ChrisD Posted October 23, 2013 Share Posted October 23, 2013 Hi Everyone Looking for help with calculating how much my 300 watt inverter is taking from my leisure battery. For instance my 60 watt TV uses .25 amps 240/60. how do I calculate that as the load on my leisure battery. All help would be appreciated. I am trying to calculate my optimum battery size for our next long trip to France. The inverter is pure sine wave. Regards Chris Link to comment Share on other sites More sharing options...
lennyhb Posted October 23, 2013 Share Posted October 23, 2013 The power remains the same so it will still be 60 watts at 12v plus say 10-15% for inverter inefficiency so base it on 70 watts at 12v = 5.8 amps. Link to comment Share on other sites More sharing options...
ChrisD Posted October 23, 2013 Author Share Posted October 23, 2013 Wow, that simple! Thanks Lenny -- great help Chris Link to comment Share on other sites More sharing options...
tonyishuk Posted October 23, 2013 Share Posted October 23, 2013 Only to add that some appliances can draw a higher current on start-up, than when on running. I would add 30% to just allow some leeway over the losses cited above. Not a problem usually, but if you a running an invert near maximum, on just adequate wiring and fuse, there could be problem with the fuse blowing. Rgds Link to comment Share on other sites More sharing options...
Cliffy Posted October 23, 2013 Share Posted October 23, 2013 That is interesting . We have two 120 Ah batteries and likewise a ,25 Amp TV . plus a satellite receiver and a couple of LED lights. On wet days I ration the TV usage as after 5 hours the battery condition is down to 10.5 Volts (with the TV on). Does that mean the Satellite receiver is using a lot of power or the batteries are on there way out. This is when running on direct battery power. not inverter. Link to comment Share on other sites More sharing options...
lennyhb Posted October 23, 2013 Share Posted October 23, 2013 Sounds like your batteries are well past there sell by date, assuming you meant 2.5 amps. Satellite receiver would normally draw less than 1 amp. 5 hours at say 3.5 amp use plus 3 amp for lighting that's 32.5 amp hours that's only 13.5% of your battery capacity. You should never run your batteries that low, a sure way to shorten their life. After running for 5 hours turn everything off leave for at least 10 min then check the voltage it will give you an idea of the state of charge. 100% 12.70v+ 75% 12.40v 50% 12.20v 25% 12.00v 0% 11.80v These are figures for wet cells (standard lead acid). Link to comment Share on other sites More sharing options...
Cliffy Posted October 23, 2013 Share Posted October 23, 2013 Lenny You are right it is 2.5 Amp, When I switch the TV off the voltage goes up to 12.2 Volts. then creeps up 12.6 Volt. So does this still have an ill effect on the batteries? Cliff Link to comment Share on other sites More sharing options...
lennyhb Posted October 23, 2013 Share Posted October 23, 2013 Either your batteries are naff or the TV is taking a lot more than 2.5 amp. I would do a test on the batteries, fully charge the batteries let them rest for ½ hour check the voltage, then put a known load on them easy way is to switch the lights on in the van until you are drawing say 5 amps leave them on for 12 hours(5x12=60=25% of 240 a/h), turn off leave battery to stand for½ hr check voltage should be 75% charged, repeat the test should then be 50% charged then again for 25%, I wouldn't go below that. I recently did a similar test on my 5 year old Exide Gels gave results you would expect of new batteries.. Link to comment Share on other sites More sharing options...
Dave Newell Posted October 24, 2013 Share Posted October 24, 2013 Running TVs from 300 watt inverters and the like is a pretty surefire way to knacker a battery. Inverters are often quoted as being 90-95% efficient but what is rarely explained is that efficiency is only true at (typically) 2/3rds of maximum load, so for a 300 watt unit it is most efficient at around 200 watts. Move away from that load in either direction and the efficiency drops off, even more so when going downwards as the inverter itself takes current to work. I would suggest that a 300 watt unit providing just 60 watts of 230 volt power would probably be around 50% efficient. My advice would be to bin the inverter (figuratively speaking) and get a proper low power 12 volt TV. D. Link to comment Share on other sites More sharing options...
Robinhood Posted October 24, 2013 Share Posted October 24, 2013 Cliffy - 2013-10-23 9:35 PM Lenny You are right it is 2.5 Amp, When I switch the TV off the voltage goes up to 12.2 Volts. then creeps up 12.6 Volt. So does this still have an ill effect on the batteries? Cliff ......if the off-load voltage is recovering to 12.6v (without any form of charging, e.g. solar or on-board charger) within a reasonable amount of time, and then staying there, then I doubt there is anything critically wrong with your batteries. The on-load voltage will always drop, and, depending on how/where you are measuring it, sometimes quite dramatically. Voltage drop along inadequate wiring to a panel measurement can often give misleading results, as can a poorly-calibrated panel. Measurement across the battery terminals with a good multimeter is a somewhat better indicator. Where/how are you measuring the voltage, and if it is at the panel, what is the normal (full) reading when it has been off-charge and off-load for at least an hour? Link to comment Share on other sites More sharing options...
tonyishuk Posted October 24, 2013 Share Posted October 24, 2013 Don't know if this now banned by the Chief Ealth & Saftey Officer, but when I were a lad, I used a battery hydrometer to read the SG of the battery acid. A bit stuck of course if you have gel batteries ;-) A right of passage, wondering why small holes were appearing in your jeans ! Rgds Link to comment Share on other sites More sharing options...
Cliffy Posted October 24, 2013 Share Posted October 24, 2013 The readings are taken from the Control Panel. Next time I have the van at home I will test it as you suggested and will check it with a multimeter. Thanks to all for your help Cliff Link to comment Share on other sites More sharing options...
Brambles Posted October 24, 2013 Share Posted October 24, 2013 Cliffy, everything indicates to your batteries being shot. WHAT you can do if they are not sealed types is check the electrolyte level, it may be very low and top it up, fully charge and then see how they perform. But dropping to 10.5 volts and creeping back up to 12.6 with the low current you are using indicates they are well shot or well down on electrolyte and that itself will have probably 'murdered' them. Link to comment Share on other sites More sharing options...
Guest 1footinthegrave Posted October 25, 2013 Share Posted October 25, 2013 Very interesting article in this months CC club magazine about so called leisure batteries, surprise surprise many of them are almost total crap, although they refused to name the crap ones, only the two good ones.mmmmm ;-) In any event I was told some time ago that some are only good for around 150 charge / discharge cycles. :-S But I too cannot understand why the OP doesn't get a 12 volt TV, in my view a much better option. Link to comment Share on other sites More sharing options...
Barryd999 Posted October 25, 2013 Share Posted October 25, 2013 Why is the OP running a 60 watt TV in a motorhome in the first place and then through an invertor? Seems like a recipe for disaster if you ask me. How big is the TV? Must be huge! I spend a lot of time off hook up so I researched TV power usagequite a bit. It seems a lot of the cheap ones are power hungry between 20-40 watts but some are less than 20 watts. The one I opted for in the end was an Akura 16" from Makro which was just 14 watts or 1.2 amps. Its superb and only cost £90. We stayed of hookup pretty much the entire summer and watch TV every day. Single 100w solar panel and MPPT Controller. Get a new telly, probem sorted Link to comment Share on other sites More sharing options...
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