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I currently use OpenSprinkler to control the solenoids on my aeroponic vegetable systems. I am adding some flood and drain modules to the operation and wondered if OpenSprinkler DC could control and run small DC pond pumps. They are listed at 12VDC and 5 watts. I understand I can use a relay to control the 110VAC version of the pumps with the AC version of OpenSprinkler, but it would be nice to control the pumps directly. Thanks.
Kerry Kakazu
MetroGrow HawaiiIf the pump is only 12VDC 5watt, you can directly connect it to a station on OpenSprinkler DC and control it like a normal sprinkler station. 5 watt means the current is about 410 mA, and is well within the limit of OpenSprinkler DC (up to 1 amp per station).
Thanks for the good news. Can you recommend the specs for the power supply to pair with the unit? I expect to control 4 pumps. Maybe 12V and 2 amp?
In response to Ray’s comment your pump at 5watts and 12VDC will be using about half an Amp not the 83mA stated.
P(Watts) = I(Amps) x V(voltage)
So to calculate for I we have:
I = P/V
or in your case Amps = 5Watts/12VDCYour amperage would be about 0.41
Sorry, I made a stupid mistake in my calculation and Shawn is correct that the current draw is 410mA. To find out what power supply you need:
1) Either 9VDC or 12VDC should work. OpenSprinkler DC comes with a 9VDC power adapter. Although technically this is lower voltage that the required 12VDC of your pump, in many case this is OK. OpenSprinkler DC has a built-in boost converter that builds up a high voltage from the input voltage, and that’s sufficient to energize solenoids / pumps. Once energized, the solenoids / pumps typically can operate under a lower voltage. So 9VDC to operate 12VDC solenoid / valve is often just fine. If not, you can also switch to a 12VDC adapter.
2) Regarding current output: it depends on how many pumps you need to turn on at the same time. If at any point all four pumps need to turn on at the same time, you need at least 0.4 * 4 = 1.6A output current from the power adapter. So 2A should be good enough. If only one pump needs to turn on at any given time, 1A should be sufficient.
Thanks for the feedback. I probably won’t need to run multiple pumps at once, but I got a 2 amp power supply just in case.
I tried connecting the OpenSprikler DC with a 12V 2 amp transformer I picked up. I connected my 12VDC 4.8 submersible pump to station 1 and set it to run for 5 seconds as a test. Pump didn’t run. I hooked up my voltmeter to station 2 and ran it for 5 seconds. It registered -20VDC. I then reversed the polarity of the pump and it did run, but I didn’t want to go longer than 5 seconds. I checked it with the voltmeter with a run of 90 seconds. The voltage starts at 20V and then decreases steadily to about 9V by the end of the run. I’m guessing this is the normal behavior to make it run with the solenoid valves, but I don’t know if this will work with using the timer to keep the pond pump on to fill my flood and drain hydroponic system (needs to be on for 75 to 90 seconds at 12V. I don’t know how the pump will react to the voltage ramp. Any suggestions would be appreciated. Thank you.
Kerry
@Kerry: most pumps need a good impulse current draw to be activated, and once activated they can remain on with a lower voltage.
The voltage dropping to 9V by the end of run seems a bit strange — it will certainly be lower than 12V but dropping to 9V seems a bit too much. To understand the setup:
– Did you test with just one pump or multiple pumps?
– When it drops to 9V, can you test the output voltage of the transformer? You can do so by measuring the voltage between and GND pin and the pin on the back of the black power barrel (i.e. where the transformer is plugged in). Normally the voltage presented to the station would be somewhere between 0.5V to 1V lower than the input voltage (due to the diode explained below). So if the input voltage is already dropping to 10V or below, then it’s normal for the voltage to be 9V at the pump.Now I think about it, OpenSprinkler DC circuit has a 2A diode on the input to COM path which practically limits the total current supply to all valves to about 2A — it can probably go above 2A but the voltage drop on the diode will become more significant. This shouldn’t be an issue if the total current draw is well below 2A. And if you do need more than 2A total current, there are ways to bypass the limit.
Sorry, I think I did the ramp test with the supplied power supply. The 12V 2A transformer started at 20V and declined to 12.23 and stabilized by the end of the 90 second cycle. The power output of that transformer was 12.4 V so it looks like the OpenSprinkler is doing what it is supposed to.
So you think running the DC pump at the higher initial voltage should be okay? I’m guessing if its a DC motor it will just spin a little faster initially? I can switch the leads on the pump so it’s not a big deal, but is the reverse polarity output the normal operation for the unit?
Thanks for the help.
Kerry
Most motors / solenoids are ok with a higher impulse voltage in the beginning. In fact, for solenoids this is a good thing as it ensures the solenoid will be reliably energized. Because the voltage comes from charge stored in a capacitor, and the energy is limited and shouldn’t cause any damage.
If you don’t need the boosted voltage, go to Edit Options and set ‘boost time’ to 0. This way the boost converter will be turned off and won’t produce the initial high voltage.
Thanks very much for the tips. If I wanted to control a larger pump, can you recommend any DC relays to operate 110VAC pumps?
Kerry
Generally for irrigation system you can use ‘Pump Start Relay’, for example:
https://www.amazon.com/Orbit-57009-Sprinkler-System-Horsepower/dp/B000I19I5E/
These are designed to control high power pumps. OpenSprinkler DC works well with many existing pump start relays such as the above one.An alternative, low-cost option is solid state relay. Search ‘Solid State Relay’ on Amazon and you can find plenty of choice. Choose one that uses DC input (e.g. 3-32VDC, because you are using OpenSprinkler DC), and controls AC output (e.g. 110VAC should be within the range it controls). Also make sure the solid state relay meets the current rating of your pump. Solid state relays are semiconductor-based so they don’t wear out over time, and they are optically isolated internally.
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