Can I charge my laptop battery at 20V and 5A if the specs state 19.5V and 3.33A? - Page 1
Forum section: electronics / beginners

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 24, 2024, 01:46:58 pm
content: My HP Pavilion's battery charging requires a wall wort that delivers 19.5 VDC and is capable of 3.33A, but what would happen if I supply it with 20VDC and up to 5.4A (from a 13.6V when full to 12.8V when 80% discharged, and 8Ah rated LiFePO4 battery, via a boost converter that outputs at 20VDC). I know that the laptop was tested to draw 3.33A max, and will therefore likely at most times draw far less than 3.33A, and that the 5A capability on the supply side is therefore not an issue of concern, but my concern is specifically in regard to the 20 VDC.

author: p.larner
author_rank: Frequent Contributor
timestamp: January 24, 2024, 01:52:50 pm
content: give it a try,just let us know when the fires out!.

author: langwadt
author_rank: Super Contributor
timestamp: January 24, 2024, 02:06:45 pm
content: it'll most likely work just fine with 20V, why don't you change the boost converter to ooutput 19.5V? a single resistor is probably what it takes

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 24, 2024, 03:46:22 pm
content: Quote from: p.larner on January 24, 2024, 01:52:50 pmI just measured the voltage on my nominally 19.5V wall wort that came with the laptop, and it's 19.87V.

author: Infraviolet
author_rank: Super Contributor
timestamp: January 24, 2024, 05:15:34 pm
content: I've heard rumours that 19.5V in a lot of equipment is effectively a way to relabel a 20V device, either because there are resistive losses expected in the cabling, or because some countries put extra bureaucracy around the sale of items with >=20V subsystems (considering it an intermediate category the way 48V is often seen as the upper end of "low" voltages and 50V sometimes considered the lowest "high voltage" for which shocks become possible) so by setting a 20V tolerant system up to work with 19.5V+/-some_percentage manufacturers can sidestep this. I'd be very surprised if anything made for 19.5V wasn't tolerant for voltages +/- several volts from this, though wouldn't be confident introducing more voltage to an expensive device than I'd measured it to use unless I'd reverse engineered its power input schematic to be sure nothing in there was absurdly tightly spec'd.

author: Veteran68
author_rank: Frequent Contributor
timestamp: January 24, 2024, 07:07:44 pm
content: If the original laptop charger is rated at 19.5V, then 20V should be fine and well within the design tolerances of the laptop and charging circuit.The supply's current capacity is irrelevant as long as it's enough for the circuit's demand -- the battery/BMS circuit will only pull the current it's designed for. If it's designed to pull 3A max, then you could use a 10A supply and it will still only pull 3A. Unless there's a short to ground somewhere in the path, but you'll find out pretty quickly if that's the case, as the laptop won't operate and either the supply itself or some part of the circuit will likely burn out.

author: zilp
author_rank: Frequent Contributor
timestamp: January 24, 2024, 07:09:11 pm
content: I guess it should be pointed out that nothing inside the laptop is running directly off the voltage that you plug into it. The computer part runs at 5 V and less, so there is a (switching) regulator in between the power input and all of that, and the battery, of course, needs a controlled charging current, so there needs to be a (switching) regulator in between the power input and the battery, too.So, this isn't about "is there some component inside the laptop that can't deal with 2.5 % higher voltage?" (which there might be ... but even that isn't really all that likely), it's about "are the input regulators specced with extremely tight margins?" ... and no, they most certainly are not. That would be the dumbest thing ever, because there would be no advantage to doing so, and a significant risk for the manufacturer, not only due to warranty claims from mixed-up power supplies (whether they are legally responsible or not, customers *will* try to have that fixed under warranty), but also because of higher susceptibility to transients, power supply tolerances, and to otherwise benign faults (think: power supply filtering cap fails, regulation overshoots, and instead of having to replace the faulty power supply, you now have to replace the laptop ...).So ... well, never say never, I guess, you never know for sure how dumb some device has been designed, but really, I would be surprised if a laptop specified for a 19.5 V supply wouldn't work just fine with a 24 V supply.

author: Veteran68
author_rank: Frequent Contributor
timestamp: January 24, 2024, 08:20:40 pm
content: Quote from: zilp on January 24, 2024, 07:09:11 pmWhile it is true that in modern laptops there are many LV regulated power rails derived from the input main power rail (e.g. 0.8V, 1V2, 3V3, 5V), in some laptops the full input voltage/current is supplied to the battery. Some laptops have lower voltage batteries and step down the input to something like 15V, 12V or 8V for charging, while others do take the full 19-20V into the battery. I can't swear to it but I'm pretty sure not all use a separate buck regulator to "cap" the battery voltage. More likely, I'd expect either the BMS, or the main input MOSFETs before it even gets to the BMS, would monitor the input voltage and shutdown in an unsafe over-voltage scenario.Quote from: zilp on January 24, 2024, 07:09:11 pm24V would likely be fine for many laptops, I agree. I wouldn't want to make an overly-broad assumption though, nor even if it functioned would I want to apply that much over-voltage over an extended period of time.

author: langwadt
author_rank: Super Contributor
timestamp: January 24, 2024, 09:35:30 pm
content: Quote from: Veteran68 on January 24, 2024, 08:20:40 pmI find that hard to believe

author: Veteran68
author_rank: Frequent Contributor
timestamp: January 24, 2024, 10:30:07 pm
content: Quote from: langwadt on January 24, 2024, 09:35:30 pmWhile I wouldn't call it common, out of the hundreds of laptop repair videos I've probably watched, I've seen it. Not sure how I'd go back and find them now, but will post if I do.Most laptop batteries are going to be somewhere around 11-15V, but there are exceptions.

