[GreenKeys] Loop supply

[Ralph Mowery]

They are interesting power supplies to work with and not very expensive.  I
started looking into this when someone on the Green Keys mentioned something
about an inexpensive loop supply.  Not counting the case I don't see getting
much cheaper and easier to build than using one of them and a wall wart.  I
picked up some wall warts at a hamfest for $ .50 to $ 2.50 just today.  The
converter is less than $ 10 shipped and I priced some power resistors off
ebay for around $ 5 including shipping.  That puts the thing under $ 15 not
counting the case and can be put together with just a screwdriver and a way
to cut and strip wires.


While I would never say you can not have too many fuses, if power by a wall
wart of around 10 to 20 volts and an amp or so of capacity they should not
need any other fuses.  Hopefully the wall wart will be made with some
internal protection, and as the output should be limited by the amount of
power the wall cube can supply it should shut down if the output is
overloaded.  

Much of the time the inexpensive fuse is protected by a much more expensive
device going out first. (grin).

If powered by a big husky bench supply then fusing is certainly desired. 

As cautioned before , even though the thing is powered by a safe at 12 volt
wall wart, the output can be deadly as even 60 ma at 90 volts can kill or
cause other damage to the body.
I put one to a 12 volt  supply capable of 30 amps.  It would light up a 60
watt filament bulb to almost full brightness.
 

> -----Original Message-----
> From: GreenKeys [mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of
> John Nagle
> Sent: Saturday, June 11, 2016 12:47 AM
> To: greenkeys at mailman.qth.net
> Subject: Re: [GreenKeys] Loop supply
> 
> 
> Nice. Those are cute little switching power supplies.
> 
> I'd suggest fusing both input and output; those things have no
> protection circuitry and too much power capacity.
> 
> 			John Nagle