Coltri MCH 6 question/ advice appreciated

[Tony Pr]

Good morning scubaboard,

Long time reader, first time poster. I have been doing a lot of learning about compressors thanks to this site.

So, I have bought a Coltri MCH 6 Compressor electric powered (2.2kw, 14 amp, 220 volt, 50 hertz) motor which is about 20 years old and have been trying to get it filling tanks. Bit of a story below, feel free to skip down to my questions (dot point) if you are the TL;DR type.

Bought an MCH 6 compressor without a whip. Got one made up and fitted onto it.

Got it filled with Bauer oil and ran it to see if it would get up to pressure. The pressure relief valve went off, so assumed it was getting up to 200 bar or so (the gauge was broken).

Learnt that you are not to put Bauer oil in it, so drained it out and put the correct oil in. Bought and installed a PMV, a new filter and a new pressure gauge. Installed. Runs at about 130 bar (or 1900psi). Initially hooked it up to a tank with the valve closed in order to determine where the pressure relief valve will start venting air. Adjusted the valve to around 200 bar.

Hooked up to a tank and tried to fill. Found that there were leaks between the cooling pipes. Removed the pipes, cleaned them all up and put back together. Fixed the leaks. The transmission belt began slipping, found a replacement for that.

The electric motor then began making some horrible noises when under load, so removed the pulley (80mm pulley) by cutting it off (was rusted on) and took the motor apart and changed the rear bearing. I did not change the front bearing as I thought it was fine (I am still learning). Bought a replacement pulley 80mm and also a 50mm pulley with the corresponding transmission belt. Put the 50mm pulley on and put it all back together and started filling tanks.

Given the reduction in pulley size, I would have assumed that there would be a lot less load on the electric motor, therefore would not heat up as much and would run well. Also would be good in terms of heat dissipation on the compressor side, as it is filling slower and allowing more heat to escape before going through the filters. I am not in a rush to fill tanks at this stage.

Started to try and fill some tanks. The PMV is set at 130 bar (1900 psi). Runs for about 25 minutes and then the electric motor cuts out. It feels pretty hot to touch. I assume there is some form of an overload switch inside it. The tank I was trying to fill got to 160 (2320 psi) bar before the electric motor cut out. It just stopped turning. I can spin the compressor fan no problems, so I would not say there is any excessive load on the compressor side (or anything seizing it up). Tried straight after filling a different empty tank, but similar cut out issues after about 3 minutes. I assume this is because of the PMV maintaining the pressure at 130 bar and a relatively high load on the electric motor.

I think that the issue with the motor is load related, as when it goes to compress higher pressures it cuts out sooner.
The internet in all its wisdom says that this compressor can compress to 300 bar, but I would be more than happy with 200 before the electric motor cuts out and needs to be cooled down before working again. Or at least has a rest.

I have the motor plugged directly into a 220 v socket, with no extension cord. The electric motor is clean and there is a fan on it blowing air across the heat sink fins.

My questions are:
• What to do next? The only options I can see are:
1. change the front bearing on the electric motor and hope that it makes the motor less likely to overheat (I don’t think this will solve my problems) or
2. replace the motor. I am based in Vanuatu and cannot source a 2.2kw version of the motor, I would be able to get something more like a 1.5kw motor. I would think that with the reduced pulley size, a 1.5kw motor would work? Given that Coltri sells them with 1.5kw motors and 50mm pulleys or
3. Checking the cut out switch to see if faulty, corroded or need of replacement.

• Is there anything else that I can do to verify if the compressor part is working well? There is a bit of a rattling noise coming from somewhere on it, however, I assume this is external as it is does not correspond with RPM (more a pulsey rattle every 2-3 seconds or so).

Anyone with a bit of experience in this space providing a bit of advice would be appreciated. I don’t think it is the compressor part of the machine, as it seems to be a similar temperature and is still spinning. From my readings of the forum, I cannot see anyone who has had this issue in the past, however, would appreciate a link to the post which does cover it if you find it.

Thank you

Tony

 

[Dsix36]

Without more testing I would venture that the motor itself has gone bad. they usually have a thermal limiting switch and those can go bad too but you say it is getting too hot anyway. It sounds like the motor is just overheating.

To the best of my knowledge Coltri does not have a 1.5kw motor, only the 2.2 (3hp) and 3.0kw (4hp) motors. The main difference is the rpm of the compressor. 3hp is 2240rpm and 4hp is 3500rpm.

