Voltage Sag -- What is the most suitable battery cell?

ESK8 Electronics
#1

Gd day boys n girls, using a dual motor setup in 10s3p I experience HEAVY voltage sag (some Chinese batteries of unknown origin). I typically draw 20amps continuous and peak (going up hill no more than 40amps).

Thinking of building myself a proper battery pack 10s3p (can’t go bigger than that unfortunately because of size) and would like to know if it would be better to use

aa) Sony 18650 VTC5 (20A // 2500mah) or bb) Sony 18650 VTC4 (30A // 2000mah)

to avoid this king of sagging.

My thinking is that having a larger buffer between my actual amp draw and the battery’s theoretical max amperage draw ability would result in less stress on the battery…but of course I might be completely off track and it may have no effect whatsoever on preventing voltage sag?

Any ideas what would be the best to do while keeping the config at 10s3p?

Cheerio!

#2

3p is not good enough if you have cheap li ion chinese battery. Not powerful enough to discharge. Do 4p at least with constant capable 20-30A. The higher the constant amp the better. More than around 60A is not very useful.

If size hits you, I go for 6s5p. Should be more enjoyable to ride, powerful acceleration with less top speed.

#3

I have gone back to zippy 8000 mAh lipos personally. The power I get from these are so much better than li-ion. Not quite as indestructable but I used to sag 50-80% of my 18650 12s4p battery pack at times. Now with high discharge lipos, I sag at most 15% on steep hills and less than 5% on moderate hills.

I’ll probably be the only guy here trying to convince you lipos are the way, but from real world experience, lipos not only sag less, but their discharge curve keeps the voltage higher for longer. This means you don’t slow down as much while late into your riding. It just drops off quicker near the end instead.

If performance is your top priority (as is mine), than lipos are the way to go. I personally think li-ion are not that much safer. Things can still happen in li-ion, look at boosted recalling their batteries due to venting with the A123 cells…

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#4

thanks @laurnts @evoheyax. I will reconsider lipos, but for the time being for my enclosure i am kind bound to 10s3p., so cannot really go any larger than that, but 6s5p is certainly an option. i will see what kind of max speed that will give me.

Have you guys heard of Nick Hayek (the guy owning the Swatch Brand) with his new company http://www.belenoscleanpower.com in Switzerland? Hope they bring out their new battery pack next year…unfortunately did not happen this year.

#5

Does that mean from 4.2V a cell down to 2.1V (50%) till 0,84V (80%) a cell? :joy: Never trust a statistic that you didn’t cheat yourself.

#6

I thought this related to the the voltage range up to the point where the low voltage kicks in?

#7

No it means I can sag from 4.2 down to 3.4 or even less.

And as I tried to tell you a while ago, lipos solved all my sagging issues… higher discharge rating == less sag, this is just a fact That you seemed to want to deny…

#8

And with Lipo’s? I know that they sag less, but the sag is normal for the Li-ion batterys and for the most people no issue at all. And would you recommend a Lipo to somebody that has no glue about batteries. And would you sell a board that has Lipos to any person who orders it? Think about those who would put the board in the trunk of their car in the summer. Or who leave the board switched on for a week. Or who adjust the voltage cutoff to 0V. Do you charge your lipos and leave the house and trust the charger that it will switch off?

Not saying they are extremely dangerous but you need some knowledge. Quality Li-ion battery’s mostly just simply die when you handle them wrong. The chance that they fail badly is much lower.

#9

With lipos, I sag from 4.2 down to 3.9 at 100 amps. With 18650 4p (larger battery), I sag from 4.2 down to 3.4 or more at 72 amps.

I never said the sag wasn’t normal for li-ion batteries. But every manufacer gives you the volt with respect to mAh graph at different amp draws. The higher the draw, the higher the sag. Simplistic solution… use cells rated to higher a discharge.

