# Compressor loader/unloader motor



## erics37 (May 7, 2009)

Unfortunately this thread would be MUCH better with pictures, but alas, I didn't take any. I will try to keep it quick.

At the fish plant - the same one with that confounded blast freezer motor that many of you offered advice on - there is a pair of big ol' compressors for their ammonia-based refrigeration system. Like, really old. They look like they came off a World War 2 battleship, and more or less run like they did too.

I was lucky enough to dig up a proper wiring diagram of the thing recently, which is what I intended to take a good photo of but wound up forgetting. There is an issue with the load/unload system.

Long story short, the loading system was not working as intended and the compressor wound up shutting off as safety cut-outs tripped. Once they figured out what was wrong, they manually cranked the loader motor shaft as needed, and called me out to see what was up with it. I wound up staring at the wiring diagram for a good 15 minutes trying to make sense of part of the circuit (here is where I wish I had a damn picture).

The control circuitry is 120 VAC. A quick metering through the primary cut-out circuit indicated everything was closed or open as it should be. Control relays and such all actuated properly. I noticed a crappy old terminal strip in the control box all loaded up with like half a dozen diodes and a capacitor. It looked like something your grandpa would rig up in his workshop to boost his HAM radio or something. Really ghetto. After staring at the wiring diagram for a few minutes I realized that it was the world's crudest rectifier. WTF is it for? Well I got my flashlight and monkeyed my way through the plumbing and took a look at the loading motor: 115 VDC. Ah ha!

So this ghetto rectifier is making DC for this little motor, presumably for ease of switching direction depending on loading/unloading requirement for the compressor at a given time. Sure enough, testing the control circuit found that if you use the manual loading/unloading switch, the DC voltage changes polarity to the motor. There is also a cluster of limit switches mounted around the loading motor for max/min position and also extra safeties for overtorque. All of those work fine. Ultimately, the little motor is receiving DC voltage but isn't spinning. Pulled the brushes out and they are fine. Manually cranked the shaft which is connected through a gearbox. It all turns.

So... bad little DC loading motor? Anyone seen that sort of thing before with the ghetto rectifier circuit and such?


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## Big John (May 23, 2010)

Get an incandescent drop light and hook it to the output of that rectifier. Put your voltmeter on it and turn on the lightbulb. Read your DC voltage. Switch to AC and read that to see how much ripple is present. It sounds like it should be pretty solid, pure DC, but if the DC supply is that cobbled god knows if you've got a diode gone or a shorted capacitor or some damn thing that's messing up the output.

Measure resistance across the disconnected motor leads and slowly spin the rotor 360° and look for a bad spot in the commutator. I once about defenestrated myself over a small DC motor that would work great 99.9% of the time and sometimes wouldn't start when the brush was sitting on a high resistance point in the com.

Check the circuit that switches polarity, and preferably do it with your drop light connected so you can load it up and don't miss a high-resistance contact that a DMM won't see.

The other option is to get a little bridge rectifier from Radio Shack and plug this into the wall and connect it to the motor. If the motor spins, your problem is in your controls.


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## micromind (Aug 11, 2007)

When you test resistance across the motor and spin the shaft, the motor will become a generator. An analog ohmmeter is much better than digital. 

I agree with using a 100 watt incandescent light for troubleshooting 120DC circuits. 

Very often, bad semiconductors (diodes) will read ok with a meter, but will fail under load.


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## Big John (May 23, 2010)

Two very critical things I forgot to mention:

1) When we get pictures of the control diagram, one had better include Hot QC Girl.
2) This fish plant is whooping your ass.


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## micromind (Aug 11, 2007)

erics37 said:


> Anyone seen that sort of thing before with the ghetto rectifier circuit and such?


Seen it.....I've done it!!!

Old machines that had 120VDC solenoids, CNC machines that used 90VDC positioning motors, stuff like that. But instead of single diodes, I usually use 4 terminal bridge rectifiers. 

Generally speaking, DC motors don't need much filtering of the DC, they can handle a lot of ripple. Solenoids though, need pretty good DC or they'll buzz and hum and overheat.


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## erics37 (May 7, 2009)

Big John said:


> Two very critical things I forgot to mention:
> 
> 1) When we get pictures of the control diagram, one had better include Hot QC Girl.
> 2) This fish plant is whooping your ass.


