OT Diode tester on digital multimeter

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Model T Ford Forum: Forum 2017: OT Diode tester on digital multimeter
Top of pagePrevious messageNext messageBottom of page Link to this message  By Michael Deichmann, Blistrup, Denmark on Tuesday, August 15, 2017 - 07:49 pm:

I had some issues with generator and cutout where the generator may have run without being connected to and hence moderated by the battery.
I checked the generator - it ran fine and smooth when 6 volts was applied.
The I tested the diode cutout with my digital multimeter. It have a beeper function marked also with a diode symbol as if it can be used to test diodes.
Now - my problem is that it beeps both ways - with the current goes both ways.
But when I assemble it all - no current goes through the generator and when I start the engine it charges ok = i.e. the diode works as it should.
What am I missing here?


Top of pagePrevious messageNext messageBottom of page Link to this message  By JohnH on Tuesday, August 15, 2017 - 08:26 pm:

Have you actually measured the reverse current through the diode when installed in the car?
The meter is testing the diode at a very low current; about 1mA is typical.
The diode could be slightly leaky so it fails the test on the DMM but doesn't show up on the car's ammeter.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Michael Deichmann, Blistrup, Denmark on Wednesday, August 16, 2017 - 02:35 am:

No. I have a main cut in the car that is always shut off even when parked, so a small leak does not do much harm. As long as it charges the 6 amps I measured I'm happy for now. I'm just wondering why I saw that measurement on the DMM.
Long term plan is a renovated generator with a Fun project voltage regulator.
And a small dashboard with Fun project Ampmeter and voltmeter :-)


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