Laptop chargers - why 19 volts? - Page 1
Forum section: electronics / general

author: Circlotron
author_rank: Super Contributor
timestamp: May 23, 2025, 11:16:57 am
content: A number of laptop battery chargers I have looked at have an output of 19 VDC. That sounds like an odd figure. Why not 20 V? Why did multiple manufacturers settle on this figure?

author: Berni
author_rank: Super Contributor
timestamp: May 23, 2025, 11:27:42 am
content: It is because most laptops use a Lithium battery pack in a 4S configuration so you get a max pack voltage of 16.8V.The easiest and most efficient DC/DC is a buck converter with a small difference between input and output. But you do need some regulation headroom and most DC/DCs are happy running at 90% duty cycle so if you take 16.8V and add 10% you get 18.5V and if you round that up (and leave some for cable voltage drop) you get 19VAny why is 4S so popular? If you go down to a cell voltage of 3.3V (where the battery is pretty much empty) you get 13.2V on the whole pack. So that again leaves around 10% of regulation headroom to get 12V. If you had less than 4 cells that would no longer hold, while more cells adds complexity and potentially gets you out of range of some DC/DC chips that are rated for up to 20V to 28V

author: tom66
author_rank: Super Contributor
timestamp: May 23, 2025, 09:05:36 pm
content: Berni's explanation seems pretty reasonable. I suspect there is an additional reason: once laptop manufacturers settled on voltages around this range, DC-DC converter ICs which had hardware in them to support transitioning from e.g. a battery pack to the AC adapter and vice versa became commonplace and supported, say, up to 20V DC input. MOSFETs that have a 20V or 25V Vds rating are also often specified, since MOSFETs can be safely used up to their maximum Vds if transients do not occur. There will be numerous power supply manufacturers comfortable with 19V output power supplies and have reference designs that can be packaged with minimal changes. This creates a lot of industry inertia, where changing something doesn't happen even if it became somewhat more efficient to do something another way. As an example, my LG Ultrabook charges at 20V @ ~40W via USB-C, but it only has a 2S battery pack inside. It can charge from 15V @ 3A sources as per the USB-C standard but LG decided to ship it with a 20V adapter since it will be a common part used for more powerful laptops.

author: tooki
author_rank: Super Contributor
timestamp: May 23, 2025, 09:30:21 pm
content: Quote from: Circlotron on May 23, 2025, 11:16:57 am19ish is a better way of wording it, since some do/did, in fact, use 20V.See also:https://www.eevblog.com/forum/beginners/why-is-_19-5v_-used-as-a-common-laptop-charger-voltage/

author: Zero999
author_rank: Super Contributor
timestamp: May 24, 2025, 09:43:26 pm
content: It isn't just laptops. My desktop runs off a 19.5V power supply.

author: amyk
author_rank: Super Contributor
timestamp: May 25, 2025, 02:54:40 am
content: Quote from: tooki on May 23, 2025, 09:30:21 pmSome have put 21V as their rating too, e.g. HP F1072A. As my post in that thread says, anything below the likely 25V rating of the input caps should be fine.

author: SiliconWizard
author_rank: Super Contributor
timestamp: May 25, 2025, 04:36:42 pm
content: Quote from: Zero999 on May 24, 2025, 09:43:26 pmThat's usually the case for "mini-PCs" and in general the thin-mini-ITX motherboards too (which are larger than what you typically find in a "mini-PC"). I have a headless Linux box with a thin-mini-ITX motherboard that uses a 19V supply.Is it a Mac though? I haven't followed all versions over time, but it looks like their Mini and Studio are AC-powered (mains) now?

author: Zero999
author_rank: Super Contributor
timestamp: May 25, 2025, 08:24:45 pm
content: Quote from: SiliconWizard on May 25, 2025, 04:36:42 pmYes. It's a mini-PC. It came with Windows 11, but I wiped it and installed PCLinuxOS.

author: amyk
author_rank: Super Contributor
timestamp: May 25, 2025, 08:28:42 pm
content: Early Mac Minis usedan external laptop-like adapter (apparently18.5Vnominal, so same voltage range), newer ones have it inside and lowered to 12V:https://logi.wiki/index.php/A1347_2010-2014_Power_Supply_Voltage_Test

author: Andy Chee
author_rank: Super Contributor
timestamp: May 26, 2025, 12:32:03 am
content: FWIW, here's ChatGPT's response when I copied and pasted your question;QuoteAs Berni suggested the 4S lithium configuration first in this thread, affirmed by subsequent posters, and also appeared in ChatGPT's results, I'm inclined to agree with this principle.I will suggest another data point, that the DC voltage for NiMH based adapters was more variable, because there was also more variability in the different NiMH cell configurations with only 1.2V difference between cells (versus 3.7V for plus or minus a Lithium cell).

