Off-Cycle Compressor Motor Heat

[Saturatedpsi]

I'm sure some of you are familiar with an old/early method of crankcase heating which energizes the compressor run capacitor during the off cycle. Since the capacitor is in series with the start/aux winding, there is current flow and the winding generates some heat. If not familiar, here's a link explaining it:

Off Cycle Motor Heat (http://www.icemeister.net/files/compressors/copeland/Copeland%20Off%20Cycle%20Crankcase%20Heat.pdf)

For those who are familiar: does anyone know a typical current/amperage value for the circuit?

I've seen a lot of units with this crankcase heating method over the years but never measured the current till yesterday and found it to be 3.0± amps. For some intuitively based reason, I always expected it to be much lower, as some comments I've seen referred to it as "trickle" current...and 3 amps seems more than a "trickle" to me. :confused:

My reason for being on the call in the first place was to investigate a "hum", which turned out to be the off cycle heating arrangement.

The 30µf capacitor "tested" OK, but I tried a new one to be safe, and the amp draw was the same 3 amps. The "running" amps on the aux are 6-7.

It's an old GE unit, some 30 years (believe it or not) and I'm wondering if the motor winding has lost some "integrity" resulting in a higher than normal amperage.

Thanks in advance... ;)

[Grizzly]

Hi.
After 30 yrs. Anything would start to hum!
A trace voltage through the motor windings is as you say quite common On large comps anyway.
However not as efficient as an actual crankcase heater (on small Comps.) I believe.
3A is quite a lot for a crankcase heater system, usually they are 1- 1,5A.

When do you intend to retire the unit?
Grizzly

[Saturatedpsi]

Hi.
After 30 yrs. Anything would start to hum!

3A is quite a lot for a crankcase heater system, usually they are 1- 1,5A.

When do you intend to retire the unit?
Grizzly

Thanks...

I'd have been less surprised with a 1-1.5 amp range reading. :o

Retirement isn't an option for me and I don't force retirement on equipment. So the old GE will run till it expires...which may not be much longer. :D

[Grizzly]

I know you were concerned about the load being drawn.
But Hey as you say "if it isn't broke don't fix it!"
Grizzly

[Saturatedpsi]

I know you were concerned about the load being drawn.


I found some related info that said the power consumption is supposed to be 40w-80w...which obviously ain't much. I know volt-amps and watts aren't the same but at 3 amps, 80 VA would require 90% of the voltage dropping across the capacitor, which I didn't think to measure at the time. The weather in my part of the world is warm anyhow, so I disconnected the heater circuit until I could learn more about what's supposed to be.

But I'm concerned the "hum" is more the result of a stall condition than magnetic flux noise...I also didn't do a ground-fault check on the motor windings. I suppose a high resistance fault could conceivably result in an abnormally high amp draw.

Needless to say, I've got to do some more analysis...

[Saturatedpsi]

Here's a good reference from a Bard manual on the particulars of the off-cycle motor heat wiring connections and some numbers useful in making an intelligent analysis.

15008

[Saturatedpsi]

I went back today and measured 24V between C and S, so the-off cycle heat circuit is performing as it should...or at least close. The 72VA (3 X 24) would probably result in a wattage within design range.

[chemi-cool]

Its an old way to keep the compressor warm instead of a crankcase heater.
Amperes drawn in the US will be higher as they use half the voltage in Europe.

[Saturatedpsi]

Its an old way to keep the compressor warm instead of a crankcase heater.
Amperes drawn in the US will be higher as they use half the voltage in Europe.

I knew what it did...didn't know to what degree it did it. :)

It operates on 240V/60Hz...