Battery consumtion

[Bigpeetee]

Ok, I'll give it a bash....

Well, my laptop charger says it uses 1.5A @ 100 - 240V to deliver its output at 19V and 4.74A.

19v is a step-up of 63% on the voltage from nominal 12v, so ......

4.74 / 0.63 = 7.52A (assuming exact voltages and 100% efficiency of a 12v - 19v inverter). So lets say 9A to be on the safe side, or about one-third of the 230VAC power supply to run the same laptop?

As the load is the same, then that can only suggest to me that the 230VAC power supply is VERY inefficient?

Addendum. Working back from the 19v, 4.74A then..... 19v is 12.1 x less than the 230v mains, and .

So... 4.74 / 12.1 = 0.39Amps (say 0.5A to allow for efficiency?) off a 230v supply.
At the 115v end it should need then maybe 1 Amp using the same power supply.

So the dataplate saying it needs 1.5A has to mean its pretty crap then, right?

I realise I could be missing something here, so happy to be corrected

Number one rule, power stated is not a constant power, but a max for a short period of time.

It's very confusing to understand power requirements, your charger gave a clue 1.5A @ 100 - 240V, it will require a peak current at 110 volts but less than half that at 240v

Given that Watts = Amps x Volts, then you assume that the power supply will consume 1.5x100=150 watts
The power out is 19vx4.74A=90watts, so you might think that there is a difference of 60 watts, given as heat. Just think of a 60 watt lamp and how hot it gets, does your power supply get that hot? NO, it'd set things on fire!!

So the input is not necessarily the power value to use. The output at 90 watts is again only for a short period of time to allow for the initial surge into the battery and to run the PC (if you plug a charger into a flat laptop, you can usually use it almost immediately)

Some devices stop you using it immediately, our blackberry, if totally flat, can't be used until about ten mins of charge has been put into the battery.

Going back to your laptop charger, at 240v it probably has a peak current in the region of 0.6A so a 150 watt inverter will cope.

Now look at inefficiencies:

The charger that gives 19v@4.74A is outputting 90 watts, so at 12v, 90w=7.5A that's not allowing for inefficiencies. An inverter has about an 80% efficiency (some better, some worse) so your 12v demand becomes approx 9.4A, close to the fuse rating of some cigarette outlets.

But this is again momentary whilst everything starts up.

In my experience, a flat laptop uses about 5A initially then reduces to about 2- 2.5A whilst charging. It does however take a little longer than when connected to the mains charger, about 25%.

Out of interest, take the mains charger as before, outputting 90w therefore inputting approx 113w, if we use a standard 12v to 240v inverter we add the ineffieciecies of that inverter and get 140w or 11.8A, that's 2.3A more or approx 1/3 more current, very inefficient use of power.

Obviously I'm talking of peak power so in reality, it's not quite that bad, but power loss is power out of that precious commodity, the battery.

Confused? Possibly, it's a minefield out there

 

[Poppy]

Number one rule, power stated is not a constant power, but a max for a short period of time.

It's very confusing to understand power requirements, your charger gave a clue 1.5A @ 100 - 240V, it will require a peak current at 110 volts but less than half that at 240v

Given that Watts = Amps x Volts, then you assume that the power supply will consume 1.5x100=150 watts
The power out is 19vx4.74A=90watts, so you might think that there is a difference of 60 watts, given as heat. Just think of a 60 watt lamp and how hot it gets, does your power supply get that hot? NO, it'd set things on fire!!

So the input is not necessarily the power value to use. The output at 90 watts is again only for a short period of time to allow for the initial surge into the battery and to run the PC (if you plug a charger into a flat laptop, you can usually use it almost immediately)

Some devices stop you using it immediately, our blackberry, if totally flat, can't be used until about ten mins of charge has been put into the battery.

Going back to your laptop charger, at 240v it probably has a peak current in the region of 0.6A so a 150 watt inverter will cope.

