What's the easy way to get 12V power and ground to test some car parts?

April 3, 2013 8:10 AM

I've got some car parts I'm selling on eBay, and I need to hook them up to power in order to check a few things and make sure that they work.

The items I need to test are mostly gauges and electronics and won't take much power at all. I don't want to mess around with my vehicle's wiring to hook these up. What is the easiest and cheapest way to get 12V power and ground like I would from a car? Is there an easy way to connect the right wires to a cigarette lighter adapter in a car, or can I get something that I can plug in to AC to convert to DC power with the right wiring?

posted by iknowizbirfmark to Technology (12 answers total)

Look through all of your phone style chargers. Typically called wall warts, you might have one sitting around that puts out 12V. It will be labeled. Note that actual phone chargers will most likely be ~5V.

Every once in a while I go to the local thrift store and buy wall warts for ~$0.75, cut off the end plug and use them for whatever project needs a voltage source. Where you don't need extremely stable, high power, or variable voltages these things are a blessing.
posted by Quack at 8:21 AM on April 3, 2013 [1 favorite]

Go to amazon, search for "12V DC power supply", buy one for 5 dollars. Cut off the plug to get bare wires, or make an adaptor with a soldering iron and a part from radio shack.
posted by RustyBrooks at 8:26 AM on April 3, 2013

Response by poster: "Typically called wall warts, you might have one sitting around that puts out 12V"

When I strip the wires, will it be obvious which is to be connected to the 12v power and which is to be connected to the ground wire?
posted by iknowizbirfmark at 8:34 AM on April 3, 2013

If the car is convenient to you, the easiest way is to take a live and ground right off the battery (length of wire and hold it on each terminal or trap it inside the battery clamps). Beyond that, the 12V power supplies and bare wires/crocodile clips is probably your best bet.
posted by Brockles at 8:34 AM on April 3, 2013

When I strip the wires, will it be obvious which is to be connected to the 12v power and which is to be connected to the ground wire?

Usually one has a white line or a groove and that is the ground in my experience. A cheap voltmeter would soon tell you, though. If you're doing much messing around with electrics you'll likely need one anyway.
posted by Brockles at 8:35 AM on April 3, 2013 [3 favorites]

Wall warts generally don't provide much current (usually less than half an amp) and most aren't 12V. I would suggest a battery booster. These are sealed 12V lead acid batteries (just like a car) for jump starting cars.

I would also humbly suggest that if you can't figure out how to test for supply polarity you might not be qualified to do this sort of thing. Please be careful. You won't kill yourself but you can ruin your equipment or blow some fuses.
posted by chairface at 9:26 AM on April 3, 2013 [1 favorite]

A spare computer power supply can be used, too.
posted by mrrisotto at 9:51 AM on April 3, 2013

OBD-II pin 16 for power and OBD-II pin 4 for chassis ground. You don't even have to turn the vehicle on to have OBD-II power.
posted by Dansaman at 9:52 AM on April 3, 2013

A car's electrical system is nominally 12 V, but in reality it's more like 13.5 or even 14 V (because it has to charge the battery). To be safe you should test at 14 V. But if you don't want to invest in a bench power supply that might be difficult.

A battery booster (as chairface suggests) would work -- those are lead-acid batteries, exactly like a car -- fully charged they will be around 12.8 V.

Polarity: the wires are usually color coded (red/brown etc. are positive) but the easiest and safest thing to do is to get a cheap multimeter for around $25.
posted by phliar at 10:59 AM on April 3, 2013

Best answer:

chairface: Wall warts generally don't provide much current (usually less than half an amp) and most aren't 12V. I would suggest a battery booster. These are sealed 12V lead acid batteries (just like a car) for jump starting cars.
I would also humbly suggest that if you can't figure out how to test for supply polarity you might not be qualified to do this sort of thing. Please be careful. You won't kill yourself but you can ruin your equipment or blow some fuses.

The items I need to test are mostly gauges and electronics and won't take much power at all.

Agree with chairface. Please check the specs of the gauges/electronics you want to test to get an idea of the current requirements. "won't take much power at all" is quite relative.

If you want to just use the car, you can get this car adapter plug from Sparkfun for $1.50.

If you want to test at home with you wall supply, you can get a 12V/2A power supply from Sparkfun here for $10 if that 2A rating is sufficient for you. And you can get a cheap multimeter on Amazon for $10 as well.
posted by thewildgreen at 11:27 AM on April 3, 2013

A computer power supply will work if you have one laying around. Short the green wire on the ATX connector (the big wide one) to ground and it will stay on as long as there's power. Any yellow wire on the various connectors should be 12 volts (the red ones are 5 volts).
posted by neckro23 at 2:13 PM on April 3, 2013

Best answer: The cheapest, fastest, easiest way to do this is to go to $MAJORAUTOPARTSSTORE and get something like this

it won't show the price on the page, but last time i needed one it was like.. $2.75
posted by emptythought at 4:17 PM on April 3, 2013