Can a cutout be tested?

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DHort
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Can a cutout be tested?

Post by DHort » Mon Oct 18, 2021 3:34 am

Is there a way to test a cutout with a multimeter? I have a couple and do not know if they are any good. Have a friend that needs one and they appear to all be back ordered. Might have to ground his generator and run on battery.

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Humblej
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Re: Can a cutout be tested?

Post by Humblej » Mon Oct 18, 2021 7:09 am

Yes, its a dead simple electromagnet, you should be able to check if the points open and close by applying and removing power to it. To bench test, use a battery charger and a test light. One battery charger connection to the mounting arms, the other to the generator output side of the cutout. Place a test light on the battery side of the cutout and it should light up with power applied to the generator side. Reverse the connection by putting the a battery charger on the battery side and the test light on the generator side and the light should not come on with power applied. You can take the cover off to inspect the condition of the points and watch them open and close. Points should spring load open when no power is on the generator side of the cutout, and close when there is power at the generator side. Generator side has the large fork opening for the generator post terminal, the battery side has a small screw connection for a wire terminal. My experience with a cut out is one or more of the following: 1) points stuck together; 2) broken spring; 3) points need filing; 4) points too far gone to clean with a file.


jab35
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Re: Can a cutout be tested?

Post by jab35 » Mon Oct 18, 2021 12:25 pm

You can check the c/o with you multi meter, the battery terminal to case, obviously, should be open, Batt-Gen also open. Gen to case should give resistance of the 'voltage latching' coil. If that is open the points will not close and cutout will not function. A little 9 v battery will be sufficient to close the points, which you should be able hear as you apply/remove voltage between the generator terminal & ground of the c/o. That coil is the one that first 'connects' the generator to the battery when the generator self-energizes on start up. The tension in the spring holds the points open until the generator output voltage reaches ~7volts, and the little 9v battery is adequate to test that. Multimeter can verify electrical connection through the points (read low resistance between Batt-Gen terminals) and maybe identify severely eroded/dirty/high resistance contacts.

As Jeff suggests, best to remove cover and check/clean points if it functions with 9v. IIRC the fine wire for voltage latching coil is connected (grounded) to the frame just under the edge of the cover and if you get too aggressive with cleaning the outside (ie, wire brush, etc) that little wire can become disconnected and the cutout will not work. (And as I learned, the wire can be resoldered to restore function). There's a note on pg 12 in the mtfca guidebook The Electrical System on cutout function that made a lot more sense to me on the third reading AFTER I tinkered with the thing using 9v battery and my cheapie vom. ymmv, respectfully, jb


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Re: Can a cutout be tested?

Post by Art M » Mon Oct 18, 2021 1:49 pm

I like the mechanical cutout because a diode once failed which cost me an armature. I thought about using two sets in parallel, each set having two diodes in series. If one diode fails, the system will continue to function. I have checked to make sure two diodes in series work the same as one

I set my cutout to close at about 7 volts. Connect an analog volt meter to the generator side of the cutout and to ground, run the engine fast enough to check voltage when the cutout closes. Then slow the engine to see at what voltage the cutout opens. It definitely should open when the engine is stopped. Good Luck
Art Mirtes


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Re: Can a cutout be tested?

Post by J1MGOLDEN » Mon Oct 18, 2021 2:31 pm

Measure the voltage at the cutout battery terminal with the engine not running.

Start the engine and measure the voltage with a fast idle.

You should see about 1.5 volts increase, depending on how fully charged the battery is or how high the generator output voltage is.

If the voltage is the same or less, the cutout or generator may be defective.

The ammeter should also show a charge.

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