Thread: 5.5HP 3Phase motor on Single Phase with a VFD ????

I got home from work tonight and straight down to the compressor to have a look inside.

Typically, my torch was almost flat so didn't have much light to shine in the tank, however managed to see the first half of the bottom of the tank (opposite end to where the hole is unfortunately).

What should the inside of a 7 or 8 year old tank look like?

As best as I can tell the bottom is coated with a wet, rusty orange coloured paste. Managed to get this photo from my iPhone by looking down the pressure release valve opening and shining some light down the outlet valve opening (the dark circle around about the 4 o'clock position is the drain valve:

Inside Tank by Jon_Kelly, on Flickr

I poked a long wooden dowel into the tank and the orange coloured paste reminds me very much of the kind of ocher that aboriginal paintings would have been painted with. Definitely no rusty lumps of metal in it.

Assuming that I get the motor and compressor off the tank, foot off and the hole welded up, Im thinking that a fairly strong caustic solution swirled around the inside of the tank would lift that orange paste off and leave a much cleaner surface inside, then swill out with water and then leave a heat gun blowing into the tank for half a day to dry out. Its a little bit like my 60 year old Land Rover petrol tank Ive just cleaned and restored, only this is in a much, much better condition!

Any thoughts? I reckon its still worth a good try to clean up and weld the hole.

Thanks
Jon

I doubt it it's possible to see much of value without using an inspection cameras and also getting rid of the rust paste. The view you have through a hole like that is waaaay too restrictive.

The only thing I would consider washing the rust out with is a molasses solution. Put a 10% molasses solution in there and park it in the direct sun for a week, slosh it around every day and then tip it out and rinse a few times with water - then inspect it again - this way you will see if there are any pits in the surface. you might need to repeat this a couple of times. Sorry it's such a slow method but it is the safest method.

Thanks Bob.

Im not in a speedy rush, so a slow clean-out process is no problem... Indeed I cant afford a motor or VFD just yet anyway as I have to strip and rebuild the front axle of the Defender first.

Ive never used molasses before, but have heard of people using it to gently strip steel. Is this the kind of thing I would need, then mix to a 10% solution?
http://www.ebay.com.au/itm/Molasses-...item4d2ec33eb5

Thx
J

Originally Posted by ventureoverland

Thanks Bob.

Im not in a speedy rush, so a slow clean-out process is no problem... Indeed I cant afford a motor or VFD just yet anyway as I have to strip and rebuild the front axle of the Defender first.

Ive never used molasses before, but have heard of people using it to gently strip steel. Is this the kind of thing I would need, then mix to a 10% solution?
http://www.ebay.com.au/itm/Molasses-...item4d2ec33eb5

Thx
J

Yep - that's it. Its a very gentle method that is not supposed to attach steel if used in a dilute form. Maybe to play it save just try a couple of days before a first inspection.

If you wanted to get fancy you could also make a stirer that you could stick down inside the tank. A foldable propellor attached to the end of a battery powered drill - makes sure it's tight on the drill though!

Not sure about making a foldable propellor Bob - probably a bit beyond my expertise!

I did quickly make this tonight though, a little side-pointing nozzle for the high pressure hose. My idea is that I can push it to the end of the tank, turn on the water and pull it back to the opening in the tank and as I do so it will lift / dilute some of the gunk.

Sidewards pressure washer nozzle by Jon_Kelly, on Flickr

After looking at that brass close up I need to put it back in the chuck and dress it up - looks much worse in the photo compared to feeling it in my hand!

A few wash outs later and then I'll be able to put the Molasses in... which my wonderful better half brought back from the stables for me as a little surprise tonight
Molasses by Jon_Kelly, on Flickr

Well today's my lucky day

Ive just had the sparky round that reno'd our house before we bought it 12 months ago to do some warranty work. Whilst he was here I asked him to give me a price to install a 20A circuit so I could plug in a 4kW VFD.

Straight away he told me that we had 3 phase into the house and so he could just run me a 3 phase circuit from the existing DB

That saves me from buying a 4kW VFD and a 4kW delta motor.

Im now a happy chappy - Despite the tank issue, the compressor effectively just got a whole lot cheaper

Lucky b*gger... That's the best solution. Not normally the cheapest, make sure you get a couple of 3 phase power point installed in the workshop at the same time.

Ray

PS.. Someone was telling me the other day, it's not uncommon to have 3 phase power in new homes these days, they install it for airconditioning , so he tells me...

Originally Posted by RayG

Lucky b*gger...

Thats more or less what I thought!!

Originally Posted by RayG

PS.. Someone was telling me the other day, it's not uncommon to have 3 phase power in new homes these days, they install it for airconditioning , so he tells me...

