Hacker News Reader

Comment by nanomonkey | Hacker News Reader

The old Dell barrel jack power supplies use 1wire communication to identify the power supply's capabilities. It would likely be cheaper to purchase a compatible 1wire memory module.

Here is an article on reverse engineering the memory module. https://hclxing.wordpress.com/2014/02/06/hacking-the-dell-la...

View on HN

> and the battery will not charge (the picture is from internet but it has almost identical information)

Yikes! I used a no-name charger on my Dell Latitude for quite a while, and it never stopped me from charging. Just annoyed me about it (press F1 to continue on boot) whenever I took the battery out (wiping the CMOS) and didn't turn off the AC warnings in the BIOS. The one I was using didn't have a serial chip in it, so the laptop flagged it as unknown.

It goes further than warnings though - at least circa 2012 using an unofficial charger (or official charger where this fragile extra wire is broken) would underclock the cpu dramatically. It happened silently, such that I didn’t realize what was happening and why my laptop was so slow until stumbling upon a random forum post about it. I was pretty sour on Dell after that experience.

Really? I have a 2013 Latitude and I haven't experienced that yet (or never noticed). I still have the no-name adapter here, so I'll have to check (I only just got a proper 130W).

If that is the case, part of me wants to play Devil's advocate and say that Dell have erred on the side of caution: these no-name adapters really are quite terrifying with thermals, which makes me wonder what wattage they're actually rated for. I was frequently in WTF mode because the adapter block was too hot to keep my hand on. I didn't really have a choice either, as my battery was at like 38% capacity. This official 130W is barely warm under load.

Aside: one thing that really eek'd me out about that no-name adapter is that it has a green LED inside it. The only thing is, you can only (just barely) see it through the slits on the sides because the plastic isn't clipped together properly. The manufacturing quality is atrocious.

Update: looks like you were right[0], although it doesn't affect my 2013 Latitude, if Linux's cpufreq diagnostics are anything to go by.

   # Running on battery power.
   cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_max_freq
   3500000
   3500000
   3500000
   3500000

   # No-name charger inserted.
   cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_max_freq
   3500000
   3500000
   3500000
   3500000

   # Genuine charger inserted.
   cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_max_freq
   3500000
   3500000
   3500000
   3500000

[0]: https://unix.stackexchange.com/questions/576692/ignore-ppc-s...

Try applying load to the CPU and see what cpuinfo_cur_freq reports. If I boot my ThinkPad W530 (workstation laptop with a large power envelope) with no / dead battery, it will say full speed is available, but it will remain at the minimum speed until the battery is partially charged and I reboot.

This happens even on new Dell machines, even if the PSU is detected but a lower wattage than the shipped PSU. I have wondered if it affects Linux more than windows though

A quick way to check would be to `cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq` while you're on battery, then do it again after you've plugged in the PSU. I checked mine[0] and it apparently doesn't affect this model (the adapter I tested with does not communicate with the laptop at all).

[0]: https://news.ycombinator.com/item?id=30458632 (god I really suck with the links today, lol)

The original source linked from that article has unfortunately disappeared, but the archive still remembers:

http://web.archive.org/web/20100329110047/http://www.laptop-...

An explanation of (one of) the design flaws:

http://web.archive.org/web/20100412160453/http://www.laptop-...

Not only is it clearly hostile to the aftermarket, but putting a chip that has 12V absolute maximum ratings in an environment where it could easily be shorted to the 19-20V output of the PSU seems almost like "engineered unreliability" to me.

On the other hand, when IBM/Lenovo had to solve the problem of identifying the wattage available, they used a simple and robust solution of a single resistor:

https://www.thinkwiki.org/wiki/Power_Connector#Signal_Pin

https://www.thinkwiki.org/wiki/Power_Connector#Signal_Pin_2

The only improvement I could make upon that scheme would be to make the correspondence between resistance and wattage monotonic, but otherwise it's an example of non-overengineering and aftermarket-friendly solution.

Reply on news.ycombinator.com