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Code Issues Wiki Activity

Clarify virtual current sensor documentation

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Andrew Payne 2015-04-26 10:10:07 -04:00
parent 006e39c422
commit c2f66b54f9
1 changed files with 32 additions and 5 deletions
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docs/Battery.md
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@ -19,7 +19,7 @@ All targets support battery voltage monitoring unless status.
When dealing with batteries **ALWAYS CHECK POLARITY!** 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 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. has a voltage divider capable of measuring your particular battery voltage.
@ -43,7 +43,7 @@ Notes:
### Sparky ### Sparky
See the (Sparky board chapter)[Board - Sparky.md]. See the [Sparky board chapter](Board - Sparky.md).
## Configuration ## Configuration
@ -133,14 +133,41 @@ current_meter_scale = (Imax - Imin) * 100000 / (Tmax + (Tmax * Tmax / 50))
current_meter_offset = Imin * 100 = 280 current_meter_offset = Imin * 100 = 280
``` ```
#### Tuning Using Battery Charger Measurement #### 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 1. Fully charge your flight battery
2. Fly your craft, using >50% of your battery pack capacity (estimated) 2. Fly your craft, using >50% of your battery pack capacity (estimated)
3. Note Cleanflight's reported mAh draw 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 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 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
```