Car cigarette lighter - cheap energy?

mbbetter

Hi people.

This is may be a bit of an odd question. Plus its the first time post on this board. Also a bit technical:

I commute an hour in my car - not green or ethical I know. Putting that to one side for a moment, it has dawned on me that I have a cigarette lighter sitting there that could be a potential charging point for a number of items. This is not new or news or even that insightful.

My question is. If I charge my tablet, phone, kindle, laptop, even? from this cigerette point is this essentially free power, or is the load on the battery such that the extra fuel to power it means it isn't really free. I have realised that I could charge or top-up an interesting array of devices on my daily commute.

Just now, I have plugged my tablet into my (now stationary parked) car to charge to full for two hours. Presumably, when I use my car tomorrow I will pay for this in extra fuel? (albeit a very small amount) OR will the engine just charge the battery over the hour commute as normal?

Sorry if I've clogged the board with something quite trivial, but I really am curious. To the point of considering buying something like this: http://www.gooutdoors.co.uk/20-led-rechargeable-lantern-p179048

Free reading light power right?

Martyn1981

Your car charges the battery, or supplies power via the alternator. The alternator will increase or decrease it's demand on the engine depending on what is being asked of it. For instance driving with the rear de-mist on can knock about 1mpg off your car, as more demand is being asked of the engine, so it will have to burn more fuel.

Some items are very little, others are quite high, but all, at the end of the day are being powered by electricity being produced by a petrol or diesel generator - and not a very efficient one at that.

Mart.

rogerblack

You will use a small amount more fuel.
Fuel costs about £1.33. This is about £2/kg or so.
Petrol has about 12kWh/kg energy.
Or 16p/kWh. (comparable in price as the more expensive deals for electricity).

But.
The efficiency of most car engines is about 25%, add 80% efficiency for your alternator - and you're at about 20%. Or about 80p/kWh.
So, considerably more expensive than mains power.

mbbetter

Wow, great replies people!

Very much appreciated. All very logical and makes sense as explained like that. It just seems a shame that i cant utilise some of the energy of a hulk of metal being hauled for 2 hours a day.

I think i was thinking that once a car was "in cruise" the alternator may be wasting aload of energy anyway by spining up, so why not channelnit into an ipad.

How about a wind generator? I appreciate this is bordering on ridiculous, but sticking a wind generator out of the window (only when braking) would generate "free power"

Cardew

mbbetter wrote: »

How about a wind generator? I appreciate this is bordering on ridiculous, but sticking a wind generator out of the window (only when braking) would generate "free power"

On the same principle F1 racing cars have a system called KERS(Kinetic Energy Recovery System) http://www.formula1.com/inside_f1/understanding_the_sport/8763.html

This can produce up to 80bhp(about the power of a smallish car) for a few seconds.

Next year's regulations will allow more power to be recovered and in time similar systems will appear on our road cars.

As a sop to some on this section of MSE we should have more solar panels on the roof of cars(there are some) to enable you to charge your phones etc on the move. In keeping with the spirit of Solar PV such a system should attract huge subsidies that we could all pay for by an increase in petrol prices;)

iltisman

I have put several self adhesive solar panels on my car roof to keep the car battery charged as I use the car infrequently. The tricky bit is connecting them to the car battery safely and not causing any extra drag .

zeupater

Cardew wrote: »

On the same principle F1 racing cars have a system called KERS(Kinetic Energy Recovery System) http://www.formula1.com/inside_f1/understanding_the_sport/8763.html

This can produce up to 80bhp(about the power of a smallish car) for a few seconds.

Next year's regulations will allow more power to be recovered and in time similar systems will appear on our road cars.

As a sop to some on this section of MSE we should have more solar panels on the roof of cars(there are some) to enable you to charge your phones etc on the move. In keeping with the spirit of Solar PV such a system should attract huge subsidies that we could all pay for by an increase in petrol prices;)

Hi

Regarding KERS - Mrs Z doesn't have a F1 car, but certainly has a braking energy recovery system on her car .... there's also a factory fit option for an integrated solar roof.

I think that the OP was simply looking for information on whether charging items on the move would tap into a cheaper source of energy, in which case Roger's post applies .... If the reasoning for doing this is environmental or just for fun, I'd look at something like a 12V/12W(Min) solar panel, a charge controller and a switchable DC/DC voltage converter with a set of alternative plugs/connectors as being a reasonably low cost solution (~£100), that way it would be possible to power/charge most portable battery powered items you would find around the house ..... If the reasoning is moneysaving, either have a grid-tied array installed for long term savings and only charge the items during the day, or continue to use standard mains electricity.

HTH
Z