[GreenKeys] Inexpensive loop supply

[Ralph Mowery]

Just to show how inexpensive you can put together a loop supply and
interface it to Erics USB board for those that do not have much to work
with.

The parts are simple.

Wall wart that will put out from about 11 to 20 volts at over .75 amp ( 750
ma).

Resistor of about 1200 ohms and 10 to 20 watts for a 90 volt supply board.
Somewhat higher if a higher voltage is used. I used an adjustable one that
was rated about 2000
Ohms and set it for about 1200 ohms.  Not too critical as I used the voltage
adjustment to set the 
Current to exactly 60 ma. That gave a voltage of about 90 volts from the
board.

Boost converter off ebay from China. There are several boards that can be
used.
The one I used is rated for about 45 to 95 volts. The input voltage is not
critical as 
Long as it is between the minimum and maximum values.  If you change the
input voltage, the 
Output voltage will not change.  Ebay item number 191674539868.
There is another that others may want to use that is rated for about 50 to
390 volts.
They are less than $ 10 shipped.  Be careful of the boards.  While they
operate off low voltage DC
They will light up a 120 volt 60 watt light bulb.

The connector between the resistor and loop wiring is a Wago lever nut part
number 222-413. 
 They are about $ 15 for 50.  They make good connections between different
size
wires and can be used over and over. Not really needed, but put in for a
demonstration.
The resistor could be soldered to, but for those without a way to solder,
the screws work.

I did cheat and use a Molex connector on the loop connection and some Power
Poles on the 
Wall wart, but you do not have to. 

I used an old aluminum box to put it in. The resistor and boost board will
get warm so 
ventilate the box. The board from Eric was put in a plastic pill bottle.
You may be able to see the hole where the push button can be pressed if
needed.

If you do not have a meter to set the current, the 'free' one at Harbor
Freight will work.

I do have a reasonable well equipped shop, but thought it would be fun to
see how inexpensive 
this could be done.

Here is a link to the finished supply.


https://drive.google.com/drive/folders/0B7wJcih38lRAM2dwRm1aNW9CSWM

Ralph
KU4PT