DB26

How to Build a Diode Generator Cut Out Replacement

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Hello everyone. I have a 1926 Dodge Brothers Deluxe sedan. It has a 4 cylinder engine with a 6 volt charging system. The generator and starter are separate units. I have read a comment somewhere (I can remember where) that you can modify a generator cut out with a diode to eliminate the possibility of the points sticking and possibly draining your battery or starting a fire, etc. 

 

Does anyone know how to do this modification? I am not an electronics expert, but know enough to be able to do it if I had the insurcrions. I have a bunch of diodes on hand too. Can anyone offer some advice? 

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https://www.modeltford.com/item/5055DIO.aspx      This link is for a diode with insurcrions. A common upgrade for Ford T & A. Searching those forums bring many results. You can also add voltage regulation within the cutout housing. Positive & negative ground too.

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Is the Dodge positive or negative ground?  Do you know the generator output in amps?

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19 minutes ago, TerryB said:

Is the Dodge positive or negative ground?  Do you know the generator output in amps?

It’s positive ground. I don’t know the amp rating, but will try to find out. 

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2 minutes ago, DB26 said:

It’s positive ground. I don’t know the amp rating, but will try to find out. 

The model t link is for neg ground, not that the diode cares but how the diode is inserted in the circuit matters as does the  amp rating that the diode has to have for the amount of charging current flowing through it.  Too small of amperage rating and the diode will overheat and fail.

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The purpose of the cut-out or the diode is to stop current (amps) going back to the generator when its producing less voltage than the battery. This occurs when the generator rpm is too slow (ie, at idle) to produce enough voltage. Generator voltage is directly proportional to its speed. 

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So I gather that once I have a diode with the proper size amperage, all I have to do is use it to bridge between the cutouts input from the gen and output to the battery? Bypassing the cutouts windings and points I’m assuming.  

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4 minutes ago, DB26 said:

So I gather that once I have a diode with the proper size amperage, all I have to do is use it to bridge between the cutouts input from the gen and output to the battery? Bypassing the cutouts windings and points I’m assuming.  

 

Basically, yes.

 

The higher current diodes often need a way to dissipate some heat, so consider that when installing the diode within an old cutout housing. On the other hand, I did this for my car back in 1978 and didn't pay too much attention to heat sinking and it is still going strong today.

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1 hour ago, 23hack said:

https://www.modeltford.com/item/5055DIO.aspx      This link is for a diode with insurcrions. A common upgrade for Ford T & A. Searching those forums bring many results. You can also add voltage regulation within the cutout housing. Positive & negative ground too.

 

I don't understand how they say its only for a -ve ground, you just reverse it for +ve ground.

 

Here is one I made for my '28 Chrysler but didn't use because I gave up on the generator.

Diode - ZP20A 20AMP Power Stud Silicon Rectifier Diode 1000V 50A Silver

 

IMAG2195.thumb.jpg.f68a3c830cc75f3f861fa32701626613.jpgIMAG2197.thumb.jpg.9082cd63ff948a17f3af284b5cf3c032.jpg

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10 hours ago, maok said:

 

I don't understand how they say its only for a -ve ground, you just reverse it for +ve ground.

 

Here is one I made for my '28 Chrysler but didn't use because I gave up on the generator.

Diode - ZP20A 20AMP Power Stud Silicon Rectifier Diode 1000V 50A Silver

 

IMAG2195.thumb.jpg.f68a3c830cc75f3f861fa32701626613.jpgIMAG2197.thumb.jpg.9082cd63ff948a17f3af284b5cf3c032.jpg

Yes!  The only requirement for polarity is making sure the diode is connected in the proper orientation to allow current to flow from the generator to the battery.  When the generator output is 0.7 volts higher than the battery’s voltage current will pass from the generator to the battery.  The trick is having a diode that will handle the load and your choice of diode fits the bill.  Some internet searches show this modification using a 5 amp diode which is too small for most automotive applications.