1) I hadn't seen her in a while because she works at the shrimp plant down the street, and I have been working at the fish plant lately. However the other day I had to go down there because they had a tote dumping machine break down. She was really excited to see me because one of her metal detectors in the processing room wasn't working and she wanted me to look at it. A little while later she was standing around staring off into space and I went up and asked her, "WTF is your deal?" (that's my way of being sensitive and inquiring about her feelings) and she vented at me for 15 minutes about how no one else there pulls their weight and she is over extending herself trying to cover other people and so forth, blah blah blah. Then she started complaining that some of the workers have been literally F*CKING IN THE SUPPLY CLOSET and how gross it was!!! I was immediately distressed because that was my plan all along; get to know her a bit, get her comfortable around me, and then ask if she wants to go f*ck in the supply closet. God dammit.

Anyway she was really grateful for me letting her vent and yadda yadda yadda and now she gets all flirty with me. On Friday it was raining and I only had a t-shirt on and she walked by on the sidewalk and said, "Heeeeeeeey too bad your t-shirt isn't white!" and I said, "I'll take all my clothes off right here on the street I don't give a f*ck do you do anal?" but all that came out was "Duhhhh"

2) Sort of kicking my ass! You guys only get to hear about the stuff that's really messed up. The aforementioned tote dumper was a breeze. Maintenance guys thought it was the drive, then thought it was the motor brake, then thought it was single-phasing, etc etc. Proved them all wrong and diagnosed the issue in about 10 minutes: bad proximity sensor (it had gotten full of water and corroded up).

This week I wired a new condensor/evap combo for a big drive-in freezer they are converting. Went like a breeze. There are always random little things going wrong everywhere so I spend a good chunk of time putting out fires when they pop up.

But you are definitely right about this old Mighty Mo surplus refrigeration system. Geez. I'm getting sodomized by it.


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## Big John (May 23, 2010)

erics37 said:


> 1) I hadn't seen her in a while because she works at the shrimp plant down the street, and I have been working at the fish plant lately. However the other day I had to go down there because they had a tote dumping machine break down. She was really excited to see me because one of her metal detectors in the processing room wasn't working and she wanted me to look at it. A little while later she was standing around staring off into space and I went up and asked her, "WTF is your deal?" (that's my way of being sensitive and inquiring about her feelings) and she vented at me for 15 minutes about how no one else there pulls their weight and she is over extending herself trying to cover other people and so forth, blah blah blah. Then she started complaining that some of the workers have been literally F*CKING IN THE SUPPLY CLOSET and how gross it was!!! I was immediately distressed because that was my plan all along; get to know her a bit, get her comfortable around me, and then ask if she wants to go f*ck in the supply closet. God dammit.
> 
> Anyway she was really grateful for me letting her vent and yadda yadda yadda and now she gets all flirty with me. On Friday it was raining and I only had a t-shirt on and she walked by on the sidewalk and said, "Heeeeeeeey too bad your t-shirt isn't white!" and I said, "I'll take all my clothes off right here on the street I don't give a f*ck do you do anal?" but all that came out was "Duhhhh"


 I'm sitting in a coffee shop and the more I read, the harder I laughed, and now people are staring at me the way they always do when some idiot is sitting there laughing to himself. Good job.


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## BT Electric (Feb 7, 2014)

erics37 said:


> Anyone seen that sort of thing before with the ghetto rectifier circuit and such?


Seen it and done it as well! Worked on some old 200HP DC motors driven by large M-G sets and giant Powerstat rheostats that were turned by 120V DC motors with gearboxes just like you have described. They dated from the 30's and 40's. Kept the controls going with hand built rectifiers, hopefully not that ghetto though! I always built them on a breadboard and soldered all the components.


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## dronai (Apr 11, 2011)

erics37 said:


> 1) I hadn't seen her in a while because she works at the shrimp plant down the street, and I have been working at the fish plant lately. However the other day I had to go down there because they had a tote dumping machine break down. She was really excited to see me because one of her metal detectors in the processing room wasn't working and she wanted me to look at it. A little while later she was standing around staring off into space and I went up and asked her, "WTF is your deal?" (that's my way of being sensitive and inquiring about her feelings) and she vented at me for 15 minutes about how no one else there pulls their weight and she is over extending herself trying to cover other people and so forth, blah blah blah. Then she started complaining that some of the workers have been literally F*CKING IN THE SUPPLY CLOSET and how gross it was!!! I was immediately distressed because that was my plan all along; get to know her a bit, get her comfortable around me, and then ask if she wants to go f*ck in the supply closet. God dammit.
> 
> Anyway she was really grateful for me letting her vent and yadda yadda yadda and now she gets all flirty with me. On Friday it was raining and I only had a t-shirt on and she walked by on the sidewalk and said, "Heeeeeeeey too bad your t-shirt isn't white!" and I said, "I'll take all my clothes off right here on the street I don't give a f*ck do you do anal?" but all that came out was "Duhhhh"
> 
> ...


