Electronic cut out

Ted in NE-OH

Well-known Member
I want to make my own electric cutout relay, can any one suggest an appropriate diode max generator output is 20 amps. I also want to pot it to help with heat dissipation.Can anyone suggest an appropriate potting compound
 
I think you would be dollars ahead to just buy one unless trying to reuse any original case or something like that.
 
It's "easy as pie" to build your own stealth electronic cutout for just a couple of bucks. Surf on down a couple of Forums below to the Ford N Forum and ask "Soundguy" to repost his info, or with a little searching you can find it for yourself.

There's CHEAP little square bridge rectifiers that make this EASY 9Even though only half the diodes in the "bridge" are used.
 
I used a single diode for mine which I made about 15 yrs ago. Using more than one might be a problem as each diode has a .7 volt drop. It was for mine as it's a three brush set up for 8 volts. Diodes are rated by PIV (peak inverse voltage) and ampacity.
 
"Using more than one might be a problem as each diode has a .7 volt drop."

They get connected in parallel, so no added VD.
 
Diodes do not "share" current well when connected in parallel. They share better if they are on the same die, such as a "bridge rectifier" or "dual diode".

I would recommend finding a Schottky diode that will handle the entire current.

I found a STPS30M60ST that has a rating of 30A @ voltage drop of Vf = 0.590, and a reverse holdoff voltage of Vr = 60V. $2.80 at Digikey. There are some better diodes available in surface mount, but they are difficult to solder for the most part. Heat sinking is critical because 20A * 0.590 = 11.8w. A heat sink such as Aavid Thermaloy 530002B02500G ($1.65 at Digikey) with some white silicone heat sink grease provides a temperature rise of 40 degrees C at 12w.

Cliff(VA)
Practicing Electrical Engineer
 
If its a 20 amp genny, I'd still use a single (for simplicity) no less then 30 amp rated diode having a PIV rating of no less then 50 to 100 volts. To aid in heat dissipation instead of potting, Id mount it on a finned metal heat sink mounted on heavy metal and be done with it. The 0.7 volt drop isn't any worse then a burned or carboned or pitted relay contact. PIECE OF CAKE AND SO CHEAP

John T
 
Cliff, You're a "Practicing Electrical Engineer" while I'm a too long RETIRED Engineer rusty as an old nail grrrrrrrrrr lol but I still enjoy sparky chat.

John T
 
I understand the "diodes in parallel thing" but in this case (overrated) it works very well, and is easy and CHEAP to do and the bridge bolts inside the OEM cutout, hiding it and providing some heat sinking if mounted directly to the base.

Here's what others have done:

<img src = "https://photos.yesterdaystractors.com/gallery/pieces/v5567.jpg">
<img src = "https://photos.yesterdaystractors.com/gallery/pieces/v762.jpg">
<img src = "https://photos.yesterdaystractors.com/gallery/pieces/v764.jpg">

Parallel diode drawing by "Sou8ndguy", to photos of using ONE diode of a bridge by "Rick from TX".
 
(quoted from post at 19:40:11 08/22/16) You should not put in the jumper wire, that is incorrect
t sure will not do any harm! At some current level there will be some sharing, although not necessarily equal. Next, such a blanket statement is sure to be wrong in some circumstances. I have ordered hundreds of "matched pairs &amp; quads" from semiconductor companies. Sometimes there is simply not a larger diode. Works fine. Additionally that setup described was for old 9N's and even the single diode will handle those anemic generators, so the parallel harms nothing. Absolutes are like Zero Tolerance........sure to be wrong sometimes.
 
JMOR, EXACTLY, That's why after over 15 years on here I learned NEVER SAY NEVER AND NEVER SAY ALWAYS cuz sure as the world some Troll who gets off playing GOTCHA crawls out of the woodwork with some rare isolated obscure situation where its not true lol Keep your guard up.

Take care and have a good day

John T
 
Your unqualified ( look that one up ) statement is actually incorrect based on the application.

As it has been pointed out.. a single diode can handle the entire load by these old gennies. Sharing in parallel in this application will have -0- problems.

I've made dozens of these for people and never had one come back!

PS to recap.. these diodes are on the same die. ;) They each are more than capable to handle the load.. and there will be no issues running them parallel. Proof is out there on running tractors for years and years!
 
I actually blame this problem partially on schools and partially on genetics.

Some students lack good common sense, and rely only on book knowledge.

Then you factor in lack of experience and lack of knowledge in practical application, and lack of deductive analysis, and you get a situation like this.

As many ..er.. SOME of us know.. this bridge rig was designed for a ford anemic full tilt 11amp genny. A single segment is nearly 50% over rated giving a huge safety margin.