author: amyk
author_rank: Super Contributor
timestamp: May 26, 2025, 03:05:40 am
content: As usual, AI created a soup of truth and nonsense. IBM/Lenovo used 20V nominal for all their models since 2005 and pre-USB-C, and as I showed above, 21V nominal has also seen some use. The truth is a combination of needing to charge a 4S pack without a boost converter, 25V rated input caps, and a desire to reduce resistive losses. The silicon facing the DC input is more likely to have 30V or higher ratings.In practice, measure any adapter with an 18-20V rating unloaded and you'll probably find it's somewhat higher and closer to 21V.

author: Berni
author_rank: Super Contributor
timestamp: May 26, 2025, 05:44:28 am
content: Yeah as 19V or 19Vish power bricks got popular, some mini PCs started using them too. Probably because those are likely the cheapest power bricks in that wattage range due to the massive volumes they are produced in for the laptop market.There is likely not much difficulty in making a motherboard run from 19V rather than from those 12V (that most stuff on motherboards runs from). So makes sense to pick the more common input voltage.The 20V USB-PD spec was likely also chosen with this in mind since it was meant to charge lighter laptops. Tho they are now pushing for 48V USB-PD, this is going a bit too far in my opinion. That is a lot of power to be sending trough that tiny plug and DC/DCs for 48V get a lot more tricky as the vast majority of IC solutions stop at around 32V to 36V. But i suppose if it becomes popular then the semiconductor vendors will start making more chips for those voltages.

author: Ranayna
author_rank: Super Contributor
timestamp: May 26, 2025, 07:05:58 am
content: Quote from: Berni on May 23, 2025, 11:27:42 amNow i wonder what is in a current laptop that actually uses 12 volts directly...I can't think of anything from the top of my head, now that optical disk drives are all but non existant in laptops nowadays.

author: Zero999
author_rank: Super Contributor
timestamp: May 26, 2025, 10:52:33 am
content: Quote from: Ranayna on May 26, 2025, 07:05:58 amThe display might have LEDs in strings of four, but that's not 12V, it's constant current.

author: Berni
author_rank: Super Contributor
timestamp: May 26, 2025, 11:29:28 am
content: Quote from: Ranayna on May 26, 2025, 07:05:58 amYeah the role of the 12V bus has shifted around a fair bit over the years.It was used a lot to power transceivers like RS232 or analog circuitry for buffers, audio stuff etc.. and that's why the 12V rail also comes with its -12V brother on ATX PSUs. The other use being driving motors in drives. But those are slowly going extinct as we move away from mechanical storage in general. Don't the modern motherboards use the negative rails at all, but it is in the ATX spec so the PSUs have to provide it.But the 12V rail got a second wave of popularity as computers got more power hungry. Now that CPUs draw 50 to 250W we need a reasonably high voltage coming in so that the currents are not insanely high (250W at 3.3V would be 75A!), and the 12V rail is the highest voltage rail available so now the majority of power is drawn from 12V and locally switched down to ~1V for core supply rails. Heck even 12V is starting to turn out to be too low. We still have high end graphics cards catching fire when they shove 600W trough a single 12V power connector (so ~50 Amps), this is the 3rd revision of that failing PCIe high power connector and they still haven't gotten it to stop catching fire here and there (Tho well designed graphics cards have shunts to detect current imbalance from bad contact and shut down).Laptops likely share a lot of this power architecture so they will prefer something 12ish volt for powering the CPU and GPU core. So having the battery voltage in that range is useful so that it can be fed directly into those motherboard switching supplies.

author: tooki
author_rank: Super Contributor
timestamp: May 28, 2025, 02:26:19 pm
content: Quote from: Zero999 on May 26, 2025, 10:52:33 amOften but not always CC. It’s not uncommon to see long series strings that require over 30V.

