Why does my PSU KEEP blowing fuses?! - Page 2 - diyAudio
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Old 14th October 2002, 10:26 PM   #11
jwb is offline jwb  United States
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You need in inrush supressor on the primary for a toroid of this size. Try a NTC thermistor.
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Old 14th October 2002, 10:27 PM   #12
skaara is offline skaara  Slovenia
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did you used a soft start circuit or thermistor?
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Old 14th October 2002, 10:30 PM   #13
Rarkov is offline Rarkov  England
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Hi,

No, I didn't use anything like that. I dont really know anything about them or the point of them. I am using a ceramic slow blow fuse though. Is that the same / adequate?

Just checked ESP website....I did notice the lights dim briefly but no humming or any audiable noise.

Thanks,
Gaz
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Old 14th October 2002, 10:42 PM   #14
skaara is offline skaara  Slovenia
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Soft start circuit or thermistor limits the current (which is very high with big transformers) when you switch the transformer on.
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Old 14th October 2002, 11:27 PM   #15
Jean is offline Jean  United States
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IT does matter how you wire primary and secondaries . There should be a little marking or dot telling you which end is the starting point.

1. ------
*) |
) |
) |
2. ------ |
3. ------ |
*) |
) |
) |
4.-------


You would connect 2 and 3 together, and use 1 and 2 for input. If you wire it for 120volts, then 1 goes to 3, 2 goes to 4.

Same goes for secondaries.
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Old 14th October 2002, 11:44 PM   #16
Rarkov is offline Rarkov  England
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Sorry, I worded that wrong. I mean "does it matter which way around Live and Neutral are connected to the transformer"

EG:
Live -> 4 (numbers correspond to post above)
Neutral -> 1

OR

Live -> 1
Neutral -> 4
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Old 15th October 2002, 12:00 AM   #17
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Your suspicon is correct. It does not matter which is Live or Neutral.

I suggest that you completely unsolder the secondaries and see if the fuse blows. As far as I know an unloaded transformer is quite content sitting by itself. Then you can check the voltages. If this fails, send it back, for it is broken.

Good luck,
Dan
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Old 15th October 2002, 12:03 AM   #18
herm is offline herm  United States
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Gaz;

Tough to troubleshoot from around the world but;

I don't think that it is normal inrush that is blowing the fuses.
It is possible, but unless you are using high speed fuses,
I doubt it.

So lets assume you've got it wired wrong. I'll try to explain
what I did wiring my transformer. This could take a while...

I have a dual primary 750 VA transformer, and I didn't know
the lead color codes, so I had to experiment. I applied 120
to two leads randomly and watched the secondary voltage.
When I saw voltage on the secondary, I knew I had one primary
winding connected properly.

OK, so now I need to hook up both primary windings to 120.
Take a look at the schematic posted by Jean above. If I put
the hot on 1 and 3, and the cold on 2 and 4, life was good.
But if I put the hot on 1 and 4, and the cold on 2 and 3, the
fuse blew.

Moral of the story: If your primary windings are connected
in opposition, they cancel and flux in the core is zero. No back
EMF means your windings look just like low impedance wire
to the source, and they will blow fuses.

This is really just a long way to say disconnect everything from
your secondary and plug it in. If the fuses still blow, check
your primary...

-herm
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Old 15th October 2002, 03:31 AM   #19
Jean is offline Jean  United States
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Default correction

"You would connect 2 and 3 together, and use 1 and 2 for input. "

Sorry! Use 1 and 4.
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Old 15th October 2002, 04:01 PM   #20
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Hi Rarkov,

It sounds like you have an old ILP transformer, they are the only ones I know that use that combination of colours!

On the output side, you should connect yellow and blue together and use them as your earth, and the grey and red should go to your rectifier,(red/ yellow is a pair, and blue/grey is a pair).

This should give you then your plus and minus and earth, ready for smoothing.

On the input side, ILP used various schemes, ( but mostly using black/white as the 240v markings and joining the pinks), so your best bet is to use the technique described by herm to find the particular way your trannie is wired.

Good luck, and stay safe
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