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Can 10 HP Rotary phase converter power a 15 HP Compressor? Please advice

L

Leo000

Plastic
Joined
Oct 29, 2020
Hello members, I hope you can help me with the following issue:

I bought a 180 gallons air compressor with a 15 HP 3 phase motor. I want to use a 10 HP 3 phase motor as rotary phase converter which is 5 HP less than the power of the compressor motor, would it work? What do you advice to make the compressor work properly?

Thanks in advance
 
Leo000 said:
Hello members, I hope you can help me with the following issue:

I bought a 180 gallons air compressor with a 15 HP 3 phase motor. I want to use a 10 HP 3 phase motor as rotary phase converter which is 5 HP less than the power of the compressor motor, would it work? What do you advice to make the compressor work properly?

Thanks in advance
Click to expand...

No.

30 HP Idler? 20 HP Phase-Perfect? 30 HP VFD? DC motor and drive?

IC motor?

CAVEAT: Large idlers are a bitch to start in their own right, and may need more power than you can get.

15 HP compressor will almost certainly ALREADY have unloaders & such to reduce drama of starting. Compressors start a LOT, most places they are put to work.

10 HP on the pump, 15 HP idler might not even do it "well".

You had a different answer before you bought it?
 
Is it a genuine 15HP compressor? Apparently some cheap ones use marketing rubbish ('peak' HP etc.).

The smart big ones use a solenoid unloader valve and keep the motor spinning unless there's been very little draw for a long time, so they try to avoid starting more than every few hours and modulate output using the unloader. Consider running a second much smaller compressor in tandem with a higher setpoint so the large one only kicks in when you really need air.

Or throw a suitable VFD on it and maybe a pressure sensor.
 
Just a Sparky said:
Use a VFD or install a single phase motor. Trying to start an air compressor on an RPC is like trying to push a rope.
Click to expand...

LOL! Wellll I could DO a 15 HP load-motor.. with the full 28 HP worth of idlers (4) online.

But damned if I'd want to do it TWICE....let alone all day!

Too much OTHER drama... given the service upstream of it is shared with an all-electric residence.. and on the same vault-pig as several other homes!
 
"Borrowed" from another thread for illustration:

Just a Sparky said:
This comparison demonstrates the starting torque issue with rotary phase converters.

10HP air compressor powered by RPC - unloaded start
12HP air compressor powered by RPC - unloaded start

10HP air compressor powered by utility - loaded start
Click to expand...

Note that the two pumps being started on an RPC are struggling to do so in an unloaded state. Most big compressors (except Quincies) will start fully loaded just fine on utility or VFD power.
 
Years ago my 7.5 RPC was in no way able to start a 5HP three phase 2 stage compressor - until I spliced in another 3HP idler - and even then it did not sound like i was an easy go

On the other hand, the 10HP Phase Perfect (now 16 years old) thought it was no trouble at all
 
Leo000 said:
Hello members, I hope you can help me with the following issue:

I bought a 180 gallons air compressor with a 15 HP 3 phase motor. I want to use a 10 HP 3 phase motor as rotary phase converter which is 5 HP less than the power of the compressor motor, would it work? What do you advice to make the compressor work properly?

Thanks in advance
Click to expand...

If you want the RPC then use the 15 HP motor as the idler and install the 10 HP motor on the compressor. It would do fine.

or,

Install the 10 or 15 HP motor on the compressor and use a VFD with no less than 10 HP.
 
As was said.
It might be you could start it, perhaps not always depending on loads on your local power, but it is likely to be iffy.

Swapping the motors "sounds" redneck but is probably actually easy, cheap, and will work.
The compressor could not care less if You have a smaller motor - or not.
If it needs certain torque and the smaller motor does not have it, it will likely burn out in short order.


If You actually really truly need the full output of a 15 hp compressor vs 10 hp, on an ongoing basis, then you will need a 20 hp idler.
(This is unlikely, unless it is industrial type use of some kind. - You probably new this. Redundant).
You can cheaply buy a new 20 hp motor from surpluscenter or similar.
Much better than fricking around with it, if You have any real work needs - as a 10 hp would indicate.

Most times it is better to work smarter.
In this case, You probably just need a bigger hammer.

Just buy the 20 hp motor from a rebuilder or surpluscenter or whatever.
A bigger motor running cooler will always last longer and make less noise and less demands for "service daddy".
 
dalmatiangirl61 said:
I've yet to see a factory unit already set for minimum speed, so he might have a little wiggle room. I know Phase A Matic suggests idler should be twice the rated hp of a compressor motor, not sure about other mfrs, but quick math tell me he needs a 20hp idler to run a 10hp compressor.
Click to expand...

They shouldn't mind if they error on the +HP. They make more money.
 
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