I am looking to use an irrigation solenoid designed for use with AC 24 volts with DC 24 volt supply. I have not been able to find a non latching DC irrigation solenoid, and my current design uses DC. So my question is;

Can I safely lower the DC voltage and operate the solenoid? Currently it does operate, however at above normal temperatures. My understating is that the worry is overheating the coil do to the higher sustained power usage, so I am hoping a lower voltage would work. If so what voltage? Or how could I test for the best voltage?

 

Lower the voltage to where it doesn’t work, then raise it a bit. Or, to be more accurate, check the current and set the voltage to get the current the solenoid is rated for.

 

Try this link. AC/DC My memory (not good) is that about 7VDC will work. Do not use 24VDC!

It has been a while since I tried it. I think a solenoid draws 600mA when first hit with AC and drops to 100 to 150mA when it open. That is why a solenoid overheats if it is stuck off. I used a bench power supply with voltage and current meters. Adjusted the voltage to get 125mA.
This voids the warrantee.

 

Thanks,
Unfortunately, the solenoid does not have a current rating.
At 24 vac the solenoid draws .215 Amps.
At 15 vdc the solenoid draws .5 amps.
At 12 vdc the solenoid draws .45 amps. and .41amps after a period of time

Should I keep going under 12 VDC, I don't think I will get the same amps at lower voltages being DC power.

 

Should I keep going under 12 VDC, I don't think I will get the same amps at lower voltages being DC power.

Yes, I would lower the voltage until you get about 0.215Adc (likely around 6Vdc), otherwise you may overheat the solenoid (that heating is what caused the observed current to drop with time).

If the solenoid doesn't pull in properly at that low voltage then you may have to use a hit-and-hold type of driver, which initially applies a higher voltage (say 12Vdc) for a fraction of a second to pull in the solenoid, and then lowers the average voltage to 6Vdc to minimize the solenoid power dissipation.
The most efficient way to do that is with a varying duty-cycle PWM signal.
I have a circuit that uses a 555 timer chip to perform that function, if you need that.

 

okay, it looks like possibly something a bit more complicated than just 12VDC is needed.
However, the temperatures do look reasonable, I am not sure 12vdc constant would overheat it.
The 12vdc keeps the solenoid at 55c
The 24vac keeps the solenoid at 45c
FYI at 23c ambient

If I am just worried about overheating, the 10 degrees over ideal conditions (24vac) seems small and not very concerning.

 

Try this link. AC/DC My memory (not good) is that about 7VDC will work. Do not use 24VDC!

It has been a while since I tried it. I think a solenoid draws 600mA when first hit with AC and drops to 100 to 150mA when it open. That is why a solenoid overheats if it is stuck off. I used a bench power supply with voltage and current meters. Adjusted the voltage to get 125mA.
This voids the warrantee.

this link was very helpful

 

Do you require the protection from the elements that the AC style irrigation style offer?
Other wise there are is a fairly large selection of reasonably priced standard DC solenoids out there.

 

A fewyears ago, in the dead of a cold winter, the power went out in a relative's area, and so the gas fired steam boiler would not heat. We used the 12 volt battery from a travel trailer to power the 24 volt gas valve, through the thermostat and associated wiring, to operate the gas valve. It worked OK for three days, then the power returned. And the gas valve continued to function correctly with the 24 volt AC supply for the next five years, until he got a much more efficient boiler installed.
If you really want to reduce the current more, use a higher powered incandescent 12 volt light in series. That will allow an inrush to operate the valve and then reduce the current to hold it operated. AND the added benefit is you can visually see that the valve has been operated from quite a distance.

 

My personal preferences is always to use the correct device for the job, where possible, I so no exception here, even if it requires a little more work to conform to the elements etc,

 

An extended power outage in the dead of winter tends to become sort of an emergency situation. At least for some folks.

 

An extended power outage in the dead of winter.

??????

 

I did this exercise as a young electrical engineer. For an AC coil on dc you apply the same dc volts to the coil then reduce the coil current. It's done by inserting a resistor after the relay closes. The resistor is held out of circuit by a N/C contact around the resistor of the relay.

 

An incandescent lamp of suitable rating can also provide the appropriate resistance, which increases when the bulb lights. That provides the appropriate inrush to engage the magnetic solenoid valve and drops the current for holding.
AND, @ Max, yes! several years back, in mid January, a tree branch fell during a snow storm and took out the power to a small group of homes, one of which a relative of mine lives in. There were also some much larger areas of outage, which demanded first attention by the repair crews. I was not in a position to repair the power distribution system, but I was able to restore the boiler operation. As the temperature was in the twenty degrees F range, that was needed. And three days did constitute "an extended outage" in an area where even a minute's power interruption is considered "an outage."

 

To me it sounds from the OP's posts that this is NOT an emergency situation??
If the OP has the luxury of considering options I would still hold to what I said and definitely consider using the right device for the job!.

 

You might consider some variant of a circuit idea I first saw years ago in a Bob Pease article.
https://www.electronicdesign.com/te...0/whats-all-this-solenoid-driver-stuff-anyhow
The basic idea is to include a simple series RC element in the coil current path. At turn-on a high inrush current from the DC source pulls in the solenoid as the cap initially charges. With the cap charged, the series resistor limits the steady-state current.