Mega Laptop Battery

[Madscientist267]

You all know me and some of my crazier hair brained schemes.

Well, this one is no exception.

After countless attempts at trying to find the ultimate electron reservoir for my itty-bitty Asus EeePC 900HD, I've finally created one that does the job.

Well, sorta... If I could just get the chip in the "original battery" to at least head toward the concept that there is more capacity than what once was...

One problem (aside from the "holy crap, what is THAT?!" factor) is that there is a known issue with Asus batteries and some serious miscalculation that takes place in the management hardware.

All of that aside, this is one hell of a performer, with a whopping 18 hours of runtime, if I decide to take it down to the 'danger' zone. More on that in a minute...

The completed pack is 200Wh by design.

This is what I did:


I took two extended batteries for HP laptops and removed the cells from each pack. These are 100Wh each, with 9 cells per pack, 3 paralleled sets of 3 in series, for 11.1V nominal.

EDIT - I realize that the filename here says "93Wh"... The actual batteries pictured here in fact ARE 93Wh, but this pic was actually taken AFTER I built the new battery, and the 100Wh shells were long gone. There were two flavors of battery available to me at the time - 93Wh and 100Wh. I of course ran with the 100's. Thats an hour plus of extra run time, dangit! My purpose here is served - they illustrate what the original packs LOOKED like.




This little difference in nominal voltage posed a problem for my application however, as the EeePC uses a 7.4V battery. So what to do with one in hand and coming to this realization? I quickly grabbed a second extended pack; to get 9 sets of 2 in series. Here they are after the wiring was complete. I moved the thermistor from the original Asus battery into roughly the center of the pack to get it "as good as it gets". I didn't have the time, resources, or money to play around with trying to convert over to multiple thermistors. This isn't a big deal, because peak charging current for each set of cells is only about 110mA. The thermistor will only ever kick in if the ambient temp has brought them too high to charge. I'm too anal to let that happen, but just in case. I've seen the youtube videos...




This is a shot of the new battery layout, next to my (now seemingly standard) size comparison tool, a good ol' pack 'o smokes, and one half of the case for the original Asus battery. Big difference.




I had the opportunity to leave the original cells in the original battery, but I decided against it for two reasons. One, they only would have added an hour or so, and two, the wiring would not have "neatly" fit up inside like it does. Everything WAS looking like it would be much neater until I ran up against the itty bitty holes that the thermistor originally was soldered into. Dodging the monkey wrench meant a little rat-nesting, but it didn't turn out that bad I suppose. At least it appears "neat" in the finished product...




This is the front view of the completed battery assembly, as if the screen were facing you. The aluminum plate is actually a set of 3 plates, loosely stacked upon one another. They spread the heat out coming from the bottom of the laptop so as to not "thermally age" certain cells before others. Works very well, actually, better than I ever expected. The velcro's purpose is hopefully, well, obvious.  




Another shot from the left side...




And another from the back. Now you can see what I mean by "neat"... That's pronounced "contained".




Here it is, laptop perched up on top, held on by the velcro strips (which still need adjustment, but do the job adequately for the moment). And apparently, coupled with the Droid, I can post to here from anywhere (I tried to say that you'd get back all you have given me and more, didn't I?) What will you do now? LOL




And now for the power shots. Here is the voltage discharge curve for a calibration attempt I did. The calibration didn't take, but I have a real good understanding of how much juice is left at any given point by referencing this little gem. The X axis is time in minutes, the Y is mV. "Reaching" the end of this graph to see the knee takes a LOT of patience and careful timing. I didn't bother with all that for this particular discharge however; I disabled all the "oh crap" features of power management and let it go until the battery said "Danger Will Robinson! Danger! Danger!" and cut the cord for itself.




