DPDT switch for Solenoid

[grayocean]

I'm trying to make a circuit that is hooked up to a single button and a solenoid. Press the button and the circuit fires a solenoid the left, press it again and it fires the solenoid to the right, press it again and it fires the solenoid to the left, hit the button again and the solenoid fires to the right, …you get the idea.

What I've got is a D flip-flop, hooked up to two one shot timer circuits, which in turn are hooked up to a relay bank. I’m just a Mech and can’t figure out why it won’t work well. Basically it seems to work fine until the solenoid is integrated and then there seems to be some ground bounce/ voltage spike problems, that cause the flip-flop to flip when the solenoid fires.

I've added 5000uF of capacitance to try to stabilize the 9VDC line voltage but no success. I can’t add a diode across the solenoid to shunt any voltage spike to ground because the voltage flips with each cycle.

Does anybody have any ideas as to what it might be?

Lucas

 

[imok2]

This may be of some help:

http://www.automatictiming.com/pages_div/alternatingrelaysandcontrollers.html

 

[TurboXS]

As you have suggested, it is likely that the back emf of the solenoid is placing a voltage spike onto the power supply and causing your logic to switch. The large capacitance you have added will help but as its ESR is likely to be high (relatively) it won't be as effective with fast transients such as the back emf of the solenoid.

You can use 2 zeners in series, in opposing directions to suppress the back emf.

In addition you can add some power line voltage spike suppression and filtering. The voltage spike suppression can be a zener/transient suppressor at say 12V. The power supply filter can be a small series resistance before your capacitor plus a ceramic capacitor in parallel to your capacitor to help suppress the high frequency component.

Alternatively you can use a toggle relay such as;

http://www.controlsupply.net/a4757.htm

I suspect you should be able to configure your existing relays to do the same function (i.e relays only) but haven't worked out the circuit as yet.

regards
Pete
(TurboXS)

 

[ScottI2R]

TURBO!,
Hot Dog! You just provided me with something I need to solve (prevent) an operator error at work that wrecks tooling! I hadn't gotten a chance to sit down and draw it up but this unit coupled with another relay spdt for interlock of the pushbutton is THE TICKET!!!!!!! Now, it was well worth it to stay up and train the new pup, and surf this increasingly more valuble forum!
Thanks a million!

Scott
(Soon I shall once again find favor in my bosses eyes!)

In a hundred years, it isn't going to matter anyway.

 

[buzzp]

They also make bi-directional zeners so only one would be necessary instead of two. Alternately, an RC circuit would work as well.
Remember that whatever you use will affect the operate and release time of the solenoid. To what degree depends on what you use. If timing is critical then make sure you look into this.

 

[elfgriper]

Gray,
It looks like you might be overwelming the 9v battery. You may have luck isolating the 9v drive from the 9v logic circuit. Try adding a diode from the battery to a Cap then to your logic circuit (Connected between diode and cap). Then take the 9v battery straight to two relays driven by your one shots, connect the commons to the soleniod.Connect the NC contacts to ground and the NO to the 9v battery. With a litte luck when the battery voltage goes down the diode will be rvs bias and at this point the cap will hold the voltage for the duration of the spike time.
elf

 

[grayocean]

Thanks all, two zeners across the solenoid seems to have worked perfect. More testing will be done to make sure it works 999/1000.

funny thing, tring to get this to work I went to UCSD and talked to a circuit prof and a couple of grad students. The prof had no ideas, stating that most people at the university were just theory people and maybe one or two profs at the university might be able to help me, one of which was on sebatical and the other seemed to me to always be in hiding. To be honest the prof did have some ideas, he sugested hooking the ground plane to a large metal object....I'm still not sure is he was with me or not?

 

[IRstuff]

That's a rather sad story ;-(

Even a theoretical prof ought to be able to come up with a theoretical solution...

TTFN

 

[buzzp]

I don't think he meant that to mess with you. Large ground planes have their place they are also great at dissipating junk on your lines. However, in your case the large ground plane probably would not have helped - at best it would have been a band-aid to the real solution.