Let me start by saying that I haven't had a whole lot of experience with vfd's so bear with me. I have a motor starter that I need to switch to a vfd. The starter has a 120 v coil. My question is since the start input on the vfd is 24v and the existing coil power in 120v, is there anyway the vfd will allow me to do this without using a relay? There is no start or stop button. Motor is controlled by a pressure switch and I can't run the 24v thru the pressure switch either.
Vfd question
- Thread starter fireryan
- Start date
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- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Some VFDs have option boards for 120V control interface, mostly those are the higher end industrial drives, not the inexpensive Asian drives. If you have already bought one and it does not have plug-in boards, just a control terminal strip, then you will have to use a relay. Shouldn't be too hard though, just wire the pressure switch to the coil of the relay, then wire the relay contact to the VFD input.
But why a VFD if all you have is a pressure switch? A VFD's value is in changing the speed, a pressure switch is just on-off control. Are you using it to get 3 phase for the compressor at a site with only single phase power?
It is a ABB powerflex drive. The motor is for a high pressure water pump. The engineer wants to slow down the motor a little. Gonna set at 50hz. Also gonna ramp up motor slowly
Rampage_Rick
Senior Member
- Location
- British Columbia, Canada
The A-B 1336S drives have 120V input boards.
Some Powerflex drives, like the 755, support both 24V and 120V on one of the digital inputs.
Some Powerflex drives, like the 755, support both 24V and 120V on one of the digital inputs.
Cow
Senior Member
- Location
- Eastern Oregon
- Occupation
- Electrician
I can't say I've ever needed to use a pressure switch with a drive. I've always use a pressure transducer and PID loop to maintain a constant pressure with a drive. If the pump doesn't need to run all the time, say if demand drops off, then I program in a sleep mode.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
PowerFlex is Allen Bradley (AB), an American company.
ABB is an entirely different Swiss company, short for Asea Brown-Boveri.
A VFD was a waste on this, could have attained the same effect by changing a sheave and using a soft starter. But oh well, you have it now...
You can only get a 115V interface board for PF 70, 700, 750 drives.
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