Can a T40 take 20v in?

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Pyroraptor · #1 Post by **Pyroraptor** » Fri Dec 21, 2007 6:06 pm

Hi all,
I just got a super-neato USB GPS receiver, and it works awesomely on my T40. The family and I are driving up to Virginia on the 24th to spent Christmas with my grandparents, and I figured I should take my T40 and GPS along, just for kicks. However, the battery will not last 4 hours, so I figured I should get an inverter.

Before I spend $60 buying an unnecessary DC - AC one, I figured I should look around and see what I can do for DC - DC instead. I found the auto/air adapter my dad used with his dell latitude, and it does 20v out. I figured that's close enough to the thinkpad's 16v that the thinkpad would probably drop it to 16 and be happy, but before I do anything drastic I thought I should ask.

If it can't take 20v, I'll just get some zener diodes and drop it "manually".

Thanks & Happy Holidays,
John

aaa · #2 Post by **aaa** » Fri Dec 21, 2007 6:35 pm

I doubt it would work. The plugs are different so you'd have to do some mangling at the least.

Inverters cost $15 you know. That's the reason I go the DC-AC route, a DC-DC adapter is usually the one that costs $60.

Pyroraptor · #3 Post by **Pyroraptor** » Fri Dec 21, 2007 6:41 pm

Plugs not working: Not a problem, making a new cable takes about 30 seconds considering how many parts I have

Price: Again, not a problem, seeing as I already have a DC-DC adapter that uses modular cables.

#4 Post by **Harryc** » Fri Dec 21, 2007 7:15 pm

You're going to have a hard time finding 1.) someone who is familiar with the T40's charging and power circuitry (since schematics don't exist outside of Lenovo labs) and 2.) someone who's been foolish enough to try shoving 20v down a 16v pipe to power a T4x specifically to answer your question correctly. I say it's a risk and not worth it. Ray Kawakami might know about this circuit enough to answer correctly, I'll defer to him.

Pyroraptor · #5 Post by **Pyroraptor** » Fri Dec 21, 2007 7:35 pm

I just found this, interesting:

http://forum.thinkpads.com/viewtopic.ph ... 902#198902

Saying all that and knowing exactly what I'm talking about - having 20V instead of 16V wont do ANY damage to T4x series.

Nothing will "fry" inside due to few volts more - voltage coming out of 20V AC adapter fluctuates from 18 to 22 volts (depending of the mains voltage and the load). Voltage regulators are in the laptop itself, running in switching mode (to reduce heat) and they should tolerate (at least) up to 28VDC (standard spec) on the jack.

In terms of warranty - unless you connect something like 50VDC and explode input capacitors there's no way for anyone to say for sure what killed switching circuitry. In fact, those mosfets can be replaced on desktop pc motherboards without major drama.

Which is what I figured from the beginning, these inverters are not smart enough to do voltage regulating, esp. the inverters made to work with a huge range of laptops. A friend of mine has a DC-DC one that outputs anything from 10-24v, it's up to the laptop to regulate that.

#6 Post by **Harryc** » Fri Dec 21, 2007 7:53 pm

Well then, if Mirage from South Africa is the expert that you want to rely on to determine the fate of your T40, then go for it. Good luck.

Pyroraptor · #7 Post by **Pyroraptor** » Fri Dec 21, 2007 7:54 pm

How does him being from South Africa make any difference?

#8 Post by **Harryc** » Fri Dec 21, 2007 7:55 pm

It doesn't. You were quoting Mirage to be the expert, and you seem to agree with him. Are you looking for someone to collaborate with that opinion?

#9 Post by **rkawakami** » Fri Dec 21, 2007 8:03 pm

Pyroraptor wrote:A friend of mine has a DC-DC one that outputs anything from 10-24v, it's up to the laptop to regulate that.

If you can, please post a manufacturer and model number on that adapter. All of the DC-DC and AC-DC adapters that I'm aware of that can provide a wide range of output voltages on just two pins, usually need some sort of manual switch or plug to adjust the voltage.

Pyroraptor · #10 Post by **Pyroraptor** » Fri Dec 21, 2007 8:05 pm

I did not "quote him to be the expert". I just found an interesting bit of info that I happened to agree with, so I put it in a post. I've yet to find a post on this forum saying "I connected a 20v power supply to my thinkpad and it exploded" or anything like that. Plus, (to me anyways) it makes sense that IBM would have used a voltage regulator that can handle higher voltages, since not every non-IBM power supply is going to be exactly 16v, and not all 16v power supplies will deliver exactly 16v all the time.

Pyroraptor · #11 Post by **Pyroraptor** » Fri Dec 21, 2007 8:07 pm

rkawakami wrote:
Pyroraptor wrote:A friend of mine has a DC-DC one that outputs anything from 10-24v, it's up to the laptop to regulate that.
If you can, please post a manufacturer and model number on that adapter. All of the DC-DC and AC-DC adapters that I'm aware of that can provide a wide range of output voltages on just two pins, usually need some sort of manual switch or plug to adjust the voltage.

I'll ask him next time I see him.

#12 Post by **Harryc** » Fri Dec 21, 2007 8:08 pm

Pyroraptor wrote:.. I've yet to find a post on this forum saying "I connected a 20v power supply to my thinkpad and it exploded" or anything like that.

And why do you suppose that is? The point is that you won't find it because nobody has done it.

#13 Post by **bill bolton** » Fri Dec 21, 2007 9:52 pm

Pyroraptor wrote:Can a T40 take 20v in?

DEFINITELY NOT!

All the power supplies that IBM/Lenovo have supplied for a long time are switchmode types which produce highly regulated output voltages. The overall constraints on thermal management inside a laptop package mitigate against providing for uncessary levels of over voltage protection.

As far as I am aware, you might get away with 10% over voltage on the input but certainly not 25% over voltage.

I do occasionally see ThinkPads that have blown fuses on the planar from time to time in our field fleet of ThinkPads. None of the users will ever admit to over-volting them, but usually there are some sheepish looks when asked power source they were running them off at the time of failure.

Cheers,

Bill B. (IEEE)

Pyroraptor · #14 Post by **Pyroraptor** » Fri Dec 21, 2007 10:14 pm

Interesting. I guess I'll have to bust out my parts box and get some diodes.

Pyroraptor · #15 Post by **Pyroraptor** » Sat Dec 22, 2007 11:07 am

Well, rest assured fellow thinkpad lovers. I have decided not to be foolish and modify this adapter to work with my T40. Instead I went down to our local radio shack to look at what they had in the way of inverters. Oddly, they had none.

However, they did have quite a great little gem; a 12volt to 15-24v @70W(selectable voltage) adapter, with a tip that fits my T40! It was $35, but that's fine with me really, a new logic board would cost at least twice that. Plus I can use it with a lot of my other devices.

On our way home I busted out the GPS and we cruised around a bit MS Streets and Trips 2008 is quite a program; here's a screenshot:

http://i19.tinypic.com/86imcur.png

And it had power the whole way

ricerocket · #16 Post by **ricerocket** » Sun Dec 23, 2007 6:48 am

bill bolton wrote:I do occasionally see ThinkPads that have blown fuses on the planar from time to time in our field fleet of ThinkPads. None of the users will ever admit to over-volting them, but usually there are some sheepish looks when asked power source they were running them off at the time of failure.

Cheers,

Bill B. (IEEE)

Shouldn't overvoltage decrease the thermal load on a fuse? P=VI, and if P stays constant, and V goes up...

Can a T40 take 20v in?

Can a T40 take 20v in?

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