The big question - How low can you go on Discharge rate (cont amps) for batteries (li-ion)?

ESK8 Electronics
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Hi! I think this topic has been brought up many times but I have not heard a somewhat ‘‘definitive’’ answer to this one…

So - what would exactly be the ‘‘minimum’’ pack size / discharge rate to go with?

I know there are many variables in this one (wheel size, terrain, weight of rider, hills, voltage etc) but as we have seen, there are these chinese and even some ‘‘american’’ commercial boards which use a lot less cells than we do here on the forum…

So my question is - what Cont Amp rating battery pack to go for, if an average user wants only 20-30kph ‘‘regular’’ speeds, and, perhaps, only, occasionally push till 40kph (if his board is able to) ?

This is without hills, I can take some general setup, like 83mm wheels, 2.25(?) - 16/36 ratio, perhaps 90kg total weight (board included), 10s system…

So yeah, would like to hear the answers to this one :slight_smile:

Otherwise, a poll might be a good idea to collect info about all sorts of battery (especially li-ion) ppl tend to use here :slight_smile:

If this discussion does not go well or steer in the right direction, I might consider to just close it… till someone else comes with the answers…

I know all of this can be proven / tested with a simple vesc telemetry app/data collection but I wanted to hear the opinion, too… besides the reason that I’d need to ask someone to log the data for me and have the right setup to make the test :slight_smile:

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10S3P for cruiser. 2160 watts 10S4P for power. 2880 watts 10S5P for performance. 3600 watts

But with a gearing for 40km/h and your chilled riding style a 10S3P would be enough.

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2000w still seem quite a lot… for ‘‘normal’’ cruising, it looks like it is sufficient to have around 300-400w available…

Anyways, wont argue, as I understand I should investigate some of these vesc log/monitor videos more closely to look at the data…

Me, included, 800-1200w seems like enough in some scenarious, and at the moment, im having a mountainboard, so for longboard the wattage might be even lower, I think.

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Depends on a lot of factors like you said down to the cell you use.

For continuous power: 10S3P 25R: 600W 10S4P 25R: 800W 25Rs although they have a high max power output they dont do too well above 7A/cell due to voltage drop.

Now if you use HG2s, 30Qs or VTC6s. You can do hogher continuous rates.

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i would change the verding. power seems to be more aggressive than performance. just change these two words but they describe it very well!

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That’s something I wanted to see more likely!

@PXSS thanks for pinning out the 7A discharge curve for the samsung’s 25r, had not heard/seen before about it :slight_smile:

So, essentially to mitigate (lower) the voltage sag for 25r’s, users would essentially use only less than a half of their rated cont discharge.

Which would translate to 21A/3P and 28A/4P. Will probably look up some more datasheets after you mentioned this :slight_smile:

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A boosted board has plenty of power. Not the most power but enough for good riding. It only has a 1000w motor (or two).

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Plenty of discharge curves data on lygte-info.dk Henrik (the guy that runs the site) is awesome too, He won’t mind sharing any of his work.

I’ve reached out to him several times to confirm my own tests and discharge models.

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Im not sure how but personally I think we would need to develop a model at what criteria/scenarios what cells/conig is best suited.

It somehow seems that ebike builders dont have such a hard time deciding what cells to use as they also usually have quite big capacity packs.

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I started on a calculator but am out of town for the next 2 weeks flight testing. E-bike builders have more space/less power requirement. They mostly use GA cells. Most of their packs also have at least twice as many cells so yeah. Not that big of a deal when they’re drawing similar maybe slightly higher amounts of power

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Yes, plus they have reliable human power helping the motor of about 200w-300w in power (internet stats)… :smiley:

I think i saw the power demand for bicycles somewhere and it was quite similar to what elongboards consume (10wh/km - 25-30kph avg)

Of course with higher speed wh consumtion goes up

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@PXSS ok please post / share it once you get back. If it is somewhat completed or something others have not done yet, then it might be really useful

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It is hard to tell how low you can go with the continuos discharge… I (60kg 1,73m) have a Mini cruiser, 90mm, 15/36 teeth, 149kv FOC, 12S and went up to 30km/h and had only a peak of 10A/500W!

Screenshot_20170115-104410.png1920×1080 742 KB

Maybe i could have reached a higher peak but if i would limit The battery to 10A battery max i still could ride quite normaly

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@DeathCookies Cool. Thanks for sharing this! That is one really low peak value!

I hope that more ppl show up who can prove that in some cases it is possible to “live” with such low discharge because their setups just dont consume anymore!

Wind is something we should take tests on! It may not be regular / strong enough for all cities/places but I just remember my times riding underpowered scooter/motorbike against the wind and not being able to achieve the max speed!

So this should be probably planned, that even if there are no hills, that this board will be strong enough against a wind blowing in the face! :slight_smile:

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@DeathCookies your setup is wrong. Great to see a picture of my app because it makes the analysis much easier. You have a higher Max Battery then Max Motor. Your should not do that. So you can switch the values to 100 Max Motor and 70 Max Battery. And in the picture you did not even touch the limits, so if you did a full throttle something must be wrong. Tell me about your battery, motor and setup.

@PXSS there is no need to reduce the max amps we draw from a Samsung 25R to 7A. Don’t think in continious discharge curves because that doesn’t happen when we ride.

To everybody. You can use the Samsung 25R with 20 A each cell when you have a 10S3P (60 A) or 10S4P (80 A). There are only a couple of things which limits those values.

  1. It’s too much power for you
  2. You have a fuse that can’t take that much current
  3. You have a BMS in the discharge cycle that can’t take that much current

And to reduce it to 7A is like buying a Ferrari and reduce it to 100 km/h top speed because it might get a bit warmer when it goes faster. When you drive a car you don’t push the throttle 100% all the time. Only people who had problems with their battery are reporting about issues. And in the end they have a terrible gearing ratio, wrong cells, wrong VESC setup or no glue and not even a board.

And when you are worried about your batterys life cycle then ask yourself the question if you will ride more than 10000 km with that battery. If the answer is yes then you can be worried. If no then don’t care about it.

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Well… My Motor is rated to 70A so i wont change it to 100A! Why shouldnt i do that? I know that i should Set up a even acceleration like devin said but these settings are quite old. I wont reach The 100a battery because The 70a Motor preventing it?

I already told you my setup… Overread it?

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What Devin tells about even acceleration is wrong. Really sad to see that he can convince so many people with that stuff and that they believe it. Sadly English is not my first language so i don’t sound that intelligent when i explain the stuff.

Correct

Did you do full throttle before the picture above?

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@Ackmaniac. Im sure his question asked what CONTINUOUS amp rating cell to choose. If we talk about continuous then yes 7-10A should be their limit if you want good endurance.

Look at the discharge curves for 15A and 20A. They sag a lot. Voltage drop is 0.22V from 7-15A and 0.37v from 7-20A per cell.

And you should really think in how many times you ride not total distance as batteries only care about charge cycles but I agree you’ll ride the same batteries for 2 years riding every other day

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Your battery limit should always be lower or equal to motor limit. That way theres less that can go wrong if something fails.

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Well, honestly i do not know if i had Full throttle. It is a Mini cruiser. The torque with this Setup so much that i did not need to go Full throttle. I just wanted to point out that you can achieve a good performance up to 30km/h with only 500W and 10A max battery!

I will test this setup even more and make tests like Full throttle.

@PXSS yeah, better be Safe than sorry

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Why is he wrong? His math does make sense and it explains The boost many people get on a certain RPM!