Can I charge my laptop with DC-DC boost converter - Page 1
Forum section: electronics / beginners

author: Reksyong
author_rank: Newbie
timestamp: May 27, 2018, 05:01:36 am
content: I'm not good at explaining but I will try my best.The thing is will my laptop be damaged if I charge it directly with a dc to dc boost converter from a 12V battery? Like this automatic buck-boost converter which I have at the moment:https://www.aliexpress.com/item/100W-Automatic-Boost-Buck-Converter-CC-CV-5-30V-To-1-25-30V-8A-5V-12V/32704420331.html?spm=a2g0s.9042311.0.0.1aca4c4dhAqoYGSince this is a switch mode converter and I don't have an oscilloscope, I'm not sure if the output will be clean or does any noise in the dc output will damage anything inside the laptop. I did search on youtube that other people are actually powering it with a boost converter but didn't really say much if it's safe or not.

author: rx8pilot
author_rank: Super Contributor
timestamp: May 27, 2018, 05:23:18 am
content: There are no guarantees, but as long as the voltage matches and the current capability is the same or higher..... you should be fine. Even if it is somewhat noisy, the computer should be able to cope with it.Perhaps you can add a ferrite just before the connector just to be safe.Short and misplld from my mobile......

author: David Hess
author_rank: Super Contributor
timestamp: May 27, 2018, 04:49:34 pm
content: Unless there is some other problem, it will work fine. Noise should not be an issue and if it was, it would not damage the laptop.The most likely problems are failure of the external boost converter which applies high voltage to the laptop or drawing excessive current causing the external converter to drop its output voltage or shut off.

author: Rick Law
author_rank: Super Contributor
timestamp: May 27, 2018, 05:41:44 pm
content: Quote from: David Hess on May 27, 2018, 04:49:34 pmAnother possible failure - I hit that one likely due to my own lack of experience....The laptop will soak up quite a bit of current. Your plugs, connectors, better be made well. Poor connections will heat up. My connector was cut from a failed laptop brick with some of the strands already broken at the stripped part. With a very short wire already (plug with about just about a couple of inches of wire), I did not re-cut that to strip it better - and I soldered the rest poorly, the connection got rather hot and eventually broke by itself during my first go. It looks to me the remaining strains got too hot burnt away - I think. In any event, I ended up cutting and re-strip it nicely just to prove it can work. It did work but I ended up buying a replacement laptop brick with a long and un-patched cabled.I can imagine, piping 6A over a poorly made plug to charge your laptop overnight may not give you a good night sleep.

author: Reksyong
author_rank: Newbie
timestamp: May 28, 2018, 04:07:38 am
content: Quote from: rx8pilot on May 27, 2018, 05:23:18 amI was thinking of adding the ferrite as well.Quote from: David Hess on May 27, 2018, 04:49:34 pmIs there any safety measure that I can use to shutoff the boost converter from going over voltage if it ever occur?Quote from: Rick Law on May 27, 2018, 05:41:44 pmThanks for the heads up, I didn't know my power brick was supplying maximum of 6A as well.This mean that this boost converter will produce a lot of heat as well.

author: David Hess
author_rank: Super Contributor
timestamp: May 28, 2018, 04:40:01 am
content: Quote from: Reksyong on May 28, 2018, 04:07:38 amAbsolutely, it is called a crowbar circuit and it is very simple. It requires an SCR, zener diode, resistor, and small capacitor. The capacitor in combination with the resistor prevent triggering due to noise.http://electronicsinfoline.com/pin/12440/http://axotron.se/index_en.php?page=26Usually a fuse is included before the crowbar circuit so that when the crowbar triggers, the fuse blows for safety.

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: May 28, 2018, 05:05:58 pm
content: The majority of laptops require 19v at around 4A. Some rely on the PSU to limit the charging current, though most have their own charge regulator. Thus if you set it to limit at 4-5A you should be OK.As mentioned, some form of OVP might be wise (crowbar, relay or similar) since the monetary value of the load is far more than the cost of the additional bit of circuitry. Might also be worth thinking in terms of reversed battery protection.

author: Reksyong
author_rank: Newbie
timestamp: May 30, 2018, 12:04:48 pm
content: Quote from: David Hess on May 28, 2018, 04:40:01 amWhat value should I need to adjust for a 19.5V power brick and +- V range that should be given to this power brick? Is there anything than a fuse that I can use so that I don't need to change it every time if it blows? Something that would reset itself once going back to normal condition.Quote from: IanMacdonald on May 28, 2018, 05:05:58 pmThanks for mentioning about that!

