# Let's Discuss Battery Max Amps In Depth

I’d really like to get a more in depth conversation about Battery Max Amps. More specifically at what point do you really see a difference in performance. So to set a standard for the topic we’ll use this set up to help keep things consistent for now.

12s5p 21700’s 18.5ah 120amp continuous discharge. Each cell can do 30amps sustained however I reduced the maximum to 24a each to not wear the cells prematurely.
TB110’S with 1:2.4 ratio (theoretical top speed 42mph loaded),
Flipsky dual 6.6 v1
Dual 6374 170kv

How much performance if any am I getting if I set my battery max to a total of 120amps vs 100amps? While being mindful that the cell starts to lose its ability to supply the full capacity of 3.7ah past 20amps.

If I decide to set it at 80amps vs 100 or even 120, how do I calculate the benefits?

Discuss!

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I suspect you will rarely if ever hit that current unless accelerating up a steep hill or holding absolute top speed uphill or in extremely windy conditions, against the wind, at top speed.

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Sure, I understand that part. What I’m trying to do here is get people talking about what the sweet spot is for this current set up and why. From there we can add more configurations to give people an idea of what to shoot for in terms of performance for their weight, gear ratio, battery, and wheel diameter.

So for example, I’m racing up a 2mile hill (call it 20% grade) my gear ratio is 1:2.4 with dual 6374 170kv and 110 wheels, I weigh 160lbs and my boards top speed on flat is 42mph. To reach that top speed with my gear ratio, up a 20% grade hill would require how many bat amps? How does one go about doing the math for that?

Once I’m done building my new board I’ll be doing real world tests at various battery settings up hills to find the sweet spot and what range of amps from 60a-120a is best for performance. But that will only help me so I’m more interested in finding a way to give a rough estimate (like the sk8calcs) so people don’t overshoot their battery needs and waste money, space or even performance.

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I feel like a good measure for acceleration is your watts drawn over your top speed, amps is the source of your torque but it doesn’t account for gear ratios, higher values have more oomph overall

A reference would be a Boosted has a value of 83 watts/mph (2000 watts / 24 mph)

I think it’s better to use nominal voltage and continuous current as the number for the value

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I run my 12S5Ps on unities at 55 amps, 16/36 on 100mm wheels. 37mph and not slow getting there. Hills aren’t even a question.

ideally you want the max amps just below the BMS cutoff, and if you’re bypassing, you want it just below the nominal (sustained) discharge rating. You’ve got it set up right.

You will probably not see any additional benefits going from 100 to 120 unless you gained a lot of weight while you were making that configuration change.

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This is certainly a question for @professor_shartsis

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I’d turn to @deckoz with these types of questions. He the king of amps.

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This is where logging becomes really useful.

I rarely see over 70A drawn from my 12s5p battery with 2x6374 190kv sealed Maytech motors set at 60A each. Even when I increase the motor amps, it does not make a significant difference in the battery amps.

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I guess I’m a shitty planner. I’ve settled on finding my limiting reagent and working backwards. My tattu 10ah 25c 12s pack is good for 250a on paper/marketing. I decided 200a for 4wd. 200/4=50 per esc.

In reality, I only touch peak total amps of 140 on metr telemetry. My limiting factor is really my skill and fear.

Clearly you are trying to avoid the trial and error approach. But sometimes it be that way.

I recommend pouring over your telemetry and matching corresponding actions/feels to the EEE stuff and maths.

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2.4:1
170kv
110mm tire
160lbs rider → 190lbs vehicle
top speed on flat 42mph → battery current to sustain 40mph on flat vs 20% grade:

53a motor current limit per motor:

18a motor current limit per motor:

^results:
40mph on flat ground: 32.2a battery amps total (1610.2w electrical total)

40mph on 20% grade: 98.53a battery amps total (4926.9w electrical total)

4926.9w/1610.2w = ~3.05

*correction on the charts, the battery voltage shown in the charts is 50v, but the charts mistakenly say 46v at the top

the assumptions are:
50v battery, 0.05ohm, 170kv, 2.4:1, 110mm tire, 53a motor limit vs 18a motor limit

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17 posts were merged into an existing topic: Welcome to Derail Jail

Wow beautiful. Gonna study this like crazy, thanks for the reply, it’s above and beyond.

I think i got my gear ratio wrong, motor gear 15t and wheel gear 36t is what it is. 3d servisas says its 2.4 so idk, I think my top speed is closer to 35mph rather than 40mph.

15t motor 36t wheel is 2.4:1

36/15=2.4

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your actual riding voltage is probably lower than 50v, that’s why I had to boost it for the chart

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Thanks, it’s a little above my head at first glance but it’s making sense. I have a feeling a lot of people over do it on their batteries because they overlook this part.

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I think I fudged the chart ever so slightly, I multiplied the 5% grade slope force lbs@ 40mph * 4 to get the 20% value, it’s close, but this was a bit lazy and I think it isn’t exactly correct.

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I use max battery amps as a way to limit maximum system power. So I set my motors to the maxium they can do then set the battery amps quite low. Then increase the battery amps a bit at time till its enough power for my needs.

High motor amps only effects slow speed acceleration. Motor amps are much lower at speeds below 60kph.

Peak amp draw happens during acceleration, so limiting battery amps will limit acceleration.

On my system 12s1p, under load (heavy acceleration) my voltage drops to 46.2v X 32a (battery draw) = 1478 watts is my peak system power.

My two vesc battery amps are at 17.5 amps, I will only see 32a (battery) under heavy acceleration for a second or so then it starts to drop. My motor amps are 65a in vesc tool.

To answer your question I feel any difference in increasing the battery amps with the way I set mine up.

I like to run the battery amp limit low as a way to keep the acceleration from being too savage and to save my battery from unnecessary wear.

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I agree.
I also don’t like the high battry amp setting.
It has a large voltage sag.
distance is reduced.
I can not control if the acceleration is too sharp.
If I can hit the fastest and climb the hill without inconvenience I’m fine.
I think that more battery amp is unnecessary.

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But why buy a thorium 4wd and then limit the batt amps to 10A? Honestly makes no sense. Even the 2WD would be too much for you.

But back to boards…

If you used 60a bat limit per motor @ 50v with these 2 motors in a race, you wouldn’t want to use 2:4:1, you’d want to use 2.15:1 for 45.10mph on 20%…

and in fact, anyone with the same voltage and battery amp limit on the same grade will get the same speed to a close approximation regardless of kv and tire size as long as their gear ratio gives a 48.31mph no load virtual ground speed.

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