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Coltri MCH5-EVO, single phase electric motor upgrade, part 1

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  • Coltri MCH5-EVO, single phase electric motor upgrade, part 1

    Remember: use at your own risk. If you're not comfortable or knowledgeable working with electricity or other hazardous things, leave it to the professionals.

    I purchased a used Coltri MCH5-EVO compressor in early 2016 from a guy in Canada; it was sold because the owners truck got totaled. The compressor had less than 100 hours on it, the cost was around $12,000 after shipping/freight.

    Soon after purchase in early 2016, I used this compressor exclusively to fill two dedicated CNG Ford pickup trucks. Both were used as delivery vehicles and racked up high mileage.

    The compressor currently has over 6,500 hours on it. The compressor runs on average about 12 hours a day. Oil changes have been done every 250-350 hours. Basic valve changes on the second and third stages are done at 1000 and 500 hours, respectively. The first stage valve seems good: I visually check it every 2000 or so hours, and it seems to be in good working order.

    Over the last couple of weeks, I have noticed some noise coming from the compressor and discovered that the electric motor manufactured out of Italy by Elprom was on its way out. I called a few electric motor repair places to see if it could be salvaged, but had no luck.

    I purchased a new 182T/184T frame 5 horsepower single phase 3600 rpm motor. It is a sealed non-sparking unit from WEG. The Elprom was 4 horsepower and ran at about 3300 RPM.

    To shorten my fill times I increased the drive speed on this new motor by about 25% to 1600 RPM vs.1250. The old Elprom motor always ran quite high amperage, over 19a it also ran very warm - warm enough to cook your breakfast on. The WEG starts much easier and despite the overdrive always runs under 17 amps, and much much cooler, even after extended fill times.

    The following is a brief synopsis of the transplant:

    The Elprom motor is bolted upside down directly underneath the compressor block. After removing the motor, ground and the two hot wires from the control panel, I removed the compressor cooling fan/pulley from the compressor hub. This required the removal of the four large starplate bolts and the medium sized crankshaft bolt. I then cut out the old motor mount bracket with a Sawzall. I used a pair of vise grips to remove the vertical stabilizer plate from the center of the compressor located directly under the middle of the compressor block; this was accomplished by grabbing the plate and wiggling it back and forth until the welds weakened and snapped off. This allowed for more clearance for the new larger motor.

    I then drilled approximately 10, 1/4" holes in the bottom pan of the compressor to facilitate drainage. My compressor is covered, but I wanted to insure that if any rain made its way into the cabinet it would be able to drain out the bottom. I then reinstalled the compressor fan/pulley back onto the hub.

    After installing 5 feet of 12 gauge 3 wire SOOW cord (less than $2.00 per foot at Home Depot) and 1" strain relief with sealant onto the heavy duty cast iron gasketed WEG conduit box located on the right side of the motor, I installed a 182/184T adjustable motor mount base. This makes belt changes much easier than the original setup, as you can easily move the motor to loosen and tighten the belt.

    Link to Motor Base

    I then installed the motor with base plate into the frame and and marked the location where it aligned best with the compressor pulley.

    After marking the location I removed the motor w/ baseplate and drilled 4, 1/2" bolt holes to accommodate the base plate. I then reinstalled the the motor and secured with 4, 3/4" long, 3/8 stainless steel socket cap bolts with 2 large diameter stainless steel washers on each side, securing on the bottom with stainless steel nylock nuts. the larger 1/2" holes allow for slight adjustability, this allows for minor tweaking in case the belt is not perfectly aligned.

  • #2
    Part 2

    I then installed a new 3/4 inch strain relief in place of the original due to the new cord being slightly larger in outside diameter then the original cord. This is located in the top right corner of the electronics mounting board.

    Then, I installed the ground cable pointed out here with screwdriver and looped it as seen, just as the original ground cable was routed.

    I then installed the two hot wires in the 2/T1 and 6/T3 location.

    I needed a slightly larger belt (A-70) due to the new motor location.

    A-70 Belt Purchased from Amazon

    Finally, I secured the wires together similar to how it was from the factory. and reinstalled the panels.

    The compressor runs exceptionally well, running amperage is just under 17 amps at around 3600-3800 PSI. At 230V the motor is rated for up to 21.85 Amps. I expect more compressor wear due to the added RPM, however the compressor has already paid for itself in the fuel I have saved.

