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Thinkpad X32 boot problem

1192 Views 1 Reply 2 Participants Last post by  reventon
I recently acquired a X32 but it fails to boot from a charged battery. It needs AC power to boot but if the AC is unplugged shortly after booting then it continues happily on the battery.

The battery holds a reasonable charge and charges OK.

Oddly it restarts OK if on battery only during the standard shutdown option in XP.

It is running XP Professional.

I have tried re-seating the hard disc, removing/replacing the CMOS battery, removing/replacing the memory and holding the main power button down for 1 minute with the battery removed.

Its a sweet machine with 2 hours from the battery but annoying that it won't boot from battery.

Any suggestions welcome please.


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This situation seemed to be pretty unexplainable at first, but after seeking opinions I believe we have a plausible explanation for what is occurring here.

Technical Explanation

Logically we can say there are two possible sources of power that can be used to power on

DC input via power supply or Battery.

In either case an output voltage that is less than the minimum required voltage will not allow the laptop to start.

On many occasions the starting Voltage is NOT either the working voltage or the Power OFF voltage (which is the voltage that will force a power down situation because of a "Low Voltage" condition)

So, should the Battery voltage be LOW, ie; not high enough to trigger the "Battery Good" condition, and an alternative supply is given that both
1. gives the battery a charge & raises the Voltage level
2. bypasses the Battery "source" mode to deliver the required "start up" Voltage

the laptop would start normally.

If the battery has the ability to give the required current without the Voltage falling to the level where the low voltage control steps in to power down the laptop, it will naturally keep working until it considers that it has exhausted its energy.

When any electronic equipment powers on from Cold, what is known as a "cold start" a very high current is drawn from the power source. This could be several times more than the actual working current.

When taking that current from a battery or power supply, it is important that the "source" has a very low impedance or resistance to the current being drawn.

For example a car when being "started" will probably try to take 100 Amps or more from the battery when starting, trying to turn over the engine. The battery MUST have an extremely low internal resistance otherwise that 100 amps will cause the 12 Volt supply be lost before it reaches the starting motor.

Anybody remember Ohms law ?

Voltage = Resistance * Current

If the INTERNAL resistance of a car battery (or the resistance between the cable and the battery pole) was 1 Ohm then the voltage lost passing 100A would be 100 Volts. That means that the resistance between the source and the load has to be less than or equal to 1/100 Ohm in order to lose only 1 Volt (which is still quite a loss considering that the battery is 12 Volts total).

The same principle applies to laptop batteries and any other battery if it comes to that.

The laptop may only require a 4 amp surge at start up before it drops down to around 1 amp. I would suggest that the battery may well have a 1 ohm internal resistance and can cope with that 1 amp drain once the initial 'start up" has been overcome. However when the battery is required to make a cold start it loses 4 Volts or more of it's supply due to that initial surge current, which puts it into low voltage power off.

In the warm start situation (when you restart from Windows) the current draw on the battery is far lower as it has already been warmed up. Hence it is able to complete the restart.

Technical Explanation End - Thanks a lot to Done_Fishin for this explanation

What all the above means is that your battery is most likely at fault and needs to be replaced to solve the issue.
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