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  1. #1
    Join Date
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    Default A tale of two compressors

    For many years I've thought that a small compressor in the workshop would be handy. I don't use air tools or want to spray paint cars, so little is fine - just for those odd times when sir would be nice to blow out a hole, try a steam engine or even use an air spindle on a grinder.
    I obtained two some time ago and this break thought I'd have a go at getting them going (or out the door...) Here's where things get odd.
    This is the first one. I found the 'odd' before I took the photo, but it is a nice little unit. The tank on top is probably 2 to 3 litres and even has a pressure switch on it. Originally it had a bit of normal single phase flex hanging out of it so I thought it single phase, but the name plate suggests something different
    P1040721.JPG P1040715.JPG
    When I took the cover off the motor, this is what I saw - a typical 3 phase terminal block wired in star, but the single phase flex was connected to L1, L2 and L3 (which got the covetted twin colour wire). The pressure switch was wired similarly, although it is a 3 pole switch (ie pole per phase). Part of the mystery is the broken brown wire. Sneaks out the side of the terminal block, don't know what it does or whether it is meant to attach to anything.
    P1040716.JPG P1040717.JPG
    The other is a single phase unit, complete with plug and it even runs - but no pressure switch and half the fittings are missing as there is no input air cleaner, pressure gauge, the relief valve has been gutted and I can only guess that the air out is from that spigot in the big wing nut (that has a filter to take out any oil mist.There is also a drain plug on that 'receiver' for draining carry over oil).
    From the paint runs on it, I'm guessing that it could have been used for an air brush?

    P1040719.JPG P1040718.JPG P1040720.JPG

    So, the questions for the electrical types -
    • Does anyone have an idea what the mystery wire might be for? (haven't opened it up yet)
    • I really like that little 3 phase unit but don't want to wire it up to my only 3 phase socket, so I guess VFD?
      • Who is the latest cheap and cheerful supplier?
      • Is there a 'best' type for this application?
      • I'm guessing that with that pressure switch I'm going to have to interface that to the VFD - should I stick with the three contact version I have or are there small single contactor versions that would be a little more compact and sensible.

    • The golden unit is a Roymac 'Middi' model
      • Does anyone have any instructions for these?
      • Without a pressure switch this thing would just run, but the (current) wiring does not suggest there was ever a PS on it. Not sure whether to use it as is with manual off/ on, get rid of it, put a PS on it, use it as a vacuum pump. Does anyone run anything similar?

  2. #2
    BobL is offline Member: Blue and white apron brigade
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    Guessing here, but It could have been for a capacitor with the 3P motor run as a kludge 2P + cap ? Not really advisable for a compressor given the loads they are under.
    Have you checked that it really is a 3P moto I have seen a few SP motors using a 3 x 2 terminal block like those.

    There are plenty of cheap and cheerful VFDs around.
    There are plenty of sub$100 VFDs on ebay but beware the manual which is sometimes no more than a couple of pages of illegible Chinglish.

    Seeing as its only a 1/2HP I'd recommend a 0.4kW Powtran PI130-0R4G I have one running the coolant/lube pump on my mill - very compact and quite robust little beasties with a true english manual although the print its tiny . I think it cost about $115 including shipping, I can send you the manual if you like.
    Unfortunately Powtran have no website but search for Powtran threads about how to order etc.

    I can send you the 130 manual if you like.

    You will have to convert the motor to delta to get it to run at full power but it looks like the common point might already be available to you with those 3 top connectors joined together.

  3. #3
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    My Dad had one more or less the same as the Roymac, he bought it from McEwans in the 60's for pumping up car tyres, it never had a pressure switch just a pressure gauge to indicate tyre pressure.
    As you suggested, there was a 12 foot hose on the wing nut barb with a simple clamp on schrader valve on the end. Rock solid little unit, slower to inflate a tyre than a full on compressor but a lot faster than a Dead Easy. Let me know if you want some photos of the missing bits and I'll get my brother to take some
    Cheers,
    Greg.

  4. #4
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    That would be nice if you could Greg - at least I would know what should be where. If you could do an experiment and work out what pressure the releif valve is meant to trip, that would be even better. I'm guessing it is just a ball bearing on a seat with a spring holding it down. A ball is easy but exactly what size/ strength the spring needs to be... (particularly in light of what I have discovered below).

    For the other unit, I got onto the Fini website. They are an Italian company who specialise in compressors. My model is long discontinued although I have an enquiry in for any information. However, the one that has replaced it as far as I can tell is called a Shuttle 97/15. If the specs are basically the same, then it would have a 2.4l tank, 87l /min delivery but most surprising is a maximum pressure of 15 bar (most compressors these days are around 8 to 10 I think so you can get around 6 at a tool). I'm keen to see what this one really is...

    It could mean that the cut off switch needs to be retained, just because finding one for a higher pressure may be difficult.

    Michael

  5. #5
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    If you need a relief valve let me know, i should have a few good 2nd hand spares around, have to replace them every 12 months at work.

  6. #6
    Join Date
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    Hi Michael,

    Those compressors look like nice little gems.

    15 bar, 220 psi is very high. Given that not many tools would need or could be used at that pressure you would need a pressure reducer.

    This also effectively increases the size of the receiver.

    Simon

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  7. #7
    Join Date
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    Hi Michael, for the top one I would take it to a motor rewinder and get them to check it and give it a test run, should only cost a few $. Then you will be sure and if all is ok get the VFD Bob suggested.
    For the bottom one, you could go to a dump shop and get a stuffed one and add this to it's tank, but watch out they are usually a lower pressure tank. Good finds you got there.
    You won't regret having a small one, think of the electrical energy you save. My big guy has a 200L tank, a 4Kw motor and pumps up to 120psi, so it uses a lot of energy. I bought a real cheapie, a Spear & Jackson from the big green shed with the compressor sitting on a flying saucer tank, pump it up and it does the bikes, wheelbarrows and trolleys on one charge. BTW it's ideal for my small nail and staple guns.
    Rgds,
    Crocy.

  8. #8
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    Quote Originally Posted by simonl View Post
    ...15 bar, 220 psi is very high. Given that not many tools would need or could be used at that pressure you would need a pressure reducer.
    Yes, a filter/ regulator is on the list. The grinder air spindle runs at 6 bar (don't know what consumption); everything else will be less I would think so 15 bar would be a waste otherwise. At the moment I'm assuming it gets to 15 bar. Need to get that confirmed though.

    Quote Originally Posted by Old Croc View Post
    ...You won't regret having a small one, think of the electrical energy you save. My big guy has a 200L tank, a 4Kw motor and pumps up to 120psi, so it uses a lot of energy...
    One of the reasons I was looking for this size - if I had lots of air tools continually in use then a large unit would be justified, but the idea of running a compressor for 5 - 10 minutes just for a small volume of air does seem excessive. However, there are some things that you just need compressed air for.

    Michael

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