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Solenoid not working

billrvolz

Jun 28, 2021
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I'm trying to operate a solenoid for a sprinker valve from a controller (not important). The solenoid is from Hunter 458200. I can't find much on the specs. It is a latching solenoid that runs off a 9v battery. What I can find is that it takes 9-11 volts pulsed to actuate it. I've constructed some relays to apply the voltage. The system is powered from a battery with solar so the voltage varies between 12- 14.5 volts, over the rated voltage of the solenoid.

I used a 10v 0.5 W zener diode in series with a 470 ohm resister to provide 10 V to the solenoid.

Here's the problem - when I check the voltage WITHOUT the solenoid attached I get the 10V across the leads. When I hook up the solenoid I get only 0.13 Volts and the solenoid does not operate. I'm not sure why the solenoid doesn't work.

I checked the amps drawn when the solenoid operates and I'm measuring around 0.19 amp.. That would mean that the solenoid is drawing about 1.9 W, which is above the 0.5W rating of the zener I'm using.

Would increasing the watt rating of the zener to 5 W fix this?

Thanks for your help
 

crutschow

May 7, 2021
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You need to learn Ohm's law.

How do you expect to get 0.19A through a 470 ohm resistor with only about a 3-5V drop?
To drop 3V @ 0.19v requires a resistor of 3V / 0.19A ≈ 16Ω in series with the solenoid.
You don't need the Zener.
 

billrvolz

Jun 28, 2021
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To Bluejets, there is no such thing as a 'zener resistor', it's a zener diode.

To Crutschow, I know Ohms law. The zener is connected to the battery ground, then the 470 ohm resistor and then battery positive. The 470 ohm resistor drops the remaining 3V. I'm taking 10V across the zener. This configuration is a common simple DC voltage regulator. This explains how it's connected: https://www.electronics-tutorials.ws/diode/diode_7.html

Thanks for you input.
 

Harald Kapp

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@billrvolz : premature to be flippant. The answers you've been given are good. Just take some time to think about them.

To Bluejets, there is no such thing as a 'zener resistor', it's a zener diode.
I think he meant the combination of zener diode and resistor.
I know Ohms law.
Do you? Then you should understand @crutschow 's explanation.
The 470 ohm resistor drops the remaining 3V.
Only for the case when no current is drawn by the solenoid.

Have a look here:
upload_2021-6-29_8-20-4.png
--- Operating Point ---

V(out): 10.1772 voltage
V(n001): 12 voltage
I(D1): -0.00387824 device_current
I(R1): -0.00387824 device_current
I(V1): -0.00387824 device_current
With no load current through R1 is ~ 4 mA, output voltage is 10 V.

Your solenoid has ~47 Ω (9 V ( 0.19 A). With this load the circuit looks like this:
upload_2021-6-29_8-22-16.png
--- Operating Point ---

V(out): 1.09091 voltage
V(n001): 12 voltage
I(D1): -6.01091e-010 device_current
I(R2): 0.0232108 device_current
I(R1): -0.0232108 device_current
I(V1): -0.0232108 device_current

R1 and R2 form a voltage divider 1:11. your sourece voltage of 12 V is reduced to 1.1 V (V(out = 1.09091 V). The zener diode is ineffective as the voltage across it is less than 10 V. The resulting current of 0.023 mA is insufficient to operate the solenoid.

No consider @crutschow 's proposal:
upload_2021-6-29_8-25-33.png
--- Operating Point ---

V(out): 8.95238 voltage
V(n001): 12 voltage
I(R2): 0.190476 device_current
I(R1): -0.190476 device_current
I(V1): -0.190476 device_current

You now have 0.19 A through the solenoid (R2) and a voltage of 9 V across R2. Perfect for your application.
 

Bluejets

Oct 5, 2014
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To Bluejets, there is no such thing as a 'zener resistor', it's a zener diode.
It was quoted as a combination of zener diode and resistor as the OP quoted, hence zener resistor.......merely a form of shorthand.
Quite agressive little responder aren't we.
 

DBingaman

Jun 27, 2021
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You may want to modify slightly Harald Kapp's circuit:

Mod.PNG

Some solenoids have this diode built into them some do not. To find out place a DMM on diode check mode check with both polarities for a forward diode drop. If you do not have this large inductive spikes could damage whatever is generating the 12V pulse for the latching solenoid. A 1N4001 will work fine here. Any standard diode with at least 1A max forward current is good. For this circuit the max current being 14.5V/63 or 230mA. You should as a general rule always over-rate things by at least a factor of 3 in my book.
You need an R1 of sufficient power being it will be consuming a maximum of 0.85W. As long as the pulse is not continuous you could probably get away with a 1W resistor.
 
Last edited:

DBingaman

Jun 27, 2021
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It was quoted as a combination of zener diode and resistor as the OP quoted, hence zener resistor.......merely a form of shorthand.
Quite agressive little responder aren't we.