Now look at inefficiencies:

The charger that gives 19v@4.74A is outputting 90 watts, so at 12v, 90w=7.5A that's not allowing for inefficiencies. An inverter has about an 80% efficiency (some better, some worse) so your 12v demand becomes approx 9.4A, close to the fuse rating of some cigarette outlets.

But this is again momentary whilst everything starts up.

In my experience, a flat laptop uses about 5A initially then reduces to about 2- 2.5A whilst charging. It does however take a little longer than when connected to the mains charger, about 25%.

Out of interest, take the mains charger as before, outputting 90w therefore inputting approx 113w, if we use a standard 12v to 240v inverter we add the ineffieciecies of that inverter and get 140w or 11.8A, that's 2.3A more or approx 1/3 more current, very inefficient use of power.

Obviously I'm talking of peak power so in reality, it's not quite that bad, but power loss is power out of that precious commodity, the battery.

Confused? Possibly, it's a minefield out there

Well u lost me!!!
I do believe it's time to call a pro'

 

[wildman]

2 things firstly a battery should never go below 50% so you have 55amp/hrs at your disposal.
Secondly when trying to work of the power consumpton from 240 to 12V first find how many Watts it uses on 240 then apply that to 12V or any other voltage its much simpler.

To reduce the load
A netbook charges in an hour whilst driving and has approx 6 hour battery life.
A kindle carries all the books you need and save fuel hauling paper around
LED lights are a must
150 Watt inverter runs my 240V TV, Sat box and DVD player for a max draw on 12V of 4.74 amps and all of the other chargers work on that though obviously not all at the same time. in the summer an 80w solar panel just about keeps pace with the TV and entertainment/charging laptops etc. But we do have 2 x 110 batts just for that and another 2 plus another 80W solar for lights, step, raising the bed, gas solenoid etc. Owrs is such a power hungry van that to survive in the winter am adding a third 80W panel and a wind charger.

 

[sparrks]

I've just tried my Inverter with my camera charger.

I thought my inverter was rated at 150W, it's actually a 300W constant, 1000w peak.

Switched on with nothing plugged into it it draws 0.4A, plugging my camera charger plus battery in the draw goes up to 1.7A - that's with an 80% charged battery. 1.3A charger, 0.4A inverter

 

[Poppy]

I've just tried my Inverter with my camera charger.

I thought my inverter was rated at 150W, it's actually a 300W constant, 1000w peak.

Switched on with nothing plugged into it it draws 0.4A, plugging my camera charger plus battery in the draw goes up to 1.7A - that's with an 80% charged battery. 1.3A charger, 0.4A inverter

Me thinks I don't need the BIG 2000w inverter I've brought!!!

 

[sparrks]

Me thinks I don't need the BIG 2000w inverter I've brought!!!

Me thinks probably not!

Have you finished your list yet?

Stick with lists for the time being untill you're sure of what you need, it's much cheaper.

 

[Poppy]

Me thinks probably not!

Have you finished your list yet?

Stick with lists for the time being untill you're sure of what you need, it's much cheaper.

Almost, finished it...I add to it, then I revisit it & take something off.
Will keep hold of the inverter, till I know wots, wots, then try & sell it if needs be.

 

[sparrks]

Poppy, the chargers I've got for my Laptops and Rad/cass are a brand called Nikkai from maplin, very well made and have worked flawlessly. Last time I checked they had stopped selling the Nikkai, but have an identical one branded Vanson which hopefully is the same in everything but name. Click here it's £34.99. You just need to check they have the correct tip for it - very important it's the correct size and not too loose. There are cheaper makes and models, but generally you get what you pay for.

 

[Poppy]

Poppy, the chargers I've got for my Laptops and Rad/cass are a brand called Nikkai from maplin, very well made and have worked flawlessly. Last time I checked they had stopped selling the Nikkai, but have an identical one branded Vanson which hopefully is the same in everything but name. Click here it's £34.99. You just need to check they have the correct tip for it - very important it's the correct size and not to loose. There are cheaper makes and models, but generally you get what you pay for.

Fanx love