Actual experiences mod'ing laptop bricks?

Why not get a couple of power Schottky diodes and put them in series with the DC output, to drop the voltage a bit. You can get the diodes out of an old ATX power supply from a dumpster. The diodes could be bolted to a 1 inch wide piece of aluminium strip as heatsink and spliced inline with the DC cable and covered with heatshrink. It would be somewhat wasteful and would get a bit warm if the laptop ever really draws 200W, but it would avoid cracking open the plastic case of the charger and reverse engineering it. Also there is very little risk of the diodes not behaving as one would expect them to, at least within their ratings.

Chris

I don't know. I spent some time yesterday digging through a barrel of laptop power adapters looking for similar units. I noticed a variety of output voltages (presumably, there is a reason for these decisions and consequences of them! :> ) The most noteworthy was one that listed *two* different output voltages: one for "operation" and one for "charging". So, *something* is telling *that* charger to switch between "operating" mode and "charging" mode. While not conclusive,

of this particular adapter/laptop combination!

I don't think delivering "charge current" is the issue. Rather, I think instrumenting and/or tightly controlling the process is where most of the value added lies (or, will likely lie).

E.g., a "smart" charger (for some definition of "smart") can look to see *how* the battery is accepting charge under various conditions and, presumably, deduce the condition of the battery (not just how much charge it is holding but how close to replacement it is, etc.).

Consider the efforts that laptop makers already make to try to eek a bit more performance out of a given battery pack. Anything they can glean about the battery's performance could enable them to boast of higher nominal run times. Or, downsize the battery for a given runtime. E.g., I suspect it is only a matter of time before these sorts of devices start "learning" their usage patterns: "When MSOffice is running, the user will tend to have longer sessions than when, for example, browsing Facebook."

There's always some "fundamental" level of protection you have to apply to any input -- esp power. (unless you can galvanically isolate the inputs until you know what's connected to them)

I'm opting for inductive coupling in current projects (best fits the application domain). While it doesn't guarantee immunity from these sorts of issues, I think its relative obscurity works in my favor. Certainly enough to offset the risks of exposing "bare conductors" and hoping nothing "crawls in" that way! :>

Well I don't know how much of this they do in laptops nowadays. I did practically all of it still on the first nukeman (20 years ago). Used to measure battery resistance during charge/discharge etc., its change is pretty indicative to its age. Under the score it did not buy me much if anything, once the battery needed replacement I had to replace it - and it is easy to see without all the subtleties. I had (still have) even two charge currents, one could set either of them to a signed value and both could be set to different durations. Thought this might lengthen the battery life; if it did I did not notice it.

And all of this is done in firmware, the hardware part it takes is on the circuit I posted formerly. Well measuring the battery temp is not shown there.

May be but just measuring the battery current & voltage while knowing its internal resistance (and its initial value when the battery was new) is enough to give a precise enough assessment of the % charge (i.e. time before shutdown) you have left (I would consider 10% for that almost good enough, 5% would be quite OK; I don't remember how precise I was doing on the nukeman, it's been a while since, then we did not sell that many units to have a very broad view on that).

This makes good sense for your current project. It will add some complexity but once you get it right it will make your life a lot easier with many related things I guess.

Dimiter

------------------------------------------------------ Dimiter Popoff, TGI

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Dunno. But one thing is for sure -- the trend is towards smarter battery interfaces! The days of resistive trickle charging are long gone...

I think it takes a boatload of "research" before you can come up with definite "wins" and "losses". And, you probably need to have a close relationship with the battery vendor to ensure you have some consistency in the "batteries" that you are provided for these experiments!

I.e., you're either a huge battery consumer *or* a battery manufacturer to be able to get these sorts of data.

I think the incentive, nowadays (with CPUs) is to decide how best to

*consume* that power. The goals being to get the most usable charge from the battery *and* to get the most cycles out of the battery.

In a casual sense, you can consider (actual) instruction cycles as a measure of *effort* (towards a goal). This is related (by some magical formula) to power consumption. Which, in turn, impacts battery life and usable charge.

But, "effort" doesn't correspond to "work done". For example, a burst of a million instruction cycles in a tenth of a second every second (10% duty) is the same effort as those same one million cycles spread out over the entire second (100% duty). But, they may not achieve the same amount of *work* (e.g., if they are waiting on an external event and the event doesn't occur "while they were looking", then they've accomplished nothing).

