# Car voltage fluctuation advice



## ahmed24

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


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## Norm

Moved to: Transportation Lighting
Norm


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## mvyrmnd

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.


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## VegasF6

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?


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## DrScott

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.


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## MBLED

Looking at getting a [h=1]Outdoor SKY*RAY L1 5xCREE XM-L T6 4500Lumens Flashlight LED Torch[/h]
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_index/emitter index.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


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## HotWire

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.


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## 127.0.0.1

HotWire said:


> 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


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## nocte-diem

Electric/electronic components with critical Voltage requirements will usually contain a Voltage regulator that supplies stable output.


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## Alaric Darconville

MBLED said:


> 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.


By "bike" do you mean a bicycle, or do you mean a motorcycle? You speak of an "electrical system" which seems to indicate a motorcycle.


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## Light Bringer

Automotive electronics must be able to function from as little as 9V or less (during starting) to 15V (charging via an alternator), and be able to withstand at least 40V transients ("load dump" from the alternator when turning off the engine).

The range you gave is perfectly normal.


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## Lynx_Arc

Somehow I don't think someone with only 2 or 6 posts back in 2012 will be reading a reply to his post made over 4 years later.....


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## Alaric Darconville

The OP has abandoned this thread, and potentially the entire board.


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