14S VESC ?

General topics and discussions about the VESC and its development.
joe90
Posts: 49
Joined: 15 Dec 2015, 16:52

Re: 14S VESC ?

Postby joe90 » 14 Jun 2016, 17:11

No problems with magic smoke, I am just hitting programmed limits

My absolute max current is 150A
Max phase current is 90A

Max measurable current is 160A with 0.001ohms shunts. it's the max current the DRV is able to read.
So to have protection you need to be under that.

I was not willing to go higher than 150A because before the esc enter protection it need a little time and sometime it shut dowm and the reading is 153A
but those are spikes while my phase current is set to 100A

You have to play with phase current to keep absolute max current under 150A
everything is fine for me like this.
Last edited by joe90 on 15 Jun 2016, 13:03, edited 2 times in total.
Michel Cote
Twin v4.7 + SK3 6374 149KV
Bicycle
2500W peak/unit on 12S

Hummie
Posts: 105
Joined: 10 May 2016, 04:05

Re: 14S VESC ?

Postby Hummie » 15 Jun 2016, 00:56

The battery current won't go higher than the phase current though right?

Hummie
Posts: 105
Joined: 10 May 2016, 04:05

Re: 14S VESC ?

Postby Hummie » 19 Jun 2016, 04:42

Will the current be pushed through faster with higher voltage and allow for quicker amps and better acceleration

rew
Posts: 905
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: 14S VESC ?

Postby rew » 21 Jun 2016, 08:34

Right. The battery current will be at most the phase current (plus what the control electronics uses).

No, a "slow acceleration" due to low voltage would only happen if the inductance is really, really high. In practice it is at least orders of magnitude lower than what would be necessary to cause a noticeable effect on acceleration. (and a BLDC motor wouldn't even be able to function with that kind of inductance).

Hummie
Posts: 105
Joined: 10 May 2016, 04:05

Re: 14S VESC ?

Postby Hummie » 06 Aug 2016, 19:24

rew wrote:In the VESC you can configure motor-max-current and battery-max-current separately. Configure them to whatever your motor and battery allow.

With modern motors you are not limited in amps by the battery voltage. My testing-motor does 50A, 50V or 2500W. Nice! It has 14mOhm resistance. So of 24, 36, 48 or whatever volts, about 0.7V is taken for "causing the amps", the rest is used for "speed".

Efficiency of the VESC is IMHO very good, I have not noticed a difference in running my motor from a "much too high" battery voltage. (on the other hand, I don't have a real VESC).


I've come to realize the no-load speed is constantly varying with duty cycle so staying close to the no-load speed is soley decided by if the motor is big enough for the load. Knowing that and that the esc is effectively converting the "unused" voltage at lower duty cycles to amps...are you saying u could run a 2000kv skate motor at 12s and it would be just as efficient system as if a typical 200kv motor were used? (Keeping under the max erpm) Why or why not? Thank you!!

rew
Posts: 905
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: 14S VESC ?

Postby rew » 07 Aug 2016, 08:26

Generally speaking I'm willing to help. But when it becomes really difficult to decode your question, the chances of me providing a wrong answer becomes too high.


I've come to realize the no-load speed is constantly varying with duty cycle s
The no load speed is determined by the effective voltage. The effective voltage is battery voltage times duty cycle.

Knowing that and that the esc is effectively converting the "unused" voltage at lower duty cycles to amps...are you saying u could run a 2000kv skate motor at 12s and it would be just as efficient system as if a typical 200kv motor were used? (Keeping under the max erpm) Why or why not? Thank you!!
Let's round 12S to "50V". So your 2000 Kv motor will be able to run 100k RPM at 50V. The 200kV motor will only run 10k RPM. Suppose both are sized to be able to provide 2kW of output power. Then both motors will draw 40A at 50V. So far so good.

But now you mount the 2000kV motor where the 200kV motor used to be. Now you want to drive at say 25km/h at 8000 RPM of the motor. For the 200kV motor the effective voltage needs to be around 40V. So 40A * 40V = 1.6kW of power is available. On the other hand, the 2000kV motor in that place will need an effective voltage of only 4V. So it's maximum power at that speed is only 160W! Of course you could try to put 400A through that motor, but both the motor and the VESC will not like you for trying that.

The situation I was talking about is:
Suppose you reach your maximum speed at say 4000RPM. Say you're only allowed to go 25km/h and the gearing is different from the example above. Now that 200kV motor will need only 20V. What I tried to say is that in this case, it doesn't matter much if you have a 24V, 36V, or 50V battery.

Long story short, you usually want the lowest Kv motor you can find, unless at the highest expected RPM, your voltage becomes too high for your ESC.

Hummie
Posts: 105
Joined: 10 May 2016, 04:05

Re: 14S VESC ?

Postby Hummie » 09 Mar 2017, 06:58

Been running at 45 battery amps and 200 motor amps happily. Is there a risk doing this? I'd heard there was some loss of over current protection or something. Running a single hub motor with 12s foc.
My other confusing question before..is it less efficient to run with a high voltage battery that gives a top speed way beyond what I'd ride, compared to riding with a lower voltage?

Have to say on 200motor amps I have much less cogging and can take off from practically a standstill and much greater torque an acceleration from a standstill. It's much better!

rew
Posts: 905
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: 14S VESC ?

Postby rew » 09 Mar 2017, 08:44

The VESC cannot measure a current of 200A. This would make it hard for the VESC to run a motor at 200A.

At the current sense resistor: 200A * 1mOhm = 200mV.
At the DRV current sense amplifier: 200mV * 10 = 2V.

Offset that to 1.65V: 1.65+2V = 3.65V which is more than 3.3V so cannot be measured.
And with the current going the other way: 1.65 - 2V = -0.35V which is less than 0V so cannot be measured.

artteth
Posts: 28
Joined: 22 Jul 2016, 00:28
Location: Belarus

Re: 14S VESC ?

Postby artteth » 09 Mar 2017, 10:26

but if use 0.5miliohm shunt?

Hummie
Posts: 105
Joined: 10 May 2016, 04:05

Re: 14S VESC ?

Postby Hummie » 10 Mar 2017, 08:11

I'll bring it down to 165 which is seemingly the limit then I guess but if it truly can't measure the current why haven't I blown up? maybe the 200 amp currrent is smoothed out to a lower current by the time it makes it to the sensors? the 200 is the best performance I've had and without getting the motor amps up high such as this the power output of the vesc is decreased at lower duty cycle. With a pulley setup maybe it's not as significant.


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