What happens when you run a 240V motor at 120V

DCContrarian

I have the opportunity to buy a small air handler with a four speed motor. It's not very big, it's only rated for 40VA and on the highest speed the unit is 300 CFM. But it's rated for 240V and I can only get 120V to the spot where I want to put it.

So what will happen if I wire it to 120V? Will it run at half speed? Same speed but twice the current? Blow up? Or do I have to try it and see?

I know that if it draws the same 40VA it will double the current, but only from 0.16A to 0.33A. So burning out the wiring is a concern. But looking at an ampacity table even a 32ga wire would be able to handle that, at a certain point the wire has to be big enough to prevent breaking and I think I'm probably past that.

Thoughts?

pecmsg

Over amp and burn out. If it starts at all!

ChrisJ

If you don't mind me asking, you have me curious, what kind of air handler is only 300 CFM?

pecmsg

And what motors have a VA rating? That’s transformers. 

GGross

ChrisJ said:

If you don't mind me asking, you have me curious, what kind of air handler is only 300 CFM?

perhaps a small concealed ducted mini split indoor unit. Most would probably call it a "fan coil" rather than air handler. something like this maybe https://www.supplyhouse.com/LG-LMDN097HV4-9000-BTU-Flex-Multi-F-Ceiling-Concealed-Duct-Air-Conditioner-Heat-Pump

DCContrarian

ChrisJ said:

If you don't mind me asking, you have me curious, what kind of air handler is only 300 CFM?

It's a hydronic fan coil unit.

ChrisJ

pecmsg said:

And what motors have a VA rating? That’s transformers. 

I'd think any inductive load could have a VA rating.

mattmia2

It depends on what type of motor it is.

DCContrarian

mattmia2 said:

It depends on what type of motor it is.

It's a four-speed motor. It has a wire for each speed, yellow, red, blue and black, and a white common. Does that help?

Jamie Hall

Without knowing what type of motor it is, it isn't possible to say what will happen. As a very broad generalisation, an AC induction motor -- shaded pole, split phase, that sort of thing -- may run, but with very low starting torque and running torque. Most likely won't run at all. An ECM motor probably won't run at all. However, a "universal" motor (characterised by the presence of a commutator, among other things) will likely run fine, but at a low speed and torque.

DCContrarian

OK, it looks like it's a permanent split capacitor (PSC) induction motor. A little internet reading tells me that the speed of each winding is entirely determined by the frequency of the power supply. At a lower voltage it runs at the same speed and same power, so a higher current. The only question would be whether the windings can handle the higher current. I don't see a way of finding out other than trying.

ratio

At 40 VA, you should be able to find some kind of transformer that will work. https://www.ebay.com/itm/266090802476 for instance.

Shoot us a pic of the nameplate or something.

PRR

At 40VA, you could just use a transformer. Or any 2-winding 120V:240V transformer primary rated over 20VA.

JUGHNE

What does it say on the name plate of the motor. Not necessarily the nameplate of the air handler.
The transformer, if it has one may be rated at 40 VA.

ChrisJ

DCContrarian said:

OK, it looks like it's a permanent split capacitor (PSC) induction motor. A little internet reading tells me that the speed of each winding is entirely determined by the frequency of the power supply. At a lower voltage it runs at the same speed and same power, so a higher current. The only question would be whether the windings can handle the higher current. I don't see a way of finding out other than trying.

Please show us a picture of the motor or spec sheet for that unit

pecmsg

DCContrarian said:

OK, it looks like it's a permanent split capacitor (PSC) induction motor. A little internet reading tells me that the speed of each winding is entirely determined by the frequency of the power supply. At a lower voltage it runs at the same speed and same power, so a higher current. The only question would be whether the windings can handle the higher current. I don't see a way of finding out other than trying.

Take a video of it when you energize it!

JUGHNE

Pecmsg, so you too want to see the smoke escape.

