How long will my lamp last ?

[Devon County Shooter]

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.
Please share your maths if you can help?

Regards

Carl.

 

[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.

 

[trouble]

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

 

[stag1933]

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.

 

[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

 

[stag1933]

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.

 

[limulus]

Granted....12w should read 12A

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

 

[User00004]

Granted....12w should read 12A

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

I wasn't.....But I'm intregued?

TJ

 

[pete evans]

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.

 

[stag1933]

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.

 

[stag1933]

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.

The wire adds a problem as it incurs `resistance`. Twice as much length of a given substance has double that factor and resistance introduces `voltage drop`.
Thicker wires have less voltage drop.

HWH.

 

[bewsher500]

I can guarantee whatever you work it out to be using physics it will get less than 75% of actual life!

my phone apparently has 4 hours of talk time!!
I can kill it inside an hour and a half!

 

[Devon County Shooter]

Great feed back again lads, can some one list the maths layout for other and myself to use on any battery?

 

[stag1933]

SIMPLE !
First you must know the wattage of your bulb and its voltage.
Assuming the bulb is 100 watts and the required voltage is 12 , divide the 12 into the 100 and this will give you its power consumption in amps which is 8.33 .
Batteries are like milk and come in cartons of various sizes. If you have a leaky carton you will lose some milk, this is true of an old battery which will not hold all its `juice`.
Assume that one amp is one pint of milk and your battery is 12 A.H. or a twelve pint container.
In one hour you will have used 8.33 pints with that bulb and this presupposes that you have a perfect battery and a 100% efficient system.
My electric scooter has two 12 volt 70 A.H. batteries of vehicle type.
These are large and heavy which is the reason why portable units are often 7 or 12 A.H. capacity.
The modern Lithium and NiCads are different technology compared with the older conventional lead-acid or jelly batteries.
The larger the A.H. capacity of your battery the longer it will last at the same discharge rate.

HWH.

 

[scotspine]

Great feed back again lads, can some one list the maths layout for other and myself to use on any battery?

