tonyfletcher Posted November 10, 2013 Share Posted November 10, 2013 This is one for an experienced electrical boffin. I have a 12 volt 225 ahr battery powering a 2kw Inverter. For peace of mind I have fitted a Battery cut off switch on the +ve lead. We use a Microwave 700 w and a Hairdryer 1400 w (not at the same time) . The switch has melted. My question is what rated switch should I have fitted. Can someone out there do a calculation and advise me Cheers Tony Link to comment Share on other sites More sharing options...
Tracker Posted November 10, 2013 Share Posted November 10, 2013 1400 watts at 12 volts is around 117 amps, add in 10% for inefficiency and resistance and you get up to about 130 amps current flow. A proper engine battery cut off switch should be capable of handling starter motor amperage which can be a lot higher than that - what voltage and amperage is the switch rated at? Link to comment Share on other sites More sharing options...
Robinhood Posted November 10, 2013 Share Posted November 10, 2013 Tracker - 2013-11-10 2:21 PM 1400 watts at 12 volts is around 117 amps, add in 10% for inefficiency and resistance and you get up to about 130 amps current flow. A proper engine battery cut off switch should be capable of handling starter motor amperage which can be a lot higher than that - what voltage and amperage is the switch rated at? .....but to be sure, and to allow for the maximum rate of output of the inverter, rather than the current stated load, I think a 200A rated switch would be more appropriate. Link to comment Share on other sites More sharing options...
lennyhb Posted November 10, 2013 Share Posted November 10, 2013 Battery cut out switches normally come in 2 flavours 300 & 500 amps, your hair dryer would draw about 130/140 amps allowing for inverter inefficiency, you may have had a 100 amp switch they used be the norm. I'm not sure how the switches are rated it is probably for xx min at max power as in normal use they will only see max current for the few seconds when an engine is being started. In your case you are running high current for much longer periods which is probably why the switch melted. You could try a 500 amp switch or replace it with a 200 amp fuse do make sure your cables are rated higher than the fuse. Link to comment Share on other sites More sharing options...
tonyfletcher Posted November 10, 2013 Author Share Posted November 10, 2013 Thanks again, I knew that there would be some knowledgeable chappies out there. The rated amperage for the switch I had was supposed to be 275. Which makes it suitable for your collective calculations. I have my doubts over this rating and may try a Durite 500a switch. Is there any difference to with polarity the switch should be on? +ve or -ve? Once again thanks for the info Kind Regards Tony Link to comment Share on other sites More sharing options...
lennyhb Posted November 10, 2013 Share Posted November 10, 2013 Just checked a 300 amp switch has a continuous rating of 100 amps. Link to comment Share on other sites More sharing options...
sshortcircuit Posted November 10, 2013 Share Posted November 10, 2013 The switch would normally be in the +ve . Have you fitted a fuse at the battery end with an increased size of cable. Heat can be created by a bad connection???? Link to comment Share on other sites More sharing options...
tonyg3nwl Posted November 10, 2013 Share Posted November 10, 2013 Hi, not only is the switch a potential problem, solvable with a big enough clumpy great thing, but my concern rests with the battery duration, .The current drain around 150 amps out of a 220 amp hour rated battery will drag the battery down from fully charged nominal 14 volts, down to working voltage of 12 volts very quickly. the battery rating of 220 amp/hours will be on the assumption of a 10 hour rate, ie 22 amps for 10 hours. By drawing 150 amps, the battery will be exhausted, or overcooked very quickly , maybe as little as half hour and suffer potentially serious internal damage, distorted plates etc. You might get your microwave meal done in ten minutes, but dont expect to dry your hair as well, unless you are very thin on top.. one cycle of discharge, recharge you might get, but be ready to replace the battery very very soon.. For the kind of load you wish to use, a generator would be much more realistic, provided you are willing to apologise to your neighbours. tonyg3nwl. Link to comment Share on other sites More sharing options...
Keithl Posted November 10, 2013 Share Posted November 10, 2013 tonyg3nwl - 2013-11-10 5:27 PM For the kind of load you wish to use, a generator would be much more realistic, tonyg3nwl. Or stay on a site with EHU, much simpler :D Link to comment Share on other sites More sharing options...
lennyhb Posted November 10, 2013 Share Posted November 10, 2013 Keithl - 2013-11-10 6:03 PM tonyg3nwl - 2013-11-10 5:27 PM For the kind of load you wish to use, a generator would be much more realistic, tonyg3nwl. Or stay on a site with EHU, much simpler :D Not everyone likes sites with EHU's Link to comment Share on other sites More sharing options...
Iain Strachan Posted November 11, 2013 Share Posted November 11, 2013 Use Gas, it cooks much better than a micro! Link to comment Share on other sites More sharing options...
bolero boy Posted November 11, 2013 Share Posted November 11, 2013 Iain Strachan - 2013-11-11 12:07 AM Use Gas, it cooks much better than a micro! ......and does your hair in a trice! Love it, Iain. Seriously, for those of us with short hair, especially the men, we don't see hairdrying as an issue and can manage without microwaved meals when not on EHU. We use a mix if stops with and without Ehu so domt resort to dryers but, for some with longer hair (ladies especially) the lack of a dryer can be a marriage breaker. Our pals have a gas powered tongs for styling hair, but perhaps not for drying it fully? May just abaout do the job but there are some fussy campers out there..... Link to comment Share on other sites More sharing options...
lennyhb Posted November 11, 2013 Share Posted November 11, 2013 Brought 'er indoors one of the gas straightener/curler before our last trip works a treat for hair drying with the brush attachment, takes a bit of time but much easier than finding EHU when you are on top of a mountain. :D Link to comment Share on other sites More sharing options...
tonyfletcher Posted November 12, 2013 Author Share Posted November 12, 2013 Thanks for the early comments, slightly lost the thread toward the end. . Link to comment Share on other sites More sharing options...
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