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Open Source Thinkpad T420 Battery Design

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Re: Open Source Thinkpad T420 Battery Design

#41

Post by iam4722202468 »

cl3misch wrote: post #40
userbinator wrote: post #12

Currently remaining battery %'s aren't exact because I'm assuming there is a linear coorelation between voltage and capacity (Which is wrong). I don't plan on fixing this, as the exact % is unimportant to me. There are dedicated ICs which will give the remaining charge accurately, which may possibly be even cheaper than this ad-hoc solution.

Could you measure a calibration discharge curve with a (digital) bench power supply draining constant current (or constant power) and use it as a LUT?

That would probably work. That's how I was originally planning on doing it, but I got annoyed with the voltage logging not working properly when I set it up so I gave up and just went with the linear voltage -> capacity reading. A potential problem with this is that every battery pack would be different, and people who make this project on their own would need to generate a table for their pack.

Re: Open Source Thinkpad T420 Battery Design

#42

Post by jart »

linguae wrote: post #7
dividedbyzero wrote: post #2

Apparently those Thinkpads are from 2011-2012, that's old. What do people do with such old devices that makes building a battery from scratch worthwhile?

The T420 is the last model to feature the traditional ThinkPad keyboard (except for the special 25th anniversary ThinkPad), though it is possible to install the T420 keyboard in a T430. There is still a segment of ThinkPad users who prefer using the traditional keyboard, and some of them are willing to forego the performance and other features of more recent laptops in order to use the traditional keyboard. There is…

This. I bought my ThinkPad T420 around 2011 and have loved it ever since. In many ways, I could feel at the time that it signified both the pinnacle and end of an era. While the keyboard doesn't feel as nice as a model f, or beam spring, there's something to be said about using the red dot as a mouse, the aesthetics, the willingness to have every i/o interface imaginable, e.g. ethernet, wimax, wifi, serial, etc. I hope my T420 lasts forever, since the new ThinkPads come across as a cringeworthy attempt to be Apple, and I never settle for lesser inauthentic forms of things.

Re: Open Source Thinkpad T420 Battery Design

#43

Post by Joeri »

iam4722202468 wrote: post #3
dividedbyzero wrote: post #2

Apparently those Thinkpads are from 2011-2012, that's old. What do people do with such old devices that makes building a battery from scratch worthwhile?

The T420 is old, but still has some advantages over laptops currently on the market. Up until 2018 many laptops still had dual core cpus like the i7-7500u which are worse than the i7-3840qm that can be put in a T420, and the few currently available laptops that have 1440p displays and quad core cpus are still pretty expensive. Some other reasons people still use the laptop are being able to use coreboot with it and t…

For reference, I just looked up the benchmarks for the i7 3840qm. Seems to perform in the same ballpark as an i5 10210u for multicore, which is the base cpu in the current thinkpads. Intel really hasn’t made faster cpu’s in a long time.

https://browser.geekbench.com/processors/929

https://browser.geekbench.com/processors/intel-core-i5-10210...

Re: Open Source Thinkpad T420 Battery Design

#44

Post by unicornporn »

bluejellybean wrote: post #31

The T420 has been my main daily driver for nearly 6 years (using it right now to type this!) and I super excited to check this post out in more depth as battery duration is one of my biggest personal complaints about the system. To those wondering about the T420, they are fantastically rugged and I still think they are the best laptop on the market assuming you can handle either a slightly crap monitor or the hassle…

I can unfortunately not live with the crap display (I do image editing). What's the hassle like?

Re: Open Source Thinkpad T420 Battery Design

#45

Post by Waterfall »

As an owner of a T420 and x230 thank you but these laptops are too old. The CPUs use like 25w, the screens are 99% really bad TN screens and a few touchscreen IPS on the x220t and x230t. The screens are the deal breaker. Lugging around a heavy laptop or a small laptop with a crappy screen sucks. The new generation starting wirh 40s are modern battery can have internal and external batteries and the screens aren't overpriced crap, you can easily find a cheap IPS in FHD for under $60 on eBay. These need adapters or expensive crappy screens that aren't produced anymore.

I wish they had better screens to make them worth using. Using an IPS and going back to these is hell, and the 720p on the T420 is also really saddening. It's the worst part of these computers.

Re: Open Source Thinkpad T420 Battery Design

#46

Post by iam4722202468 »

unicornporn wrote: post #44
bluejellybean wrote: post #31

The T420 has been my main daily driver for nearly 6 years (using it right now to type this!) and I super excited to check this post out in more depth as battery duration is one of my biggest personal complaints about the system. To those wondering about the T420, they are fantastically rugged and I still think they are the best laptop on the market assuming you can handle either a slightly crap monitor or the hassle…

I can unfortunately not live with the crap display (I do image editing). What's the hassle like?

Pretty easy, but a bit expensive considering the laptop itself only costs around $150. A 1080p display + adaptor board for it costs about $100 and the 1440p display + adaptor is around $150. If you look up "T420 ips mod" you'll find lots of pictures and tutorials.

Re: Open Source Thinkpad T420 Battery Design

#47

Post by megous »

cl3misch wrote: post #40
userbinator wrote: post #12

Currently remaining battery %'s aren't exact because I'm assuming there is a linear coorelation between voltage and capacity (Which is wrong). I don't plan on fixing this, as the exact % is unimportant to me. There are dedicated ICs which will give the remaining charge accurately, which may possibly be even cheaper than this ad-hoc solution.

Could you measure a calibration discharge curve with a (digital) bench power supply draining constant current (or constant power) and use it as a LUT?

Not as simple. Voltage also changes with load and temperature for multiple reasons. You'd also need to account for that.

Re: Open Source Thinkpad T420 Battery Design

#48

Post by Waterfall »

userbinator wrote: post #27
zelly wrote: post #24

It really speaks to how badly innovation has slowed in chip design that a 10+ year old budget laptop is still comptitive hardware

I wouldn't consider the ThinkPad line "budget" in any way --- that would be the IdeaPads.

You can find them on eBay for cheap. That makes them budget. Nobody cares if they were $9000 last year or a million when they were released. They are commonly found as cheap old business equipment or found in the trash. You can get a thinkpad today for under $600 new and and old ones for under $200. Ideapads have sometimes been more expensive than thinkpad so it's not a good metric.

Re: Open Source Thinkpad T420 Battery Design

#49

Post by knaik94 »

I had a big brother model of the t420, which uses the same battery and can also coreboot, the w520. It's the workstation model with i7 quad and a dedicated quadro graphics card. I understand the audience targeted here uses it mainly for development work.

So hardware video acceleration for newer formats isn't seen as a priority. That is an issue I came across, even with a quad core i7 and quardo, it struggle with h265 4k playback smoothly, and 4k vp9 pushed it a little hard too. 1080p youtube is fine as is x264, no problems there but x265 always gave it a little trouble.

There are many great things about it, but I thought I would mention the one drawback of an older thinkpad with older intel chips, is poor hardware accelerated video playback of newer codecs. If you stream online, it's a non issue mostly.

I had mine for 9 years before it finally died. I think the gpu overheated and burnt out, it gets to the login screen and then freezes. I was pushing it hard in terms of video encoding so part of it was my own fault. I still miss machine and that keyboard and nub.

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