This is why you see companies using a different chemistry for smaller packs. But they seem to degrade quickly too when discharged heavily. It is always a compromise when building smaller packs.
what’s up with not choosing nkon.nl? I think they are quite legit and their prices are also appealing… for lower priced batteries search around ES forum././
I’m not against nkon.nl. I just wanted to know whether there are other option to go with inside the EU…
@davidov Oh ok, sorry for that… thought you had a reason why not choosing nkon site… Quite happy we have it in Eu, at least a decent source of batteries righ inside of eu…
You seem to have great knowledge of batteries. Could you summarise these things:
What voltage sag would be ‘‘allowable’’? Do you only look at the ‘‘lower end’’ of the battery’s voltage spectrum or you start to look already at fully charged battery?
What I meant is - Should it be important to watch out not to let the voltage sag under 2.7 when underload (which would probably mean batt’s voltage is at 3.0 or so…
or that, for fully charged battery the sag should not be more than 0.5 volt, which would mean around 3.6/3.7 when underload max…
I hope you catch my point - what would be your recommended max voltage sag (for charged battery and for the ‘‘low end’’, too) ?
I do remember you said that battery should not be let under 3.3 volts…(for longevity purpose, as under 3.0 volts it’s been said there’s very little ‘‘juice’’ in the battery… and you just do more harm than good by taking these last drops of energy out…
I recall seeing his recommendation having at least 60 cells in a pack. At 10s6p this provies 120A of discharge current for most esk8 18650 cells. You’ll likely never discharge continuously at 120A but that extra buffer leads to lower voltage sag.
Yeah, Cannot get the exact numbers for what ‘‘amp buffer’’ we should aim… only know that cell should not go lower than 3.0v… and heat should be taken into consideration, too.
At 3.3v the cells are on the edge of a voltage “cliff” so to speak. Below 3.3v resistance builds considerable and they get hot so I set my VESC “Battery cutoff start” at the equivalent of 3.3v per cell (10s / 33v) and the cutoff end at 3.0v per cell.
The higher the amperage draw per cell the high the voltage sag. This means you will be able to pull more mAh from cells that are being discharged at a lower rate before hitting the 3.3v threshold. If you are following what I am saying you will see that doubling the size of your pack will actually provide more than double your usable range.
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Just a data point on my 10S3P NCR18650B , today I did a full discharge from 4.13V to 3.1V, extrapolating from one of the rides energy consumption I got 280Wh out of the battery, when i should’ve got 340~360Wh (2800 mAh from a 3200 mAh cell) So, comparing with the HG2 or 30Q discharge curves I will probably get more range from then than my actual setup and of course a better performance
Why/how does braking put a strain on the battery pack? Just pushing more amps back into the pack than it wants to handle?
Do you think that regen braking, in the way we use it on our boards, actually provides more range in real-world usage?
For the regen part, my average regen is 10%, not a lot, but is good to have a few kilometers more, if you ride slow when going down in a way that wind resistance is low, this number can go higher
We need to remember that the factory specs on these cells is assuming you are discharging to 2.5v per cell. A 3000mAh cell will only yield around 2000 mAh when discharged at 5 amps constant. Interestingly an HE4 2500 mAh cell yields only 200mAh’s less under the same load.
If you had to build a smaller 10S5P pack, which cell would you choose ?
10s5p is fairly stout, just about any cell with low resistance will serve you well. My favorite cell right now is the HE4.
I think they test the hg2 down to 2v cutoff to get 3000mah rating so i think im going 2500mah like you recommend. What are your thoughts with lg he4 vs samsung 25r? (In 12s4p configuration)
They are about the same. The 25R cells I have tested were slightly lower in resistance, they are about the same.
I would like to test the LG HD2 soon for smaller packs. It seems to perform better in smaller packs. At least it does on paper.
LG HD2 is even lower capacity (2000mah),and if you stop at 3.2v ?? In a small pack you would’nt get much range no??
The LG HD2 is actually similar in capacity at higher discharge rates and has more capacity when pushed to it’s 25 amp max constant current.
I need to test it to be sure, but like I said, on paper it out performs the rest at high discharge. Of course this type of use would degrade the pack much faster than in a very large pack but in a racing scenario it may be a very good contender.
So is the Trade off for having high Capacity cells like the (HG2 or 30Q giving you Power and Range) …the reduced life cycle compared to Lower capacity cells (2500mah) like the HE4 ?
One thing i would like to know is , …how long is a (Reduced life cycle) compared to a normal cycle . This would make it easier to know if the trade off is worth it ??
If we are talking about smaller packs that will see higher temperatures, then yes the lower capacity cells will have a longer cycle life.
I know it seems counter intuitive, we all want to use the highest capacity cells in a smaller pack to maximize our range but it isn’t a healthy choice for the cells because of the higher average discharge rates.
But there are so many variables at play… You can reduce your gear ratio so you will not pull many amps and safely use the high capacity cells in a smaller format because your average amp draw will be very low. My area of experience just happens to be in boards geared to top out at 35mph so take my advice from that frame of view.