Computer Power Supply?

[sourapple613]

I have an extra power supply from a dell computer laying around and figured maybe I can put it to use as a power supply for a radio

It says its rated for 18amps for 12v DC.

I want to hook up a 110 maratrac to it.

Calculating watts to amps at 12v DC it seems like it should work.

Anyone ever attempt or try anything like this?

Thanks

[tvsjr]

You can use a computer power supply to power radios or anything else 12VDC if you wire it properly, but 18A isn't sufficient for a Maratrac. A 110-watt Maratrac needs a 35-amp power supply. Nothing is 100% efficient... most radios far from it.

[sourapple613]

well rats...

i thought it might work. In our station we have a similar setup and its only run off a 20A Astron Power Supply.....

I might give it a shot anyway. I won't be transmitting much off of it. Mostly setting it up to have a base unit in my house to function as a pager since Maratracs can decode Quick Call II.

Can you put a maratrac on low power in RSS?

[WB6DGN]

Given the notorious unreliability of computer power supplies, and computer parts in general, for that matter, I would definitely want some overvoltage protection for that setup. It would be a shame to fry a nice radio because of a cheap power supply malfunction.
Tom

[Zack08]

This has me thinking..... Has anybody ever actually tried this on a low band or VHF radio? Since they arent exactly designed with radio in mind, I wonder how much RF noise is present on the output.

I'm looking for a new supply for my desk, but I've been leaning away from switchmode supplies because I'm afraid theyll cause trouble down on 46 MHz....

[WB6NVH]

I agree with Tom here. Why run the risk of cooking a nice radio with a junky switcher power supply like that? Especially if it's in a business application?

There are several web pages out there describing how to modify the typical computer switcher supply to run radios. It seems popular in Australia. Some of the power supply designs require a minimum load at all times, others don't seem to care. I am told the newer supplies are actually pretty quiet, especially running VHF and higher band radios. I think I would want to add a crowbar circuit to keep from toasting what was downstream, and as our esteemed panel has warned you already, a 100W radio needs more current than your supply can provide.

Switching power supplies designed for use with radios should be quiet at 46 MHz. Doesn't Astron have a full line of switch mode supplies? Icom and others have been making internal switchers for HF radios for decades without RFI problems. Homebrewed switchers at 46 MHz would, I think, be on a case by case basis.

[sourapple613]

Well.... I am glad I read all those replies before actually trying it.
I never imagined I'd fry the radio doing that. My worst case scenario was I'd key it up and toast the power supply and junk it!

I don' t have the electrical knowledge to know what a crowbar switch is let alone do it.

I guess I'll hunt around for the proper tool for the job... An astron or similar power supply.

TVSR (or anyone else) is there anything that COULD go wrong with only using a 20 AMP supply like in our fire station??

[Bill_G]

A crowbar is short circuit protection. In the olden days it meant the protection circuit blew the fuse (crowbarred). Modern supplies shut down the power supply if the current exceeds it's maximum. They generally reset automatically when the load is removed.

Someone should measure the actual current drawn by your station radio. Then you can determine if a 20A supply is sufficient or not. Your 20A supply may have a lot of headroom too. It might be able to supply intermittent 25A without breathing hard.

[WB6DGN]

With the caution of overvoltage protection in mind, I have to agree with Bill G. about the current ratings. Remember, the current ratings on the power supply's label assumes that ALL available voltages are running at their maximum current. In the case of a radio supply, probably the only output that will be used is the +12volt output, thereby allowing that output to safely operate at a higher current draw than if all outputs were fully loaded. So, I don't see current rating as the limiting issue here. My concern remains the potential for a gross overvoltage situation in the event of a component failure in the supply.
Tom DGN

[515]

The newer Astro Consolettes have power supplies that are very similar to those in a PC. I believe they are made by this outfit:

http://www.sparklepower.com/proPCPS_EPS.html

I don't have one in front of me at the moment, so I'm not sure if Motorola uses one of their standard models, or if they have one custom made for them. But it looks like they've got a model or two that can do 36A at 12V.

[WB6NVH]

Crowbar protection is over-voltage protection, not over-current, just to be clear. Typical simple designs trigger an SCR which causes a short across the power supply output rail (hence the term "crowbar") which ideally blows the fuse, but in any case is supposed to prevent the over-voltage condition from damaging whatever is being fed from the power supply. In some cases the crowbar does not act fast enough to prevent damage.

[RKG]

The newer Astro Consolettes have power supplies that are very similar to those in a PC. I believe they are made by this outfit:

http://www.sparklepower.com/proPCPS_EPS.html

I don't have one in front of me at the moment, so I'm not sure if Motorola uses one of their standard models, or if they have one custom made for them. But it looks like they've got a model or two that can do 36A at 12V.

They are indeed computer-type power supplies, with a special p/n for the connector. Not much power; limited (I believe) to 15W 800 radios.

I'm not a fan of these power supplies. We had one burn up (after 1 year in service) so badly that it actually turned the housing a scary shade of dark brown. Manufacturer replaced the power supply on warranty.

[WB6DGN]

"http://www.sparklepower.com/proPCPS_EPS.html"

"Sparklepower" huh? Sounds like pure QUALITY to me! Also sounds like it came from more than "26 miles across the sea". SHAME ON YOU, Motorola!
Tom DGN

[resqguy911]

I gotta tell you, the astro consolette power supplies are some garbage. And what they charge for a replacement PS is outrageous!

[Paul]

I have used two el-cheapo 400w PC psu in parallel powering a 100W UHF Syntor-X in a taxi co. dispatch, while in an emergency (the smoke escaped from the old psu, Saturday night)
I can say that it worked flawlessly for over a month, without any effects on the receiver, and I kept it as a fail-safe back-up.