TheBeastie Posted November 18, 2007 Share Posted November 18, 2007 I want to hard wire my 300W inverter through a fuse and relay so when ignition off so is the inverter. I cannot get my head around what sort of DC current will run through the wiring to power the inverter. I was thinking of going for 84/0.30mm, 6mm2, 50amp thinwall cable and using a 40amp fuse to protect the cabling. I know not whether this is hopelessly inadequate or wildly over the top. I would prefer not to see The Beastie burst into flames Can anyone who understands these technicalities please enlighten me. I would also love to know what the equations are so I can fathom it myself if I ever do again - such as if I decide to put a bigger inverter in. I know the inverter does 12v DC to 240v AC (or thereabouts). Furthermore I can follow 300w on 240v = 1.25amp but I guess it is going to have to suck quite a lot of 12v to come up with that - hence my guessing 50 amp cable. Any enlightenment would be wonderful - thanks Malcy Quote Link to comment Share on other sites More sharing options...
101nut Posted November 18, 2007 Share Posted November 18, 2007 Power=Amps*Volts so 300=Amps*12 therefore Amps=300/12=25A Cable size in this case will be more to do with the voltage drop you get across it at this current since if the voltage drops the inverter performance will drop ... 50A cable should be ok as long as the run isn't too big and make sure you have a good negative feed as well. AndyG Quote Link to comment Share on other sites More sharing options...
TheBeastie Posted November 18, 2007 Author Share Posted November 18, 2007 Thanks. I thought there would be some fancy jiggery pokery going in with the DC to AC conversion. Had not realised that the W=A*V equation worked regardless. I am looking at about a 2m run and was planning to feed the relay from a fused link off battery and to earth back to battery too. So on that basis my 50 amp cable should be fine but should I try to lower the 40amp fuse back to 30amp to give more protection or is it likely to keep blowing? Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted November 19, 2007 Share Posted November 19, 2007 101nut's numbers are bang on for a 100% efficient inverter, however I'd wager it will blow the 25A fuse, you'll probably want a 30A fuse and may have to crack out the 40 depending how good an inverter it is (some can provide higher surge currents, for example 300W continuous / 600W surge) in which case it may hit higher draw for a second or so at it's max output. Quote Link to comment Share on other sites More sharing options...
Mark90 Posted November 19, 2007 Share Posted November 19, 2007 If the invertor has an on/off switch I would remove this and replace with a relay and use this to switch the invertor on/off rather than switching the high current DC feed. Quote Link to comment Share on other sites More sharing options...
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