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 25, 2024, 12:22:39 am
content: I can boost the voltage from my LiFePO4 battery (13.6V when fully charged, and 12.8V at 80% discharged) up to 19.5V instead of 20V, but how can I buck the current of this 8 Ah battery down to 3.33A max while I'm boosting it to 19.5V? Resistors?

author: Doctorandus_P
author_rank: Super Contributor
timestamp: January 25, 2024, 12:26:28 am
content: Best I know wallwart voltages for laptops are vendor buy-in issue. It started long ago where the input voltage had quite narrow margins to be accepted as "valid", and as far as I know it was only a DRM thing, It would be quite easy to make a laptop charge from anything between 12V and 30V. The laptop already has built in SMPS circuits, to the only change is probably the difference between a buck or a sepic converter.But it's not completely bollocks either. If the laptop tries to pull more current out of a wall wart then it can deliver, strange things can happen. Some will go into an overload or hickup mode, others will just blow a fuses or release the magic smoke.Manufacturers have no incentive to make laptops with "universal" inputs. They much rather sell you double marked up spare power supplies instead.EU started harmonization in phone chargers long ago (15 years?) and lately USB-C with built in power management and delivery is gaining traction.

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 25, 2024, 01:21:28 am
content: I just watched a YouTube video of a gent powering his laptop off of a car battery with only the assistance of a boost converter. No smoke.https://youtu.be/oxy10TYGh5A

author: IanB
author_rank: Super Contributor
timestamp: January 25, 2024, 01:42:57 am
content: Quote from: Silver_Is_Money on January 25, 2024, 12:22:39 amYou can't, and you don't need to. You cannot fix both current and voltage at the same time. If you fix the voltage at 19.5 V, the laptop will decide the current. You have no control over it. Just make sure the supply is good for at least 3.33 A and you are golden.

author: Psi
author_rank: Super Contributor
timestamp: January 25, 2024, 02:29:57 am
content: I personally wouldn't think twice about applying 20V to something designed for 19.5V if that thing has an internal switchmode system. I would just do it without thinking.It's close enough.

author: kjr18
author_rank: Regular Contributor
timestamp: January 25, 2024, 08:35:12 am
content: I think there is one more thing to consider. What type of plug does this laptop charger has? Simple 5.5/2.5 mm jack or some other with third contact? While 20V are close enough to work here without problems you might encounter problems with those pesky "smart" power supplies that use third pin for some type of power supply identification, and maybe limit power drawn from power supply or not work at all.

author: radiolistener
author_rank: Super Contributor
timestamp: January 25, 2024, 10:21:55 am
content: Quote from: Silver_Is_Money on January 24, 2024, 01:46:58 pmI think it should works fine. 20V is about 2.6% overvoltage for 19.5V input which should be within tolerance.In addition there is also some voltage drop on the wire between charger and notebook. So the actual voltage on notebook input will be close to the expected 19.5V.

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 25, 2024, 10:22:16 am
content: Quote from: kjr18 on January 25, 2024, 08:35:12 amMy HP Pavilion laptop's 4.5mm x 3 mm power jack looks like this. Given that there are three wires, how should I connect it to my boost converter?

author: radiolistener
author_rank: Super Contributor
timestamp: January 25, 2024, 10:27:18 am
content: Just make sure that you're using reliable power supply which can handle max possible current with no issue.Also make sure that you're using thick enough cable and good connectors which can handle at least 4 Amps with no significant voltage drop and heating at 65 Watt.And don't forgot to double check polarity before connection...

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 25, 2024, 10:54:45 am
content: Errata correction: I've been referring to my HP laptop as a Pavilion model throughout this thread due to brain fade, but it's actually a HP ProBook. That changes nothing much...

author: kjr18
author_rank: Regular Contributor
timestamp: January 25, 2024, 11:03:15 am
content: Well, those laptops use plugs and sockets with three contacts: Outer shell is negative, inner shell is positive and pin in middle is typically some kind of sense pin, probably used to detect power supply type or current capacity. I just checked my charger (only 45W) and I have negative on outside, positive 19,87V inside and about 15V on inner pin.

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 25, 2024, 12:59:54 pm
content: Quote from: kjr18 on January 25, 2024, 11:03:15 amIt appears that the blue wire on the 4.5mm-3mm jack is the center pin. The black wire is negative (outer jack wall/shell), and the white wire is positive (inner jack wall/shell). Voltage measurements are as follow:For my original HP wall wort:---------------------------------------Across the black wire and the white wire my volt meter reads 19.88V when common on the multi-meter is on the outside shell, and red is touched to the inside.Across the black wire (outer shell) and blue wire (where blue = center pin) my volt meter reads 19.15V (best I can tell)For my replacement wall wort (which just arrived yesterday):--------------------------------------------------------------------------------Across black and white (jack shell outer and shell inner) my volt meter reads 19.98VAcross black and blue (the center pin) my volt meter reads 19.30V (best I can tell)Both wall worts seem to charge the battery of the old HP ProBook just fine. My intent is to use the new wall wort for my typical home computing use, and to connect the jack and three wire set from my old/original wall wort to my boost converter and power it via a small 12.8V to 13.6V 8Ah LiFePO4 battery for field use. But the lower voltage on the center pin has presented me with a setback that wasn't anticipated. A quandary in need of guidance.

author: MrAl
author_rank: Super Contributor
timestamp: January 25, 2024, 02:13:48 pm
content: Quote from: Silver_Is_Money on January 25, 2024, 12:59:54 pmHow are you connecting the blue wire with your new wall wart?Is it left open?

