Power Supplies

I fancy building a 12 volt regulated power supply with short circuit protection.

I had an old ATX PC power supply that was garbage so I gutted it and now I'm left with a nice metal box, plus I have an old beefy mains transformer that looks like it can deliver half decent current & puts out 30 volts AC. I already have a full wave rectifier to convert the AC to DC and a smoothing capacitor I will also still need to drop voltage down to 12 volts while maintaining the current but I know I will need a lot more than that. I'm hoping to be able to draw at least 7 Amps from this power supply at the bear minimum but 10 amps would be satisfactory as long as its not below 7 amps. 

I'm not sure if there are ready made boards but I'm guessing I'd probably need to build one from scratch...

any ideas on some schematics &  component list?

Thanks.

It's great that you want to build your own power supply, that's what the hobby is all about.

I also need a power supply for when I operate in the house (the shack is off grid.) But after thinking about modifying a computer PC PS, I realise that I can't guarantee near zero spurious emmisions, and I need 30 amps. So I'm going bite the bullet and buy a quality switched mode PS.

Good luck with your project.

Deb

PC power supplies can be good and pack plenty of current to power a transceiver but I find that its only ever a temporary solution. I'm not really a fan of switch mode power supplies.

I've watched YouTube videos of people modifying microwave transformers by removing the secondary coils and replacing it with thick wire to get more current... I was thinking I could do something like that and create a 50 Amp to 100 Amp power supply.

I really wouldn't advise anyone to rewind a microwave transformer, even if you think you know what you're doing!

I also wouldn't suggest someone builds a mains driven power supply unit unless they knew what they were doing either no matter how much they 'fancy' making one.

You can ignore the warnings as much as you'd like...you could be successful or at a minimum you'll blow something up and at worse you'll injure or kill yourself. You could also kill someone else who attempts to recover your person if still connected to the mains and maybe even start a fire which could potentially kill many others.

If you actually knew what you were doing you wouldn't need to ask for schematics or parts lists having already acquired the knowledge required to do so and understanding any dangers that such a project could pose.

There, I've said it.....and I know full well the response may be an ugly one from either yourself or others but my main concern is for the safety of individuals attempting such projects let alone those around them.


Some think that you only require a modicum of knowledge to pursue an 'interest' (watching YouTube videos is one ugly example) but I really suggest you acquire all the knowledge you can and need before undertaking any project that could cause you injury or worse.

Even so called simple experiments with batteries and such can pose dangers with high currents through underrated cables causing injury burns or fires and once you get onto Lithium based battery technology....well the danger possibilities are endless. (Lithium battery fires and explosions are no joke!)

I'm all for people "learning" but in many instances it's best to gain the knowledge required beforehand as with some things you won't get to learn by your mistakes them only being able to be made once.


I'll await the flack that might be the response to my concerns of safety (some don't like to be 'told' something no matter the basis) but my intentions are good.

It's bad enough when you hear stories of radio enthusiasts falling from heights putting up antennas (and why they have the ladder safety question at Foundation) but many are also injured or worse 'playing around' with mains voltages or high current supplies.

Safety First.


All the best,
Victor

Sorry but i have to go with Victor on this one.
Repaired many years ago and have thought about building one with plenty of amp's but had second thoughts and never tried.
I bought a 60a Palstar some years ago way too big but the way i look at it it is just ticking over with my requirements.

Same here Alan with repairing such units (or upgrading their useless component design even from manufacturers!) and also designed them for a living in the course of my electronics profession.

Even when I needed a higher current supply for my radios in recent years I simply purchased one as the parts cost to build your own is often higher to individuals than bulk buying manufacturers.

I've always pointed out the danger risks for such projects and why I didn't go into details with my station mains filtering unit I mentioned some time back in my pursuit for a lower noise floor.

I understand your concerns I am an electrician, I also used to work on washing machines & kitchen appliances for a second hand electrical goods company. I also still have my PAT tester and other test stuff. I have had a few of 240 volt shocks in my time which hasn't done me any harm not that I intend to work on things while they are live. I'm quite knowledgeable on electrical safety but this doesn't mean I have the knowledge to build what I want. I still have to look up schematics if I want to make something half decent.

I can build a basic DC power supply from a mains transformer but it would only be basic and I'd be lucky to get more than 2.5 amps from it. This is why I have to ask about "schematics" and I always interested with new ideas of how other people have built stuff. 

I will probably end up looking at a board inside an existing 10A power supply and then reverse engineer the same board for a home made power supply.

It was the notion of even considering trying to rewind a microwave oven transformer for a power supply that concerned me especially with the lack of copper and iron. (To keep microwaves cheap.)

Under a no load condition you'll find that the core would saturate with the excess magnetic field causing the output voltage to drop and the current to increase often to a dangerous level seriously overheating the core.

You might get away with a short duration primary operation, shorted output load for a short time with the typical examples of 'spot welders' but not much else.

Five minutes of a Google search will hark results for many types of power supply unit especially of the linear variety. Old ARRL Handbooks have some great projects along with other old radio magazines so might be worth taking a look at the world radio history site here :- https://www.worldradiohistory.com/index.htm

(Most have complete construction articles.)


I wish you well and hope that no further mains shocks are added to your self professed past experiences that so far have luckily done you no harm. (You only usually get one shot at high voltage, high current shocks and that'd be your first and last!)

Keep safe.

All the best,
Victor

There are plenty of schematics available for 13.8V regulated supplies. Many Hams have made their own in the past, me included, may years ago. The cost of parts these days and the time involved means it's often just as cost effective to just buy one. However if you have the experience, the time and can follow a schematic there is no reason you can't give it a go. With so many designs already on the internet you should probably use google and find one that best suits your needs and for which you can source the components. I can recall the times we used to run a car battery on trickle charge as a capacitor and connect the rig directly to the battery terminals. It worked fine but looked ugly, but don't try this at home :-)

I've found quite a few schematics online... I also had a an ATX power supply with some bad electrolytic capacitors and another spare mains transformer in my parts box and some decent heat sinks and thought I could build two power supplies while I'm at it. Those older ATX PC power supplies have nice solid metal boxes to build stuff into, not like the modern flimsy ones, plus the board inside has a few useful components I could re-use for my power supply projects like the diodes to make the bridge rectifiers plus the ferrite cores are also worth saving for other ham things. 

Two nice mains transformers and boxes plus heat sinks and a bunch of parts. I've also got spare terminal posts, I don't really have to buy many other parts. I tested all the diodes I removed from the ATX power supplies and they are good. 

I enjoy making stuff I could spend hours building things. The first transformer I have looks decent and fits nicely into the gutted ATX box with plenty of room for the board I will make.

The second transformer is a bit larger but doesn't fit an ATX box but I found something suitable to mount that into. I also have some old toggle switches I can use.

The hardest part is making sure I have the current I need at the other end. A lot of schematics I found were only good for 1 amp. 

For the smaller transformer I want to get at least 4-5 amps out of it once its all built. That is the one I am building into the ATX power supply box.

The larger transformer I would like to aim for 7-10 amps for that one.

I'm quite enjoying my power supply builds and learning more as I go along. The mains transformer needs to have at least 35 volts AC at the other end then the bridge rectifier to get DC and then a voltage regulator to get the voltage down to 13.8 volts DC and then for over voltage protection encase the regulator shorts out in the event of a fault comes the crowbar circuit... for current I will use extra transistors. For now I will build an experimental power supply just to get an idea of things. I will post some of my schematics a bit later on.