Capacitor Voltage Ratings

I am trying setup one of these circuits shown in the special applications relay section of the board.

https://www.the12volt.com/relays/page5.asp#pts

I set this circuit up just as shown with the exception of the capacitor. I did have nor could I get a 10k uf capacitor. The guy at the supply house where I got the rest of the parts said that 10k uf was not a way of noting the value of the capacitor. Anyways, I used a 220 uf 16volt Capacitor in my setup. When I applied power to the input of the circuit the relay did not stay closed for ANY amount of time, at least not any length of time detectable by the human ear (via the tone of my fluke meter). Does my problem lie in the Capacitor I am using? How long of a hold should I get off of the given capacitor rating in this diagram?

I have been looking for a capacitor of a 10k uf rating in the radio shack catalog. They only carry capacitors rated at 35 and 50 volts in the store, but they do offer RSU special orders for Capacitors that are rated at 16 volts. Does the voltage rating matter when using them in a 12 volt situation? If so, is 16 volt the rating to use? Once again, the highest value of (Electrolytic) Capacitor that is in the radio shack catalog is 4700 uf at any voltage. ATTENTION MODERATORS! Maybe its time for a basics page on Capacitors!!

lastly, are resistors directional? Or do they work no matter which direction they are inserted in the circuit?

First things first.  Resistors are NOT directional.  As far as capacitor voltages are concerned, it is ok to use 35 volt or 50 volt capacitors in automotive applications.  And remember electrolytic type capacitors are directional, they have a positive and a negative.  There are non-polarized electrolytics out there, but are more commonly seen in crossover set-ups, etc.

Avoid special ordering parts thru radio shack.  They are too expensive!  I use Digi-Key, All Electronics, Parts Express, and a host of others.

Thanks

That partially answered my questions. I figured that Resistors were non-directional but had no way of knowing for sure.

In regards to Capacitor voltages, by using higher voltages that does not change uf value?

So any ideas as to why the circuit I mentioned didn't stayed closed for any amount of time?

Does a 10k uf cap. exist?

So is there a formula that would give me a rough idea of how long a given capacitance rating will hold a relay coil?

This diagram https://www.the12volt.com/relays/page5.asp#ctm seems to say that a 1000 uf (1k uf) will hold a relay coil for 1/2 a second. Can I assume from this that a 10,000 uf (10k uf) cap. will hold a relay for 5 seconds?

Thanks in advance

If it were me I would just solder or hold the larger cap in and time it, changing values until I got the exact time I was looking for. Am sure you could use a formula to figure it out but I assume you dont have a way to measure the inductance of your relay coil to plug into the formula either, not to mention just experimenting will probably be easier/faster.

Thanks Toru

I get the feeling that pretty much no one even understands capacitors on this board much less has any practical experience with them. I come to this conclusion after reading through all the posts on large caps used for amps and the confusing myths that float around about those. The 10,000uf cap. that is specified in the diagram I originally sited in this thread reinforces my thoughts about the knowledge of caps. A cap of that size in the micro farad range is not readily available unless you want to try to order one from one of the large suppliers and even then you have wade through pages and pages of parts to find the right one. I am going to try a 4700uf cap. and see what that does for me. I don't need a fast recovery rate for this circuit, in fact it doesn't need to recover until the next time I start my truck, but I do want it to latch the relay for at least a second or two. Which be long enough for me to push the button and then reach over and put the key in the ignition and turn it. I will let you know it goes.

THanks