roto pase conveter VS vfd
- Thread starter domnic
- Start date
- Status
- Occupation
- Licensed Electrician
VFD is a good way to convert single phase to three phase, but you have to get one that will do it. Manufacturer will help with the the type and sizing.
Oh, and not all motors like VFD's.
Last edited:
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Assuming 240V?
You will need a drive that is at least twice the size of your larger motor, so 20HP minimum and if you have less than ideal conditions, like high ambient, I'd go 25 or 30HP. Most drives are rated 40C (104F) ambient, then say 50% derate for single phase. But they rarely mention that you need to also derate the temp to 25C (77F) ambient to avoid damaging the caps (something I just learned myself). That's tough to maintain. But you can regain the ambient by using a 65% derate. So 10HP /.35 = 28HP. If the drive is rated for 50C (122F), then 25HP gets you to 40C ambient. It's a numbers game if you want to play it safe.
No such issue for an RPC, but then you pay for it in throughput efficiency; you'll lose about another 5% beyond your motor's normal efficiency, so 2-3% worse than the VFD. If running a lot, that ratchets up your energy bill at the end of the year.
However if this is a centrifugal pump and you are going to employ flow control of any sort, then the VFD blows those energy numbers out the window, because the VFD saves energy compared to any other form of flow control.
You will need a drive that is at least twice the size of your larger motor, so 20HP minimum and if you have less than ideal conditions, like high ambient, I'd go 25 or 30HP. Most drives are rated 40C (104F) ambient, then say 50% derate for single phase. But they rarely mention that you need to also derate the temp to 25C (77F) ambient to avoid damaging the caps (something I just learned myself). That's tough to maintain. But you can regain the ambient by using a 65% derate. So 10HP /.35 = 28HP. If the drive is rated for 50C (122F), then 25HP gets you to 40C ambient. It's a numbers game if you want to play it safe.
No such issue for an RPC, but then you pay for it in throughput efficiency; you'll lose about another 5% beyond your motor's normal efficiency, so 2-3% worse than the VFD. If running a lot, that ratchets up your energy bill at the end of the year.
However if this is a centrifugal pump and you are going to employ flow control of any sort, then the VFD blows those energy numbers out the window, because the VFD saves energy compared to any other form of flow control.
Last edited:
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
you least expensive option may well be to just replace the motors.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
If standard NEMA motors then yes this would generally be the best way to go
- Status