# Drop the current of a couple of peristaltic pumps for a microscope use

I have a system to drive two peristaltic pumps (labelled 12V, that draw 300mA) in a microscope in the lab in order to refresh the media of my cells for long term experiments. In the current setting I'm pumping 40mL/min, which is too much. I need to be able to control the flow-rate (lets say, in a perfect world, between 0.5ml/min to 10mL/min).

I am using a 2A 12V DC power source.

Pumps are in parallel. I have two 8 ohms resistors right before each pump (in each parallel branch). (it was my first try to reduce the speed of the pumping that's why they are there)

I also, now, have 4 paralleled 4ohm resistors right after the power source (I needed to drop the current for today's experiment and it was all I had nearby and I didn't want them to fume even though they are higher than 1.2watts, 6 I believe).

So my question. I want to have a way to regulate the flow. Potentiometers usually come in high resistance forms and low wattage (I found a few 100 $\Omega$, and a 10 $\Omega$ - 5W online. Should I use the 10 $\Omega$ potentiometer?

Can I connect a potentiometer in parallel with the pumps trying to create a resistive voltage divider? However I don't know how to calculate the value to that potentiometer. Is this the best way to do it? I also can't to spend a lot of money on this.

I am concerned about temperature since the whole system (except the 12V power supply) is inside of a 37ºC enclosure to keep the microscope warm and the cells happy.

I saw this related post, but I have no idea on what values and pieces to use. Slowing Down a 12 volt pump with a potentiometer?

This is the state of the thing right now:

simulate this circuit – Schematic created using CircuitLab

• I think I'd restrict the flow using a valve or other fluid control device, rather than trying to control it by slowing the pumps. Do you really need two pumps? I'd think that using only one pump would reduce the flow to half. – Peter Bennett Oct 30 '15 at 2:35
• Hello, I need two pumps, one to put liquid from a container to the experiment and another to remove liquid form the experiment to a container (the culture plate has to always have the same volume or it will leak to the microscope),they flow at same rate, I checked. I can try to make it with only one pump (I could put a second tube that would go to through the peristaltic pump). Other problem is the vibration the pumps are doing, I need to keep focus on the sample and I noticed a bit of vibration going through the connecting tubes,reducing the rotation would help with that.Thanks for the input. – João Mamede Oct 30 '15 at 2:56