Latching relay with a timer?

[MountainBiker]

Is there such a thing?

I want to set up a circuit to shut off my electric radiator fans for water crossings, as well as being able to force them on. I want the fans to automatically return to normal operation after about 5-8 minutes, so I was thinking I could use a momentary switch and some kind of latching relay with a timer built in. Does such a relay exist?

I plan to use the momentary DPDT fan switch from these guys:
http://4x4mods.com/Product/Jeep/Rockerswitches/rockerswitch40.html

 

[njtaco]

The first thing that comes to mind is a timer for an ADA (handicap) door operator. I'll look at work for a manual tomorrow...and post up if I think it would apply here.

 

[PhulesAU]

Check with your local police car equipment installer, ask them about a timer for a shotgun lock. they usually are good for about 30sec. before you have to hit the button again. this might not be long enough for Ya. If this is for fording, what about a float switch mounted close to the bottom of the radiator? like a bilge pump switch, but backwards?

 

[goodtimes]

http://relays.tycoelectronics.com/datasheets/SSF.pdfhttp://relays.tycoelectronics.com/datasheets/SST.pdf

http://relays.tycoelectronics.com/datasheets/VTM2.pdf

http://relays.tycoelectronics.com/datasheets/VTM2.pdf

http://www.ics-timers.com/op4142.html

There are some others out there....

 

[ntsqd]

Latching relays @ Allied Electrical

 

[MountainBiker]

Latching relays @ Allied Electrical

Thanks! Bouncing around on that site, I found that what I'm looking for is an "off-delay" relay. They are all too expensive for me at >$40.

Instead of an Off-Delay relay, I'll just use a standard relay. To make sure I turn things back to normal operation, I think I'll use an annoying flashing LED next to the switch, or in the dash somewhere. That should remind me!

 

[nvprospector]

The following is just a basic idea and can be improved. What you want to do is very easy with a relay, I just need to get ready for work . If I have time, I can come up with a more complete solution. For right now you need to live with my hyjack.

Later

Taken from The12Volt.com
Constant to Momentary Output

The capacitor allows the coil of the relay to be energized until the capacitor stores a charge, thus de-energizing the coil. The resistor bleeds off the charge of the capacitor when positive voltage is removed from the other side of the coil. You can increase the output time by simply changing the value of the capacitor. This one will give you about a 1/2 second output.

View attachment 6598

 

[MountainBiker]

The following is just a basic idea and can be improved. What you want to do is very easy with a relay, I just need to get ready for work . If I have time, I can come up with a more complete solution. For right now you need to live with my hyjack.

Later

Taken from The12Volt.com
Constant to Momentary Output

The capacitor allows the coil of the relay to be energized until the capacitor stores a charge, thus de-energizing the coil. The resistor bleeds off the charge of the capacitor when positive voltage is removed from the other side of the coil. You can increase the output time by simply changing the value of the capacitor. This one will give you about a 1/2 second output.

View attachment 6598

I like that! What size capacitor would I need to get about 5-10 minutes?

 

[nvprospector]

I like that! What size capacitor would I need to get about 5-10 minutes?

Sorry about that, I forgot that you where look for a large amount of time. For that amount of time, the capacitor would have to be very big. Then you will have to add a resistor and calculate the total resistance of the coil in the relay and the resistor to use, along with the capacitor size to determine total discharge rate. You might be able to get away with a 1000uF capacitor and play with some very big resistors. Using a 555 timer is a lot better way to go.

What I ended up doing is using a 555 timer IC to energize the relay coil. This is the best example I can find. I had a hard drive crash and lost a lot of data and I am trying to muddle though a bunch of backup disks right now. When I do find the circuit I built I will post it. The attached circuit works well and only cost about $6 and I have installed the attached circuit on a few of my friends rigs.

Pinout of a 555 timer
View attachment 6652

Circuit of a simple 555 timer
View attachment 6649