The student that becomes alergic to this probably has no real world experience dealing with this application, sees the topic ( parallel diodes ), and thinks back to that 5 seconds in class where it was said that they may not parallel well * ( yes.. you can get matched sets.. same with vacume tubes! and drive belts! ).. and then they clutch their chest and declare that the project will fail.

Due to their lack of experience they fail to realize that the system will run parallel or not.. each segment is way mor ethan fully capable.

In this case.. the detractor clearly does not understand the scope or application.
 
The rig I made up was done so for easy to find parts.. back when radio shack was around and sold fairly big silly-con on the shelves.

We both know the jumper causes no problems and the circuit will work as intended. ;)
 
To be fair, this particular application's validity is based entirely on "experience" which can be a double-edged sword. Just because some grizzled old tinkerer has had success with a particular method in the past does not mean it will work for everyone, or that it was even a valid method in the first place.

As an example, let's say I step over running PTO shafts all the time and never had a problem. That's my experience, even though the "book learnin'" says you should NEVER do that. Is it good advice to tell someone to ignore the book learnin' and step over running PTO shafts? The old bus driver who's missing some of his manly bits and walks funny might take issue with that kind of "experienced" advice.

Moral of the story is, just because you haven't had your manly bits torn off by an innocent looking PTO shaft doesn't mean its a good idea to step over one.
 
(quoted from post at 15:20:12 08/24/16) To be fair, this particular application's validity is based entirely on "experience" which can be a double-edged sword. Just because some grizzled old tinkerer has had success with a particular method in the past does not mean it will work for everyone, or that it was even a valid method in the first place.

As an example, let's say I step over running PTO shafts all the time and never had a problem. That's my experience, even though the "book learnin'" says you should NEVER do that. Is it good advice to tell someone to ignore the book learnin' and step over running PTO shafts? The old bus driver who's missing some of his manly bits and walks funny might take issue with that kind of "experienced" advice.

Moral of the story is, just because you haven't had your manly bits torn off by an innocent looking PTO shaft doesn't mean its a good idea to step over one.
A false statement:"this particular application's validity is based entirely on "experience"".
 
soundguy,

You are right. The problem can be blamed on the swimming program in all schools. Schools have emptied the gene pool, yet kids are still diving in the deep end.
Geo
 
(quoted from post at 09:09:44 08/25/16)
A false statement:"this particular application's validity is based entirely on "experience"".

Care to explain how so?

All the books and the science say you should not do it. Only personal experience with actually doing it says it "works."
ALL the books &amp; science, huh?" You need to go back and read this entire thread my friend, as on Monday, I clearly answered the question.
 
Here's a photo and a schematic of a commercially-produced hd bridge rectifier for a high-power audio amp.

<img src = "http://i167.photobucket.com/albums/u125/27Grainfield/Stuff/rect2_zpsrml1ev2r.jpg">

<img src = "http://i167.photobucket.com/albums/u125/27Grainfield/Stuff/rect1_zpsos1ju0xc.jpg">

Care to comment on how the diodes (on the same die) are paralleled?

And you are telling us that paralleling a pair of diodes (likely on the same die) in a little bridge rectifier to carry under 20 Amps at low voltage in a 70-year-old is bad practice/isn't gonna work? LOL!
 
(quoted from post at 15:35:24 08/25/16) Here's a photo and a schematic of a commercially-produced hd bridge rectifier for a high-power audio amp.

&lt;img src="http://i167.photobucket.com/albums/u125/27Grainfield/Stuff/rect2_zpsrml1ev2r.jpg"&gt;

&lt;img src="http://i167.photobucket.com/albums/u125/27Grainfield/Stuff/rect1_zpsos1ju0xc.jpg"&gt;

Care to comment on how the diodes (on the same die) are paralleled?

And you are telling us that paralleling a pair of diodes (likely on the same die) in a little bridge rectifier to carry under 20 Amps at low voltage in a 70-year-old is bad practice/isn't gonna work? LOL!
wwww, come on Bob.......you gotta know that that unit wasn't designed! Some yokel just threw a bunch of parts together, powered it up &amp; it didn't smoke, so boxed it up and shipped it out. After all, ALL the books in the whole wide world say it won't work....at least according to some poster. :twisted:
 
(quoted from post at 23:38:54 08/25/16) Yep trying to use original case. A fined heat sink does't work inside a box with no air circulation
ou didn't say what generator/tractor, but the arrangement described here was for 9N/2N tractors with 11 1/2 amp generators. By the time Ns were 20 amp, they used voltage regulators instead of the simpler cut outs. If does correctly, you can heat sink via the cut out can, its mounting to the metal of the tractor, where you do not count on air flow around the diode package. They didn't need much additional heat sink at 11 1/2A, as they were good for about 8A with no heat sink.
 

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