Help in a project - how do I control a pulsed latching solenoid?

Telecommando: You may need to experiment to find a suitable capacitor value, but this should work:

I would add a flyback diode, anode to ground, cathode to common switch terminal - otherwise you will get arcing in the switch. Make sure you get a break-before-make switch,

The capacitor doesn't need to be non-polarized if its value is high enough to make the circuit overdamped, which it needs to be anyway in order to get a good current reversal.

works like a charm!

The only problem I have now is that I need a 2-state switch. The one I was going to use is a simple foot switch, 2 leads, on-off only...

Telecommando, if you have a similar magic solution with a 2-lead on-off switch, that would be great.

But the relay will consume power. I need the whole system to be battery operated get good battery life. So I can only tolerate power consumption when pulsing the solenoid.

What voltage are you using to pulse the solenoid? Do you know how much current it takes? is the foot switch a momentary type (in which case, can you tolerate a small current draw while the foot switch is held down), or is it push on/push off?

This is the switch I use now. It is very low profile and is easy to push with your foot.

But currently, I use a normally closed solenoid which needs constant power to be kept open. So I have a large 7000mah battery or a 110/220 -> 12VDC power supply.

The solenoid take about 200-300ma to operate. The switching will be mostly slow (10-30 seconds apart) but sometimes, it should be able to operate at 1-5Hz.

I built a small prototype circuit with a 9V battery and a 10V 3300uF capacitor. It works really well even at 2-3Hz switching.

But as I said, I need a circuit with an on-off switch...

szangvil: I built a small prototype circuit with a 9V battery and a 10V 3300uF capacitor. It works really well even at 2-3Hz switching.

But as I said, I need a circuit with an on-off switch...

For that simple circuit you need to use either one SPDT switch or two SPST switches. Can't think of any other solution for your manual switching needs.

Lefty

This added complexity with single coil latching relays that require voltage reversal is why I prefer to use G6SK-2-DC5 relays. http://www.components.omron.com/components/web/PDFLIB.nsf/0/3AB780E03885359085257201007DD68A/$file/G6S_1012.pdf

http://pwillard.com/?p=148

Telecommando: Also, I don't think there will be much of an inductive kick in this type of circuit so a flyback diode should be unnecessary.

The switch changeover won't be instant. There will be the usual large inductive kick-back when the upper contact opens, which is likely to cause arcing until the lower contact closes. How serious it is depends on the self-capacitance of the solenoid.

szangvil: I built a small prototype circuit with a 9V battery and a 10V 3300uF capacitor. It works really well even at 2-3Hz switching.

But as I said, I need a circuit with an on-off switch...

I presume you mean without an on-off switch. But you haven't fully answered my questions in reply #14 yet.

dc42,

What voltage are you using to pulse the solenoid? Do you know how much current it takes?

It's rated at 6VDC and 250ma.

is the foot switch a momentary type (in which case, can you tolerate a small current draw while the foot switch is held down), or is it push on/push off?

It's momentary type. As long as I keep it pressed, the circuit is closed. How small of a current draw do you suggest? A few micro amps is fine but if it's a few milli amps, that would greatly reduce battery life making this project not very practical.

Telecommando:

dc42: There will be the usual large inductive kick-back when the upper contact opens,

Inductive kickback from what exactly? When the capacitor is fully charged, there will be no current flowing in the coil. Opening the switch contact at that time will cause no arcing since there is no magnetic field being generated. You're likely thinking about a continuously held coil, which has current constantly flowing into it (and an associated magnetic field), but that's not the case here.

That's a good point. There will only be inductive kickback if the switch is pressed and released very quickly, before the capacitor is fully charged. There will be a small amount of inductive kickback when the switch first closes and is bouncing; but the current won't have built up much by then, so the self-capacitance of the solenoid will probably take care of it.

Telecommando, yes, I mean an on-off switch (to wires only). If that can be done, it will make my live much easier. I have no real background in circuit design (I'm a mechanical engineer), so I don't think I can come up with a solution myself :(

szangvil:
It’s momentary type. As long as I keep it pressed, the circuit is closed. How small of a current draw do you suggest? A few micro amps is fine but if it’s a few milli amps, that would greatly reduce battery life making this project not very practical.

Is 130uA while the foot switch is held down OK? If so, then attached should work. The input RC network debounces the switch, the MCP1407 provides drive to the mosfets, and the mosfets act like the changeover switch. I’ve included the two 4.7 ohm resistors to reduce the shoot-through current while the mosfets are switching.

dc42, 130uA is acceptable.

I don't have the parts on hand. Will give it a try as soon as I get them.

Thanks.

Docedison: have you ever heard of Gal? They make controllers and clocks for irrigation and pilot valves that are bi-stable latching solenoids. The method I used was to charge a 4700 uF cap to 12V and dump it into a solenoid with a DPDT relay and a Mosfet. The relay for polarity reversal and the Mosfet for switching the load. I could drive a solenoid through 300 meters of 16 Ga wire at 10 bars of pressure.

I'd very much like to see you circuit Docedison as I'm in the same boat. Trying to control 4 Hunter latching solenoids (9V) and a bit lost in the process :( Not trying to achieve 300mts distance as the solenoid will be very close to the controller (Arduino based, code written by me). The controller and the solenoids are battery operated (12V 5Ah) and it's solar powered by a 10W panel. TIA, Pedro

[EDIT] Was thinking about using this DPDT relay: http://www.ebay.com/itm/1-x-Relay-5V-1-25A-2-Form-C-DPDT-2-Contacts-Free-Shipping-/180966617444?pt=LH_DefaultDomain_0&hash=item2a22737164 It has a 5V coil, perfect for my needs.