How can I test my cutout?

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NY John T
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How can I test my cutout?

Post by NY John T » Wed Dec 01, 2021 5:57 pm

Hi All,
At some point, when testing the timer (another topic for another time), I smelled wire burning and saw smoke coming from the generator cutout. I shut everything off and later took the cutout apart. I saw the winding wire which attaches to the outside yellow wire melted. Apparently the yellow wire connecting screw came in contact with the generator body and shorted it out. I'm about to re solder the winding wire back together (I made a new gasket to keep the external screw from touching the generator body)
cutout.jpg
My question is this: How can I test this cutout to see if it's working properly? And, what is the correct gap for the points?
Thanks,
John


Scott_Conger
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Re: How can I test my cutout?

Post by Scott_Conger » Wed Dec 01, 2021 6:05 pm

The correct gap and tension of the points is where the electromagnet "pulls in" and closes the contacts at about 7.0 - 7.2 VDC, assuming this is for a stock 6V system.
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Re: How can I test my cutout?

Post by Moxie26 » Wed Dec 01, 2021 6:14 pm

John, I'm sure there are responses you'll get for suggested repairs. When this happened to me I went directly to www Nu-Rex.com for a negative grounded diode style cut out. .. ... internal contacts welded themselves together and started to emit some smoke I bet surely scared the heck out of you and those standing around. I thought to get in there and rewire that cut out but was even afraid of making a mistake that would lead to a good fire source. The cutout from Nu-Rex saved a lot of headaches and saved my car.


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Re: How can I test my cutout?

Post by Art M » Wed Dec 01, 2021 10:53 pm

When something similar happened to me, I filed the points and adjusted it so that the contacts would close at 7.5 volts which was supplied with 5 flashlight batteries. It worked well. This is not factory setting but it was the best I could do at the time.
I now have a laboratory quality dc power,supply 0 to about 40 volts at 20 amp.
Art Mirtes

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Re: How can I test my cutout?

Post by TRDxB2 » Wed Dec 01, 2021 11:48 pm

NY John T wrote:
Wed Dec 01, 2021 5:57 pm
Hi All,
....
My question is this: How can I test this cutout to see if it's working properly? And, what is the correct gap for the points?
You'll need to create a non-conductive test platform so you don't shock your self "testing" it when you connect a car battery A piece of wood will do, with the cutout screwed down and leads to the input and output terminals. In comparing it to one I have like it - it may be minus some insulation under the coil, I'd pitch it and modify it with a diode or buy another (Nu-Rex negative ground from Snyders)
But if you want to test it. Yes you can use flashlight batteries as indicated above - safer too
It is a simple electromagnet switch (an iron bar with a copper coil around it). The voltage from the generator side to the BAT side will create a magnetic force to pull down the lever arm that cause the points to open and close. The idea is when that voltage reaches 7+ volts it should pull the lever arm down and cause the points to close. I ran a feeler gauge between the one I have and it was .014" so maybe use that as a starting point. Before you run any voltage, do a continuity test on everything to make sure nothing is grounded - there should only be continuity from the GEN terminal to the BAT side when the points are closed. You will need a variable DC power source to set the gap properly. But you can use a 6V battery to see if it will close the points. Remember the point of the cutout is to be open when the battery voltage is higher than the output of the generator regardless of the engine running.
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NY John T
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Re: How can I test my cutout?

Post by NY John T » Thu Dec 02, 2021 10:01 am

Thanks for all the suggestions. Now I have a bit of work and understanding to do. How does one install a diode in this unit?
John


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Re: How can I test my cutout?

Post by MichaelPawelek » Thu Dec 02, 2021 10:24 am

Image


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Re: How can I test my cutout?

Post by Norman Kling » Thu Dec 02, 2021 11:03 am

I suspect there is an internal fault in the cutout and that it was not your yellow wire grounding. If that wire had grounded, you would have put direct battery to ground and would have most likely burnt out the ammeter or if you have a fuse, it would have blown the fuse. But you can do the tests above if you want to. I would recommend a diode cutout. Or you can even remove the inner parts of your existing cutout and install a diode yourself. The current should flow from the generator through the diode, but not from the battery to the generator.
Norm


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Re: How can I test my cutout?

