Would like to add a VFD to a 10HP compressor motor
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  1. #1
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    Post Would like to add a VFD to a 10HP compressor motor

    I have a Scales Air Compressor with a 300 gal tank, Baldor 3-ō 200-volt 10-H.P. motor. My service is 3-ō 208-volt. I would like to add VFD to it. Can some one suggest what unit I should get. I might also want to add a variable pressure regulator if practical. I believe it has a pressure onlooker that releases when it turns off. Can someone answer the following questions:
    Should I get a 10 HP VFD or the next size up?
    Can we get an electronic pressure regulator?
    What would a good ramp up time be?
    What is the Min the motor should run at if we install a pressure sensor reader?
    What brands of VFDs do I stay away from of which are good ones to use?
    Should I install a electronic Pressure unloader if I decide to modulate the motor speed to keep up wit demand?

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    I suggest you think carefully before raising the rpm of your compressor to increase cfm as needed. Since you have a large storage tank, think about adding another separate compressor, whose ON pressure is set 10 psi lower than the one you already have. That way the new one won't turn on until you actually need it, and you gain total cfm without possibly over reving your main compressor.

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    I think we need more information on what you are trying to accomplish to provide meaningful answers. What do you need that would not be provided by just connecting it up to the 208 and using it?

    Is this compressor only being used for one process at a time?

    Electronic pressure regulators are available. Might cost more than your compressor. I have used them and they can be quirky and troublesome. I have also created them using hydraulic valves and PID controllers on high flow systems.

    You have to be careful running a compressor too slow as lubrication may be an issue and the maximum speed may be riddled with issues of lubrication, valve problems, and heat generation.

    Unless you have a government picking up the cost of this and controller knowledgeable staff on call I would use the simple, proven, brute force methods.

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    A couple pictures and more details about your compressor would be helpful.
    All piston type compressors have minimum and maximum RPM limits that should not be exceeded.
    A cheaper EBAY VFD from China can get the job done, but best to up the HP to 15 I would say.
    EBAY is a source for digital pressure sensors/gauges as well.

    Edit: I've used one of these, they can be had on EBAY for less. Seems to be quite accurate.
    Aliexpress.com : Buy DC24V 0 10Mpa Air Compressor Pressure Switch Digital Pressure Gauge Relay output from Reliable output suppliers on Pneumatic Tool1 Store

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    Another clarification from the op would be his definition of "electronic pressure regulator". My definition makes it very different from a pressure switch.

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    Quote Originally Posted by rons View Post

    Can you elaborate a bit more on your setup, connections, ...?
    Are you running +/-10V from the pressure sensor into the VFD?
    What VFD did you use?
    Wiring?
    Cutoff/startup setup/config?
    ...
    Suggestions?

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    Quote Originally Posted by rpseguin View Post
    Can you elaborate a bit more on your setup, connections, ...?
    Are you running +/-10V from the pressure sensor into the VFD?
    What VFD did you use?
    Wiring?
    Cutoff/startup setup/config?
    ...
    Suggestions?
    I didn't mean to mislead you. The SMC and Festo are digital readout pressure switches. The digital pressure switches are used for switching the VFD on and off. They can also be installed on a manual turn valve to see pressure. I looked at their electronic pressure regulators. Quite expensive and won't go past 120 PSI.

    https://www.smcpneumatics.com/electronicregulators.html

    The pressure switches operate with 12 to 24V dc. Although my VFD has a 24v source that is only supposed to be used with external switches which provide control
    to the VFD, it also powers the SMC device. But I decided to use a separate 24V source to obey the rules.

    Allen Bradley PowerFlex 70 VFD.

    There are three wires to the switch, 12-24Vdc, ground, and a transistor switch output that connects to the VFD with 12-24Vdc high and 0Vdc low.

    125psi on & 150psi off.

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    Default Would like to add a VFD to a 10HP compressor motor

    Thanks for your response!

    Quote Originally Posted by rons View Post
    I didn't mean to mislead you. The SMC and Festo are digital readout pressure switches. The digital pressure switches are used for switching the VFD on and off. They can also be installed on a manual turn valve to see pressure. I looked at their electronic pressure regulators. Quite expensive and won't go past 120 PSI.

    https://www.smcpneumatics.com/electronicregulators.html
    I

    I probably can get one of those.
    I wonít be going past 120 PSI


    Quote Originally Posted by rons View Post
    I
    The pressure switches operate with 12 to 24V dc. Although my VFD has a 24v source that is only supposed to be used with external switches which provide control
    to the VFD, it also powers the SMC device. But I decided to use a separate 24V source to obey the rules.
    I

    Iím confused. Are you saying you were originally using the VFDís 24V source for the SMC switch, but then changed your mind?


