[Milsurplus] Fuses to protect transformers

[WA5CAB at cs.com]

Wayne,

What is the transformer HV secondary RMS voltage (center tap to one end if 
the rectifier is full wave and not bridge)?  If it is 300 VAC or less, a 500 
V rated fuse would be adequate.  For ampere rating, if the rectifier is a 
full waveI think I would try first a Slow Blow rated at about 75% of the 
rated DC full load current.

Robert Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480

In a message dated 03/13/2014 14:31:12 PM Central Daylight Time, 
hwhall at compuserve.com writes: 
> No, that'd be fine to kill spikes on the output but won't disconnect the 
> windings when there is a short or overload that could burn out the winding. 
> That's what I want to look into, protecting the vintage transformer from 
> damage by failures of other parts (tubes, caps, etc.).
> 
> 
> Wayne
> WB4OGM
> 
> 
> 
> -----Original Message-----
> From: Mark K3MSB <mark.k3msb at gmail.com>
> To: hwhall <hwhall at compuserve.com>
> Cc: List Milsurplus <milsurplus at mailman.qth.net>
> Sent: Thu, Mar 13, 2014 7:37 am
> Subject: Re: [Milsurplus] Fuses to protect transformers
> 
> 
> Is using a transorb an alternative? 
> 73 Mark K3MSB
> Sent from my Android phone 
> On Mar 13, 2014 12:27 AM,  <hwhall at compuserve.com> wrote:
> 
> For this 40s vintage Link Trainer electronics I'm working on, I'm thinking 
> that it'd be a good idea to fuse not only the primary but the secondary HV 
> winding, since these transformers are not too easy to find anymore. I'm 
> thinking of pigtail fuses inserted in the wiring under the chassis, to 
> maintain appearances. But I'm not sure about what fuse selection would be 
> adequate protection.
> 
> Would a 1A fast blow fuse be OK for the secondary that probably delivers 
> around 100ma DC? Or to put it another way, how much over the normal current 
> output should I select a fast blow fuse? The filters are dual section choke 
> input with 15 &25 mfd caps. I haven't reached the point of firing up the 
> whole thing, so I have to guess for now at the current.
> 
> The common fuses I have available are marked 250V and the HV is 450V. Can 
> they be relied on to open and not arc?
> 
> Any advice? Thanks!!
> 
> Wayne
> WB4OGM