Transformer question.....

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Fulthrotl

Fulthrotl

~Autocorrect is My Worst Enema.~
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HB, CA (19 Hrs. 22 Min. from Winged Horses)
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E
i have a 5 amp, 240 volt dedicated load, and the only thing
i have is a 20 amp 120 volt circuit available
to power it.

would it be kosher to use a 240 volt primary / 120 volt
secondary transformer reversed to power this load?
a 2KW one should handle it. if the 240 volt side had
windings in series, i could ground the center tap, so
that it wasn't an isolated secondary. i think the only
place an isolated secondary is permitted is in critical
care patient areas in hospitals.....

anyone ever done anything like this?
 
T

T.M.Haja Sahib

Guest
Isolated secondary means ungrounded supply. May be useful in other places also where stoppages due to single phase ground faults are not tolerated......
 
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augie47

augie47

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Location
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State Electrical Inspector (Retired)
I see no problem with the plan.
Take a look at Art 450 for transformer protection, 240.21(C) for conductor protection and 250.30 for grounding.
 
H

hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
problem it be a problem, keep in mind that your new "primary" amperage will be twice the "secondary", so there may be a voltage drop issue, but at even ten amps, there shouldn't be if the circuit was properly designed. We do it a lot the other way around where we need a 20 amp 120 volt circuit, but only a 277 volt is available.
 
J

jim dungar

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Wisconsin
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PE (Retired) - Power Systems
Tiny transformers smaller than about 1kVA have a fairly high amount of voltage regulation issues (ever notice the open circuit voltage of a doorbell transformer?). Transformers up to about 3kVA are built with some extra 'compensating' windings on the high voltage side to deal with the magnetizing of the core. When you run these transformers backwards, you may experience 'below intended' voltage on the output.
 
T

templdl

Senior Member
Location
Wisconsin
jim dungar said:
Tiny transformers smaller than about 1kVA have a fairly high amount of voltage regulation issues (ever notice the open circuit voltage of a doorbell transformer?). Transformers up to about 3kVA are built with some extra 'compensating' windings on the high voltage side to deal with the magnetizing of the core. When you run these transformers backwards, you may experience 'below intended' voltage on the output.
Click to expand...

Yes, aand those who try to use a cpt or maching tool transformer as a step up transformer will be extremely surprised when the output voltage is significantly lower that they expected. I had an outside salesman who tried to use one with a simple voltmeter with a cpt which really didn't require great accuracy but a he soon found out that the voltmeter reading was way off as it wasn't even in the ball park. These transformers are not a simple 2:1 or 4:1 ratio as are the larger transformers. I always viewed it as a way to deal with regulation when dealing with high inrush as are common with control circuit loads.
 
Fulthrotl

Fulthrotl

~Autocorrect is My Worst Enema.~
Location
HB, CA (19 Hrs. 22 Min. from Winged Horses)
Occupation
E
templdl said:
Yes, aand those who try to use a cpt or maching tool transformer as a step up transformer will be extremely surprised when the output voltage is significantly lower that they expected. I had an outside salesman who tried to use one with a simple voltmeter with a cpt which really didn't require great accuracy but a he soon found out that the voltmeter reading was way off as it wasn't even in the ball park. These transformers are not a simple 2:1 or 4:1 ratio as are the larger transformers. I always viewed it as a way to deal with regulation when dealing with high inrush as are common with control circuit loads.
Click to expand...

thanks for the regulation concern.... i'll experiment first if i have to go that route...

i've got two air handlers that are being changed out, and they are 110 volts,
and the new ones are 220 volts. i haven't gotten into the wiring yet to see,
but if they are dedicated circuits, i can change them at the panel, put a couple
quads in, and be done with it.... but if there are other outlets and 110 volt loads
on the circuits, then i have to do something different. this was something different.

cutting holes, and getting power from the main or subpanel is not a viable thing to do.
the whole house is done in venetian plaster, on the water in new porsche beach.
three stories, low 8 digits, maybe 18~20 M... nicest house i've ever worked on.
two seriously nice owners, as well....

so if i have to buy a xfmr, put a load on it and see how it regulates, and test first,
that's easily done... going across that house cutting holes from one side to the other
would be $20k in patching....
 
Fulthrotl

Fulthrotl

~Autocorrect is My Worst Enema.~
Location
HB, CA (19 Hrs. 22 Min. from Winged Horses)
Occupation
E
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Fulthrotl

Fulthrotl

~Autocorrect is My Worst Enema.~
Location
HB, CA (19 Hrs. 22 Min. from Winged Horses)
Occupation
E
BullsnPyrs said:
Buy one designed for the use you are putting to and save yourself the time and trouble of experimenting.

http://www.grainger.com/Grainger/Voltage-Converter-18C925?Pid=search
Click to expand...

got two of these.... they work great.....

hooked up one in the shop, to see if there were any issues...
the air handler only draws 1.1 amps at 240 volts, full speed...
but that doesn't have a duct load on it, just free spinning.

i'm guessing maybe double that fully loaded. these air handlers
use a soft start vfd, and are very quiet.. nice units.
 
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