Battery Capacity

Honest John Back Room » Motoring discussion
What is life like with your car? Let us know and win £500 in John Lewis vouchers | No thanks
View Threaded
Sun 20 Nov 2005 13:08
Battery Capacity - mss1tw
How long can a 12v battery power 200w for? Battery is on a diesel so has a higher rating but of course diesels are also harder to start.

I bought one of those little 12v heater things last year and with the mornings getting chilly it would be handy to be able to plug it in for a while before I leave.

I know there's a formula but it's been a while since I did electronics!
Reply | Report as offensive | Link
Sun 20 Nov 2005 13:15
Battery Capacity - Caveman
To work out current used, you have to divide the wattage by the voltage.

ie, 200 / 12 = 16.67 amps being drawn.

Or in layman's terms approx 4 headlight bulbs worth of power being zapped from the battery.
Reply | Report as offensive | Link
Sun 20 Nov 2005 13:17
Battery Capacity - Quinny100
Depends on the capacity - car batteries are rated in Amp Hours.

200W at 12v is 16.67 amps. Typical car battery would be about 70Ah so theoretically you should be OK for 3.5 hours but it wouldn't start the car after that.
Reply | Report as offensive | Link
Sun 20 Nov 2005 13:24
Battery Capacity - mss1tw
Much appreciated guys.

So half an hours worth of useage while I eat brekkie would be Ok then? :^D
Reply | Report as offensive | Link
Sun 20 Nov 2005 13:31
Battery Capacity - mss1tw
Oh for an edit button...

Is 16 amps even safe to pull through the 12v socket? (Bearing in mind it's a Peugeot, and we all know about French electrics ;-) )


Reply | Report as offensive | Link
Sun 20 Nov 2005 15:20
Battery Capacity - Altea Ego
They are normally rated at 30 amps max, Fag lighter elements draw a lot of current.
--
RF - currently 1 Renault short of a family
Reply | Report as offensive | Link
Sun 20 Nov 2005 15:51
Battery Capacity - Ruperts Trooper
It would be worth using an "Automatic Battery Over Discharge Protector", £3 last time I bought one. This cuts out at 11.2V to prevent the car battery being discharged too far, ie so it'll still start the car.

We use ours to run a cooler box so that we can leave it running while we go for a walk, and still get a cold drink out of it.
Reply | Report as offensive | Link
Sun 20 Nov 2005 16:17
Battery Capacity - mss1tw
Many thanks RF and RT!
Reply | Report as offensive | Link
Sun 20 Nov 2005 18:05
Battery Capacity - Dynamic Dave
They are normally rated at 30 amps max,


On my Vectra the sockets are rated at 10 amp max. Still has a 30 amp fuse in the fuse box for it though.
Reply | Report as offensive | Link

Our honest used car pricing is a little bit different to all the others. You can get to our values through make or model - you don’t have to follow a prescribed route. Plus, it’s live, which means we can react to changes in the market quicker than any printed price guide.

Honest Used Car Prices

Our Fuel Cost Calculator shows you which will be the best choice for you.

Compare the running costs of petrol, diesel and electric cars to make the right choice for you.

Petrol or diesel ... or even electric?