Deckoz
March 16, 2018, 12:47am
21
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
2 Likes
Sebike
March 16, 2018, 12:47am
22
You could probably set your batt max to 30 if your bms allows a 60a discharge, and you wonāt kill your batteries. So with batteries that are still working, Iād say thatās a performance boost
GJHS
March 16, 2018, 12:49am
23
I donāt have a discharge BMS, only a 80a charge only
Deckoz
March 16, 2018, 12:50am
24
Regarding motor amps vs battery amps
1 Like
Sebike
March 16, 2018, 12:59am
25
Then either go the conservative route with 30a batt max per vesc, or go crazy with the - up to- 40a /vescā¦ I donāt think one should exceed that though.
GJHS
March 16, 2018, 1:00am
26
to think I have been running 50a for weeks. Luckily short rides
Sebike
March 16, 2018, 1:01am
27
80a bms for charging only is unnecessary bulk. You could as well use something a lot smaller.
Deckoz
March 16, 2018, 1:23am
28
The gist I got from PM
Itās 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 ampsā¦
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 canāt overpower the motorā¦
1 Like
Nordle
March 16, 2018, 3:09pm
29
Itās the white wire coming out of your āreceiverā, sure there are also resistors inside that one, but 2 different storys actually
@GJHS here is some related information from a different discussion:
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 āmotor ampsā are numerically higher than the ābattery amps.ā 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
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
(1/KV)*RPM=BEMF V
(1/100kv)*100RPM=1V BEMF
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.
1 Like
Whoops, that was a hell of a slip. Stupid fingers.
Deckoz
March 16, 2018, 6:30pm
32
That reminds meā¦I once accidentally text a real estate agent I shampooed my balls instead of the carpetā¦
It was really awkward after that as I didnāt catch it for a day or two when I wondered why he never responded. @faithfulpuppy
2 Likes
abenny
March 17, 2018, 5:12pm
33
he was obviously giving you time to clean the carpet before he came to look at the house
1 Like
b264
March 11, 2022, 7:44pm
35
PPM is pulse position modulation, but VESC actually uses PWM and has it mislabeled as PPM. PWM is is pulse width modulation.