solenoid pick and hold circuit help

Thread Starter

minkey01

Joined Jul 23, 2014
185
Hi. Please excuse me if this is super easy, probably is. Would this attached circuit work for activating a solenoid? The ratings on the solenoid say 24V 33 ohm. The intent of the circuit is to be able to turn on the manual switch and have double the voltage for a short time in order to pull it in and then hold at the lower voltage. Does this look right? What value should the cap be if so?

Thanks!!

question.jpg
 

dl324

Joined Mar 30, 2015
15,439
That idea is unlikely to work. A solenoid has two important voltages. One for actuation, 24V in this case, and one for hold. Hold is unlikely to be 50% of the actuation voltage.

Capacitive voltage doublers are only useful in very low current applications.

There's no voltage doubler in your circuit...
 

Thread Starter

minkey01

Joined Jul 23, 2014
185
That idea is unlikely to work. A solenoid has two important voltages. One for actuation, 24V in this case, and one for hold. Hold is unlikely to be 50% of the actuation voltage.

Capacitive voltage doublers are only useful in very low current applications.

There's no voltage doubler in your circuit...
I was thinking that when the capacitor is charging you would get both 12.5V thus 25V total. After the capacitor is charged you would only get the top 12.5V. I think it would work the first time you flip the switch, but there is no way for the cap to discharge right now. Hmm...

I see a lot of delay circuits out there with the cap to ground. I guess maybe I'm trying to do opposite of that. Delay turn off that bottom voltage.
 

dl324

Joined Mar 30, 2015
15,439
but there is no way for the cap to discharge right now.
There's no way for it to charge either. Assuming the 11.5V source is the same, there would be no voltage across the capacitor; hence, nothing for it to charge to.

If your 11.5V source has the current capacity, you could use a boost regulator.
 

Thread Starter

minkey01

Joined Jul 23, 2014
185
There's no way for it to charge either. Assuming the 11.5V source is the same, there would be no voltage across the capacitor; hence, nothing for it to charge to.

If your 11.5V source has the current capacity, you could use a boost regulator.
I'm sorry for being unclear. There are two separate 11.5V sources.
 

Thread Starter

minkey01

Joined Jul 23, 2014
185
Still no voltage across the cap.

Putting the sources in series might be a solution.
I see now. Ya, this won't work. The cap is + at both ends.

I somehow need both 12.5V supplies in the beginning and then one to turn off after a short time.
 

crutschow

Joined Mar 14, 2008
31,112
Here's a circuit that should do what you want.
It requires a DPDT relay or switch.
It charges the capacitor to the battery voltage with the contact position as shown, and then connects the charged cap in series with the power supply and coil when the contacts go to the opposite position.

Diode D1 provides voltage to the solenoid after the cap has discharged.
I used a Schottky diode to minimize the diode forward drop.

R1 limits the C1 charge current to protect the contacts.

upload_2017-4-18_13-22-42.png
 

Thread Starter

minkey01

Joined Jul 23, 2014
185
Here's a circuit that should do what you want.
It requires a DPDT relay or switch.
It charges the capacitor to the battery voltage with the contact position as shown, and then connects the charged cap in series with the power supply and coil when the contacts go to the opposite position.

Diode D1 provides voltage to the solenoid after the cap has discharged.
I used a Schottky diode to minimize the diode forward drop.

R1 limits the C1 charge current to protect the contacts.

View attachment 124985
Cool. Thanks!

I was looking at these monostable multivibrator (one shot) circuits connected to a relay too. I think either way would work - this or yours. Do you have any examples of these, so I can compare? Most examples I see have a momentary button. I'd like to use a regular switch that will be left on and have the pulse only at the beginning.
 

Thread Starter

minkey01

Joined Jul 23, 2014
185
non-retriggerable monostable multivibrator (one shot)

that's what i'd like to take a look at. if anyone has any example circuits. figuring out the name was half the battle! lol
 

djsfantasi

Joined Apr 11, 2010
8,652
Have you found the hold in voltage from the datasheet!! As someone has said, it is unlikely to be 50% of the pull in voltage. I think you going to need two power source, one supplying the hold in voltage and a second source equal to the difference between the pull in voltage and the hold on voltage.

Then, use a circuit that activates or bypasses this second circuit.

This is a lot of work and parts. Why do you want to do this ?
 

crutschow

Joined Mar 14, 2008
31,112
As someone has said, it is unlikely to be 50% of the pull in voltage
I think that's not usually true.
Some articles I've read on relays and solenoids indicate that the holding voltage/current is typically less than half of the pull-in voltage/current.
So I think holding the solenoid at half its voltage rating should be okay with the volt doubling circuit to pull it in.
 
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