We should wait for the name plate/spec sheet....who knows.

jumper

Hitachi told Canadian customers not to use 550 volts on their 480 volt machines.

mattmia2

so..find one with a 120v motor or change the ckt to 240 v

EdTheHeaterMan

I want to know where someone can get a 120 VAC source of power but can not also get a 240 VAC power source? Is this a local or portable generator?
I have seen some really old houses with a 120 VAC service from the electric company wiring on the closest utility pole. Those are the only two cases I can think of.

And if the service cable to the location is ~240 VAC but the wire from the service distribution panel to the motor location is only 2 conductor with a ground, then just wire one leg to the black wire and the other leg to the white wire (after wrapping the white wire with black or red electrical tape at each end) of the 240 VAC panel. Use the bare or green wire for the ground. There is no need for a common wire on a 240 VAC appliance unless it specifically indicates that you must have a 3 conductor feed wire.

And if you really need to use 120 VAC then you can remove all the 240 loads, (transformer, relay, motor) and replace them with the same device that will operate with 120 VAC parts. Which you will need to do anyway after you let the factory installed smoke out of the motor, transformer, or relay that you underpower for an extended time period. I think I would like to see that video also @pecmsg .

hot_rod

Or get a 120 to 240 inverter
The first Grundfos Alpha pumps were all 230 v and they came with a small cord type step up inverter.

Same with Viessmann boilers in the early years, they had inverters onboard, as they were all 230v 50hz

DCContrarian

ratio said:

At 40 VA, you should be able to find some kind of transformer that will work. https://www.ebay.com/itm/266090802476 for instance.

Shoot us a pic of the nameplate or something.

I think this is the winner. I didn't realize RIB made transformers, I was able to get one off of Ebay for $25.

To those asking why I don't just run a 240V circuit or convert a 120V circuit to 240V, it's in finished space and on a shared circuit. 240V would require a dedicated circuit.

mattmia2

can you run heating equipment off a shared circuit?

mattmia2

if you use a control transformer(or an inverter) you'll need to make sure it can handle the starting current of the motor and that has to do with the characteristics of the core.

EBEBRATT-Ed

Just buy a 240-120 volt step down transformer and use it as a step up transformer 120-240 transformer But lets see the motor nameplate first.

If you

If you run a motor made for 240 on 120 you will let the smoke out

If the wire feeding this AHU come from your panel just install a two pole circuit breaker and you will have your 240 volt. If your tapping on to a 120v circuit (which you shouldn't do) you will have to use a transformer.

EdTheHeaterMan

I did not know that you could operate an air handler from a shared circuit. I though that an air handler, or any appliance that is not equipped with a plug in type electric cord, needed a dedicated circuit. And I have never met an electrician that could not get a wire run from one location to another. That is what electricians do for a living. Bury under ground, exposed with a decorative conduit, run a fish tape behind the wall or thru the ceiling,

I'm still interested in the video!

mattmia2

so much lack of knowledge of motor loads here. not sure about the code issue. i know central heating equipment must be on its own ckt.

HVACNUT

DCContrarian said:

It depends on what type of motor it is.

It's a four-speed motor. It has a wire for each speed, yellow, red, blue and black, and a white common. Does that help?

Yes. It helps a lot. It means NO, you can't use 120 volts to a 230 volt blower motor. Or any motor for that matter. The White isn't a Neutral, it's 120 volts to the motor windings and run capacitor. 
What's the make and model of the fan coil unit? It seems like you have a typical PSC 48Y frame motor. I don't see why you can't track the correct motor.

jumper

Common problem is somebody not realizing that 240 & 215 are different.

pecmsg

How did we come up with 214?

Jamie Hall

pecmsg said:

How did we come up with 214?

That's the admittedly rather unusual connection that you get from three phase delta. Vanishingly rare in residences, but very common in downtown areas and businesses.

EBEBRATT-Ed

Although step down transformers are not technically approved to be used as a step up transformer, they can be used in an instance like this and it is commonly done.

As some mentioned above the AHU should be on it's own circuit as it is a fastened in place appliance even though the amperage is very low.

HVACNUT

DCContrarian

mattmia2 said:

can you run heating equipment off a shared circuit?

Fixtures that require 240V require one circuit per fixture. Fixtures that require 120V can share a circuit so long as the combined full load ampacity of the appliances doesn't exceed 80% of the circuit breaker capacity.

