How do I prevent cycling?
My 2868 is set to low volt cut at 3 volts. After a few seconds, the battery recovers and so it cycles every few seconds.
And while you’re at it, let’s say if we want LV to cut at 6v, 9v, etc…
Hi.
On the S9V11MACMA regulator an EN voltage below 0.7V turns the regulator off and an EN voltage above 0.8V turns the regulator back on. With the on-board potentiometer and resistors that means setting the cutoff to 3V would require a VIN voltage of about 3.4V to turn the regulator back on. That hysteresis cannot be adjusted.
What kind of battery are you using? How much current does your load draw? Can you measure the VIN voltage when the regulator cuts out and also turns back on?
-Claire
currently standard lithium ion 3 to 4.2 v. powering rasp. pi 0w ( variable) and LCD (120ma).
once it needs to LVC shut off, it should stay off. As you see, cycling destroys the pi.
but also for whatever future project at different voltages.
When the battery voltage drops and the regulator cuts-off the RPi and LCD will also turn off and stop drawing current. If their current draw was large enough, removing it could cause the battery voltage to recover high enough to let the regulator turn back on. Can you measure the VIN voltage when the regulator cuts out and also turns back on?
-Claire
yes, it draws a total of about 360ma to 460ma approx. an it does bounce around a few times. so there is no built-in mechanism to have it just stay off?
I have the board installed very deep, not accessable anymore.
maybe im not understanding how this board’s LVC is supposed to work.
The low-voltage cutoff works as described in the “Setting the cutoff voltage” section of the regulator’s product page. The only way to ensure the regulator will stay disabled, irrespective of the VIN voltage, is to connect EN to ground or some other low signal.
Since it does not sound like the current draw of your RPi is that high, you might try checking that the cutoff on your regulator is set properly. You could also see if increasing the cutoff a bit helps. 3V is pretty low to discharge a LiPo to.
One additional thing you might check is that the wires between your battery and the regulator are not too long or too thin (and that the connections are making good contact) so that there is not an excessive voltage drop across them when the RPi turns on.
-Claire
If you were to build a portable pi, how would you do it? Maybe I should re-think the whole situation.
And, yes, I know there are already full solutions already out there easily purchased off amazon. But I’m a glutton for punishment. I want to build my own.
For your situation, it might not be good to rely on the low-voltage cutoff of the regulator. Some bounce back of the battery voltage is unavoidable when a load is removed, and this is probably exaggerated by the low discharge voltage. Since the hysteresis of the regulator’s cutoff is not adjustable, it would probably be hard to tune it to be reliable.
One way to prevent the RPi from getting repowered would be to add one of our low voltage pushbutton power switches after your regulator.
-Claire
thanks.