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Computer Power Supply?
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jonnymac
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Post Computer Power Supply? Reply with quote
Ok, So here is a new question. I have tons of computer power supplies sitting around, can I use one of these to power a MaxPro? I see the yellow line is +12vdc and supports up to 3 amps? I am assuming these are quite regulated seeing as they are computer supplies.

What do you think?

thanks.

-jon

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Sun Mar 16, 2003 2:35 am View user's profile Send private message AIM Address
pcs
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Post Yes, but... Reply with quote
Yes, but....

12V output is very badly regulated. What you will have to do is
modify the power supply. This is done so that you open it up and
find where the regulator samples +5V and cut that line. Than
make a voltage divider to get 13.8V to +5V and attach that
sampling point to 12V output. A small potentiometer can make
your voltage variable, but make sure it stays below 15V if your
potentiometer breaks.

Another problem is the noise from the 12V ventilator, that might
be heard, if not filtered properly.

Good luck!

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Sun Mar 16, 2003 10:19 am View user's profile Send private message Visit poster's website
jonnymac
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Post Thanks Reply with quote
Ok, thanks for the reply. However I am still very much an amateur when it comes to electronics. How would I find where the regulator samples the 5 volts and what is a voltage divider? I am sure I sound stupid asking this so if it is too complicated to explain don't bother.

Thanks again.

-jon

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To the engineer, the glass is twice as big as it needs to be.
Sun Mar 16, 2003 7:44 pm View user's profile Send private message AIM Address
pcs
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Post I know, and it is also dangerous Reply with quote
If you're an amateur, you better stay away from it!

There are lethal voltages present in the PC power supply,
even after you disconnect the mains cable.

For others: The 5V line is usually very narrow and is going from
the +5V smoothing caps at the output to a resistor divider
and towards the controlling electronics.

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Marko - PCS Electronics
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Sun Mar 16, 2003 11:57 pm View user's profile Send private message Visit poster's website
Grogster
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Post Reply with quote
I've tried this a couple of times, and I find that the results are not really worth the trouble - you're better off with a simple linear(transformer) based regulated PSU.

Most PC power-supply units can be very noisy, creating heaps of crackle or hum or both on your chosen frequency.

Also, most PC PSU's require a signal from the PC that the power is O.K. before the 5v and 12v lines become active. This is done via a "PG" wire(Power-Good), and some supplies happily work with this line tied low or high, or even not connected.

What all this means, is that if you take a PSU from a PC and plug in a mains cable and switch on, the supply might not want to work for you, without a load on it's output of at least a few amps.

Yet other(older) supplies are current-load sensitive, meaning that they need to be connected to a mother-board and CPU(which draw a least several amps when working), so that the supply output lines are loaded before the supply will maintain a constant voltage.
(not a matter of not being regulated, rather a matter of a certain load-current must be drawn from the unit before they work correctly - this loading is USUALLY provided by the CPU itself, as it draws a reasonable current.)


G.
Tue Mar 18, 2003 3:46 am View user's profile Send private message
pcs
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Post Not quite right Reply with quote
Grogster,

if you do the mod I described above, you don't need a few amps
to make it work. That's one of the points of the mod.

Besides a much better regulation.

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Marko - PCS Electronics
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Tue Mar 18, 2003 7:04 am View user's profile Send private message Visit poster's website
Grogster
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Post Reply with quote
Oh!
Fair enough!

I never bothered to modify the PSU - figured it was quicker and easier to start with a linear.

Nice work.



G.
Tue Mar 18, 2003 11:03 pm View user's profile Send private message
pcs
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Post Linear is better for low power Reply with quote
I agree, linear is simpler for a few amps.

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Marko - PCS Electronics
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Wed Mar 19, 2003 12:15 am View user's profile Send private message Visit poster's website
zael
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Post Reply with quote
What about a laptop power adapter? , it has an output of 18.5 VDC 2.7A, with a 12V regulator to get the right voltage.
Can it be used as a power supply unit for the MAXPRO1?
Sat Apr 12, 2003 12:07 am View user's profile Send private message
pcs
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Post 18V is too much Reply with quote
If you use a linear regulator, such as those in the guides, to get the voltage down to at least 15V.

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Marko - PCS Electronics
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Sat Apr 12, 2003 12:08 am View user's profile Send private message Visit poster's website
galaxyfm
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Post Reply with quote
So, are laptop's power adapters good for transmitters?,
they are stable, no noise, and good amperes, but maybe they get too hot.

A 14.5 VDC 2A power supply from old laptop for example.
Is it good for the MaxPRO?
are they good for RF amps too?

What do you think?
Mon Sep 15, 2003 7:25 pm View user's profile Send private message
pcs
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Post Reply with quote
Give it a try

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Marko - PCS Electronics
--------------------------------------------------------
Turn your PC into a FM radio station!
http://www.pcs-electronics.com
fax +386 4 2316 128
Mon Sep 15, 2003 7:52 pm View user's profile Send private message Visit poster's website
dcmicroradio
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Post Reply with quote
Depending on where you live, get a Radio Shack or similar power supply that can supply the 3 amps on a regulated continuous basis. Switched mode power supplies are nortoriously noisy as thoe who used the first generation of PCI transmitters discovered.
Hope this helps.

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Sun Sep 21, 2003 4:17 pm View user's profile Send private message Visit poster's website
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