Yep, thats what the sparky told me also. After he went and I stopped smiling I went to have a look at our AC unit... 7.5kW @ 415V!!

Back at my DB, all 3 phases come in from the street and through the 3 phase master breaker, then each phase appears to break out into 3 individual rails, one per phase. My DB has 3 rails with various single phase circuit breakers on it - total loading of the various breakers appears to be approximately similar on each phase. Then I have a 4th rail which appears to be configured as three phase and has (currently) 1 breaker on it for the Air Conditioning unit.

None of this made any sense to me just by looking at it, but once explained it was pretty obvious and apparent what was going on.

Jon

I stripped the compressor today, washed out the tank with my home made sprinkler thingy - that worked well and got some seriously orange water out. The inside of the tank didn't look too bad after that but it was still quite orange.

IMG_3898 by Jon_Kelly, on Flickr

20L of 10% Molasses water added after the wash-out... swirled it around every hour for half the day and will now leave it until next weekend to empty (working away form home this coming week).

It will be interesting to see what the tanks like in a week's time..

Once the inside's clean I'll cut off the feet and get the grinder the the rusty spot(s) to identify the hole.

Quick update...

Things have moved on slowly this weekend... Spent yesterday continuing with the old Landy restoration and today at the hospital with the Mrs (she fell and broke here wrist and arm, she's waiting to go into theatre now).

Anyway, I popped home to get her some things and had to have a look inside the tank now the molasses is out and tanks rinsed. Must say Im impressed how the stuff eats the loose and leaves the steel.

I cant get any photos yet, but I can now see lots of small areas of clean steel and similar dirty / rusty bits.

Based on previous external inspections and what I can now see inside, Im sure the hole is repairable.

Interestingly enough, no water or molasses leaks out of it, only air when under pressure.

I'll hopefully get the tank into the garage this week (having a few days off work to help the mrs out) to get the foot cut off and the outside of the tank cleaned up so I can finally see what Im looking at.

Ive been a bit preoccupied lately, the mrs fell over and broke her arm quite badly - resulted in very little time in the shed!

Anyway, I managed to get a few hours last Monday to attack the tank. I cut off the feet and ground away all the surface rust with a worn out flap wheel and wire wheel. I then put a bit of pressure in the tank and sprayed some detergent over the suspect area to show up some bubbles.

I had to make quite a bulbous weld to stop any bubbles and seal the tank - thats probably a sign of my rubbish welding skills though! Good news is that the rest of the tank bottom was in good condition and didn't have any other leaks.


Compressor tank during repair. by Jon_Kelly, on Flickr


Compressor Tank Weld by Jon_Kelly, on Flickr

All being well the feet will get welded back on this weekend. Sparky is due to come over for an hour in a few weekends time to connect the 3 phase socket into the distribution board

Jon

OK, update time guys...

Sparky came last weekend and connected my 3 phase socket into my distribution board. I did all the wiring and cable pulling, just left him to check and connect into the main board.

Last night I hoped to get my compressor up and running... Didn't quite turn out like that

First job was to change the oil and then put everything back onto the repaired tank.

This is the disgusting oil that came out Im pretty sure it was old engine oil because its WAY thicker than the new proper stuff!!!

Old Compressor Oil - Gross by Jon_Kelly, on Flickr

I replaced it with nice new compressor oil, then switched it on to find my next problem:

https://youtu.be/fsq45aAykX8

Any ideas whats wrong? To me it sounds like its in the top end, but Im far from sure. When I turn it over by hand I cant hear anything in the bottom end and everything turns freely.I suspect I need to remove the heads and have a look, but any pointers and hints would be appreciated.

Being 3 phase, are you sure its turning in the right direction?

Whats it doing when it slows down / stops. I looks like its lost power. Is it throwing the breaker, or is that just a mechanical stall when it stops?

Regards Phil.

Originally Posted by Machtool

Being 3 phase, are you sure its turning in the right direction?

Whats it doing when it slows down / stops. I looks like its lost power. Is it throwing the breaker, or is that just a mechanical stall when it stops?

Regards Phil.

Thanks Phil,
The motor is running in the right direction - at least its running in the same way that the arrow on the larger pulley is pointing!

Compressor Pulley by Jon_Kelly, on Flickr


I have just changed L1 and L2 round to make the motor run in the opposite direction (in case the large pulley had been installed the wrong way round by the previous owner) and it sounds / behaves exactly the same.

The motor definitely isn't throwing the breaker - I just turned the power on until it got up to speed and then turned it back off. I suspect that last part second of the pulley turning is simply resistance to the compressor.


When I bought it the bloke said that he had just replaced one of the head gaskets - is it possible that the head / valve assembly could have been put back together upside down or wrongly? Ive never had a compressor cylinder apart.

Thx
J