Thinkpads Forum

Does a T61 require that a battery -- good, bad, dead, or otherwise -- be physically attached before it will power up at all, or if I have everything EXCEPT a battery, can I run it entirely off of AC until the battery arrives?

The T61 will run without any battery installed. However, if the battery is defective...it may not start if that battery is installed.

Yes, that's true.

Also, if you run without a battery, and use a 65W power supply, your CPU will be locked to minimum speed. Weird Lenovo feature. With a 90W power supply, there will be no limitation.

Speaking of odd power things...

Does anyone have any idea why a computer (T61p) that uses a 10.6V battery pack, with a nominal need for 12.x volts to recharge that, also requires an 18 volt power supply brick??

Every once in a while I ask but no one seems to know. It would be very convenient if these laptops could run directly off 12V power supplies, and in theory that's all they need. But the bricks are all~18 volts.

??

AFAIK they switched to 20V (not 18V) power bricks, because these are more energy-efficient.
Here is some more food for thought:
http://forum.thinkpads.com/viewtopic.ph ... 39&start=0
http://forum.thinkpads.com/viewtopic.ph ... 98&start=0
http://forum.thinkpads.com/viewtopic.ph ... 78&start=0

Actually, running at anything except the "necessary" voltage simply cannot be more efficient. Simple physics. It doesn't matter where the conversion is done, in the brick, in the laptop, etc., but at some point the input voltage has to be matched to what the battery needs, and if the battery is a nominal 12v battery, and you run an 18 or 20 or 16 volt power brick, you still have to do twice the work, with twice the losses, when you REconvert that down to a proper "12ish" volts to charge the battery. And presumably 5 or 12 volts again to run the electronics in the computer. (Which may all be 5VDC now except the screen and drive motors needing 12?)

Which leaves only the question of what needs the higher voltage, or why. No vendor seems willing or able to comment, no users seem to be that intimate with the hardware.

WRT one unanswered question from one of those threads: Pretty much all the LiOn battery packs are series-parallel arrays. they'll run two stacks of three cells each, to get the voltage (roughly 12) from three cells, but doubling the amperage by cross-connecting two stacks. Which makes the packs fit into a slimmer profile (think of two sets of "C" cells side by side, instead of one set of fatter "D" cells) but makes the charging way more complicated, as the charge controller has to monitor the condition of EACH CELL in the pack. Every player in the lithium battery business has different ideas about how to properly charge them, but one thing they agree on is that you get the best life, the most bang for your buck, by never charging the batteries to 100%. Some say 80% max, some say 95% max, but everyone says never fully charge them. Which is part of the reason why a battery stack may be "rated" for 10.x volts, when it consists of 3x4.1 volt batteries (i.e. 12.3 volts).

I think one reason you'd need a higher voltage is so you can charge the battery. One law is heat will flow from a place of high concentration to an area of low concentration. The other law is that it will flow faster when there is a higher difference. Now, heat is energy, electricity is energy. Current will flow faster when there is a higher difference. So, increase the voltage, increase charging current so the battery charges faster.

E = I x R

I think this is the reason you need say, 15 or 16 volts to charge a battery rated for 12 volts. Or else you'd be sitting at 80% charge for a long time.

Not so much. The battery is confusingly shown as "12.39 Volts, design voltage 10.80 Volts"

So if we assume there are three LiOn cells with a nominal 4.1V maximum voltage, they'd still require some 10% more than that for optimum charging. Anything more would just blow 'em up faster. If they are actually being cycled to less than 100% voltage in order to provide better life--which is what all the LiOn makers seem to be doing today--then assuming the 10.8 volts is the maximum they want to reach, ~12V is all they'd need.

No way that 16-20V is needed in any case. More amps charges faster, until things overheat and blow up. More volts, fairly useless unless you plan to blow things up.