author: tooki
author_rank: Super Contributor
timestamp: May 28, 2025, 02:31:32 pm
content: Quote from: Ranayna on May 26, 2025, 07:05:58 amBasically nothing. Desktop hard disk drives still use 12V, IIRC.Otherwise, as Berni said, the 12V is used as the “mains power” for getting power to all the components on the board, where local regulation (using buck converters) is used to generate the exact voltages needed right at the point of consumption, so you’re not losing tons of energy to voltage drop from shuffling around high-current, low-voltage power.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 29, 2025, 01:25:26 pm
content: Quote from: tooki on May 28, 2025, 02:31:32 pmYeah, it turns out that going from 100-240VAC directly to something like 0.9V is not very easy or efficient, so a cascade of PFC -> then to isolated 12VDC -> then to unisolated 0.9V - is close enough to sweet spot such that existing "familiar" 12V intermediate DC voltage number has stayed in use.Let's remember that some 15 years ago or so this intermediate CPU voltage was 5V (with core voltages around 1.5-2V). Vcore was similarly done with a buck converter as it is today. Buck works better with the old smaller ratio, but going from 5V to 12V is small enough sacrifice, and in bigger picture it gives significant improvement in wiring efficiency between the PSU and the buck, and in the conversion efficiency of the PSU itself too.What we see as a result of this <1:10 buck ratio is polyphase design with a lot of phases. It's hard to keep on track how many phases are typical today. Maybe not countable with our fingers anymore.But that 12V really is an arbitrary design - if you now design a laptop or new mini desktop PC from scratch, you sure could run the CPU buck from 19V brick, or maybe use 12V brick directly, or any other voltage value really close to that range. Nothing really needs exactly 12V anymore.And for very low performance computers - think about Raspberry Pi class - running everything off 5V is appealing.

author: madires
author_rank: Super Contributor
timestamp: May 29, 2025, 02:09:04 pm
content: IIRC, many of the old netbooks had PSUs with 9.5 and 10.5 V, matching their Li-Ion battery packs (2S).

author: tom66
author_rank: Super Contributor
timestamp: May 29, 2025, 02:29:08 pm
content: IIRC, Google used to have datacenter servers that were modified so their 12V rail ran at 13.8V, with a commodity lead acid battery inside the server acting as an integrated UPS. They had hard drives that were rated for higher operating voltages. (In my experience, most hard drives have no issue running at 13.8V vs 12V, but you will want the HDD manufacturer to give you assurances on reliability, if you are as big as Google.)

author: SiliconWizard
author_rank: Super Contributor
timestamp: May 29, 2025, 03:16:19 pm
content: It's all in the use case. Now for the higher-power stuff, keep in mind that the higher the voltage, the lower the current. At 19V, you need to pass 1.58 times less current than at 12V for the same power. That has consequences for the cables and connectors.

author: guenthert
author_rank: Frequent Contributor
timestamp: May 29, 2025, 03:42:02 pm
content: Quote from: Ranayna on May 26, 2025, 07:05:58 amThe fan(s).

author: tooki
author_rank: Super Contributor
timestamp: May 29, 2025, 08:58:28 pm
content: Quote from: SiliconWizard on May 29, 2025, 03:16:19 pmIndeed.Heck, you know all the brouhaha with the self-immolating 12V GPU power connectors (first 12VHPWR, then the updated 12V-2x6)? It seems to me much, perhaps all, of that problem could have been avoided by running perhaps 48V or 60V to the GPU instead of 12V.

author: langwadt
author_rank: Super Contributor
timestamp: May 29, 2025, 09:04:33 pm
content: Quote from: tooki on May 29, 2025, 08:58:28 pmor just using a better suited connector, if it was 48V they would probably have used the same connector with 1/4 the pins ...

author: SiliconWizard
author_rank: Super Contributor
timestamp: May 29, 2025, 11:01:02 pm
content: Some GPUs use two connectors, I think, which is easier than changing the ATX standard completely. Now if users only plug one of the two, that's a bit on them. Manufacturers that can't get it right (using only 1 connector when 2 would be warranted, or using cheapass ones not rated for the current the card draws) should get what they deserve: being ignored.

author: langwadt
author_rank: Super Contributor
timestamp: May 30, 2025, 12:34:18 am
content: Quote from: SiliconWizard on May 29, 2025, 11:01:02 pmthe problem isn't multiple connectors, it is using multiple pins in a connector in parallel at close to their max rating so if one has a bad connection or crimp it get hot.Some cards have sense resistor for each pin to check that the currents are balanced

author: amyk
author_rank: Super Contributor
timestamp: May 30, 2025, 02:45:08 am
content: Quote from: Siwastaja on May 29, 2025, 01:25:26 pmIt's 2025, not 2015Vcore regulators started out as linears off the 5V rail in the AT days (through the mid 90s), then briefly as linears off 3V3 when ATX came in the mid-90s, and soon switched to buck converters in late 90s/early 2000s, first off 5V and 3.3V, and then 12V with ATX12V.

