Repairing smaller 400V HVAC flu motor with open wire

[DAVEISGREAT]

It won't explode like what he used, but better safe then sorry. You will melt your transformer when you input double the nominal voltage.

Remember, purpose is for a 2 second test,, would it still melt,, any other major concerns?

[pcprogrammer]

I would not risk my transformer even for only a couple seconds.

[Gregg]

Check the capacitor and its winding; the motor won't want to rotate without a proper capacitor.   

[Jwillis]

I should have looked at the wiring more closely. I wonder if the starting cap is toast or not connected properly. Can we get a closer look at the connection of that?

[DAVEISGREAT]

Capacitor measures spot on using my old reliable battery sucking UNI-T multimeter.  Earlier I questioned wiring using 120V so reversed them,, very similar results using 120V.  Will reverse leads again using 220V,, this time wiring will be as per diagram,, and report back.

UPDATE:  Can confirm cap holds charge for a long time.  For safety, shorted it with an insulated set of pliers and got a big spark.  Note to self,, make a proper cap discharger.

[Zero999]

It won't explode like what he used, but better safe then sorry. You will melt your transformer when you input double the nominal voltage.

Remember, purpose is for a 2 second test,, would it still melt,, any other major concerns?

I don't think it's much of a risk. Transformers take a long time to overheat. A 100VA transformer can happily be short circuited for a few seconds, without smoking.

Heck, I would wire the 120V:220V transformer, as an autotransformer to give 340V, which will stand more of a chance of getting it to turn. To this, the 220V secondary needs to go in series with the 120V primary, which is connected to the mains as usual. Some experimentation with the phase might be necessary: if you get it the wrong way round, it'll drop the voltage by 220V, so give close to 100V; if that happens, just reverse it and try a gain.

[DAVEISGREAT]

I questioned wiring earlier using 120V so reversed them,, very similar results using 120V.  Will reverse leads again using 220V,, this time wiring will be as per diagram,, and report back.  <-- WRONG

Double checked wiring diagram only to note above tests with 240V test was made correctly, as per diagram.  So I did not test with reverse cap/motor wiring since error noted, and because I don't really understand this assemblies wiring
Still trying to comprehend getting 340V from 120V--240V step up T in USA?

[Jwillis]

As Zero999 says, the only way to step up single phase 120V or 240V to a higher voltage is with a transformer.

[DAVEISGREAT]

Working on this motor has been my introduction to 220V.  Always have respected 120V and haven't been zapped since I was a kid.  After yesterdays escapades jumping to 480V scares the crap out of me.  All my safety fuses and switches only have 220V ratings.  Still, want to briefly pump 480V in this sucker with my 120V to 240V transformer,, come hell or high water,, any tips wiring for safety, etc. would be greatly appreciated.

UPDATE:  Another question.  How to add a bleeder resistor to circuit.  Last 240V test, I measured 240V across motor several minutes after I thought power was off?  Lastly, I do not understand 3 phase very much,, is it important for this test?

[Jwillis]

Depends on the size of the cap will determine the power of the resistor in watts. A 15K to 56K resistor 1W should be about right for that cap. That just goes across the capacitor terminals to discharge cap when not in use. Won't effect the motor performance as long as the resistor isn't to low in value. You don't need to worry about 3 Phase with that motor since its single phase.
Imagine a sine wave as single wave or single phase . Then imagine 3 sign waves equally spaced 1/3 apart from each other as 3 phase.

[DAVEISGREAT]

Dug up the step-up/step-down transformer.  The T is contained in a metal box and intended for travel, though quite heavy spec'd at 1000VA and 20+lbs.
The million dollar question:  How to wire 240V into this 120V to 240V step up transformer, and get 440V out to briefly run motor.  Here's pictures of transformer and wiring.  Thinking the two 120V bare hot wires on the big 240V plug should clip into the smaller hot and neutral of 120V plug??  Not sure if it matters,, the small 120V plug is non-polarized?  Also, current wiring scheme leaves both grounds open?  Should this set-up work? any advice greatly appreciated!

[Jwillis]

Yikes. I'm going to say you can't or shouldn't. Simply because the impedance of the 120V will be twice as low as it should be for 240V input. You could very well fry the transformer but at the very least trip the breaker. Keep in mind that tripping breakers repeatedly weakens them. I'm not that experimental or brave enough to try.
If you could find a second transformer like that then you can wire the primary in series and secondary in series. I can't advise plugging the 120V side into 240V source.
I'm not afraid of high voltages, but I do respect them.

[Gregg]

Most of those type of step up/down transformers are auto transformers meaning that the primary and secondary are NOT ISOLATED from each other.  Since you earlier indicated a desire to learn, I suggest you read up on transformers and learn before doing something you may regret.
 