Post by Ron Patterson » Thu Dec 02, 2021 12:14 pm

NY John T
I don't think the cutout screw touching the generator case (ground) caused your problem at all.
Your cutout appears to have the correct 5/16 length screw which was selected to prevent ecaxtly that from happening.
If as you suggested that the yellow wire connected to the cutout bat terminal would be a direct short to ground and the entire circuit wiring from the cutout to the starter switch via the ammeter would have get very hot quickly. If you had this circuit fused somewhere near the starter switch a 25 Amp fuse would have also quickly opened the circuit. Norman Kling made these observations in a reply post and I agree.
A much more likley scenerio that caused your cutout's current winding to open was the cutout contacts had stuck closed (a common problem with the relay type reverse current cutout) when the engine was last shut down and the full 6.4 voltage of the batteries was shorted to the 1 Ohm resistance ground inside the generator and the ammeter would have been reading 6 amps discharge. The cutout case will get very hot until something in this circuit finially burns out. In your case it was the cutout current winding.
Because this area of the Model T charging system is very commonly misunderstood I wrote an article for the Model T Ford Fix Website. Here is a link to the article: https://modeltfordfix.com/the-model-t-f ... patterson/
The other advice offered about using a Nu Rex diode cutout or make you own diode cutout is probably your best bet and install one 25 amp fuse in the #12 yellow wire near the starter switch.
Ron Patterson


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Re: How can I test my cutout?

Post by J1MGOLDEN » Fri Dec 03, 2021 7:13 am

I recently acquired a Variac Test Set that was used to test Selenium Rectifies in early AC radios.

I also have a 120 Volt AC to 6 Volt AC transformer that when fed to a diode and capacitor will provide a 6 to 9 DC Volt variable voltage.

With an accurate DC Voltage Meter attached I can vary the voltage to a 6 Volt battery and note at exactly what voltage the Cutout will close.

That seems to be an accurate test, but it is less work and easier to convert the Cutout to a Diode Type.

The diode is also far more reliable for long term operation.


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Re: How can I test my cutout?

Post by Art M » Fri Dec 03, 2021 2:41 pm

I agree that a diode statistically is more reliable; however a diode has a negative exponenial failure rate. You just cannot predict when it will fail. A new one is just as likely to fail as a used one.
A mechanical one can be cleaned and set periodically.
I had a diode fail and burned out the generator armature. Consequently, I use a mechanical one that I periodically check. It is just one of the joys of the hobby.
Some like polishing brass, others like to tinker.

Art Mirtes

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Re: How can I test my cutout?

Post by TRDxB2 » Fri Dec 03, 2021 6:29 pm

Art M wrote:
Fri Dec 03, 2021 2:41 pm
I agree that a diode statistically is more reliable; however a diode has a negative exponenial failure rate. You just cannot predict when it will fail. A new one is just as likely to fail as a used one.
A mechanical one can be cleaned and set periodically.
I had a diode fail and burned out the generator armature. Consequently, I use a mechanical one that I periodically check. It is just one of the joys of the hobby.
Some like polishing brass, others like to tinker.

Art Mirtes
Art M wrote:
Fri Dec 03, 2021 2:41 pm
I agree that a diode statistically is more reliable; however a diode has a negative exponenial failure rate. You just cannot predict when it will fail. A new one is just as likely to fail as a used one.
A mechanical one can be cleaned and set periodically.
I had a diode fail and burned out the generator armature. Consequently, I use a mechanical one that I periodically check. It is just one of the joys of the hobby.
Some like polishing brass, others like to tinker.

Art Mirtes
This is a question not a criticism There is no reason that the diode or even a voltage regulator has to be inside the cutout body (unless its for show)
Can one do this and check them regularly?
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NY John T
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Re: How can I test my cutout?

Post by NY John T » Sun Dec 05, 2021 3:32 pm

Hi again,
trying to find the time to get to the engine to check why some of the coils are not firing. Then I'll go to work on the cutout. Is it general consensus that a diode is questionable? Thanks.
John


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Re: How can I test my cutout?

Post by Norman Kling » Sun Dec 05, 2021 3:36 pm

I use diode cutouts on all my T's. If the ammeter shows charge with the generator running and the lights off, and it shows zero when everything is off, the diode is good. I haven't had one go bad yet.
Norm


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Re: How can I test my cutout?

Post by Art M » Sun Dec 05, 2021 8:13 pm

Diodes are quite reliable. I just had bad luck.

A safer way to use diodes would be to connect 2 in series and connect another 2 in series then connect these two sets in parallel. If one fails open the system will still work. If one fails closed, the system will still work.
This may be considered an overkill but better than loosing a 200 buck armature.

Art Mirtes


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Re: How can I test my cutout?

Post by Art M » Sun Dec 05, 2021 8:15 pm

And no, a cutout,system does not have to be in that case. It just has to be in the circuit.

Art Mirtes

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