High internal resistance on new 18650's?

ericmeds

1 µW
Joined
Aug 12, 2018
Messages
3
Hi all,

New to the forums but have been riding my electric bike since 2012!

Recently "upgraded" my pack from the one I purchased in 2012 (52v 10a split into 2 packs in series).

After 6 years my internal resistance of the packs was 8.1 and the pack was going strong (always stored in cool environment with lower voltage etc) but decided to sell it to get a single pack that is easier with 25% more range 12.5 amps

New 12.5a battery not only has an IR of 8.1-8.9 but it gets the same range than my old 10a. Not seeing benefits of the extra weight, size and 2.5amps.

Seller out of PA claims they are brand new but I'm curious if they were left in a 100% charge state, heat, etc (which he denies).

Is there a normal IR range of new 18650's?


Cheers,
Eric
 
Not all cells are created equally.

There are low power cells that have high capacity, but higher IR. They get hot when pushed hard and so have less usable capacity.

There are high powered cells with high capacity and low IR. They can be pushed hard and still deliver most of their capacity but you pay more for these. (like Samsung 30Q or LG HG2 or Sony VTC6 cells)

"18650" is just a code that tells you the size of the cell. It doesn't tell you anything about the performance characteristics. You need to dig deeper into the specs of different model cells, and then take into consideration that there are a lot of fake cells out there. There are also sellers that overstate capacity. It really is a minefield out there for consumers.

What cells did your old pack have and in what configuration?
What cells does the new one have and in what configuration?
 
Yeah, 18650 means 18mm diameter, 65mm long, the last digit was there for special codes but nobody is doing that any more.

I believe the most recent "king of current" is the LG HB4? I seem to remember it can provide 30A, so the IR must be very low. for ebikes, the problem would be its low capacity, somewhere around 1500-mAh?

Each one of the top three cell producers (Samsung, LG, Panasonic) have a 3400-mAh cell designed for max capacity. They are all publicly rated for 10A, but they get warm at 10A, so they are safer and longer lasting at 5-ish amps. (using the 10A number as the peak, instead of continuous rating).

The Samsung 30Q provides 15A peaks and close to 3000-mAh, and as long as you can fit a 4P size of battery pack, they can provide peaks of 60A, so any amp-draw lower than that will allow them to run cool enough to last a long time. Regardless of what "the book" says, the 30Q has proven to perform well by many ebikers, out in the real world...
 
ericmeds said:
Hi all,

New to the forums but have been riding my electric bike since 2012!

Recently "upgraded" my pack from the one I purchased in 2012 (52v 10a split into 2 packs in series).

After 6 years my internal resistance of the packs was 8.1 and the pack was going strong (always stored in cool environment with lower voltage etc) but decided to sell it to get a single pack that is easier with 25% more range 12.5 amps

New 12.5a battery not only has an IR of 8.1-8.9 but it gets the same range than my old 10a. Not seeing benefits of the extra weight, size and 2.5amps.

Seller out of PA claims they are brand new but I'm curious if they were left in a 100% charge state, heat, etc (which he denies).

Is there a normal IR range of new 18650's?


Cheers,
Eric

Make sure you cycle the new pack a good few times before making a final judgement on the capacity and range.
 
If cells get stored for a while especially at full charge the IR will go up.

If you're after low internal resistance 18650s are the wrong place to look. High discharge (high C-rate) RC Lipo is the only way to go. As a bonus the discharge curve is a lot flatter (I usually finish the cells at 3.6-3.7 volts or 85% discharged, with a charge to 4.1) whereas 18650s need to be taken a lot lower to get most of the energy out.

End result? With RC Lipo not only do you get less sag under load your top speed at the end of the pack will be a lot closer to when you started (assuming no speed limiter or power-drag limits at either end).

Nothing comes for free so the caveat is you need to pay more attention to balancing, and take great care not to overcharge or over discharge. 18650s can catch fire too but it's usually a lot harder to make that happen unless there's a short or manufacturing defect.
 
Back
Top