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MEP 003A Blew its Ammeter Circuit


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  #11  
Old 08-05-2018, 03:27:16 PM
Vanman Vanman is online now
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Default Re: MEP 003A Blew its Ammeter Circuit

My vote is for a stuck or otherwise physically damaged meter movement. If the secondary (meter side) of a current transformer opens at any point, high voltage results and I'd expect to see some smoke as the CT is being damaged. But maybe not , if the load was light...
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Old 08-05-2018, 05:02:47 PM
Thaumaturge Thaumaturge is offline
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Default Re: MEP 003A Blew its Ammeter Circuit

Example of options now available.
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https://www.amazon.com/ELEGIANT-80-2...dp/B06XRW1ZHK/
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Old 08-05-2018, 06:54:45 PM
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Default Re: MEP 003A Blew its Ammeter Circuit

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Example of options now available.
Doc
https://www.amazon.com/ELEGIANT-80-2...dp/B06XRW1ZHK/
Wonder if a clamp-on tester would be useful. I have one, a Canadian one.

This is the 6625-01-038-6829 meter
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Old 08-05-2018, 07:08:51 PM
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Default Re: MEP 003A Blew its Ammeter Circuit

Nothing on meter face to reveal actual meter specs, other than it is a REAL D'arsonval movement. (Jeweled pivots with balanced armature.) To test meter movement power with a single battery series connected with a 10k potentiometer, a 1 megohm resistor. Reduce value of potentiometer until meter reaches full scale. If full scale not reached return pot to max and lower resistor by half. Repeat until meter reaches full scale. Then measure ohms of pot and series resistor, then voltage of battery. Ohms law will reveal current and extrapolate full scale voltage. Can measure current in series, but measure meter with resistors for proper total.
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Old 08-05-2018, 07:34:28 PM
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Default Re: MEP 003A Blew its Ammeter Circuit

Interesting. I'll file that.

I looked at the schematic and found two transformers of interest: one labeled current transformer and one called a current voltage transformer.

Locating these on a schematic is a whale of a step away from knowing where a part is physically, and its specs. All my experience has been in front of the dashboard, not behind it.
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Old 08-05-2018, 08:15:12 PM
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Default Re: MEP 003A Blew its Ammeter Circuit

Uh, in addendum above method works on DC meter movements. If meter contains integral rectification you must either dissasemble to reach zctual movement or use AC in place of battery. As to locating components, CTs are typically toroids, so look for a donut shape.
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Old 08-05-2018, 08:31:07 PM
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Default Re: MEP 003A Blew its Ammeter Circuit

The Ct and CVT is a black bakolight type plastic rectangle with the output wires to lugs looping though it. Sitting on bottom of output box.
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Old 08-05-2018, 08:33:21 PM
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Default Re: MEP 003A Blew its Ammeter Circuit

The meter, on its face, says FS 1A AC. I looked carefully on the photo for a wound former between the pivots, but didn't see one. That plus the non linear scale may indicate a moving iron meter. However running a CT with an open circuit secondary is inviting trouble, expensive trouble. Check the meter still has continuity, check the CT has secondary winding continuity. Moving Iron meters will respond to DC as well as AC so it is easy to check the movement with a D cell and a swamp resistor.

Mike
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Old 08-05-2018, 08:36:58 PM
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Default Re: MEP 003A Blew its Ammeter Circuit

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The Ct and CVT is a black bakolight type plastic rectangle with the output wires to lugs looping though it. Sitting on bottom of output box.
Are they equally suspect in causing this? The circumstance -- turning on the AC kicked the overload switch --certainly suggests a part got overloaded, not some other demon like mouse-gnawed wiring.
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Old 08-05-2018, 08:39:53 PM
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Default Re: MEP 003A Blew its Ammeter Circuit

I would be inclined to *guess* that that current meter reads to the 100% mark on the scale when 5 amperes AC are flowing through it... Just since 5 amps is a fairly typical full load CT secondary current. Have no idea if the military stuck with that standard or not!

Whoops! Just saw Mike's post. So not 5 amps to 100%, 1 amp all the way to the 133% mark... Interesting.
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