I'm an engineer but just the mechanical kind... Also, this is my first post! =D

Background:

I'm setting up a simple flow control system for my aquarium with a set of solenoids to direct the water flow as it leaves the pump.
I currently have 2x 24v DC latching solenoid valves activated by an optocoupled relay module driven by a raspberry pi. The relays are actuated by the pi's onboard 3.3v supply and they close the 24v line to the DC solenoids. I have a single 24v 2A wall-wart powering the whole system. The pi gets 5vout of a voltage converter which is wired in parallel to the normally open 24v line going to the switch side of the relays.

Problem:
I managed to fry both solenoids. I'm an idiot. I know.
What I don't know is why this happened. Before wiring the solenoids to the relays, I manually tested both of them with a DC 24v 0.6A wall-wart and they worked fine, even at constant load. The issues only arose when I began using the 2A supply with the relays. When the relays were activated (manually with jumpers but with the pi still wired up), nothing apparent happened on the solenoid side. The relays definitely closed, but the solenoids didn't move. No smoking, no vibrating, no nothing. BUT when I left the relays closed for more than ~3 seconds, the power supply would reset. I'm guessing the wall-wart has some sort of current protection. Bless the EE gods.
So I unhooked the relay circuit from the solenoids and retried the 24v 0.6 amp power supply that I was using for initial testing. They both worked! Needless to say, I was getting very confused. So, I reconnected the relay circuit to the solenoids and retried that with the 2A supply. Again, nothing but the power supply resetting when the load was constant. I tried this maybe 5 times with no better result. So again, I unhooked the relays and tried with the 0.6A supply. This time, the relays didn't do anything. I managed to fry them somehow during this round.

Best Guess:
I looked it up and turns out I ought to be using a diode across the solenoid. Duh. I went ahead and wired this up but it's obviously too little too late.

Question:
I've already got a new set of solenoids on the way to replace the fried ones, but before I fry another set, I wanted to get an opinion on why this happened and what I can do to prevent it. Is the lack of diode really the only problem? Or should I try current limiting the solenoids somehow?

Thanks!!

 

If you applied no more than the rated voltage, then you shouldn't have to limit the current, unless the solenoids are intermittent type and not rated for 100% duty-cycle.

The lack of diodes may have caused the inductive kickback voltage to go so high that it broke down the solenoid insulation, causing them to short.

 

I currently have 2x 24v DC latching solenoid valves

hi Nik,
Do you have a type number or web link for these solenoids, they maybe designed for a short current pulse operation, not continuously powered.
E

 

This time, the relays didn't do anything. I managed to fry them somehow during this round.

So the relays and the solenoids died?

 

Can you share more info on the power supplies? Part numbers, datasheets, pictures of the labels? Any chance one was an AC transformer and the other a DC supply?

 

Normally DC latching solenoids require a pulse to operate and a reverse pulse to release.
Do you have it set up this way?
Max.

 

Another possibility is that the 24 volt 2 amp power supply is unregulated. If so it's output will be higher than 24 volts if it is driving a light load.

Les.

 

Thanks all for the replies!!

here is the best I found for the datasheet on the solenoid:
http://galconc.com/product/solenoid/

Looking over this, I see that the solenoids are rated at 18V not 24. (Amazon page was inaccurate...). I have since changed the power supply to an 18V 1.5A wall-wart.

This is the wall-wart I'm using:
https://www.amazon.com/Excelity®-Charger-Supply-Switching-Adapter/dp/B01KXX32SA

I just got my replacement solenoids and I am still having the same problem of the power supply resetting despite adding diodes across both solenoids. I'm using 2x 1n4007 wired across both because that's what I had on hand. Not sure if that is an appropriate diode or not but what I see online is that the 1n4xxx series is generally recommended for this. I also tried a 1n5xxx series with no luck.

Interesting to note that when I connect the solenoids directly to the 24V 0.6A power supply, the solenoids do activate. But when I am using the 18V 1.5A supply with diode protection, no activation is observed. The power supply just resets after a second or two.

I've also tried adding a resistor in series with the solenoid. This prevents the power supply from resetting but still no activation from the solenoid... I tried a range of resistors from 10ohm to 2k. The 10ohm literally caught fire. None of them made the solenoid activate.


