Powering laptop from car battery (no inverter) - Page 1
Forum section: electronics / general

author: esrevinU
author_rank: Newbie
timestamp: September 11, 2016, 05:59:06 pm
content: Hi,my laptop (Toshiba Satellite U845-10N) has a(n internal) battery of 7.4V. The power adaptor is a standard 19V.Is it possible to power the laptop directly from a 12.xV provided by a car battery? I heard about some laptops that can be powered this way. Should I try? Will this burn my laptop?Thanks!

author: Ampera
author_rank: Super Contributor
timestamp: September 11, 2016, 06:31:36 pm
content: Not directly, but if you can either A. up the voltage to the 19V at the appropriate current, or B. Down it to 7.4V and power the laptop directly off it.The issue here is that a car battery is meant for a lot of current very fast, and thus isn't meant for constant loads. You would want a deep cycle marine type battery that is intended for longer, weaker loads. However if the reason you want to power a laptop off a car battery is that you have the car battery, you just need to knock it down or up and stick it in the right slot.Power's power, and it will power the laptop, just not without modification.On HOW to do that, there are DC-DC power supplies on places like EBay, some of them variable, I suggest you look for something among those lines.

author: G7PSK
author_rank: Super Contributor
timestamp: September 11, 2016, 06:47:58 pm
content: I have run Panasonic laptops from 12 volts the input jack is 16 volts but 12 volts seems to work quite well. would not run it from the cigar lighter socket while the engine is running due to voltage spikes.I have also made power units for laptops using cheap Chinese DC to DC converters off Ebay and run Hp. dell and panasonic's from them.

author: fubar.gr
author_rank: Unknown
timestamp: September 11, 2016, 09:23:47 pm
content: Theoretically, there's nothing wrong with supplying a laptop with less than 19 Volts. Either way, the input voltage is buck converted to much lower voltages.The problem is that lower voltage would result in higher currents through the power connector and some parts of the circuit board and the laptop might not be designed to handle that.I've tested my no-name laptop with my bench power supply, and it seems that it won't power on if the voltage is below 15 Volts. This is probably some built-in protection feature.So even if the laptop works directly off the cigar lighter socket, that could result in overheating and long term damage. Get a proper car rated laptop charger instead.

author: TheBay
author_rank: Unknown
timestamp: September 11, 2016, 11:08:16 pm
content: Car power adapters are available for most laptops, 19v is a very common voltage.These use convert something like 10v-15v to 19v, some will even take a 24v input.

author: esrevinU
author_rank: Newbie
timestamp: September 12, 2016, 07:59:49 pm
content: Thank you all for the answers!My conclusion is: "Not a good idea!".I will go with my actual solution (12 to ...19V DC converter).Regards,Stefan

author: Ice-Tea
author_rank: Super Contributor
timestamp: September 12, 2016, 09:33:21 pm
content: Done that a couple of Times, but there's always a risk. One of the machines would not charge at 12V (higher voltage batt pack). To reduce the risk a bit: don't keep it plugged innwhile starting

author: senso
author_rank: Frequent Contributor
timestamp: September 13, 2016, 11:35:45 am
content: I wouldn't risk it with a toshiba, crappy input protection mosfet's, they might burn to a crisp with the increased current from the lower voltage.

author: System Error Message
author_rank: Frequent Contributor
timestamp: September 14, 2016, 01:09:57 am
content: Actually you can easily power a laptop directly if it is the rights volt even toshiba with its crappy input protection. If the current was the problem than laptop PSUs or their own internal lithium batteries would damage them. Dont forget that PSUs can easily output a lot of current if needed and so can lithium battteries even though they arent capable of outputting as much as a capacitor or lead acid battery.It sounds to me like you guys dont even know electronics. Im sure even EEVblog will agree with me. If you convert the 12V output of a lead acid battery into 19V it will power a laptop without any issue. The current is limited by the resistor which so happens to be the cabling and the laptop itself. Just imagine the laptop as a big resistor which will resist how much amps and it is the resistance that determines how much power is actually used. Its the same issue as with electrocution as whether it has to pass through skin or blood as the resistance and voltage that determine how many amps actually go through. Try putting a meter to measure resistance between input and output on the laptop or device itself. Its going to be some significant resistance.If this were not true than putting a 1KW ATX PSU into a desktop that only draws 50W would burn it out yet it doesnt. Even if the PSU itself doesnt have all that fancy protection it will not output all the power it can. It is the load you are powering that matters.Avoid connecting the lead acid battery to the laptop's battery slot unless you have calibrated the laptop for lead acid battery. This is because discharge profile are different between different batteries. Infact lead acid batteries can be used for slow discharges and they will have more Ah if they are discharged slower. Deep cycle batteries on the other hands are lead acid batteries that are designed to be discharged and recharged frequently from lower %. On a normal lead acid battery you do not want to drop it below 40% charge before recharging it. A deep cycle battery will allow you to discharge down to 20% or less before you should recharge it back or or risk wearing out your battery. This has nothing to do about the drawing of amps. Infact lead acid batteries were used in PC UPS and werent the deep cycled kind because they were the cheapest per capacity.

author: Ampera
author_rank: Super Contributor
timestamp: September 14, 2016, 03:20:59 am
content: Quote from: System Error Message on September 14, 2016, 01:09:57 amI thought I was pretty spot on with my explanation. Car batteries would work, it's just that they aren't meant for constant high current loads. They can output a LOT of current in a VERY short amount of time (To start the car), but they aren't intended for a constant load, hence why cars have alternators in them. Deep cycle batteries can't output as high of a current, but they will be able to output what they can on a constant for a damn sight longer than a car battery.In terms of charging it, you literally only need a 12v to 19v DC-DC converter, and to know that the car can provide enough current to charge the laptop. Excess current won't fry anything, as long as the voltage doesn't fluctuate too greatly (The charging circuit is expecting a solid 19v, so unlike a battery it probably won't take kindly to voltage drops)But there are commercial car chargers if that is what your looking for. They go into your cigarette lighter slot and take power from the car. Hunt around, spend the extra dollar, and get a decent car charger. It will work on most 12v supplies, even if it's not a battery.