hi there i have an electronic question we own a hydroponics farm i am a sparky by trade by are limited on electronics, I have a blue lab pro controller unit for hydroponics monitoring it has its own power supply it has an option to plug in a 4 way dosing pump that blue lab sell i cant afford it, it can send a sig to a dozer pump to dose nutrient or acid to adjust the ph and ppm on the water .it has a plug at its base for out put to max 50 ma out put not sure off voltage going to put an oscilloscope on it to determine the out put, the doser pumps that blue lab sell normally plugs into it normally ,i have found a plug that fits it to extend the wiring to a controller i will build, i need to to control my 3 x 24 v dosing pumps i have a 24 v power supply to power the pumps i under stand how to wire in a relay to switch the 24 v supply to pumps via n/o contacts, what do i use to trigger the relay ,if i determine the out put on the controller do i try to step up the out put to drive say 24 v coil on relay note the comments from blue lab below as i already have a power supply available blue lab want 4k for a 4 way dosing pump was bad enough i spent 2k on the monitor asked blue lab in usa for pin out puts this is the response. email from blue lab below Firstly suggest using an oscilloscope on the Pro Controller pins. The pro controller provides no power and can switch no power, but effectively provides “dry” contacts to signal a pump unit driver. Pin 1 – Common Pin 3 – pH Pin 4 – ECA Pin 5 – ECB Pin 8 – Temp The customer will need to provide 24VDC (max) to pro controller for it to pull signal to gnd. The max current you can pull is 50mA to prevent damage to components within pro controller. Do NOT wire anything to the other pins. question can some please help me to draw a wiring diagram for a pump unit driver and what i need to get to make this work i really appreciate your help
link to type off controller
blue lab controller link

 

I read this as the controller providing an open collector output (a transistor-controlled switch) with a 50mA rating. So your own dosing pump would need to provide a voltage through a current-limiting resistor to this controller. Maybe a 12V supply with a 470 to 1KΩ resistor, for instance. When the controller switches on, the voltage on the controller side of the resistor will approach zero and will be 12V while the controller is "off". Your dosing pump would be controlled by watching that voltage, and activating a relay to power the pump when the voltage goes low.

Before going much further, I'd experiment with an LED to verify the controller behavior. Hookup a battery to share ground with the controller. Send the battery power through a 1K resistor and through a standard LED and finally to the controller pin. Manipulate the controller to switch on and off and verify that the LED turns on and off.

 

I suggest using optically isolated solid state relays to work with the existing controller. The reason is that then there is just a small current and no chance of an inductive spike. The opto SSRs can often be had that will operate on five volts DC., so the power for them can be small and simple.
The second benefit is that the controlled side of the SSR connection is farther awayfrom the input part, giving even more safety.