author: Someone
author_rank: Super Contributor
timestamp: May 30, 2025, 03:33:14 am
content: Quote from: amyk on May 30, 2025, 02:45:08 amPoint of load bucks were already a thing in 1995 with the Pentium Pro, you got it mostly right about 5V -> core voltage. Some retro recreations:https://www.vogons.org/viewtopic.php?t=82517and details of the programmable output voltage in an application note for the L4990A regulator chip:http://rcl-radio.ru/wp-content/uploads/2014/09/AN908.pdfunlike the RC5042 which integrated the VID decoder.

author: tooki
author_rank: Super Contributor
timestamp: May 30, 2025, 07:00:34 am
content: Quote from: langwadt on May 29, 2025, 09:04:33 pmI have wondered why they didn’t just use something like Andersen Powerpole.All the same, it seems to me that a higher voltage than 12V would have been smart, given the power requirements of high-end cards.

author: Berni
author_rank: Super Contributor
timestamp: May 30, 2025, 07:07:44 am
content: Quote from: langwadt on May 30, 2025, 12:34:18 amExactly this is the problem why the 12V connectors on high end graphics cards are catching fire.The official Nvidia reference design for the RTX5090, RTX4090 etc.. that use this new 12 pin 12V connector simply connect all the pins together on the card side. So if any of the pins develop a bad connection then the current moves to the other pins and starts overloading them. The extra heat this causes tends to slowly make the problem even worse until the connection becomes so bad that the connector starts dissipating many 10s of watts and melts.This initial bad contact happens rather easily because the cable is pretty chonky and stiff while the location of the connector requires most users to sharply bend the cable. This puts a lot of sideways force on the connector (these connectors are finer pitch than the regular molex minifit) this can bend it far enough that the pins are not seated properly inside, causing a high resistance contact between the male and female side.The AIB partner cards like MSI, Gigabyte, Asus..etc that don't use the Nvidia reference PCB design typically solve this problem by either striking 3 of the old connectors on the card and/or have shunt resistors on the pins that detect a pin being overloaded. That shuts down the card, causing a black screen, this way the user knows something is wrong and investigates the fault.But since Nvidia somehow still keeps doing the same stupid mistake after 3 generations of GPUs the industry started loosing hope in Nvidia fixing this and so ATX PSU manufacturers started putting shunt resistors on the wires going to these new 600W 12 pin connectors. That way the PSU can shut down the whole computer if it detects that the GPU connector is about to catch fire due to current imbalance.Higher voltage like 24V would likely be a good idea but it is hard to go against the existing industry momentum as users would need all new PSUs. 48V might be a bit high for the DC/DCs making 1V from it. But it seams you can take the 12V pretty far. I have a GPU server around that has tripple 1600W PSUs (redundant, hotswappable) that only output 12V and they all just feed a huge common 12V rail over a card edge connector. The amount of current that could potentially flow trough that is pretty insane up to 400A! Yet it seams to work fine, then again servers tend to be built to better standards of quality.

author: tom66
author_rank: Super Contributor
timestamp: May 30, 2025, 07:48:16 am
content: Intel has proposed moving systems to 12V only design, with the 5V & 3.3V being provided, as needed, by the motherboard or by individual loads. The logic is that regulation and voltage drop over the wiring harnesses isn't brilliant with the current solution, and the majority of current is now drawn on 12V. Indeed, most newer ATX PSUs just use buck converters internally to provide the 5V, 3.3V and sometimes -12V via a buck-boost. This is already practiced by Dell in most of their PCs - they have a proprietary PSU that provides 12V only, with a 5V or 12V standby rail - but they use a proprietary hardware ecosystem.

author: tooki
author_rank: Super Contributor
timestamp: May 30, 2025, 07:51:50 am
content: Quote from: Berni on May 30, 2025, 07:07:44 amI doubt it’s that simple. If it were, they’d have figured out a solution that works. Yet the problem persists.These are latching connectors, so they should be making good contact even under some force, as the latch is supposed to enforce the seated position. I think there’s some other aspect that isn’t yet fully understood. (But let’s leave that for the numerous existing threads on that topic.)Quote from: Berni on May 30, 2025, 07:07:44 amThey aren’t based on Mini-Fit Jr. (what people actually mean when they say just “mini-fit”), they’re based on Micro-Fit 3.0+ (which actually is rated for higher currents than the 12VHPW/12V-2x6 connectors!!).

