Hi,
I've got a ~200W laptop brick on which I'd like to tweek the output voltage (~5% -- 19.5V down to 18.5V). Anyone know what sort of margins they design into these? I'm not keen on risking the laptop for the sake of a $10 power supply... (i.e., "it
*should* work" is not an acceptable reply :> )Thx,
--don
I use laptop power supplies for all kinds of stuff. Just change the sense resistor value. Changing 5% shouldn't be a problem. But the answer to your concern is in the risk/reward ratio. If you can get the right one for $10 and your laptop is worth much more than $10, it's a no-brainer.
You might get better help if you listed more detail on what/why you're doing it? At that power level, there might be negotiation between the laptop and the brick. I've seen some power supply interface designs that I'd classify as stupid.
My experience with sourcing custom OEM power supplies is that they're like everybody else...half of them are below average. And average ain't nearly good enough. So asking them ain't gonna be helpful either.
That was my plan -- but, I'm concerned with the downside risk (derating plus any "smarts" in the power supply that might be "confused" because they are unaware of this change)
Not my laptop. These are laptops that were donated (without power supplies... sheesh!), will be "refurbished" and "gifted" to disadvantaged kids. (I.e., the sorts of folks who can least afford to bear the consequences for a bad decision on my part!)
I can get my hands on a supply of these larger 200W supplies (virtually) "free" but am hesitant to *use* them "as is" (not knowing how tolerant the laptop is of variations in input voltage *above* spec). So, it's basically just my (donated) time to make the changes.
OTOH, if I have to purchase power supplies (even "used"), they're in the $20+ range, each. (assuming I can find a single source at that price!)
See above.
Exactly. And, I'm sure any "smarts" therein won't take into account an *observation* of any component changes that have been made "post production" :<
I know some of these power supplies refuse to work on "competitor's" products (despite having the same V+I characteristics)
This is one reason why I want to avoid the "off brand" replacement products. So, I'm stuck with either "name brand"
*new*... or *used*.
Hi Don, some years ago I tried this on a small 15V (IIRC) adaptor. It was somewhat smaller, not an ordinary laptop one but I got it because it stated its output was settable. It was not so I opened it hoping to find the feedback divider and change it (it was a cheap DX box). Turned out the designer had been pretty good and had done things not that obvious without having the circuit. The feedback was somewhat hard to modify, a "zener" (TL431) serially feeding current into the feedback optocoupler - and there was more to it than that which would have taken hours to understand so I just abandoned the idea (got another brick). I suppose there are many different designs out there and most of them likely (the one I abandoned unchanged included) allow a small change like the one you need but I think your only reasonable option is to open the thing and see for yourself. May be you'll know what to do within a few minutes, may be you'll give it up as impractical. Opening may not necessarily be easy; recently I had to cut the plastic of my laptops brick in order to open it to fix the outgoing cable....
Dimiter
------------------------------------------------------ Dimiter Popoff, TGI
------------------------------------------------------
Hi Dimiter,
Happy New Year!
The adapter is rather large -- probably 20+ cu in. Hopefully, not as cramped as some of the tinier beasts out there.
And, as it's so large (power), I suspect (?) it may be a bit better designed than the "500mA disposables".
My main concern is no knowledge of the information that is exchanged (one way? two way? *interactive*??) between the adapter and the laptop.
I.e., at the very least, the laptop will know that this is a "native" adapter (same manufacturer) vs. a "foreign" one. Will it know which
*model* adapter? Will it only be willing to operate with *known* models (BIOS update)?Will it *command* the adapter to "switch to normal output voltage" (perhaps it is initially in a low voltage mode that enables the two devices to converse without putting either in jeopardy)? Will it query the adapter dynamically to determine current operating conditions?
If there are smarts in the adapter, will it notice that Vout is not what it *should* be? Will it try to compensate? etc.
(once you open the door for smarts *in* the power supply, it no longer is a "trivial component")
I'm not keen on discovering these issues via "smoke signals"! (they aren't my laptops to "destroy")
--don
I have not seen that many laptops but those I have seen don't have such a thing, just a plain two wire connection. These I have opened have been far from suggesting the cable could be carrying anything else but power. I'd be very surprised to see such a thing.
