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JJ Member Since: 18 May 2009 Location: Winchester Posts: 932	Inverter current draw Can anyone advise how long it would take to flatten a battery using an inverter. I am at the Romsey show tomorrow and plan to use an inverter to charge a small Nexus 7 tablet using a 150w inverter plugged in to the 12v socket , the last thing I want is a flat battery at going home time. I have a car as a static display but can't run the engine. Thanks John
13th Sep 2013 4:42pm

leeds Member Since: 28 Dec 2009 Location: West Yorkshire Posts: 8582

Not a question which leads to a simple answer. OK a broad stroke calculation with lots of assumptions Power = Voltage x current. 150/12 =12.5 amps Now assuming that the 150 watts is the output power and that losses are 20% then current draw could be 15 amps (12.5 x 1.2) Assuming you have a 68 amp hr battery then the invertor will work for a minimum of 4.5 hours. (68/15 =4.5 hrs) Next question what is the current draw of your actual tablet? Difficult to say but if a late model nexus then the battery is reported to last about 8 hours. So chances are that if you take a fully charged late model Nexus then it should last all day. You could safely top up the Nexus from your invertor. Another possibility if this is going to be a regular occurrance is a hyperjuice battery. In summary you should be ok, but take your jump leads just in case you need to start another vehicle Brendan

13th Sep 2013 5:13pm

JJ Member Since: 18 May 2009 Location: Winchester Posts: 932	That is a very comprehensive and re-assuring answer, Thank you. Jump leads on standby.
13th Sep 2013 7:14pm

Lou Sparts Member Since: 15 Apr 2012 Location: Kent Posts: 1501	I,m no expert but is,nt the 150 watts at 240 volts as its on the output side of the inverter ? I had a 400w inverter that you could plug into a ciggy lighter that has a 10 amp maximum and a 15 amp fuse and that never blew. Confused ? I am. 2005 Td5 90 XS Steve
13th Sep 2013 7:41pm

leeds Member Since: 28 Dec 2009 Location: West Yorkshire Posts: 8582

Whilst the invertor might be rated at 400 watts maximum output that does not mean it is actually supplying the maximum power. It is probably a good idea for the maximum power required to be less then the actual maximum power output of the invertor. Also the wiring and fusing to be capable of coping with the maximum output of the invertor. A 12 volt power socket rated at 10 amps is capable of 120 watts. Plugging a 400 watt invertor into it, means that there is a strong possibilty that you could overload the 12 volt socket and wiring. The fact that you have not blown a 15 amp fuse basically means you have not drawn more then 180 watts. Brendan

13th Sep 2013 8:18pm

leeds Member Since: 28 Dec 2009 Location: West Yorkshire Posts: 8582

Whilst the invertor might be rated at 400 watts maximum output that does not mean it is actually supplying the maximum power. It is probably a good idea for the maximum power required to be less then the actual maximum power output of the invertor. Also the wiring and fusing to be capable of coping with the maximum output of the invertor. A 12 volt power socket rated at 10 amps is capable of 120 watts. Plugging a 400 watt invertor into it, means that there is a strong possibilty that you could overload the 12 volt socket and wiring. The fact that you have not blown a 15 amp fuse basically means you have not drawn more then 180 watts. Brendan

13th Sep 2013 8:19pm

leeds Member Since: 28 Dec 2009 Location: West Yorkshire Posts: 8582

Whilst the invertor might be rated at 400 watts maximum output that does not mean it is actually supplying the maximum power. It is probably a good idea for the maximum power required to be less then the actual maximum power output of the invertor. Also the wiring and fusing to be capable of coping with the maximum output of the invertor. A 12 volt power socket rated at 10 amps is capable of 120 watts. Plugging a 400 watt invertor into it, means that there is a strong possibilty that you could overload the 12 volt socket and wiring. The fact that you have not blown a 15 amp fuse basically means you have not drawn more then 180 watts. Brendan

13th Sep 2013 8:19pm

leeds Member Since: 28 Dec 2009 Location: West Yorkshire Posts: 8582

Whilst the invertor might be rated at 400 watts maximum output that does not mean it is actually supplying the maximum power. It is probably a good idea for the maximum power required to be less then the actual maximum power output of the invertor. Also the wiring and fusing to be capable of coping with the maximum output of the invertor. A 12 volt power socket rated at 10 amps is capable of 120 watts. Plugging a 400 watt invertor into it, means that there is a strong possibilty that you could overload the 12 volt socket and wiring. The fact that you have not blown a 15 amp fuse basically means you have not drawn more then 180 watts. Brendan

13th Sep 2013 8:19pm

Lou Sparts Member Since: 15 Apr 2012 Location: Kent Posts: 1501	This electrickery stuff confuses the hell out of me but why would a 400 watt inverter plug into a 10 amp socket that will blow a 15 amp fuse if you use even half of your 400 w max output ? 2005 Td5 90 XS Steve
13th Sep 2013 8:28pm

Tiger Member Since: 06 Jul 2012 Location: Wales Posts: 2265	Am I missing something Why would you not just use 12v to power the Nexus??
13th Sep 2013 10:17pm

Tiger Member Since: 06 Jul 2012 Location: Wales Posts: 2265	Am I missing something Why would you not just use 12v to power the Nexus?? What advantage does an inverter do? 12v -> 240v -> 5v ???? why not just do 12v -> 5v ???
13th Sep 2013 10:18pm

JJ Member Since: 18 May 2009 Location: Winchester Posts: 932	Tiger wrote: Am I missing something Why would you not just use 12v to power the Nexus?? It was a last minute plan and I didn't have a 12v connection for charging the tablet but I do have an inverter lying around. All went well and no drama with a flat battery.
15th Sep 2013 12:13pm

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