Cigarette lighter power socket

Scottjames1uk
Scottjames1uk Forum Participant Posts: 17
edited December 2015 in Caravans #1

I am fitting a cigarette lighter to my caravan to enable me to plug a 300 watt invertor into it. The only main item that will be powered is a 24 inch led tv.I also need the cigarette lighter to charge a mobile phone. What rating of inline fuse do ineed to
do this?

Comments

  • rogher
    rogher Forum Participant Posts: 609
    500 Comments
    edited December 2015 #2

    In theory 25A.

    12V X 25A = 300W.

    More importantly, make sure that the wires you use are thick enough to carry that amount of current and place the fuse at the battery terminal.

  • ChemicalJasper
    ChemicalJasper Forum Participant Posts: 437
    edited December 2015 #3

    The in line fuse should be matched (lower than) to the lower of the rating of the socket used or the cable used - I do not know what cable or socket you have used so could not be more specific.

    I=P/V so a 300W transformer will draw a minimum of 300/240 1.25 Amps + losses but that is much lower than the rating will be on the 12v system, subject to what cable you have used - 10A, 15A, 20A ??? 

    Out of curiosity, does the TV have an external transformer brick? If so, is the TV already 12V (most are)?

    Rather than use a transformer to go from 12v to 240 volt and then a transformer to go from 240v to 12v - just put a plug and socket in the wire in the output from the transformer (check polarity) and plug the TV directly into the 12V.

    A much more efficient (ie less losses of electricity so you will extend the life of your battery) way to do this.

  • ChemicalJasper
    ChemicalJasper Forum Participant Posts: 437
    edited December 2015 #4

    In theory 25A.

    12V X 25A = 300W.

    More importantly, make sure that the wires you use are thick enough to carry that amount of current and place the fuse at the battery terminal.

    Is that correct Rogher? (you posted as I was typing)

    300W is the output (240v) side of the transformer not what the transformer required to produce 300W output at 240V?

    Have I got this wrong?

     

  • rogher
    rogher Forum Participant Posts: 609
    500 Comments
    edited December 2015 #5

    We are talking power. So, assuming no losses, 300W is 25A@12V or 1.25A@240V. 

    Whatever power comes out must have gone in.

  • ChemicalJasper
    ChemicalJasper Forum Participant Posts: 437
    edited December 2015 #6

    Yes looking at google it would apprear I have it wrong with respect to the amps a 12V! - my bad!

  • TheAdmiral
    TheAdmiral Forum Participant Posts: 506
    edited January 2016 #7

    I thought most vans had a fag socket fitted as standard 

    Admiral

  • Woody19
    Woody19 Forum Participant Posts: 43
    edited January 2016 #8

    Note that cigarette lighter sockets are only designed to handle 10A maximum and usually no more than 5A at which they will be fused. Pull 25A or more through it and it will melt or catch fire.

    If the OP has no option but to use an invertor then he should make some sort of arrangement to connect direct to the battery. Having said that the invertor is capable of providing 300W but will only actually provide what the TV takes - for a typical LED
    TV that should be around 35-45W (i.e. with invertor losses that is a maximum of about 4-4.5A) and that will be OK for a cigarette lighter socket.

    One word of warning: most of the cheaper invertors put out a 'modified sine wave' which is actually a series of voltage steps that equate to a normal mains sine wave - ish. You cannot be sure that it will not damage the TV power supply. It is good advice
    to get a 'pure sine wave' type but these are typically about double the price.

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