[GreenKeys] Loop supply options

[epvgk at limpoc.com]

On Mon, Sep 09, 2019 at 10:16:08AM -0600, Paul Heller wrote:
> Does anyone use a rheostat to fine tune the loop current, or is that a silly idea and close is good enough? 
> 
> Paul
> W2TTY

I have a big fat wirewound one in there because if I connect a bunch of machines the
current drops quite a bit and I might want to reduce the resistance to bring it back up.

> 
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> 
> > On Sep 9, 2019, at 9:10 AM, Ralph Irish <w8roi at wowway.com> wrote:
> > 
> > This transformer is  EXACTLY  what is needed for a trouble-free loop supply.  With a bridge
> > rectifier and a healthy cap, it will provide fairly clean 170VDC at one amp.  This is not an
> > unheard of voltage for a loop supply.  Several experimenters in past decades used voltages up
> > to 250VDC for test purposes and found no ill effects to selector magnets, etc.  No matter what
> > the 'supply voltage' is, the voltage applied to the actual magnets will be less due to the
> > dropping resistor and hopefully, an adjustable resistor to set the loop current at idle to 60ma.
> > 
> > The external resistors carry the extra voltage and if properly sized wattage wise will easily
> > dissipate the heat from I squared R losses.
> > 
> > If I were going to build a loop supply, that would be my first purchase.  Price is reasonable
> > and ratings seem conservative for long life.
> > 
> > Good luck to all who are going to build a loop supply for some machine or system.
> > 
> > Ralph - W8ROI
> > 
> > -   -   -   -   -   -   -   -
> > 
> > 
> >> On Sep 9, 2019, at 10:21 AM, Jeff G wrote:
> >> 
> >> When I first saw this thread, I had the exact thought of just a 1:1 transformer with a bridge and cap.
> >> 
> >> FYI - 1:1 transformers are readily available yet, I work on arcade games and nearly every game has one, both for safety reasons as well as being required by the open frame monitors. You can still buy them new.
> >> 
> >> I'm sure you can find them on Amazon, etc, but here's an example from one of the popular vendors: http://www.arcadeshop.com/i/1346/monitor-isolation-transformer.htm
> >> 
> >> These are usually good for an amp or two, as they generally run everything on the game through it. Add a bridge, a cap, and a couple fuses and you're there, for much less than $100.
> >> 
> >> Jeff
> >> 
> >> 
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