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 25, 2024, 03:32:48 pm
content: Quote from: MrAl on January 25, 2024, 02:13:48 pmThe blue wire feeds the center pin with 19.30V on my new wall wort, and on my old (now disassembled) wall wort the same is 19.15V. Will two 10Kohm resistors in series drop ~19.9V to ~19.3V? If so I can come off of the positive output of the boost converter with two leads, one at ~19.9V for the jacks white wire, and one (with the two resistors in series) going to the jacks center pin via the blue wire at ~19.2V to 19.3V. The center pin seems to (as has already been stated) be an HP planted tricky sort of safety to verify that one of their brand of wall worts is being used.

author: soldar
author_rank: Super Contributor
timestamp: January 25, 2024, 05:33:05 pm
content: Dell laptops use a similar system where the central pin uses SMbushttps://en.wikipedia.org/wiki/System_Management_Busto communicate with the battery pack.

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 25, 2024, 05:45:21 pm
content: Will this get me to 19.23V on the center pin (blue wire)?

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 25, 2024, 06:36:56 pm
content: Perhaps a better way of presenting how to send 19.9V to the white wire of the 4.5mm-3mm Jack, and 19.23V to the blue wire of the 4.5mm-3mm Jack for my HP ProBook Laptop computer:Oops, I forgot to define R2 in my image. R2 = 10K Ohms. Will this work?

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: January 26, 2024, 10:07:34 am
content: A very interesting thread. My old Asus laptop (a Vivobook) charged and ran well from a generic 12 Volt to 19 Volt laptop car adapter. The adapter only has 2 wires in the cable, indeed several generic car adapters have 2 pin adapters to use with a variety of different laptops...My replacement laptop is a Dell Vostro and presumably uses the inner part of the DC connector "sleeve" as some sort of sensing that a valid charger is being used (thanks soldar for the diagram). Any idea how to fool the laptop into accepting a generic 2 wire charger, or should I pay the Dell price for an adapter (72 GBP plus 7.4mm to 4.5mm adapter)?ThanksSJ

author: MrAl
author_rank: Super Contributor
timestamp: January 26, 2024, 10:59:23 am
content: Hello again,I was wondering what to do with that 'blue' wire too because I have a laptop with the same connector and I often thought about using a different wall wart but was not sure how to handle that blue wire. I'd hate to burn anything out.I can apply just about any voltage from 3.3v up to maybe 30v, so 19.5 volts I can get right on the money 19.500 volts, but I'd have to know what to connect to that blue wire. If it is a communication line, that would probably be too complicated, but if someone opened up their wall wart they would know right away if there was a chip in there or just a couple of resistors. Hopefully just a couple of resistors.

author: DavidAlfa
author_rank: Super Contributor
timestamp: January 26, 2024, 11:28:37 am
content: The laptop has a charger controller, will work just fine.

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 26, 2024, 03:48:10 pm
content: Quote from: DavidAlfa on January 26, 2024, 11:28:37 amHP laptops seem to look for a unique voltage on the center pin. And by year and laptop series this center pin voltage is different, such that you are forced to use the correct wall wort for your model and year of laptop. They apparently refer to it as a "Smart Pin". My concern is as to what they mean by "Smart". Unconnected my HP wall wort's center pin reads 19.15V, while the jack reads 19.87V (with + on the inside wall, and - on the outside wall). Perhaps when connected this center pin "Smart" voltage changes. I can only make a voltage divider that sends one 'fixed' voltage (19.87V) down the white (inner shell wall) wire leading to the jack, and another 'fixed' voltage (19.15V) down the blue (center pin) wire of the jack. I hope that works so I can run my computer (and the oscilloscope which uses it as it's screen) in the field.

author: IanB
author_rank: Super Contributor
timestamp: January 26, 2024, 04:43:07 pm
content: Quote from: Silver_Is_Money on January 26, 2024, 03:48:10 pmThis has not been my experience, unless it has changed recently. My company for a long time sourced laptops from HP, and so we had many different models and years floating around, and all sizes of power bricks from small travel bricks to giant docking station bricks. All of them were interchangeable. Any HP power brick would work with any HP laptop or docking station.My best guess is that the centre pin might indicate the power rating of the power brick, so the laptop or docking station could know how much current it could draw. For instance, a laptop might show a message saying something like, "The connected power supply is too small, so the performance of the laptop might be limited."