author: David Hess
author_rank: Super Contributor
timestamp: May 30, 2018, 04:20:57 pm
content: Quote from: Reksyong on May 30, 2018, 12:04:48 pmThe crowbar should never activate under normal circumstances so using a fuse is not a big deal.The crowbar voltage is set by the zener voltage plus the forward voltage drop of the SCR's gate which is roughly 0.6 volts. To protect the output of a 19 volt supply, you want to be at least 10% high or even better 20% high so a 22 or 24 zener diode would be suitable.The value of the resistor across the SCR gate is set to sink leakage current from the zener diode and should be as low as possible. Typically the gate voltage divided by the zener test current is a good value. The zener test current at about 24 volts is about 5 millamps so 0.6V/5mA=120 Ohms.Put a 0.01uF capacitor across the SCR gate in parallel with the resistor to prevent false triggering from noise.Some designs include a low value resistor in series with the gate to prevent the SCR from being damaged if the zener diode shorts but in that case, I just replace the SCR when I replace the zener diode anyway.

author: Reksyong
author_rank: Newbie
timestamp: June 06, 2018, 02:11:47 pm
content: Quote from: David Hess on May 30, 2018, 04:20:57 pmThanks, I will design it in Proteus or Multisim and show it here later on but currently, I'm busy with another project so I'll get back to you quite late. Could you check if the design is correct later on then?

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: June 06, 2018, 02:59:20 pm
content: There's a high possibility it won't work depending on your brand of laptop. Some use a sense wire to confirm that the power supply is a brand one (there's a EEPROM or similar in the supply itself). If it isn't the right one then either the laptop will simply refuse to charge or deliberately cripple the charging rate. Usually, the laptop will display a message.

author: Audioguru
author_rank: Super Contributor
timestamp: June 06, 2018, 04:06:41 pm
content: The boost converter is extremely cheeeap(!) and it is Chinese. Then is it reliable? Is it worth saving a few bucks to blow up your expensive laptop?

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: June 06, 2018, 04:54:15 pm
content: How about a portable 12VDC to AC converter and plug the laptop's power supply into that?

author: ejeffrey
author_rank: Super Contributor
timestamp: June 06, 2018, 05:10:10 pm
content: Many laptops use an EEPROM on the charger that is needed for correct operation. In addition to implementing "lock in" on their chargers, it communicates the current rating to the laptop. So the laptop may start by drawing a relatively small current, then after identification increase the charge rate. If you don't have the proper ID, the laptop may charge slowly or not at all.Here is a hackaday article about spoofing this for a dell charger. They use the 1-wire protocol:https://hackaday.com/2014/03/03/hacking-dell-laptop-charger-identification/

author: Dukov Ahzrukhal
author_rank: Regular Contributor
timestamp: June 12, 2018, 01:49:50 pm
content: I use a similar converter to power my laptop all the time. It works fine but the converter does get very hot.

author: grythumn
author_rank: Contributor
timestamp: June 12, 2018, 04:57:08 pm
content: If you're running off 12VDC, I'd look for a commercial car charger unit... some of them even have the right eeprom to charge the picky laptops. It's highly model specific, though.A universal one like this:https://www.amazon.com/Outtag-Universal-Charger-Detachable-Notebooks/dp/B071SDW4QG/Or there are brand-specific ones available for a lot of laptops.-R C

author: amyk
author_rank: Super Contributor
timestamp: June 13, 2018, 12:00:50 am
content: Quote from: ejeffrey on June 06, 2018, 05:10:10 pmOthers use a resistor on the sense pin to determine how much current to draw, similar to USB. Of course there are also the completely "dumb" ones that just take +/-. Inspecting the plug (and schematic, if available) will determine what type you have.

author: firehopper
author_rank: Frequent Contributor
timestamp: June 13, 2018, 02:25:27 pm
content: yeah most are around 3-5 amps at 18-19.5 volts, mine however is 19.5 volts at 12.3 ampsinput is 100-240 volt at 3.5 amps rated 240 watts.Quote from: IanMacdonald on May 28, 2018, 05:05:58 pm

author: amyk
author_rank: Super Contributor
timestamp: June 14, 2018, 12:21:15 am
content: The difference between 19.5 and 19 (less than 3%) is probably a sneaky attempt at vendor lock-in. You can find 18, 18.25,18.4,18.5,18.6,18.75, and a bunch of other voltages in that range, with no real reason for the distinction. Measure one of those loaded and unloaded, and you'll find the voltage changes again.In practice, anything from just above the minimum input of the buck converters up to the voltage limit of the input caps (usually 25V) will be fine. Anyone who thinks a 20V adapter will damage a laptop originally supplied with a 19V adapter is electrically illiterate.