 

[Dsix36]

Mine is 3hp with a 4-1/2" pulley on the compressor, a 3" pulley on the motor, and the motor runs at 3440rpm. The compressor runs at 2240 rpm.

 

[Tony Pr]

Thanks for the advice and information.

To the best of my knowledge Coltri does not have a 1.5kw motor, only the 2.2 (3hp) and 3.0kw (4hp) motors. The main difference is the rpm of the compressor. 3hp is 2240rpm and 4hp is 3500rpm.

Correct you are. I don't know where I got that idea from.

How hot does your electric motor get when filling tanks? Can you keep your hand on the fins of the motor for 20 seconds?

 

[tbone1004]

be careful about slowing it down too much, most of these are splash lubricated and can't take with that much of a slowdown.

the motor should not be egregiously hot, you should definitely be able to put your hand on it for 20 seconds or more.

It is possible and highly likely there are other things going on in that motor that are causing the issue. It should not be hitting it's thermal cutoff that soon. The internal fan could be bad, the windings could have an issue, etc etc. I'd go to a local motor supply house and see if you can get the motor rebuilt. May have to/want to replace it as those small motors are usually not worth the cost to repair. That motor is around $350 USD at least in the US *the 60hz version, but no issues running 60hz motors on 50hz, they just run around 20% slower*.

 

[Tony Pr]

@tbone1004 Thanks! I did not think of the lubrication impacts when slowing it all down. I thought it would be ok to slow it down based that one of the Coltri MCH6 compressors comes with that sized pulley. But upon looking at it further the one which comes with a 60mm pulley is a 60Hz motor (rather than 50hz), which would be 20% faster than mine. Back to the right sized pulley for me.

I had the motor apart, there is no internal fan that I can see, only the external one. I will have a look at the rest of the motor and see if I can see anything obviously wrong with it.

I am reluctant to buy a new electric motor until I can work out that the compressor part of it is ok, however, looks like am headed down that track.

 

[tbone1004]

@Tony Prcevich I would still recommend taking the motor out and send it to a motor repair shop. It may be something in the windings, brushes, etc. that is acting up and causing the excessive heat and shutdown.

 

[Tony Pr]

@tbone1004

Thanks, that will be the next step.

 

[SurfLung]

Good morning scubaboard,
...Given the reduction in pulley size, I would have assumed that there would be a lot less load on the electric motor, therefore would not heat up as much and would run well. Also would be good in terms of heat dissipation on the compressor side, as it is filling slower and allowing more heat to escape before going through the filters. I am not in a rush to fill tanks at this stage...

- A couple of thoughts on cooling the compressor: If you slow down the RPMs, you are also slowing down the cooling fan. I think Tbone has suggested it before that you should add an auxiliary electric cooling fan if you slow down the compressor RPMs.
- Also... If you are operating outdoors, be sure and orient the fan to suck directly into the wind. I have a gas powered MCH-6 and started off orienting it so the exhaust pointed downwind. This positioned the cooling fan sideways to the wind and the compressor ran very hot on a hot day. Then I re-read the instructions and pointed the fan into the wind. This results in a wind assist... I swear the difference was huge. Compressor ran much cooler.

 

[SurfLung]

Good morning scubaboard,
...Started to try and fill some tanks. The PMV is set at 130 bar (1900 psi). Runs for about 25 minutes and then the electric motor cuts out. It feels pretty hot to touch. I assume there is some form of an overload switch inside it. The tank I was trying to fill got to 160 (2320 psi) bar before the electric motor cut out. It just stopped turning. I can spin the compressor fan no problems, so I would not say there is any excessive load on the compressor side (or anything seizing it up). Tried straight after filling a different empty tank, but similar cut out issues after about 3 minutes. I assume this is because of the PMV maintaining the pressure at 130 bar and a relatively high load on the electric motor.

I think that the issue with the motor is load related, as when it goes to compress higher pressures it cuts out sooner.
The internet in all its wisdom says that this compressor can compress to 300 bar, but I would be more than happy with 200 before the electric motor cuts out and needs to be cooled down before working again. Or at least has a rest...

Tony

- This is probably not the problem, but it occurred to me that if the motor is stopping at the same pressure every time... Is it possible you have a pressure switch on this machine and it is simply turning off the power when the pressure reaches 2320 psi? 2320 is pretty close to the 2250 psi standard tank pressure for steel 72 cf tanks that used to be so common.