Thinkpads Forum

Hello all,

I had a T42 and acquired 4 or 5 'bricks' of the 16V, 3.5A variety. This was great because I could leave one in my briefcase for travel, one in the living room, one in the den, in addition to my office one. Laptops are made to move and it was nice not having to pull and take the power supply everywhere.

I recently got a T400 which has one of those 20V, 4.5A bricks with a very unique plug. I really dont want to deal with the inconvenience of unplugging this brick every time I go into a different room, so my question is - is there any way I can use my OLD bricks for this laptop?

I've read that the T400 battery is 14.4 V, so the old brick can handle that, and I wont be burning DVDs, powering/charging iPods, or playing graphic games, so I doubt i'll go over the 3.5A limit of the old brick. I dont even care if it charges the battery when I use the old bricks, as long as it powers the machine.

So, is this do-able?? If I can find a plug/adapter (any ideas where?), can I do this with no harm to the laptop?

Thanks for any help...

CHR

I wouldn't. If you need a 4.5A brick at 20V you would need more amperage using a lower voltage (in your case 16V), and since the 16V brick is already rated lower then the 20V brick to start (1A less at its rated voltage) it would most likely fail.

Those 16V 3.3A 56W adapters are too weak even for your T42, which requires 16V 4.5A 72W.
Apart from having a different DC plug, the new T400 requires a 20V adapter, not a 16V unit!
If you want to kill your T400, that's one way to do so...

It won't work. Even if you were to splice in a new plug on the 16 V charger, or make an adapter (I'm not aware of any even remotely legit ones available in retail), there's more to an adapter than just "more volts than the battery". The entire system is designed to run on 20 V, not 16 V. It's not the just battery; for one, the screen backlight is -- I believe -- run off a high voltage from a step-up transformer, and while I'm sure there is some tolerance in voltage input range, the steps up and down for screen and battery have a limited range they can accept.

You probably wouldn't outright kill the T400 -- but might overheat and kill the 16 V bricks, and there is a high chance of T400 being unstable or not booting at all.

cnr wrote:is there any way I can use my OLD bricks for this laptop?

No.

Cheers,

Bill B.

OK, those were my first thoughts and then after reading that the battery was less volts than the bricks I had, I started to think maybe I could use them.

Its just so nice to not have to lug that thing around...

Thanks for the replies

I found this link:
Using 16V powersupplies for new 20 V laptops
Has anyone tried it ?

Guessing:
20V Thinkpad will draw higher amperage from a 16V powersupply to compensate for lower voltage (See: Watts = Voltage*Current) than usual. I wouldn't know how safe this is (If even.) but as long as the power circuitry in your Thinkpad does not draw too much current (Read: Exceeding wattage limit on brick) and neither the powersupply or Thinkpad is operating excessively out of normal regimes (IE: Power circuitry not overheating, you're not doing some intense benchmark.) then in theory it should work.

Wouldn't recommend this until someone has done this for a long while with no ill effects on their Thinkpads. I also believe the power circuitry, if capable of running off a 16V powersupply, will be also under additional load (Guessing, but if the system natively takes a DC in of 20V, then it will have to step up the voltage if capable of it, possibly making the DC-DC components be under more load.)

This is, of course, all educated guessing. Wouldn't try this unless you want to.

Since there is a 60W AC adapter for T6x, T40x (with integrated graphic ?) so I think the wattage is not a problem unless the laptop is on a heavy load + charge battery.
I have a schematic of T60 (including DC-DC converter) and will ask people how safe to use 20% lower voltage to feed it.

Navck wrote:Guessing:
20V Thinkpad will draw higher amperage from a 16V powersupply to compensate for lower voltage

No, a Thinkpad can't do that.

Cheers,

Bill B.

So the DC in circuitry is unable to draw higher current and use the DC-DC transformer to compensate for a voltage drop?

Just wondering, which part of NO don't you understand?

No one has "tested" this yet and just me but I think there has to be some type of DC-DC circuit capable of handling a specific input voltage range (Down to 16V or not.)