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Old 24th April 2005, 09:33 PM   #1
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Default Query about torroid temps

Hello,

I'm just about to test my P101 amps with a +/- 15v supply from BMM (pre-built)

The thing thats worrying me is that the 18v 0.42A torroidal is getting hot after around 2 minutes whilst connected to the PSU, almost to hot to touch but not quite.

Is this normal???

I've tested the voltage output from the PSU and they read around 18-19v.

I've had a good look at all power connections and they seem to be correct.
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Old 24th April 2005, 09:53 PM   #2
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Come on folks please

I know its only 5 minutes ago since I posted this but I'm wanting to get the testing done tonight and I'm somewhat concerned by this heat. Doesn't seem normal to me.

PS. The PSU is a resin encapsulated type.
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Old 24th April 2005, 10:35 PM   #3
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That transformer sounds awfully small for a power amp...

Have you got the amp's bias cranked up too high?
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Old 24th April 2005, 10:39 PM   #4
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Quote:
Originally posted by pinkmouse
That transformer sounds awfully small for a power amp...

Have you got the amp's bias cranked up too high?
Sorry PM, guess I wasn't clear, I'll try again:

The 15v PSU is simply a way of testing the amps with a low voltage source, the final PSU is 56v DC.

The PSU hasn't actually been connected to any amp yet as I'm concerned about the very hot torroidal. So at the moment no current is being drawn at all from the PSU, its simply power on, thats all.
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Old 24th April 2005, 10:46 PM   #5
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Hmm, that doesn't sound healthy...

Does it have twin secondaries, or is it centre tapped? Dual bridge or single? Got a pic?
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Old 24th April 2005, 10:49 PM   #6
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Quote:
Originally posted by pinkmouse
Hmm, that doesn't sound healthy...

Does it have twin secondaries, or is it centre tapped? Dual bridge or single? Got a pic?
Twin secondary windings, single bridge rectifier.

One question the dot on the windings diagram, is it to indicate the start or end of the winding?

I assume its the start and thus + ???

Click the image to open in full size.
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Old 24th April 2005, 11:09 PM   #7
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Ok, well, the first thing I would do is disconnect the traffo from the board. Could you knock up a basic supply with just a bridge and a couple of 1000uf caps? Check the traffo with that and see if it still overheats. I'm loath to try and identify the wiring from your traffo as every maker seems to have a different scheme...
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Old 24th April 2005, 11:14 PM   #8
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Here's a link to the manual for the transformer I'm using:

If you get an error refresh your browser and it will load.

http://www.bmm-electronics.com/docum...plimo/50va.pdf

Can't knock up a PSU at the minute since I have no rectifiers.

I'm not actually sure I've got the wiring correct to the 230v side. The start of the winding indicated by the dot on the winding diagram does go to positive doesn't it?
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Old 24th April 2005, 11:20 PM   #9
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The primary wiring shouldn't make any difference on the heating issue.

If you look at the underside of the board, are AC2 and AC3 joined? If so, yellow and blue should go to them, and the other two wires can go either way round to 1 and 4. If that doesn't work, you may have a problem on the psu board.
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Old 24th April 2005, 11:26 PM   #10
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Cheers PM,

Yes, looking at the underside of the PCB, both AC2 and AC3 are connected.

I do indeed have yellow and blue to these, with red to AC1 and grey to AC4.

Thing is the PSU actually works fine, I can adjust the output voltage using the pots from ~2v to 19v.

So it definitely doesn't matter which wire goes to '+' and negative on the 230v side, its confusing since both are white.
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