Bauer K17 min speed?

[BRT]

@BRT when I spec drives at the plant I oversize them as well, but you are limited when using it as a phase converter because they are severely downrated by the manufacturer for heat. You have to go up to a 60hp drive to get 15hp single phase. The one I linked is a 25hp drive and even the 50hp drive in that series is only rated for 10hp1p. The 60hp is way overkill IMO for that, certainly at 3x the cost.
He's trying to run 10hp, so running 2/3 the RPM will give him that with the same pulleys. It's not really ideal, but it is what it is when using the VFD's.

I'm sure there are some other 15hp1p vfd's out there if you go digging, that's just a decent series to find. General rule of thumb if using a generic VFD for single phase is to double the hp rating. Technically only have to go 1.73 (sqrt3) which in this case is 25hp, and you'll be fine since the amp draw is the same. I don't know why those are derated as far as they are. If concerned, just go to double the HP rating and you'll be fine.

Problem with a normal phase converter is you still need to add the soft starts in there and the costs get crazy.

You are correct. I didn't look carefully at what you were proposing. I do believe the 15hp motor will still draw more amperage than a 10 hp under the same load but that may work ok. I have bought a lot of stuff from Automation direct but never their drives. Have they been reliable?

Normally any VFD can run single phase at 66% of capacity. The limitation is the rectifier setup having to provide power through only 2 legs. Which makes me curious why that 25hp drive is rated 10hp 1 phase instead of 15hp???

 

[broncobowsher]

We looked at VFD. Very much like the one you posted at $1400+.
But I can find a 10HP singe phase motor for much less. Leeson Compressor-Duty Electric Motor — 10 HP, 1,740 RPM, 230 Volts, Single Phase, Model# 140311 | Northern Tool + Equipment
Get the pulley size right and things get a lot easier.

Something like that was my plan.

I was looking at the compressor today but forgot to bring the tape measure to measure the pulley sizes to get the existing ratio (and figure what the existing compressor RPM is).

 

[BRT]

We looked at VFD. Very much like the one you posted at $1400+.
But I can find a 10HP singe phase motor for much less. Leeson Compressor-Duty Electric Motor — 10 HP, 1,740 RPM, 230 Volts, Single Phase, Model# 140311 | Northern Tool + Equipment
Get the pulley size right and things get a lot easier.

Something like that was my plan.

I was looking at the compressor today but forgot to bring the tape measure to measure the pulley sizes to get the existing ratio (and figure what the existing compressor RPM is).

That VFD price is a great deal. A big advantage is that with the VFD you can "soft start" the motor which will really take starting loads down which will help with breaker size and "brown out". Another advantage is it will allow you to adjust the motor speed to fine tune your load. Like being able to adjust pulley sizes on the fly.

 

[tbone1004]

@broncobowsher what I said earlier and what @BRT said above. You still need a soft starter which is a few hundred bucks on top of it.

More importantly, since you haven't posted the actual breaker size for that circuit, you may not be able to draw a full 10hp off of it.... You can find VFD's for less money than what I posted, that was just an example of one that was factory derated for single phase.

The ones we have have proven reliable from that supplier, but we don't use them on any heavy machinery. Only on lathes, drill presses, etc. The rest of our stuff is on full PLC systems as the machines typically have 5+ drives in them

 

[broncobowsher]

Sorry, I forgot to open the panel and look at the breaker when I was at the shop yesterday.

I know the existing compressor is a 10HP as well. And very old. There was talk of removing the motor from the old compressor and putting it on the new, but it was decided that the old compressor (which still works) would be worth more in working condition. And the frame is probably different (old Mako).

 

[tbone1004]

Sorry, I forgot to open the panel and look at the breaker when I was at the shop yesterday.

I know the existing compressor is a 10HP as well. And very old. There was talk of removing the motor from the old compressor and putting it on the new, but it was decided that the old compressor (which still works) would be worth more in working condition. And the frame is probably different (old Mako).

check the panel service, but if there are electrical concerns, there is a lot of benefit with the VFD vs. buying a new motor since you can always turn it down if you're concerned. Can't do that with a straight running motor. You can go in and program them with a current limit on input and/or output which is what you really want. The motor couldn't care less if it is running at slightly lower speeds.

So the important formula for this. HP=Torque*rpm/5252 This is why torque will always equal HP at 5252 RPM and why torque literally can't be higher than HP above 5252 rpm. Your torque requirement is going to be fixed as a function of pressure in the pump and doesn't really matter. You have a 15hp motor at 3490rpm motor and to run it at the equivalent of 10hp, you literally just slow it by 10/15 to ~2300rpm. Whatever the pump speed comes out to is obviously directly proportional to that.
I did some quick checking, and for $800-$1000 you can get a 30hp VFD which will be cheaper than the new motor + soft starter.

 

[Coztick]

Torque=HP*rpm/5252 This is why torque will always equal HP at 5252 RPM and why torque literally can't be higher than HP above 5252 rpm.

HP= torque*rpm/ 5252 is what he meant to say I'm sure.

 

[tbone1004]

HP= torque*rpm/ 5252 is what he meant to say I'm sure.

correct, sorry