Vfd recommendation for air compressor

[micromind]

waiting on a reply on this any reason this wouldn't work

That's a direct replacement for the motor shown in post #47.

The starter pictured is too small for a 5HP single phase motor plus the coil is for 208 volts, not 230-240.

For short-term operation, like an air compressor, there's a good chance it'll hold up but not for very many years.

 

[Cruzan80]

The starter pictured is too small for a 5HP single phase motor plus the coil is for 208 volts, not 230-240.

For short-term operation, like an air compressor, there's a good chance it'll hold up but not for very many years.

I believe you are saying "it" meaning the starter and not the motor, correct?

I don't see any reason the motor would not hold up for a long time.

 

[wyliesdiesels]

I saw somewhere where someone used one VFD to run several machines. It was not setup to run all at once but they had a system of disconnects so one machine couldn't be used while another one was in use. I need to look at my VFD's instruction manual again as I think it stated in it you could do the power switching either way if you programmed it a certain way.

unless all the motors had the same parameters, it wouldnt work without changing the settings on the VFD each time. you would also have a mess of wiring connecting the controls from each machine to the VFD.

it's really a waste of time and pointless

 

[micromind]

I believe you are saying "it" meaning the starter and not the motor, correct?

I don't see any reason the motor would not hold up for a long time.

That motor will hold up for many, many years. The starter, not as long.

A NEMA size 2 starter will last a very long time. The existing one is a size 1, designed for max 3HP at 240 volts single phase.

 

[arangov3]

Post 16 had this option.

Possibly 3600rpm is better....depends on pump sheave, pump max speed and guarding size.

shouldn't i replace with similar stats, I'll have to measure pulley sizes but I believe the pump is rated for 700 rpm. Form googling I believe the pump is a sc23

 

[arangov3]

That's a direct replacement for the motor shown in post #47.

The starter pictured is too small for a 5HP single phase motor plus the coil is for 208 volts, not 230-240.

For short-term operation, like an air compressor, there's a good chance it'll hold up but not for very many years.

I'm sure I've made it painfully clear how ignorant I am but the starter pictured says 7.5 hp or is there something I missed on the baldor

 

[arangov3]

That motor will hold up for many, many years. The starter, not as long.

A NEMA size 2 starter will last a very long time. The existing one is a size 1, designed for max 3HP at 240 volts single phase.

Where is the sizing you see?

 

[Cruzan80]

I'm sure I've made it painfully clear how ignorant I am but the starter pictured says 7.5 hp or is there something I missed on the baldor

The 7.5HP listed on the starter is for 3ph 240v, not 1ph. The top center of the starter (under L2) is where it says NEMA Size 1. Starter sizes are standardized, which is how @micromind knows it will only support 3HP for 1ph (the starter you showed does not show the 1ph values on the sticker).

 

[mm08822]

shouldn't i replace with similar stats, I'll have to measure pulley sizes but I believe the pump is rated for 700 rpm. Form googling I believe the pump is a sc23

That's why I stated possibly. Run the numbers for both motor speeds against the existing pump pulley size and max permitted pump rpm.

 

[arangov3]

The 7.5HP listed on the starter is for 3ph 240v, not 1ph. The top center of the starter (under L2) is where it says NEMA Size 1. Starter sizes are standardized, which is how @micromind knows it will only support 3HP for 1ph (the starter you showed does not show the 1ph values on the sticker).

Tyvm I was assuming phase wouldn't impact capacity

 

[MKSJ]

You want to replace the motor with the same type "1750 RPM, 4 pole," a 3600 RPM wouldn't make any sense and will be noisier. The motor starter contactor should have a current rating indicated on the model information, given that the overload relay range is listed as 9-27A, the contactor must be rated for at least 30A which may be adequate but would look up the model number specifications. Technically you need to wire the contactor/overload relay for single phase with a 3 pole magnetic starter (look this up on any motor starter, it is basically the addition of a jumper wire. I would use it until it fails, replacement starts are not that expensive.

 

[Cruzan80]

Tyvm I was assuming phase wouldn't impact capacity

The reason would be that there are three wires in a 3ph carrying the current, vs 2 in the 1ph, making each "channel" have to carry a higher portion of the load.

IIRC, the conversion factor is ~ 1.7 (✓2 or sqrt2). If I am wrong, someone will be along to correct me.

