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Homemade PSU help

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Overload

Member
Joined
Dec 18, 2000
I am trying to build a PSU. I have it all put together but when i plug it it i get a large current spike on the 120v primary side of my transformer. i have removed all components exept the two rectifiers (their soldered in) and it still occurs. i lost my schematic and board design (due to format and reinstall) but here is a crude paint sketch of the way my board looks:
PSUboard

Can anyone help or tell me what i have done wrong?
 
Is this the right topic to post this under? if not sorry, its not realy computer related but i am realy frustrated and cant figure out why it isnt working. I thought there must be someone that knows about power supplys in the forums that could help me out
 
The picture confused me a bit, but ehh...
Is the transformer before the rectifiers ?
Becouse I don't see it anywhere.

You also should keep in mind that a coil likes things the way they are, putting a current through it suddenly will make it give you a big current peak anyways. Shutting it off suddenly when it had a current running through it will again give you a current peak.
 
What you experience is the inrush current. This is something you get with every transformer and is the reason for many a "pop" in the speakers when plugging in equipment.

Now, my knowledge is minimal at best, but it should be possibel to "buffer" this inrush somewhat, maybe some sort of current limiting? There are some resistors that have resistance depending on current, they may work?
 
thanks for the input everyone

yes, the transformer is before the rectifiers. its 120v primary and 20-0-20 on the secondary i only showed the 20-0-20 with "wires" in the drawing.

and i thought the same thing about the inrush current, so i tested for this with a smaller 12v prefabricated unit. with no load there was no noticable inrush current using an analog ammeter. however with mine it spikes to well over 6 amps(with no load). and i can feel the cable vibrate when i go to plug it in! i have never built anything like this before but it seems excessive to me

as long as my real board matches my picture noone sees any faults in it?
 
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