12v Battery advise

monseiur

I have just ordered a 12v hand held spotlight, it has a 100w halogen bulb. I need to order a suitable battery separately. This battery will be carried in a back pack (the spot light comes with a long cable etc. to suit this set up) Hope to be able to charge battery with my car battery charger. Would a 6AH lead acid sealed battery do? Or would a lower AH battery be OK ? Could never get my head around the correlation between watts & ah😒 Need to have enough charge to last a minimum of 2 hours continuous use between charges.

Thanks.

Wearb

You'll need about 20 ah

10-10-20

I think 20Ah will be too low as it will be under too much stress, will fade quickly and won't last more than a small number of charge/discharge cycles. Plus if it's a sealed-lead battery the V will drop very quickly and the lamp's output correspondingly.

Quick calculation here suggests a 66Ah flooded cell (sealed lead) battery would be better sized, or 48Ah if it's gel or AGM.

https://www.batterystuff.com/kb/tools/calculator-sizing-a-battery-to-a-load.html

Lots of info here too:

https://batteryuniversity.com/articles

monseiur

https://www.boards.ie/discussion/comment/121482055#Comment_121482055

Thanks 10 10 22 for info, greatly appriciated.

MrCostington

OP, just for your illumination (sorry, couldn't resist!) this is how you calculate such things.

Your lamp is a 12V 100W lamp. Watts "consumed" by a device is the voltage * the current flowing through it. So, knowing the watts and the voltage, the current is 100W/12V = 8.3Amps. It gets more complicated for things like AC motors, but for your application it's this simple.

So you need it to last 2hrs, that's 8.3*2 = 16.6 Ah which is the draw on the battery. I'm not well up on batteries but others have given reasons why a 20Ah would be very marginal to say the least. Data sheets will be available for batteries showing discharge curves, depth of discharge vs charge cycles life and many other parameters.

As an aside, is there not an LED spotlight available that will do the job? Would need a much lighter battery to lug around, if not already build in?

Wearb

Is there a forum on boards like hunting where posters there might do a bit of "Lamping". If there is then those lads will be up to date on the latest such technologies.