author: tooki
author_rank: Super Contributor
timestamp: May 30, 2025, 07:53:52 am
content: Quote from: tom66 on May 30, 2025, 07:48:16 amI thought this was well beyond the “proposed” stage and actually already in use by a lot of manufacturers.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 30, 2025, 08:18:35 am
content: Quote from: Berni on May 30, 2025, 07:07:44 amSure, but that isn't a fundamental problem of using parallel connections; no, it's a problem of underrating, something which can happen with a single connection, too. Parallel connectionsincreasereliability if properly rated; cascade failure only happens if ratings are catastrophically close to failure even during normal use. A single connection is much more prone to failure, given the design is otherwise the same (just for higher current).Designers just need to check the worst-case pin rating of the middle pins when all pins are used for full current - this is specified in every decent connector datasheet - and then apply some derating; a good idea is to make sure that when you parallel N pins, N-1 can still provide the full current without overheating. This way, single failure does not cascade into total failure. The one connection which develops high resistance simply stops taking any significant current.

author: tooki
author_rank: Super Contributor
timestamp: May 30, 2025, 08:43:52 am
content: Quote from: Siwastaja on May 30, 2025, 08:18:35 amEhhh… I disagree on all counts.The 12VHPW and 12V-2x6 connector standards already significantly derate the current, from 13A per pin to 8.3A per pin. (600W/12V/6 pins = 8.3A per pin). I checked, and the 12VHPW and 12V-2x6 connectors use the exact same crimp terminals as the standard 13A Micro-Fit+ connectors. So a single failed pin shouldeasilybe handled by the remaining 5, since the resulting 10A/pin is still well below the 13A the terminal can handle.As for reliability of parallel connections: the whole problem is that, absent explicit monitoring of each conductor, a parallel connection doesn’t exhibit failure when one of the conductors breaks, even though it’s now operating in a compromised condition. If you only care about continuity for a signal, no problem. But for high-current connections, this is hugely problematic, because you have a problem, but you don’t know it. Failing open is better in that situation. This is absolutely an inherent problem with parallel power connections, which is why it’s generally avoided.It’s like a piece of equipment that failed at work last year, an old, large incubator cabinet. The users came because there was no more air circulation. Along the back, it has a row of 10 fans to circulate the air. Turns out that over the years, one by one they had all failed. Only once the very last one failed did the users notice. Who knows how many years it had been operating in a compromised condition, and who knows whether the reduced, asymmetrical airflow compromised the chemistry done within.

author: Ranayna
author_rank: Super Contributor
timestamp: May 30, 2025, 09:03:32 am
content: Quote from: tom66 on May 30, 2025, 07:48:16 amA lot of OEMs already have adopted 12VO in many of their systems.As more and more periphery moves to PCI Express, this will get easier and easier to push into a standard. The only thing left in many PCs that is connected directly to the power supply and not using 12 volts are SATA devices. And NVMe storage that is connected directly to the mainboard is used more and more

author: Berni
author_rank: Super Contributor
timestamp: May 30, 2025, 09:18:26 am
content: Quote from: tooki on May 30, 2025, 07:51:50 amQuite a few people tested these connectors independently and it turns out that in some cases you can get pretty bad current balancing problems between the pins under what should be considered normal use.Yes they are latching connectors but the plastic that the housing is made out of is not particularly hard, so it has a fair bit of give to it. If you put enough bending force on the mated pins then you can get them to make contact where they are not designed to make contact while loosening the contact in the spot where they are supposed to make contact.But it is not like all of these are failing. The vast majority of these are fine. You need to be particularly unlucky for these problems to stack up enough to actually get it to melt (ie multiple simultaneous bad pins). But when it does happen people usually post pictures of it on reddit and such (since yeah who wouldn't be upset that their $4000 GPU killed itself), there are many many of these cards out there, so it looks like it is a more common problem than it actually is. But still this should not be happening, we never had the old connectors melt like this.Quote from: tooki on May 30, 2025, 08:43:52 amExactly the problem. If it keeps working, people will keep using it.But if your computer turns off before the problem, it will never get far enough for the connector to catastrophically fail.It is possible that this same fault can occur with the old 6pin 8pin PCIe power connectors. But because they are separate connectors the graphics card vendors were worried about people not plugging all of them in properly (high end cards typically have 3x 8pin), so most cards back then had shunt resistors to make sure the current is being properly shared. Hence the computer would stop working before the imbalance becomes big enough to be fire hazzard.