The associated current plot for the above graph. It's worthy to note that the spikes (except at the very end) are when I woke it up to grab a sample here and there. The end spike is as the battery voltage dropped, the current went up drastically to keep internal regulation. It's a snowball effect for sure. Wattage plotting is coming, but I need to write the code. I know however from another plotting program (the built-in plotter in Ubuntu) that the "snoozing" draw is about 10W for this particular laptop. And again, X is time in minutes, and Y is mA.




Here is the voltage plot for the charge cycle that followed the complete discharge above. Same axis attributes apply as the discharge voltage plot above.




And the associated current plot.


Both of the charge graphs are "zoomed" slightly - It actually took 36 hours (ish) to completely recover the charge that was used!!! Some of this is paranoia, as I have the current limiting (presently) set to about an amp - I'm not sure exactly how much juice the MOSFETs in the original battery can handle without popping, and I can't afford to find out! The OEM power brick is rated 12V at 3A, so I am pulling slightly less than an amp from it when charging is at it's highest. It still gets very warm if the laptop is doing any "crunching".

One other thing worthy of mention, is that at one point during the development and trials of many different batteries and configurations, I managed to get the polarity going into the laptop backwards not once, but twice, and got smoke from TWO DIFFERENT LOCATIONS, one for each event! How the hell this thing still powered up and ran after all that was beyond me, honestly...  

The ultimate result was that the laptop's internal charging circuit is shot, and therefore won't charge the battery. For this, I modified a buck converter and tinkered with the current limit sense resistors until I got a reasonable balance between charge time and heat. Doesn't work bad, considering.

The other effect is that curiously, the laptop will only turn on if the battery is present. Once powered up, it will continue to run on the power brick if the battery is removed, but plays dead from a cold start. Even reboots are fine... Not sure I'll ever completely understand what is going on there...  

My biggest problem with all of this right now is that the original battery management chip doesn't see the full capacity of it's "new and improved you", which isn't to be expected right away, but according to many things I read online, the chips eventually adapt to the larger battery by taking note of the extra energy required to charge it, as well as the additional capacity during discharge. This one is still LOSING capacity, and I don't understand why, other than a known issue with Asus batteries manufactured in a given window.

The most annoying aspect of this however, is that even though I can tell power management to ignore the "I'm dead" signal coming from the chip, I can't tell BIOS the same thing. The result is that once the chip reports "0.0%", BIOS goes into a lock-down, and there is no recovering from a power cycle, or even a reboot. The machine will flat out refuse to power on until it sees a charge source.

Now, funny thing about that... All I have to do is briefly connect the power brick, hit the power button, and then disconnect the brick. Then it's back to binnis-as-uzhul.

There is a wierd hiccup too that happens at about the point where the chip thinks there is 15% or so remaining. It stops counting down (in power management) and hangs there as if it were trying to calibrate or something and "give it a chance to prove itself" kind of deal. I verified that this is in fact the chip getting "stuck" around the "2.7Wh remaining" mark. The problem with that is, this plateau can last several hours, or only 1 or 2, and I can't predict it. I can cycle the machine as long as the chip is reporting that there is usable capacity, but once it's gone, I could have as much as somewhere between 14 and 16 hours remaining, but CANT USE IT!!! At least until I do the little "brick trick"...

Hmmmph... Oh well, I don't regret this one. It sure can run the laptop all day long and then some, and I don't have to worry about the damn thing going dead regardless of whether I'm surfing the web or watching a movie, or if I'm froggy, BOTH!

TTFN,

Steve

[Bruce S]

Mad;
All I can say is WOW!!
IF you need a few more of those HP laptop batteries to "play" with let me know 
I think I could scare up a few 
Most of the time when I open the up, it seems to be the thermistor that has come loose from dab of silcone they use to hold it in place.
Of course by then the case is toast. I can save about half of the Li-ion batts inside.
You might shoot Comanda a PM she's done tons of stuff with BMS for LiPos.
STILL WOW!!

[Madscientist267]

These are actually brand new, believe it or not.

