# Undervolt the input of a transformer - what happens?

Discussion in 'General Electronics Discussion' started by fatman57, Jun 29, 2015.

1. ### fatman57

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May 27, 2013
If I overvolt the input voltage of a transformer things can get hot and the insulation can suffer and ultimately the unit can/will fail...but what happens if I undervolt it?

My presumption is that the output voltage will drop almost in proportion but not in an ideal or linear way. My understanding here is that the unit will not have been designed for such voltages so will/could work in an unstable/volatile way - so the output could also be variable and more unstable than could be expected under optimum conditions. Is this correct?

Use Case: I have 12v capacitors that lead to a 12->72v transformer that runs an electric motor. When the caps are at half power they will be at 6 volts but will still be connected to a 12v transformer - so if I measured the power output what type of output could I expect to measure? How will the motor react to such conditions? Will the transformer have a greater chance of failing under these conditions and me having to buy a new one?

Much obliged for any help!

2. ### cjdelphi

1,096
104
Oct 26, 2011
The caps can't be directly connected to the primary winding...

Undervoltage in undervoltage out, with less available current on the secondary winding..

duke37 likes this.
3. ### shrtrnd

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Jan 15, 2010
I don't remember the theory, but in practical application a lot would depend on your load.
Like cjdelphi I'm not sure what your circuit looks like.
It seems to me that if you undervoltage what a transformer is designed for (not a problem by itself), but your load draws more current than what the transformer
was designed for, that the transformer windings themselves could become an additonal 'load' all by themselves.
Maybe somebody else here could point out practical application if I am in error.
I've seen motors overheat when driven undervoltage.

4. ### cjdelphi

1,096
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Oct 26, 2011
I think motors should be designed in a way little fins could be added to draw in air to cool itself while working?

5. ### shrtrnd

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Jan 15, 2010
Sounds good. Unfortunately there are a lot of different types of motors, and some applications call for sealed motors to prevent the introduction of contaminants, and/or are restricted in physical size for the application.
All we know from fatman57 so far, is that he's using an 'electric motor'.
He may not know the motor type, and may have to just run what he's got and see what happens.

6. ### fatman57

108
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May 27, 2013
Thanks for the replies!

Makes sense that lower voltage in primary will result in high amp draw on the secondary...will there be a higher amp draw on the primary too because of the lower voltage?

7. ### ver chan

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Jun 27, 2015
learn through experiment, try it,

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Jan 15, 2010