Can i calculate the battery side current?

[__Tango]

Hey folks

So, with my arduino and canbus setup, I can talk to my Kelly KBL brushless controller via CAN. from this, I can get the battery side voltage, motor side current, and motor side voltage (the motor side values come as triplets -- one for each of the 3 phase wires).

Is it possible to calculate the battery side current given this info?

I want to be able to calculate things like watt-hours and watt-hour/mile, but I feel like that info is better done from the battery side. I could always get a current sensor, but was wondering if I could do it without an external sensor.

Thanks!

[Nuts & Volts]

Battery Current should be...

bat_I = (motor_V * motor_I / bat_V )*Cntlr_eff

I would say controller efficiency should be around 96-98% in general.

[lugnut]

Battery Current should be...

bat_I = (motor_V * motor_I / bat_V )*Cntlr_eff

I would say controller efficiency should be around 96-98% in general.

I don't think this equation applies to three phase AC controllers. You have a factor something to do with the square root of 3 and also maybe the power factor (applies to sine wave but I don't know about other types like BLDC). The straight forward method would be to use a current shunt or hall sensor in the battery line.

[__Tango]

I don't think this equation applies to three phase AC controllers. You have a factor something to do with the square root of 3 and also maybe the power factor (applies to sine wave but I don't know about other types like BLDC).

Yeah, this is what i was thinking about. I think i remember something about how AC or BLDC controllers send about 0.7 of the voltage down the phase wires. I'm really reaching here, so i don't know.

Anyone else know?

Thanks.

[markcycle]

It's very difficult to calculate the RMS of a non sinusoidal or other well known AC waveform (such as square or triangle). The AC peaks can be as high as 5 times the DC current. On the controller I'm working on the AC peak is as much as 2.5 times or more the DC current. The average power is always a little less than the DC power or equal to when including the controller losses

[frodus]

doesn't the kelly have battery current on the canbus? If not, seems a bit of a letdown.

[DaveAK]

doesn't the kelly have battery current on the canbus? If not, seems a bit of a letdown.

My Sevcon only gives motor side current. It does spit out battery voltage, but not current. I'm going to have to do that separately as well.

[frodus]

Measure it with Noah's circuit and show on the tach.....

[DaveAK]

I have a hall effect sensor I'm going to use when I get around to hooking it all up. Then I'll be able to feed it in to a microcontroller along with the CAN stuff from the Sevcon and have it all synced up and dataloggable. I could throw in a cellular module and be able to give you a real time feed.

[GUFF]

I have a hall effect sensor I'm going to use when I get around to hooking it all up. Then I'll be able to feed it in to a microcontroller along with the CAN stuff from the Sevcon and have it all synced up and dataloggable. I'll could throw in a cellular module and be able to give you a real time feed.

Haha! Now that would bad ass!

Facebook Status: 120MPH.....

I also vote measuring with the hall effect sensor. If you go that route I would be very interested to see what you come up with similar to Dave is describing above.

This thread has me rethinking if my Curtis spyglass is showing me motor amps or battery amps. Since the spyglass and the programmer share the same connection point I would wager that if I cannot see battery amps in the software program then no, its motor amps. I did not see a battery amps value in the monitoring function listed in the manual (Frodus, correct me if I am wrong).