It's been a passion to make the most of a battery for the laptops for quite a while, and when I dug into this one, I made sure I went all the way and did it right

I probably should mention that although the above discharge curves are during mostly "idle", the battery will perform very well with intermittent use, and I have several other plots that show the ability to hang on for 16 hours, with repeatable accuracy. I even did a drain at a friend's house running games that the system could handle (openArena for example) for 10 hours, and the remaining charge (as checked/compared afterward) showed that 4 hours were left!

This thing is awesome, and can perform under the most significant drain I've seen yet. The only reason for going so far out there is for the same reason that audiophiles use 150W/channel amps and run them at 5W peak output - I wanted to be able to use it, for extended periods, without affecting lifespan. Audiophiles want CLEAN audio. I want it to last. The logic is the same. My typical daily drain is about 30% down from full. That's 8-ish hours, hit and miss with variable draw. I'm pleased to say the least.

My only regret is that I apparently didn't do enough homework on the calibration front.

There are scattered articles here and there about adding to laptop packs, and most of them end in success. One guy used a bunch of used cells and managed to hit something like 150Wh, and even on an Asus, so I figured I would give it a stab.

No such luck with the calibration here though, so I'm looking at a workaround.

Thought of a few things last night, one of which was a charge pump to trick the DC input into getting just enough power to start the machine. Probably would work, but the schematics and datasheets I found were less than appealing.

Leaning now toward a common ground boost converter. All it needs to do is give something inside enough juice to think that it's on a charger. The beauty of that is, I won't "waste" any power by "recycling" it into the battery, since the internal charge circuit is gone. (Wow, when did you ever think you'd see 'waste' and 'recycle' in the same sentence like that? LOL)

I've heard that it's simple to convert a buck to a boost, by just switching a couple components around and changing the feedback resistor network, but never tried such a thing.

Got any ideas?

Steve

[taylorp035]

Could you just fool the computer and use the battery as the power brick input?  12v is 12v in my books.  You may have to go to a 4s configuration.  For power monitoring, you could use a cheap rc power meter... the ones I use for my car only draw 0.4 watts in idle mode... almost nothing at 200 Wh.  You could keep it plugged in over night so you don't loose your Wh count.

I wonder if the Thinkpad power manager would install on your laptop.... it might just record Wh's used (it would read all 200 Wh after it was discharged).


On a little laptop like that, are you really averaging 200/18 = 11 watts?  My thinkpad t-40 used about the same while activity using it.  I have seen 6-8 hours on a 73 Wh battery with a 14" screen on full brightness.


I wonder if a simpler solution would be to keep the laptop unmodified and just have a separate battery to plug into the laptop to recharge it on the go.

[Madscientist267]

I have actually used battery like that to run it, a 9Ah set of NiMH at 12V nominal...

There are pitfalls to going that direction, but it does work. The biggest problem there is that in order for the laptop to be "happy", I have to keep the voltage between 11.0 and 13.0V at the input.

The low end isn't difficult, but on a full charge, the MH's can keep well over 13.0V for an hour or so, and as such, regulation (via a buck converter) is required, which does waste some power.

It's not an impossible situation, but of course for portability, the idea was to only have the Li-Ion's in the mix.

Here's a shot of the 9Ah that I used to use to operate the laptop (before the "big mod")



You can see that this isn't exactly "portable" in terms of "stick it in your pocket and go".

Hence the wish for a small boost converter that can charge a sizeable cap to trick the internals just enough to "jumpstart" the laptop.

Steve

[joestue]

Leaning now toward a common ground boost converter. All it needs to do is give something inside enough juice to think that it's on a charger. The beauty of that is, I won't "waste" any power by "recycling" it into the battery, since the internal charge circuit is gone. (Wow, when did you ever think you'd see 'waste' and 'recycle' in the same sentence like that? LOL)

you won't save any power.

