Problem Coltri MCH6 - compressor stops by itself - no pressure switch

[Stooff69]

I have a COLTRI MCH6 compressor, 3 horse power, single phase, 2.2 kW from 1998 (no pressure switch). I bought it second hand few month ago. I have to say that it is my first diving compressor, (I use to fill up cylinder from a filling station but I have not done any maintenance on it). However I have download, printed and read the manual of the Coltri and have respected all instruction in it.

This is what the previous owner wrote me about it : « I did all the normal things to service it. Then I rechecked the output volume it was down so I removed all the valves and replaced and refaced them (all stated in the auction), I even replaced the first stage rings as this is where the compressor gains its capacity from. I fitted a new low volume reed valve head and reassembled with new gaskets and synthetic oil. The compressor has been fully pulled apart, cleaned out and rebuilt it is in as new condition and I can assure you all parts were original and new.»

When I received it some oil had leaked during the transport. I have cleaned the outside, but I noticed the intake filter was soaked in oil as well, so I wiped the oil off and let the compressor run with nothing on the other end for a while. I checked the oil level before and it was good. I had a look at the belt, looked ok. Other than that, I admit the compressor looked new, and appart from the oil it was very clean. Could not expect any better for a compressor of this age.

I check oil level and safety valve before each day of work. I purge moisture every 7 to 10 minutes.I have been running it for less then 4 hours in total ( I keep track of every use ).

Now the problem that I have is that the compressor stop by itself randomly and I do not understand why. I believe it should do so if overheat, but today it did it after only 8 minutes if use ! It happenned 4 times in total. The first time I waited ½ hour and start again : no problem, I finished my filling. The second time, I waited 5 minutes started again without a problem and then it stopped after an other 10 minutes. I noticed that time some kind of white smoke coming off the intake hole. I did not start it again that day, and today. Starts fine, and stop after 8 minute of running. (went from 60 bar to 100 bar). What can it be ? What shall I check ?

I have tried an other socket but same problem happen. The compressor has no problem loading to 230 bar as it does so when I check the safety valve.

Thanks for your time.

 

[rcontrera]

That "smoke" coming from the filter is actually oil mist. That is how the first stage is lubricated. If there was a filter cartridge in there, you most likely would not see it.

As for the stopping, sounds like you have a motor problem. It could be a worn out thermal overload, bad switch, twitchy run capacitor, loose connection or any number of things. Electricity is pure freaking MAGIC and way frustrating! So start at the plug end and work your way to the motor winding inspecting everything for damage.

 

[Stooff69]

Thanks rcontrera. I have done a few test since, and yes it is definitely an electrical/motor problem.I must say for a start that I have not used extension cord previously, the compressor was plugged on the socket in the garage. However it is an old house and I don't know how the electric has been run in the walls. Problem could be from there.
First I had a look in the box above the motor. By the look of them, the capacitors look fine. I then took the motor off the unit and tried it inside the house. First socket, the fuse went off straight away. I tried twice on the socket, same result. 2nd socket the motor started, so I left it running for 22 minutes. No problem. Then tried a 3rd socket, motor started so I left it running for 1/2 hour, no problem.
I have then reassemble the unit. I plugged the unit with a 5m heavy duty extension cord on the 3rd socket, fuses went off the first time, and started the second time. Left it run 5 minutes, then stopped it. Tried again a couple of times, the compressor did not start. I then tried on same socket without extension cord, but same result, compressor did not start, fuse went off.
The fuse which went off is 16A, could that be the reason? I had a look in the manual, but did not find this info.
So this where I am at the moment, I am going to keep inspecting other part of the motor, and may speak to an electrician.

 

[rcontrera]

Yes ... that is a BIG problem. Your compressor draws 29 amps if it is 115 VAC. Household plugs are only rated for 15 amps. You need to run a heavy gauge cable to a 35 amp plug and twist type of outlet.

 

[mrfixitchapman]

I wonder if Stoof69 is in Wanaka, New Zealand. IIRC, NZ is 230VAC, 50HZ.

DC

 

[rcontrera]

I wonder if Stoof69 is in Wanaka, New Zealand. IIRC, NZ is 230VAC, 50HZ.

DC

Ah ... OK ... my bad! The 230 VAC motor only draws 14 amps of running power. However, using an extension cord CAN cause additional draw and heating... at lease according to the local electrical guru. There is a thermal overload switch somewhere in that controller box. If the motor is a 60Hz and you are running it on 50Hz, then the volts to frequency ratio goes up and that will probably result in overload. Oh, and the power goes down so high pressure strains may shut down the motor. I would get your electrician to take a good look at what is happening.

 

[CraigAClark]

Even if the power is 220-230v, single phase, 50hz, and the motor is set up for that supply, we are talking about amp draw (compressor motor) vs wattage (most house hold appliances). The starting amperage, not under load, of a single phase motor can be 5-7 times the FLA. I doubt house hold outlets are designed to handle start up amperage.

 

[Suzuki416]

From experience they dont.

If the compressor was 'warm' I could start it & be usable though would sometimes stop over 200 bar- but dead cold - not a hope.

I struggled with my MCH6 on a extension 32amp cable until I used the cooker circuit.