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 26, 2024, 04:55:07 pm
content: Quote from: IanB on January 26, 2024, 04:43:07 pmIf that's so, then perhaps I should just solder the white and blue wires together and feed both with 19.5V. But some have measured their center pin roughly at the voltage I discovered, and some measured 18V, and one guy measured only 8V on the center pin (blue wire).

author: IanB
author_rank: Super Contributor
timestamp: January 26, 2024, 05:09:17 pm
content: I just measured a 150 W HP power supply that I have lying around, and the main voltage was 19.7 V, while the center pin was 19.5 V.[Edited to clarify make of power supply]

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 26, 2024, 05:32:27 pm
content: Quote from: IanB on January 26, 2024, 05:09:17 pmIs it intended for running (or more technically correct, charging) an HP laptop?

author: Bud
author_rank: Super Contributor
timestamp: January 26, 2024, 05:39:07 pm
content: Quote from: Silver_Is_Money on January 25, 2024, 06:36:56 pmNo you cannot use a voltage divider with such values. Use the Ohm's law to calculate the current that will flow through the divider to see why.

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 26, 2024, 05:43:14 pm
content: Quote from: Bud on January 26, 2024, 05:39:07 pmI consulted a ChatBot and then confirmed it via this online voltage divider calculator.https://ohmslawcalculator.com/voltage-divider-calculator

author: IanB
author_rank: Super Contributor
timestamp: January 26, 2024, 05:52:36 pm
content: Quote from: Silver_Is_Money on January 26, 2024, 05:32:27 pmYes, it is an HP power supply--19.5 V, 7.7 A, 150 W.A 90 W HP power brick (19 V, 4.74 A) shows 19.6 V as the main open circuit voltage and 19.0 V on the center pin.

author: nightfire
author_rank: Frequent Contributor
timestamp: January 26, 2024, 05:58:04 pm
content: Having some Probooks at work, and also doing some appliance testing of the power supplies, the voltage differs a bit between generations.Older stuff was around 19V, more modern PSU do the 19.5V- but as far as I am aware, for the notebok itself does not matter.Open circuit voltage of those 19.5V versions are often around 19.8V when measured with a multimeter.Just for interest: Which model is your Probook, and Generation?For the wiring maybe this helps:https://www.parkytowers.me.uk/thin/hp/hp_psu.shtmlHave not checked if this still applies to the recent PSU of HP.

author: tunk
author_rank: Super Contributor
timestamp: January 26, 2024, 05:59:04 pm
content: Quote from: Silver_Is_Money on January 26, 2024, 05:43:14 pmTechnically it's correct, but it assumes that the outputimpedance/resistance is 1-2 orders of magnitude higher.Or, what's the voltage if there's a 10k resistor in parallelwith R2? And with 100k, or 1M?

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 26, 2024, 06:04:31 pm
content: Quote from: IanB on January 26, 2024, 05:52:36 pmOnce again it shows that the center pin voltage is below the jack's voltage. There must be significance in this, but what that significance is remains a mystery.I popped open my HP laptop wall wort and confirmed directly at the output pins that there is a measured 19.87V on the white wire, and 19.15V on the blue center pin wire. I didn't further disassemble it whereby to see how the 19.15V is generated. The center wall is positive, and the outside wall is negative on the 4.5mm x 3mm Jack with center pin.As an aside, I've heard that Dell leaves the center pin blue wire disconnected. No idea as to the truth value in this.

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 26, 2024, 06:21:22 pm
content: Quote from: nightfire on January 26, 2024, 05:58:04 pmThe back panel identification is completely worn away, but the battery model# 805292-001 indicates Probook 430 or 440. The date of the battery states 11/2016. It is 14.8V, 44Wh, and something like 2790 mAh. I bought it used/refurbished a good number of years ago. I can't remember how many years that might be though. And I have no way of knowing if the 2016 dated battery is original whereby to pin down a date for the computer mfg..Edit: I'm running Linux Mint on it. Is there a means in Linux whereby to assess better model number and date info?Edit #2: A fading sticker to the right of the touch-pad states Intel CORE i5 Inside.

author: nightfire
author_rank: Frequent Contributor
timestamp: January 26, 2024, 06:53:03 pm
content: In the BIOS setup screen should be the serial number displayed. Usually beginning (at least here in germany) with something like 5CG...... With that, on the HP.com support page you can enter that and HP gives you the right model/generation.From the age, I would take some bets that this is a 4x0 Probook gen1 or 2, the second number denoting the screen size- 440 being 400 series 14" screen.

author: IanB
author_rank: Super Contributor
timestamp: January 26, 2024, 07:13:39 pm
content: Quote from: Silver_Is_Money on January 26, 2024, 05:43:14 pmBe aware that ChatBots can be very unreliable with technical questions, especially ones involving numbers or calculations.

author: tooki
author_rank: Super Contributor
timestamp: January 26, 2024, 07:53:12 pm
content: Quote from: Veteran68 on January 24, 2024, 08:20:40 pmNot a snowball’s chance in hell that the bolded sentence is true.The only conceivable thing would be if a laptop put the entire battery circuitry — BMS, safety, and charger IC — in the battery pack itself. Then you could deliver raw voltage to the pack. But I don’t believe for one second that any laptop ever made puts raw AC adapter voltage directly onto a lithium battery itself without a charger circuit in between, because doing so would be wildly reckless and such a thing would never pass safety review, never mind legal review.

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 26, 2024, 07:57:35 pm
content: Quote from: nightfire on January 26, 2024, 06:53:03 pmThanks! It is indeed a model 440 G3.

author: Bud
author_rank: Super Contributor
timestamp: January 26, 2024, 08:03:22 pm
content: Quote from: Silver_Is_Money on January 26, 2024, 05:43:14 pmSeems you missed that I asked to calculate the Current through the divider, not the Voltage. You want to supply 5A or something to the battery. That means 5A have to flow through the divider. This will never happen even remotely. You can ask your buddy GPT to calculate Current but it will be better for You if you do it yourself, this will give you understanding of Ohm's law.