I have to say all the laptops i've taken apart buck the ~19v pwr sup down to say ~13 volts for 3 li ion cells, or ~17 volts for 4 cells.
the battery is charged by a buck dc-dc converter from this bus, which is then bucked down into the 1.1-1.8 volts for the processor, 2.2-2.5 volts for the ram, 3.3 volts and 5 volts.
drawing off battery the highside fet is driven on at 100%, the 1.8, 2.5, 3.3 and 5v buck regulators adjust the duty cycle for the battery.

thus its one less conversion step to run the laptop off the battery, but the difference may only be 3-5%

[Madscientist267]

There's no delusion about saving power...

The whole problem is boosting the "7.4V" up to 12.0V to 'trick' the laptop just long enough to start it when it thinks the battery is dead.

The laptop will not run on the "upped" power - it will only be given this (which draws about 60mA, thanks to the blown charge circuit) for a few seconds while the power button is pressed.

At that point, the 12V can disappear, and life resumes as it would have, while the machine continues to boot and run from the "7.4V" battery.

There is no 19V power supply here. Ever.

The highest voltage seen by ANYTHING is the 12V (which is about 12.28V) from the OEM power brick.

And none of the other voltages mentioned mean squat. They all happen inside the laptop, which I am not concerned about.

Damn, I hate it when people don't READ!

Steve

[artv]

Hi Steve,...I've read through this post a couple times now....95 percent is over my head
"( draws 60ma, thanks to a blown charge circut) , "the 12 volt can dissapear"
Couldn't you just by-pass that circut, so you only need the 7.4  , or maybe by-passing the circut is not such an easy thing to do?
thanks for sharing....artv

[Madscientist267]

Without the charge circuit, the laptop off only draws about 60mA at 12V. Not sure where all of that goes, other than 20mA of it to the "I'm charging" LED (which is the ONLY part of the "charger" that still works).

The rest is probably the standby circuitry, just waiting for someone to hit the power button.

If the DC jack sees 12V on it, there is seemingly a MOSFET somewhere that turns on and allows the unit to power on. Its not completely clear at this point however if the DC jack needs to actually support any load whatsoever in order to allow the machine to power on, or if it is simply a "rite of passage" type thing.

I suppose its easy enough to find out, I just need to do some tests.

What comes to mind is basically a boost converter with some form of current limiting, that charges a reasonable size cap up to 12V and then wait for the user to hit the power button, at which time the cap would discharge, and the battery would take over through the normal connector.

The whole contraption would essentially be a small dongle with a momentary push button on it.

The key is, it needs to be as physically small as possible. I have a few very small buck converters that would probably handle the situation just fine, if the parts are big enough to be able to dig them out and flip them around to change it over to a boost converter. I figure worst case inrush currents will be at most 250mA or so.

That's about as far as I've gotten with it, other than a conceptual testing apparatus, probably comprised of simply a resistor and a cap, connected to the OEM power brick...

EDIT - Also, I apologize for my 'sharp' response earlier - It's been a rough week...

Steve

[joestue]

At that point, the 12V can disappear, and life resumes as it would have, while the machine continues to boot and run from the "7.4V" battery.
"there is no 19 volts"

Then substitute 8-9 volts for the 2 cell battery.

the point is its one less conversion step to run your laptop off the battery, rather than the dc input.

[Madscientist267]

It wouldn't be set up to run from battery into the 12V DC input.

The 12V is only on long enough to trick the machine into "seeing" a charge source, so that it will actually power on.

Since the charge components within the laptop itself are hosed, there is no actual charging taking place.

The whole thing works kinda like a pacifier for a baby.

Once it powers up, there would be no power going to the converter that generates the 12V from the battery; the "starting" button gets released, and the boost converter goes dead.

Make sense?

We're talking a couple hundred mA (absolute worst case) for a few seconds out of the battery, not running the laptop from the boost-derived "12V".

I am almost certain that I can't just connect the positive connection from the battery to the input jack via a momentary switch as a resolution to this issue... The laptop will just ignore it's presence. It "politely" disconnects itself from a source that is either below 11.0V or above 13.0V, hence the need for a booster.

