5hp 600v compressor on AC tech mc1551

macds · Nov 6, 2017

Im looking for recommendations to get my old quincy running on a vfd (that I already have).
The reason i want to do this is to reduce the current inrush of the compressor starting up while running my CNC equipment.
Im pretty tight as to the amperage available in the shop, so i'm figuring that a nice ramp up using the actech should keep the current slam to a minimum.

I'm thinking a 24vdc pressure switch to pull in a contactor, that will close\open the remote relay inside the vfd.

Im no circuit designer, so if anyone has any input, it would be appreciated.

Would prefer a fully adjustable, reasonably inexpensive pressure switch\contactor setup to use in a small enclosure.

Thanks!

rons · Nov 7, 2017

I'm planning on using one of these. Operates on 12-24V DC. It can be easily setup with any hysteresis I want. It has a internal transistor switch that can pass up to 60mA. I bench tested one with a cut-in/cut-off pressure range of 125/150 PSI with a 24V coil relay. It works great. The back side has a 1/8 NPT connection but you can get other connection variations.

SMC ISE3-1-65-L pressure switch, h/precis, ISE3/ISE3A PRESSURE SWITCH

This is the ISE30-T1-65-L.

Jraef · Nov 8, 2017

Reciprocal compressors are problematic for VFDs. You may not be able to achieve the starting current reduction you are looking for without having to ramp it slowly, and if it relies on splash lubrication of a crankshaft, you may end up shortening the life of the bearings.

DDoug · Nov 8, 2017

Does your Quincy have head unloaders ?

IIRC you can restrict how fast the oil come up to actuate them upon start up.

Mine take upwards of 3 seconds after starting.

macds · Nov 8, 2017

digger doug said:
Does your Quincy have head unloaders ?

IIRC you can restrict how fast the oil come up to actuate them upon start up.

Mine take upwards of 3 seconds after starting.

The pump is an older model 325-7.
Has the geroter pressurized oil system and hydraulic unloaders.
I had read that recip pumps can be tough on vfd's, but considering im feeding the 5hp vfd 575v three phase from my 40hp RPC (to run a 5hp motor), i dont think i need to be overly concerned about that.

Or do I?

macds · Nov 8, 2017

rons said:
I'm planning on using one of these. Operates on 12-24V DC. It can be easily setup with any hysteresis I want. It has a internal transistor switch that can pass up to 60mA. I bench tested one with a cut-in/cut-off pressure range of 125/150 PSI with a 24V coil relay. It works great. The back side has a 1/8 NPT connection but you can get other connection variations.

SMC ISE3-1-65-L pressure switch, h/precis, ISE3/ISE3A PRESSURE SWITCH

This is the ISE30-T1-65-L.

View attachment 212197

Pardon my ignorance, with that SMC piece, I could wire the output directly to the low (28ma) remote input on the VFD?

mksj · Nov 9, 2017

Normally I would suggest a motor soft start module (like a WEG SSW05 or SWW06 5.5kW 575V SSW050010T4657), but these are pricey ($300). If you have a VFD, then all you need is a mechanical pressure switch to switch ON/OFF a VFD control input that turns on the forward run command. Set the VFD acceleration to something like 3-5 seconds. Use the pressure switch you have and just directly connect to your VFD control input terminals across the NO pressure switch. There is no need for the current contactor or overload relay, as the motor is directly wired to the VFD. You could use the contactor to switch power on/off to the VFD and just use small switch to the contactor coil to switch it on/off. I do this with my 5Hp compressor.

DDoug · Nov 9, 2017

macds said:
The pump is an older model 325-7.
Has the geroter pressurized oil system and hydraulic unloaders.
I had read that recip pumps can be tough on vfd's, but considering im feeding the 5hp vfd 575v three phase from my 40hp RPC (to run a 5hp motor), i dont think i need to be overly concerned about that.

Or do I?

Just see if there is a adjusting needle valve to slow down the speed (actually a time delay) to where
it starts pumping.

Might not need expensive electronics at all.

rons · Nov 9, 2017

macds said:
Pardon my ignorance, with that SMC piece, I could wire the output directly to the low (28ma) remote input on the VFD?

Not with the ISE30-T1-65-L. The "65" means PNP output. A "28" means 4-20mA output. The parts label for analog current output are what you need. I suggest that you download the product manual and read it (over and over....).

macds · Apr 3, 2019

Just to cap this thread off, I managed to wire a regular old pressure switch to trigger the on\off points on the VFD.
Been running it this way for quite some time now. No problems.

I have the vfd dialed in at 47.5 hz, and a 5 second ramp, as that seems to be the sweet spot between inrush, noise and vibration.

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