Ground connections in BLH motor drives

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Ground connections in BLH motor drives

Postby cristitranca » Fri Jun 24, 2016 5:05 am

I have a question regarding one of your drives.
Since the technical specifications are just general stuff, and there is no detail about it, I would like to ask the following:

1. Is the power supply GND (black) as the same potentian as the orange signal GND? ( or are they isolated on the board)?

2. Is the VRL the same as GND or is the analog input isolated with respect to the battery ground?

3. What is the maximum common mode voltage between the VRL and battery ground?

4. is the VRL the same as the GND for signals? or is it any problem if they are connected together through the controller that controls the drive?
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Why I ask the questions:

I want to make a controller with the following features: it commands two BLH drives. The controller is powered from the battery and with non-isolated power modules I reduce the voltage to 5V(for digital signals and analog signals).

If the GND of the controller is common to the minus ( - ) ...GND of the battery, I am curious if there is any problem with the drive? (the signal GND, VRL and the battery GND will be tied together through the controller).

5. If there is a problem, then I will need to generate two 0-5V output isolated with respect to the GND of the battery. The same should be for the inputs for the drive. At leas is it ok if i have VRL the same as the signal GND, and use the same signal GND and VRL for the two drives that I command?

For example when the driver is running the motor is pulling current, so there will be a voltage drop across the minus (GND ) wire from the battery. So there will be a little difference between signal GND and battery GND.

What recommendations do you have?

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Re: Ground connections in BLH motor drives

Postby om_tech_support_JT » Tue Jun 28, 2016 11:09 am

Hi cristitranca,

The BLH driver's power supply GND, signal GND and VRL are common in the circuit. There should be no problem to connect the grounds together.

The battery ground = 24V and the VRL = 5V. Therefore, the common mode voltage is: Vcm = (V1 + V2) / 2 = (24 + 5 ) / 2 ~14.5V. Normally, we don't check common mode voltage between the two grounds, and we don't think there will be any impact from this voltage. (V1 + V2) / 2 is defined as the common mode voltage at the input of a difference amplifier.

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