300watt inverter

Discussion in 'Tech/Mech General' started by Petros, Jun 2, 2016.

  1. Petros

    Petros Funster

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    I have a 300 watt inverter and want to wire in a plug so that i can use it to charge phones and small items. Is it acceptable to wire in a cigarette lighter socket direct from the leisure battery and if so what thickness of cable do i need? I am also adding a second leisure battery, what thickness of cable do i need for that?
     
  2. pappajohn

    pappajohn Funster Life Member

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    Phone charging etc is far better done by a USB socket or a USB adaptor in the cig socket.
    In effect what you will be doing is changing 12v to 230v then back to 5v via the plugged in charger or for 12v its back to 12v for other stuff....torches etc. Completely pointless.

    Battery cable size depends how far between batteries...the further apart, the heavier the cable.
    Next to each other (and using an inverter) I would use a minimum 16mm cable.
    One battery under the seat and the other at the back....at least 35mm cable.

    AND....unless there is absolutely no possibility of the cable being trapped or damaged ie: next to each other, fit a fuse at BOTH ends of the link cable.
     
    Last edited: Jun 2, 2016
  3. John Laidler

    John Laidler Funster

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    I would fit a USB socket so you can plug things in directly to charge. You can get double ones, ideally both or at least one being a two amp outlet. If you buy the wire in Halfords it is marked by current, 10A or 15A should be fine. They also sell in-line fuses, and a 5A fuse would be wise but if your USB socket is two 2A outlets then an 8A might be best.

    You can wire them directly to the batteries, it isn't very "elegant" and the socket will take a small current drain. If you can find an "Aux" circuit which can be switched off that would be better.

    For the extra leisure battery use the same thickness cables as are going to the existing battery. There is a best practice way of connecting the two, you can find wiring diagrams on line, the aim is to ensure both batteries are loaded equally. On which subject if your existing battery is getting on you would be wise to fit two new ones - but I accept that isn't a cheap option.

    Edit: PJ beat me to it! I had assumed the second battery would be next to the existing one, if not, much thicker as PJ recommends. :)
     
  4. Petros

    Petros Funster

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    Thanks very much the info very helpful. Both batteries will be side by side and the existing one is only 15 mths old so i am hoping i don't need to replace that.
     
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  5. Petest

    Petest Funster

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    How about something like this. I've wired it into a connector block that was already in the wiring.
     

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  6. Stealaway

    Stealaway Funster

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    One of these -


    $_12.JPG
     
  7. mitzimad

    mitzimad Funster

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    i would go up a size on what the van builder has used they seldom use cable with any headroom
     
  8. Techno

    Techno Funster Life Member

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    Mmm cable with headroom (n)
    Like it :LOL:
     
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  9. autorouter

    autorouter Funster

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    A 300 watt inverter running at its maximum output will draw 300/12 = 25 amps from the 12V supply. Because the voltage conversion is only 90% efficient I'd guess that's more like 28 amps. That is rather too much for a cigarette lighter socket - in my experience most will get hot if passing 15 amps.

    Having said that, phone and small battery chargers are unlikely to be using more than 100 watts or so. If you really want a plug and socket you could wire it up with a 10 amp fuse in the cigarette lighter plug, which will let you use 10 x 12 = 120 watts.

    Otherwise, wire it up to the leisure battery using a 30 amp fuse, 2.5mm2 flexible cable and a switch that can handle 30 amps. Instead of a switch I'd prefer to use a 30 amp relay and controlled by a small switch. The switch/relay is to cut off the inverter completely. That's because even when off they draw a small current that can drain the leisure batteries if left for a few days, and motorhomes often are. It's a good idea to use an illuminated switch to remind you it's on.
     
  10. pyro

    pyro Funster

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    Personally I hate invertors. As pointed out above, a 300 watt invertor will draw around 25 amps at full tilt. This entails serious cabling.

    I use one of these



    It is what is known as a "buck convertor", draws 15 watts and provides 1.5A at each of the two 5V USB sockets with next to no heat Alternatively one of these will do the job:

     
  11. autorouter

    autorouter Funster

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    Yes, I hate inverters too. I have a 4-way and two 2-way cigarette lighter adapters wired to spare fuses in the 12V distribution box from the leisure battery. And that's just in the cab area.

    I use two of these:

    http://www.maplin.co.uk/p/belkin-road-rockstar-4-port-passenger-car-charger-n70eg

    with the 'backseat passenger extension' stuck on top of the dashboard to power the satnav, tablet, bluetooth GPS unit etc. They will supply up to 2.4 amps per USB socket.

    But there are some things that just need an inverter. A gizmo that charges phone batteries out of the phone, that plugs into a wall socket. My CTEK charger to charge the scooter battery. The bluetooth speaker charger with the funny plug that gives 7.5 volts. And even the 120 watt slow cooker that cooks as we are driving along.

    I have two inverters, 100 watt and 150 watt pure sine wave, both with cigarette lighter plugs, and I use them frequently. I think the OP would be better off with smaller inverters like these, but if the 300 watt one has already been obtained, then either of my suggestions would get it up and running.
     
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