Thinkpads Forum

The T60 needs 20V DC input voltage but what would be the maximum power supply voltage? I'm asking because I have a spare 12V to 24V up converter lying around which could be put to good use. Does anybody know or point me in right direction? Thanks - Jos

Welcome to the forum.

Get a proper 12VDC-20VDC adapter.

Thank you very much for your most welcoming message. It struck me that nowhere the maximum input supply voltage could be found. An electronics engineer would be interested to know. I'll probably do a test with my lab power supply but I thought a friendly soul on this forum knew already. - J

Most laptops I've seen have a single voltage rating, with no listed tolerance. My gut feeling says that the system could probably stand + or - 10% (i.e., in the case of the T6x, that's 18V to 22V) but I wouldn't risk the possible damage that might occur if I'm wrong .

Don't the newer (20V) power supplies "talk" to the computer?

In a review here of T61 by a resident multimonitor expert--or multimulitmultimonitor more accurately if that helps anyone that knows who I mean and wants to search--IIRC he stated that plugging in a smaller supply than included, the computer noticed this and said something about not allowing highest performance.

I think that the center pin in the 20V plug is what "tells" the laptop what type of power supply is being used (65W vs. 90W). How it does that, I'm not sure (could be a voltage or resistance value). However, the difference between the two power supplies is with the current capability, not the voltage. Both supplies provide 20 volts DC. The original question asked what the maximum voltage that the T60 can safely handle.

My point is that if you build your own supply, you'd have to provide the same "talk" as the OEM supply, whatever that is.

On the 16V supplies, this might not have been an issue.

That might be the case if the power control system in the T60 absolutely requires that signaling function to be present in order to run off the AC adapter. My guess is that it does not. It may simply use whatever voltage is being supplied through the DC jack to power the system and if the proper signal is not present, then it defaults into thinking that the 65W supply is being used.

I am using a 3rd party PS for travel, a nice flat design that fits into my bag well. I am sure it doesn't "talk" to the computer.

Generally speaking, the in computer power circuit may regulate more than the common 10%. But higher voltage usually means higher temperature and potentially shorter life of the power component and worsen the already hot internal temperature. All in all, not really worth the risk.

I plugged a 3.3V HDD into the 5V Ultrabay tray. It worked a little while, got really hot then stopped.

jgysenbergs wrote:The T60 needs 20V DC input voltage but what would be the maximum power supply voltage?

It would be 20V DC.

Laptops rely on either battery energy or external energy supplied by a REGULATED switched mode power supply, neither of which should ever be expected to provide a higher voltage than the rated maximum.

There is no additional power regulation circuitry in the laptop to handle over voltage situations, so you should not assume there is any over-rated-voltage tolerance at all.

Cheers,

Bill B.

Thanks very much for your concise and clear clarification. Meanwhile I found out how to change the output voltage of the LT1070CT step-up converter to 20V and the T60 is now happily running consuming around 25W (display off but HD and wireless on). - Jos

bill bolton wrote:Laptops rely on either battery energy or external energy supplied by a REGULATED switched mode power supply, neither of which should ever be expected to provide a higher voltage than the rated maximum.

There is no additional power regulation circuitry in the laptop to handle over voltage situations, so you should not assume there is any over-rated-voltage tolerance at all.

I'll have to take slight exception to that statement. There is always some sort of tolerance, explicitly stated or not, when it comes to electrical equipment. Not every power supply is 100% "on spec". And not every 20V laptop is going to get exactly 20V (and not a millivolt more) in its lifetime. In an ideal world this may be true but we're talking about components made by man and machine and variance is going to occur. "How much?", was the original question posed.

Laptops are not simply powered by 16V or 20V on every part. There's several power controller chips which take whatever input voltage is provided by both the battery and the AC adapter and further reduces and regulates it to 3.3V, 5V, 12V, whatever. Most of those controller chips are designed to accept a wide range of input voltages. For example, the datasheet for the MAX1631 that's in the T23 is rated up to 30V. Would I want to try and connect a 30VDC adapter to any of my T23s? Nope, it would probably go up in a cloud of smoke. However, I would connect a power supply that reads 16.6V (with three separate voltmeters) to my systems without a second thought.

This just gave me an idea... I went and checked the HMM for the T23 and in the Power System Checkout guide it listed the voltage for the AC adapter as 15.5 to 17.0V. So that's about a +6% tolerance. I looked at the HMM for the T60 and it just says "20V" . The X60 HMM says 19.5 to 21.0V; a +5% tolerance. So I guess that means that the X60 supply, which I just measured at 20.6V, should not be used with a T60.

rkawakami wrote:I'll have to take slight exception to that statement. There is always some sort of tolerance, explicitly stated or not, when it comes to electrical equipment.

No, not always.

For non-compact electronic systems with variable input voltages (that is, they are usually mains powered devices only), there is a degree of an board regulation (of one form or another) provided to cope with variation in the "mains" power supply. For a laptop that is handled by the circuitry in the external power adapter, and it is EXPECTED to produce a closely (pre)regulated voltage to the laptop. This is EXPLICITLY done so the components which would otherwise be needed to regulate the somewhat variable external power supply voltage don't have to be included in the the tricky size/weight/heat tradeoff that necessarily occurs in laptop designs.

A contemporary laptop still needs some power management circuitry but that is because the REGULATED DC input voltage needs to be higher than the battery voltage, to enable the battery to be efficently recharged. The complexity of that circuitry can be significantly reduced if the input voltage is already (pre)regulated.

So, laptops are not a "general case" in terms of power supply variation tolerance for over voltage on the input socket. They are rather a "special case" where an externally regulated voltage must be provided.

We have plenty of evidence from Thinkpad x6x and later builds that the internal temperature needs to be very carefully managed when particular classes of tasks are are being run. So while a contemporary Thinkpad may tolerate a small over voltage under some circumstances, it may not do so when being pushed hard, as over voltage will translate directly into heat.

Also, the technology packed into today's Thinkpads is now sigificantly different from the T2x (or even the T4x) era, so comparisions with Thinkpads from that time are not relevant, IMO.

rkawakami wrote:"How much?", was the original question posed.

And my advice remains as nil, none, zero.

YMMV

Cheers,

Bill B.