Testing a cutout

fred93

fred93

Senior Member
I saw a post that said the way to test a generator cutout was to take the fan belt off and see if the generator starts turning like a motor.

Wouldn't it be easier just to turn off the engine and put a test light to the output wire of the generator. If it lights up then the contact points are stuck together.

With that thought I am thinking that a small indicator light could be connected to the output wire of the generator. If the engine is turned off and the indicator light stays on then you know that the contact points are sticking and you WILL have a dead battery in the morning!

To test the cutout to see if it is working (making contact from the generator to the wires on the outlet side of the cutout you would need a multi-meter that shows DC voltage. The voltage into the cutout will be around 8 volts and it should be about the same on the outlet side of the cutout. If the voltage is way low on the outlet side of the cutout then it is not working.
 
That would tell you that the points are stuck together but it's risky. The light connected to the output would light up due to the battery connection.

To test for stuck points, you need either an ohms meter to just check for continuity through the cutout or you need to just disconnect (isolate) the generator output terminal from the cut out input terminal and then see if it will light the test light when touching the input terminal of the cut out. It current flows through then the points are stuck closed.

The cutout shouldn't take much more than 6-volts to close the switch when applied to the input terminal. A 6-volt battery set up to operate the cut out should work to close the points as long as there is a ground path connection. A person can momentarily operate it that way but I wouldn't let it stay closed very long. If a 6-volt test lamp is connected to the output side, you can see if it lights up when the cutout closes. A volt meter would work just as well.

One thing that is important though is that a person needs to be sure that the unit is a real cutout switch. A diode is a different thing and a fun projects regulator is too.
 
I think your set would work, but the light would be on when the running above idle. Why not just use the ammeter. If it is discharging when you turn off the engine, it is stuck. Easier just to put a new cut out on. Diode or not. We all use 6 volt alternators. Good luck.
 
Hi Ho Silver.

Every now and then I watch the show. I enjoy the simplicity.

The fight scenes are terrible, no one ever gets killed, tonto is always the yes man, silver is a cool horse, some of the scenes are shot in a studio, you can hear the echo when they talk, always a great story, the end of the show is always "hey who was that masked man, I never got to thank him", Well don't you know that was the Lone Ranger.

That is truly early TV. Different that shows today.
 
with as stock cutout testing is done with ammeter and voltmeter, --to make it simmple the generator side has to get to or a little above battery voltage to close cutout contacts --6.2-7.5 volts or so when generator comes back to idle--not charging the cutout has to open---this should happen by about 3 amps discharge into the generator, but no sooner than generator voltage equal to battery voltage

with a diode cutout when the generator side gets to about 1/2 volt above battery voltage it "connects", and will remain 1/2 volt above battery side voltage until generator voltage gets less than 1/2 volt above battery ---think of it as a "one way valve"
 
Diodes will generally pass current as soon as it starts to flow. It just can't go back the other direction. It's like a one way check valve for current/voltage.

Diodes can get hot though and some of these units have no heat sink. If it has a heat sink, it should last longer. Nurex uses one but I don't know how effective it is.
 
When buying a diode cut out be sure to get one of the proper polarity for the vehicle that you plan on putting it on, as they are polarity sensitive.
 
katy said:
When buying a diode cut out be sure to get one of the proper polarity for the vehicle that you plan on putting it on, as they are polarity sensitive.
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I took the numbers off the one that went bad and found a new one on Amazon.

That should be ok???

The only difference is that the one on Amazon is a 1N1183A and the one in the bad cutout is 1N1183 --Does the "A" make a difference???
 

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rotorwrench said:
That would tell you that the points are stuck together but it's risky. The light connected to the output would light up due to the battery connection.

To test for stuck points, you need either an ohms meter to just check for continuity through the cutout or you need to just disconnect (isolate) the generator output terminal from the cut out input terminal and then see if it will light the test light when touching the input terminal of the cut out. It current flows through then the points are stuck closed.

