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Thread: Car voltage fluctuation advice

  1. #1

    Default Car voltage fluctuation advice

    Hello,

    My first post here, I'm hoping someone can help and advise me on the following situation:

    I have a car LED light unit with a label that says 12V 6.5A

    I want to power this unit from the fog light power source on my car and having just tested the fog power source with multimeter, it seems to fluctuate from 12V - 14.5V. I know that the fog light circuit is most likely on a 10a or 15a fuse but what do I do about the voltage fluctuation? will this damage the unit?

    Can I maybe just add an inline fuse to it to prevent too much current being drawn during voltage spikes?

    Any advice would be very much appreciated.

    Many thanks

  2. #2
    Administrator Norm's Avatar
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    Default Re: Car voltage fluctuation advice

    Moved to: Transportation Lighting
    Norm

  3. #3
    Flashaholic* mvyrmnd's Avatar
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    Default

    The voltage will fluctuate depending on a number of things, eg. The alternator is charging/not charging the battery, whether or not the aircon is running.

    If your light is designed to run in a car, it should be able to handle the voltage changes. I wouldn't bother adding another, smaller fuse.

  4. #4
    Flashaholic* VegasF6's Avatar
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    Default Re: Car voltage fluctuation advice

    A fuse will not limit voltage nor control current current. Granted if power demand is higher than the fuse rating it will blow, but that's not a protection you want to count on. I haven't seen the particular unit you have so I can't be certain, but many I have seen are not designed to handle the voltage fluctuation from a cars charging system. An additional voltage regulator would be required in that case, but a 6.5A current requirement is very high. I can't recommend a regulator for you, sorry.
    Can you post a link or additional specs?

  5. #5

    Default Re: Car voltage fluctuation advice

    Lots of folks use LM317 adjustable regulators set to the correct voltage or to current-control mode. Or some use Sharp PQ09RD21 (9v) or PQ12RD21 (12v) regulators.

  6. #6

    Default Re: Car voltage fluctuation advice

    Looking at getting a Outdoor SKY*RAY L1 5xCREE XM-L T6 4500Lumens Flashlight LED Torch

    but the application would be..unusual. I'm looking to make LED spots for my bike. I want to see if possibly I can run (without a driver) it of 14.5 - 14.8V DC. That is the range for the electrical system of the bike. When the battery is not what is should be range can be between 13-14V.

    This light has 5 X Cree T6 LED emitters, and if I look at the index page for emitters (http://www.lumensreview.com/emitter_...er%20index.htm)

    Then 5 X T6 max voltage (3.337V) = 16.69V... I know the voltage fluctuation for this torch varies from website to website, but...looking at the max voltage per T6 emitter, the aforementioned would be correct, no?

    If that's the case - will I be able to run it off my Bike's electrical system with NO DRIVER? Would the LED's be negatively affected by a fluctuating voltage and current? It seems the bike would not be able to give more than it can take, right? (it's got a 150W alternator but has DC due to diode). I'm super keen to fit this flashlight, modify it (making it much shorter) and simply connecting to the battery...question is, will it work, and would the LED's be fine with the bike's electrical system supply?

    Cheers

  7. #7

    Default Re: Car voltage fluctuation advice

    The voltage fluctuation you are seeing is normal. The alternator regulator detects what is needed to run the engine and to charge the battery. The voltage should be about 12.6v with the engine off, and up to 14.5v (or so) with the engine running.

  8. #8
    Flashaholic*
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    Default Re: Car voltage fluctuation advice

    Quote Originally Posted by HotWire View Post
    The voltage fluctuation you are seeing is normal. The alternator regulator detects what is needed to run the engine and to charge the battery. The voltage should be about 12.6v with the engine off, and up to 14.5v (or so) with the engine running.
    this.

    these stated ranges are exactly what my vehicles show at various times during operation. completely normal and anything
    designed for 12v auto current should be OK on the usual 14.1-14.5 that occurs
    most if not all '12v' electronics can handle a little lower or a little higher than 12v
    posted by jh333233
    Dont cheat me, im expert in using crap light

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