Transformer Question

[milmat1]

Folks,
I am designing a control system for an industrial machine. Machine is 480VAC / 3PH powered.
And I have a 480 / 120V transformer for control voltage etc. (Transformer can be wired for 240 or 120 on secondary)

Now we have added a 230VAC servo drive. Is it considered OK to use this transformer for both my 240V , and the 120V control voltage?

If so, should I tap the winding at 120V and use the 240V winding?

Or do I need to add a 2nd transformer just for this 230V servo.

 

[James Mcquade]

you will need another transformer. the existing transformer is sized for the existing equipment rated at 120 volts.
you will not be able to power both from this transformer.
if i am incorrect, please point that out and explain why.
james

 

[Rob...]

Not 100% sure but I have a feeling UL differentiates a "control transformer" and "power transformer" and they aren't interchangeable.

As 24V DC systems are so common now, haven't had to use a Tx in the states in a while.

 

[milmat1]

Thanks for the replies..


Another forum suggested using the existing control transformer. Center tapping it for common etc. And sizing it accordingly.


However, I was very reluctant to do that. I really think I'll add a 2nd transformer for this axis. Just to be safe.




Thank You for the replies !

 

[TheWaterboy]

you will need another transformer. the existing transformer is sized for the existing equipment rated at 120 volts.
you will not be able to power both from this transformer.
if i am incorrect, please point that out and explain why.
james

Electrically it might be "possible". But certainly not a good idea and no one would or should ever use it in a real setting. But it got me wondering if it would indeed function even close to the same. The tapped load would become part of the transformer coil affecting the inductance so what would that even do to the output. Add a switcher to the output with all its harmonics and wow what a waveform that would become.

 

[I_Automation]

Another forum suggested using the existing control transformer. Center tapping it for common etc. And sizing it accordingly.

That's one of those "On Paper" or "Fresh Out Of College With No Experience" things.


The 120 load on one 'side' of the 240 output would effect the output voltages, as one side of the transformer is putting out double(ish).


Even a 12.6VCT gave me a problem with a not-balanced load that should have been 2 6.3V readings (and yes - that was a long time ago in high school)

 

[TheWaterboy]

Even a 12.6VCT gave me a problem with a not-balanced load that should have been 2 6.3V readings (and yes - that was a long time ago in high school)

Sounds like filament voltages...

 

[James Mcquade]

the original post stated the secondary voltage could be 120 or 240.
if the input is 480. yes, you can wire the secondary for 240 and then get 1 leg to ground to be 120 volts. BUT ! the control power is x kva and the servo power is y kva. this is a very bad idea in my opinion.
the servo transformer is a power transformer as stated with its own fusing requirements. control transformers also have requirements.
i don't think it will be allowed based on nfpa79, electrical standards for industrial machinery.
james

 

[jaden]

Some servo's do not like ground referenced power sources, while control voltage is usually tied to ground on one side.

 

[Gene Bond]

It's a bad idea to allow the voltage surges created by the servo's current surges into the regular control circuit. The noise/transients can easily damage components on the 120v circuit, like power supplies for PLC's, HMI's, etc.

Just add a transformer with the servo drive. They are relatively cheap.