The connection I have made with relay to solenoid is as follows: I connected NO of the relay to a lead of a solenoid and COM of the relay to +12V and another lead from solenoid to GND. Similarly the second solenoid.
The problem I am facing is the solenoids are getting heated too much after a while. Since I need the project to run for hours, I don't think the solenoids will be able to withstand that long.
Can someone please guide me if I need something extra so that the solenoids don't heat that much or I am supplying them with a wrong power source?
Hi,
I agree with Wawa, the solenoids are dissipating 12W, so they will get warm.
A controller would use full power to activate them then run a lower holding current through them.
Found the specifications for your power supply. The output could be at 16V and only be at 12V when fully loaded.
The solenoid is 12V, 4W, 36Ω, 0.33A. Both solenoids will draw 0.67A, so there might be 14V-16V powering the solenoids, considering negligible loss across the relay contacts.
Could use 5 or 6 1N4007 diodes in series to drop the voltage. Don't forget to add one across each solenoid coil (anode to +14-16V +'ve end of coil, cathode to switched end of coil). This clamps the fly-back voltage.
No, that will just get you hot resistors. Or big resistors. Or big, hot resistors.
As someone has already suggested to you, you could devise logic to switch them on using full power then switch to lower power to keep them 'energised', as it were.
To achieve this, member Wawa suggested logic level MOSFETs which would allow you PWM control of the output power - full power (ie 255) to switch them on, then reduce to, say, 100, to keep them on. By experimentation you would refine that last PWM output figure, of course, which I plucked out of the sky. A bit like latching a relay then reducing the (drop-out) voltage until it can't hold it anymore (spec sheets for relays give you the voltages for this, so I guess it's a technique used in industry).
IMHO that's far better than dropping resistors, or diodes or what you suggested. In fact, it's quite elegant!
It's a little more than 12 volts. It shows 12.13V when all of the solenoids are triggered.
I suppose it's normal that they will be heated. Do you think they are going to blow up or something, if I leave them so it is?
Thank you Sir for your suggestion. I guess I will stick to the relay for a while. I will give them a trial run by keeping them triggered for a while. If it doesn't work I will switch to the MOSFETs logic control.
Resistors not needed (and not suggested as a solution).
Do you think they are going to blow up or something, if I leave them so it is?
It mentions limit temp of 130 deg C.
One diode (i.e 1N4007) in series with the 12V supply will lower the coil's heat dissipation by about 12.5%, two diodes in series will decrease the coil's heat dissipation by about 25%.
You can use two outpus to control each relay.
Look at this schematic
Use one I/O to pull in the relay and the other to hold it in.
Initially, set both high together, but about 20ms later, return the PULL-IN signal low, while leaving the HOLD signal high – until it’s time to release the relay.
How are you powering the relay module.
I hope not from Arduino's 5volt pin.
That 4-relay board plus the Arduino itself gets you close to 400mA.
USB supply will just be possible.
External supply, e.g. 9volt on the DC socket, could easily overheat the onboard 5volt regulator.
Replace the relay board with mosfets, and you eliminate that problem.
Leo..
