Computer power supply

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I have a few computer power supplies, a couple of which have outputs rated at +12 Volts at 20 or more Amperes. I was thinking this could work great for powering 12 Volt gear. But most 12V gear actually wants 13.8 Volts.

So I found a control to raise the voltage. When I got to about 13.4 Volts, the overvoltage protection circuit cuts in and shuts down the unit.

Can anyone direct me to a schematic diagram of a typical unit so I can change that circuit to allow 13.8 Volts? I only need a few percent. increase.
I raised the output as high as I could but the thing still cuts out. I put it aside and tried another one. This one works better but has lousy regulation. There was no control pot so I had to bridge resistors to get the voltage where I want it.

Yes I need 13.8V for ham radio stuff in order to get full output power. I think it's wrong but that's how they do it.
But most 12V gear actually wants 13.8 Volts.

Yeah, 13.8V is common in automotive equipment, but if it isn't working at 13.4 then there isn't much chance that an extra 0.4 volts will make a difference. Turning the voltage up will only increase the likelihood of the supply shutting down due to excessive current draw, if that is what is going on. It certainly won't make an appreciable difference in transmit output power, if that is what you're concerned about. Have you got a ham licence? Usually you have to learn some electronics to get one.

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This page has several schematics. The overvoltage protection typically has several voltage dividers, one for each voltage, which reduces each to a certain level. If any of the (normalized) voltages exceeds a specific threshold, it triggers the protection. To increase the threshold on the +12V, you just need to tinker with its voltage divider.
macboy, thanks! I will look through those diagrams to see if something comes close to what I have.

As for the extra 0.4 Volts, sure I agree that the power won't drop that much. But it seems that you can't get specified performance from ham gear unless you run it at 13.8 V. I tested a Yaesu rig recently that wouldn't put out rated power at anything less. I don't like Yaesu but I imagine the other brands are similar.

I did test this poorly regulated one on two meters (one of my very rare appearances on that awful band) and it worked well. But I am thinking more in terms of running my TS-440S with it. That radio draws serious current, so I need a good power supply.

My main concern here has to do with noise. Will I hear QRN from the switching circuits, or are these units well enough designed to avert that? After all, the receiver sensitivity runs to well under one microvolt.
I don't know if it would work to charge the 5 Volt sources. That's what would happen with the bucking of the 12 and 5 to get 7. I'd have to try it. But two power supplies would be defeating the purpose of saving space over an analog power supply.

Anyway, there are some options here and I will play with it when the mood strikes. Actually I have several power supplies here I don't use, each capable of driving my rig, so it's not that I need more. I just hate to see these units go to waste when they are really rather capable.
My my, aren't we getting negative here!

I will answer your questions, including the one from the earlier post above.

First, I have an Amateur Extra license (first ticket in 1949), and when I test myself with the latest online exams I always pass. I also have a Bachelor's degree in Electrical Engineering. Further, I owned and operated a stereo repair shop for 13 years, very successful. So I think my technical qualifications are appropriate.

Second, I mentioned that I already have several power supplies capable of powering the rigs. I only didn't want to waste these old computer supplies which have been laying fallow for years. A side benefit might be higher efficiency, but that's not really an issue because most of my operation is with my TS-940S and the TS-440S is both backup and occasional mobile. And I have a TS-930S as well, also in the closet. Plus an antique, a Heath HW-101 but I won't use that.

The bottom line is that I love electronics and like to play with these things.

Your callsign, with the M prefix, what does that allow you for privileges?
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