# Running a spot light off of a car battery?



## Cgm2414 (Sep 8, 2011)

So I bought an off brand spotlight for about 19 bucks, and I was wondering if I could run it off of a car battery by taking the original connectors to it's battery and connecting it to a car battery? Since it was cheap I might as well try to do what I want with it.


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## Echo63 (Sep 9, 2011)

I would assume its ok, providing the original battery it ran off was also 12v

you are better off checking the voltage before connecting it to a car battery, otherwise you will instaflash the bulb


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## Cgm2414 (Sep 9, 2011)

Thanks for replying, the battery that was in the spotlight was 7.2. Is there any modifications I can do better suit the spotlight for the car battery?

I'm new to all of this so bare with me if I ask a stupid question.

Thanks


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## Echo63 (Sep 9, 2011)

If the battery that came with the light is 7.2v, then a car battery will probably damage it.
Car batteries are normally 12v (and big, heavy and a pain to carry around)

Stick with the supplied battery


You may be able to change the bulb over to one more suited to the 12v of the car battery.

Pics would certainly help too, someone here may have modded one before


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## Cgm2414 (Sep 9, 2011)

Well, just one problem with using the supplied battery, It takes a good 8 hours to charge and is drained within 5 minutes, shoot, maybe not even that long. That is kind of why I wanted to run it off of a larger battery.

Yeah they are big and heavy but I would say the only carrying I would be doing is from the garage to the truck or ATV, so im not to concerned with the weight, getting it running off of the car battery.

As for Pics I will try to upload them within a couple of days.


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## FRITZHID (Sep 20, 2011)

sounds to me like you got a sulfide'd SLA batt, and a unit that probably wasent all that high quality to begin with. you could replace the stock 7v batt and play it safe. upgrading however could be risky, putting a higher wattage 12v bulb in that housing Could result in molten plastic and/or fire in short order, not just because the bulb burns hotter but the internal wiring may not be sufficient enough to handle the higher current/voltage ratings of say 55w 12v upgrade. if you do decide to upgrade, please be careful and do NOT leave light on unattended for any period of time untill you've preformed a long time burn test to make sure it doesn't go into meltdown.


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## Lynx_Arc (Sep 20, 2011)

7.2v is rather uncommon for a SLA and for spot lights. Most likely you have a 12v or 6v spotlight. If it drains in only 5 minutes your battery is probably toast needing replacement. I would either take the light back or open it up and double check bulb and battery types.


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## FRITZHID (Sep 21, 2011)

Cgm2414 said:


> Thanks for replying, the battery that was in the spotlight was 7.2. Is there any modifications I can do better suit the spotlight for the car battery?
> 
> I'm new to all of this so bare with me if I ask a stupid question.
> 
> Thanks


 
7.2.... are you sure thats not the Ah (amp hour) rating? i have about a dozen 12v 7.2Ah batts kicking around the house. 7.2 volts does seem a lil odd. BUT i again stress, if the lamp you speak of IS of a lower rating than 12v, PLEASE be cautious when upgrading so as to not cause a fire or other harm to yourself or those around you.


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## Cgm2414 (Oct 4, 2011)

Positive it is not the amp hour rating, It is a very cheap light so I wasn't expecting great things from it. Do you have any tips on modifying it? 

Sorry it took me so long to reply, I have been vacationing on Hilton Head Island and have not really bothered with Technology


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## FRITZHID (Oct 4, 2011)

Cgm2414 said:


> Positive it is not the amp hour rating, It is a very cheap light so I wasn't expecting great things from it. Do you have any tips on modifying it?
> 
> Sorry it took me so long to reply, I have been vacationing on Hilton Head Island and have not really bothered with Technology



well, like i said before, you can upgrade it to a 12v system, be-it halogen or HID if it will fit the slim line ballast, you can cram that inside where the batt was, but again, it will most likely require upgraded wiring since i can't expect the stock to be up to par, but more than that, make sure the reflector is metal & lens is glass or you will likely have a catastrophic meltdown with 55w of Incd or 35w of HID. but with the HID upgrade, bulb shimming will be likely required, as well as an external power source.


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## xul (Oct 5, 2011)

Cgm2414 said:


> the battery that was in the spotlight was 7.2. Is there any modifications I can do better suit the spotlight for the car battery?


Use a dropping resistor in series with the bulb. 

R in ohms = (Vcar - Vlamp)/I, where I is the rated lamp current and Vcar is 12.8 with engine off and 14.4 otherwise. The resistor wattage is between one and two times [(Vcar - Vlamp)^2]/R. 

So with 12.8 v and 1 amp current you'd need 5.6 ohms at 6 w to 12 w or more. For a buck or so you could cobble together some power resistors from Hosfelt.com or others to get these values.

Or, you could almost use another 7.2 v bulb for the resistor.


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