Whats the highest watts you can run in your truck, using a power inverter?

Discussion in 'Trucks and Trailers' started by TimTim2008, May 18, 2008.

  1. TimTim2008

    TimTim2008 LawnSite Bronze Member
    Messages: 1,772


    Whats the highest watts you can run in your truck, using a power inverter?

    I wanted to get a power inverter for my truck, to run a laptop, and maybe a portable printer for job estimates..

    Just wondering, does the larger ones rundown & kill the trucks battery faster?

    And whats the most you can have? Is a larger one really needed?

    If my laptop is only using 100watts, do i really need to buy a 1000watt one?

    How do you know how many watts your battery can put out?

    Thanks guys..
  2. SiteSolutions

    SiteSolutions LawnSite Bronze Member
    Messages: 1,114

    Bigger will kill your battery faster, but that's mostly according to how much load is on it.

    Your battery should have an amp-hour rating although it will be harder to find than the big CCA (cold cranking amps) that is the big number usually compared to sell batteries. That number is how many amps for how long. 10 Ah is 10 amps for one hour or 1 amp for ten hours or something in between.

    Basically, Watts = Volts x Amps

    If your laptop is pulling 100 Watts from your inverter, then your inverter is maybe pulling 120 Watts off your battery due to it not being 100% efficient... that is, the extra 20 Watts is all used up in the inverter and mostly turned into heat and sound.

    120W / 12 V = 10 Amps

    Of course this is real basic and not taking into account all the subtle real world things that can happen. 10 Amps is not a lot if your engine is running, but I wouldn't run this load for half an hour with the engine off. Definitely more juice than a dome light, it is closer to leaving your headlights on... in fact, I think headlights are around 55 watts each, or 110 Watts for both, so this load is a little more than headlights.

    You might be able to figure out what the output of your alternator is, how many amps it can produce...

    If you go up to more than a couple hundred watts, you're going to need to make sure you have the thing wired to the battery using some heavy gauge wire, like 8 gauge or better. You can probably get it hooked up at a reputable stereo shop for less than 50 bucks and have some piece of mind.
  3. ATL Lawn

    ATL Lawn LawnSite Senior Member
    Messages: 318

    just get a flux capacitor
  4. SiteSolutions

    SiteSolutions LawnSite Bronze Member
    Messages: 1,114

    Yeah but then you gotta drive around at 88 mph for it to work...
  5. topsites

    topsites LawnSite Fanatic
    Messages: 21,653

    There's a lot more to it...

    100 watts at 110volt = almost 1,000 watts at 12 volts.
    So around 80 amps...
    Because to go from 12v to 110 something is getting 9x'd.

    Roughly speaking, 100 watts at 12 volts if it were to be converted to 24 volts would result in 50 watts (at 24v).

    There's no way these power inverters just take 12volt wattage and deliver the same wattage at 110 without further ado...
    I don't think voltage can be increased by a factor of 9 with out some type of compromise.
    And laptops DO run 110, yes?

    And for those that can run 12...
    Don't they make cigarette lighter power adapters for laptops?
  6. Saltydawg

    Saltydawg LawnSite Member
    Messages: 48

    Sitesolutions is correct and without going into further detail just leave your truck running when you have your gadgets turned on and you'll be fine.

    Deep cycle marine batteries are better for extended periods of battery load without the truck running.

    Modern vehicle alternators output anywhere from 60-135 amps depending on what your vehicle came with ... which is more than enough for a laptop and a modest printer.

    If your laptop requires 100 watts of power you will be drawing about 10 amps off your 12 volt vehicle system.
  7. SiteSolutions

    SiteSolutions LawnSite Bronze Member
    Messages: 1,114

    Dude... you're close but not quite getting it.

    Watts is Watts.

    Watts is only a measure of how much energy the load consumes. The laptop consumes the same Watts no matter where they come from.

    Mathematically, Watts = Volts x Amps

    At the output of the inverter, the load is around 100 Watts. At 110 volts, this means the laptop is drawing about 100 / 110 = .9 Amp

    At the input of the inverter, where it is drawing energy from the battery, the load is still around 100 Watts. (I acknowledge that since it is not 100 % efficient, the inverter will consume slightly more energy than it can put out the output.) If the inverter is only 80% efficient, then the actual load now is about 125 Watts. At 12 volts, this is 125 / 12 = 10.4 Amps

    Looks like SaltyDawg was right on the money.

    That's what goes up: the Amps. The Watts stays pretty much the same except for losses due to inefficiency.
  8. johnyredd99

    johnyredd99 LawnSite Member
    from gap,pa
    Messages: 163

    But no one really answered the question on what size invertor would be best suited. Im running a Ram 2500 and would like to install one so I can run small items like 2' flouresant light small fan maybe a drill in my trailer when needed.

    Any thoughts/advice about this?
    sorry to bump an old thread but after all it is what the search button in for.
  9. unkownfl

    unkownfl LawnSite Gold Member
    Messages: 3,837

  10. Patriot Services

    Patriot Services LawnSite Fanatic
    Messages: 14,260

    Topsites has been gone from here for over a year now.:usflag:

Share This Page