Not trying to get picky but actually Bluejets is right. A typical resistor has mostly constant resistance as a function of voltage. A zener or any diode for that matter has a non constant resistance as a function of voltage. But at any given voltage it will exhibit a specific resistance. This is why datasheets plot V/I curves for zeners and diodes.
 

billrvolz

Jun 28, 2021
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Thanks for the input. It took Harold's explanation to understand what Crutschow was saying. Yes, my understanding of Ohm's law is rusty enough to cause a short...

Speaking of short - I put the 16 ohm resistor in series with the solenoid and it works - kind of. About every other or third time I activate the solenoid, the entire 12 power bus shuts down for a fraction of a second, rebooting everything. This only happens when the solenoid is in the circuit. Without the solenoid, I activated the circuit 20 times and it worked so there's no short. It killed the power bus the first time after hooking up the solenoid again. Right now I'm using a 9V battery to activate the solenoid and that's working. I'm not sure what's going on but I have 2 theories. I'd like to operate this from the 12 V batteries so I don't have to replace the 9V batteries. First an explanation of what I have.

The nominal 12 VDC power is supplied through a combination of solar and 12 V batteries with a charge controller to mediate the power between the solar panel, batteries and the load. The controller can handle a load up to 20 A and it does have over load protection. I'm drawing under 1 A, perhaps 2A for short periods. The charge controller says the load consumes an average of 150 watts/day with a max of 200 watts/day. Because of the solar and batteries, the 12 VDC is actually between 12.5 and 14.5 volts. That is the reason I wanted to use the zener - to limit the voltage but the resistor works too (and is simpler).

The solenoid is a latching solenoid that takes between 9-11 volts to activate with a short pulse. Reversing the polarity of the pulse drives the solenoid in the opposite direction. As suggested by DBingaman I checked the solenoid for diodes and I didn't find any. That may be part of the cause why the system shuts down - the charge controller senses odd voltages and protects the system and shuts down.

As mentioned to open or close the solenoid I need to reverse the polarity every other time. What I'm using is a latching DPDT relay that changes state using a pulse from another controller. The +/- for the solenoid is connected to the poles on the relay and I cross wire the contacts in a way that voltage reverses on the contacts depending on the relay state. The output from that relay contacts is wired to another SPDT relay that is also operated from the same pulse that sends the voltage pulse to the solenoid. So what happens, in theory, is that when the latching relay gets the pulse it changes state and the pulsing relay turns on for the duration of the pulse sending a short pulse to the solenoid, changing polarity every time.

What I think might be happening is the pulsing relay turns on sending voltage to the solenoid and then a few millisecond later, the latching relay changes state, reversing the polarity of the voltage. I'm not sure what happens when the solenoid first gets one voltage and is reversed a short time later but i can imagine there are a few transients. I think these transients are what's tripping the charge controller to shut down the power to the entire load.

So if this is the case, would inserting an RC circuit on the pulse that operates the pulsing relay to delay that activation work? I was thinking of a 100 ohm resistor with a 1000 microfarad electrolytic capacitor which would delay the pulse about 0.1 seconds and give time for the latching relay to change state. Or is this happening due to the absence of the diodes? Or both? If I add the RC circuit would I need a resistor to bleed off the capacitor charge or would the relay coil be enough to do that and if so what size?

Thanks for your help in advance.
 

Harald Kapp

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I checked the solenoid for diodes and I didn't find any.
Can't use any as the latching/unlatching works by reversing the voltage.

Show us a schematic of your wiring, please. Understanding an electric circuit from a verbal description may lead to misunderstanding of the actual circuit.
 
Last edited:

hevans1944

Hop - AC8NS
Jun 21, 2012
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...

Show us a schematic of your wiring, please. Understanding an electric circuit from a verbal description may lead to misunderstanding of the actual circuit.
Absolutely! A picture (electrical schematic) can be worth a thousand words (or more). A properly annotated electrical schematic provides a common means of understanding and discussing the operation of a circuit. I have been guilty of trying to verbally describe circuits, but this should always be done with a schematic diagram in hand, with properly identified parts and parts values, i;e., R1 - 120 ohms, 1/4 watt, metal-film, axial-lead resistor. Sure, you could say "a resistor in series with a 10-volt zener diode" and leave it to the reader to "fill in the blanks," but this forum should not be a contest in obscurity. Say, and illustrate, what you mean up front so no one has to guess;

BTW, a 9V battery operated sprinkler system appears to me to be the height of absurdity, especially with a power-hogging shunt zener diode voltage regulator. Or maybe you have a life-time supply of free 9V batteries laying around. And it sounds like you need a "snubber" circuit across your solenoid coil, to prevent a large switching "spike" from resetting your control system.
 
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