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Ford 9N, 2N & 8N Discussion Forum
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Diode Confusion

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AlanC

05-03-2006 11:11:29




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I’m confused about which size diode to put in the wire between the alternator and battery. I’m converting a 52’ 8n to 12v. I’ve read about the importance of adding this diode but have seen three or four different ones mentioned. I’m sure they might all work but I don’t know which is the correct size for my system. I’ve even read where someone installed a resistor and diode in series. When soldering a diode into a 10 awg wire, is the little wire sticking out of the diode capable of handling the amperage? Is it big enough to keep from burning up? Thanks in advance for the info!

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RockyMo

05-03-2006 20:27:43




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 Re: Diode Confusion in reply to AlanC, 05-03-2006 11:11:29  
Why not eliminate the diode altogether and install a wire with an accesory position. Install the wire that would have had the diode to the accesory post and all the other wires the same as you were going to. By doing this the tractor will shut off and charge with no diode to fail.

RockyMo



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Hobo,NC

05-03-2006 15:18:38




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 Re: Diode Confusion in reply to AlanC, 05-03-2006 11:11:29  
When soldering a diode if you use solder that’s hard to melt the heat could damage the diode. I use Radio shack # 64-008E use it and it will make a pro solder out of ya.



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Phil (NJ,AZ, Sask)

05-03-2006 14:13:27




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 Re: Diode Confusion in reply to AlanC, 05-03-2006 11:11:29  
[quote]When soldering a diode into a 10 awg wire, is the little wire sticking out of the diode capable of handling the amperage [/quote]

AlanC, The Excite current is a fraction of 1 amp. Bob
has a Picture of one spliced into the wire that will work.

I think i would use spade lugs such that the diode plugs into the ALT (as short as possible) & the wire then plugs into the diode. (look like a Alt connector Extender)

The important thing is that heat shrink should cover all electrical connectors & provide strain relief, "beyond" the point where the wire is soldered.

Hope this Helps,

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Bob

05-03-2006 13:55:30




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 Re: Diode Confusion in reply to AlanC, 05-03-2006 11:11:29  
I use a single 1N5008 diode, which, by it's ratings is WAY overkill, but I've never had one fail. They are CHEAP. I used to use lighter-duty diodes, and would occasionally have one fail. An industrial electronics place will have them, a "hobby-type" place should be able to cross that number to what they have.

I have been selling a few on ebay, for those who don't want to track down the diode, or the correct connector to match the alternator.

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james forrester

05-03-2006 18:42:16




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 Re: Diode Confusion bob in reply to Bob, 05-03-2006 13:55:30  
cant find you on ebay



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Bob

05-03-2006 19:35:29




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 Re: Diode Confusion bob in reply to james forrester, 05-03-2006 18:42:16  
Email me. It's frowned upon to excessively "hawk" ebay stuff on here. I do sell a few of the harnesses for those who don't want to gather up the parts themselves, and it's not a big money deal for me, and I don't want to make our gracious host, Kim, mad!

bigcoulee@hotmail.com



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old

05-03-2006 14:31:26




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 Re: Diode Confusion in reply to Bob, 05-03-2006 13:55:30  
Bob, have you ever checked out the Radio shack diode # 276-1661?? If I knew how I would send you the info brom the back of the pack to see if my diode or your diode has the most over kill. The one I use is a 6 amp 400 amp surge rating diode



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Bob

05-03-2006 14:15:03




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 Re: Diode Confusion in reply to Bob, 05-03-2006 13:55:30  
OOOPS... forgot the photo... the wire to the diode is 18 GA. At startup, there is a current flow of only a couple of amps, and once the alternator begins to charge, the diode is actually reverse-biased, so there is NO current flow.

Third Party Image



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old

05-03-2006 12:20:08




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 Re: Diode Confusion in reply to AlanC, 05-03-2006 11:11:29  
I'll make it so easy on you that all you have to do is find a Radoi shack. The part number for what I have used in say 50 differant tractors and so far none have ever quit working because of the diode going bad. The # is 276-1661. Shoot if you lived close to me you could drive on over and I can hand you one right out of my tool box. I keep them on hand all the time. A pack of them costs around $3 give or take a little. The line on the diode goes to the side that is the alternator by the way

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soundguy

05-03-2006 11:27:04




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 Re: Diode Confusion in reply to AlanC, 05-03-2006 11:11:29  
If everything is working, the field excite line won't draw much power at all.. just enough to tell the VR to turn on.

