[sdiy] blowing fuses

ColinMuirDorward colindorward at gmail.com
Sun Feb 16 16:49:45 CET 2020


Ahhh OK, I'm sure you're right, thanks Neil. I've got this horrible feeling
of just looking at my newly assembled synth tower while I wait for slow
blow fuses to be delivered to where I live in Yukon. That's enough to make
anyone panic, right?
Maybe they have them at automotive parts suppliers.
Cheers,
Colin

On Sun, Feb 16, 2020 at 1:37 PM Neil Johnson <neil.johnson71 at gmail.com>
wrote:

> Colin,
>
> You're over thinking this issue.  You have two large transformers
> feeding into rectifiers and large empty capacitors.  With quick-blow
> fuses the startup current will probably blow a QB fuse (not always,
> its a chance thing).  As well as the magnetising current in the two
> transformers you also have the initial capacitor charge-up current
> surge.  Both will kill a QB fuse.
>
> Time delay slow-blow fuses are the recommended type in this application.
>
> Neil
>
> On Sun, 16 Feb 2020 at 18:28, ColinMuirDorward <colindorward at gmail.com>
> wrote:
> >
> > Thanks, Neil.
> > I can see two transformers, each one is maybe half a fist size. There is
> also a massive blue can, a capacitor?  Must be two inches long and one inch
> diameter. It's a Lambda PSU. I've searched the model number but can't find
> any data.
> >
> > How does this magnetized transformer problem work? Doesn't that
> magnetism dissipate after a short time? Reason I'm asking is because last
> time I waited overnight before turning it back on again, by which point I
> thought any residual charges/magnetism would have dissipated, but it blew
> the fuse nevertheless.
> >
> > Sorry if I'm dragging this out!
> > Colin.
> >
> > On Sun, Feb 16, 2020, 10:19 AM Neil Johnson, <neil.johnson71 at gmail.com>
> wrote:
> >>
> >> Don't use quick-blow, use (T)ime delay (slow blow) fuses.  I'm
> >> guessing the transformer is quite large, the magnetising current
> >> "thump" is probaby killing the QB fuse.
> >>
> >> Neil
> >>
> >> On Sun, 16 Feb 2020 at 18:06, ColinMuirDorward <colindorward at gmail.com>
> wrote:
> >> >
> >> > Unfortunately, there seems to be no mention of a fuse.
> >> >
> >> > On Sun, Feb 16, 2020, 9:46 AM Richie Burnett, <
> rburnett at richieburnett.co.uk> wrote:
> >> >>
> >> >> Usually the rating label tells you what fuse to fit?
> >> >>
> >> >> -Richie,
> >> >>
> >> >>
> >> >>
> >> >> -----Original Message-----
> >> >> From: ColinMuirDorward
> >> >> Sent: Sunday, February 16, 2020 2:43 PM
> >> >> To: Richie Burnett
> >> >> Cc: *SYNTH DIY
> >> >> Subject: Re: [sdiy] blowing fuses
> >> >>
> >> >>
> >> >> Thanks Richie.
> >> >> I should have mentioned, it's a transformer/linear supply.
> >> >> Not only us it eating fuses for breakfast, but dinner, too. In a
> couple
> >> >> hours, I'll be able to test lunch.
> >> >> So I suppose there is some faulty (or non-existant) inrush current
> >> >> protector, and it's costing me one fuse to charge up whatever is
> sucking
> >> >> those amps?
> >> >>
> >> >>
> >> >>
> >> >> On Sun, Feb 16, 2020 at 12:36 PM Richie Burnett
> >> >> <rburnett at richieburnett.co.uk> wrote:
> >> >> If it's a SMPS the inrush current at turn-on will probably eat
> quick-blow
> >> >> fuses for breakfast.
> >> >>
> >> >> -Richie,
> >> >>
> >> >>
> >> >>
> >> >> -----Original Message-----
> >> >> From: ColinMuirDorward
> >> >> Sent: Sunday, February 16, 2020 2:21 PM
> >> >> To: *SYNTH DIY
> >> >> 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!
> >> >> Colin
> >> >>
> >> >>
> >> >> --
> >> >>
> >> >> https://www.instagram.com/colinmuirdorward/
> >> >> -
> >> >>
> >> >> https://www.instagram.com/ssdp_synthesis/
> >> >>
> >> >> Virus-free. www.avg.com
> >> >>
> >> >>
> >> >>
> >> >>
> >> >>
> >> >> _______________________________________________
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> >> >>
> >> >>
> >> >>
> >> >>
> >> >> --
> >> >>
> >> >> https://www.instagram.com/colinmuirdorward/
> >> >> -
> >> >>
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> >> >>
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