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57 minutes ago, TerryB said:

 

That unit is rated for 15 amps, might want to check to see if that is sufficient. For example, my '33 Plymouth generator is rated for something like 22 amps so that could be undersized for my car. On an appearance note the stock Delco-Remy cut out on some cars, including Plymouth, are mounted 90° different than this Brillman one. That will not affect operation but if you are worried about appearance it could be an issue.

 

Nonetheless, it is good to see that a product like that exists and you don't have to build your own.

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10 minutes ago, 1937-44 said:

 

 Are you sure this doesn't have points? The description doesn't say anything about it having a diode in it.

Yes, they build them for the antique tractor guys who are also wanting to get away from mechanical points. The tractor guys seem to like this company from what I found on tractor discussion sites.

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Posted (edited)

 Okay I'll take your word for it,  just surprised they didn't mention it in their description. 

 

 I know Mac's sells a cut-out diode kit for positive ground cars for $5.

https://www.macsautoparts.com/ford_model_a/model-a-ford-generator-cut-out-diode-kit-for-converting-old-style-cut-out-to-solid-state-positive-ground.html

 

 

Edited by 1937-44 (see edit history)

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7 minutes ago, 1937-44 said:

 Okay I'll take your word for it,  just surprised they didn't mention it in their description. 

 

 I know Mac's sells a cut-out diode kit for positive ground cars for $5.

https://www.macsautoparts.com/ford_model_a/model-a-ford-generator-cut-out-diode-kit-for-converting-old-style-cut-out-to-solid-state-positive-ground.html

 

 

Hold on- that first one could be mechanical, try this

https://brillman.com/product/universal-electronic-cutout-relay/

 

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  I've purchased items from Brillman in the past and been very happy with my purchases. Your second link it states it's electronic and if I wanted to go that route I wouldn't hesitate to purchase it if I didn't mind the looks. 

 First one I would call first to confirm if it's mechanical or electronic though.

 

Carl

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The diode you need was used in Chrysler and Ford alternators in the 1960"s. It is 25A rated. You use a positive diode for positive ground and a negative diode for negative ground. The hardest part is soldering the diode to the plate inside the cutout. Most DIYer's do not have the proper type of soldering equipment to do this.

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Thanks for the replies and links, everyone. I think I have a better understanding of what I need to do as far as amperage required and what connections to make. I will report back with what direction I’m going to go ( make my own or purchase) and I still need to go find out what amp output my gen makes. 

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3 minutes ago, DB26 said:

Thanks for the replies and links, everyone. I think I have a better understanding of what I need to do as far as amperage required and what connections to make. I will report back with what direction I’m going to go ( make my own or purchase) and I still need to go find out what amp output my gen makes. 

 

I wouldn't worry too much about the max. output of the generator, having a diode that will handle your maximum system draw is fine, but it wouldn't hurt having it bigger either, they are cheap to buy. 20-25amp diode is more than adequate, unless you are going to have a amplifiers for subwoofers,  thermo fans cooling the radiator, A/C etc....lol

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3 minutes ago, maok said:

 

I wouldn't worry too much about the max. output of the generator, having a diode that will handle your maximum system draw is fine, but it wouldn't hurt having it bigger either, they are cheap to buy. 20-25amp diode is more than adequate, unless you are going to have a amplifiers for subwoofers,  thermo fans cooling the radiator, A/C etc....lol

Haha, no amplifiers here! Right now the only thing it runs that isn’t factory is a set of turn signals. 

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I just bought two diodes to experiment with, a 25 amp, 200v cathode to case and a 40 amp 400v anode to case. They should be here this weekend. We’ll see what kind of setup I can cobble together. 

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Do they have a screw type mounting stud as part of the case?

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Posted (edited)
34 minutes ago, TerryB said:

Do they have a screw type mounting stud as part of the case?

Yes, they both do. One is an NTE5864 and the other is an NTE5991

Edited by DB26 (see edit history)

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