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Old 20th June 2004, 09:53 AM   #1
tcl2 is offline tcl2  France
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Join Date: Jan 2004
Location: Nice
Default BOSOZ PSU problem

I'm in the process of building a Bosoz, but I have a problem
when testing the PSU.
The fuse blows out when I plug the PSU (I used 1 amp then 1.6 amp
All connections are ok.
The schema is the same as original, the only thing i changed
was the bridge, i used fast diods instead.
I used 2 15k resistors on V+ and V- as advised in N. Pass article
for testing.
Transformers are 2 toroïdal transformers
2x30 each to get 1x60 (120 VA)
I join a picture of the PSU.
Thank you for your help.
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Old 20th June 2004, 02:24 PM   #2
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Alain Dupont's Avatar
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Location: Paris - France

Are you shure of the wiring of the bridge...

The only thind that differs from the original I have...

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Old 20th June 2004, 03:20 PM   #3
tcl2 is offline tcl2  France
diyAudio Member
Join Date: Jan 2004
Location: Nice
thank you Alain for your answer but i checked
of course the wiring of everyhing, mainly of the bridge,
and i was not much concerned about that since
i always use that kind of bridge with fast recovery diods
and coupling capacitors
on all PSU i build and i never had problems like this one.
All worked perfectly.
I'm still trying to find out why it does not work.
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Old 20th June 2004, 09:34 PM   #4
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BobEllis's Avatar
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Location: Upstate NY
how about the transformer wiring? you might want to check with them not connected to the psu. Do the fuses blow without the psu connected? do you get 60 volts across each pair of secondaries?

how about the polarity of the zeners? Condition of the pass transistors? are they in the rght spot with proper orientation? filter caps OK?

I think I have made all of the above mistakes a few times. good luck
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Old 21st June 2004, 02:34 AM   #5
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kilowattski's Avatar
Join Date: Aug 2003
Location: Long Island, New York
I feel funny asking this but are you using a slow blow fuse? There is a little current surge when powering up. You could also try inserting a CL-60 thermistor in series with your primary if you have one laying around.
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Old 22nd June 2004, 03:46 PM   #6
tcl2 is offline tcl2  France
diyAudio Member
Join Date: Jan 2004
Location: Nice
thank you for your answer
BobEllis: i checked everything, everything is ok

Kilowattski: i do use a slow blow fuse

So I still don't understand such a current surge at start, able to
blow a 1.6 A fuse ! This is the first time it happens to me .
As i'm not so familiar with regulation with zener diods, if i can't
find the reason why of this problem, maybe i will make a
typical regulation with lm317,lm337 instead, this always works.
Unless somebody can help me...
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Old 23rd June 2004, 01:41 PM   #7
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Alain Dupont's Avatar
Join Date: Sep 2003
Location: Paris - France

The big amount of current is due to:

- HexFred diodes tend to have a pic of current at startup
- The condenser just after the bridge is taking a lot of current at startup
What type and make is it?

To verify if the mosfet regulation is in cause, inplug the MosFet
and verify the current at startup...

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Old 5th July 2004, 03:08 PM   #8
tcl2 is offline tcl2  France
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Join Date: Jan 2004
Location: Nice
Thank you for your answers.
I finally solved the problem by putting a 10 OHMS thermistor
between the mains and the phase of each primary winding.
I've been testing the psu for about an hour end everything
seems to be fine, the fuse does not blow out.
I still do not know why this happened before as there were no
mention of thermistors in Nelson Pass article for inrush current.
Moreoever i could find on the posts people having the same
problem, so i was a bit confused...
I hope this will help anyone having the same problem if it occurs.
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