[sdiy] blowing fuses

[Neil Johnson]

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/
>> >>
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>> >>
>> >>
>> >>
>> >>
>> >>
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