Solid State Relay Puzzle

[Paul Elliott]

Originally Posted by goboatingnow

Just to be picky, The diode is there not to clamp the current, but to prevent an inductive voltage spike as the magnetic field of the valve collapses. MOSFETS, particulary power MOSFETS have a relatively low trench breakdown voltage and hence can be damaged by such a spike. Anyone with a scope can easily see what is happening.

The resistance of the wire has a damping effect so the solid state internal proptection is actually probably sufficient, but good practice is to 'snub' the ringing at the coil. hence the diode. The actual current flowing when the diode is forward biased is very small, but the diodes forward voltage rating is a key factor.

dave

The diode clamps the voltage spike, and when it clamps current is flowing. This current can be fairly large, roughly the same as the normal coil current. This is the nature of inductors: they resist changes in the current flowing through them.

I'm not sure what you mean by "the diode's forward voltage rating" being a key factor. The reverse voltage rating is important, but the forward drop shouldn't make much of a practical difference.

As for Dockhead's situation, I agree that the relay's built-in protection diode should suffice. This protection diode appears to be a Zener or other clamp (a different configuration than the diode we have been discussing).

I also doubt very much that the lack of an external clamp diode is causing his AP problems. Adding the clamp diode is probably a good "belt and suspenders" approach -- at least it will do no harm.

[s/v Jedi]

This thread has also gone down to declaring what others write to be wrong and then saying the same thing with different words. This is not CF anymore.

[Dockhead]

Originally Posted by s/v Jedi

This thread has also gone down to declaring what others write to be wrong and then saying the same thing with different words. This is not CF anymore.

Urgh, a good technical argument is a thing of beauty. It's important not to get emotional about it. Where is the intellectual detachment which is the hallmark of a truly inquiring mind?


Back to the original topic --

I have installed the diode as you guys generously explained to me how to do. I rewired the entire relay circuit. I have been torture testing it, switching the pilot on and off, on and off. It seems to work fine now. Here's hoping I absolutely love the B&G/Simrad pilot control, beautifully integrated with the chart plotter. I can actually steer the boat manually from the nav table -- not just operate the pilot! Maybe I will get ahead of all these installation pains soon in order to start actually enjoying these new toys.

I've had a pretty good day today. Got the radar working It's a real morale booster to sit here at my nav table and watch boats go up and down the river on my new 4G radar Another good thing which happened is one of my VHF antennae spontaneously started working. For good measure, I lopped off the PL259 and soldered on a new one, taking extreme care and applying all the knowledge I have gained here. I have no idea why it would behave this way, unless it is because the connector is not screwed down well enough. I'll go aloft and check as soon as I have two able bodied seaman on board to hoist me up.

[Paul Elliott]

Originally Posted by s/v Jedi

This thread has also gone down to declaring what others write to be wrong and then saying the same thing with different words. This is not CF anymore.

If you're referring to my last post, I believe you're mistaken. I pointed out two errors of fact and one difference of interpretation, and offered an explanation. This may have been useless technical digression, but it was definitely not "saying the same thing with different words".

[hellosailor]

How did the Monty Python skit end? "Argument? You came here for an argument? Oh, no that's two doors down to the left, this is Abuse."

Say, Dockhead, aren't you going to add a protective fuse for that diode? <VBG>

[Dockhead]

Originally Posted by hellosailor

Say, Dockhead, aren't you going to add a protective fuse for that diode? <VBG>

Say what?! :11_confused:

[Reefmagnet]

Originally Posted by s/v Jedi

This thread has also gone down to declaring what others write to be wrong and then saying the same thing with different words. This is not CF anymore.

I hope to god no one suggests soldering this stuff together. All hell could break loose.

[Paul Elliott]

What brand of anchor makes the best heat sink for my protection diodes? I'm afraid that the lead-filled ones might melt. Should I be concerned?

[hellosailor]

Once upon a time the internet was all text based. VBG stands for "Very Big Grin" and should be your tipoff that something has just been said in jest.

You know, every time there's an electrical discussion, someone HAS to ask if you're going to fuse it. Whatever it is.

So...You're going to fuse that diode, right? <VBG>

[s/v Jedi]

Originally Posted by Paul Elliott

If you're referring to my last post, I believe you're mistaken. I pointed out two errors of fact and one difference of interpretation, and offered an explanation. This may have been useless technical digression, but it was definitely not "saying the same thing with different words".

Not at all Paul, not at all. Like you say, you were fixing things; it's just tiring that it's needed

[Paul Elliott]

Originally Posted by s/v Jedi

Not at all Paul, not at all. Like you say, you were fixing things; it's just tiring that it's needed

OK, thanks, We're still friends.

Darn, I'm looking for a fight!

[Dockhead]

Originally Posted by hellosailor

Once upon a time the internet was all text based. VBG stands for "Very Big Grin" and should be your tipoff that something has just been said in jest.

You know, every time there's an electrical discussion, someone HAS to ask if you're going to fuse it. Whatever it is.

So...You're going to fuse that diode, right? <VBG>

LOL. OK, got it now.

So back to your question -- yeah, I was thinking of one of those 25,000 amp PCB-filled fuses -- what do you think? Just a question of where to put it, I guess . . .