Again, I have not seen this done but then I am far from having seen them all... If you dedicate a day's work on opening the laptop and investigating (oops, just opening might take you a day... I remember opening one for cleaning the air path 1-2 years ago, took me hours). I have bought 3-4 type of different "laptop chargers" from DX (to use on anything but laptops, that is) and none of them had any indications of such a thing (and I have opened... let me see, I think 4 if not 5 types, one really old, all models would be older than say 3 years, may be more).
Dimiter
------------------------------------------------------ Dimiter Popoff, TGI
------------------------------------------------------
These have a third connector that carries *some* sort of a signal. E.g., if I take a power supply from HP and try to plug it into a Dell laptop (same Vout, Imax, connector dimensions) the Dell laptop will complain. Most typically, it will refuse to charge the battery (or, will not charge it completely, etc.)
The two conductor power supplies are admittedly dumb. Easy to repurpose a power adapter from vendor A for vendor B's equipment (as long as V & I are compatible and you can get an appropriate connector on the end).
I've done this many times in the past. E.g., one of our TV's is powered by a laptop power supply (because the original power supply died).
Have a look at:
Oh so some have started to put some I2C eeprom or whatever to make people buy exactly their charger. The laptops I have been buying are Acer, no such thing. Why should I be surprised really. I think I have seen a Sony which did not have that sort of thing either but I am not so sure about that. If you have one of these laptops with "encrypted" power I don't think you have many options but to pay them up (likely around $100 rather than $10...).
One more thing to watch for when buying, one could easily overlook it I guess.
Dimiter
If ~188W output is acceptable at 18.5V tweaking the voltage should be possible with no ill effects. (in other words same maximum DC output current)
Typically switchers use a slosed loop matching a (resistive) voltage divider off the output against a fixed reference, you just need to find the divider and tweak the ratio.
measure it and test it on a dummy load before connecting the laptop.
-- For a good time: install ntp --- news://freenews.netfront.net/ - complaints: news@netfront.net ---
I would be surprised if the laptop cared; most are probably good from
16-25V. Inspecting a few laptop motherboards, it looks like there's a "HV / bulk" supply from which all the others are derived; some battery management circuitry selects the battery or charger (the adapter of course being higher in voltage so a sync buck and battery controller handle the actual charging). 14.4V batteries are common (four cells in series, plus however many in parallel), and so are 18-19V chargers.Of course, if "probably" isn't good enough, trimming resistors will be in your future. :)
Assuming it's a flyback supply, the lower limit will be due to UVLO on the probably UC3842 controller, supplied by the aux (line side) winding. Once you crack it open, you could probe the controller or the little electrolytic in there to see what it runs at, and from there, figure it can go as low as the turnoff limit. Any lower and it'll always bob on and off, which is obviously bad. But that's probably 30% lower than you need.
Tim
-- Seven Transistor Labs Electrical Engineering Consultation Website: http://seventransistorlabs.com "Don Y" wrote in message news:lai821$ci$1@speranza.aioe.org... > Hi, > > I've got a ~200W laptop brick on which I'd like to tweek the > output voltage (~5% -- 19.5V down to 18.5V). Anyone know what > sort of margins they design into these? I'm not keen on risking > the laptop for the sake of a $10 power supply... (i.e., "it > *should* work" is not an acceptable reply :> ) > > Thx, > --don
I would expect to see something like that, too. At least this is how I did it on the nukeman (design 1993,
Anyway, Don's issue is with the "smart" part of the adaptor, which has little to do with voltages.
Dimiter
------------------------------------------------------ Dimiter Popoff, TGI
------------------------------------------------------
That's the case for the example I *showed* you. But, I2C can easily allow more than "identification" to reside in the power supply! You could just as easily put an MCU in there that monitors voltages, gates the output on/off, etc.
I.e., the power supply can now become an *integrated* part of the laptop instead of just some "external voltage source".
In my case, the concern is whether a *different* power supply (by the same manufacturer as the "ideal" power supply) would "behave" when connected to the laptop.
The laptop could decide not to recognize the power supply ("wrong ID"). Or, some feature may become unavailable (e.g., battery charging seems to be the most common one). Or, something even more nefarious (e.g., if the power supply is "actively smart")
Yup. I've seen "universal power supplies" with assortments of interchangeable "connectors" (and adjustable Vout). Even those including these "three pin" connectors. But, if they don't know how to identify themselves as the appropriate *actual* power supply, then what good are they?
