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patriz

patriz

Member
Joined 2002
lencohell.wordpress.com/
sq225917 said:
Patriz, Please list all the parts in your psu, transformer, in/out voltage and VA, diodes, caps chokes etc.

A standard psu build based around the group buy psu specification and using Hammond 158T 1H chokes, (300mA) needs to output about +/-39v DC unloaded to deliver about 26v when loaded.

It sounds to me like your transformer VA may be too low.


I still have transformer and rectifier smoother boards for a full PSU build if you need them.
/31052845355_e5ae9c0bc3_b.jpg[/IMG]
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Hi, the part list are all the same as the original board stated except the transformer that is a 25VA 24Vx2 Triad and capacitor that are 6800mF.
Yes loaded with the regulator it deliver 26Vdc but only two of the leds on the back are lighted.
Sorry iti is not clean like yours but I'm just testing it.
nxUfkA3.jpg
 
R

RollE2k

Member
Joined 2007
What value is the last series resistor in your pre-reg?

Sounds a bit like there is some kind of trouble with the CCS/regulator part to me.. but i haven't had this trouble so i don't really know.. i think i read somebody else a long time ago in this thread that also had trouble with exactly those leds, so you could maybe search and see if you find it..

I'm also using 2x24VAC transformers, but Selectronic R-core (30VA) instead of the default ones, because i had trouble with hum on all eight i tried.
 
A

AndrewT

R.I.P.
Joined 2004
patriz said:
I wasn't clear, 26,5Vac loaded with the regulator. My mistake, unloaded Vout is 37Vdc
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sq225917 said:
.................
It sounds to me like your transformer VA may be too low............
Click to expand...
37Vac unloaded dropping to 26Vac loaded is an enormous drop.

if the load is taking the transformer to it's full rated output then those two voltages indicate a transformer regulation of 39.6% (37Vac/26.5Vac= 1.396)

That is higher regulation than I have ever measured on very small transformers. 30% is common on 3VA transformers.
I would expect <20% on a 30VA transformer, and dropping to ~6% on a 200VA transformer.
 
patriz

patriz

Member
Joined 2002
lencohell.wordpress.com/
to make it clear:

the main board are rev.2
output transformer is always 26Vac
output pre-regulator is 36Vdc unloaded
output pre-regulator is 21Vdc if loaded with just the regulator
the Hammond 158T is rated as 40R and I have a drop of 5V the last resistance in the clrc net is 47R 20W and I have a drop of 5V on it
the regulator is absorbing 127mA. can anyone confirm this is a correct value?
 
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