My reverse osmosis water filter solenoid valve broke so I ordered a replacement from another manufacturer. Inspecting the broken one closer I noticed there's an electrical component soldered across both electrodes (image).

What is it? The replacement valve does not come with it, do I need to add one? If so, what are the specs for this component?

The solenoid with the attached component is 24v DC 7w, the replacement is 24v DC 4.8w

Thank you,

Electric dummie

 

It appears to be a diode to suppress the inductive voltage transient when the solenoid is turned off, so you need to add it (be sure to observe the polarity band).
Without that, the electronic driver for the solenoid will likely get zapped.

 

Most likely there is a part number written on it, probably one of the 1N4xxxx series of diodes which are widely used. If you cut it off you will probably be able to read it. If you carefully unsolder it you may be able to reuse it but you’d need to check if it still works first. It should conduct current in the direction from the blank end to the ringed end but not in the other direction. Simple way to test is with an automotive bulb and a 9 or 12 volt battery in series with the diode which should only light up with the diode in one direction

 

To answer your question about adding it; did you get the exact replacement part from the manufacturer, or something generic or made by a 3rd party online somewhere? I would be tempted to add a diode, there is no harm in adding it and it might be needed. As mentioned above, it might save the controller that turns the valve on and off. When a solenoid is suddenly turned off, there is a very large voltage spike. The diode provides a path for that energy to dissipate harmlessly. Without the diode, the controller would have to deal with the spike. The controller might be designed to handle it, and it might not be, we don't know without more info.

 

Awesome! Makes sense.

There are a few different 24v power supplies that can be used with this valve, from a direct wall outlet power supply to dedicated computer controlled modules. Anyway, I wouldn't want to rely on the power supply to be able to take the spike, so I'm going to add the diode to be safe.

I removed the diode and tested it but its dead, so I cant re-use it and need to purchase a new one. I just need to know which one I need. I was able to read IN400.. on this one but the last digit is faded out (see images).

Looking for a replacement I found that there are (apparently) only for different digits that would fit; either 1, 2, 4 or 5. For 100, 200, 400 and 500 volts, respectively (see image) (https://leeselectronic.com/en/search?controller=search&s=DIODE+1N400).

Which one would it be? My (dummy) guess would be 1 (100v) because the house voltage is 110v which would be the highest spike possible.

Thank you guys, I'm almost there.

 

Which one would it be? My (dummy) guess would be 1 (100v) because the house voltage is 110v which would be the highest spike possible.

The should be fine.
The highest voltage it will see would be the DC supply voltage, which you state is 24V.
The inductive spike is in the reverse direction, so the driver transient voltage is clamped to the supply voltage plus the diode forward drop (about 0.7v).

 

I removed the diode and tested it but its dead, so I cant re-use it

Just to confirm, you didn't use the resistance scale on a modern VOM by any chance?
They cannot test diodes.
Also you may already be aware but the valve voltage supply polarity is now important when a diode is fitted.
The service supply does not enter into the diode selection if it is LV DC fed.

 

Looks like 1N4001 diode to me.

 

The should be fine.
The highest voltage it will see would be the DC supply voltage, which you state is 24V.
The inductive spike is in the reverse direction, so the driver transient voltage is clamped to the supply voltage plus the diode forward drop (about 0.7v).

Got it. I found a 50v diode, is it ok?

https://www.amazon.com/MCIGICM-Rect...x=diode+1n4001+rectifier+100v,aps,187&sr=8-10

 

Just to confirm, you didn't use the resistance scale on a modern VOM by any chance?
They cannot test diodes.
Also you may already be aware but the valve voltage supply polarity is now important when a diode is fitted.
The service supply does not enter into the diode selection if it is LV DC fed.

I was made aware of the polarity here and I don't think I screwed up, but I'm going to get a new one just to make sure. Its too cheap to waste any more of your guys time. Just want to make sure I get the right one.

 

I always pick up the 1N007, covers all eventualities instead of being restricted/limited by voltage.

 

Bringing this thread back to life...