That's kind of the problem here actually. We have three fan coil units on the same 120V circuit. I want to switch one of them out for a different one, the form factor I want is only available in 240V.

ChrisJ

DCContrarian said:

can you run heating equipment off a shared circuit?

Fixtures that require 240V require one circuit per fixture. Fixtures that require 120V can share a circuit so long as the combined full load ampacity of the appliances doesn't exceed 80% of the circuit breaker capacity. That's kind of the problem here actually. We have three fan coil units on the same 120V circuit. I want to switch one of them out for a different one, the form factor I want is only available in 240V.

I'll be honest. 
I'm not sure where you're located but I have never heard of 240v circuits requiring a dedicated circuit.  We have plenty of 208 and 240 circuits in our shop that have multiple receptacles.  Of course that's 3 phase but regardless I know of no such rule in the US.

But typically HVAC equipment by code is required to be on a dedicated circuit regardless of it's voltage.

pecmsg

DCContrarian said:

can you run heating equipment off a shared circuit?

Fixtures that require 240V require one circuit per fixture. Fixtures that require 120V can share a circuit so long as the combined full load ampacity of the appliances doesn't exceed 80% of the circuit breaker capacity. That's kind of the problem here actually. We have three fan coil units on the same 120V circuit. I want to switch one of them out for a different one, the form factor I want is only available in 240V.

Fan coil units require dedicated circuits. 

DCContrarian

pecmsg said:

DCContrarian said:

mattmia2 said:

can you run heating equipment off a shared circuit?

Fixtures that require 240V require one circuit per fixture. Fixtures that require 120V can share a circuit so long as the combined full load ampacity of the appliances doesn't exceed 80% of the circuit breaker capacity.

That's kind of the problem here actually. We have three fan coil units on the same 120V circuit. I want to switch one of them out for a different one, the form factor I want is only available in 240V.

Fan coil units require dedicated circuits. 


The circuit with 3 FCU's was drawn up and stamped by a mechanical engineer, approved by the permit office, installed by a licensed electrician and approved by an inspector.

The FCU's are only rated at 18 Watts.

ChrisJ

That sounds like a mic drop by @DCContrarian

EBEBRATT-Ed

@DCContrarian,

Not true. 240 volt baseboard heaters are commonly installed with multiples on the same circuit.


As far a 120 volt circuits on a general use circuit you can only load the circuit to 50% with say a window ac if it is on a circuit with lights and receptacles.

If it is not a general use 120 volt circuit HVAC equipment can only take up to 80% of the circuit rating because all HVAC equipment is considered or should be considered a continuous load.

There is no reason a circuit regardless of the voltage can't supply multiple loads as long as it is sized properly

DCContrarian

EBEBRATT-Ed said:

@DCContrarian,

Not true. 240 volt baseboard heaters are commonly installed with multiples on the same circuit.


As far a 120 volt circuits on a general use circuit you can only load the circuit to 50% with say a window ac if it is on a circuit with lights and receptacles.

If it is not a general use 120 volt circuit HVAC equipment can only take up to 80% of the circuit rating because all HVAC equipment is considered or should be considered a continuous load.

There is no reason a circuit regardless of the voltage can't supply multiple loads as long as it is sized properly

Thanks. If that's the case maybe what I should do is convert the circuit to 240V and put step-down transformers on the 120V units.

DCContrarian

I had some time to look at this today so I'm circling back to it. First, many asked for a picture of the label on the motor, here it is:

I decided to just hook it up to 120V and see what happened. This was prompted by two observations. First, the motor is rated for 20W and 0.2A, that would imply it can handle 120V. Second, I googled the model number and found I could buy a replacement on Ebay for about $20, so I figured I had little to lose.

So I plugged it in. It didn't destroy the motor, but it didn't run well either. It's a four speed motor. On the two high speeds it ran very slowly, on the low speeds it didn't have enough starting torque to run, although on one it ran with a push. Hooking it up to 220V confirmed that it ran on all four speeds.

So transformer it is.