author: tom66
author_rank: Super Contributor
timestamp: May 30, 2025, 11:04:56 am
content: Quote from: tooki on May 30, 2025, 07:53:52 amIt's definitely used by Dell in most of their systems, and HP and Lenovo in their lower end systems. But in the hobbyist/self-build market, and from most other OEMs, the standard ATX multi-voltage power supply still rules the roost in 2025. My guess is it's a bit of a headache to support 12V only when spinning rust and some SSDs still want 5V. And motherboard manufacturers don't want to put 5V & 3.3V converters on their board with power connectors to support drive connections... lots of additional board area used on high cost board technology compared to phenolic PCBs in a PSU. Incidentally, despite SATA 'requiring' 3.3V, in practice drive manufacturers have stayed away from depending upon it since the Molex adapters don't include it. It's messy.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 30, 2025, 12:37:44 pm
content: Quote from: tooki on May 30, 2025, 08:43:52 amThen there is something seriosly wrong with the product ratings, manufacturing quality or something. Paralleling power connectors is done all day long in every field and somehow only PC hardware gets it wrong.Why I'm saying this is, thinking some alternative single high-power connectors as magic silver bullet is dangerous. If we had such a change, still with absolute cheapest manufacturing, are you sure it would be problem free?It probablywouldbe better, but only because it would be a fresh new design, with legacy cut off and better chances of learning from mistakes; not non-parallelism in itself.QuoteSingle connector can also develop partial failure and localized heating. There is no other way preventing high current connectors from melting than extremely good design and manufacturing quality, significant derating (to allow them working in said "compromised condition"), or monitoring (e.g. temperature sensor)QuoteApplies to non-paralleled connections as well. For example, US 120VAC plugs and European Schukos are notorious from burning; to the point we have national official non-binding recommendation of derating 16A Schuko sockets to only 8A when used for EV charging.Or PV DC MC4 connectors. Ridiculously small current, should be easy-peasy, yet it became a mess of non-compatible manufacturing tolerances. Single connectors. Paralleling two would obviously nearly completely solve the problem (publishing and mandating the manufacturing tolerances would be of course even better).Most examples of burned connectors I can figure out are of non-paralleled.QuoteSure, but single connection does not magically offer that. It has exact same contact wear and tear mechanisms increasing resistance and heating, with no backup parallel paths to limit voltage drop over the connector.QuoteCitation needed - I see plenty of paralleled power connections, have used them myself too never with any issues.

author: tooki
author_rank: Super Contributor
timestamp: May 30, 2025, 12:57:00 pm
content: I’m probably going to largely leave this as “agree to disagree” (because I think you’re wrong), but:- We could, but don’t, use parallel connections for anything where large currents normally flow: mains power (grid, generation, distribution). EV batteries. We use fat single connections instead. Why do you reckon that is??- What are the “every field”s that use parallel connections all the time? The only one I can think of is computers.- A voltage drop across a single failing connection is liable to give an indication of malfunction, e.g. lights flickering, weird behavior in a device, a computer crashing, etc. That’s good.- I wouldn’t be trying to invent a new parallel connector, I would use one that has a long history of being successfully used for that type of electrical load. Like Powerpole.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 30, 2025, 01:17:49 pm
content: Quote from: tooki on May 30, 2025, 12:57:00 pmBut this is literally false. Do google image search for "power line", and the first thing you see is two paralleled supplies of 3-phase HV AC - very usual configuration. Also 3 paralleled wires close (within tens of centimeters) from each other is a common arrangement, with spacers every dozen meters, then you can have 2-3 or such bundles. See e.g.https://commons.wikimedia.org/wiki/File:Cable_spacer-damper_on_power_lines_-_geograph.org.uk_-_970517.jpgOther example are Meanwell AC/DC bricks with 2-4 paralleled screw terminals. Very widely used everywhere. They rarely melt.QuoteYet PC stuff like video cards use switch mode supplies with regulated output voltages, with negative resistance characteristic - increasing voltage drop does not cause any lights flickering, itincreases currentwhich further escalates the heating, which further increases voltage drop - until it eventually fails with a burned connector. You would need a separate sense wire to know how much voltage is actually dropped in the connector to shut it down.QuoteMaybe? I have heard horror stories of Powerpoles crimped incorrectly. Why are you so sure that the tiny minority of burned GPU power connectors is an epidemic caused by paralleling, and simply not quality issue - for example, in crimping?But yeah, with "new", I really meant the new work of qualifying, testing and specifying/standardizing a connector not used for CPU/GPU before; Powerpole would be one such candidate.Sure, if ittrulycascades from asinglefailed pin, then paralleling was either wrong idea, or implemented incorrectly. Because if single failure escalates to total failure, reliability compared to single connector is 1/n. On the other hand, if two failures are required, then.... someone do the math for me. Remember that paralleled connections have negative coefficient so is self-correcting. If one connection develops more resistance, it carries less current. That's the whole idea.Really, I'm 100% sure that if you take the current "melting" type of connector and "scale it up" with exact same design principles and construction quality, but larger current (to reach same amount of heating during normal use), and use that instead of paralleling, problems are not going anywhere. We can agree to disagree, but as usual, I have a tendency of being right. You have the same tendency however which makes it interesting

author: Siwastaja
author_rank: Super Contributor
timestamp: May 30, 2025, 01:26:35 pm
content: Seehttps://hackaday.com/2022/10/28/nvidia-power-cables-are-melting-this-may-be-why/. So in this example case, nothing to do with paralleling, and everything to do with poor construction.

