Hi Guys I'm trying to do a simple project . Im using a solenoid 12 VDC and max current is >3 A . I would like to include a capacitor so that the capcitor stores the charge and operates the solenoid for 3-4 sec even if the power supply is cut off . Can any one help me with a circuit diagram and values ?

 

and max current is >3 A

What does this mean?

 

Sorry its less than 3 A current .

 

Is it a one time project?
Can you find out at what voltage the Solenoid drops out?
The one can work out a rough idea of the capacitor required.

 

Is it a one time project?
Can you find out at what voltage the Solenoid drops out?
The one can work out a rough idea of the capacitor required.

It is 0.95V.

 

hi Ernest,
You will need a very big capacitor in the order Farads, for a 3 sec hold on.
What is the solenoid used for.?
E

 

See

 

See

 

3 amps is a lot of current for a capacitor to provide while maintaining sufficient voltage to hold the solenoid active for 3 to 4 seconds. I've done some work in Naval Power Systems and the sort of cap you'd need is going to be rather large. It all depends on how much voltage the relay needs to hold it active. Without that information I don't think anyone can do better than a guess at what you need. Perhaps a 3 farad SUPER cap may hold sufficient energy to do the trick, but like I said - it's all guess work until we know all the parameters. But they are typically very low voltage. So to get the voltage you'd need you'd have to place a number of them in series to handle the voltage.

 

hi Tony,
A point he should also consider is the required recharge current, I guess his PSU will trip its current limit.
E

 

@ericgibbs Good point. Hadn't thought about what's supplying the 12 volts to begin with.

Sounds to me like the thread starter just wants to keep a solenoid active for a few seconds in the event a power failure occurs. Sometimes an interruption can last just a second or two and keeping the solenoid active may prevent some sort of loss of control.

OR perhaps he wants to send a command to the solenoid and then have it self sustain for that short period of time. Without more details we're just guessing at what may be needed.

I'm SURE there's a solution. Possibly a better solution. But we need to know all the details and the goals.

 

Use Supercapacitor / Ultracapacitor 100F 2.7V:
https://eu.mouser.com/Passive-Compo...s-Ultracapacitors/_/N-5x76s?P=1yftxjrZ1z0x2ud

 

I don't think a 12 V solenoid will hold in all the way down to 1 V. 9 V is more realistic, 8 V if you feel lucky. According to Bordodynov's plot that means three 3 F caps in series.

ak

 

Sorry, I made mistake with voltage in post #12 . Below is link to 12V capacitor.
http://uk.farnell.com/kemet/fs1b505zf/super-capacitor-5f-12v-radial/dp/2777893

 

Interesting part, very expensive.

AND, the only hint about its ESR is at 1 kHz: 4 *ohms*. At three amps, that is the entire 12 V dropped inside the cap, with nothing for the solenoid.

ak

 

20F, 15V, US $110.00
https://www.alibaba.com/product-det...l?spm=a2700.7724857.main07.162.64f410d6ttseZd

 

This calls for a mini-tutorial on reading relay datasheets.

This calls for the datasheet.

ak

 

This calls for the datasheet.

ak

Yes, if you want to do it for the TS. I'd prefer to see him learn something in the process.

 

Did he say "relay" or did I miss something?

 

I would like to include a capacitor so that the capcitor stores the charge and operates the solenoid for 3-4 sec even if the power supply is cut off