Momentary push button DPDT switch with alternate action

Visitor said:

So why not replace the momentary push button with a push-on / push-off button and eliminate the latching relay and all the rest?

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That came up in post #6.

ak

AnalogKid said:

That came up in post #6.

ak

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Not with any analysis of the problem to be solved.

AnalogKid said:

With that extra detail in post #15 - ! (tsk), it is clear why an H-bridge was in the discussion.

But ...

If it is "latching" solenoid, why does the button have to be held down continuously? Or are you saying that *changing* to a latching solenoid removed the continuous requirement - ?

And to be clear, both the switch and the solenoid are out at the nozzle, and the only thing running up and down the hose is continuous +12 Vdc?

ak

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Yes, changing to a latching relay removed the need to hold down the button continuously. That is the main gist of his requirement.

Re the switch and the solenoid ... the switch is definitely out at the nozzle ... but I don't know for certain about the solenoid ... I had the impression it was actually in the nozzle. I recall him saying the nozzle manufacturer supplied the latching solenoid.

... so yes, I believe it is just a continuous 12 volts running out to the nozzle.

Is it a requirement that if the hose is dropped that it must turn off? A kind of dead mans handle? If so, modifying it would be illegal. Might be worth checking.

Mike.

Visitor said:

So let's go back to the beginning here, and what I think the story may be.

The nozzle requires 12 volts to activate it. Originally, it was operated via a momentary push button switch. Press the button, and it's on, release the button and it's off. This seems like the likely scenario.

So why not replace the momentary push button with a push-on / push-off button and eliminate the latching relay and all the rest? That seems like a needlessly complex and potentially unreliable solution that depends on using a switch that doesn't exist.

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Originally, it was operated via a momentary push button switch.

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Nope, originally it had a latching push button switch ... so you could click it on ... concentrate on fighting the fire ... then click it off to stop it.

What he was trying to get away from was having someone run out of water ... leave the switch ON ... and burn out the solenoid.

A latching solenoid was his solution to the problem ... and in the circumstances, to me it makes sense.

And on top of that, the nozzle manufacturer supplies them as an option. (I don't know what they recommend for a switch though before someone asks me that )

Apparently they are expensive ... not to mention that after refilling the tank and going back to the fire, he can't squirt water. It's not just inconvenient, it's dangerous.

He claimed that the water flow keeps the solenoid cool and prevents this ... but of course when they run out of water and in the likely frenetic running around in the thick of a fire .... it would be easy to forget to check.

So why not replace the momentary push button with a push-on / push-off button and eliminate the latching relay and all the rest? That seems like a needlessly complex and potentially unreliable solution that depends on using a switch that doesn't exist.

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See above.

First I heard of all this was yesterday when I got a call about it.

He was looking for help because he'd been told the only way to achieve his aim was to use a H-Bridge and and Arduino!!!

Now that is what I'd call a needlessly complex and potentially unreliable solution ... and I'd add dangerous and foolhardy even.

Pommie said:

Is it a requirement that if the hose is dropped that it must turn off? A kind of dead mans handle? If so, modifying it would be illegal. Might be worth checking.

Mike.

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Haha, I have no idea. Bear in mind, this is a fire fighting nozzle designed to be held with one hand while leaning out the window of a ute while driving around the edges of a fire. It's not some two man fire hose setup.

Western said:

Haha, I have no idea. Bear in mind, this is a fire fighting nozzle designed to be held with one hand while leaning out the window of a ute while driving around the edges of a fire. It's not some two man fire hose setup.

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I've seen these used here in Australia. Are you sure the button/switch isn't opperating the pump instead of opening the nozzle? Could the pump run continuous and a garden type trigger nozzel be used to control flow?

Mike.

Here is one version of what was requested. (Press for on, off when released, Press for reverse, off when released ) repeat
LEDs indicate next direction and current direction, LED changes on button release.
See comments on YouTube comments.

And here is another version described - a press for On, Off, Rev, Off (repeat)
I left the reverse biased diodes across the coils off. Be sure to add them.
Use 4000-series logic (cd4013 dual flip flop) for 12V circuits

gophert said:

Here is one version of what was requested. (Press for on, off when released, Press for reverse, off when released ) repeat
LEDs indicate next direction and current direction, LED changes on button release.
See comments on YouTube comments.

Click to expand...

Wow, awesome circuits ... thanks Gophert. The leds would be useful to help prevent problems if the system runs out of water too.

And small enough to bury in silicone for waterproofing.

Certainly beats a H-bridge and an Arduino.

I've been waiting for the guy to message through more of the details he promised ... but nothing today so far.


After all your efforts, I'm not sure I'm game to put up my thoughts ... but here goes anyway. Not quite as high tech.

Obviously I need to know what current flow the solenoid requires to latch, to determine the capacitance ... then adjust the discharge resistor to get it to discharge quickly enough to allow another press ... without having too much residual current through the solenoid coil.

I usually try to set the switch denounce capacitor resistor to
0.05 seconds = farads x resistance.
Or,
50000 uSeconds = uF x ohms.
Hard to press twice in 0.1seconds and you have a pretty bad switch if it is still bouncing that long. If it is a large switch, it is hard to press twice within 0.15 seconds so you can increase the cap size if you do have bounce issues. Depending on the internals (electromechanical or semiconductor logic) some latching relays are going to be more sensitive to switch bounce than others.