I have been looking at several threads on here about laptop power supplies. Using 12V, 24V, invertors, convertors etc.
What I am wondering is whether I am overlooking something as to why I can’t make a lead up with a resistor in to drop the 24v to the 20v required for my laptop (presumably most run at around that voltage). From what I remember from my electrical education its just a matter of calculating the correct resistance and having a suitably high current rated resistor.
i was thinking the same.i was going to go to local electrical shop in town the lad who owns it is always messing about with things like that,im sure you would be able to get something to just plug into lighter socket to drop it down 6-8 volts.
It wouldn’t work as the voltage drop over a resistor is proportional to the current through it and so as the voltage presented to the laptop would vary as the current demand varied.
I thought there must be a good reason why I shouldn’t try it. I guess it would be ok if the laptop drew a constant current, but as demand for power varies then as you say that would alter the voltage. By how much I doubt we would know, and it may even be within the tolerances of the laptops supply - but not worth risking.
Ohms Law prevails - back to the drawing board to find a design for a regulated power supply - probably cheaper and easier to buy one!
And build yourself a cable with the Anderson connector in the middle of the wire so you can remove the crocodile clips and plug straight into the tail lift connector on the back of the unit (if it has one) or crocodile clip it to your battery and connect it to your inverter. Problem solved.
It is safe to run it through the door on your cab or through the side locker but be careful you do not pinch the wire on anything and cable tie it in strategic places.
Bobs your uncle and fannys your aunt laptop powered 24/7 and quickly removeable if need be
Smart Mart:
Thanks for that Giblsa, useful information - but its a laptop - not Blackpool Illuminations I want to run!
obviously these are just a rough guide, other amps are available!
i have this for when i am away (or used to be away as the case is now) and i run a tele, xbox360, kettle and laptop(charging phone and satnav) off it all at the same time. (not while i was driving ) and it didnt sup the battery either. wagon started first time in the morning.
And build yourself a cable with the Anderson connector in the middle of the wire so you can remove the crocodile clips and plug straight into the tail lift connector on the back of the unit (if it has one) or crocodile clip it to your battery and connect it to your inverter. Problem solved.
It is safe to run it through the door on your cab or through the side locker but be careful you do not pinch the wire on anything and cable tie it in strategic places.
Bobs your uncle and fannys your aunt laptop powered 24/7 and quickly removeable if need be
similar set up to mine which works fine ,no problems.
i used to have one of those dropper and ciggie lighter charger thingys and if i ever watched a DVD on teh laptop it used to lose power (more drain than charge) so i went down the inverter route and , touch wood, so far have had no problems what so ever.
i suppose it depends what power your laptop draws for cetrtain activities on it.
They also do them dedicated to your particular laptop brand/model for a bit more dosh. Go to their home page,and look up your lappy.
link not working for me but i think its a similar peice of kit i use,got it off ebay for £25 and had no problem with it at all.my one came with different end plugs to suit most laptops and loads of fuse’s which you chose one which is correct voltage for the lappy (mines 18 volt)
Still a good buy though, I have been using one of those for about two years now, it is on about 12 hours a day 6 days a week and is still working as it did when new
(i dont know much about resistors 
)
