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.

Temperature

The battery charging circuitry shall be fully functional when the ambient air temperature is between 0 and 45C (inclusive).

This shall be tested at 45C with a DC input voltage of 24V.

Normal Charging Behavior

These are tests of the normal charging behavior.

Full Charge Status Indicator

If a charged battery (SOC > 90%) 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 (SOC > 90%) is inserted into a system, the battery indicator shall turn on with a green color.

When a charged battery (SOC > 90%) is present in a laptop, and DC power or the battery is removed, the battery indicator shall turn off.

Ability to Charge a Battery

If a battery with less than 90% charge is inserted into a laptop (either turned on or off) which has DC power applied, the laptop shall charge the battery to the 100% charged state. While the battery is being charged, the battery indicator shall be turned on with a yellow color. This charging process should take no more than 120 minutes, starting from a fully discharged battery (SOC < 20%).

If DC power is inserted in a laptop (either turned on or off) which has a battery with less than 90% charge, the laptop shall charge the battery to the 100% charged state. While the battery is being charged, the battery indicator shall be turned on with a yellow color.

These tests shall be performed with a DC input voltage of 11V, 12V-14V, and 24V.

When the battery is being charged and the indicator is yellow, if the DC power or the battery is removed, the battery indicator shall turn off.

Interrupted Charge of Battery

In this test, a laptop is turned on with a discharged battery (10% < SOC < 20%). A DC power source (12-14VDC) is connected. The battery should start to charge. The DC power source is then interrupted (turned off or disconnected) for one minute out of every ten minutes. The battery should be fully charged within 150 minutes.

Behavior with a Low Battery

Many battery system malfunctions are triggered by a battery with very little charge remaining. For the XO laptops, this is indicated by a battery voltage of 5.4V or lower.

Ability to Trickle Charge a Battery

Trickle charging is the process of slowly charging a deeply discharged battery up to the point where it can be charged at a normal rate. The problem is that the voltage of a deeply discharged battery (less than or equal to 5.4V) is lower than that required to maintain proper operation of the laptop.

If a deeply discharged battery is inserted into a laptop (either turned on or off) which has DC power applied, the laptop shall trickle charge the battery, then continue charging it to the 100% charged state. While the battery is being trickle charged, the battery indicator shall regularly flash a yellow color. When regular charging is started, the indicator shall change to solid yellow. This charging process should take no more than 180 minutes.

If DC power is inserted in a laptop (turned off) which has a deeply discharged battery, the laptop shall trickle charge the battery, then continue charging it to the 100% charged state. While the battery is being trickle charged, the battery indicator shall regularly flash a yellow color. When regular charging is started, the indicator shall change to solid yellow.

When the battery is being trickle charged and the indicator is flashing yellow, if the DC power or the battery is removed, the battery indicator shall turn off. It is likely that at this time the laptop will not operate from the battery without further charging.

As the battery charger does not interrupt the EC to indicate the change from trickle charge to regular charge, a delay of up to four minutes between the actual change of state and the change in battery indicator behavior is allowed.

Ability to Fully Charge a Deeply Discharged Battery

The laptop shall reliably take a deeply discharged battery, trickle charge it back to an acceptable voltage, 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. See Trac 9251.

Indication of Critically Low Battery

The laptop shall indicate that the battery is critically low (SOC < 10%) 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.

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).

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

These test the operation of the laptop with panels of solar cells as a power source.

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!

Stability with Underpowered Solar Panels

This test simulates the operation of the laptop battery charger when powered by an under-illuminated, under-powered solar panel.

A typical example is a desire to charge the laptop batteries using a solar panel which outputs 10 Watts max. In less than optimum solar conditions, this panel may only output 3 to 6 Watts. A simple model of a solar panel is a voltage source with a resistor in series. The open circuit voltage may be quite high, up to 24V, and the equivalent series resistance may be considerable, up to 30 ohms.

A laptop, turned off, shall attempt to charge a battery (SOC < 20%) from such a solar cell simulator, with an equivalent series resistance of 10 ohms. When the open circuit voltage is slowly swept from 8 to 24V, and back down again (over a time period of at least four minutes), the circuit shall show no oscillation of the battery charger operation, as indicated by either a whining sound or oscillation of the AC_IN signal to the EC.

This test shall be repeated with an equivalent series resistance of 30 ohms.

Stability with Cold Underpowered Solar Panels

A laptop, turned off, shall attempt to charge a battery (SOC < 20%) from a solar cell simulator, with an equivalent series resistance of 30 ohms. When the open circuit voltage is slowly swept from 8 to 30V, and back down again (over a time period of at least four minutes), the circuit shall show no oscillation of the battery charger operation, as indicated by either a whining sound or oscillation of the AC_IN signal to the EC.

Charging from Underpowered Solar Panels

A laptop, turned off, shall attempt to charge a battery (SOC < 20%) from a solar cell simulator with an open circuit voltage of 22V and an equivalent series resistance of 20 ohm. The laptop shall indicate that battery charging is taking place by the battery indicator turning on yellow. The battery shall be fully charged (SOC = 100%) in no more than 300 minutes.

Maximum Power Point Tracking

This unfortunately requires a real solar cell or solar cell simulator to test.

Insert test procedure here

Multiple Laptops Sharing a Solar Panel

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

Insert test procedure here

Error Conditions

These are tests of error conditions likely to occur:

Shorted cell/Imbalanced cells

A battery with either a shorted cell or greatly imbalanced cells provides a very low voltage.

These should be identified as deeply discharged by the system, but will continue to trickle charge indefinitely. There should be no overheating of the battery or battery charger components after 24 hours of trickle charging (even at 50C ambient air temperature), and no damage to the battery charger components.

Non-communicative Battery

A non-communicative battery is one which has a defective one-wire communications channel or gas gauge. The battery cells themselves may still hold power.

When a non-communicative battery is inserted into a laptop (turned on or off) powered by an external DC power source, the laptop may draw power from the battery but may not supply power to the battery.

When external power is inserted in a laptop which has a non-communicative battery, the laptop may not supply power to the battery.

Invalid Battery EEPROM Data

We occasionally see corruption of the data stored in the EEPROM in the battery gas gauge.

Insert test here