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Car Charger for the 18V Batteries

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  • Car Charger for the 18V Batteries

    Is a 12V dc Charger in the works yet?

  • #2
    I use a 12v power inverter, with a 6 outlet power strip. I have 3 chargers, though only one sees daily use, laptop computer and printer all operatiing on it. I think it's rated at 250 watts. I think you can but them for under $30 now. I've been using this setup for 4 years. Note that it will drain your battery if left on for more than several hours (overnight) without the engine running.
    This will get you through until they do make a car charger, and has many other uses. Mine will run a Bosch jigsaw, but only at low speeds. There are larger (750 watt) that will run that jigsaw great, plus about anything else.


    • #3
      Before doing this, take a close look at the power drain of the charger. If it is stated in watts, double that figure. If it is stated in amps, take that number and multiply it by 240. The inverter you buy should have no less capacity than the result of either calculation.

      If the inverter is worth more than about 100 watts, you should think carefully about running it from a cigarette lighter socket. Some are wired with only AWG16 wires, to 5A fuses; the most you are going to see is AWG12 wire with a 15 or 20A fuse. 250 watts at a nominal 12VDC is more than 20 amps.


      • #4
        So it has an imput of 240W, and an output of 4.1 amps. so do you need a 480+W inverter or a 984+w inverter?


        • #5
          240W at a nominal 12VDC is about 24 amps. However, you have to factor in inverter inefficiency, which in the small inverters is pretty high (which is why I said to double the input). My guess is that if you hooked that inverter up to a large 12VDC power source, and then plugged the charger into the inverter and a discharged battery in to the charger, you'd see a draw on the 12V line of 40A plus or minus some. There is no way you can take that out of a cigarette lighter socket; you'll either melt the feed wires (actually, you hope you do) or start a fire.

          Likewise, if you take 40A out of the typical car starting battery while the engine is off, you'll kill the battery in very short order.

          Perhaps a bit off the point, but if you need high power out of an engine-driven environment, you have three choices:

          A high output alternator (such as the Hehr 120A) on your propulsion engine, which charges a large battery bank (500AH or more) to which is attached a big computer-controlled inverter (such as the Heart Interface). The 1kW Heart can put out 1kW continuous, 1.8 kW for 10 minutes and 3kW starting, and what the alternator can't supply, the batteries can without damage (and they will be recharged promptly).

          Second, if you need more, one of the 120VDC alternators into a power converter. You can get up to 5 kW (on three belts), but you'll need an expensive engine speed control module, and you'd best be very careful of 120VDC, which is more than lethal.

          Finally, abandon your propulsion engine altogether and put in a true 110VAC (or 240VAC) genset. There are gasoline-fueled, cage-mounted gensets of up to 10 kW (basically, a large construction generator), vapor-fueled gensets up to about 35kW, and diesel-fueled sets up to a couple of mW.

          [ 01-23-2004, 03:54 PM: Message edited by: RGad ]


          • #6
            I use a 400watt invertor in my truck to charge batteries. It was great for my DeWalt charger - one at a time - but when I put both batteries on at once with the ridgid it shuts itself off. I had a hunch that would happen. It's no big deal to charge one at a time in the truck.

            I did run a fused line directly to the battery to be on the safe side. Don't need to melt wiring and start the truck on fire.

            The invertor is fretty spiffy. Automatically detects low battery voltage and shuts off, overload protection etc. Seems like a great little toy.


            • #7
              Not to ruin your day, but most power supplies (things that take a nominal 110VAC and convert it to a DC voltage) should NOT be used with an inverter. The reasons are complicated, but most modern power supplies use "switching" technology (to save cost and weight) -- this includes the chargers that come with DC-powered hand tools -- and the switcher is dependent upon uniform zero voltage crossing points. However, most small and inexpensive inverters use a wave form known as Modified Sine Wave," which does not yield uniform ZVC points. There is nothing wrong with MSW inverters for most loads, but they should not be used with switching power supplies, microwave ovens, or anything with a clock in it.