On the diode.. one end will be marked with a stripe.. that is the cathode.. the other end is the anode. Put the cathode towards the alternator #1 plug, and the anode towards your switched power source.

This keeps the alternator from backfeeding the ignition and also protects the alternators sensitive vr from -having- to backfeed the ignition line in case of a bad ignition switch.
Yes.. some people put the marker lamp or a resistor inline with the diode.. but it shouldn't be necescary. Once the alt starts charging, the potential on either side of the diode will be functionally the same.. thus no current flow... ( same reason why the idiot lamp goes out... no current flow ).

If you are using a monster solder gun, do the diode a favor and heat sink it.. It doesn't take much heat or time to tin wires then solder.. i usually like to use crimp connections as mechanical joints.. then oversolder for better electrical contact.. the heatshrink and strain relief like Bob does. Use some paste solder flux non acid type.. and the soldering should be fast and easy..

Soundguy

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jdemaris

05-03-2006 11:24:05




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 Wrong wire I think . . . in reply to AlanC, 05-03-2006 11:11:29  
You've got me confused now. There is no need for a diode anywhere in the system except in the exciter lead which is not 10 gauge wire - more like 14 or 16 gauge. Sounds like your're talking about the main output lead, not the exciter. The exciter comes from #1 terminal on the alternator if it's a Delco 10 or 12SI, and gets switched power - usually from the key-switch if you have one. Rarely exceeds one ampere in current. The diode is needed because, once the tractor starts, and the alternator is charging, it will backfeed power to the ignition circuit - so when you turn the key off, the engine won't shut off. There are many easy ways to fix it. One, is the diode. It only needs to be rated a little over an amp. I buy them at radio shack - for insurance I usually use two 3 amp diodes hooked in parallel - cost about a dollar each. Another way is to use an automotive type ignition switch that has both a IGN terminal and an ACC terminal. Have you ignition circuit hooked to one, and the alternator exciter hooked to the other. When the key is off they will be isolated from each other - so no diode is needed. And yet another way is use an oil-pressure switch and run the alternator exciter wire through that.

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DavidO

05-03-2006 11:42:15




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 Re: Wrong wire I think . . . in reply to jdemaris, 05-03-2006 11:24:05  
"usually use two 3 amp diodes in parallel"

Why?



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jdemaris

05-03-2006 11:48:39




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 Re: Wrong wire I think . . . in reply to DavidO, 05-03-2006 11:42:15  
Because it can't hurt having an over-rated or an extra diode and my local Radio Shack does not have anything larger than the 3 amp diodes. If I took the time to order them on-line, I could buy any size I want - but it's usually a spur-of-the-moment thing with me. With the two in parallel, if one burns out, the other will do the job. It's just a dollar's worth of insurance.



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DavidO

05-04-2006 05:19:30




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 Re: Wrong wire I think . . . in reply to jdemaris, 05-03-2006 11:48:39  
There is not really any reason to use two. One of the 3 amp diodes will do the job just fine. As for "insurance", the probability of both failing is almost identical to the probability of one failing. The 2nd one just isn't needed. Do two tractors for the price of one.



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jdemaris

05-04-2006 06:02:46




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 Re: Wrong wire I think . . . in reply to DavidO, 05-04-2006 05:19:30  
Well - you're free to do your work anyway you like. But - I don't have a problem spending an extra 35 cents to add some redundancy. And in regard to the other guy's comments about how diodes don't break circuit - but only short ?? That's not been my eperience - I've replaced many that were just plain open - I suspect sometimes from vibration. I just replaced three failed rectifiers in my genset - they were all open - not shorted - IN1185s, 35 amps and 150 volt. You telling me I'm wrong to add some redundancy is like telling someone they're wrong for filling their gas tank in their car when they only have to drive 10 miles. I don't understand the percieved problem. If there something factually wrong with something I said - that's a different story. But to complain about doing a little overbuilding is a little silly.

