name. If you want to make a 36v 20-cell pack, you need high discharge rate cells, like Samsung 30Q, LG HG2, etc.

You must install a BMS and charge at 42v. As an alternative, you can make two 5S2P bricks, add a lipo-type balance connector and use a lipo balance charger to charge them.

All things considered, it's probably easier and cheaper to buy a ready-made battery from Ali-express. There are some nice cell-packs with BMS for around $150.

Re: Why doesn't a li-ion battery take load?

Posted: Dec 03 2019 12:04pm
by E-HP
If the tests on the 9800 mah version of the cells is accurate, then they seem to be good for about 5% of the capacity stamped on the battery (~425 mah, in the case of the 9800s).
https://www.youtube.com/watch?v=yoCaWByTwUQ

If that holds, then the OPs cells would have an actual capacity of about 600 mah. If those cheap cells are capable of 1C, then the 10S2P pack would be able to supply 1.2 amps. 2C would give you 2.4 amps. In theory, with a running start, the bike may be able to maintain 7 mph or so, but any slight hill would kill it.

Re: Why doesn't a li-ion battery take load?

Posted: Dec 03 2019 1:17pm
by john61ct
9900mAh, almost funny

Kind of like the nigerian prince scam, you immediately filter out all but the totally clueless

Re: Why doesn't a li-ion battery take load?

Posted: Dec 04 2019 11:43am
by MAXIMUM_AMPS
d8veh wrote:
Dec 03 2019 5:08am
As already said, you can't believe anything about the specification of any cells with "fire" in the name. If you want to make a 36v 20-cell pack, you need high discharge rate cells, like Samsung 30Q, LG HG2, etc.


Interestingly enough, the cells with "fire" in the name carry the greatest risk of fire.

Re: Why doesn't a li-ion battery take load?

Posted: Dec 04 2019 12:11pm
by miro13car
As far as I know
There are no 18650 cells with more than 4000mAh of capacity.
Again
don't buy any cells which have word "fire" in description.

Re: Why doesn't a li-ion battery take load?

Posted: Dec 04 2019 12:25pm
by E-HP
Based on the information provided, it does look like there's at least one application for the battery pack, since it seems to work when there's no weight on the bike....
space bike.png
space bike.png (123.7 KiB) Viewed 1300 times
Of course, this is the backpack battery version.

Re: Why doesn't a li-ion battery take load?

Posted: Dec 04 2019 6:32pm
by amigafan2003
OP has got to be trolling, surely.......................

Re: Why doesn't a li-ion battery take load?

Posted: Dec 05 2019 1:18am
by john61ct
Many noobs believe in unicorns and rainbows.

By the time they learn most sellers in this niche are outright scammers, they aren't total noobs anymore.