Combustion Engine/BLDC generator

Support for creating custom user applications on the VESC.
arvidb
Posts: 234
Joined: 26 Dec 2015, 14:38
Location: Sweden, Stockholm

Re: Combustion Engine/BLDC generator

sagaris wrote:Up to what battery voltage it is adapted? To Input Max Voltage, actual battery voltage, other?

The BEMF will be boosted up to the battery voltage. The VESC won't decrease the BEMF if it's above the battery voltage, but the battery will try to keep the BEMF at the battery voltage by absorbing whatever current is required to do so (not a good thing, probably!).

sagaris wrote:As far as I understand I have to choose BLDC's KV with maximum BEMF not exceeding battery voltage and manually control reverse current regarding battery voltage.

Yes, I think that's right.

sagaris
Posts: 6
Joined: 14 Sep 2016, 15:33
Location: Kyiv

Re: Combustion Engine/BLDC generator

arvidb wrote:Yes, I think that's right.
If talking about typical ICE driven UAV it have 3S Li-Po onboard battery, so If I need to have highest possible BEMF lower than 12.6V at maximum 7000 RPM, then I should use about 600KV motor on ICE shaft or respectively higher KV when using multiplication transmission.

The only concern I have - will my motor have enough torque at start and should I use sensored motor?

rew
Posts: 943
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: Combustion Engine/BLDC generator

The motor constant in RPM/V is inversely proportional to the torque per ampere. Both can be called "The motor constant".

The limit is "about 50A" for the VESC. So your "max 12.6V at 7000RPM" dictates a limit on your motor.

If you were to chose that 600KV motor, at 1V your motor would do 600RPM, or 10 rev/sec. or about 60 rad/sec. So the motor constant in SI units is 60rad/sec/V. This means that the torque constant is 1/60Nm/A. So with 50A you'd be able to generate almost 1Nm of torque. If that doesn't start your motor you need a lower KV motor, and a bigger voltage on your battery. Simple!

sagaris
Posts: 6
Joined: 14 Sep 2016, 15:33
Location: Kyiv

Re: Combustion Engine/BLDC generator

rew wrote:The motor constant in RPM/V is inversely proportional to the torque per ampere. Both can be called "The motor constant".

The limit is "about 50A" for the VESC. So your "max 12.6V at 7000RPM" dictates a limit on your motor.

If you were to chose that 600KV motor, at 1V your motor would do 600RPM, or 10 rev/sec. or about 60 rad/sec. So the motor constant in SI units is 60rad/sec/V. This means that the torque constant is 1/60Nm/A. So with 50A you'd be able to generate almost 1Nm of torque. If that doesn't start your motor you need a lower KV motor, and a bigger voltage on your battery. Simple!
Thanks! It's the thing I looked for. I didn't look to this scenario through the formula "Power=I*V=angular_speed*torque". But what about stall torque at start? Can I estimate it from motor specifications?

Anyway it made things much clear.

rew
Posts: 943
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: Combustion Engine/BLDC generator

In theory, stall torque at start of a BLDC motor is simply the torque constant times max amps. In practice if the load is high, sensorless startup may take some tuning. Or you can use sensors.

I don't know the starting torque of your ICE.

stigan
Posts: 3
Joined: 20 Sep 2016, 17:47
Location: Sweden, Goteborg

Re: Combustion Engine/BLDC generator

Hello,

Did anyone move further using the VESC as generator ?

I am building a wind turbine and I would use VESC (v4.12 I think)
Did anyone get to make a custom application?

Would be great with one that keeps RPM constant and voltage constant while generating current. Nice if the RPM could be varied using some input channel.

BR
Stig

rew
Posts: 943
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: Combustion Engine/BLDC generator

If you simply tell the VESC to use the ADC app, you have an analog signal for "braking force".

Or if you command the VESC to run at a certain speed, it will adjust the torque to maintain that speed. If the wind would run your rotor at 1000 RPM, and you command 700 RPM, the VESC should be able to continue to extract energy from the rotor at 700RPM. You do have to take a bit into account that when the wind drops the VESC will start to drive the rotor at 700RPM... So you'll have to maintain an eye on the situation and command a lower RPM when the energy goes positive. (because it is normally used as a motor, postive energy use is battery->motor).

Apparently ICE engines exist that require about 50Nm of starting torque.... (I learned that since my last post in this thread).