Use car battery for lighting

theuns · January 2012

HI
I would like to hookup up a 9watt, 230volt light to my 12V car battery, with a 12V 150watt DC to AC inverter.
The battery is not huge the car is a 1.6l opel, i have no idea about the amps hours.
Now i know that there is a huge difference between a car and deep cycle battery.

1. Will this work?
2. For how long will i be able use the light?
3. What will happen to the battery, in the long term?

Any answer will be appreciated, thank you.

icarus · January 2012

Re: Use car battery for lighting

Please seems reply here:

http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

Tony

mike95490 · January 2012

Re: Use car battery for lighting

The inverter you are looking at, is likely a cheaply made "hunk-of-junk". They sell them by the thousands here in the USA. While they generally work, the self-consumption of the inverter will be more than the 9 watts the bulb consumes. I'd guess 20W just to power up the inverter, and then 9 watts consumed by the light. So you would be pulling about 30watts off the battery (2.5A)

A small car might have an 60 ah battery, and for occasional use (once a month) you can maybe consume about a fifth of that (20%) before you would have trouble starting the car and needing a jump. So I think 12A is 20% of 60, and that comes out to about 4.8 hours of light. Or maybe I made a mistake before my AM coffee, and someone else will set your right.

LucMan · January 2012

Re: Use car battery for lighting

I use a Wallmart 12v trolling motor battery ( deep cycle), a 250w Cobra 12v inverter, and 35w solar panel to light my barn with a 150 watt halogen and a small cfl. The lights are only used for 15-20 min per day 2-3 times per week, no problems for the last 3 yrs. When not in use I turn the switch off on the inverter.

BB. · January 2012

Re: Use car battery for lighting

As an example for the math (you can fill in your own numbers:

Assume:

85% efficient inverter
6 watts of losses (minimum power to turn on inverter)
use 15% of battery of available battery capacity (recommended car battery "deep cycle")
60 Amp*Hour battery capacity (smaller car battery)
12 volt system

And the math would be:

60 AH battery * 12 volt * 0.15 of capacity / (6 watt inverter tare + (9 watt load * 1/0.85 inverter eff)) = 6.5 hours

So, while your battery can supply much more energy, the recommended maximum cycling for a 9 watt 230 VAC lamp would be around 6.5 hours.

Of course, if you have more accurate information, you can plug in your own numbers.

Also, for small loads, notice how much the inverter "costs" you for power:

6 watts tare + 9watts*1/0.85 inverter eff = 16.6 watts

If you could find a "12 volt" LED type lamp, you would be much better off... A 1 to 5 watt LED lamp outputs a surprising amount of light.

If you need general lighting, a 12 VDC florescent lamp might be better (LED's tend to be a bit more focused light).

It might be more difficult for you to find a good assortment of LED/CFL lighting--but if you can search boating and camping vehicle stores, you might find something there (probably not cheap).

Note that good LED lamps need a lot of heat sinking. The "cheap" bunch of LEDs soldered to a circuit board may only last 50-100 hours before they "turn black" from overheating.

-Bill

Use car battery for lighting

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