I actually gained range with a 1/5th smaller battery… now I can do 8 miles, with lion, I could only get 6… 4 miles in and I only lose 2-3 mph off my top speed instead of 5 or 6 mph off my top speed. This is due to the curve.

Are Lipos safer than li-ion? No but li-ion batteries are not high discharge batteries. We are attempting to make them high discharge, but unless you build a 6p or higher, they aren’t high discharge batteries.

Yes, people can mess them up, but if I ever sold a board with them, I would clearly state what you shouldn’t do to avoid problems. Use a bms and and tell people not to mess with their battery settings. Don’t leave it in a car above x degrees. And if your board blows up because you ignored my warnings, that’s your problem, not mine.

If you would like to bottleneck your board with li-ion cells, then go for it. But let’s not pretend they perform better cause lipos outperform li-ion any day.

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#10

Where did you buy the li-ions 18650?

#11

30 of the cells were from the space cell, the other 18 where from Amazon. I checked carefully sellers and the comments for a seller who was supposed to have real cells.

But this brings up the other problem with 18650s. Fake cells are very common. Lipos can have this issue, but buy the respected lipo manufacturer cells from hobby king and your far less likely to get a fake than 18650s…

#12

Indeed! I was just wondering where you bought them. Because the lipo 18650 should be quite good if you buy some branded like LG/Samsung.

But if you are going back to LiPo 18650 here is some recommended and legit sites:

https://eu.nkon.nl/

#13

They were all LG HE2. Not saying they aren’t good cells, just that I draw too many amps due to hubs + I’m a heavier guy + San Francisco’s hills, so to mitigate sag, at 12s, 120+ con amp rating is necessary. With 18650s, that’s a 12s6p. Most of us don’t have that kind of space. So lipos make more sense to get a higher amp rating.

If your going to stick to 18650s @FloRider , the Samsung 25R is highly recommended by many in this community. The VTC4 might reduce your sag (since they are supposetly 30 amp con cells), but from looking at tests in the past, they may not be any better in terms of sagging than the other 18650s out there as they may not really be 30 amp con cells.

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#14

I would agree. There were vape tests on other forum and the guy who made the test said that these vtc 4 are more like 23A… and already at such discharge they get quite warm or so.

He did mention that they work better than other cells at load and does not get as hot as others… but he went into detail that 30A is something like a theoretical discharge which is only meant for a short time anyways…

So, if I were in your place and price would be okay I would probably just go with vtc 5 and enjoy the added capacity…(on the contrary, samsung 25R seems to be similar (at least have not seen tests of both of them side by side) and samsung’s might be a bit cheaper.

#15

I think im gonna order these: https://eu.nkon.nl/lg-18650-hg2.html I think they should quite good enough?

#16

LG HG2s in the graphs posted here a few months ago showed similar performance to the LG HE2 and Samsung 25R.

Idk if that’s a good source or not. This is my issue with 18650s right now. You need a good source or you’ll likely get fakes that do a fraction of what you expect.

#17

He’s gonna get his batteries from Eu distributor of Li ion cells, not from some shady chinese seller.

Btw, here’s where I look for tests / reviews:

http://lygte-info.dk/review/batteries2012/Common18650comparator.php

And here’s a good one about vtc5.

It states that the cell reaches 82 degrees celsius (at 20A)… that’s crazy actually. But I think they keep the current for prolonged time when running at 20A…

#18

Nobody of use drains his battery continuously at this amperage. I think I should implement the average consumption in my app. Actually that’s not a bad idea.

#19

There is one guy on this forum that buys 18650 and makes battery packs, he had no problem with them and he says they’re legit.

#20

Do you think this battery is good? https://eu.nkon.nl/review/product/list/id/1852/#review-form They said its good vaping battery etc. And one guy has used this for over 8 months with no problems.

Nah I will buy the Samsung INR18650-30Q 3000mAh - 15A Its cheaper and on the comparason it was better then lg hg2 on from 1 to 15 amp with Ah