Converting three phase power to single phase

W

Whale Rage Forever

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Location
Missouri
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Electrician
I feel like I should definitely know the answers to these questions, but I'm having some trouble.

I have a customer that purchased a second hand 3 phase HVAC condenser that wants to install it in their single phase residential auto garage. I have attached a picture of the nameplate.

1-If it's rated at 60A per phase, for a three phase system that means 180A, right? The nameplate is not as informative as I am used to and research online shows this as being a 5hp unit which is nowhere near that size, so I'm a little confused as to what the actual draw of this unit is. Obviously, the difference in load draw between a 5hp unit and 180A is huge and significant. If it is truly only a 5hp unit which would be like a 15A draw, than why does it specify 60A per phase?
2-If it is a 180A unit, that would mean if I used a phase converter to convert it I would need something sized like this?

Any information would be appreciated.
 

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This requires a 60A three phase _circuit_, not three separate 60A supplies.

It isn't 5 horsepower, it is 5 tons (ish). That unit is large enough to air condition a whole house. It provides more than enough heat for my small New England house on the coldest winter day.

You need to delve into the innards of the unit and find a wiring diagram to see if there are any internal 3 phase loads, and not single phase loads distributed across the 3 phases.

84000 BTU per hour is about 24500 watts, which works out to about 60A at 230V 3 phase. This suggests that for heating the system is just doing straight resistance heating. Resistance heat could be reconfigured for single phase but is terribly inefficient compared to heat pumping. But you won't even need a 60A phase converter; just reconfigure the resistance heat to single phase.

66000 BTU per hour for cooling would need perhaps 20A of 240V three phase (for an old inefficient 3 phase compressor, round numbers), but again I don't know the details of the unit. It might have a single phase compressor.

-Jonathan
 
winnie said:
This requires a 60A three phase _circuit_, not three separate 60A supplies.

It isn't 5 horsepower, it is 5 tons (ish). That unit is large enough to air condition a whole house. It provides more than enough heat for my small New England house on the coldest winter day.

You need to delve into the innards of the unit and find a wiring diagram to see if there are any internal 3 phase loads, and not single phase loads distributed across the 3 phases.

84000 BTU per hour is about 24500 watts, which works out to about 60A at 230V 3 phase. This suggests that for heating the system is just doing straight resistance heating. Resistance heat could be reconfigured for single phase but is terribly inefficient compared to heat pumping. But you won't even need a 60A phase converter; just reconfigure the resistance heat to single phase.

66000 BTU per hour for cooling would need perhaps 20A of 240V three phase (for an old inefficient 3 phase compressor, round numbers), but again I don't know the details of the unit. It might have a single phase compressor.

-Jonathan
Click to expand...
I am fairly certain that it is a 3 phase compressor. It's an old military field deployable environmental control unit that they bought from surplus or some such.

Your numbers align with what I was thinking.

60A x 230V x 1.73 = 23874...which is roughly equivalent to your estimation from the heating BTU.

Does that mean that this unit would require a 100A breaker and circuit wiring to safely feed a phase converter? 23,874 / 230V = 103.78A

Am I correct? That's a pretty big unit for just a garage. I doubt this guy is going to want to have to upgrade his entire service for a $400 surplus condenser he bought without knowing whether it even works.
 
Whale Rage Forever said:
I feel like I should definitely know the answers to these questions, but I'm having some trouble.

I have a customer that purchased a second hand 3 phase HVAC condenser that wants to install it in their single phase residential auto garage. I have attached a picture of the nameplate.

1-If it's rated at 60A per phase, for a three phase system that means 180A, right? The nameplate is not as informative as I am used to and research online shows this as being a 5hp unit which is nowhere near that size, so I'm a little confused as to what the actual draw of this unit is. Obviously, the difference in load draw between a 5hp unit and 180A is huge and significant. If it is truly only a 5hp unit which would be like a 15A draw, than why does it specify 60A per phase?
2-If it is a 180A unit, that would mean if I used a phase converter to convert it I would need something sized like this?

