Power inverter help...

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Patriotleasing, Mar 4, 2019.

  1. Patriotleasing

    Patriotleasing Bobtail Member

    Jan 1, 2017
    Installing a 2000 watt power inverter in my Pete. I've been told to install an inline fuse / relay on both positive cables between the batteries and inverter. My question is, what size fuse / relay should I use?
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  3. Working2party

    Working2party Medium Load Member

    Feb 10, 2018
    2000w/12v=167amps or 2000w/14=143 amps
    sometimes the power inverter has a peak and continuous wattage. so take the peak wattage and divide by 12 or 14. If your running it direct and not through a key power I would use 12. Since all the inverters I’ve seen usually have at least an internal fuse protection, Find the smallest breaker or fuse that’s above that number from the equation and you should be close enough. So Incase of the numbers above I would try to find a 175amp or 200 amp breaker.
  4. fss99701

    fss99701 Medium Load Member

    Feb 14, 2019
    none of your business
    Last edited: Mar 4, 2019
    Tb0n3 Thanks this.
  5. Rideandrepair

    Rideandrepair Road Train Member

    Aug 8, 2015
    Great question. There’s so much conflicting information on this. No real clear rules. I finally decided on 100 amp for my 1000 watt and 150 amp for my 1500 watt. (Based on what Ive read 2000 watt would need 200 amp fuse). But don’t take my opinion as I know very little about any of it.I Bought them at Advance Auto Parts.I’m assuming they’re mounted between battery post and cable. Any input is appreciated,don’t want a fire.
  6. Working2party

    Working2party Medium Load Member

    Feb 10, 2018
    51371FCD-3332-4576-A247-5E19A40E1894.png The science of it says, gauge it off the lowest voltage and the highest amperage the inverter is likely to be used at. To start, If you likely plan on the last dying wish of you batteries is to keep your sandwich meat cold in you refrigerator, figure on 10v and and 2000 watts which puts you at 200 amps. If you wire it to only come on with the key, figure 12V which is @170 amps, or if it will only ever run with the engine on figure 14V which is 150 amps.

    The way it’s installed will effect this as well. When the length, size, and quality of connection of your cables is taken in account you can add 10% for the right size cables with clean protected connections. If you end up using too small of cables for the length, only crimp your connectors, and leave your connects un-protected (open to corrosion) then you’ll need to add over 50% more amp protection and you may still have the risk of failure.
    I use the chart above from Standard Motor Products anytime I’m wiring in something new. It gives you the size for cable compared to the length for the amperage that’s expected.

    So in this case, if 2000w is the peak/surge power. And this is in a truck with an APU that should almost always see 14 V and both the cables for the inverter are less than 10 ft and both run back to the batteries. I would still use 12v ( to add my roughly %10) in my math. I would use 6 gauge cable, with soldered and protected connections. And a 175 or 200 amp breaker /fuse. If I don’t have the ability or time to solder the connections and try to ground back to cab, I would run 4 gauge power wire with 275 or 300 amp (or higher) fuse or breaker.

    So start with the peak watts, figure your clean amps needed, decided your mounting and routing of your inverter and size your cables according to your installation method, add your percentage accordingly

    And always protect with a lower amperage than your cables are designed to handle.
    Last edited: Mar 5, 2019
    Reason for edit: Clicked post before I was finished
    Rideandrepair and Tb0n3 Thank this.
  7. Tb0n3

    Tb0n3 Road Train Member

    Oct 5, 2012
    OP definitely needs to make note of the recommended wire gauges. 4/0. Not 12 gauge. This is what causes the majority of fires with this. And protect any body penetrations with grommets to prevent shorts to ground.
    Working2party and fss99701 Thank this.
  8. loudtom

    loudtom Road Train Member

    Aug 26, 2016
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