What voltage is my power supply? Supposed to be 240v but I think it is 220v - diyAudio
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Old 7th August 2007, 07:12 AM   #1
wixy is offline wixy  Australia
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Default What voltage is my power supply? Supposed to be 240v but I think it is 220v

I just bought a new amplifier with a separate psu. The psu according to the dealer was supposed to be 240v, however it is labelled as 220v.

I took off the cover. Inside there is a large circular thing with a label on it that says "IN: 0v-110v, BLK BRN, OUT: 0v-110v RED ORG" Below that it says "OUT 0v-16.5v <3A> BLK RED"

On the circuit board there are 8 tall round things which each say "25V, 3300uF" on them.

Could anyone please tell me based on the above what the power supply is (if possible)?
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Old 7th August 2007, 07:25 AM   #2
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The main input is 110V+110V = 220VAC
The output is 16.5V AC = 16.5x1.41= app. 23 V DC - 0.7V drop over the rectifier diodes = app. 22.3V DC

In your case, using this with 240V AC, the output is app. 9%higher than for 220V use, so your output will be 18V AC = 25.3 V DC - 0.7V = 24.6V DC.

As the caps are rated 25V, and the output from PSU will be higher than calculated above when unloaded, your caps will likely in short time.
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Old 7th August 2007, 07:36 AM   #3
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Thanks for that explanation, although to be honest i don't really understand. So basically, it is a 220v power supply? Is there something wrong with the way it is configured?
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Old 7th August 2007, 08:00 AM   #4
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Many transformers are made that way...
You put the two 110V mains in parallel for use with 110V AC and in series for use with 220V AC.

Your main problem is the Voltage ratings of your caps.
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Old 7th August 2007, 08:04 AM   #5
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So even a 240v psu would have the two 110v mains in series? Or would it have two 120v mains in series?

If it was a 240v psu, then what voltage caps should have been used, as opposed to 25v caps?

Thanks for your help!
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Old 7th August 2007, 04:35 PM   #6
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A 240V transformer would have either two 120V main or one 240V main....

You should go for either 30 or better 35V caps
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Old 9th August 2007, 07:39 AM   #7
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ACD, a few updates:

The supplier, who is very friendly and helpful, informed me this:

They just emailed me the measurements for the 255vAC test.
It looks like they measure a 0.7v drop from each diode in the rectifier.
The voltages going into the first group of capacitors is 23.9vDC, so it is within threshold of the 25v rates capacitors in your PSU.



I was then informed I will be able to get a replacement PSU with 35v capacitors rather than the 8 x 25v capacitors in mine, as per the diagram attached to this post.

The supplier said:

They will be sending out new PSUs for us, which are the v2, which have the 35v rated capacitors.
The transformers will still be 220v, but they have extensively tested it with 255v and did not experience any problems.

The LM317 regulator is able spec'd to handle the extra voltage and the first array of capacitors are also rated to operate without problems. .


Most of this goes over my head . You have been very very helpful so far, I just want to confirm with you that the replacement PSU will be able to satisfactorily operate with 240v?

Many thanks!
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Old 9th August 2007, 08:19 AM   #8
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I can understand why you are confused..........

I did make that mistake in my calculation, so the Voltage is "only" 23.9 Volts after the rectifiers!

The specified Voltage from the toroid are when it's loaded (delivering current to a load), but unloaded the Voltage will be higher....

They may have tested it with 255VAC and the caps may have survived this for a short test period if the PSU was loaded (so output Voltage was lowered), but in the long run the caps will be at or over their specified Voltage limit (like running a car over the max recomended RPM all the time)..
Why do you think they change to 35V caps in v2 ??
Because they know there is a problem there......

The Voltage is no problem to the LM317 as it can handle 40V DC.

With 35V caps your supply will have a long life
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Old 9th August 2007, 08:48 AM   #9
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Thanks

So to wrap it all up, 5 x 35v and 3 x 25v would be ok?

And the 220v transformer is not a problem?
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Old 9th August 2007, 09:20 AM   #10
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All should be ok now
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