diode direction?

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madvan

Member - Posts: 15

Joined: August 21, 2007

Location: United States

Posted: August 21, 2007 at 7:36 PM / IP Logged

Link has diagram of circuit. My question is. Are the diode's in the correct direction to protect the ground inputs? Relay #1,#2 are triggered from a PCM (output ground). When both inputs lose the ground the relay's will sig the 3rd momentary relay thus causing a momentary ground output sig. Approx 1/2 sec. Just want to be shure not to leak + back to PCM.

http://photos.thedieselstop.com/showphoto.php?photo=32449&papass=&sort=1&thecat=998

Thanks

Bill

dualsport

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Joined: September 27, 2005

Location: United States

Posted: August 21, 2007 at 9:37 PM / IP Logged

If what you want to do is protect your two ground signal inputs, you should place the diodes across the coil like you have in the third relay. Putting the diodes in series doesn't do much to limit the voltage spike that occurs when the ground signal tries to abruptly stop the flow of current through the coil.

This setup is going to be constantly drawing power through those first two relays on standby; is that what you wanted? Unless this is only going to be used while the car is running, it'll drain your battery in short order. You might consider using solid state devices to do the controlling; it'll be safer on your input signal and draw negligible power.

madvan

Member - Posts: 15

Joined: August 21, 2007

Location: United States

Posted: August 22, 2007 at 6:29 AM / IP Logged

Yes motor running. I really do not need power relay's. The load is small. I would like to go solid state. Really most interested in the speed of transfer (ms,ns) and length of time for the momentary connection. How can i go electronic? I would have to drop to 5v dc for and IC.

Thanks Bill

madvan

Member - Posts: 15

Joined: August 21, 2007

Location: United States

Posted: August 22, 2007 at 6:49 AM / IP Logged

Cannot edit post. The first 2 relay's, the input grounds are allway's changing (pcm control). When the combo of both lose the signal (ground) it then sets momentary output ground (3rd relay).

Thanks Bill

dualsport

Silver - Posts: 983

Joined: September 27, 2005

Location: United States

Posted: August 22, 2007 at 8:58 AM / IP Logged

If you use a CD4011BCN (available at mouser.com for 45 cents last I checked), it'll run off the car's 12V supply, so you don't need to go to 5V.

It's a NAND gate, so you can just connect your two inputs to it, and whenever either one goes low, the output will go high, and you can use that signal output to drive your output relay pulse circuit.

madvan

Member - Posts: 15

Joined: August 21, 2007

Location: United States

Posted: August 22, 2007 at 9:04 AM / IP Logged

Thoughts were to use JWD-170-7 as per link. Will check data on CD4011BCN.

http://www.mouser.com/search/refine.aspx?Ntt=655-JWD-107-7

Bill

madvan

Member - Posts: 15

Joined: August 21, 2007

Location: United States

Posted: August 22, 2007 at 9:27 AM / IP Logged

Checked the CD4011BCN. Its has 100mw max. Have to figure how to wire due to i'am electronics dumb. (nand,nor,cmos,ect). My momentary load is a solenoid in a auto transmission (200ma). Also have to use trimable resistor to tune momentary time.

dualsport

Silver - Posts: 983

Joined: September 27, 2005

Location: United States

Posted: August 22, 2007 at 2:18 PM / IP Logged

You would use the logic gate output to control a transistor that can drive the actual relay instead of doing it directly, so the power of the gate doesn't really matter.

You can use a BS170 transistor to drive your output, also available from mouser, for about a dime. It can be considered to be like a relay that is driven from a voltage input, and provides a switch to ground when it's on.

I'll sketch out a possible setup if you need it-

madvan

Member - Posts: 15

Joined: August 21, 2007

Location: United States

Posted: August 22, 2007 at 3:25 PM / IP Logged

A sketch would be GREAT!

Thanks

Bill

dualsport

Silver - Posts: 983

Joined: September 27, 2005

Location: United States

Posted: August 22, 2007 at 11:50 PM / IP Logged

If your input signals aren't clean and free from voltage spikes, you should add filtering to the inputs to protect the gate from damage. Otherwise you could connect directly to the inputs.

Tweak the pot value from midrange to adjust the momentary on-time up or down.

The gate and transistor are ESD sensitive, so be careful to avoid static buildup when handling them.

By the way, the three gates shown above are all on a single chip, so you don't need three chips to do this. Just connect the pin numbers shown for the individual gates- less than 75 cents in parts, not including your relay.

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