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 26, 2024, 09:30:03 pm
content: Quote from: Bud on January 26, 2024, 08:03:22 pmI just watched a video in which a guy disconnected the blue wire after first getting his HP laptop to charge, and while it was actively charging, and the battery continued to charge to full. But the laptop would not initiate charging with the blue wire removed. Perhaps the voltage signal from the blue wire is only required whereby to initiate charging.In this video the guy made a circuit much like the one I drew above, but where I have a 350 Ohm resistor he placed a 200 KOhm resistor, and where I placed a 10 KOhm resistor he placed a 100 nf capacitor. Is that a better solution?Edit: Adding the video.

author: IanB
author_rank: Super Contributor
timestamp: January 26, 2024, 09:49:50 pm
content: Quote from: Bud on January 26, 2024, 08:03:22 pmNot at all. There are no indications that the blue wire has to supply charging current to the battery. It is a signal wire, and probably has to source a few µA at most. In fact, if you look at the connector pin inside the plug, it is very small and thin.

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: January 26, 2024, 09:59:55 pm
content: Having spent a couple of hours searching the web, the Dell 3rd wire in the charger lead is a data comms wire between the laptop and an IC in the charger. The purpose is to identify the charger, although the cynical side of me suspects it is to discourage the use of 3rd party adapters... I don't know about HP, but suspect it works in a similar manner.Before I try it, does anyone know if using just a 2 wire connection powers the laptop but doesn't charge the battery? If so, it could be useful as charging with a generic adapter may not be needed when powering from 12V.FWIW, speaking with Dell Support, they seem to know very little about powering some models of their laptops from a 12 Volt "auto" adapter, even though they sell adapters...SJ

author: Veteran68
author_rank: Frequent Contributor
timestamp: January 26, 2024, 10:01:19 pm
content: Quote from: tooki on January 26, 2024, 07:53:12 pmThat’s exactly what I’m saying. I’ve seen laptop battery packs with circuit boards inside that manage the battery charge. Obviously I know you don’t pump 19V directly into a bare cell. I’ve seen technicians cut open the battery pack and replace ICs and fuses on the internal board. I’ve seen them inject 19V from their bench PSU directly on the battery cable pins on the motherboard, unless the battery had a rated voltage lower than that.Not saying it’s universal or even common, nor am I saying it’s a recommended practice. Just saying I’ve seen it done.

author: MrAl
author_rank: Super Contributor
timestamp: January 27, 2024, 10:35:10 am
content: Quote from: Silver_Is_Money on January 26, 2024, 09:30:03 pmAccording to that guy and his video, when he does not use the blue wire the laptop is powered but the battery does not charge.When he connects the blue wire to the 200k and 100nf capacitor, the laptop battery starts to charge.It also looks like when he disconnects the blue wire after that the battery continues to charge, so maybe it only has to be connected for a short time.Also according to him, the 200k resistor allows for 65 watts of charging power, and a different resistor presumably would allow higher or lower power, but he does not say what other values to use.

author: MrAl
author_rank: Super Contributor
timestamp: January 27, 2024, 10:37:30 am
content: Quote from: Solder_Junkie on January 26, 2024, 09:59:55 pmAccording to that video if you do not use the blue wire leaving it open the laptop gets powered, but the battery does not charge.That means you would need the blue wire connected to the 200k resistor and 100nf capacitor as shown in the video in order to charge the battery.There is a chance we could use a lower power wall wart also if we used a different value resistor for the 200k.

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: January 27, 2024, 11:03:36 am
content: I have just remembered that when I first powered up my laptop a message popped up on screen about insufficient power being available, even though the charger was "plugged in". However I then realised the plug was not pushed fully into the laptop power socket...Running the experiment again, I am currently using my Dell laptop with the Dell charger and have not fully inserted the plug, the battery symbol shows external power, the charge light is not on, and the battery charge level has remained at 73% for many minutes. So it is possible to run a Dell Vostro using a generic 12 Volt to 19 Volt "2 wire" adapter, even though it will not charge the battery. For some purposes charging may not be needed.Attached is a circuit from the web showing the circuit of a Dell charger, I don't know what the 9CM543E IC does, the Zener diode is shown in another circuit diagram as 12.8 Volt...SJ

author: tooki
author_rank: Super Contributor
timestamp: January 27, 2024, 01:57:39 pm
content: Quote from: Veteran68 on January 26, 2024, 10:01:19 pmLaptop battery packs practically always have a PCB inside, containing the BMS and authentication chips. But not the charger IC (and its support components) itself.

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 27, 2024, 04:18:13 pm
content: What advantage does the resistor and capacitor method (as per the video) bring to the blue line (center pin) voltage and current that the double resistors method fails to similarly provide?

author: MrAl
author_rank: Super Contributor
timestamp: January 27, 2024, 06:51:57 pm
content: Quote from: Silver_Is_Money on January 27, 2024, 04:18:13 pmWell, the R+C is a tried and proven method, presumably from the video.If the R+R works too, then maybe that's ok also, but you'd have to do some long term testing.

