[GreenKeys] Loop supply, or are we still beating out wifes and kicking the dog

[Ralph Mowery]

I received a board in from Ebay that will convert about 10 volts to 30 volts
up to about 60 to 90 volts.  I was able to get about 95 volts out of the one
I bought.

 

It is almost like a DC transformer in that the higher the input voltage the
less current it will take to produce the same high voltage out.

 

Playing with it I inputed 12 volts at about ½ of an amp.  The output was
around 80 volts at 60 ma. Changing the input voltage does not seem to change
the output voltage if between 12 and 24 volts (the limit of my test).   By
using around 1080 ohms of resistance in series and the USB to RTTY loop
conveter that Eric just put out to drive the Model 15 printer it works just
fine.  I used some fixed resistors that I had on hand and adjusted the
voltage to about 80 volts for the 60 ma loop current.  I then used about
1200 ohms and adjusted to about 90 volts to give me the  same 60 ma loop
current.  

 

For someone that wants a very simple loop supply of a high enough voltage
this is a simple way to get it.  Just feed the board with any voltage from
about 11 volts up to 24 volts and you will get a constant voltage you can
adjust from about 60 to 90 volts.  Then Get any resistor of about 1000 to
1200 ohms , maybe less if you have several printers in series,  and one of
the wall warts from 12 to 24 volts at about half an amp or more.  

 

Two words of warnings.  While it  is fed with 12 volts, be aware that it is
putting out about 90 volts and enough current to be like sticking your hand
in the wall socket. If using a resistor like I show below, make sure you cut
the supply off and wait for the capacitors to bleed off the charge.  I lit
up a 60 watt 120 volt  bulb with mine just to check it out. 

 The other is the input and output is not totally isolated and the negative
leads are connected together.

 

You will need a case to put the supply in as it does have dangerous voltages
in it. Not counting the case You should be able to put one together for $ 15
to $ 20. If you need a meter to adjust the loop current you can get one of
the ‘free’ or $ 5 ones from Harbour Freight if there is one near you .

For those that do not have anything in the junk box or cannot build much,
you cannot  get any simpler than this.

 

This is the one I used, it costs about $ 7 shipped from China.

http://www.ebay.com/itm/191674539868?_trksid=p2060353.m2749.l2649
<http://www.ebay.com/itm/191674539868?_trksid=p2060353.m2749.l2649&ssPageNam
e=STRK%3AMEBIDX%3AIT> &ssPageName=STRK%3AMEBIDX%3AIT

 

 

 

item number:

191674539868

 

Use a resistor like this.

http://www.ebay.com/itm/152088667131?_trksid=p2060353.m1438.l2649
<http://www.ebay.com/itm/152088667131?_trksid=p2060353.m1438.l2649&ssPageNam
e=STRK%3AMEBIDX%3AIT> &ssPageName=STRK%3AMEBIDX%3AIT

 

 

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