Running T23 from an external battery.

[Zaph]

Hello!


I'm working on a project to extend the operational period of my T23 by feeding it power from a 18Ah AGM battery 12Volts.

The powercord is not a problem since the connector is availaible at the local electric supply store, and I'we read the maintanance manual and it should be well within tolerance even with the 14.4V 1.8A transformer recharging the external battery at the same time.

There are however a couple of things that I could use some feedback on.

1) When the external battery hits 11.8V it is considered depleted and in need of recharge, what is the lowest voltage that i can safely run my T23 with all the speedstep options on low power, lcd on the lowest brightness etc.

2) Would it be reasonable to remove the internal battery during the times when i'm operating on the external battery. I guess that charging a battery with a battery is counterproductive.

3) At what voltage level does the T23 deside to start recharging it's internal battery.

4) While charging the external battery to maximum, the voltage rises to somewhere around 14-15 volts, does this pose a problem.
Even thoug the maintanance manual say's this is in tolerance and I'we measured 16volts on the standard IBM power adapter.

5) I'm working on an external switch to connect/disconnect the internal battery, are there any previous work that you know of involving this kind of tinkering. I'm going for 2 copper films separated with an insulating film with wires coming out for the switch in between the contactors of the internal battery and the T23 battery connector. If so could you point above mentioned work so i can learn from it.

6) Any other pointers and thoughts you might have on this kind of setup would be greatly appriciated.

Thank you in advance for any and all ideas you might have on the subject.

--Zaph
(T23/256mb/30Gb - 2647 - 4MG)

[RealBlackStuff]

I'd say you should do your own research!
You probably get paid quite well to do this, whereas this is just a forum of people who like and use Thinkpads.
Any help or info given here is totally out of the goodness of people's hearts, and not meant to create any profits for anybody.

(Mods: if I am out of line here, delete this post).

EDIT: My apologies for the above wrong interpretation of the questions.
I had a golf game first and went to the pub afterwards to celebrate my winning. Must have seen things from a 'nebulous' perspective.

[rkawakami]

@RealBlackStuff: I'm not so sure that the OP is trying to tap the resources here in the forums in order to produce a commercial product or have the R&D cost provided for free. It appears that he is just a user that wants a little more run time from his/her T23.

@Zaph: It sounds like you are trying to plug in an external battery directly into the DC power jack on the back of the system, correct? In other words, the same place you would normally plug in the AC adapter. If so, there are several things to consider. These are mentioned in the order of your original questions:

1) Unknown at what point the laptop would have problems with a significantly lower voltage (your 12V battery) than the nominal 16VDC provided by the IBM AC adapter. This would be a function of the internal power conditioning circuits. You could locate a variable DC power supply and experiment with the input voltage at the DC jack but you assume all of the risk for any damage to the T23. I understand that at least one poster here has slightly overvolted a T21 (I believe) in an attempt to solve a power-on issue.

2) Charging a battery with a battery does seem to be a useless thing to do. However, this would only occur if the main battery has been depleted enough to warrant a recharge (see next point).

3) No specification (as far as I know) exists that says at what the voltage drop from the 10.8V main battery needs to be before the internal charging circuits are active.

4) If you are also attaching a separate power supply to recharge the external battery, what's the point of having the battery? Is this for a UPS (uninterruptable power supply) situation? Or do you just want several more hours of run time without being "plugged in"? Also, since the recharger for the external battery can only provide 1.8A, you may have a problem with it if for some reason the external battery dies (or becomes disconnected).

5) Simply disconnecting one of the battery terminals of the internal battery (and leaving all of the other connections intact) may not work like you think. There is a serial data pin on the battery that is used by the motherboard to communicate with a circuit board inside the battery pack. Cutting off the power and leaving the data connection would tell the motherboard that the battery is defective (it's physically connected but no voltage is coming out!). I'm not sure what would happen in this situation.

As far as I know, there are already commercial battery packs that provide this function. They are generally rated with the same voltage as the AC adapter that they are replacing. Your problem/questions appear to be related to the fact that you know the voltage is going to be different.

[Zaph]

I really don't think anybody is going to profit from the fact that i could play mud's in the park the whole day through GPRS.

But thanks for assuming bad faith.

--Zaph

[Zaph]

Thankyou Ray for your input on the matter.

Yes, the situation is indeed that i plan to attatch a off the shelve AGM battery typically used in UPS devices in order to extend the runtime to such lengths that i don't have to worry about being power depleted in the middle of a game in a park where the nearest power outlet is a half miles hike away. Straight from the battery to the jack in the back of my T23. The main question in fact is that could this be done with a straight connection from the battery to the laptop without these 'cigaret lighter' converters that could be set to provide the 16V. The thing is that these 'warts' are lossy and i would like to squeeze as much of play time as I possibly can out of the battery.

I allso have a mascot brand 'battery eliminator' charger that i plan to include in this system in order to recharge the 18Ah battery from power outlets in cafes and such.

