# Guess how many Amps this 220 VAC HVAC motor draws at 110 VAC?

Guess how many Amps this 220 VAC HVAC motor draws at 110 VAC?
After running a GE 5KCP392G M730BS fan/motor (salvaged from a
condenser) for a week at 110 VAC, and after all the naysayers said it could not be done, I finally meaured the current.
There was no large insurge of current as seen on an analog 0-30 Amp Simpson meter.
The spec on the motor reads 208-230 VAC 1.9 Amp
It has a run cap of 5 mfd/370 V
BTW The motor case was hot but I could still hold my hand on the metal case.
. The motor starts easily and runs smoothly and quietly at 110 VAC
What is your estimate of the Amp draw at 110 VAC?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>

My guess would be between 3 and 4 amps.
These motors are routinely slowed down by effectively decreasing the voltage ("effectively" means by putting more turns on the windings.)
A "high slip" motor slows down with decreased voltage.
A "low slip" motor doesn't slow down as much but, rather, "sucks" more current from the supply.
Single speed motors tend to be "low slip" for efficiency reasons. When you reduce the voltage they tend to maintain speed (slight "droop" of course but not much). With nearly the same speed they have nearly the same load and must draw nearly the same power. With reduced voltage the motor draws more current to keep the VAs constant. That would be "OK" except that the heating of the wirings is proportional to the square of the current (I^2*R).
Single speed induction motors run at reduced voltage tend to overheat and have a much shorter life.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
| Single speed induction motors run at reduced voltage tend to overheat and | have a much shorter life.
Even when a motor normally expecting 240 volts get connected to 208. Even with this little of a voltage drop, there's 33% more heating due to I^2*R. In extreme usage (continuous operation in high ambient heat) they can burn out with even a 15.47% voltage decrease. I know this from experience.
This is why I believe that switching from 240CTD/120 to 208Y/120 is a bad idea. It means we have yet another voltage to worry about and many things have to be made for both 240 volts and 208 volts. We need to reduce the number of voltages available, not increase them. And that can be done while eliminating delta services.
Power companies do want to reduce the costs by eliminating 240CTD/120. But they should not do so by passing the costs on to the customers.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>

I won't try to estimate the current as it depends on the load. In general:
Lower no-load current at 110V -due to a lower magnetising current. Full load current will be higher. There is some in between load where there is the cross-over. Note that available torque will be lower so that the motor won't drive a fan as fast as it would at 220V and with some loads might not start.
I note that you have not given any load measurements.
Note that Ohm's Law doesn't apply to motors except at standstill (where the inrush occurs) .
--

Don Kelly snipped-for-privacy@shawcross.ca
remove the X to answer
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
snipped-for-privacy@aaronj.com wrote:

is there a prize involved?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
TimPerry wrote:

This is a motor turning fan blades 1075 rpm at 220 VAC.
The prize is knowing the parameters when running a split capacitor 220 VAC HVAC motor at 110 VAC.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
snipped-for-privacy@aaronj.com wrote:

I would say about 4 amperes. You can do strange things with motors. In 1975 I ran a 120 volt motor on single phase 208 using a variac. It was used by painters painting a fuel line that ran about a mile out across the tundra at the Pow 2 Dewline site in Alaska. I ran a 1500 foot No. 14 extension cord to the paint motor and set the input voltage at about 180 volts from a 208 volt volt supply. The motor ran fine for about 4 hours then burn up!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
snipped-for-privacy@electrician2.com wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
snipped-for-privacy@aaronj.com wrote:

If the motor runs at the same speed the electrical power would stay the same - resulting in high current - would saturate the iron?
But if the RPM went down the power could go down a lot. If the motor is still running a fan - IIRC the mechanical power is proportional to the 4th power of the RPM. A relatively small change in RPM could produce a large change in mechanical power used, and electrical power, and current. Could run below 1.9A? The temperature would indicate that happened.
bud--
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
wrote:

-------- No saturation- flux density proportional to voltage for AC machines.
--

Don Kelly snipped-for-privacy@shawcross.ca
remove the X to answer
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Don Kelly wrote:

Magnetics is not one of my storng points. Isn't flux density proportional to Ampere turns [until saturation]?
bud--
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>

Yep! The key word is "net."
For an example, you might have a transformer where with no load it would only take a fraction of an amp to saturate the iron. Yet the transformer can easily draw many amps in service. The secondary amps cancel the primary amps.
In an induction motor there are currents "induced" in the rotor. For "saturation" considerations, these cancel the current in the windings.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
| Don Kelly wrote:
| |>>If the motor runs at the same speed the electrical power would stay the |>>same - resulting in high current - would saturate the iron? |> |> -------- |> No saturation- flux density proportional to voltage for AC machines. | | Magnetics is not one of my storng points. Isn't flux density | proportional to Ampere turns [until saturation]?
Yes, it is proportional to current until the saturation is reached. With an unloaded transformer, that is also proportional to voltage. And it is inversely proportional to frequency because the impedance goes down and current goes up at a lower frquency. But as soon as you put a load on the transformer, the secondary current flows in the opposite direction and cancels out the magnetic field. Then more current flows on the primary and brings it back, along with a wee bit more that keeps the core magnetized.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
wrote in message