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 27, 2024, 09:10:22 pm
content: Quote from: MrAl on January 27, 2024, 06:51:57 pmI tried running simulations, and resistor/resistor seems to do as intended, whereas resistor/capacitor does not.

author: BillyO
author_rank: Super Contributor
timestamp: January 27, 2024, 09:29:27 pm
content: Quote from: langwadt on January 24, 2024, 09:35:30 pmI'm in perfect agreement. For two years I helped out at a local computer shop fixing laptops. Averaging 4 a day I have had over 2000 pass through my hands. The batteries are either 3-cell or 4-cell and either LiFePo or Li. Every one of those machines had a nominal battery voltage of between 9.8V and 14.8V. Not a single one had a PS of the same voltage as the battery. If they exist, they are extremely rare or very old.

author: MrAl
author_rank: Super Contributor
timestamp: January 28, 2024, 09:52:57 am
content: Quote from: Silver_Is_Money on January 27, 2024, 09:10:22 pmHi again,Well, I would think you need to test something like this on an actual Laptop not in a simulation unless you know exactly what the circuitry inside the Laptop is made of. This is a critical issue. I guess there is also the chance that it will work on one Laptop and not another.Unless the guy in the video is faking it, the resistor + cap seems to work pretty good. Of course I cannot verify this and I don't want to have to cut up my Laptop wall wart to test. I'll see if I can find my secondary wall wart I had some time ago, maybe I can cut that one up and test. I have the same basic type Laptop and charger with the two sleeves and one small center pin. I am not exactly sure when I will be able to try this though.

author: MrAl
author_rank: Super Contributor
timestamp: January 28, 2024, 09:58:52 am
content: Quote from: BillyO on January 27, 2024, 09:29:27 pmI had designed power supplies and battery chargers both as a hobby and professionally and I can say with confidence that no designer in their right mind would design an Li-ion or similar battery charger without a sophisticated circuit that keeps track of what is going on, such as terminal voltage and terminal current, max current, and often even temperature.Oh that reminds me, often there is a thermistor installed with the battery pack that measures temperature and sends that information to the charger. That could very well be what that blue wire is actually doing rather than just a resistor.This has been an important point about charging semi-dangerous batteries because when there is a problem the temperature rises and if you catch it in time there is no flame or fire or smoke.I had also designed software for battery charging that was made to be used with a special IC chip I used to sell. I always recommended using a thermistor with the IC chip and software. It's a simple way to prevent a serious problem with overheating batteries.

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 28, 2024, 05:43:11 pm
content: I just watched a video in which an HP laptop owner first measures his center pin voltage at 19.4V, and then right after plugging the jack into the computer this voltage on the center pins blue wire drops to 6.8V and holds there as battery charging commences.Unlike the other HP video in which the computer runs whether or not the blue wire is connected, in this video as soon as the blue wire is disconnected the computer dies, and a comment is made that this is what happens every time it gets disconnected.

author: langwadt
author_rank: Super Contributor
timestamp: January 28, 2024, 05:44:33 pm
content: Quote from: MrAl on January 28, 2024, 09:58:52 amit is unlikely that it is anymore that simple constant voltage power supply, all the charging circuitry is build into the laptop

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 28, 2024, 07:54:35 pm
content: I measured my wall wort with no load and then when plugged into my Powerbook 440 G3 when it's battery was fully charged and this is what I found:1) Wall Wort with no load:-------------------------------------------------------------------Voltage on white wire (inside wall) of jack = 19.87VVoltage on blue center 'Smart' pin wire of jack = 19.15V2) Wall Wort when plugged into the Powerbook, and when it's battery is fully charged:--------------------------------------------------------------------Voltage on white wire (inside wall) of jack = 19.87VVoltage on blue center 'Smart' pin wire of jack = 2.77V

author: MrAl
author_rank: Super Contributor
timestamp: January 28, 2024, 09:11:31 pm
content: Quote from: langwadt on January 28, 2024, 05:44:33 pmWell that's almost true, except for the fact that these wall warts seem to have some sort of sensing circuit as simple as it may be. If it does not sense the right signal it may not perform all the functions it was supposed to.On the other hand, the Laptop could be sensing the wall wart and not allowing all functions to work properly unless the wall wart can be identified in some way. It may have a thermistor in it also so if it overheats the Laptop may stop charging or operating in some way. This is my guess.We also have to keep in mind we could be seeing different designs as they evolve over time which may have more or less functionality.

author: Bud
author_rank: Super Contributor
timestamp: January 28, 2024, 10:02:38 pm
content: Quote from: BillyO on January 27, 2024, 09:29:27 pmAre you confusing machine supply voltage ( PS voltage) vs battery charging voltage. I wonder how you determined that full PS voltage was applied to batteries - did you measure voltage on battery terminals installed in laptops while charging?

