rudiratlos
Posts: 160
Joined: Tue May 01, 2012 8:47 am

prevent throttling on undervoltage

Tue Nov 26, 2019 12:15 pm

my pi4 switches motors on and off. The pi is backpowered to a 50W powersupply.
If a motor is switched on, I get this warnings (under-voltage has occurred, throttling has occurred).
Due to the throttling the PID algorithm and in the specific application log I can see that the processor runs slower, which leads to lower precision in the motor regulation. Sometimes I can hear a short stutter of the motor.

Is it possible, to turn off throttling which is caused by very short, small and negligible voltage drops?

jamesh
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Re: prevent throttling on undervoltage

Tue Nov 26, 2019 12:26 pm

No, the throttling is there to stop the device crashing completely due to lack of power.

You need to fix the power supply, not turn off the protection.
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rudiratlos
Posts: 160
Joined: Tue May 01, 2012 8:47 am

Re: prevent throttling on undervoltage

Tue Nov 26, 2019 12:33 pm

The powersupply has 50W!! also a capacitor is connected to the motor as "charge pump".
The undervoltage throttleing is to quick. A hystereresis (e.g. delayed undervoltage alert) is required

jamesh
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Re: prevent throttling on undervoltage

Tue Nov 26, 2019 12:39 pm

rudiratlos wrote:
Tue Nov 26, 2019 12:33 pm
The powersupply has 50W!! also a capacitor is connected to the motor as "charge pump".
The undervoltage throttleing is to quick. A hystereresis (e.g. delayed undervoltage alert) is required
If it drops below a certain voltage, then there is a risk the CPU will crash, so the device is throttled to reduce the power demands. You need to figure out why the power supply to the Pi is dropping below 4.65v, which is irrespective of the wattage of the supply itself. It just means you have lots of power that is NOT getting to the Pi.
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PhilE
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Re: prevent throttling on undervoltage

Tue Nov 26, 2019 1:18 pm

It could be that your 50W power supply, though not short on grunt, is slow to respond to the changing current demands.

hippy
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Re: prevent throttling on undervoltage

Tue Nov 26, 2019 3:06 pm

You could also look at adjusting your PID algorithm so it is more independent of what the actual clock speed is, more immune to throttling.

rudiratlos
Posts: 160
Joined: Tue May 01, 2012 8:47 am

Re: prevent throttling on undervoltage

Sat Dec 07, 2019 10:48 am

just added a 3300uF capacitor between pin2 and 6 of the 40pin header. that prevents the voltage drop.
Thanks for pointing that out.

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