Add a diode to my solenoid valve?

[Soundguy]

So what happens when the cap fails? Does the motor get any spark at all?

Depends on how it fials. If it fails closed, no spark, if it fails open, you get spark till the point sburn.

Think of it as a switch debouncer, and the points are a switch.

 

[Soundguy]

Diodes ... However, it does add one more thing that can go wrong and they always short closed. .

They always short closed. I guess that's like saying you always find something you are looking for in the last place you look.

I think you meant to say that they always FAIL closed, as by saying short, you are implying closed already.

However I can assure you.. they can also fail open. And... if they do fail shorted, many times that is a temporary condition, as they usually become open not long after shorting, assuming the supply wiring or traces can handle enough current to burn the diode junction open.

 

[k0ua]

Good to know about the old ignition.

So (silly me) has to wonder, if you don't have a diode and not a set of fingers to go through, what happens to that energy?

I too, learned that unpleasant shock from my 150 in one electronics kit.

I would assume that when the field collapses that the energy is dissipated in the form of heating up the wires (slightly) of the inductor.

So to paraphrase the old "if a tree falls in the forest" thing, "if there is no-one there holding on to the wires of the inductor getting the pizz knocked out of them, was there really energy there?"

 

[Soundguy]

it will try to arc somewhere.. the larger the spark gap, the higher the kv will go, untill it reaches it's maximum capable potential or it finds insulation it can break down, etc.

not uncommon to see poorly times distribuitors where the rotor is sparking to to the wrong tower.

also a good way to find the least insulated spot in your KV wiring.

 

[Industrial Toys]

I guess when I said "short closed" it was kind of an expression like "stone dead" or well, who knows what I was trying to say. I don't think I ever saw a defective open diode.

I once won first prize in a grade 7 or 8 science fair. All I did was buy a model T coil from Montgomery Wards and put something together in a night. A lot of people got a good shock!

The best one was the guy that thought his wooden (graphite) pencil would protect him, placing it into the jacobs ladder. The guy touching him , got a good one too.

I still have that old (plastic) Ford Coil. It brings back so many fond memories. Like hooking it up to a door knob! It ran on 6 volt, but I always ran it much higher.

 

[bigdeano]

I still have that old (plastic) Ford Coil. It brings back so many fond memories. Like hooking it up to a door knob! It ran on 6 volt, but I always ran it much higher.

I have a wood one. Did they have wood ones on model Ts? My dad had it around since before I was born, and I'm 70. I had some fun with it too.

 

[Soundguy]

I guess when I said "short closed" it was kind of an expression like "stone dead" or well, who knows what I was trying to say. I don't think I ever saw a defective open diode.

.

Think about it.. if a diode shorts closed.. it's a dead short from + to - lead.

if the circuit traces or wires are large enough to conduct more current than that diode junction can handle.. it will go from failed shorted to failed open very, very soon.

 

[tjkubota93]

They have been putting clamping diodes on a/c compressor clutches and fuel injectors for a long time.

 

[Industrial Toys]

I too would think that excess current would open the (shorted) diode junction again, but I have never seen a failed open diode, and if I did, I don't remember.

I suspect the OEM ford coils were wood and the later version, like I bought in 72 or 3 were plastic.

 

[Soundguy]

Except in an alternator, just about every rectifier failure I have seen is an open