Query about torroid temps

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ShinOBIWAN

ShinOBIWAN

diyAudio Member
Joined 2004
#1
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.
 
#2
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.
 
#4
pinkmouse said:
That transformer sounds awfully small for a power amp...

Have you got the amp's bias cranked up too high?
Click to expand...

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.
 
#6
pinkmouse said:
Hmm, that doesn't sound healthy...

Does it have twin secondaries, or is it centre tapped? Dual bridge or single? Got a pic?
Click to expand...

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 + ???

An externally hosted image should be here but it was not working when we last tested it.
 
#7
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...
 
#8
#9
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.
 
#10
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.
 
#12
pinkmouse said:
Nope, at this stage it shouldn't make a blind bit of difference...

If you turn up the output voltage to the maximum, does the traffo still get as hot?
Click to expand...

I've had the transformer off from the PSU board to test on its own and its fine. Temps stay stable, hardly above room temp actually. Output voltage is 23v AC which again is fine since this is no load.

Hard to tell if the transformer is hotter running higher voltages on PSU -- its already too hot to hold you hand on for any length of time.

I guess its a problem with the PSU but it should be childs play to connect it. Follow AC wiring diagram in the PSU instructions, simple as.
 
#14
Well, I can't think of anything else it could be, but I was at work at eight this morning, so I am a little tired and my brain may not be working at 100%

I suggest you get some kip like I'm going to do and look at it fresh again tomorrow.

Night night!

:edit: AC2 and 3 are ground! Voltage is all relative!
 
#15
pinkmouse said:
Well, I can't think of anything else it could be, but I was at work at eight this morning, so I am a little tired and my brain may not be working at 100%

I suggest you get some kip like I'm going to do and look at it fresh again tomorrow.

Night night!
Click to expand...

Aww, I was hoping you'd take a quick look at my last post before bed 🙂
 
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