author: tooki
author_rank: Super Contributor
timestamp: May 30, 2025, 02:51:54 pm
content: Quote from: Siwastaja on May 30, 2025, 01:17:49 pmI don’t actually think those are examples of what you think they are.The fact that you have multiple cables of the same phase running near each other (with the damper) does not mean they are being paralleled: they could just as likely be terminating at separate endpoints, be they separate substations, or separate transformers within a substation. (Even if the loads are ultimately joined, there will be individual fuses, monitoring and switching, not just “dumb” paralleling, which is the issue at hand. Everyone agrees that individually-monitored conductors are fine.)Similarly, industrial power supplies don’t have the 2-4 screw terminals because one screw terminal couldn’t handle it, but because you want to offer flexibility to connect multiple loads. Note that the really high output current supplies actuallydon’thave multiple screw terminals, but instead use one negative and one positive only. I looked at the highest-current power supplies on DigiKey, and every single one I randomly clicked on the first page of results uses exactly one bus bar pair for the output:https://www.digikey.ch/short/1qz3qtc7If multiple paralleled wires made sense as a way to carry large currents, they’d provide for that. But they don’t.If it made sense to parallel, why don’t we use mains plugs with 15 low-current pins for 3-phase construction site power, rather than the IEC plugs with 5 giant pins?If it made sense to parallel, then how come on the rare cases that connector datasheets/application notes do address doing this, it’s to tell younotto do it?Amusingly, when searching for examples of that,one that came up is for Micro-Fit+, the very connector upon which 12VHPWR and 12V-2x6 are based on. And it says this: “This connector system is not designed for current sharing (i.e., splitting one current load across multiple circuits).” Presumably the derating from 13A down to 8.3A was intended to address this.)

author: tooki
author_rank: Super Contributor
timestamp: May 30, 2025, 02:52:46 pm
content: Quote from: Siwastaja on May 30, 2025, 01:26:35 pmThat’s the old 12VHPW (and an odd one at that), whose flaws 12V-2x6 was intended to fix. But apparently without success.

author: tom66
author_rank: Super Contributor
timestamp: May 30, 2025, 02:58:28 pm
content: UK low voltage power (in homes and offices) is typically wired as two parallel connections in a "ring" configuration. Occasionally one half of the ring fails, which is an undetectable failure. However, it only slightly overrates the cable: we use 2.5mm^2 for ring circuits, which is rated to 23-27A in typical cases, and the circuits are protected with a 32A breaker. So it is seen as a 'reasonable' compromise given it is very uncommon to load a socket circuit up fully with a continuous load. Also in terms of parallel connections used elsewhere, lots of automotive circuits use parallel connections to provide better flex when going through joints etc. For instance looking at the wiring manual for my old car, the power to the doors (for windows and puddle light etc.) is supplied as two parallel 12V wires (with chassis return) because it is more flexible than one thicker wire.

author: tooki
author_rank: Super Contributor
timestamp: May 30, 2025, 03:37:35 pm
content: Quote from: tom66 on May 30, 2025, 02:58:28 pmDo they use individual connector pins, or do they crimp both wires into the same pins?

