[GreenKeys] Loop supply options

[Ralph Irish]

Paul

Most TU designs have either a 'set and forget' resistor inside the chassis/cabinet or a 
panel mounted pot of adequate power rating to use to set loop current close to or right
on 60 ma.  My DOVETRONS have two 1/4" loop jacks, and a "LOOP ADJUST" pot right next to
one of them.  It is a simple matter to connect a 1/4" plug to one's ammeter and set the
loop current to 60ma.  It is not something that requires a daily check.  Mostly it can
be considered a 'set and forget' thing.  Occasional checking won't hurt though, and
the interval can be determined by how much you use the equipment.  Some TU designs
have a Loop Current Meter on the panel.  Designer's choice, I guess.

Ralph

-   -   -   -   -   -   -   -


On Sep 9, 2019, at 12:16 PM, 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
> 
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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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