Any ideas?

 

Those appear to be latching solenoids so they need a brief energizing pulse they have a 3Ω resistance so it requires a very brief High current pulse.
You may be getting collapse of the P.S. if it does not have the capacity.
If you keep the power on too long, you will fry them.
Max.

 

The solenoid coil resistance is only 3Ω so the current at 18V is 6A (you need to learn Ohms' law) which is why your 1.5A supply is complaining.
And the solenoid's minimum pulse time to actuate is 20-100ms so I would suggest applying power for no more than a second.
The high-current pulse could be generated from a large capacitor (likely about 10,000μF) charged to 18-24V and then connected across the coil.

Do you have the 2-wire version of the solenoid?
If so, you need to reverse the direction of the pulse to turn it on or off.
That typically is done with some type of bridge connection.

 

It sounds like you need a CDU to activate the solenoids.

 

It sounds like you need a CDU to activate the solenoids.

I'll bite.
What's a CDU?

 

I currently have 2x 24v DC latching solenoid valves activated by an optocoupled relay module

Post a schematic of that relay module.
Is there more than one module?

 

"What's a CDU?"
I have no idea but here is the circuit of the module I sell to fix the problem:

 

The specs say 6 to 18 volts for the coil. I would try operating near the minimum, which would still require something in excess of 2 amperes.

These valves are invariably pilot operated - a small orifice controlled by the solenoid allows flow that controls the main diaphragm. This is what permits control of a large flow with comparatively little power and allows the latching behavior. It also means they will not open without some minimum pressure. Typically the solenoid plunger has the elastomer "stopper" for the small orifice on the end. Everything else is contained in the main valve assembly.

Switch mode power supplies typically have relatively small capacitance at the output and reasonably fast-acting overcurrent detection that will shut down the supply in the event of gross overcurrent. Most will attempt to restart then shut down again if the overload still exists, repeating indefinitely. Crude supplies don't limit current - they just burn up or blow a fuse on prolonged overload.

 

Thanks all for the replies!!

here is the best I found for the datasheet on the solenoid:
http://galconc.com/product/solenoid/

Looking over this, I see that the solenoids are rated at 18V not 24. (Amazon page was inaccurate...). I have since changed the power supply to an 18V 1.5A wall-wart.

This is the wall-wart I'm using:
https://www.amazon.com/Excelity®-Charger-Supply-Switching-Adapter/dp/B01KXX32SA

I just got my replacement solenoids and I am still having the same problem of the power supply resetting despite adding diodes across both solenoids. I'm using 2x 1n4007 wired across both because that's what I had on hand. Not sure if that is an appropriate diode or not but what I see online is that the 1n4xxx series is generally recommended for this. I also tried a 1n5xxx series with no luck.

Interesting to note that when I connect the solenoids directly to the 24V 0.6A power supply, the solenoids do activate. But when I am using the 18V 1.5A supply with diode protection, no activation is observed. The power supply just resets after a second or two.

I've also tried adding a resistor in series with the solenoid. This prevents the power supply from resetting but still no activation from the solenoid... I tried a range of resistors from 10ohm to 2k. The 10ohm literally caught fire. None of them made the solenoid activate.


Any ideas?

A solenoid is a coil is a short. The reason the power-supply is resetting is it is trying to protect itself from frying-- eg too much current is going through it.

You need to understand your solenoid specs, your power-supply specs, and how to control voltage and current in such a way as to utilize the solenoids properly.... Glad you're asking here, wish you'd asked before you fried them

 

I have provided the answer with the circuit above. I have sold over 15,000 modules to protect coils and power supplies with the same features and characteristics as described by the poster.
No-one has provided any sort of answer or resolution or circuit for this type of problem as it is way over the head of all those involved.
That's the reason why I normally don't provide free advise or circuitry.

 

That's the reason why I normally don't provide free advise or circuitry.

So why are you being so magnanimous here?

 

I have two wives and I support both of them with $500 per week for food and clothes.

Do you think that is big o' me?

 

I have two wives and I support both of them with $500 per week

Anyone with two wives has my fullest sympathy.
And supporting both on $500 per week is a miracle.