One thing I forgot to mention in all of this is, the charger is now "external", and connects via an old P4 motherboard connector dangling off of wires that run inside the case and that are soldered to the board.

The "jump start" device would plug into this, and held on to the laptop by a small strip of velcro. Hence the need for a physically small and lightweight device.

The 4 pins on this connector are like so, with their soldered-to locations on the MoBo in parenthesis:

Pin 1: +12V (At the OEM power jack + pin), normally supplies power to the external charger
Pin 2: +7.4V (At the battery connector), normally returns the charging current to the battery
Pins 3 & 4: Ground (Tied together and then run to the OEM power jack; there are only 3 wires entering the laptop.)

Steve

[Madscientist267]

Minor update...

Waiting to try out my booster theory; the battery has to drain to the point that the chip gets out of "wait and see" mode.

Once that happens, I'll try my little resistor and cap thing to see if it's going to be enough to start it.

Looks like that "deep" discharge during the calibration attempt has *something's* attention inside there anyway... I'm on day 3 of casual usage, and it's still going... LOL

More as it comes...

Steve

[Madscientist267]

Well, what I would call a pseudo-success has occurred.

Although I'm not exactly dealing with the problem as I had intended. For now...  

For completeness, I tried several different methods to bring the thing online. They are:

1 - Just jumping straight from the 7.4V rail to the 12V rail. Nobody really expected that to work, honestly.

2 - 12V through a resistor by itself. Tried a few different values, and there were mixed results with this, but in the end it was deemed unstable. At one point I even had to disconnect and reconnect the main battery to restore "normal" function. It got stuck in some quasi-powered-on state and refused to budge from it. No go.

3 - 12V through a resistor, stabilized by a cap. This was better, and given a big enough cap, probably would have worked. Key word, big. Like >10k uF

4 - 12V directly. Well, duh.

5 - With #4 in mind, and losing patience with my inability to just 'crap out' a suitable boost converter, I cheated and went with what ultimately worked.

A set of two "9V" NiMH batteries in series, momentary pushbutton, going through a 7812, and into the main DC jack. I did a couple of tricks with 3 diodes to allow charging without irritating the 7812, like ground lifting and such to isolate it from "reverse" polarity (I'll explain that when I put the schematic up). Long story short, it works.

Press the red button, press the laptop's power button while holding the red button, see green LED on laptop, let red button go.

And everybody's happy.

Now I can use the rest of the battery's power even when it says "I don't think so, scooter".

I'll put pics up tomorrow, the goo that will hold everything in place in the little box I put everything in is curing at the moment.

Steve

[ghurd]

I'll put pics up tomorrow, the goo that will hold everything in place in the little box I put everything in is curing at the moment.

Hot glue.  Gets un-gooey a lot faster!
G-

[Madscientist267]

LMFAO

As soon as I put that in there, I *KNEW* you were going to bring that to my attention hahaha

Here are the pics...


The innards. Not really much to see. And what IS there is covered up by goop.




The finished product.




Mounted to the back of the laptop.




The schematic. Dead simple. The diode arrangement keeps current from flowing "backwards" through the 7812 while allowing charging to take place through the same connector that goes into the laptop.

The drawback to this whole thing is that I can't charge the jumper with the laptop's power brick, although I have an idea of how to do this in the future, by combining the jumper into the laptop's external charger box. It would involve a series/parallel switch to put the charging voltage within a range that the laptop's brick can push current through.

As it sits, it appears that the NiMH version of the Radio Shack 9V rechargeables has been redesigned from what it was back in the day. From what I can tell, there are now 7 cells inside, rather than only 6 as in the NiCD version of old. The result is that the set's total voltage is between roughly 19 and 20V at full charge, so I have to use yet another box to charge them.

No big deal since they don't need it all that often.

Steve