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Old 06-06-2012, 11:22 AM   #1
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Magnetek Century electric motor problem


Hello,

New to the forum here, so I appreciate your help and patience with a newbie.

I have a Magnetek Century blower motor that I salvaged when I replaced my central air system. I wanted to rig it up like a fan where I work and I've had some problems. It's a 220v-only motor, 3.5-3.6 amps. I don't have any 220 wired at work, so I bought a 1500w transformer meant for foreign travel. When I rigged it up, all I did was blow fuses in the transformer. The issues I've been able to identify so far are these:

1) The motor is apparently set up to receive two hot wires at 120v each, as you'd expect for 220/240 connections in the U.S., but the transformer puts out a single hot 240v on one prong and neutral on the other.

2) I understand that electric motors spike when starting up, and perhaps that's the reason for the fuse blowing.

So, do I need a transformer with a higher capacity, or is there a more fundamental problem with my idea? I thought 1500w would be enough to accommodate the motor, but maybe I was wrong.

Thanks in advance for your help!


Last edited by kilgoretrout71; 06-06-2012 at 04:06 PM.
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Old 06-06-2012, 03:37 PM   #2
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Magnetek Century electric motor problem


With just two power wires on the motor (and the ground wire) it does not matter whether you use two 120 volt hot wires on opposite sides of a 120/240 volt circuit or two wires 240 volts and common from a transformer.

Can you get "slow blow" fuses,? These are meant to sustain an overload for a second or two as a motor starts up.

Note that the 3.5 -3.6 amp draw at 240 volts from the secondary of the transformer means a little over 7.0 - 7.2 amp draw (a little over 850 watts) at 120 volts from the wall receptacle.

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Last edited by AllanJ; 06-06-2012 at 03:42 PM.
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Old 06-06-2012, 04:03 PM   #3
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Magnetek Century electric motor problem


Thanks! I'll check on the slow blow fuses. I hope they can take a good spike, though. The ones I blew went pretty quick and hot.

So, then, if the method of delivery of the 240v doesn't matter, that means the spike this motor causes is substantial. 1500w is *almost* twice what I need. If the slow blow fuses don't work out, it leaves the tricky question of how much more of a transformer I would need.
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Old 06-06-2012, 04:09 PM   #4
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Magnetek Century electric motor problem


If the fuses are glass and the fuse element is splattered all over the glass it was a pretty serious overload.
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Old 06-06-2012, 04:24 PM   #5
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Magnetek Century electric motor problem


Well, I wouldn't say it was "splattered," but the center 50% of the strip was gone and the glass was somewhat blackened in that area.
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Old 06-06-2012, 07:07 PM   #6
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Magnetek Century electric motor problem


Some of the travel transformers are nothing but a diode and a reactor that will effectively reduce voltage but not increase it.

How much does the transformer weigh? a 1500 VA transformer should weigh around 30 lbs.

If it is indeed a true transformer, it will work in either direction. But the fuses must be time-delay. What size are they? 5MM X 20MM, 1/4" X 1-1/4", 13/32 X 1-1/2", or something else?

If it's a real transformer, and it's being used solely to run the motor, fuses are not required. The 120 volt circuit breaker in the panel will suffice for short-circuit and ground-fault protection, and the overload in the motor is good for the the transformer too.

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Old 06-06-2012, 07:56 PM   #7
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Magnetek Century electric motor problem


I'll have to check on the size of the fuses to be sure. I left them at work. To guess, though, I'd say they were 5x20 or 6x30. I'm pretty sure they weren't time delayed, though. And the unit is a true transformer--about 22 pounds and both step-up and step-down.
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Old 06-06-2012, 08:08 PM   #8
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Magnetek Century electric motor problem


Did you look at the name plate to see if you can rewire it for 120?
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Old 06-06-2012, 10:48 PM   #9
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Yes, it definitely can't be rewired for 120.
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Old 06-07-2012, 06:11 AM   #10
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Magnetek Century electric motor problem


If you don't have 240V at work how is a transformer that is supplied by 240V supposed to work?

Unless you are in a foreign country currently and by foreign travel you mean travel to the US. Otherwise its like you are asking how you can plug in a 240V-120V transformer to a 120V receptacle and you expect to get 120V out of it.

I am going to ask how you know this motor can be rewired to 120V? Usually this is only possible if the motor has multiple voltage leads...and I haven't seen a resi AC fan motor with multi taps.

It seems you are making a lot to do over nothing when you can go out and buy an oscillating fan for 20 bucks.

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