3 phase converter/2 loads

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TwinCitySparky

TwinCitySparky

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Minnesota
I tried to make this short..:rolleyes:. I have an a low budget customer with a boat resto. shop. He has air files, DA's and paint guns being used. He moved the 20 HP converter/10 HP scroll compressor set-up from one shop to another and I wired them back in. Now he wants more air for some big upcoming projects. At first he was eyeing up some 30 HP scroll units - I said No WAIT! Gonna need way bigger converter, wiring etc.. Gotta research, dont buy yet! Next thing I know, he sais he called Quincy compressors and they say you can run another 10 HP scroll off that 20HP converter. So he finds a identical 10 HP scroll, buys it and calls me with the news. Service is 120/240 single phase. Scroll units start/stop automatically. Start inrush current (on existing set-up) is about 180 amps then it drops to about 45 amps per leg (combined converter/scroll load)- My reserch so far has found that you can combine loads like this with the 20 HP converter as long as both loads dont start at same time. (kinda figured that part) I was going to try to find some "off the shelf unit" to toggle power between the two pressure switches for that reason. Now he sais - lets wire these so first unit comes up to operating pressure, then ONLY when the first it is running and not keeping up will we have the second one start up and assist the first as it is running. :confused: Is there such a control? Any other suggestions for verifying circuit size etc.? Thanks
 
if I am picturing this right you should be able to make it work by tapping off the coil of the starter on the first compressor, and feeding it through a pressure switch to control the coil on the second compressor.
 
If they are tied to a common air line, you should be able to adjust the pressure switches to different cut in pressures, as pressure drops, the first one cuts on, if the pressure continues to drop, the second one cuts on. A more complicated scheme would to be add an alternating relay to reduce wear on the primary compressor.
 
hillbilly1 said:
If they are tied to a common air line, you should be able to adjust the pressure switches to different cut in pressures, as pressure drops, the first one cuts on, if the pressure continues to drop, the second one cuts on.
Click to expand...
That's what I was thinking, too.
 
hillbilly1 said:
If they are tied to a common air line, you should be able to adjust the pressure switches to different cut in pressures, as pressure drops, the first one cuts on, if the pressure continues to drop, the second one cuts on. A more complicated scheme would to be add an alternating relay to reduce wear on the primary compressor.
Click to expand...


This might work if they didn't shut them down at night.

During morning start-up - both pressure switches would be in the start position calling for air right? The converter (and possibly service) wont like that. I know I could make it work with a timer or two, I just dont want to re-invent the wheel -

(If it's out there..) :confused:
 
TwinCitySparky said:
This might work if they didn't shut them down at night.

During morning start-up - both pressure switches would be in the start position calling for air right? The converter (and possibly service) wont like that. I know I could make it work with a timer or two, I just dont want to re-invent the wheel -

(If it's out there..) :confused:
Click to expand...

I started to put that disclaimer in there, but I'm bad to run on and on in my posts, if there shutting them down manually at night, then it should be no problem starting them manually in a sequence.
 
hillbilly1 said:
if there shutting them down manually at night, then it should be no problem starting them manually in a sequence.
Click to expand...

how about a time delayed relay and a normally closed contactor? when they turn the switch on first thing in the morning, the primary compressor comes on, and the contactor opens for a pre-set time allowing the pressure to build up, then the contactor closes allowing the secondary compressor to kick in when needed.
 
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Ultra

Not bad idea - Glen and I were kicking that one around.

Funny how these things go. Owner asks me to design it and gives me a week. Next thing I know he has a sales guy from Quincy come out and design the whole thing from the vented room for all the equipment to the switching sequence right down to conductor sizing :-? The guy knows his "stuff"

Next time me thinks I make the call first - mans got to know his limitations. I found another one of mine.

;)

Thanks anyway everyone!
 
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