author: SiliconWizard
author_rank: Super Contributor
timestamp: May 30, 2025, 04:32:54 pm
content: Quote from: langwadt on May 30, 2025, 12:34:18 amYes, but "the problem isn't multiple connectors" is a contradiction. Sure the problem is using pins that pass too close to their max rating (or sometimes above), which of course can be mitigated by distributing current over two connectors. Sure a single better connector could work, but 1/ a manufacturer can control only its own side - the culprit may be not in the female connector itself (or at least, alone), but in the male connector coming from the ATX supply. And, even with perfect mating, some GPUs now draw so much peak power that a single connector can't work reliably because you'll exceed its max rating. Adding a second connector mitigates that and possible bad connections. Of course as long as current is properly distributed on the card.Some high-end GPUs can draw over 600 W, that's insane.We probably need to define what we mean by "connector" here, which may have led to the confusion.There are 6-pin, 8-pin, 12-pin and now 16-pin ATX connectors typically for GPUs. Depending on the power supply and card you have, that's going to differ. For recent, power-hogging cards, you may need to plug a single 16-pin connector, or two 8-pin ones. I've heard melted connector stories both from users connecting only one connector when two were needed, and from those more recent 16-pin connectors some of which were just complete crap - they've apparently gotten a bit better.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 30, 2025, 04:56:33 pm
content: Quote from: tooki on May 30, 2025, 02:51:54 pmNo one said paralleling is always a better option. It rarely is. I'm just saying it's not inherently flawed, but a strategy widely used. For a percentage, non-paralleled connections and wires of course dominates, and probably is better solutionon average.Quote from: tooki on May 30, 2025, 02:51:54 pmHell no, you realize these dampers are not isolated? If you are going to terminate at different endpoints, possibly some disconnected, you end up current flowing through these dampers. They have to be hard-paralleled.Same in every large transformer and every large motor (windings made of paralleled strands).Skin effect (or proximity effect) is also a reason to do so, even at 50-60Hz for very large systems.

author: tom66
author_rank: Super Contributor
timestamp: May 30, 2025, 05:20:39 pm
content: Quote from: tooki on May 30, 2025, 03:37:35 pmFor UK ring main: it is usually the case that sockets have only one connection point (requiring two wires to fit into one terminal), though I *think* I have used ones with two points in the past (having internal bus bars), which make wiring easier. I don't know if a specific arrangement is prescribed or not here, though.For the car: not sure, the wiring diagram doesn't make it clear.

author: langwadt
author_rank: Super Contributor
timestamp: May 30, 2025, 05:37:04 pm
content: Quote from: Siwastaja on May 30, 2025, 12:37:44 pmsimilar here, sockets are rated and fused for 10-16A but that is only short term, it is illegal to sell chargers for normal socket that use more than 6A

author: tooki
author_rank: Super Contributor
timestamp: May 31, 2025, 06:24:46 am
content: Quote from: Siwastaja on May 30, 2025, 04:56:33 pmWe probably have to start distinguishing between parallel conductors terminated individually (like in the GPU connectors) and parallel conductors terminated together (like in motors and transformers, at least the ones I’ve seen). Because I suspect that is a relevant distinction here.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 31, 2025, 01:06:46 pm
content: I don't understand why the new GPU power connector uses a lot of small pins, wouldn't that use a lot of the connector area for insulation between pins as opposed to current carrying surface area? If I was to design it, I would just use a connector with two big pins, AKA XT90 or Anderson Powerpole.

author: madires
author_rank: Super Contributor
timestamp: May 31, 2025, 02:16:24 pm
content: Historical development.The first iteration was a 6-pin connector for 75W, then 6+2-pin for 75 or 150W, 8 pin for 150W, and 12-pin for 600W. Cable management might be also a reason. A connector with two thick and stiff wires causes more mechanical stress.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 31, 2025, 05:36:50 pm
content: Quote from: madires on May 31, 2025, 02:16:24 pmSilicone wire commonly used in R/C is flexible enough even in thicker gauges.

author: tooki
author_rank: Super Contributor
timestamp: May 31, 2025, 11:21:07 pm
content: Indeed. And it’s also perfectly possible to make PVC that is just as soft. (Like LiFY from Kabeltronik or Lapp.)

author: Circlotron
author_rank: Super Contributor
timestamp: May 31, 2025, 11:53:25 pm
content: Quote from: madires on May 31, 2025, 02:16:24 pmAnd using additional wires of the same thickness (and colour) simplifies production inventory.

author: Circlotron
author_rank: Super Contributor
timestamp: June 30, 2025, 10:55:47 pm
content: It just occurred to me that many power tool batteries are nominally 18 volts. Mine is 3Ah 54 watt hours. One of those could make a useful power bank for a laptop. Connect straight up. No electronics needed, maybe just a fuse. The battery in this old Toshiba Satellite is 48 watt hours.

author: madires
author_rank: Super Contributor
timestamp: July 01, 2025, 09:57:26 am
content: The downside is that on some laptops power saving features (backlight dimming, ...) won't be automatically activated when powered externally.

author: spostma
author_rank: Regular Contributor
timestamp: July 01, 2025, 02:27:10 pm
content: I would suggest to add 2 extra kelvin sense wires (or to use two existing lines for that purpose),which allows the graphics card can sense to +12V and 0V voltage levels at the power source,and thus it can easily detect an abnormal voltage drop on the incoming power lines before overheating occurs.