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 28, 2024, 10:50:08 pm
content: Quote from: Silver_Is_Money on January 28, 2024, 07:54:35 pmWith this voltage divider arrangement I can effectively match the blue wire volts which I measured at 2.77V (as above):

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 29, 2024, 12:50:03 am
content: I just took the next logical step. My logic was that if when the battery is full, the "Smart Pin" (blue wire/center pin) on the HP approved power adapter (wall wort) is low in voltage at 2.77V (such as it is), then perhaps when the battery is nearly fully drained and the charger is plugged in again, this so-called "Smart Pin" will recognize the need and rise in voltage to somewhere closer to the 19.15V that it reads when not under any load (IE, not plugged into the computer and charging the battery"). So I aggressively drove the battery on my Probook down until I received a low battery warning. Then I plugged the power adapter into the Probook and initiated a recharge from the depths of extreme battery depletion. When I put the multimeter on the white wire to the jack (from the power adapter/wall wort) it read 19.87V (as it always does). Then when I moved the probe to the blue wire I was stunned to see that it read only 2.87V while in the depths of rapid recharging a nearly depleted battery (vs. 2.77V when the battery was completely charged earlier today). Thus the "Smart Pin" no longer seems smart to me at all. But rather the smarts that determine battery charge initiation and termination are internal to the computer. And now I know that my voltage divider feeding the blue wire (center "Smart"pin) must reduce 19.87V to around 2.77V to 2.87V. Bingo! A two resistor arrangement just as depicted in my post immediately above this one is confirmed. The small voltage on the center pin only appears to tell the computer that the voltage source (wall wort) is acceptable. So now I can move to attempting the powering and recharging my computer via a voltage boosted LiFePO4 battery and a voltage divider, instead of the AC/DC wall wort, and ready it for field use.

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 29, 2024, 02:02:02 am
content: Whatever the center pin wire is accomplishing, at roughly 2.7 to 2.9 volts it sure isn't charging the 14.8V battery in my HP Powerbook 440 G3. And since there are several YouTube videos showing how to turn Dell power adapters into HP power adapters, it isn't very likely that Dell is wiring HP's Smart Pin charging technology into their Dell line of battery chargers.

author: MrAl
author_rank: Super Contributor
timestamp: January 29, 2024, 10:48:28 am
content: Quote from: Bud on January 28, 2024, 10:02:38 pmYeah there is no way they are going to supply the voltage directly to the batteries UNLESS the power supply has the regulation circuitry built in, and then the measurements may be the same so it could be deceiving. There's no way to do it with a raw wall wart because it would be too dangerous. Even NiCd chargers had current limiting. Li-ion or similar needs a much more sophisticated charging circuit that has to be fairly accurate too. Those batteries are very dangerous when they are not charged correctly.

author: MrAl
author_rank: Super Contributor
timestamp: January 29, 2024, 10:52:22 am
content: Quote from: Silver_Is_Money on January 29, 2024, 12:50:03 amWhy don't you just use the resistor + capacitor solution as shown in that video, or did you determine that does not work with yours?You might have to be careful whatever you do as the voltage could be showing the Laptop what it is allowed to pull from the wall wart.I would say do a full charge from nearly full depletion and see if anything gets too hot. That's a decent test but I can't say that it is sufficient for perfectly safe operation.

author: shapirus
author_rank: Super Contributor
timestamp: January 29, 2024, 11:05:03 am
content: Quote from: Silver_Is_Money on January 27, 2024, 09:10:22 pmwhat software is it?

author: ebastler
author_rank: Super Contributor
timestamp: January 29, 2024, 12:06:22 pm
content: Quote from: Silver_Is_Money on January 28, 2024, 10:50:08 pmBut if you want to use that 2.77 V voltage to e.g. charge a battery, things will change! Instead of your meter PR1, which has a very high internal resistance, you will then connect a load with a much lower resistance.One way to look at the new situation is that your load is connected in parallel with R2. So your voltage divider will now comprise R1 and a new, much lower resistance (R2 || R_load). If your load has much less than 5 kOhm resistance, the combined resistance of (R2 || R_load) will essentially be equal to your load resistance R_load.You can calculate the new output voltage. But it would not be a good idea to change your design by simply lowering the resistance R1 to make the voltage match again! Building a circuit where the output voltage is so strongly dependent on the resistance of the load you connect to it would be asking for trouble.

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 29, 2024, 12:19:48 pm
content: Quote from: shapirus on January 29, 2024, 11:05:03 amqucs-s

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 29, 2024, 12:28:19 pm
content: Quote from: ebastler on January 29, 2024, 12:06:22 pmThe 19.5V white wire (19.5V to 20V) charges the battery and/or runs the laptop. The 2.8(ish) volt blue "center pin" wire seems to only be required whereby to permit the initiation of charging the laptops internal 14.8V battery. Without the center pin (and perhaps without the center pin being at a certain voltage) the laptop will not charge it's internal battery.

author: Silver_Is_Money
author_rank: Regular Contributor
timestamp: January 29, 2024, 04:40:33 pm
content: I built a crude prototype of the two resistor voltage divider circuit using 30 KOhm and 5 KOhm resistors. When fed via my LiFePO4 battery along with my boost converter ramping it up to 19.87V, the divider voltage (voltage between the resistors) to the blue wire (center "Smart" pin) read 2.85V. Very close to predicted...The HP Probook440 G3's battery was at 78%, so I shut it down, plugged it into my battery circuit, and then turned the computer back on. It booted right up and went directly into battery charging mode. I watch it slowly charge the battery from 78% to 100%, and then the "battery is fully charged" message appeared. Just as if the computer was on the standard HP 120VAC to 19.5VDC (actually 19.87VDC) power adapter. When I disconnect the barrel jack a message now pops up and says "battery discharging from 100%", and when I plug it back in this message vanishes.BTW, I'm running Linux Mint 21.3.So far this project seems to be a whopping success!Edit: Adding that the tiny LiFePO4 battery (nominally 8Ah, and weighing only 1 Kg.) went from 13.5V (~95% full) to 13.3V (~80% full) during my test run today. This LiFePO4 battery is at 80% discharged when it hits 12.8V. 70% discharged at 12.9V, and 60% discharged at 13.0V. I'm going to add an under-voltage protection (battery cut-off) circuit set to 12.9V.

author: MrAl
author_rank: Super Contributor
timestamp: January 29, 2024, 09:57:20 pm
content: Quote from: Silver_Is_Money on January 29, 2024, 04:40:33 pmSounds good glad you got it working. I love those LiFePO4 batteries so light weight compared to the lead acid counterparts.

