I have a couple of peristaltic pumps to wash my cells with different conditions for live imaging with a fluorescence microscope. I now have the two pumps with a PWM pre-assembled module. It has a timer and 3 mostfets and a poti obviously.
I need to put media from a tube to the plate with a pump AND take the media from the plate to a waste container with the other pump.
However when I was using the peristaltic pumps prior to the PWM the liquid flow was exactly the same with both pumps. (the level of water in 50ml tubes was constant in both tubes when crossing the in and out from the pumps). However, now with the PWM signals there is a bit of a difference and one of the test tubes goes empty while the other gains volume.
I still don't know if it is mechanical or an electrical thing. I changed the peristaltic heads between motors and the same happens.
Could it be the stall start or the back EMF doing this? The pumps are connected in parallel.
Any way to solve this? Diode to reduce the EMF or a capacitor to equalize the start of the pump?
This was my previous setup in which the liquid pump rate was exactly the same (with the same motors and peristaltic heads)
Thanks for any help!