Quote:
Originally Posted by thingstodo
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So I can forget about the batteries again (for a while)
and the charging problems
and the DC to AC inverter soldering
and focus on
1 - take apart a motor and see if the coils are easy to separate
2 - build my test frame again to check the stall torque of the 5 HP motor (likely one that I don't take apart)
...
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It's so easy to forget that things take time, and that any time you invest up front will reduce your time requirement later by a factor of 10 or even 100. AND IT WILL BE SAFER!
Take for example my assumption that I would walk out to my garage, wire up the Square D VFD (that I've never worked with) and get it running in a few minutes so that I could concentrate on the testing, the part I wanted to get done.
After wiring up the motor to the VFD, a variac and a transformer for a power supply (I was too chicken to plug the VFD into my welding outlet) and skimming the VFD manual - I powered things up to see what parameters I could see, record them for later research, and see if I could figure out where the minimum speed, maximum speed, full load amps, and motor rated voltage are - the things that I normally need to change when I take a new VFD out of the box at work.
The VFD had a fault, which I managed to clear by pressing the STOP button on the keypad. THE 5 HP MOTOR THEN STARTED!!! WITH NO START COMMAND!! IT RAMPED TO 90 HZ AND STAYED THERE.
The stop button on the keypad worked while pressed (the VFD ramped down) but as soon as I removed my finger, it sped back up. I tried to put the VFD into LOCAL from the keypad so that I could enter a new speed - that didn't work for me. I'm sure that I tried a few more things that I can't remember right now, but eventually (after about a minute) I had to shut the power off to the VFD to get it to stop.
If this had happened at work, I'd be spending the next several hours filling out 'Near miss' incident forms, talking to Occupational Health and Safety, the safety officer, the Mill superintendant, going for a drug test, etc. Now I'm just typing this up and kicking myself.
The good things:
- the motor was bolted down, so it did not roll off the bench and fall on me or other equipment or pull cables out of the junction box ...
- the motor did not have a belt on it
- the 3 phase wiring to the motor is good
- I put the motor back together again after checking for the multiple poles and windings, and it appears to turn just fine
- I only hurt my pride
The bad things:
- the manual that I skimmed turned out to be for a newer VFD than I have, so the control wiring that looked OK was actually an issue
- since it was the first time I'd powered up the VFD, I didn't realize that I did not have the correct passwords to get into the parameters and change anything
- the previous use for the VFD required auto-start, auto-restart, and a fixed speed of 90 Hz. The STOP button on the keypad was not disabled, but the two-wire control scheme does not latch the stop button
Things learned:
- power up a VFD with no motor connected. That one sounds a bit obvious, but I managed to get it wrong
- check that the manual matches the VFD that you have. Again, pretty obvious
After I calm down a bit, I'll go back to the garage and do this again, without skipping steps.