 

[Firebrick43]

I saw somewhere where someone used one VFD to run several machines. It was not setup to run all at once but they had a system of disconnects so one machine couldn't be used while another one was in use. I need to look at my VFD's instruction manual again as I think it stated in it you could do the power switching either way if you programmed it a certain way.

I have done this to power my 3 phase powermatic jointer and powermatic belt sander. I use a harting plug. On the machine side there is a loop from one pin to the next that is hooked up to the Estop circuit of the VFD. So if the plug is unhooked the drive is automatically thrown into Estop. These are dumb machines (did program soft start/controlled deacceleration) but both machines use the exact same size/speed/even brand motors.

 

[Cruzan80]

I'm sure I've made it painfully clear how ignorant I am

Forgot to add this before...

Everyone starts out at the same level of "I don't know anything about X", but the people who are willing to ask questions and learn get better. When you ask questions that seem "stupid and obvious", and listen to the answers given, that is how you get better. Once you know some, help the new guys and "punt" the harder questions to the actual sparkies (this is where I am). If you hang around, you will see those of us at this level occasionally chiming in with a clarifying question about specifics in threads to the sparkies.


The ones who know a little bit but think they know a lot are the most dangerous, especially when they try and "throw their weight around".

 

[dave*99]

IIRC, the conversion factor is ~ 1.7 (✓2 or sqrt2). If I am wrong, someone will be along to correct me.

Since you asked…. Sqrt 2 is 1.414.
Sqrt 3 is 1.7.

 

[Cruzan80]

Since you asked…. Sqrt 2 is 1.414.
Sqrt 3 is 1.7.

Thanks. Do you remember which one is for 1ph to 3ph? Guessing sqrt 3 and I just flubbed the number...

 

[dave*99]

Thanks. Do you remember which one is for 1ph to 3ph? Guessing sqrt 3 and I just flubbed the number...

Yes sqrt 3

 

[mm08822]

You want to replace the motor with the same type "1750 RPM, 4 pole," a 3600 RPM wouldn't make any sense and will be noisier. The motor starter contactor should have a current rating indicated on the model information, given that the overload relay range is listed as 9-27A, the contactor must be rated for at least 30A which may be adequate but would look up the model number specifications. Technically you need to wire the contactor/overload relay for single phase with a 3 pole magnetic starter (look this up on any motor starter, it is basically the addition of a jumper wire. I would use it until it fails, replacement starts are not that expensive.

Except a NEMA size 1 starter is only good for 3hp @240v single phase.

Expect failure of the contacts or even welded contacts if that comp is running close to 5hp at shutoff pressure.

 

[Bert_]

Honestly a size 1 starter would probably run a 5hp 1ph motor for years without failure. It's not right but they are heavy built for their rating

 

[arangov3]

Baldor guy is near impossible for me to schedule pickup(3 kids and work) I'm going the vfd route I'm shy to buy second hand because it's an electronic but I'm going to roll the dice on something off Amazon. I'm going to try to buy the breaker conduit and wire tomorrow so I can order the vfd.

I just don't no where the vfd falls in the circuit, I'm assuming between the starter and motor I guess I have to read the manual.

Dragging my feet to put things back together since I have to he-man the pump back onto the compressor had to take it apart to get it out the bed solo and learning the pump is over 230lbs has made me less capable(should have stayed ignorant)

 

[mm08822]

You won't need the starter if using a vfd.

Read the manual before you buy it.

 

[arangov3]

You won't need the starter if using a vfd.

Read the manual before you buy it.

just finished
Single Phase 220V panel
↓
Disconnect/breaker (30A 2-pole)
↓
VFD
(L1, L2 in)
↓
(T1, T2, T3 out)
↓
Motor terminals

Pressure Switch
↓
VFD Control
Terminal
↓
VFD

 

[wyliesdiesels]

The motor starter contactor should have a current rating indicated on the model information, given that the overload relay range is listed as 9-27A, the contactor must be rated for at least 30A which may be adequate but would look up the model number specifications.

Contactors for motors are rated in HP not amperage

 

[arangov3]

Contactors for motors are rated in HP not amperage

Isn't that just semantics, shouldn't they be ultimately be rated by amps?

 

[dave*99]

Isn't that just semantics, shouldn't they be ultimately be rated by amps?

Nope. Motors are inductive. High inrush current. The contacts also need to handle back EMF etc. That leads to arcing and contact erosion.

Amp ratings are not appropriate for motor switching.

Switch ratings in amps work well for resistive loads.