ETX TECHNICAL TIPS Last updated: 18 April 2004

ETX-125 Homemade Power Supply

Sent:	Saturday, April 17, 2004 15:39:13
From:	"Jacky Poupot" (jpoupot@evc.net)
On your site I searched an article that could help to build an external
power supply like the #541 from Meade.

I read that this little box gave a maximum current of 1.4 A !!
Amazing... But some friends gave there informations about the current on
a ETX-90.So....

I decided to build a cable with a 2.5mm power connector and plugged in
my ETX-125. On the other side I used my 12 V Radio-Ham Power Supply with
30 A max output. With an Amp. meter I checked the current used by the
ETX-125 and the results are :

1) when the scope is waiting without "working" : 130 mA
2) when the scope runs with all the motors : 580 to 600 mA max
3) when the scope is tracking : 200 mA

So, we can say that 1.4 A is not really necessary.

With all this informations I have built an asymetric power supply that
give 12V at 750 mA.This is very simple to build and very cheap. (sorry
the input voltage is 220 / 60 Hz it's used here)

Here is the scheme :

First, It should be possible to join these electronic part to make a
good symetric power supply. For now, It should be OK. (tested on my
scope one).

The parts to be used :

F : fuse : 100 mA
TR1 : 12V sec. / 9VA / 750 or 850 mA
C1 = C2 : 0.1F/Plastic
C4 : 47F/25V
C3 : 4700F/25V
IC1 : LM7812 on a disipator

But, this sheme can be used to make some power supply from 5V (1A)to
24V(400mA) by changing the TR1, IC1 an C3. I can give the informations
for the parts and the drawing to build the plate.

Hope you will enjoy this on the BEST EXT Site of the World ! Thanks
Mike !!

Best Regards from France

Jacky - F6JFD

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