# Thread: How long will my lamp last ?

1. ## How long will my lamp last ?

Hi all,

Any one good with battery maths? I have a 240mm light force blitz with a 100 watt bulb I think in it.
How can I work out how long that will run with a 12v battery at 12ah? I also have a 12v 7ah battery.

Regards

Carl.

2. A 100 watt, 12 volt bulb consumes 8.33 amps therefore with a fully charged 12 A.H. battery you could expect 1.44 hours of use.
With the 7 Ampere-hour battery only .84 hours.

HWH.

3. get a lithium 12volt 12amphr battery , they cost a bit but are worth it , mind you the dont go dim the just go out

4. A good trick is to have two batteries and charge one from the 12 volt cigar-lighter socket of the vehicle whilst driving around.

HWH.

5. 12v x 12w=144w
144w/100w=1.44
this requires 100% efficiency and is not achievable so typically (for lithium ion batteries anyway) you would get approximately 90% before the 'safety' circuitry kicked in to protect the battery so:
1.44 x 90/100=1.3

Remember.....virgins are rare

6. Originally Posted by limulus
12v x 12w=144w
144w/100w=1.44
this requires 100% efficiency and is not achievable so typically (for lithium ion batteries anyway) you would get approximately 90% before the 'safety' circuitry kicked in to protect the battery so:
1.44 x 90/100=1.3

Remember.....virgins are rare
Your `OHMS LAW` is rather screwed up !
Volts times amps are watts.
Watts divided by volts are amps.

The state of the battery itself will dictate the length of illumination time, if the battery is old its capacity may be considerably less than its expected 12 Ampere-hour, also intermittent usage will help as opposed to continuous.

HWH.

Where you taught to remember ohms law using 'virgins are rare' too?

8. Originally Posted by limulus

Where you taught to remember ohms law using 'virgins are rare' too?
I wasn't.....But I'm intregued?

TJ

9. Originally Posted by stag1933
A 100 watt, 12 volt bulb consumes 8.33 amps therefore with a fully charged 12 A.H. battery you could expect 1.44 hours of use.
With the 7 Ampere-hour battery only .84 hours.

HWH.
So by that calculation the wireing will last slightly longer than the Battery. I have stripped down all my lightforces and rewired as the wireing sucks.

10. Originally Posted by limulus

Where you taught to remember ohms law using 'virgins are rare' too?
Never heard that one, but remember `the angle of the dangle is inversely proportional to the heat of the meat`.

HWH.

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