[TABLE="width: 399"]
[TR]
[TD="width: 148, bgcolor: transparent"]Battery voltage[/TD]
[TD="width: 64, bgcolor: transparent"](v)[/TD]
[TD="width: 64, bgcolor: transparent, align: right"]12[/TD]
[TD="width: 64, bgcolor: transparent, align: right"]12[/TD]
[TD="width: 64, bgcolor: transparent, align: right"]12[/TD]
[TD="width: 64, bgcolor: transparent, align: right"]12[/TD]
[TD="width: 64, bgcolor: transparent, align: right"]12[/TD]
[/TR]
[TR]
[TD="bgcolor: transparent"]Battery amphere rating[/TD]
[TD="bgcolor: transparent"](ah)[/TD]
[TD="bgcolor: transparent, align: right"]4[/TD]
[TD="bgcolor: transparent, align: right"]7.2[/TD]
[TD="bgcolor: transparent, align: right"]12[/TD]
[TD="bgcolor: transparent, align: right"]14.4[/TD]
[TD="bgcolor: transparent, align: right"]22[/TD]
[/TR]
[TR]
[TD="bgcolor: transparent"]Bulb wattage[/TD]
[TD="bgcolor: transparent"](w)[/TD]
[TD="bgcolor: transparent, align: right"]100[/TD]
[TD="bgcolor: transparent, align: right"]100[/TD]
[TD="bgcolor: transparent, align: right"]100[/TD]
[TD="bgcolor: transparent, align: right"]100[/TD]
[TD="bgcolor: transparent, align: right"]100[/TD]
[/TR]
[TR]
[TD="bgcolor: transparent"]Best burn time[/TD]
[TD="bgcolor: transparent"](minutes)[/TD]
[TD="class: xl24, bgcolor: transparent, align: right"]29[/TD]
[TD="class: xl24, bgcolor: transparent, align: right"]52[/TD]
[TD="class: xl24, bgcolor: transparent, align: right"]86[/TD]
[TD="class: xl24, bgcolor: transparent, align: right"]104[/TD]
[TD="class: xl24, bgcolor: transparent, align: right"]158[/TD]
[/TR]
[TR]
[TD="bgcolor: transparent"]Probable burn time[/TD]
[TD="bgcolor: transparent"](minutes)[/TD]
[TD="class: xl24, bgcolor: transparent, align: right"]24[/TD]
[TD="class: xl24, bgcolor: transparent, align: right"]44[/TD]
[TD="class: xl24, bgcolor: transparent, align: right"]73[/TD]
[TD="class: xl24, bgcolor: transparent, align: right"]88[/TD]
[TD="class: xl24, bgcolor: transparent, align: right"]135[/TD]
[/TR]
[TR]
[TD="bgcolor: transparent"][/TD]
[TD="bgcolor: transparent"][/TD]
[TD="bgcolor: transparent"][/TD]
[TD="bgcolor: transparent"][/TD]
[TD="bgcolor: transparent"][/TD]
[TD="bgcolor: transparent"][/TD]
[TD="bgcolor: transparent"][/TD]
[/TR]
[TR]
[TD="bgcolor: transparent"]Battery voltage[/TD]
[TD="bgcolor: transparent"](v)[/TD]
[TD="bgcolor: transparent, align: right"]12[/TD]
[TD="bgcolor: transparent, align: right"]12[/TD]
[TD="bgcolor: transparent, align: right"]12[/TD]
[TD="bgcolor: transparent, align: right"]12[/TD]
[TD="bgcolor: transparent, align: right"]12[/TD]
[/TR]
[TR]
[TD="bgcolor: transparent"]Battery amphere rating[/TD]
[TD="bgcolor: transparent"](ah)[/TD]
[TD="bgcolor: transparent, align: right"]4[/TD]
[TD="bgcolor: transparent, align: right"]7.2[/TD]
[TD="bgcolor: transparent, align: right"]12[/TD]
[TD="bgcolor: transparent, align: right"]14.4[/TD]
[TD="bgcolor: transparent, align: right"]22[/TD]
[/TR]
[TR]
[TD="bgcolor: transparent"]Bulb wattage[/TD]
[TD="bgcolor: transparent"](w)[/TD]
[TD="bgcolor: transparent, align: right"]50[/TD]
[TD="bgcolor: transparent, align: right"]50[/TD]
[TD="bgcolor: transparent, align: right"]50[/TD]
[TD="bgcolor: transparent, align: right"]50[/TD]
[TD="bgcolor: transparent, align: right"]50[/TD]
[/TR]
[TR]
[TD="bgcolor: transparent"]Best burn time[/TD]
[TD="bgcolor: transparent"](minutes)[/TD]
[TD="class: xl24, bgcolor: transparent, align: right"]58[/TD]
[TD="class: xl24, bgcolor: transparent, align: right"]104[/TD]
[TD="class: xl24, bgcolor: transparent, align: right"]173[/TD]
[TD="class: xl24, bgcolor: transparent, align: right"]207[/TD]
[TD="class: xl24, bgcolor: transparent, align: right"]317[/TD]
[/TR]
[TR]
[TD="bgcolor: transparent"]Probable burn time[/TD]
[TD="bgcolor: transparent"](minutes)[/TD]
[TD="class: xl24, bgcolor: transparent, align: right"]49[/TD]
[TD="class: xl24, bgcolor: transparent, align: right"]88[/TD]
[TD="class: xl24, bgcolor: transparent, align: right"]147[/TD]
[TD="class: xl24, bgcolor: transparent, align: right"]176[/TD]
[TD="class: xl24, bgcolor: transparent, align: right"]269[/TD]
[/TR]
[/TABLE]

 

[Devon County Shooter]

SIMPLE !
First you must know the wattage of your bulb and its voltage.
Assuming the bulb is 100 watts and the required voltage is 12 , divide the 12 into the 100 and this will give you its power consumption in amps which is 8.33 .
Batteries are like milk and come in cartons of various sizes. If you have a leaky carton you will lose some milk, this is true of an old battery which will not hold all its `juice`.
Assume that one amp is one pint of milk and your battery is 12 A.H. or a twelve pint container.
In one hour you will have used 8.33 pints with that bulb and this presupposes that you have a perfect battery and a 100% efficient system.
My electric scooter has two 12 volt 70 A.H. batteries of vehicle type.
These are large and heavy which is the reason why portable units are often 7 or 12 A.H. capacity.
The modern Lithium and NiCads are different technology compared with the older conventional lead-acid or jelly batteries.
The larger the A.H. capacity of your battery the longer it will last at the same discharge rate.

HWH.

Great! This is just what users need, i know this will help me out, many thanks for every one's input on the subject.

Regards

Carl.