ABB dc drive issues.

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Sidthasloth

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Location
Texas
Occupation
Electrician
Hello all, I had something stump me last night, I had a dc motor stop working as a carry over, the other electrician told me the dc drive was bad and was giving him 140 volts dc when it was set to 90vdc so he replaced the drive, when doing so the new drive did the same to him.

I got to it and noticed when enabled the drive didn’t put any voltage out when putting meter leads on a1 and a2. But if you took the positive meter lead and put it on a1 and the negative on the cabinet ground you get -140vdc, then if you put the positive lead on a2 and then negative lead on the cabinet ground and you get -140vdc. I am assuming it is happening cause grounds are not bonded and the drive is good. We have an issue with the start signal in my opinion. If I get back to the job I will update you guys ( I got pulled away on a bigger job and had to let it carry over) . But I am curious what causes the -140vdc to show up? The drive is set to 90vdc, so I would get it if it was part of 90vdc, but it’s over 90vdc and negative. I have seen 24vdc where the ground isn’t bonded and you get 8-9vdc when the you test to cabinet ground. So I am just confused right now.

I will also be picking my technicians brain in why? But I wanted to see if anyone else had an explanation.

Thank you guys for any input, I can’t sleep right now cause I am trying to research and figure it out. Lol.
 
kwired

kwired

Electron manager
Location
NE Nebraska
A1 and A2 I am assuming are the "Armature" leads from the output and there is also F1 and F2 for "field" leads (if not a permanent magnet motor)

140 volts might be average volts of pulsing DC that has been rectified without much for smoothing capacitors, but the effective or RMS volts when utilized is closer to 90? Peak volts should be about 169 if derived from 120 RMS AC.

Do you have any load connected when taking these measurements?
 
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Sidthasloth

Member
Location
Texas
Occupation
Electrician
kwired said:
A1 and A2 I am assuming are the "Armature" leads from the output and there is also F1 and F2 for "field" leads (if not a permanent magnet motor)

140 volts might be average volts of pulsing DC that has been rectified without much for smoothing capacitors, but the effective or RMS volts when utilized is closer to 90? Peak volts should be about 169 if derived from 120 RMS AC.

Do you have any load connected when taking these measurements?
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Yes we have a motor connected I did remove the motor out of the system to see if it changed and it did not. I have always measured my dc drive voltage on the output side and never to a ground. This motor only uses a1 and a2. There is not a shunt wired in or a field wired into the drive.
 
TwoBlocked

TwoBlocked

Senior Member
Location
Bradford County, PA
Occupation
Industrial Electrician
If there is no voltage measured between A1 and A2, then the drive has no output. Doesn't matter what anything reads to ground. Have you checked the run command and speed command? Does the motor read ok, and spin by hand?
 
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Sidthasloth

Member
Location
Texas
Occupation
Electrician
Thank you for all your help!!! It turned out the speed reference wires got switch “all the sudden”. It works now and idk who’s switching signal wires but thank you for helping me get out of the tunnel lol. The other electrician figured it out. But I was so dumbfounded by the -140vdc to ground.
 
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