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Author Topic: 13.8 v power supply  (Read 1915 times)
KB1GIM
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Posts: 3




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« on: February 09, 2004, 01:53:44 PM »

Looking for a relatively simple (or cheap) idea to build my own 13.8v power supply to power a 2m rig that I bought for my car but I never get to use, having no place to drive to frequently.  Does anyone have a good plan for this type of thing, or am I just going to be better off buying an indoor transceiver or a commercial power supply.  It is my lack of funds that lead to this solution at the moment.
Thanks,
KB1GIM
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TOASTY
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Posts: 41




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« Reply #1 on: February 09, 2004, 04:14:28 PM »

i just built one out of 3 old computer psu's.  it puts out 15.4v which powers my 2m mobile fine, but i do use an old computer fan mounted to my radio's fins for extra cooling.  it'd be easy to reduce the voltage a little lower if you need it.
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G7HEU
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« Reply #2 on: February 09, 2004, 04:32:24 PM »

Matthew

What current does your 2mtr radio draw? That question put slightly differently - what is the max out-put of your radio?

If it's low ( a few amps current or say, 10W o/p )then a used CB type supply may be your lowest cost option ( judging by what they can be bought for on this side of the Atlantic at least ).

If you want to make something it's really easy - you need a transformer four diodes and a capacitor or two. Issue is current draw again though  - we need to know what you need.

Best wishes

Steve
M0HEU.


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G7HEU
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« Reply #3 on: February 09, 2004, 04:34:03 PM »

If you want to make something:

forgot, and a LM71 something voltage regulator. I can look it all up and help by e-mail if you go that route.

Steve
M0HEU.
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KC2MMI
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Posts: 620




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« Reply #4 on: February 09, 2004, 07:21:29 PM »

Toasty-
 15.4V is outside the normal tolerance for "vehicle" power supplies. Anything over 14.4 normally is a failed alternator and results in electrical damage to systems. Do your computer supplies offer any internal option to trim down the voltage in them, so they can total a volt lower?
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SEAN-SAGE
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« Reply #5 on: February 10, 2004, 01:27:27 AM »

I have a mobile 2-meter tranceiver that draws 6 amps current at 13.8vdc. I was able to find an old pentium 1 computer that had a 13-amp capable power supply. Powers mine great, but you'll have to make sure you have the connections right, as most computer power output plugs(if you don't want to mess around with the inards of it) have both a +12v and +5v connection. You can replace the +5v with the -12v wire that should be on the main lead to the mother board. Oh, and one more thing, don't keep the radio on top of the PSU. Mine is RF sensitive, so it will cut power and emit a high pitch noise if I set the radio on top. You could keep the PSU in a non-metalic box though. Good Luck,

Sean Sage
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TOASTY
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Posts: 41




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« Reply #6 on: February 10, 2004, 04:22:37 PM »

KC2MMI:

my radio handles up to 15.8v so i havent bothered to get the voltage down.  it would be quite easy to lower the voltage down to around the 'normal' alternator current in the 14s
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KD8GEH
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« Reply #7 on: February 20, 2004, 02:46:23 PM »

You can also put a cheap 12 volt regulators on the output. Simple one ins LM340-12 ~ The -12 being the voltage. Each one is about 1.4 amps rms, use in paralell for > A's. Ive used em for years with no prbs. The computer supplys could also be adapted if you wanted, as they use the similar type regulation. I have even daisy chained them in various voltages to make the voltage levels I need.  Hope this helps. 73 Dave
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W9GB
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Posts: 2623




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« Reply #8 on: March 07, 2004, 09:14:32 PM »

Several articles on good linear designs (you can repair those in the dumpster - and there are MANY)
http://www.seits.org/features/pwrsup.htm

http://www.kbt-dc-supplies.com/index.php

Parts readily available from any computer center that sells UPS units (good for transformers) or two-way shops.

w9gb
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K1CJS
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« Reply #9 on: March 26, 2004, 09:56:19 PM »

Another way to get what you can use would be a lawn tractor storage battery (Wal-Mart, about $20 and an automatic 1.5 amp motorcycle battery charger Wal Mart sells/used to sell for about $25.

Comes to lots less that the $80 to $90 for a strip down power supply for your rig.  A plus to this setup is you'll have power for your rig during a power outage.  
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N2TMC
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« Reply #10 on: April 02, 2004, 08:03:40 PM »

I use a 12 volt Gel battery from a wheelchair (I'm disabled so I always have one or two laying around) and a EverStart Automatic Charger/Maintainer from WalMart. The unit was $16.95 and works great. I can watch it swap between charged and charging. If you have it hooked up wrong or the battery is bad the trouble light goes on.  Not a bad way to go.

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