Yamaha PA30 voltage question

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Cablebasher
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Location: England, UK.

Yamaha PA30 voltage question

Post by Cablebasher » Tue Dec 15, 2020 9:39 am

Hey guys

Finally getting round to my Oakley PSU.

I Received my PA30 today and testing the pins I actually get 20.2V between and AC pin and ground. Not 18V as I thought.

Is this too much?

I don’t have the PA30 connected to anything. I am just testing the pins with a metre in AC mode.

Cheers as always.

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Synthbuilder
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Re: Yamaha PA30 voltage question

Post by Synthbuilder » Tue Dec 15, 2020 10:53 am

Cablebasher wrote:
Tue Dec 15, 2020 9:39 am
I actually get 20.2V between and AC pin and ground. Not 18V as I thought.
This is quite normal. The PA-30 is a EI core transformer in a plastic casing. The output voltage will depend on input mains voltage which varies from country to country, and with time. The output voltage will also depend on output current. Increasing the current, or load, that the transformer will have to supply decreases the output voltage. The PA-30 is specified to produce a certain voltage (18V RMS) at a specified input voltage (230V RMS for the European version) and with a specified load (1.4A RMS). That specified load is always a resistor which produces a AC current waveform that matches the roughly sine wave output voltage. So with no load, ie. no current being supplied by the transformer, the output voltage will be higher than specified.

In reality the load on a transformer is not a constant resistance. The actual load on a transformer when you connect it to a standard linear power supply is complex and the current waveform no longer matches that of the output voltage, which is also far from the original sine wave waveform of the input mains supply.

Cablebasher
Wiggling with Experience
Posts: 447
Joined: Sat Aug 03, 2013 6:51 am
Location: England, UK.

Re: Yamaha PA30 voltage question

Post by Cablebasher » Tue Dec 15, 2020 1:44 pm

Thank you for the quick and informative reply.

You have put my mind at ease

Now to finish this lovely PSU and fill the rack with modules

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