[Milsurplus] Fuses to protect transformers

[hwhall at compuserve.com]

The HV winding is 450-0-450 and a 5Y3GT is used for fullwave. 


 Wayne

 WB4OGM

 

-----Original Message-----
From: WA5CAB <WA5CAB at cs.com>
To: hwhall <hwhall at compuserve.com>; milsurplus <milsurplus at mailman.qth.net>
Sent: Fri, Mar 14, 2014 12:31 am
Subject: Re: [Milsurplus] Fuses to protect transformers


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