[sdiy] blowing fuses

Richie Burnett rburnett at richieburnett.co.uk
Sun Feb 16 18:36:11 CET 2020

If it's a SMPS the inrush current at turn-on will probably eat quick-blow 
fuses for breakfast.


-----Original Message----- 
From: ColinMuirDorward
Sent: Sunday, February 16, 2020 2:21 PM
Subject: [sdiy] blowing fuses

Maybe someone has some suggestions for me.

I'm blowing fuses on my "industrial" power supply. This is a salvaged 
+/-15v, 3a supply housed in a rugged metal enclosure. I've wired it up with 
a fuse on the AC mains side, and fuses on the +/-15v side. The AC/mains fuse 
is giving me grief.

Step1) I can turn the unit on, and everything is fine. My synth is only 
drawing 1/2 an amp (or nothing when disconnected).
Step2) Turn the unit off. At this point, I can remove the mains fuse, and 
test it: yes, still good.
Step3) Re-install fuse, switch on. Nothing. Remove fuse and test again, now 
it's blown.
Step4) Install new fuse. Go to Step1)

I haven't used the PSU much yet, but I've powered it on and off loads of 
times and this problem never manifested till now. The fuses are 2amp, 250v, 
which I think is fine, but here is maybe my mistake: they are quick blow 
type. I'm uncertain, though. Wondering if I need to try to find a fault in 
the PSU, or just order the new fuses. But why didn't those quick blow fuses 
break before?

Thanks for reading!




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