# Pushing The Limits of Motor Amps

I’m pushing 40Amax battery and 100A max motor amps on 12s4p with Samsung 30Q

The 6384s feel really torquey

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Do you have BT module to see how many amps your motor is pulling? Do they get that high?

I also have 100 amp motor max on my 13s setup…

100a Motor Max -40a motor min 50a batt max -15a bat min

I only hit the motor max from a stop…lol

This was on a flat surface no incline, that means almost 70A per motor. On an incline full throttle it might reach 90A per motor, battery max didn’t ever exceeded 40A per VESC

Very interesting. I just didn’t think it would be able to spread that far between battery and motor amps. Like if you set it to a hypothetical 10a battery and 120a motor it seems like it wouldn’t be able to reach those motor amps because there wasn’t enough battery amps coming in to support it. I just don’t understand the limits associated with it other than you get higher motor amps at lower motor rpm

It’s pretty confusing, it seems the current is accumulated between the motor and battery, like a power container, this creates immediate power/torque response whenever it’s needed by the VESC.

I wonder if I’'d have more power or torque if I increase the motor max to 120A even though I’m limiting the battery draw to 40A per VESC

Exactly. I don’t know. The Caps may be transferring some of that peak power as well. But I dunno how much

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doesn’t the speed controller for a brush less motor “pulse” the power to the motor? certain poles at certain times, at a particular frequency?

I might be wrong I’m not a EE

edit:

Jenso has his set up 130/100/175 here

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It’s very simple

Battery max of 50amps on a 50v system is 2500 watts

That means at 100% duty cycle you can have a max of 50 battery amps.

50v * 50a = 2500w

This means that above 50% duty cycle you can no longer create 100 motor amps

2500w/100a = 25v

50v * 50% duty cycle = 25v

50v * 75% duty * 100a = 3750w. But battery max is 2500w(50a on 50v) Meaning motor max will really be

50v* 75% duty = 37.5v 2500w/37.5v = 66.6a or 2500w on 37.5v…

All of this also means that below 50% duty if the fets could do it you could theoretically set upto 250 motor amps what the fets are spec’d for… But as duty cycle increases motor amp output will drop to meet the battery max requirements

2500w / 250a = 10v. Or 20% duty. Above 20% duty 250a would not be capable. Motor amps fall as duty increases to not exceed battery max

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if within the limits of the controller… what happens in reverse? (If battery is set higher than motor, but AC is higher than both)

If battery is set higher then motor…

The motor just isn’t provided more amps then max motor . There are some instances where AC is hit because of a improper motor config which causes the magnetic flux to stall and the AC is hit… But that shouldn’t happen with a good motor that’s been detected properly

Also… Another example from a PM

It will shift downward with each % of duty

30a bat max

36v * 30a = 1080w

36v * 25% duty = 9v * 60 motor amp = 540w 36v * 50% duty = 18v * 60 motor amp = 1080w 36v * 51% duty = 18.36v 1080w max/ 18.36v = 58.82 motor amps 36v * 52% duty = 18.72v 1080w max/ 18.72v = 57.56motor amps

Etc etc…

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One more example because I see this alot…

Battery and motor amps set to be the same

36v system 30 battery max… 30a motor max

As nominal is 36v but charged is 42v and discharged is in the range of 30-33.5 depending how safely you treat your li-ions.

42v * 30a = 1260w 40v * 30a = 1200w 38v * 30a = 1140w 36v * 30a = 1080w 34v * 30a = 1020w

Basically this configuration makes it feel like your board is slowly dying…vs feeling like the same!e performance across the charge as the maximum wattage slowly decreases…

With a motor amp lower then battery it will feel the same across the charge, top speed and acceleration

With a motor amp higher then battery it will accelerate the same across the pack with a lower top speed as the pack voltage drop

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@Deckoz so with 49.8v full charge (4.15v * 12) and a 44.4v soft cutoff (3.7v * 12) running 80 battery amps and 72 motor amps…

49.8v * 72a = 3,585.6w & 44.4v * 80a = 3,552w

I would have a linear power delivery and top speed across my usable battery voltage as set above (4.15v to 3.7v a cell).

Did I get that right or did I miss something?

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For the most part yes…

Battery can output 49.8v * 80a = 3984W Motor can receive 49.8v * 72a = 3585W

At 44.4v Battery can output 44.4v * 80A = 3552W Motor can only receive 44.4v * 72A = 3196W

This is probably about as close as you can get to linear without specifying watts in a firmware like ackmaniacs. Ie set a 80a batt max and 80 motor max with a 3552w limit to limit output only the max power that I can output at cuttoff voltage across the entire pack.

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Well now I understand a little bit more thanks @deckoz

I always thought the VESC adjusted the motor amps, now I know it adjusts voltage output through duty cycle. So the higher the DC the higher the voltage and more power is generated according to the preset motor current limit.

That means increasing the motor amps won’t help with more power output. However I’d like to kmow why my board feels say more powerful on full charge on 100A motor than at 80A

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Placebo effect.

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Maybe we should split this topic? some of this may be useful to someone else one day

kind of de-railed this build thread

@Namasaki

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Agreed sorry for clutter

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Agreed, very good info in this discussion. Don’t know if you guys knew it but @Hummie was one of the first if not the first to push the limits of motor amps when Vesc 4 was still relatively new. He convinced me to try it and I found a substantial increase in power just going from 60a to 80a.

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an esc works by a similar principle to a dc to dc buck converter in continuous mode which can also lower the effective voltage while increasing the amps. the battery is periodically connected and then disconnected from the winding at a frequency on the order of 25khz. During the times the winding is disconnected from the battery, the winding is shorted to itself which allows the current generated during the brief on times to continue circulating during the off times. since the current continues to flow in the winding during the off times, the “motor amps” are numerically higher than the “battery amps.” the battery may see 10a @ 50v, 10% of the time which averages to 1a, while the motor effectively sees 10a @ 5v the entire time. In reality the current rises in the motor from, say, 9.5a to 10.5a during the 10% on times, then decays from 10.5a to 9.5a during the off times.

as the back emf voltage produced by the motor increases with increasing speed, it is necessary to increase the on time (duty cycle) of the circuit to maintain the same number of motor amps, which draws more and more battery amps.

Pack V * duty cycle % = V effective

(V effective - V bemf)/Resistance=Motor Current

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