DC Power source thoughts

Well wide electrically experienced folk, here is tonight's thought.

I am shortly going to be reinstalling the wire harness on the Vauxhall. One thing I have long thought would be the benefit of having a variable DC power source - then I could test the circuits without either wearing out a battery or more to the point letting the smoke out of the wires. I can't imagine a lot of amperage would be needed but it would be nice to have a few things

1. variable voltage up to 12V

2. a variety of means of connecting wires including, possibly even battery posts, alligator clips or bullet connectors.

It should be easy to make with a DC transformer - though I am not sure if I could vary the voltage?

do such things exist or, could one make one economically?

thoughts?

Rather than variable voltage, IMO what you really want is a current limiter. Current limited DC power supplies are readily available, tho perhaps more than you want to pay for a single use. But an ordinary car battery charger (rated 10 amps or so) will work quite well for most things (starters and horns are the two exceptions that come to mind).

Transformers only operate on AC, so the usual way of creating a "DC transformer" these days is to chop the DC into AC (generally at a fairly high frequency to reduce size and cost of the transformer) and then rectify the output back to DC. It can certainly be done in a variable fashion; but generally the chopper circuit is what gets varied. Variable AC transformers do exist, but usually are designed for 60 (or 50) Hz, making them big, heavy and expensive. Building your own is probably beyond most amateurs tho, unless you buy a kit. And all the kits I saw with a quick Google were only good for 2 or 3 amps, which won't be enough for many things on a car.

Another, more rudimentary approach is to just put something in series between the car and the battery, that will limit the current. An old headlight bulb works pretty well for devices that only draw a couple of amps, and you can parallel them for more current. (4 bulbs will limit to about 20 amps) Or automotive grade circuit breakers aren't too expensive either.
https://www.delcity.net/store/12V-A...KfiAJXjf96riq1elJyCeRmAk9OT2DyssBbBoCNpLw_wcB

How 'bout an old electric train transformer? AC input creates DC voltage output, which varies to change the speed of the "locomotive".

View attachment 46659

They're on ebay (etc.) for around $5.00

I think most of those older "transformer" type train power supplies (Lionel, American Flyer) will put out AC instead of DC.

Power supply out of an old computer? I think they have 12v and 5v outputs. It's not variable, but you are testing 12v circuits right?

JP
Whatever you do be sure to put a fuse or circuit breaker into the system- I always put it on the ground side of the circuit. I use a 10 amp breaker.
The "HO" style railroad transformers usually have two outputs, 12 volt AC AND variable DC.
BillM

Portable battery pack with a cig lighter outlet. Carry one on boat for hot shots and to run aux lights and GPS

Some great ideas - I had thought about the computer power source - but, had not considered a transformer - I might even have a couple downstairs.

I would definitely use Billm's advice, and fuse the outputs. I'm thinking very conservative, like 2-5 amp quick blow fuses... depending on the power supply's amp/watt rating, and whatever you might be testing... just to protect the power supply.

kennypinkerton said:

I would definitely use Billm's advice, and fuse the outputs. I'm thinking very conservative, like 2-5 amp quick blow fuses... depending on the power supply's amp/watt rating, and whatever you might be testing... just to protect the power supply.

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absolutely!

There are battery eliminators in science supply houses. They start at very reasonable prices. They use banana plugs to connect. The other end of the cable can be anything you want.

https://www.learningaboutelectronics.com/Articles/What-is-a-battery-eliminator.php

maynard said:

There are battery eliminators in science supply houses. They start at very reasonable prices. They use banana plugs to connect. The other end of the cable can be anything you want.

https://www.learningaboutelectronics.com/Articles/What-is-a-battery-eliminator.php

Click to expand...

Now that is very cool! I went on ebay and searched - and I REALLY REALLY want something that looks like this!

https://www.ebay.com/itm/Vintage-EI...221344?hash=item43f8eeff60:g:eW8AAOSw4GVYJLX~

or this

https://www.ebay.com/itm/Heathkit-M...664534?hash=item4d52256656:g:q0IAAOSw9GhYeC37