This application note outlines the main features of the LiNX enhanced battery gauge and the process of charging when the wheelchair’s batteries are replaced.
Overview
The LiNX enhanced battery gauge integrates new technology that determines the State of Charge (SOC) of lead-acid batteries more accurately than conventional battery gauges which are based on battery-terminal voltage:
- The new enhanced gauge estimates the real SOC by looking at a number of factors, not just instantaneous terminal voltage, which on its own, is a poor indicator of SOC.
- The gauge does not measure current, which is difficult to do in a power wheelchair system.
- The gauge determines if the battery is charging or discharging, and depending on this state, applies logic and calculations to find the real SOC. Part of this is knowing the recent history of the battery use.
- The gauge models the discharge based on the terminal voltage, the rate of change of terminal voltage and how long the battery has been in this state, to get an actual SOC.
- The new gauge differentiates between real charging and regenerated voltage or recovery, which causes a distortion of the charge estimate in conventional gauges.
- If the battery is actually charging, the change in SOC is calculated based on where it is in the charge cycle, the rate of change in the terminal voltage and how long it has been charging.
New batteries
The enhanced battery gauge uses the recent charge / discharge history of the battery to calculate the SOC. When new batteries are connected, this history is no longer applicable, but the gauge will continue to calculate the SOC based on the information from the previous battery. To rectify this, the enhanced battery gauge needs to be synchronised to the new battery.
| NOTE | Battery manufacturers recommend that batteries are formatted when new. This involves cycling the battery a number of times without deep discharging them. This does not impact on the gauge synchronisation for new batteries. |
Battery synchronisation procedure
- Connect new batteries to the power wheelchair.
- Reset the battery statistics with the LiNX Access tools.
- Connect the power wheelchair to the battery charger — this must be done with the system switched ON or within 24 hours of the system being switched on.
- Leave the power wheelchair connected to the battery charger for longer than 10 minutes.
- Wait until the battery gauge displays > 80% (5 LEDs).
- Leave the power wheelchair connected to the battery charger for at least 2 hours — for a new battery, the time should be an extended period as per the battery manufacturer’s recommendations.
These steps are detailed in the table below.
Detailed description of battery synchronisation procedure
| Step | Activity | Gauge | What is happening? |
|---|---|---|---|
| 1 | Connect new batteries to the power wheelchair. | SOC displays as between 0-100% capacity. | The gauge reflects the estimated SOC based on the previous battery. |
| 2 | Reset the battery statistics with the P&D tools. | SOC displays as between 80-100% (5 LEDs) capacity. | The gauge has no knowledge of the battery SOC and estimates it as ~80%. |
| 3 | Connect the power wheelchair to the battery charger — this must be done with the system switched ON or within 24 hours of the system being switched on. | SOC displays as between 80-100% capacity | The gauge determines whether the battery is in fact charging. |
| 4 | Leave the power wheelchair connected to the battery charger for longer than 10 minutes. | SOC displays a capacity based on internal algorithm and terminal voltage | The gauge estimates true SOC based on the battery voltage. |
| 5 | Wait until the battery gauge displays > 80% (5 LEDs). | After a period, the SOC displays as 100% | The battery voltage approaches maximum charge voltage. |
| 6 | Leave the power wheelchair connected to the battery charger for at least 2 hours — for a new battery, the time should be an extended period as per the battery manufacturer’s recommendations. | The SOC displays as 100% | The battery reaches equalization voltage. The battery is fully charged and SOC gauge is calibrated to the state of the battery. |
Resetting the battery gauge statistics preloads the battery gauge with a nominal value that presents as a full SOC. This can be misinterpreted by the user that a battery is full, but the gauge is still establishing the real SOC. The battery SOC cannot be relied upon until the system has had sufficient time to determine the true SOC. The best way to do this is to fully charge the battery for at least 8 hours.
