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Thread: Lamping lamp/battery problem....

  1. #1

    Lamping lamp/battery problem....


    I need to wrack your brains please and get some advise, DIY and electronics are not my strong point....


    I have just wired up a battery with a cigarette socket to use on my lightforce 170 dimmer with a 100w bulb. The battery is a 12v 17ah one that I use on my rotary, the cigarette lighter a cheapy from the local hardware store rated up to 8 amps. I cut the croc clips off and wired some O's on the end to fit the battery.


    Plug the lamp in and it turns on, but it will not then turn off and starts really dull and just gradually gets brighter, before I wimp out and worry about damaging the lamp. Someone mentioned I may have the polarity wrong, swapping the connectors just then means the light comes on as soon as plugged in and the on/off switch does nothing.

    Anyone any ideas what I am doing wrong, obviously not being able to turn the lamp off is a worry and it obviously is not right.

    Over to you clever people to help out a simpleton!

  2. #2
    SD Regular
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    Herefordshire, Hampshire or Essex
    Polarity not wrong (the symptoms you describe when you swapped them over are the reverse polarity ones - don't do it - burns out the circuit board VERY quickly)

    Sounds like you've got an issue with the cigarette socket. Rated at 8amps is barely enough to take the current required. Possible a small short in the wires? Is the cable you've wired it up with man enough for the amp through put? Feels like you have a current bottleneck and the thing getting brighter might be something breaking down. The short might explain the lamp not turning off - and as before this may have already damaged the LF circuit board (=new LF).

    Check the lamp back in the car (or where you normally use it) and make sure it's functioning as it should.

    Just another thought - is the battery definitely drawing anything like 17Ah?
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  3. #3
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  4. #4

    Many thanks for taking the time to reply.

    I have checked the LF back in the car and all seems fine, although there is a slight humming noise from the lamp when i use the dimmer, there is none at full power but hums ever so slightly when dimmed, I assume this is normal, I just never noticed it before. All the functions work as they should so hopefully all is ok there.

    The cigarrette socket was already wired, and it does seem quite thin wire. The socket is already sealed so cannot be re-wired but it was a cheap one so I will assume that it is this that has the problem.

    Would this be a better bet: | Golf Battery to 12V Socket Lead

    Also, I have no idea how to check the draw, would I use a multimeter, but that would just show Amps right?

    Sorry for the dumb questions, electricity never was my thing!

  5. #5
    Hi is the dimmer an add on or built into the later type LF, I ask because using a 100w bulbs will require the uprated 100w dimmer, they make two types one rated for the Tracer lamps 55w.

    Have used LF lamps for yonks and found they require decent wiring and connectors especially when using 100w bulbs, or they can be troublesome and downright frustrating to use.

    Regards WB

  6. #6

    The dimmer is built in, its a brand new one.

    I think I might just need to get a decent wired cigarette adaptor for the battery and try again. Just hoping I have not knackered the lamp trying so far.

  7. #7
    Basically, 8amp is not enough current to run a 100w bulb of 12v. Also voltage drop due to minimum cable spec will increase the current being drawn. for dc power calculation power equals voltage times current so to run a 100w bulb of 12v you need 8.33333 amps, If the voltage drops, current goes up. pm me and i can give you my mobile number if you need clarification. Also, your battery will struggle to last 1.5hrs should you get the rest sorted.

    hope this helps,


  8. #8
    Karl.. your cigarette lighter is rated at 8 amps.
    Watts = volts x amps so that would be 12 volts x 8 amps = 96 watts. That doesn't stack up too well considering your lamp is 100w.
    If you are not running the engine when the lamp is on then the battery 12v supply will be dragged right down and the dimmer may not want to play at that lower voltage.
    I would say you need a better/higher rated ciggy lighter + fuse as has been suggested above and also to run the lamp with the engine on and see what difference that makes.
    Let us know how you get on.


  9. #9
    As above bud.

    you will need a 10 amp rated socket and you will need a 8 amp (most use a 7.5) fuse as a fuse will never blow at its rated amps,

    the other problem you have it the dimmer switch will not work if its wired revers polarity IE you must make sure that the positive cable is connected to the + and negative is to the -,

    the buzzing sound you get from the dimmer is the voltage dropper reducing the power to the lamp, it has to go somewhere so it takes the strain of this and is common in this type of component, but be careful these can get worm and as i found can melt the socket or the cable used if its underrated, the other thing is if you use to high amperage cable this can also effect things,

    dc voltage don't you just love it.

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  10. #10
    Clear as mud! In fact I think I am more confused!

    There now seems to be another issue here, can I assume that I will not have a problem running the lamp off the cigarette socket of my car? Am I correct in saying with the engine running, the cigarrette socket is powered from elsewhere than the battery (alternator etc?) and the only issue I may have is using the lamp with the engine off, which I very rarely do.

    The other issue is this original one, and thats the motorcycle battery for when I want to go on foot. I think here my problem is not having a man enough cigar socket connector, I will look for a fused one rated at 10amp for this.

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