The cutout shouldn't take much more than 6-volts to close the switch when applied to the input terminal. A 6-volt battery set up to operate the cut out should work to close the points as long as there is a ground path connection. A person can momentarily operate it that way but I wouldn't let it stay closed very long. If a 6-volt test lamp is connected to the output side, you can see if it lights up when the cutout closes. A volt meter would work just as well.

One thing that is important though is that a person needs to be sure that the unit is a real cutout switch. A diode is a different thing and a fun projects regulator is too.
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What is "Fun Projects Regulator" Can I find it on the web???

Never mind-I found it. Looks like everything is "back ordered". I think I'll pass. I'm tired of buying parts for this car that are junk!
 
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A person has to call them. I don't think they update their web site. John Regan sold the business to the Bird Haven Vintage Auto Supply some time back and I think they have been selling to parts vendors more than the public.
 
Good Morning....When I need parts, I go to one of two places. I call Bratton's 800-255-1929 or Arizona Model A 480-782-0266. First, both carry the 'good' parts and second, we do need to keep these suppliers in business...They and all the other Model 'A' Suppliers are part of the backbone of the hobby. Ernie in Arizona
 
The only difference is that the one on Amazon is a 1N1183A and the one in the bad cutout is 1N1183 --Does the "A" make a difference???
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the 1M1183A should work fine, the A says there is a difference but is not enough to worry about.

From Digi-Key tech expert: The only real differences I see is that the 1183A has a higher current rating and temperature range while having a slightly lower maximum forward voltage than the 1183.

So while there are some small differences between the two, I see nothing that would cause any issues to use the 1183A to replace the 1183. The lower forward voltage could possibly be a minor thing to consider, but the difference is about 0.3V maximum so I doubt it would be of any concern.
 
katy said:
the 1M1183A should work fine, the A says there is a difference but is not enough to worry about.

From Digi-Key tech expert: The only real differences I see is that the 1183A has a higher current rating and temperature range while having a slightly lower maximum forward voltage than the 1183.

So while there are some small differences between the two, I see nothing that would cause any issues to use the 1183A to replace the 1183. The lower forward voltage could possibly be a minor thing to consider, but the difference is about 0.3V maximum so I doubt it would be of any concern.
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Thanks for the reply.

One more question at this point--

Why can't I lower the amperage anymore than 10 amps??? I can't move the 3rd brush in the generator any further. Is that a problem??

Want about the voltage reading that I had last time (8.4 volts) is that going to be an issue??
 
rotorwrench said:
A person has to call them. I don't think they update their web site. John Regan sold the business to the Bird Haven Vintage Auto Supply some time back and I think they have been selling to parts vendors more than the public.
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Will their units regulate voltage AND amps??
 
Why can't I lower the amperage anymore than 10 amps??? I can't move the 3rd brush in the generator any further. Is that a problem??
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Maybe the generator has been assembled improperly by a PO?

Will their units regulate voltage AND amps??/QUOTE]

They will regulate the voltage only. According to their instructions the generator must be set to a maximum of 10 amps.
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fred93 said:
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Thanks for the reply.

One more question at this point--

Why can't I lower the amperage anymore than 10 amps??? I can't move the 3rd brush in the generator any further. Is that a problem??

Want about the voltage reading that I had last time (8.4 volts) is that going to be an issue??
Click to expand...

Measure battery voltage at the starter post and adjust third brush for 7.2-7.5 volts. If you can't achieve this, either engine speed is too high or something wrong with the gen.

It's normal to show a high recovery charge rate immediately after starting, but should drop to 1 or 2 amps in a short time. (If the coil is connected to the battery side at the junction box, add 5 amps to that.) If the charge rate remains high for more than a minute or two it indicates a highly discharged battery.

A generator produces power - voltage times amperes. With a constant load (amps) the voltage output rides the roller coaster of engine RPM. A voltage regulator maintains a constant voltage output under varying loads and engine speeds, which prevents bulb burnout and battery hydration from overvoltage.

Ideal battery float (charge) voltage is 7.2-7.9V. Your battery will hydrate at 8.4. A battery will also fail if left undercharged for any length of time.
 
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