laptop car charger.. I don't quite understand... - Page 1
Forum section: electronics / beginners

author: LeWidget
author_rank: Regular Contributor
timestamp: December 01, 2015, 05:48:23 am
content: Hi Guys,I have a TOSHIBA Satellite C50D-A laptop with power requirements DC 19v 2.37a.just wondering if anyone can recommend a car charger for it? I've come across a few on eBay, ranging from $13 > $15+, though im not sure what I need to be honest.. I've seen some rated for 80w.. some for 120w+ etc..Also, how do power supplies/chargers work exactly? My charger for the laptop states "DC 19v 2.37a" .. do I need a car charger with those exact specs? I've seen 19v with higher amps... do the power supplies feed/push the power into the device.. or is it the device that draws power 'from' the power adapter..ie.. a car charger rated at, say, 19v 4.5amp will supply 4.5amps@19v? so if the laptop only needs 2.37a@19v.. it will only draw the required amount??really sorry for the noob question, please bare with me..Any recommendations would be super

author: Deathwish
author_rank: Unknown
timestamp: December 01, 2015, 06:46:47 am
content: The forum is like an EE bus stop, your going to get a new bus along every few minutes and with it a different opinion mostly every time. But not being an EE my perception is this.1, try to match the car unit to the power brick you use at home or the rating required by the laptop stated on it's rear.2, Power bricks are rated at xV and yA, yes yes I know the designations I used is not conformist to you EE's. The brick has a maximum rating on it and the device, in this case, your laptop, draws power from it up to the bricks maximum rating. The brick does not push it to the laptop or it would kill it as it would over power it.OP, give it a few minutes and another bus will be along carrying more brain cells and knowledge.

author: rx8pilot
author_rank: Super Contributor
timestamp: December 01, 2015, 06:56:50 am
content: 19v at 2.37A = 45 watts.19v (volts) is the important number to match.2.37A (amps) is the minimum number you need, but it can be more. The device decides how much will be used.Multiply the two numbers (V*A =Watts)If you see a 120w 19v supply it is capable of 6.3A.Lastly, these are boost converters. Boosting 13.8v from your car to 19v for the laptop. Do not get too exited about a cheap one. Cars have SHITTY electrical system and boost converters can make it even worse. When you choose one, keep in mind it is feeding your laptop that you likely do not want to be fried. Cars are notorious for creating huge voltage spikes that one of these adapters absolutely has to keep isolated from you laptop.

author: amyk
author_rank: Super Contributor
timestamp: December 01, 2015, 08:24:19 am
content: A laptop which claims 19V input will usually be fine with anywhere from 18V to 24V, although I'd stay below 22V to leave some margin (input circuitry contains 25V caps, from which this range is derived).

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: December 01, 2015, 11:12:53 am
content: I'll try and give you an analogy to help understand what voltage and current means.Think of it as if the laptop as a big tower with two tubes sticking out of it, one at the ground level of the area around it and one at a high of 19 meters. This is the voltage.Our tower uses water flowing down to give it energy, like a water mill. You powersupply needs to match the high difference: Too big and the water will hit the blades of the mill with too much force and break it, too low and it wont be able to move the mill.The current rating (the value in Amperes, often shorted as Amps) is the amount of water the tower will try to let flow over the mill. The tube of your powersupply needs to be large enough to allow that much water to flow. If it is lower, again, the mill cannot operate properly - but if it is higher, it doesn't matter: The tubes in the tower will only allow for 2.37 units to flow anyways.I hope I didn't make it even more confusing...

author: Ian.M
author_rank: Super Contributor
timestamp: December 01, 2015, 12:26:24 pm
content: Its unwise to push a generic power supply to its full rated current as the cheaper ones may have over-optimistic ratings. ==> for a laptop with a nominal 45W mains PSU, get at least a 60W car charger.Some laptops 'handshake' with the power supply to determine its output current and if there is insufficient current either do not charge the battery while switched on, or throttle back their performance to stay within the power available. Without spending some time researching your laptop, I cant tell if it has sensing contacts on its power in jack. If it does, you need either an OEM PSU or a model-specific aftermarket replacement, as the generic PSUs with interchangeable connectors frequently don't communicate the available power to the laptop properly. If the jack only has two contacts (+19V & Gnd), a generic PSU will work OK.Another thing to watch out for is that car chargers almost invariably have a common ground from power in to out, and due to the large current they draw, there is likely to be a considerable ground offset with respect to the vehicle chassis and other parts of the wiring loom. This can cause serious damage if you connect to other vehicle powered electronics that doesn't have isolated interfaces.The final thing to watch out for is the condition of the car socket. If its ever been used for a cigarette lighter, the contacts are likely to be badly oxidised and unreliable, which can cause the charger power plug to overheat and be damaged.

author: fleuroman
author_rank: Contributor
timestamp: December 02, 2015, 11:40:56 am
content: As an autotech, you might also need to consider what current the DC inverter uses to up the voltage, I've seen a cheap 5v 3amp car charger blow a 10amp fuse on the lighter/power socket. the other thing to consider, is that using a laptop when driving is just as bad as using a mobile phone as far as the cops are concerned, charging ok... using... not ok