diff --git a/docs/Battery.md b/docs/Battery.md index 7d3088691..0ca448795 100644 --- a/docs/Battery.md +++ b/docs/Battery.md @@ -19,7 +19,7 @@ All targets support battery voltage monitoring unless status. When dealing with batteries **ALWAYS CHECK POLARITY!** -Measure expected voltages **first** and then connect to flight controller. Powering the flight controller with +Measure expected voltages **first** and then connect to the flight controller. Powering the flight controller with incorrect voltage or reversed polarity will likely fry your flight controller. Ensure your flight controller has a voltage divider capable of measuring your particular battery voltage. @@ -43,7 +43,7 @@ Notes: ### Sparky -See the (Sparky board chapter)[Board - Sparky.md]. +See the [Sparky board chapter](Board - Sparky.md). ## Configuration @@ -133,14 +133,41 @@ current_meter_scale = (Imax - Imin) * 100000 / (Tmax + (Tmax * Tmax / 50)) current_meter_offset = Imin * 100 = 280 ``` #### Tuning Using Battery Charger Measurement -If you cannot measure current draw directly, you can approximate it indirectly using your battery charger. The general method is: +If you cannot measure current draw directly, you can approximate it indirectly using your battery charger. +However, note it may be difficult to adjust `current_meter_offset` using this method unless you can +measure the actual current draw with the craft disarmed. + +Note: ++ This method depends on the accuracy of your battery charger; results may vary. ++ If you add or replace equipment that changes the in-flight current draw (e.g. video transmitter, + camera, gimbal, motors, prop pitch/sizes, ESCs, etc.), you should recalibrate. + +The general method is: 1. Fully charge your flight battery 2. Fly your craft, using >50% of your battery pack capacity (estimated) 3. Note Cleanflight's reported mAh draw 4. Re-charge your flight battery, noting the mAh charging data needed to restore the pack to fully charged -5. Adjust `current_meter_scale` to according to the ratio of actual mAh (given by the charger) to reported mAh (reported by Cleanflight) +5. Adjust `current_meter_scale` to according to the formula given below 6. Repeat and test -Note: it may be difficult to adjust `current_meter_offset` using this method unless you can measure the actual current draw with the craft disarmed. +Given (a) the reported mAh draw and the (b) mAh charging data, calculate a new `current_meter_scale` value as follows: +``` +current_meter_scale = (charging_data_mAh / reported_draw_mAh) * old_current_meter_scale +``` +For example, assuming: ++ A Cleanflight reported current draw of 1260 mAh ++ Charging data to restore full charge of 1158 mAh ++ A existing `current_meter_scale` value of 400 (the default) + +Then the updated `current_meter_scale` is: +``` +current_meter_scale = (charging_data_mAh / reported_draw_mAh) * old_current_meter_scale + = (1158 / 1260) * 400 + = 368 +``` + + + +