I think the same sort of things apply to, e.g., electric vehicles; burning power when it won't immediately produce results is just "waste".

Its a klunky approach. Would you design a *product* that way? :(

I think if I was trying to hack together a power supply for my own personal use (as I care little about appearance for something that I can hide under a desktop), it would be OK. But, expecting others to live with this solution may be asking a bit much.

[A neighbor was "upset" because I had to replace the molded power connector on her laptop and it no longer *looked* "brand new" -- despite having shrink wrapped the connection, etc. "Well, I can't mold custom connectors. But, you can BUY one from the laptop manufacturer. Or, an 'off-brand' replacement. Of course, they want *money* for their products; how much is 'pretty' worth to you?"]

"It should work" is all you'll get without posting details.

Is this for the laptop's sake or to re-purpose the brick for other uses? You probably don't need to change the voltage by 1 to make a laptop work. The laptop has a highly variable load and it would have local regulators to avoid needing thick wires from the power brick.

It's time to worry when the power brick voltage is very close to a multiple of 4.2V, the LiPo end of charge voltage.

Oh yes, this is certain - 20 years ago for me for instance. But there still are appliances (e.g. a haircutter machine I use to do my turtle-head hairstyle) which have exactly that, a simple current limited source, likely resistive (turtle-head meaning no hair :-), I opted for it about a year ago when my hair got too greyish and raggy,

).

This is not necessarily the case. Being small we have used just 3 types of batteries on the nukeman - first it was NiCD, then Varta NiMH and eventually a no-name NiMH came into use. I can say the Varta did not change noticeably over a course of 5+ years, don't know about the others. But there was no noticeable difference between the Varta and the noname ones. Whatever such a huge research might buy you will be within a 10% gain - if you are lucky, that is. I would consider betting even at 5% depending on current mood :D . (before betting remember I have played a lot with these settings once I had the setup implemented 20 years ago, here is a recent snapshot of it on my personal nukeman, its battery being dead for years (i.e. ignore the values, just look at the parameter names):

)

Dimiter

------------------------------------------------------ Dimiter Popoff, TGI

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Yes. But those appliances tend not to be concerned with battery performance! E.g., I would never expect such a naive approach in a cell phone, laptop, tablet, etc. -- things where the user is keenly aware of battery life and likely to compare between brands.

I'm still at the stage between "wanting it long and NEEDING it long" :> But, then again, I've been at that stage for almost 20 years, now... :<

But you are just looking at lifetime (or capacity?) in a given set of circumstances (you probably also don't "see" how the devices are used day-to-day, in detail, once they leave your hands?).

My point is that you need to be assured that the units you subject to any rigorous "life testing" have a relatively small variance (in whatever parameters you *ultimately* deem to be responsible for the characteristics you seek) in production. I.e., if each unit from the manufacturer has wide variations between them, its really hard to determine if the effects you observe (from different charging and usage strategies) are attributable to the effect or to some variation in the "supply".

I think 10% would be something that manufacturers (of battery powered devices) would *jump* at! E.g., in electric vehicles, the battery often comprises half the cost/weight of the vehicle. In a laptop, weight is important -- as is runtime (these are the same folks who will pinch pennies in a design so if they could save 25c in battery selection, they'll jump at the chance!)

Personally, I loathe battery powered products -- because the battery always ends up dead when the device is needed. :< It took a fair bit of work to find electric devices that didn't require batteries when I put together our bug-out bags!

When batteries were nice, standardized, available-from-corner-store products, this wasn't a problem -- just an inconvenience. Now, too many are "specials" and/or not designed to be replaced. Or, the products aren't designed to be cosmetically disassembled (e.g., just replaced the battery in a cordless mouse. Having removed the labels that covered all the access screws, I now have "openings" in the bottom of the mouse that I'll have to cover with opaque tape as the labels fall apart during removal)

If I was giving the thing to other people then I would be more concerned with invalidating the safety approvals of the mains voltage part by cracking open the welded-shut case and messing with it and duct-taping or supergluing it back together, than with the appearance of a lump on the DC cable.