That would depend on the actual topology used. For a trivial example, imagine a *linear* where the change would result in an extra ~10W going up as heat at that same output current.
Measure *what*? Vout is a no brainer. But, how do I know something inside the supply isn't operating closer to its limits?
Remember, this is consumer kit. Everything seems to pride itself on how close to the edge it can be designed *and* how few days beyond warranty it can survive!
The same mentality that saves fractional cents on caps is at play, here.
I'm concerned about the entire "subsystem" -- as the power supplies are obviously moving beyond "dumb voltage sources" to more of an "integrated system". When you start integrating things, you tend to use them (and design them) in ways that leverage other aspects of the system to improve their performance, decrease their cost or provide added functionality.
It seems like there is little value to encoding *just* an "ID" in a power supply. AFAICT, you can't make your initial purchase (of the laptop) without getting a power supply in the deal. So, the ID only protects sales of *replacement* power supplies.
[It also could give some liability protection if third party power supplies are resulting in battery fires, etc. "Due diligence"]Is there a big problem with folks *losing* their power supplies? Or, are there plans to artificially grow the power supply market with a move to even crappier designs/reliability??
It looks like the safer approach, for me, is to find a deal on the "Right" power supplies (buying them by the dozen can help). Or, convince a donor to foot the bill for them...
(though it would be an interesting question to have answered!)
Den onsdag den 8. januar 2014 21.30.54 UTC+1 skrev Don Y:
most laptop chargers have a similar barrel connector, only the voltage and power varies all the smarts are in the laptop
and you can get universal car adaptors that just a buck/boost to set the right voltage and a set of connectors
There's an effort to standardize laptop chargers, similar I guess to how EU mandated that cell phones must be able to charge from USB
-Lasse
If the idiotic little ID chips are doing nothing but ID, then wouldn't it be easier to modify the BIOS code on the laptop so that it doesn't care about the ID code? The BIOS is flashable, right?
That's not the case with these. *Three* conductors. The third of which carries "data" from (to?) the charger. At the very least, the laptop can say, "This is not an approved (i.e., sold by me) power adaptor. I refuse to ___________"
As seen in the URL I posted (elsewhere) for Dimiter, at least one such adapter has a ROM inside that the laptop queries. Presumably, if the ROM is absent or contains "funky" data, the laptop could opt not to perform (or, perform incorrectly).
It's unclear if other power supplies (including the ones in question) do anything *active* with the comm link (e.g., transfer information about the temperature of the power supply, load current, etc.). Or, if the laptop *commands* the power supply ("enable charging mode") during operation.
Different beast.
The fact that vendors (at least IBM, Dell and HP, from my experience) are adding this "feature" to their power adaptors suggests they want to hold onto the power adapter business (?). Note you don't see much effort to standardize ink jet cartridges :> Nor do I imagine any printer vendors will be quick to embrace such an idea!
About the only good reason I can think of to have the power supply "talk" to the laptop is to allow different battery charge rates for different sized chargers, therefore allowing the manufacturer to sell either a big "home" charger or a small "road" charger and have the laptop charge as fast as possible with either one.
I can imagine a power supply "telling" the laptop that it (the power supply) is running hot and, thus, should reduce its load (esp given that the laptop has control over a *big* piece of its load -- the charger!).
I can also imagine a power supply telling the laptop how much power it is *actually* using (adding those monitoring components *outside* the physical constraints of the laptop itself) so the laptop can better calibrate its battery monitoring algorithms (instead of just watching Vbat without any real idea as to how quickly it
*should* be falling -- when operating on battery).And, the mere presence of a third conductor could be exploited to
*move* the charger into the power adapter using the third conductor to deliver "charge current" separate from "operating power" for the laptop. Even potentially multiplexing (TDM) data onto that conductor!As I said, once you open the door to smarts in the power supply, you can come up with lots of more interesting designs with increased levels of integration across the "power cord" boundary!
[But, other than the URL I posted suggesting "ID" information, I have no idea how power supplies currently use the conductor]ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.