Connecting an AC adapter directly to laptop's battery jack

[claudem]

I am currently working on an old Dell Inspiron 8200 which is in good condition except for the laptop's converter (responsible for using the power supplied by the laptop's AC adapter, using it to both charge the battery and to power the computer while the battery is in). This is a known issue with this laptop model that has caused problems to a lot of people once these laptops start getting old.

Aside from the laptop's original AC adapter (with an output of DC20V 4.5A), I also have available a quality AC adapter that happens to have the same output as this laptop's battery, that is, DC15V 4.5A.

I want to bypass the faulty laptop's converter, get the old laptop battery out of the picture, and connect my DC15V 4.5 AC adapter (which as I said provides the same output as a fully charged battery for this laptop) directly to the battery jack inside the laptop.
Basically, this way, the laptop will "think" that a fully charged battery is in. I've tested it with another working battery I borrowed, and the laptop works perfectly fine with the power supplied by a battery inserted in the battery jack.

However, I am not sure to which two out of the six (or seven?) battery jack connectors I need to solder the + and - output wires from the DC15V 4.5A AC adapter (I will not connect the output wires from the adapter directly to the battery jack, but will make it unpluggable, for convenience/safety reasons).
Of course, after doing this, I will make it so that a battery will be impossible to insert into the battery bay. This laptop will be used mainly as a server, so it does not need a battery.

All I need to know is which (two) battery jack wires do I need to connect the DC15V 4.5A adapter output to. Anyone? Thanks.

 

[NYJimbo]

The charging system in the laptop "talks" to the battery. Lacking that handshake you will not be able to power the laptop properly if at all.

 

[claudem]

The charging system in the laptop "talks" to the battery. Lacking that handshake you will not be able to power the laptop properly if at all.

So you are saying there is no way at all of achieving this? How about leaving the battery in the battery bay, so that its presence can "talk" to whatever is listening, while still supplying some power at some point? (bypassing the converter)
It should be at least theoretically possible, perhaps not practical though. Have no idea, have never attempted anything like this before.

 

[NYJimbo]

If you want to play with different scenarios you should at least understand more about "smart" batteries and the SMBus.

Start here, it will give you some useful info:

http://media.blackhat.com/bh-us-11/Miller/BH_US_11_Miller_Battery_Firmware_Public_WP.pdf

 

[Altster]

If you want to play with different scenarios you should at least understand more about "smart" batteries and the SMBus.

Start here, it will give you some useful info:

http://media.blackhat.com/bh-us-11/Miller/BH_US_11_Miller_Battery_Firmware_Public_WP.pdf

Jimbo,

I never thought about this until you brought this to our attention. Some mighty interesting reading there.

Thanks for posting it.

 

[claudem]

THANKS NYJimbo

If you want to play with different scenarios you should at least understand more about "smart" batteries and the SMBus.

Start here, it will give you some useful info:

BH_US_11_Miller_Battery_Firmware_Public_WP.pdf

[I'm only allowed to post URLs to other sites after I have made 15 posts or more.]

Exactly what I was looking for without knowing I was looking for it.
Your pointing me in the right direction is very much appreciated. Now I have some reading to do...

THANKS!!

 

[claudem]

Just finished it....it's *incredible* stuff, seems like science fiction, but it is not.
It's an autonomous computer system within your computer system, and the ramifications/implications of what becomes possible in such contexts go quite deep.
Wish I had the time on my hand and the disposition for a more in-depth study of it, which I have not.
I think one should be afforded the choice to get rid of the smart batteries, to turn off the system circuitry supporting them in the BIOS, and to have the computer feed off traditional accumulators resembling car batteries, and transformers which output is a traditional +/- direct current and nothing else. The layperson is increasingly becoming vulnerable and exposed. Just my opinion.

 

[Rob_NNCC]

When I was in middle school I took my Pentium 1 laptop that had a dead NiCad Battery pack, gut out the battery leaving the control board and connect the leads to a barrel jack. From there I made an adapter to plug into leadacid camcorder battery as well as a car cig jack. This was an older laptop and I did not care too much for it, so I was ok with the risk. Plus, the laptop would reboot when the engine was cranked using the cig adapter.

 

[claudem]

When I was in middle school I took my Pentium 1 laptop that had a dead NiCad Battery pack, gut out the battery leaving the control board and connect the leads to a barrel jack. From there I made an adapter to plug into leadacid camcorder battery as well as a car cig jack. This was an older laptop and I did not care too much for it, so I was ok with the risk. Plus, the laptop would reboot when the engine was cranked using the cig adapter.

I still think all this is feasible, either by gutting out the battery and properly connecting a basic +/- output from a basic non-smart transformer to make the smart battery think it's getting the current from its own cells, OR it might even possible to apply the +/- wires from the basic transformer (supplying the exact voltage and amperage being supplied by a fully charged battery) directly to the computer battery jack with battery fully inserted. Unfortunately, I do not have the necessary know-how for doing this, nor the time or desire needed to acquire it. A tutorial explaining how to do it would be great, but I think it would probably have to be specific to the particular battery/system in question. I've been searching the web and it doesn't appear that anything like that is made available anywhere. So, I guess, I'll have to give up on this one project. Too much work involved if directions on how to do it are not already available...

 

[NYJimbo]

I think the problem is that you have several circuits in the smart battery that need a certain number of conditions to exist before they will talk upstream to the main processor in the battery pack and then tell the charging circuits on the laptop motherboard that we have good battery power.

Even if you keep all of the circuits in the smart battery, but remove the batteries or insert a certain voltage, the lower level circuits will want to see "something" from all the batteries before it gives the all clear and you probably cannot reproduce that easily by just putting in the power from a converter (ac adapter).

Each battery pack is designed for that specific machine and that cluster of cells. Without knowing all the signals, what circuits are involved and what voltages/resistance/whatever is expected by the smart battery circuits, you wont produce the required environment for the battery to be accepted by the laptop for providing power.

Like you said, I am sure it can be done, but how much work is it for each laptop and each battery pack ?