XO DC Input

This page attempts to detail the different tests that an XO DC power input should pass.

Extremes

These are static tests of the input protection circuitry:

Valid Input Voltage

The laptop shall operate and charge the battery when supplied with any voltage between 11V and 24V (inclusive).

The laptop shall accept a DC input with an AC ripple component up to 2V (peak-peak), provided that the the peak input voltage never drops below 11V or exceeds 24V.

Overvoltage

The laptop shall not be damaged by the application of voltages up to 40V, for any length of time.

Applying a voltage higher than 40V shall not result in fire, but may destroy the internal fuse.

Undervoltage

The laptop shall not draw power from the DC power input when supplied with voltages between 0V and 9V.

Negative Voltage

The laptop shall not be damaged by the application of a negative voltage up to -38V, for any length of time.

Applying a negative voltage larger than -38V shall not result in fire, but may destroy the internal fuse.

Maximum Power Draw

The laptop shall never draw more than 25 Watts of power from its DC power input. This is usually tested with the laptop on and running processor tests from Open Firmware, while charging a low battery (open circuit battery voltage less than 5.6V).

The actual power limit depends on the laptop model. For XO-1, this number was 17 Watts.

Charging Behavior

These are tests of the normal charging behavior.

Ability to charge a battery

The laptop shall take a battery in any state of charge (less than 80%)

Full Charge Status Indicator

If a charged battery is present in the laptop, and acceptable AC power is inserted, the battery indicator shall turn on with a green color.

If accceptable AC power is present, and a charged battery is inserted into a system, the battery indicator shall turn on with a green color.

When a charged battery is present in a laptop, and DC power or the battery is removed, the battery indicator shall turn off.

No Critically Low Battery Indicator when turned off

The laptop shall not indicate a critical battery status when the laptop is turned off.

Seen as Trac 10668.

If external DC power is inserted, the critical battery status (red battery indicator) should be replaced with either the charging status (yellow battery indicator) or trickle charging status (blinking yellow battery indicator).

Behavior with a Low Battery

Many battery system malfunctions are triggered by a battery with very little charge remaining. With a LiFePO4 battery of two cells, this is indicated by a battery voltage of 5.35V or lower.

Inability to charge critically low battery

The laptop shall reliably take a critically low battery, trickle charge it back to an acceptable level, then continue to charge it to 100% charge.

We have had cases where after coming out of trickle charge the charging system did not proceed to fully charge the battery Trac 9251.

Indication of critically low battery

The laptop shall indicate that the battery is critically low by turning the battery indicator on to a red color when the laptop is turned on.

Seen as Trac 3610, Trac 5858, and Trac 10033.

Inserting power while battery is low

Applying power to the laptop while the battery is low shall not cause the laptop to power off.

Seen as Trac 2182.

Behavior when plugging/unplugging

Power draw when turned off

The power draw of the laptop from the battery shall not exceed 2 mA when the laptop is turned off and no external power is provided.

Power brownout while charging

The laptop shall tolerate quick interruptions in DC power input without disturbing the battery charging. If must be confirmed that the battery charging continues properly, not just that the indicators indicate that charging is continuing.

Seen as Trac 9983.

Suspend/Resume

In general, all tests should operate identically whether or not the laptop is suspended. Historically, we have had some problems in these areas:

Inserting power while suspended

If power is supplied to the DC power input while the laptop is suspended, the laptop should automatically begin powering itself from the external power source. If necessary, the battery should begin charging. All indicators (power and battery LEDs) should properly indicate that external power has been supplied.

Removing power while suspended

If power is removed from the DC power input while the laptop is suspended, the laptop should continue operation from battery. All indicators (power and battery LEDs) should properly indicate this loss of external power.

Seen as Trac 10369.

Solar

Traditionally, this is the area where we don't test enough. It is important to realize that if the laptop is using solar power as a source, it is almost always receiving less power than it wants!

Operation from underpowered solar panels

I'm still thinking about this, but I believe that a respectable target is operation with 10 and 30 ohms inserted in series with the power source, with open circuit voltages swept from 10 to 24V (and the reverse) over a period of a minute, with no oscillation.

Multiple laptops sharing a panel

Multiple laptops should be able to share a solar panel which has an adequate power rating.