[Zero999]

Placed both hot leads across two motor leads,, with protective inline fuse and inline microwave switch(always off. as a kill switch).  With motor secured,, used a broom handle to momentarily depress switch for two or three seconds.  Unfortunately, similar motor hum, little if any rotation.  Mercifully, no million amp short!

Plan B:  I do have a 120V to 240V transformer rated at 500W .  Would it be possible to wire 220V into T's 120V side to  briefly get 440V output, then test motor start-up?

UPDATE:  Zero999 just noticed your post.  Like your similar, better idea but don't want to spend that much.  You think plan B is useable option?

The one you already have appears to be an autotransformer, so my idea of configuring it for 340V won't work.

The transformers I've posted links to are not expensive.

Are you really that strapped for cash? If so, then look around for second hand control transformers, similar to the one I posted the eBay link to.

Trying to save money too much appears to be a common beginners mistake. It invariably results in it costing more in the long-term. Heck I would just junk it and shell out for a brand new motor of the correct voltage, from a reputable supplier. That way it'll be covered under warranty and I don't have to worry about it burning my house down. Peace of mind is well worth a few hundred quid.

[DAVEISGREAT]

Had never used this T before so needed to test it.  Meter showed 250V output unloaded. Only 240V load I had was a discarded stove element <--(BLEW UP THE FUSE).  Worked for a second, lukewarm, then blew a fuse. What happened was the T is missing its AC indicator bulb(don't know what kind?),  and its exposed wire shorted to the transformer while testing. <-- WRONG(read Greg's correct analysis below)

Yea, I would like to avoid blowing this thing up and not trip the main 100A main house breaker ever again.  Not smart enough to know if pumping 240V across this T's 120V input plug through this "transformer" and 440V out to motor will pop/weaken main house breaker again, but sure do appreciate all the advice from everyone. :'( 
That quick 2 second 480V test may never happen,, at least with this T.  With a normal isolated T, I would definitely risk it but the wiring here is over my head.  For completeness I added more pictures of autotransformer, not T if anyone is interested.   

[Gregg]

Dave,
You need to start at the very beginning and get a working knowledge of ohm’s law.  You tried to power a stove element of at least 1500 watts from your 500 watt transformer.  What could go wrong evidently went wrong as you should have expected. 
The low resistance of the stove element was about the same as a dead short to the transformer you used. 
In one of your earliest posts you mentioned using incandescent light bulbs to limit current; ohm’s law tells you why this works.  Also you could put two 120 volt lamps of the same wattage (basically the same resistance) in series to test your 240 volt transformer output.  If you use two 100 watt 120 volt lamps in series and power them with 240 volts they will draw 200 watts of power. 

[DAVEISGREAT]

When I was about five I stuck my finger in a light bulb socket,, once a knob always a knob.   T is rated 1KW and knobs assume things like small stove element is only 750W, not 2400W(as latter measured 10 ohms).  Thanks for correcting, and for the bulb tip.   Still enjoy learning though and these lessons have been valuable yet painfully  embarrassing,, I'm old and dying,, only wish I had the time to start from the beginning again.

BTW, its Jim,, username is in honor of our host's fabulous forum--> DAVE JONES.

[Jwillis]

Nothing to be embarrassed about. Making mistakes is half the learning process. I'm not getting any younger either. Not as steady any more and can't see a darn thing without coke bottle bottom glasses.But I always enjoy learning and figuring out new things, Many times with disastrous results. Even when I don't figure out how something works after destroying it, at least I know not to do that procedure again. As Victor Hugo say's "We're all fools most of our lives, it's unavoidable"

[DAVEISGREAT]

Words of wisdom and encouragement -- Thank You Again!:

Motor rating per tag shows that at 460V, motor consumes only 47 watts.  Typical MOTs output 2.2kV,  but if 80% of the secondary winding is removed then voltage out should be very close to 460V.  Seems pretty simple.  Motor needs 1.7 amps (oops, .17 amps) at 460V per tag.  Do you all think this simple modification to a MOT would have enough juice to briefly run this motor just as a test,, possibly even continuously maybe somehow?

[CaptDon]

It says OUTPUT 47W. And the amps are .17!! You realize at 460vac 1.7 amps would be 782 watts which is about 1 horsepower. If you can't get that motor to turn over slowly after giving it a bit of a spin by hand at 240vac then its junk. How many different wiring schemes have you tried. B.T.W., yes, you may get 460vac from the partially unwound secondary of a M.O.T. but NONE of them are designed for continuous use. They run in partly saturated mode and you MUST knock out the magnetic shunts. I highly doubt you will ever see this completely useless motor spin.

[DAVEISGREAT]

I highly doubt you will ever see this completely useless motor spin.

 

UPDATE:  Will source a MOT and try this.

[johansen]

The motor can be re wired for 240.

Find the mid point between the two coils and snip it, wire in parallel.

The capacitor winding will need to be snipped as well and the capacitor value doubled