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: February 02, 2024, 02:06:03 pm
content: An update on my Dell Vostro and 12V to 20V power.I used an existing laptop car charger that only has 2 wire output. As pushing the plug from the Dell mains charger halfway into the socket on the laptop results in powering, but not charging, the laptop… I tried wiring a suitable 3 wire connector to the 2 wire output of the old adapter.Unfortunately, while it was possible to power the laptop with the above arrangement, and not needing to charge the battery, subsequently plugging in the mains Dell charger didn’t charge the battery! Panic set in, but I had forgotten that I had adjusted the “MyDell” software to only charge the battery when it had dropped below 50% charged.So, bottom line is that at least with a Dell Vostro, alternative methods of powering it are a mystery and proceed with caution.SJ

author: nightfire
author_rank: Frequent Contributor
timestamp: February 04, 2024, 12:18:09 am
content: Just opened my old and trusty HP Zbook 14 (gen1) and poked around with test leads around the battery connector whilst the system was operating.Given that I did not got good contact due to the shielded location and not having needle-thin probes, got around 8.8VDC at connector pin 1+2 without charger connected, and around 9.8V with external power supply, when battery was about 90% full.So no 19V from the PSU are directed directly to the battery.Battery was a HP 716742-422 rated 11,25V 50Wh. This would point to 3*Lithium cells with 3.7V and some BMS managing the output voltage so that even a nearly discharged Lithium cell with 3V can power the notebook.

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: February 06, 2024, 10:22:40 am
content: A friend found info on that mystery IC used in the Dell charger. There is a lot more going on than just a Voltage level:-------Dell uses the ONEWIRE (1-Wire) protocol for communication between notebook and charger, for this reason the Dell charger has a 3-pin EPROM memory with 512 bytes (DS2501 or 9CM543E) that sends a data packet with power specifications, voltage and current through the central pin of the charge connector, and the EC (Super I/O) reads this information.The data packet can be viewed with the oscilloscope set to 1v/500us. In this PSID data line there is a pullup resistor connected to a voltage of +3.3v.------I don't know if HP use the same idea.SJ

author: kkontak
author_rank: Contributor
timestamp: September 13, 2024, 09:25:57 am
content: Quote from: soldar on January 25, 2024, 05:33:05 pmThat's not correct.SMbus is indeed used in laptops, but not in the charger-laptop interconnection.SMbus(=I2C, so 2-wire plus GND system) is used in the laptop-battery interconnection.That's for another discussion, but it's the main reason why a refurbished laptop battery cannot work if you just replace the cells(the IC inside the battery's BMS has an EEPROM and registers that count the charge cycles and forbids charging after a specific amount. The workaround requires special paid hardware and software because there are so many different ICs knockoffs with no publicly available datasheets or info on the data structure.)https://github.com/laszlodaniel/SmartBatteryHack?tab=readme-ov-fileIn the charger-laptop(DELL 3-pin 7.4x5.0x0.5mm) interconnection only one(middle) pin is used for data and features the 1-wire protocol. The chargers incorporate some 1-wire EEPROM device like the DS2501 or 9CM543E which is preprogrammed with the specific characteristics of the charger (in ASCII ! , see github below...)You can trick the laptop if you can find a used EEPROM from another charger, but someone has even published an emulator with ATtiny85...https://github.com/KivApple/dell-charger-emulator

author: AWAIS91119
author_rank: Contributor
timestamp: June 05, 2025, 01:03:10 pm
content: a very Long ago I chopped my 19.5V (65-watt) Power Brick Cable there were only two wires and inside the barrell connector there was a 220K Resistor from Positive +19.5V to center Pin. i think there is a pull down resistor inside Laptop which will create a divider (from which u got 2.7 something volts).Also i chopped one chinese Charger and cable for HP Laptop 19.5V (but forgot the Power Rating of that .. i guess it was 90W) and there were three wires and inside the Adapter the blue wire was connected via two parallel 330K resistor to +19.5V.

author: radiolistener
author_rank: Super Contributor
timestamp: June 06, 2025, 06:02:00 pm
content: If your concern is that the 20 VDC input might be applied directly to the laptop’s battery charging circuit without regulation and potentially overcharge the cells, a simple precaution you can take is to place a powerful diode in series with the power line. A standard silicon diode will introduce a voltage drop of approximately 0.5 - 0.7 V, effectively reducing the input to around 19.3 - 19.5 V, which aligns with the original adapter’s rating. This can help ensure compatibility and reduce any risk of overvoltage, especially in designs where the charging circuit may not include a proper DC-DC regulator. Just make sure the diode is rated for the expected current load.Alternatively, you can use the 20 V supply directly, but monitor the battery charge level and avoid letting it exceed 80 - 90%. This precaution helps minimize the risk of overcharging in case the laptop’s internal circuitry lacks proper voltage regulation for battery charging. 0.5 V error is not critical for electronics, but may be an issue if applied to battery with no proper voltage control regulator.