--------- Not for AC excitation. For a sine wave Erms =4.44FNABmax so at a given area A, frequency f turns N, and applied voltage E, Bmax is determined. If the voltage alone is halved, then so is Bmax. This is based on Faraday's Law. Note that the core material and magnetic path don't enter into this. What they do is determine the magnetising ampere turns required at a given Bmax. A wood core excited at 60Hz, 120V will have an exciting current that is about 5000 times that of a transformer steel core of the same size but the same Bmax.
What you say is true for DC but Faraday's law doesnt' apply there.
--

Don Kelly snipped-for-privacy@shawcross.ca
remove the X to answer
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Don Kelly wrote:

Thanks to all 3. What I missed was the (now) obvious rotary transformer action, with Faraday's law as a further detail.
bud--
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
| A wood core excited at 60Hz, 120V will have an exciting current that is | about 5000 times that of a transformer steel core of the same size but the | same Bmax.
I bet that would be exciting, if the source has the available current and the wiring leading to it is short enough and big enough, and none of those pesky fuses or circuit breakers is in the way.
What if the steel core is actually laminated or insulated steel wire wound continuously in the shape of the core, with the ends connected?
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
wrote:

---------- The magnetising current would still depend on the material - whatever its B-H curve is. I should hope that the core is laminated. The steel wire core would work and I think that the original transformer may have had such a core. The connection at the ends really wouldn't matter. I note that continuous strip wound cores are being used and it is a hell of a job to connect the ends other than making a multiturn Moebus strip:).
--

Don Kelly snipped-for-privacy@shawcross.ca
remove the X to answer
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
| wrote: |> |> | A wood core excited at 60Hz, 120V will have an exciting current that is |> | about 5000 times that of a transformer steel core of the same size but |> the |> | same Bmax. |> |> I bet that would be exciting, if the source has the available current |> and the wiring leading to it is short enough and big enough, and none |> of those pesky fuses or circuit breakers is in the way. |> |> What if the steel core is actually laminated or insulated steel wire |> wound continuously in the shape of the core, with the ends connected? | ---------- | The magnetising current would still depend on the material - whatever its | B-H curve is. I should hope that the core is laminated. The steel wire core | would work and I think that the original transformer may have had such a | core. The connection at the ends really wouldn't matter. I note that | continuous strip wound cores are being used and it is a hell of a job to | connect the ends other than making a multiturn Moebus strip:).
What I was wondering is the physic of the flux loop ... if it had to be connected back to itself directly in the same material, or if there would be any difference in the fact that it went to a "different" wire the next pass around. I would think wire would help cut down hysteresis loss.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>

The flux doesn't follow a wire round and round as implied by the looping. Take a cross section of the wire core - it appears as a number of parallel flux paths. Ideally it would be nice to have the ends of the wired joined as when they aren't the flux coming to an end has to cross over to adjacent wires so for a short distance the flux distribution is not uniform. In practice this is negligable with many turns of wire. Note that with laminated cores, the laminations are not continuous but the layers overlap so flux has to cross over from one layer to the next through the varnish gap between layers.
The main problem with a wire core is that good magnetic material is also relatively brittle. A thin flat strip is easier to roll than a wire of the same cross-section in that case and (I haven't worked this out) will have lower eddy current losses (longer eddy current path and higher resistance for a given cross-section and voltage induced in the path.) Use of wire wouldn't reduce hysteresis loss per se but it would reduce eddy current losses compared to a solid core but possibly not as much as with a rolled strip or conventional laminations. These are likely the historical reasons why wire cores are not seen nowadays.
--

Don Kelly snipped-for-privacy@shawcross.ca
remove the X to answer
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
| The flux doesn't follow a wire round and round as implied by the looping. | Take a cross section of the wire core - it appears as a number of parallel | flux paths. Ideally it would be nice to have the ends of the wired joined as | when they aren't the flux coming to an end has to cross over to adjacent | wires so for a short distance the flux distribution is not uniform. In | practice this is negligable with many turns of wire. Note that with | laminated cores, the laminations are not continuous but the layers overlap | so flux has to cross over from one layer to the next through the varnish gap | between layers.
So with a bunch of wires, which would be more distinctly separate parts of the core, the flux is always going to cross over anyway? So it really won't matter if this is 1000 tiny steel wire loops, or one long wire that loops around 1000 times.
| The main problem with a wire core is that good magnetic material is also | relatively brittle. A thin flat strip is easier to roll than a wire of the | same cross-section in that case and (I haven't worked this out) will have | lower eddy current losses (longer eddy current path and higher resistance | for a given cross-section and voltage induced in the path.) Use of wire | wouldn't reduce hysteresis loss per se but it would reduce eddy current | losses compared to a solid core but possibly not as much as with a rolled | strip or conventional laminations. These are likely the historical reasons | why wire cores are not seen nowadays.
My ultimate experimental idea is to have a topology where the core itself spirals around the windings, which also spiral with it. It would be kind of like those double-pretzel sticks where 2 pretzels wrap around each other. Or like how certain snakes make love. This would then be wrapped around to connect on the ends. Topologically, the windings do wrap around the core wires, so there should be an induced magnetic field. Then the field itself would be a spiral.
Then the next trick would be to use insulated steel wire and make it wrap around itself in a double-Mobius fashion. So if you follow a bundle of wires around, you go around twice to get back to the same spot. This whole circle would be all a bunch of spirals. The steel wires would be both the electrical winding and the core at the same time. I have no idea if that could possibly work. But mentally picturing the topology tells me it should. Of course steel is not as good a conductor as copper so this is not likely to be of any practical value on a large scale.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>

## Site Timeline

• Share To

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.