extra external battery for my t43

[eigh]

ok so ive got a crazy scheme to build an external battery for my t43.

i plan to buy one of these 12 batteries, maybe 7AH maybe 5AH:
http://www.allelectronics.com/cgi-bin/c ... type=store


i will have it plug into the power line from the ac cord (ill have to get a barrell connector).

than to charge it up, ill just hook it up the charger for my notebook.




how crazy does it sound?

[jeffcrilly]

I use external batteries all the time with my thinkpad. (Currently a T22 but I'll be doing the same with the T42, and I've done this with other laptops.)

Here's some info on the subject. NOTE: THE FOLLOWING IS WITHOUT WARRANTY OF ANY KIND. PROCEED AT YOUR OWN RISK.

If you try to do ....

12 V battery -> thinkpad

That will not work. Here's what you need....

12 V battery -> 12 V Auto/air adapter -> thinkpad

With my T22 I have another adapter - looks like the AC adapter, but takes 12V DC. Mine is from ibm; lenovo's probably got them, and they are available from third parties, e.g. iGO. My understanding is that the latest thinkpad adapters have AC _and_ DC input. (I'm still waiting for my T42 - stuck in customs - so I havent seen all the details yet.)

Anyhow, the 12V side of the adapter is like the plug for the car - e.g. a cigarette lighter plug. So, you'll need to put a female one (i.e. looks like the hole for cigarette lighter in your car) on the battery. These can be had a radio shack for cheap -- or the place you found the battery...
http://www.allelectronics.com/cgi-bin/c ... type=store

Just cutoff the male part and hook to the battery. Make sure you get positive and negative correctly wired. Also I suggest you include a fuse in line.

Charging w/ the TP power adapter isnt going to work. Afaik, they are all like 16V. You need a regular 12v trickle charger. Personally, I use a Schumacher computer controlled charger; its about $50.

An alternative is to go to walmart/costco and get a small "power tank". These have a 12V battery, light, female 12v outlet, fuse, and charger all built in. (The walmart unit is not available online -- here's an example of what I'm talking about.... http://www.astromart.com/articles/artic ... icle_id=87 Radio Shack, , batteries plus, etc, all have something similar.)

Also, be wary of these small batteries. When the voltage falls _below_ the minimum rating on the DC adapter, the DC adapter will try to draw more current and blow itself up. I fried two DC adapters this way - by using small 7AH batteries w/ the thinkpad. The DC adapter is designed to run off a car battery - probably with the car running - i.e. clean regulated DC at 13.8. Most lead acid's, etc. put out 12v at most. The latest DC adapter I have does not seem to have this problem.

Finally, when in the field I use Optima spiral cell 65ah batteries. They are heavy, but last many years, and many recharges. I've been using one for about 7 years now, and it still goes strong. Depending on what I'm doing, I can go between 12 hours (when the computer is busy all the time) to about 48 hours on a single charge. These are about $170.. and you'd want the "yellow top" model if you went that way.

Oh.. one more thing.. when you run your thinkpad on the external DC supply, the TP is going to think its on AC. To conserve your external battery, set the power management for the _AC_ setting to "maximize battery", else you wont get much time out of that battery. (Been there, done that.)

All that said - I take no responsibility for how you go about hooking this up. The above directions are merely my opinion on the matter and are without any warranty of any kind. PROCEED AT YOUR OWN RISK.

jeff

[eigh]

wow jeff that post was awesome. one question though, why do you need that adapter between the battery and the thinkpad? is it because the external battery wont be able to supply a steady voltage or current after a while? or is it because the 12volts is not enough?

[jeffcrilly]

is it because the external battery wont be able to supply a steady voltage or current after a while? or is it because the 12volts is not enough?

12 Volts is not enough.

Take a look at your AC power adapter. Mine (a 72w for a T22) sez...

Input: 100-240V
Output: 16V DC

So, the thinkpad wants 16V _in_. (Most laptops after about 1998 were 16v or 18v in. Back in '96 I think there were some dells that took 12v in.)

So the DC adapter is needed. This just takes the 12v and through the magic of analog electronics turns it into 16V. (Its mostly about V=IR, i.e. ohm's law).

It turns out the DC adapter's _input_ rating is something like 11.5v to 18v. So it will handle a battery that is decreasing in voltage over time. Typically, the CAR battery puts out 13.8V when the car is running. My optimas usually start out at about 12.7 volts, and after a day or so I'm down to 12.1. Then I recharge.

I've never tried putting 12v into a laptop that wants 16v. Probably not a good idea. Something is not going to work.

Here's the power adapter from the lenovo site...
http://www-131.ibm.com/webapp/wcs/store ... d=10000001

[eigh]

i posted this idea in another forum and then was told that the only reason why the laptop charger supplies 16 volts is because it needs more than 12 volts to finish off charging the battery. my battery says 10.8v 4.8Ah. while on battery it runs off of almost 11 volts just fine. im still not an expert but i would see no reason why i couldnt try pumping only 12volts from the external pack.


HOWEVER, since you have done this before, i will listen to you.

(however i wont be trying this anytime soon since i have mid terms coming up)


edit: and the main reason i was hoping to do this is because it would be cheap. the more and more i look at what you did, the more im thinking it wont be.