diode direction?

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madvan

Member - Posts: 15

Joined: August 21, 2007

Location: United States

Posted: August 23, 2007 at 8:05 AM / IP Logged

Thanks! I will give it a shot.

Bill

madvan

Member - Posts: 15

Joined: August 21, 2007

Location: United States

Posted: August 23, 2007 at 8:37 AM / IP Logged

Dualsport

On C1 the cap. What voltage and type? Resistor type and %? Also do i need a voltage regulator or over protection device to protect from alternator (+/- 2vdc).

Thanks for all your help Bill

dualsport

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Joined: September 27, 2005

Location: United States

Posted: August 23, 2007 at 9:01 AM / IP Logged

Pick a cap with double the expected voltage, above 30V should be fine. A standard aluminum electrolytic or tantalum would be okay for this.

Resistor type and tolerance is not at all critical, the two pull up resistors on the input may not even be needed if your input goes high on their own, rather than ground switched only.

You can change the cap value and potentiometer resistance as you need to change the on-time of the momentary pulse.

If your car is working properly, you shouldn't need a voltage regulator, but if it's prone to voltage spikes, you can add a zener diode and a series resistor to make sure the gate doesn't get too high a supply voltage.

madvan

Member - Posts: 15

Joined: August 21, 2007

Location: United States

Posted: August 23, 2007 at 11:16 PM / IP Logged

I would like to add the diode and resistor for protection. This is for a diesel application. Its prone to spikes with glow plug on time. If you could show where to install and size.

Thanks you have been a major help.

Bill

dualsport

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Joined: September 27, 2005

Location: United States

Posted: August 24, 2007 at 12:30 AM / IP Logged

Here's a modification adding extra clamps and limiting circuit that should protect the NAND gate from spikes.

diode direction? - Page 2 -- posted image.

madvan

Member - Posts: 15

Joined: August 21, 2007

Location: United States

Posted: August 25, 2007 at 12:18 PM / IP Logged

Thanks!

Bill

madvan

Member - Posts: 15

Joined: August 21, 2007

Location: United States

Posted: August 26, 2007 at 12:01 PM / IP Logged

Dualsport

Would i be able to replace the relay with a mosfet? I'am looking to drive a autotrans solenoid. It has a 30ohm coil. Trying to speed up the turn on time.

Bill

dualsport

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Joined: September 27, 2005

Location: United States

Posted: August 26, 2007 at 12:22 PM / IP Logged

That would be about a half amp draw, so you should be able to drive it directly from the transistor. The continuous rating on the BS170 is 500mA which should be able to do it, especially since it'll only be a momentary pulse.

You'll definitely need to make sure the D1 suppression diode is in place to supress the large transient voltage spike coming back from your solenoid when it turns off, or else it'll destroy the MOSFET.

Basically the relay shown will be substituted with your solenoid.

Have to wonder though, would the switching time of a mechanical relay really make that much difference for the application? It's just a tiny fraction of a second; that would be a problem?

madvan

Member - Posts: 15

Joined: August 21, 2007

Location: United States

Posted: August 26, 2007 at 2:32 PM / IP Logged

With the mosfet i can get into the na second reaction time. I have to look but i think a reed is milli second. How quick on (signal) and off time (momentary) is important. I'am trying to sync a tork converter lockup with a 4th gear shift in a auto trans. I have to let the PCM unlock the TC or it will set a code. In its current form i have a momentary switch to hold the ground during the shift command to hold it locked. Works great but sets a code. So i have to let it unlock then lock. When the 2 input grounds break that is when the TC unlocks.

dualsport

Silver - Posts: 983

Joined: September 27, 2005

Location: United States

Posted: August 27, 2007 at 8:05 AM / IP Logged

If you were doing it manually before, it'd probably be a much bigger delay than a relay would add. I wouldn't think the bit of extra time would make a difference, but you can try it out and see if it works both ways.

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