    Quote Originally Posted by rons View Post
    I
    Allen Bradley PowerFlex 70 VFD.

    There are three wires to the switch, 12-24Vdc, ground, and a transistor switch output that connects to the VFD with 12-24Vdc high and 0Vdc low.

    125psi on & 150psi off.
    Thanks!
    Iím looking into 230V VFDs around 10HP.
    I have a couple of decent 380V-600V ABB VFDs, but I donít have any 230V -> 460V single phase transformers, and definitely nothing in the 10+ KVA range.
    I could spin up my 25HP RPC, but thatís what Iím trying to avoid having to do...

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    Quote Originally Posted by rpseguin View Post
    I’m confused. Are you saying you were originally using the VFD’s 24V source for the SMC switch, but then changed your mind?
    It worked with the VFD's 24Vdc. The manual for the VFD states that the 24Vdc is not to power anything external. But since the SMC switch is not using
    much current there was no issue. I didn't change my mind. The design I am building on will have a 24Vdc power supply in a control box on the compressor.

    BTW, you ever bought anything from Galco? They have a Wiegmann hinged door box I'm thinking about buying.

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    Quote Originally Posted by rons View Post
    BTW, you ever bought anything from Galco? They have a Wiegmann hinged door box I'm thinking about buying.
    No, I havenít. Let us know how it goes.

    Know anybody with a 7.5+ KVA single phase 240V -> 480V transformer? Or 240V VFDs?

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    Quote Originally Posted by rpseguin View Post
    Know anybody with a 7.5+ KVA single phase 240V -> 480V transformer? Or 240V VFDs?
    I bought a 3Ý step up transformer from this guy. He has/had a pallet of others in various sizes also. Way more than listed in his add. Worth a call, he is just NE of Bakersfield.

    Transformer - materials - by owner - sale

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    If you're sizing VFDs for a compressor, you need to use the 'high overload' rating, not the 'low overload'/'HVAC' rating. They need more starting torque for longer and the running torque doesn't back off at lower speeds like a fan or centrifugal pump. This typically means going up a size.

    Setting up an analogue pressure sensor on a PID loop with minimum and maximum frequencies that it cuts off below should be fairly doable for any mid-range modern drive.

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    Quote Originally Posted by aNYsurfer View Post
    What would a good ramp up time be?
    If your goal is a slow ramp up on the air compressor vs a hard start across the line, then perhaps a soft starter would be a better solution. A soft starter will not run the motor RPM above base speed though if that's what you want to do.

    I bought a ABB soft starter on ebay for cheap for my 3 phase air compressor. Ramps up the motor nice and smooth and doesn't affect my CNCs with an abrupt start.

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    Quote Originally Posted by rpseguin View Post
    No, I havenít. Let us know how it goes.

    Know anybody with a 7.5+ KVA single phase 240V -> 480V transformer? Or 240V VFDs?
    I called Galco and ordered my box. Very knowledgeable person on the phone.
    -They have all kinds of electrical parts for building a RPC.
    -They sell RPCs as well as VFD's.
    -They repair VFD's.
    -Check with Galco.com before Amazon.com

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    Quote Originally Posted by Philabuster View Post
    If your goal is a slow ramp up on the air compressor vs a hard start across the line, then perhaps a soft starter would be a better solution. A soft starter will not run the motor RPM above base speed though if that's what you want to do.

    I bought a ABB soft starter on ebay for cheap for my 3 phase air compressor. Ramps up the motor nice and smooth and doesn't affect my CNCs with an abrupt start.
    Soft starters are usually much more costly than comparable horse power VFD's with less features.
    Base models don't even come with overload protection. VFD's do everything a soft starter does and more, for less money.

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    Quote Originally Posted by dkmc View Post
    Soft starters are usually much more costly than comparable horse power VFD's with less features.
    Base models don't even come with overload protection. VFD's do everything a soft starter does and more, for less money.
    Got it. I should have added I picked up my soft starter for under $150 shipped for a 15hp motor via ebay.

    I also used a 30hp soft starter for my 1967 Hitachi Seiki turret lathe as I heard VFDs are really hard on the insulation in old motors.

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    Quote Originally Posted by Philabuster View Post
    Got it. I should have added I picked up my soft starter for under $150 shipped for a 15hp motor via ebay.

    I also used a 30hp soft starter for my 1967 Hitachi Seiki turret lathe as I heard VFDs are really hard on the insulation in old motors.
    You got an unusually good deal on the 15hp starter. A quick scan of current Ebay listings shows prices much higher.

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    I bought a 40Hp soft starter for $25, Ebay is not the standard for pricing.

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    Quote Originally Posted by rons View Post
    I bought a 40Hp soft starter for $25, Ebay is not the standard for pricing.
    Tell me where I'd like to get in on those deals too


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