Any information would be appreciated.
Click to expand...
There is no easy (read: inexpensive) way to do this. You cannot make three phase power from a single phase source with, for example, a transformer.
 
ggunn said:
There is no easy (read: inexpensive) way to do this. You cannot make three phase power from a single phase source with, for example, a transformer.
Click to expand...
Correct. And you (OP) are correct on the service issue, albeit the source would have to be a 150A single phase circuit (103A x 125% = 128.75A minimum circuit size).

The choices for converting are:
  1. A "Rotary Phase Converter", of which there are several variations, all of which in some way spin a 3 phase motor fed from a single phase source or "pony motor" to create a voltage on the missing phase. They are around 85% efficient, so the long term costs to run a 3 phase unit will be higher than expected.
  2. A "Static Phase Converter", which only works for motors (not heating elements) by tricking the 3 phase motors into THINKING it has the missing phase, using capacitors. Also inefficient.
  3. An "Electronic Phase Converter" that replicates the missing phase using inverter technology JUST for that one phase. More efficient, more expensive, but again, only works for motors.
  4. A VFD, which takes in the single phase, converts it to DC, then inverts the DC back into 3 phase AC. Very efficient, but still, only good for a SINGLE motor.
So options 2 through 4 will require digging into the power circuitry of the unit to separate out the 3 phase motor circuits from things like controls, heating elements etc. All 4 options will require reconfiguring the control power to ensure that it comes ONLY from the two "real" legs of AC.

Choice 5 is... petition the utility to drop 3 phase power to the customer and hope he has a spare $20k+ to waste on that..

Choice 6 is... don't try to use a large 3 phase unit in a place that only has a single phase service.
 
Whale Rage Forever said:
I am fairly certain that it is a 3 phase compressor. It's an old military field deployable environmental control unit that they bought from surplus or some such.

Your numbers align with what I was thinking.

60A x 230V x 1.73 = 23874...which is roughly equivalent to your estimation from the heating BTU.

Does that mean that this unit would require a 100A breaker and circuit wiring to safely feed a phase converter? 23,874 / 230V = 103.78A

Am I correct? That's a pretty big unit for just a garage. I doubt this guy is going to want to have to upgrade his entire service for a $400 surplus condenser he bought without knowing whether it even works.
Click to expand...

My _guess_ if it is a 3 phase compressor, then the compressor uses something like 7 or 8 kW, not the full 24kW. My _guess_ is that the full 24 kW is for resistive heat.

If I were going to make this work hell or high water, I'd only provide the phase conversion for the compressor, and I'd re-work the resistive heat for single phase operation.

-Jonathan
 
Well it looks like the system can draw up to 35A to run the cooling system, in the worst case:

And apparently it is capable of reversing the refrigerant flow to function as a heat pump.

According to Danfoss, a refrigeration compressor is a constant torque load.
www.danfoss.com

Using VFDs in Refrigeration and Cold Storage Applications (1)

www.danfoss.com

However you can't simply dial back the compressor speed on a refrigeration system to get less cooling. You also need to adjust the 'expansion valve' to match the change in refrigerant flow. So for this application the VFD would be forced to run pretty close to constant frequency.

-Jonathan
 
This job sounds like a loser. Get a big wad of cash upfront before you even start. How do you know the junk even works?

I'd walk away.

Tell him to buy a diesel powered AC unit at the military auction next time. Or get a Thermoking unit off a trailer and mount it into his garage wall
 
Joethemechanic said:
This job sounds like a loser. Get a big wad of cash upfront before you even start. How do you know the junk even works?

I'd walk away.

Tell him to buy a diesel powered AC unit at the military auction next time. Or get a Thermoking unit off a trailer and mount it into his garage wall
Click to expand...
I think it sounds like fun.
But…
A LARGE upfront payment without even a taillight warranty.

Cost effective for the customer? Nope.
 
ptonsparky said:
I think it sounds like fun.
Click to expand...
Sure I could make it work, and enjoy doing it, but this guy is never going to pay for all the time and materials, and it will never be efficient. God only knows if it is efficient running on three phase. And does this guy even have enough single phase power to run it? I's got to require mat least a 125 amp 240 single phase circuit to make it all work.Screenshot 2025-09-11 161759.png

I was wrong. try 160 input
 
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For what it would cost for phase conversion and everything, a Mr. Cool mini split would be much more economical, install wise and power consumption wise. You can get precharged line sets with it, so you don’t even have to involve a hvac tech.
 
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