cabman Posted September 19, 2005 Share Posted September 19, 2005 Does anyone know the formula for how long a laptop would run from cigarette lighter plug-in without the car battery failing to start the engine from stationary?The in-car adaptor for my laptop has an output of +16V 4.5A Output power 75W maximum. Link to comment Share on other sites More sharing options...
Mpprh Posted September 19, 2005 Share Posted September 19, 2005 HiI think I understand the scenario : you don't have access to mains current ?I know it is bad form to mention other forums, but in this case I would ask the question here :http://www.ybw.com/forums/ubbthreads.phpIt is a forum for sailors, who frequently have the same problem.Bonne chance Peter Link to comment Share on other sites More sharing options...
Nick Trollope Posted September 19, 2005 Share Posted September 19, 2005 [quote]Does anyone know the formula for how long a laptop would run from cigarette lighter plug-in without the car battery failing to start the engine from stationary? The in-car adaptor for my laptop has a...[/quote]OK, a bit of Maths....Your car battery should have a (new) fully charged capacity of (eg.) 100AH (amp-hours). Which is the capacity to complete discharge. However, you should never discharge a lead-acid battery (especially a modern one) below 50% = 50AH (say).The output power of your power supply is 75W. It is probably a basic invertor with an efficiency of (say) 50%. Therefore it's input power can be up to 150W. At a nominal 12V, this is 12.5Amps. Conveniently, 50AH (amps x hours) is 12.5A(mps) for 4 hours.However, there are several variables which cannot be predicted in any formula; a) the actual current consumption of the power supply, as this will vary considerably with CPU, screen HDD drive etc usage. b) the actual capacity of your battery, which is a function of age, design capacity, charging circuit design, etc etc (and very difficult to measure) c) the actual point at which your car will fail to start, which will be a function of age, service efficiency, battery internal resistance, air temperature, glow plugs, carburettor, fuel injection or whatever.Does that help? Link to comment Share on other sites More sharing options...
cabman Posted September 20, 2005 Author Share Posted September 20, 2005 Thank you Nick. That is a help. I know very little about electricity.My 20year old daughter likes to come fishing, but quickly gets bored if the action is slow.Seems a couple of hours of uni work or a DVD on the computer should do no harm.Probably best to park facing downhill though! Link to comment Share on other sites More sharing options...
Ron Avery Posted September 20, 2005 Share Posted September 20, 2005 Having to take a DVD player fishing!!!!!!, Sacre bleuWhat does that say for the attention span of the youth of today I suppose giving her the tin of maggots to play with doesn't occupy the mind like it used to me Link to comment Share on other sites More sharing options...
cabman Posted September 20, 2005 Author Share Posted September 20, 2005 You're absolutely right Ron.My wife calls it quality family time.2 teenagers and a twenty year old - I'm often not so sure! Link to comment Share on other sites More sharing options...
chirpy Posted September 29, 2005 Share Posted September 29, 2005 WHY NOT USE LAPTOP BATTERY-THAT IS WHAT IT IS FOR -THEN RECHARGE WHEN YOUR ASHORE.ALTERNATIVELY GIVE HER A PENCIL TO DRAW SOME SEA SCAPES---AS A LAST RESORT THROW HER OVERBOARD AND SHE WILL BE KEPT BUSY TREADING WATER.!!!!!!!!!!!! Link to comment Share on other sites More sharing options...
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