    Altogether, the cost of the new motor and parts was under $650. I have a new high torque XPFC motor that I plan on installing that will be much quieter, but will cost 3 times the price I paid for this motor. It’s currently in production queue and is going to take 2-3 months for build and delivery. This was the best choice that was available until the better motor comes in.

    Along with the motor, I purchased a new taper lock bushing and cast iron pulley. These are much more robust than the supplied aluminum pulley that was originally on the single phase Elprom motor. After removal of the aluminum pulley, I noticed it was slightly bent. The new setup runs much more true and belt slap has been virtually eliminated.

    This is the pulley and hub on the new motor.

    Last edited by Coltri-User; 12-22-2018, 04:04 PM.


    • #3
      very cool only problem I can foresee is the od as you have upgraded your cfm and may build heat just watch cylinder head temp


      • #4
        Thanks for posting this detailed description of your upgrade.


        • #5
          When will part 2 be posted?


          • #6
            Post 2 is now visible. Sorry about the delay. The anti-spam features of our forum software marked it "unapproved" -- likely due to the discussion thread having been started by a new user and having many photos. I upgraded Coltri-User to full access privileges. Post away!


            • #7
              Is the new WEG motor you installed noticeably louder? I have the same model EVO machine as this on my back patio and run it late at night in a residential neighborhood and the noise from it is borderline (almost too loud) with the original Elprom motor. I sure would like to upgrade the motor in mine like you did. The biggest problem I have with mine with the small Elprom motor is getting it to start it in cool weather. The motor is not powerful enough. I have to anticipate pumping gas by preheating the inside of the unit with a heatlamp for an hour or so. This much more powerful motor upgrade would surely cure that problem. Also, what speed (RPM) are you spinning your compressor? These were designed to run at 1200 RPM. I measured mine with a laser tach and the average speed is around 1400 RPM because the Elprom motor was made to run on 50 hertz line frequency and I have 60 hertz power, which speeds it up some.


              • #8
                That is an excellent write up and pictorial. Thanks for posting.

                Did you spend any time diagnosing the original motor? In my experience, electric motors will run indefinitely with periodic bearing replacement. As well thought out as your replacement is it seems like the bearings could be swapped out in an afternoon.

                Regardless of that, it is noteworthy that you are pumping more gas at a lower curent draw. I am too lazy to try and do the math but it would be interesting to know how much your electricity consumption will drop over the course of the year with the high volumes you are pumping.

                This could also be negated should the increased rpm result in increased maintenance costs. I recall finding black carbon deposits on my valves which I presume to be burnt crankcase oil vapor and with higher temps this may increase?



                • #9
                  Calc PulleySizes 160mm @ 3000rpm 1800 Belt.png

                  Calc PulleySizes 190mm @ 3000rpm.png

                  Calc PulleySizes 160mm @ 3000rpm 1782 Belt.png

                  Love the detailed write-up. Don't come on here much these days, and not sure if speed is an issue...
                  I think I said in previous posts, but one the best things I ever did was slow everything down. My MCH5 is now a MCH3. Coltri simply fit a smaller pulley to hte MCH3. So unless you truly need higher fill rates, I'd slow down, not speed-up.

                  Everything runs cooler, and I'm not eating 3rd stage pistons. Current 3rd stage piston now shows blow-by at 1200 hours. At MCH5 speeds I was getting half that. I put a smaller pulley on there a la MCH3.
                  I'd give you the sizing but running a 'Limey' 50Hz over here, means that won't compute 60hz Yankside...

                  MCH3 RPM 1050
                  MCH5 RPM 1250

                  I run 1050. Thus at 50Hz

                  MCH5 3000/1240 = 190mm pulley

                  MCH3 3000/1050 = 160mm pulley

                  These are calcs for 50hz to run at 1050rpm

                  Pics are from a pulley diam/rpm/belt calculator somewhere on interweb. Aim for roughly 1050rpm, but not less. Coltri tech warned me splash lube needs 1000rpm. For me, running overnight, I don't fret if it takes an hour extra to fill.

                  I'm not saying upping the speed is bad, other Coltri models run 1500rpm. Only if you don't truly need 1500rpm etc, knock it back. Cooler is better.
                  Attached Files
                  Last edited by BritCNGUser; 03-29-2019, 03:21 AM.