Hooking up New Compressor rewire Q's

[gtiboy66]

So I picked up a new compressor today.
an Emglo

its 460v but can be wired for 208/240

I wanted to have the motors rewired for 208/240v is that something a motor shop should do or could I do it?

Also I was planning on running 2 VFD's to control the motors.
What is a good way to hook them up?

Its dual 3hp 3 phase motors hooked up to pressure switches

I am not too familiar with wiring motors/equipment

 

[Charles (in GA)]

The motors cannot be converted to single phase, you will have to buy two new single phase motors.

Charles

 

[nadogail]

You have three phase motors, they can not be converted to single phase.

IMHO, You have several options: 1 Bring in three phase power. 2 replace the motors with single phase motors. 3. Install a phase converter. 4. Replace this compressor with a unit more suited to your garage.

 

[prosnowsk8er]

You have three phase motors, they can not be converted to single phase.

IMHO, You have several options: 1 Bring in three phase power. 2 replace the motors with single phase motors. 3. Install a phase converter. 4. Replace this compressor with a unit more suited to your garage.

Exactly this ^^^^^^

 

[Pwrgeek]

VFD would work but you will need two. Converting the motor over to run on 208-230 just involves making some taps in the motor junction box (located on the motor usually right where the wiring enters the housing). You can see in the lower left of the nameplate how to do it but to summarize.

1. remove jumper from T4 - T7
2. remove jumper from T5 - T8
3. remove jumper from T6 - T9
4. install jumper from T7 - T1
5. install jumper from T8 - T2
6. install jumper from T9 - T3
7. install jumper from T4 - T5 - T6

Supply lines from the VFD go on T1 T2 and T3 along with the jumpers added above.

I would rewire the pressure switch to trigger the VFD as opposed to putting the supply lines through it if it were me.

Given that they are only 3hp you'd probably save money just replacing the motors with a couple of quality Baldor single phase units over buying VFDs.

 

[md21722]

Well, I believe he is trying do number 3.

Most VFD's are used for smaller motors, though, like 1/2-1 HP on lathes and mills.

Inside the small square box below the magnetic starter is where you'd wire the motor for 208/240 instead of 460. There should be a wiring diagram in the cover that shows the wiring pattern.

I am not sure of the practicality of trying to run a 3HP VFD. Single phase 3HP motors could be used instead, and at that size magnetic starters aren't typically needed. But that is a 182T motor, which at 3HP typically is only available as a 3750 RPM in single phase so new motor mounts would be needed, or motor shieves on half the size.

Either is a lot of work for about what will amount to a 21 SCFM compressor.

 

[wyliesdiesels]

Rewiring the motors to run on 240v 3 phase is the easy part. Just change the motor leads around.

As far as a single phase to 3 phase VFD, be prepared to shell out some dough!

Would be better to switch to single phase motors but then u have issues with compatability...

 

[Norcal]

Since the motors are 3 HP, that is the top end for low cost VFD's w/ single phase input, the OP may be able to get them for around $200 each. Does the box with the Furnas tag have a alternating relay in it?

 

[sberry]

You got robbed too, it's not a new compressor.

 

[md21722]

Since the motors are 3 HP, that is the top end for low cost VFD's w/ single phase input, the OP may be able to get them for around $200 each. Does the box with the Furnas tag have a alternating relay in it?

There are 2 Furnas pressure switches (black cover) and 1 white Furnas alternating relay (white cover).

 

[md21722]

Since the motors are 3 HP, that is the top end for low cost VFD's w/ single phase input, the OP may be able to get them for around $200 each. Does the box with the Furnas tag have a alternating relay in it?

$400 doesn't seem like a bad deal to make it work.

It does seem like a lot for only 6HP worth of compressor though.

 

[wyliesdiesels]

There are 2 Furnas pressure switches (black cover) and 1 white Furnas alternating relay (white cover).

Ive never worked on a compressor like this.

What is the point to the dual PS? Why not just use one?

 

[Norcal]

With two tanks I understand the need for two but a single tank have no idea, but w/ the alternating relay and two tanks never have them set the same, don't ask how I know that.

 

[md21722]

Pressure switches are lead and lag typically +5 and -5. Alternator will switch back and forth to help provide equal hours on each pump and motor. If air demand requires, both will run simultaneously. The first one to start will be the second one to start on the next cycle. Standard duplex compressor setup. Other duplex compressors might have one big control box for it all. Jenny/Emglo still does it with individual components.

 

[wyliesdiesels]

Got it. Makes sense