We need to hear how this pans out


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## erics37 (May 7, 2009)

*Ladies and gentlemen, here are pictures*

Was running errands in town and stopped by there to take pictures and grab the wiring diagram so I could scan it. Sorry, QC girl wasn't working today 

Here is our ghetto rectifier










This control panel is a real beauty. Date on the wiring diagram says 1979 for what that's worth.










Front cover










Here is the motor in question. It looks pretty darn new. Of course it spent most of its life covered up with an enclosure of some sort, but still. Newer motor might indicate some other issue if it's not working. It's in a difficult spot, sorry for the crap pictures.



















And the diagram. First image is the wiring schematic. Second image is the panel layout, plus it has some details on the actuating motor safety and position limit switches. Our load/unload motor circuit begins around line 25 or so.


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## micromind (Aug 11, 2007)

First thing I'd check is DC voltage from 55 to X2 when the load-auto-unload switch is in the load or unload position. 

If it's in unload, and it's not at the unloaded limit, 55 should be positive and X2 negative. 

The load position would be opposite polarity. 

Also, check DC current on 55 going to the motor when it's trying to move. 

Since this is half-wave DC, the waveform will look kinda like continuous boobs on a scope. 

If you have DC on 55 and no current, then the motor would be my prime suspect, but I'd connect an incandescent lamp from 55 to X2 to prove actual power. 

If the motor is actually cooked, when the replacement is installed, make sure the limits actually kill power so the motor isn't up against end travel and burning itself up.


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## erics37 (May 7, 2009)

micromind said:


> First thing I'd check is DC voltage from 55 to X2 when the load-auto-unload switch is in the load or unload position.
> 
> If it's in unload, and it's not at the unloaded limit, 55 should be positive and X2 negative.
> 
> The load position would be opposite polarity.


Actually I did do this, and DC voltage is present. In fact, the motor was connected with some little crimp spade terminals so I unplugged it and measured voltage right there. DC voltage is present at the motor and it does indeed change polarity when switched from load to unload or vice versa. I did not, however, try it with an incandescent light bulb.



> Also, check DC current on 55 going to the motor when it's trying to move.
> 
> Since this is half-wave DC, the waveform will look kinda like continuous boobs on a scope.
> 
> If you have DC on 55 and no current, then the motor would be my prime suspect, but I'd connect an incandescent lamp from 55 to X2 to prove actual power.


I tested for current as well. Actually used a series amp meter and tried it both directions, and no current.



> If the motor is actually cooked, when the replacement is installed, make sure the limits actually kill power so the motor isn't up against end travel and burning itself up.


There are a few limit switches mounted on the gear assembly that the motor shaft is connected to. One is for minimum position, one is for maximum position, and then there are also a set of "overtorque" switches in case the motor tries to keep going. I tested all these and they appear to work, so theoretically the motor shouldn't be able to just keep cranking.


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## micromind (Aug 11, 2007)

This is pointing strongly toward a bad motor.


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## JRaef (Mar 23, 2009)

I used to have to work on crap like that used in big sterilizers; motorized valves that redirected steam to different parts of the autoclave based on where the valve stopped in rotation because it had these really complex machined ports in it. Fricken PITA. I did a lot of work at that time for a company that rebuilt these autoclaves, so I came up with a system of simpler separate motorized ball valves because they were a lot more reliable. Not saying you should do that, just commiserating on what pain these things can be. The motors are often very specialized, and you might find that the OEM no longer exists unfortunately. If you do, and you have to devise a replacement, I suggest using separate motorized ball valves made by Apollo, great stuff.


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## erics37 (May 7, 2009)

JRaef said:


> I used to have to work on crap like that used in big sterilizers; motorized valves that redirected steam to different parts of the autoclave based on where the valve stopped in rotation because it had these really complex machined ports in it. Fricken PITA. I did a lot of work at that time for a company that rebuilt these autoclaves, so I came up with a system of simpler separate motorized ball valves because they were a lot more reliable. Not saying you should do that, just commiserating on what pain these things can be. The motors are often very specialized, and you might find that the OEM no longer exists unfortunately. If you do, and you have to devise a replacement, I suggest using separate motorized ball valves made by Apollo, great stuff.


Fortunately that's not my deal :thumbup: The refrigeration contractor is the one officially on the hook for getting this thing working.


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## JRaef (Mar 23, 2009)

Perfect!


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## Big John (May 23, 2010)

That flow-sheet is hanging on my bulletin board. 

I saw one yesterday outside a bar:

......Do You Want Beer?
....._________|________ 
.....|..........................|
....Yes.......................No
.....|..........................|
.....|...................Yes, You Do
.....|.....................Don't Lie
.....|________________|
...................|
.............Buy A Beer

Can't argue with that.


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