But I thought that i'd do the math beforehand so i would know what kind of runtime i could expect from the battery. Because the ultimate qoal is to be power independent for atleast a day. (around
10 hrs)

The thing is that i havent bought the casing for this thing yet and it would be nice to know the exact size of the components, the 24Ah version of the battery is quite a bit larger than the 18Ah. Not to mention heavier.

I have to look into the battery disconnect switch thing, it might be easier just to leave the internal battery at home and save the weight.

Thanks again for your input. I'll let you guys know if i get it running(or not)

--Zaph

[Zaph]

Additional notes on the subject. I pulled put some electric gear and did some tests. The battery maximiser 'battery informaton' thingie seems to agree on the figures. Still i have a gut feeling that something doesent add up here. Please point out any and all arrors et al. you might think of. Here's what i found out. Please take thease with a grain of salt as i'm a network admin, not a techie.

All values approximates.
1.0A/11.76V/15.5w @ max powersave no cpu load

2.18A /11.46V 20.29W @ max performance heavy cpu load

1.51A/12.29V/18.44W @ ac power connected full battery

0.73A/12.29v/9.68w @ express charging mode hiperformance allmost full battery.

0.64A/12.40w/7.82w @ express charging mode loperformance allmost full battery and settings with max speed step medium cpu load.

For some reason the express charging mode seems to lower the power consumption, i don't know why.

For CPU load I used winrar to unpack some avis, while playing mp3's and watching fullscreen divx movie.



As allways all input and questions are more than welcome.

--Zaph

[Rick the Green]

If you try to feed 12 volts through the dc jack at the back, the T-23 will revert to the internal battery because the threshold voltage is 13.9 volts.

Below 13.9 the tinkpad "think" he's lost power from the ac adapter. So to work properly you need beetween 14 & 16 volts @ 4.2 amps

How do i know that ? by trying it on my t-23 while looking for the right power adapter.

My suggestion would be to use an ac inverter that plug on your external battery and plug in the Laptop ac adapter in it, like you would do if you'd use your laptop in a car.

[tom lightbody]

this is a problem onboard w/ the 16 volt machines.

> ...AC inverter...plus AC adapter...

plenty loss there: better would be a 12-to-16 volt adapter such as IBM's "AC/DC Combo Adapter" p/n 22P9003
eBay ~$30--this is what I use, thanks to Ray for calling them to my attention. But Zaph scorns what he
calls "warts." Another idea--if you can take the performance hit--is to buy a thinkpad model that uses
12 volts to start with. For years, I've run a 760 straight off the ship's battery.

a note of caution: although my thinkpads have never failed on account of improperly massaged input voltage,
a well-known 4-letter Japanese machine blew a horribly expensive little fuse one time: I personally am as a
result quite cautious about feeding in anything but the maker's recommended voltage, and in case of adapters
being needed, only from a maker-supplied adapter.

how about solar panels, or a little windmill? For charging up 12 volters, that's what the boaters use.

[Zaph]

Thanks for all the input guys!

After carefull consideration I'we come to the conclusion that a generic (noname) 12 volt -> 16vold 'cigarette lighter' inverter that i got from a local electric supply store for peanuts will do the trick. Allthough it's rated to only 3 amps, i can't imagine my t23 ever needing that much.

I'we been trying to max out the pover consumption, reading from CD, while unpacking rar's, defragmenting the hard-drive max LCD brightness, speakers on max playing techno, fullscreen mpeg-2 and the best I could manage was a bit over 2 amps consumption. For the life of me I can't seem to figure out why this machine would require the 4+ amps. Enven the AC adapter is rated at 3.36A (FRU P/N 11j8956).

Osciloscope shows that the power is clean DC even at the rated 3amp load so i'm confident that the power is clean enough for the t23. The think that remains to be tested is how much loss i'm getting from the voltage increase. Only way to find that out is by running the t23 from this setup and timing it and making the calculations from there. Literature says that the loss is somewhere in the ballpark of 10%.

Another solution that i'm thinkin about is building a batterypack that is overvolted and then reducing the voltage from 18v -> 16v. While doable, this would require a bit more tinkering. I have a gut feeling that the loss would be less this way around, and i allready got the cigarette lighter multivolt bit.

Another thing that crossed my mind is that if i'm reading this right, the speedstep tech only kicks in when prompted by the OS. Finland has cold winters and i bet the amperage is gratest when the machine is booting up without the speedstep tech engaged. I happen to have a spare 2farad condensator that i got for free a while back. Would this be enough to fill in the gap while the OS is loading in a low (external) battery situation. ie. has anyone measured the 'spike' when the machine is booting up. (I can do this in a week or so when i have access to the electric gear, but if someone knows i'd appriciate ideas on the subject)

Thanks for the 13.9 volt info it was crucial!

As allways, any and all ideas, critique, comments etc. are welcome and appriciated.

--Zaph

[Zaph]

RealBlackStuff No problem. I'we often been in a nebulous state myself and underestand what happened. No harm done, no offence taken. Cheers! and carry on.

--Zaph