In February, we purchased a new centrifuge from SubZero for a decent price. The centrifuge was delivered and installed without issue. We ran it from February 15th without issues. On April 30th, late in the day, the centrifuge refused to spin up to speed in Low, Meduim or High settings.
Normally on:
Low the 'fuge would spin up to 30Hz
Med the 'fuge would spin up to 45Hz
High the 'fuge would spin up to 60Hz
The machine now spins up to between 10-15Hz, will stay running for 7-8 minutes then throw an over current alarm (OC1) or pulse by pulse current limit fault (CBC).
We have tried the following to resolve this issue:
Adjusted various VFD settings per the manual
Tried the âauto tuneâ function (with load)
Tried the âauto tuneâ function (without load/removed the belts)
Checked the bearings and basket balance
Checked for loose wires and/or bad ground wire.
At this point we are pretty stuck. Weâve called in a âVFD guyâ who wasnât a whole lot of help. He spent 5-6 hours on this issue without success. Weâve contacted Effison out of China for instruction not much help there, but hey at least my âWeChatâ app is active now
Weâve also been in contact with Sub Zero who is trying to help us out with the manufacturerâs 1 year warranty. We havenât had much help from them either so far.
Pretty much all weâve seen out of China instruction wise is to:
Run the motor without load
Try the auto tune function
Check the bearings
Effison gave us a list of their default values to program into the VFD
Does the unit have zerks or ports for greasing the spindle bearings? If so, have you greased and what grease did you use? What temps are you running this at?
Do you have access to another VFD so you could validate amperage readings while running?
Iâm not sure about zerks or grease ports as I havenât removed the basket or spindle. Itâs only a couple months old at this point and doesnât seem to need grease attention. It spins smooth without noise or vibration. We run warm extraction (room temp) so we should be good there.
I currently have the V belts off of the motor for testing. This eliminates the mechanical issues. Iâm having the same issue with or without a load on the motor.
I donât have access to another VFD right now. The VFD is reading 14+ amps while running.
Just a few minutes ago I disconnected the motor from the VFD to see if the VFD gave an error. It didnât and just acted like normal, without giving motor values of course. This was on the advice from another VFD guy. Without an error, he claims its not the VFD thatâs broken.
Your motor could be failing internally. Iâd see if you can find someone who is handy with a multimeter to check the resistance phase to phase on the motor (with VFD disconnected), and each phase to ground or to motor casing. Your phase to phase values should all be pretty close together and you shouldnât have any resistance to ground.
Alternatively if you can pull the motor and take it to an electric motor shop they should be able to test these for you pretty easily and let you know if they spot a problem.
Itâs reading 14+ amps with the belts off? If so, it is most likely a motor problem. The overload setting in the drive should be set at a minimum 115% (depending on the motor) of the motor nameplate full-load current rating. I couldnât read the nameplate but a typical 10 hp motor would be set at right around 14 amps at high volt, so those errors add up. If you have a local motor shop, pull it and have them test it. If not get an electrician out with a megger to check the windings. Also check voltage imbalance, you should be within 3% while running.
Thank you all for your thoughts and suggestions. I took the motor to have it tested this morning and they diagnosed it as âburnt upâ. Knowing this should help out our warranty claim with the seller/manufacturer.
Make sure you size the replacement motor to the VFD or size vfd for new motor at typically 1.5x size of motor hp. If your motor wasnât connected to the correct size vfd this can also cause premature motor failure.
but youâll need a bigger VFD too)