[Milsurplus] Fuses to protect transformers

[Peter Gottlieb]

Put two in series. Yes, a hack, but one which works pretty well. If the first fuse opens and arcs there is usually enough current to open the second one. 


Peter

> On Mar 13, 2014, at 10:06 PM, "Richard Brunner" <brunneraa1p at comcast.net> wrote:
> 
> Firstly, those are ac rated fuses and will not work anywhere as well on dc. ac interruption is easier than dc because there is the current zero.  The voltage rating on a fuse is the highest voltage it will reliably interrupt. At higher voltage and dc the fuse will melt and arc, dropping the voltage, which may be enough to save the equipment and transformer, but a better solution is using hv rated dc fuses, if you can find them.
> 
> Second thought: Since it will be feeding rectifiers, the current will be dc pulses with a current pause, so there is some opportunity for current interruption.  However, since it is way over the ac fuse voltage rating it is hit-or-miss whether it will interrupt, and probably not.
> 
> Richard, AA1P
> 
>> 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
> 
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