Merge pull request #820 from payne92/documentation-edits
Battery.md: clarify current_meter_scale
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@ -19,7 +19,7 @@ All targets support battery voltage monitoring unless status.
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When dealing with batteries **ALWAYS CHECK POLARITY!**
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Measure expected voltages **first** and then connect to flight controller. Powering the flight controller with
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Measure expected voltages **first** and then connect to the flight controller. Powering the flight controller with
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incorrect voltage or reversed polarity will likely fry your flight controller. Ensure your flight controller
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has a voltage divider capable of measuring your particular battery voltage.
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@ -43,7 +43,7 @@ Notes:
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### Sparky
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See the (Sparky board chapter)[Board - Sparky.md].
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See the [Sparky board chapter](Board - Sparky.md).
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## Configuration
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@ -133,14 +133,41 @@ current_meter_scale = (Imax - Imin) * 100000 / (Tmax + (Tmax * Tmax / 50))
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current_meter_offset = Imin * 100 = 280
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```
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#### Tuning Using Battery Charger Measurement
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If you cannot measure current draw directly, you can approximate it indirectly using your battery charger. The general method is:
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If you cannot measure current draw directly, you can approximate it indirectly using your battery charger.
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However, note it may be difficult to adjust `current_meter_offset` using this method unless you can
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measure the actual current draw with the craft disarmed.
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Note:
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+ This method depends on the accuracy of your battery charger; results may vary.
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+ If you add or replace equipment that changes the in-flight current draw (e.g. video transmitter,
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camera, gimbal, motors, prop pitch/sizes, ESCs, etc.), you should recalibrate.
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The general method is:
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1. Fully charge your flight battery
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2. Fly your craft, using >50% of your battery pack capacity (estimated)
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3. Note Cleanflight's reported mAh draw
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4. Re-charge your flight battery, noting the mAh charging data needed to restore the pack to fully charged
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5. Adjust `current_meter_scale` to according to the ratio of actual mAh (given by the charger) to reported mAh (reported by Cleanflight)
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5. Adjust `current_meter_scale` to according to the formula given below
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6. Repeat and test
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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.
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Given (a) the reported mAh draw and the (b) mAh charging data, calculate a new `current_meter_scale` value as follows:
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```
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current_meter_scale = (charging_data_mAh / reported_draw_mAh) * old_current_meter_scale
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```
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For example, assuming:
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+ A Cleanflight reported current draw of 1260 mAh
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+ Charging data to restore full charge of 1158 mAh
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+ A existing `current_meter_scale` value of 400 (the default)
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Then the updated `current_meter_scale` is:
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```
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current_meter_scale = (charging_data_mAh / reported_draw_mAh) * old_current_meter_scale
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= (1158 / 1260) * 400
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= 368
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```
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