So, I got the diodes, now which way should I solder them to the solenoid valve contacts? Can't tell which is anode or cathode, no markings on them.

I tested and the valve works wired either way so maybe it doesnt matter? Just to be sure because I know the diode has to have the white ring soldered to the cathode and I dont want to get it wrong.

Thanks.

 

Your photo of the new diodes does show the silver ring at one end which is the cathode. Your original post shows the ring on the failed diode too. To keep things the same I’d solder the diode in the same direction as the original photo but it’s essential to connect the positive power terminal to the cathode.
This may sound counter intuitive but you are not looking for the diode to conduct when the solenoid is activated, it’s there to catch the reverse voltage spike when the solenoid is deactivated.

 

Its a new solenoid valve and I just wanted to make sure copying the diode direction from the previous one is correct. I believe it should be, but how can I make sure?

 

Its a new solenoid valve and I just wanted to make sure copying the diode direction from the previous one is correct. I believe it should be, but how can I make sure?

If I understand you correctly, the solenoid you have bought does work in both directions. When you activate it, you need to know or check which terminal is positive and which terminal is negative. Whichever way you have connected it, you need the cathode end of the diode (with the silver end) to be connected to the positive terminal.

 

The cathode goes to the more positive voltage. This way, the diode is reversed biased, i.e. not conducting.

 

Polarity of the diode was my very first concern. It MUST be connected correctly or it can damage the controller. Which brings me to another point I wanted to cover - the controller. You say the solenoid went bad. Maybe so. Maybe not so. Maybe the controller went bad.

I fixed a sprinkler system that had a dead circuit. I replaced the solenoid because I was seeing 24VAC control voltage at the valve. When I put the new solenoid in I got the same result - nothing worked. It turned out to be a bad wire. Corroded connection so corroded that it couldn't carry enough current to activate the valve. In that case it was just the wire, which I replaced the whole run. Someone made an underground splice using butt crimp splices and wrapped it in electrical tape. Moisture worked its way into the splices and began corroding the connection.

It could have been a controller issue. That same controller had just a few years earlier failed. They were going to throw it away and replace it with a new $170 (US) controller. I said "let me have a look at it first". Upon taking it apart I found fractured solder joints on the main controller selector switch. Re-soldered it and it's still in service to this day.

The point is to fully diagnose the problem before you start throwing money at it.

 

Got it.

Yes, it works both ways so I can solder it either way I guess, just have to check the power cable to know which is + to solder the diode cathode side to the same contact.

Thanks again.

 

Polarity of the diode was my very first concern. It MUST be connected correctly or it can damage the controller. Which brings me to another point I wanted to cover - the controller. You say the solenoid went bad. Maybe so. Maybe not so. Maybe the controller went bad.

I fixed a sprinkler system that had a dead circuit. I replaced the solenoid because I was seeing 24VAC control voltage at the valve. When I put the new solenoid in I got the same result - nothing worked. It turned out to be a bad wire. Corroded connection so corroded that it couldn't carry enough current to activate the valve. In that case it was just the wire, which I replaced the whole run. Someone made an underground splice using butt crimp splices and wrapped it in electrical tape. Moisture worked its way into the splices and began corroding the connection.

It could have been a controller issue. That same controller had just a few years earlier failed. They were going to throw it away and replace it with a new $170 (US) controller. I said "let me have a look at it first". Upon taking it apart I found fractured solder joints on the main controller selector switch. Re-soldered it and it's still in service to this day.

The point is to fully diagnose the problem before you start throwing money at it.

The old check twice cut once.

Corrosion is a big factor here, the solenoid is in the same compartment (cabinet) as a huge amount of circulating saltwater. Even if its safe from splashes its still full of sea air down there which can corrode over time. Number one complaint for solenoid valves from saltwater aquarium customers is short life span.

 

Use an ohm meter to check the solenoid and if it reads the same low resistance in both directions then it may be a shorted diode, or possibly an open diode. With the valve disconnected check if the voltage is AC or DC.