Need to make ac/ac power supply Help

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turbocoo
Posts: 2
Joined: Tue Apr 16, 2019 1:28 am

Need to make ac/ac power supply Help

Post by turbocoo » Tue Apr 16, 2019 1:36 am

Hi, newbie here.
I need to make an ac/ac power supply. A direct replacement is not available.
It's output is to Xlr with two pins at 7.5v and the remaining pin is Gnd. It needs to be 1A.
Would a 2X7.5 6VA transformer suffice?

Such as this
https://rover.ebay.com/rover/0/0/0?mpre ... 3819633912

Thanks

David
Posts: 193
Joined: Sun Oct 04, 2015 6:18 pm

Re: Need to make ac/ac power supply Help

Post by David » Tue Apr 16, 2019 3:14 pm

Probably not. Transformers are specified in VA (Volts * Amps) because the manufacturer does not know what type of load will be used - capacitive, resistive or inductive - , and so cannot supply a Wattage rating as the phase angle can vary drastically. I would suggest that you use a 2A (15 VA) transformer to get a reasonable margin.

turbocoo
Posts: 2
Joined: Tue Apr 16, 2019 1:28 am

Re: Need to make ac/ac power supply Help

Post by turbocoo » Tue Apr 16, 2019 6:31 pm

Thanks David.
Sorry but I am almost clueless re electronics. However I do know that this should be easy to make up compared to a dc , it's just that I am unsure regarding the necessary gnd centre taps and Va. The unit needing powered requires a 1A load.
I thought that if I had a 6Va at 7.5v it might be OK as it would be 0.8 A, close enough to the spec.

You specify a higher VA in your reply. Would this work.
https://uk.rs-online.com/web/p/chassis- ... %3Atrue%7D

Thanks again

David
Posts: 193
Joined: Sun Oct 04, 2015 6:18 pm

Re: Need to make ac/ac power supply Help

Post by David » Thu Apr 18, 2019 10:47 am

Hello.
You have found a transformer which may well be suitable. Two 6.3V windings might be ok as you would not be running the transformer at full output, and you could have a voltage nearer to 7.5V from this cause. However, it is difficult to be sure at a distance - can you give me any more info?
7.5V ac seems to be an unusual voltage (small transformers often go up in stages of 3V. Have you measured the output of the previous transformer at any time?) What equipment is it that draws 1A or so? you refer to the pins of the XLR plug having 7.5V on two of them - have you measured across these two pins, or is the 7.5V voltage from each pin to ground? Have a look inside the plug and see if two of the pins are shorted together.
If you get a transformer to experiment with, connect the two output tags at the bottom labelled 0V together, and also the two 6.3V tags. Be very careful to insulate the mains tags sufficiently.

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