Can I use my power supply to charge a car battery?

Discussion in 'Mobile Radio Systems' started by KC8BWS, Feb 3, 2011.

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  1. KC8BWS

    KC8BWS Ham Member QRZ Page

    I have errands today and as luck would have it, both cars are dead - as in totally flat. My regular battery charger isn't working and I'm at a loss for what to do now.

    Any advice would be deeply appreciated.
     
  2. KA9VQF

    KA9VQF Ham Member QRZ Page

    I have a home brewed 10 amp regulated power supply that I occasionally use to charge the battery on my riding lawn mower.

    I suppose if you bring your batteries inside the house and thaw them out for several hours they might take a charge with whatever power supply you might have on hand.

    Be aware that a totally dead battery will draw all the amps it can when you first hook it up. It could damage your power supply but probably not so badly you can not rebuild it.

    Since your regular car battery charger is already toast you might want to think real hard before possibly sacrificing your good radio power supply.
     
  3. KC8BWS

    KC8BWS Ham Member QRZ Page

    Alrighty, thanks much. I'll not risk it. I like operating too much to risk it. Guess I'll wait till dad gets home. 73
     
  4. KA9VQF

    KA9VQF Ham Member QRZ Page

    For not to much money you can go to radio shack and buy a 3 amp transformer and a few diodes and whip up a quick and nasty power supply that will slowly charge your batteries.

    You wont need to add a regulator chip so long as the output is pretty close to 14 volts with no load.

    You do know how to make a whetstone bridge out of four diodes right?
     
  5. AD4DQ

    AD4DQ Ham Member QRZ Page

    Get a jump start, car starters require at least 50 amps of power just to turn the engine, you could use a radio power supply to charge small batteries like KA9VQF has said, but 10 amps on a car battery would require a chrage of at least 24 hours. Ask the neighbor for a jump, or roll the car out in the middle of the street, someone will help you then :D
     
  6. N2RJ

    N2RJ Ham Member QRZ Page

    I've used a 10A power supply to charge a car battery enough to start the car. It's doable but not something I'd recommend doing repeatedly.

    I have a real battery charger now.
     
  7. WA6MHZ

    WA6MHZ Subscriber QRZ Page

    I have had good luck charging Gel Cels, which also take alot of current, by adjusting the voltage of the supply very low (say, 11V) and watching the current meter when hooking it up. As you increase the voltage, the battery will start to draw current, and if it is a 15A supply, you can allow it to take a safe value of current until it charges up to that point. Then advance the voltage some more, over and over until you are up to 14V and it is floating at minimal current. It takes watching, but you won't blow up your supply if you are careful to watch the current.
     
  8. AB9YP

    AB9YP Ham Member QRZ Page

    You also can do a quick and dirty current limit with a high powered resistor. I've used that to "trickle" charge a battery from a cigarette lighter socket on a trip, without blowing the fuse when it was really low compared to the power source.

    Not terrible efficient or fast, but it will get the job done. Just make sure to get the power rating on the resistor high enough. (I use four 10w resistors in parallel, I believe, and they still got plenty hot when the voltage differential was high.)
     
  9. AB9YP

    AB9YP Ham Member QRZ Page

    You also can do a quick and dirty current limit with a high powered resistor. I've used that to "trickle" charge a battery from a cigarette lighter socket on a trip, without blowing the fuse when it was really low compared to the power source.

    Not terrible efficient or fast, but it will get the job done. Just make sure to get the power rating on the resistor high enough. (I use four 10w resistors in parallel, I believe, and they still got plenty hot when the voltage differential was high.)
     
  10. N5YPJ

    N5YPJ QRZ Moderator QRZ Page

    I doubt that you would ruin your power supply as long as it is properly fused but unless you had a really large power supply you will very likely blow the fuse unless you can lower the voltage output on the power supply. The smaller battery chargers have some sort of current limiting circuitry that protects the unit. I've charged batteries with 15 - 20 - 25 Amp supplies before by lowering the voltage and slowly working it up.

    Years back in another life, I had float cells and a deep cycle battery as an emergency power supply that I kept maintained with a Pyramid power supply. Since I operated everyday then I didn't keep the PS going 24 / 7 floating the string but only when I was using the radios that kept the string well if not fully charged, yet every time I would switch on the PS the over current warming circuit would come on and have to be reset.
     
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