Split PPM Confusion

[GJHS]

Even if the Vesc are running independent?

[Sebike]

Someone correct me if I’m wrong, but yes, even when vescs are running independently.

Batt max is roughly how much each vesc is allowed to pull from the battery, right, and that shouldn’t exceed half of what the battery can safely deliver if you have two vescs pulling amps from your batts.

Batt min is how much you allow vesc to pump back into the batt, and cell specs stay the same even if you’d have 10000000 independent vescs , so you don’t want to charge cells with heavier current just because you happen to run dual motors.

[GJHS]

See, confusing. If I set my battery max to 25a wouldn’t it be the same as setting my Motor to 25a?

[Sebike]

Short answer is no. If battery max and motor max were the same thing, we wouldn’t have two separate settings A bit confusing yes.

[GJHS]

So if I set my Battery Max to 25a i shouldn’t see any performance difference?

[Deckoz]

30q are know to be 20a cells even though they are 15 by the manufacturer

4p * 20a = 80a / 2esc = 40a/esc bat max

Regen no more then 2c 3Ah * 4p = 12Ah * 2capacity = 24a/2esc = -12a bat min per esc

[Sebike]

You could probably set your batt max to 30 if your bms allows a 60a discharge, and you won’t kill your batteries. So with batteries that are still working, I’d say that’s a performance boost

[GJHS]

I don’t have a discharge BMS, only a 80a charge only

[Deckoz]

Regarding motor amps vs battery amps

The Derek Evo 4wd

[Sebike]

Then either go the conservative route with 30a batt max per vesc, or go crazy with the - up to- 40a /vesc… I don’t think one should exceed that though.

[GJHS]

to think I have been running 50a for weeks. Luckily short rides

[Sebike]

80a bms for charging only is unnecessary bulk. You could as well use something a lot smaller.

[Deckoz]

The gist I got from PM

It’s a 6355. Which are typically rated for 2000w.

On a dual setup of 4p 30q with a max batt amp of 40/esc or less to maintain the constant current capability of the cells

2000w \ 36v = 55 amps…

Your battery can only provide 40 amps

36v * 40a = 1440w

If you set a motor max of 60. You can achieve 60 motor amps up until 24v or 66% duty cycle. At which point every % of duty cycle increase will cause a motor amper output decrease to stay within the 40a(1440w) battery max limitation.

Basically your battery can’t overpower the motor…

[Nordle]

@faithfulpuppy

yes, you split the (usually white) wire coming out of your resistor.

It’s the white wire coming out of your “receiver”, sure there are also resistors inside that one, but 2 different storys actually

[professor_shartsis]

@GJHS here is some related information from a different discussion:

@professor_shartsis

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

@professor_shartsis

50v battery * 10% duty = 5v effective volts

(5v effective - 0v bemf) / 0.0625ohm winding = 80a motor amps

5v * 80a motor amps = 400w electrical watts

80a motor * 80a motor * 0.0625ohm = 400w copper loss

400w / 50v battery = 8a battery amps

@professor_shartsis

(1/KV)*RPM=BEMF V

(1/100kv)*100RPM=1V BEMF

@professor_shartsis

KT (torque per amp) can be calculated directly from KV:

KT (newton meters torque per motor amp) = 60/(2 * pi * kv)

0.0954nm/a = 60/(2 * pi * 100kv)

therefore 80a motor current * 0.0954nm/a = 7.632 newton meters torque @ 100kv

7.632 newton meters torque * angular speed of the motor in radians per second = mechanical watts

(1000rpm * 2 * pi)/60 = 104.719 rad/sec

7.632 newton meters torque * 104.719 radians per sec angular speed= 799.22w mechanical power

799.22w mechanical power / 1000w electrical power = 79.92% electrical to mechanical efficiency

the difference between the electrical power and mechanical power appears as ohmic heating in the motor windings.

[faithfulpuppy]

Whoops, that was a hell of a slip. Stupid fingers.

[Deckoz]

That reminds me…I once accidentally text a real estate agent I shampooed my balls instead of the carpet…

It was really awkward after that as I didn’t catch it for a day or two when I wondered why he never responded. @faithfulpuppy

[abenny]

he was obviously giving you time to clean the carpet before he came to look at the house

[mattyB]

what is PPM?

[b264]

PPM is pulse position modulation, but VESC actually uses PWM and has it mislabeled as PPM. PWM is is pulse width modulation.