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  • I have a screw type compressor with a 3 phase 5.5kw motor. The compressor is controlled by a computerized main controller. What type of variable frequency drive converter do yourecommend.

December 4, 2019 10:00

I have a screw type compressor with a 3 phase 5.5kw motor. The compressor is controlled by a computerized main controller. What type of variable frequency drive converter do yourecommend.

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Comments

December 21, 2019 10:44

A VFD or rotary phase converters are the 2 best options. RPC's have the disadvantage of needing to be running before the motor of the compressor starts, so without a fairly complex control circuit, the RPC would have to be running the whole time the compressor is needed, not just when the compressor motor is running.
As mentioned elsewhere, VFD's in this size are hard to find in single phase input (there are some Chinese options, but I haven't seen enough evidence to recommend one, in general generic Chinese inverters have gotten better through the years, but I haven't read any accounts of anyone using the more powerful units.)
Most 3-phase VFD's can be run off single phase, but need to be derated 33-50%. You would need to talk to an applications engineer to find out what you will need and how to hook it up (what to do with the 3rd input,) and how to program it (some need to have phase loss detection disabled.)

If you only plan on running the compressor at its nameplate frequency and not actually use the VFD to vary the frequency there's no reason to worry about the fan.

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December 18, 2019 10:42

As for cooling the back fan could be replaced by an electrical one i ve seen it on motors and yes coolin is important for continuous duty.

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December 17, 2019 08:54

More info. Need voltage and current to be known, watts not enough. In my experience, need a vfd rated for the voltage, it is then sized by how many amps. If single phase input, you might be expected to find a VFD rated for twice the amps to compensate for single phase input. Vfds are sized for continuous load and can handle start up currents, this can be offset by ramping up over 5 seconds and more for a softer start. Running a motor under speed may not have adequate cooling. Seek a reseller in your area, they will spec it for you.

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December 17, 2019 08:59

Also consider rhe starting current of your compressor so your converter should be sized a little more than 5.5kW

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December 17, 2019 08:59

Power for 3 phase
IV square root of 3
Then you cab workout the power needed on single phase side
The converters are very efficient
If you have 380v on 3 three phase current perphase will be about 8 amp
On the single phase side you will need 23 amp if you supply is 230v rms.
The above assuming 100% efficiency of the converter but this is ideal so you can assume 90% efficiency this means the input current on single phase s8de will ve slightly higher than 23 amp rms

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December 17, 2019 08:59

You could possible use Danfoss VLT Aqua drive FC202, 0.25 - 90 kW.
There are also 200 - 240 V single ph. input models up to 22 kW output power, see: files.danfoss.com/download/Drives/DKDDPB202A702_FC200_SG.pdf

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December 17, 2019 09:00

Check frequency converters on ebay
Input single phase, output 3 phase, varible voltage variable frequency

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December 16, 2019 14:43

I don't believe you will find a 1ph input drive at 5.5kW rating. Most 1ph input drives are much smaller than this.
Even if you could find one, I'd suggest a 5.5kW compressor load is way too much power & rms current to be thinking of powering from a 1ph mains supply. A 32A supply would be marginal - You'd probably need a 63A supply to cope with the input power factor and harmonic content of the drive's input side. Don't fall for youtube videos that claim otherwise - there's a lot of bad understanding/engineering knowledge being touted as fact on there.

I think your options are:
(1) Use a 3ph generator (rated 10kW or higher);
(2) Use a smaller compressor (depends on your application requirements);
(3) Move it to a location that has a 3ph supply;
(4) Upgrade your supply to 3ph (= most expensive).

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December 16, 2019 12:49

If you want to obtain 3 phase from 1 phase you need a frequency converter and an appropriate motor. The motors up to 2,2kW are designed with coils voltage 230 Delta or 400 star. If you use frequency converter supplied with 230v at its output you will have 3 phase but only 3x230 so you need to connect the motor for 3x230v. That's the main problem with such applications.

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December 16, 2019 12:49

For max.2,2Kw you can use ABB ACS55 i don't tink its available for 5,5 kw.
So you nead 3ph power.

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December 16, 2019 10:53

The only inverters I have any experience of are ABB ones, who offer a 5.5KW - but for that power output it requires a 3 phase input. The largest single phase supplied varible frequency inverter I've seen "only" produces 4KW out.
The problem is that there's only so much a single phase can provide.

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December 16, 2019 10:53

you can use an electric or diesel motor to drive a 3 phase generator.

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[Comment was deleted]

December 4, 2019 09:06

I forgot to mention the reason I will need a variable frequency drive is because i no longer will have a three phase line. So I will need a single line and converted to a three phase power.

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December 5, 2019 08:44

@Oding I cannot locate the module I used about 10 years ago now but for a 1kW variable frequency drive to a conveyor belt motor to control both speed and direction I used a Danfoss module. This was 230V single phase input so a higher power version of this may be available? You may not require variable frequency from what you describe, but they may come with this anyway. One warning is check the motor cooling as if it is a fixed fan on the shaft it may overheat at a lower than spec rotation speed. A quick search here https://uk.rs-online.com/web/c/automation-control-gear/electric-motors-motor-controllers-peripherals/inverter-drives/ did not show anything that obviously met your requirements as the high power units seemed to be 3phase input but it does provide a list of potential manufacturers to investigate/discuss with. RS may also be able to advise.