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DavidO

05-04-2006 10:02:00




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 Re: Wrong wire I think . . . in reply to jdemaris, 05-04-2006 06:02:46  
Well, since it is clear that you do not understand, I will not burden you with further explanations. Do it your way and be happy.



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jdemaris

05-04-2006 11:28:42




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 Re: Wrong wire I think . . . in reply to DavidO, 05-04-2006 10:02:00  
I think I understand very well - but thanks for not "burdening" by brain with your brand of complex reasoning.
Seems at one time this forum's main focus was information and experience sharing - but lately seems to be a symposium for nitpickers. Keep in mind - in direct reference to my dual diodes that has obviously put a bug in you a*s, I never advised anyone to do things as I did - just related what my personal choice was. I never said it was necessary nor did I advise anyone to do it - yet you feel it necessary to make an issue of it. It appears that YOU are one giving advice based on your personal preference, and the only CORRECT way is YOUR way.

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dan hill

05-04-2006 01:48:40




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 Re: Wrong wire I think . . . in reply to jdemaris, 05-03-2006 11:48:39  
the problem with diodes is that one will carry more load than the other and they dont burn out,but short circuit.



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Bob Harvey

05-03-2006 19:46:35




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 Re: Wrong wire I think . . . in reply to jdemaris, 05-03-2006 11:48:39  
1 amp works.



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jdemaris

05-03-2006 20:11:43




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 Re: Wrong wire I think . . . in reply to Bob Harvey, 05-03-2006 19:46:35  
Yes . . . and what is your point? A one amp rated diode will work fine unless a surge occurs and then it's likely to blow. The fact that a 15 watt diode is normally sufficient is already evident. In most diode or rectifier controlled circuits however, over-rating is usually standard procedure. So, an exciter circuit that normally draws 1/2 an amp is better served with a 5 or 10 amp diode than a 1 amp if longevity is desired - especially when there is little added cost involved. I just had the exciter plate apart on a 17KW genset - factory rated at 3 amps at 14 VDC and factory equipped with 50 amp at 600 VDC recifiers. That's typical over-rating that provides reliability.

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old

05-03-2006 20:49:14




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 Re: Wrong wire I think . . . in reply to jdemaris, 05-03-2006 20:11:43  
Why not just use Radoi shack part number 276-1661 diode which is rated at 6 amps and 400 amp surge and be done with it. Yes its over kill but in more then 20 years of putting on 12 volt systems I have never had one go bad and when you buy a pack of them for say $2.29 and it has 4 per pack thats 4 tractors you can set up and that comes out to less the $0.60 each

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jdemaris

05-04-2006 05:51:43




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 Re: Wrong wire I think . . . in reply to old, 05-03-2006 20:49:14  
That's fine - but as I said earlier - my local Radio Shack only has the 3 amp diodes. Every time I go there they have less when it comes to small semi-conductors. They don't want to be in the semi-conductor business anymore - they'd rather sell cell-phones and toys. If I was to plan ahead, I'd buy from a real electronics company like Allied or Newark. They sell industrial rated standard-recovery diodes for 35 cents for a 3 amp and around 75 cents for a 6 amp.

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old

05-04-2006 07:39:16




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 Re: Wrong wire I think . . . in reply to jdemaris, 05-04-2006 05:51:43  
Ya I can understand that as far as radio shack. Guess I'm lucky the one I have close still keeps some of the good stuff on hand.



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jdemaris

05-04-2006 11:12:56




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 Re: Wrong wire I think . . . in reply to old, 05-04-2006 07:39:16  
We used to have two Radio Shack stores - and old one and a new one. An old radio and ham nut owned the old store and ran it by himself. He had just about everything you'd ever want and he knew his stuff. Then a bunch of farms got sold and broken up, a mall, Lowes, Home Depot, etc. came in - along with a new "modern" Radio Shack in the mall. It soon put the old store out of business, and the new store is about as useful as t*ts on a bull. I've been thinking it's time to move one more time in my life and try to escape development. Problem is - I don't know where to go - that I can afford.

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old

05-04-2006 11:51:50




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 Re: Wrong wire I think . . . in reply to jdemaris, 05-04-2006 11:12:56  
Yopu need somne place like the area I live in. You can still find places out this way that are clear out in the middle of no where but still close enough to towns that it doesn"t cost an arm and leg to drive in and shop.



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