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Current Limiting and Low Battery Limit
Prerequisites:
- Hydra firmware is installed
- you understand how to use CLI mode
- you have performed sensor calibration
The current limit value is set in milliamps. If you want the current limit to be set at 10A, then the value currlim should be configured to 10000.
The default settings should have a curlimkp (current limit PID loop's kP) value of around 100 by default. If the current draw is 1A over the limit, this should cut the power completely in under half of a second. It's not a hard sharp power cut, the PID loop will gradually lower the voltage during this time. Simulation shows that the current should reach a steady state in around 120 milliseconds, but at a current slightly higher than the specified limit (for example, a current limit set at 10A will settle at 10.5A).
If you want to operate at the current limit frequently or for long durations, then lower curlimkp and also have a slightly lower currlim.
There are two motors and only one current sensor, so please specify the current limit as the combined limit for both motors. For example, if you want to limit each motor at 4A, then please specify currlim as 8000. The firmware will automatically apply the correct limit as appropriate. For example, if you are only using one motor instead of two, the firmware will apply a limit of 4000 automatically even though currlim is set to 8000.
The ESC can be configured to detect low battery in different ways, and react in different ways.
This means the voltage limiting is active when the detected voltage is below a voltage threshold you set. The threshold value is the voltlim value specified in millivolts. To use this method, keep the value of cellmaxvolt at 0.
This means the ESC will try and guess how many battery cells are being used, and automatically determine the low battery voltage limit. You need to specify the limit as voltlim in millivolts-per-cell, and also specify each cell's maximum voltage with cellmaxvolt. For example, regular Li-ion and Li-poly batteries should use cellmaxvolt set to 4200, and Li-HV batteries should use cellmaxvolt set at 4350. voltlim should be set at about 3000, but you can raise or lower this according to preference.
WARNING: This automatic-cell-counting feature only works well if your battery is not already dead. For example, if you used a 6S battery that's so dead that it is at 18V, the firmware might think it is a 5S battery instead, since a full 5S battery is 21V.
It is recommended to use the absolute voltage limit method instead.
Set lowbattstretch to 0 and the ESC will completely stop if the measured voltage goes below the voltage limit.
Set lowbattstretch to a very high number, such as 1000. For example, if the voltage limit is at 6000 millivolts, and the lowbattstretch is set to 1000, then it means when the ESC measures 6000 millivolts from the battery, it will begin to slow down, and when battery voltage reaches 5000 millivolts, the ESC will have come to a complete stop. If you want to use this feature, you will want a slightly higher voltage limit, so that the motors slow down earlier.
This is useful in a competitive environment, where you want to sacrifice the health of your battery to win. This is also how RC boat ESCs typically behave, it makes the boat slower but you'll be able to safely bring home the boat.
This feature is used if templim is set in degrees-Celsius. It is not very useful because it is using the temperature of the microcontroller, not the temperature of the MOSFETs. Setting templim to about 80 might be an acceptable value.