Ok so I’ve got an Adafruit 4 channel motor shield driving a 150mA 12v DC Brushless motor, a 120mA fan and a 1.2A 9V DC water pump at alternating times. I’m using a 12V external power supply with a 1.5A current rating to power the motor shield. Issue is all the motors function properly accept when its time to turn the pump on. The pump initializes with strong voltage to begin with but then drops off almost instantly. I’m thinking of using a Relay module off my channel 2 driver off the shield. I do understand the principles of how relays works except one thing. The question is can i use this channel to switch the relay on with another 9v power supply dedicated to the pump through the relay. And if I can, do I just hook the INT terminal from the relay module input to the positive channel 2 on the motor shield to receive the high to low or low to high switch?

motor sheild.jpg

Are those running-load or stall current ratings?

Are you using PWM to ramp up the motor drive?

Thmbarry: The pump initializes with strong voltage to begin with but then drops off almost instantly.

I suspect you mean high current which causes the voltage to fall (thus interfering with other things).

Your description isn't completely clear. Do you mean that the pump is drawing its current from the 1.5a supply to the motor shield? And are you considering giving it a separate power supply controlled by a relay?

That would seem likely to work. The relay could be switched by the motor shield in place of the motor.

Alternatively as @MarkT has said, you may be able to solve the problem with software by ramping up the power to the pump using analogWrite()


couple of things.

first, a schematic would help.

second, how does the pump run when you connect it directly to your 9V power supply ? if it runs fine, then the relay would obviously work.

what relay driver ? if you have a simple relay board from e-bay, then you most likely have an opto coupler. that needs to be fed properly.

your question is a bit confusing, are you asking if you can use the same output pin for multiple things ? or that you want to run the relay from an output from the driver board ?

it sounds as though you want to use an output from the driver board to turn on the relay. if you have a regular 12VDC relay, you should be able to connect it as if it were a motor. but only on or off, do not try to pwm the relay.

without seeing a schematic or the code, it is hard to determine your problem.

need more data.