Testing a diode with a 9V battery tester

[jicman]

Greetings!

I have seen multiple videos of how to test a microwave diode with a 9V battery using a multimeter. But, I don't have a multimeter. However, I do have a 9V tester, which I think can be used. But, I want to make sure this is true before I think I have a good diode.

According to the videos, when I use a multimeter, if I place a diode between a 9V battery and the multimeter while set to display volts, I should get about 6.3-6.6 volts. I have a 9V tester, and if I set the diode between the 9V battery and the tester, I get 6.6 volts. If I take the diode out, I get 9.3 volts. So, is this test good? Thanks for your help.

josé

 

[duke37]

If you place a diode in series with the multimeter, you should get a drop of about 0.6V so show 8.4V.
A microwave rectifier will contain several diodes in series to manage the high voltage. A drop of 2.4V would indicate four diodes. If each of these can handle 1kV then the assembly would be able to rectify 4kV.

 

[kellys_eye]

However, I do have a 9V tester

What's one of those? Is it a tester for 9V batteries?

I think you'd be better served by getting yourself a proper test meter - they aren't expensive (a few $) and could assist with many other forms of fault location.

 

[debe]

If you already have a battery tester then it should work testing a Microwave oven Diode.

 

[jicman]

If you place a diode in series with the multimeter, you should get a drop of about 0.6V so show 8.4V.

Thanks for the response, but according to every video I've seen, there is a voltage drop for good microwave diodes/rectifiers of about 3 volts. So, your response is not correct, here.

IA microwave rectifier will contain several diodes in series to manage the high voltage. A drop of 2.4V would indicate four diodes. If each of these can handle 1kV then the assembly would be able to rectify 4kV.

Thanks for this. My microwave only has one.

 

[jicman]

What's one of those? Is it a tester for 9V batteries?

Yes. One of those thingies that you connect and tell you if the 9V battery is good.

I think you'd be better served by getting yourself a proper test meter - they aren't expensive (a few $) and could assist with many other forms of fault location.

Yes, thanks. I am thinking about that, but right now, I want to use the battery tester. From what I can see from the videos, it should work.

 

[duke37]

Thanks for the response, but according to every video I've seen, there is a voltage drop for good microwave diodes/rectifiers of about 3 volts. So, your response is not correct, here.
Thanks for this. My microwave only has one.

How do you know? Have you cut the gubbins open to see how many diodes are inside?

 

[Alec_t]

A 9V battery may not provide a high enough voltage to test all microwave oven diodes. The NTE517 diode, for example, has a rated Vf of as much as 14V, so would not conduct appreciably with only 9V applied.

 

[jicman]

How do you know? Have you cut the gubbins open to see how many diodes are inside?

Touché! Newbie here thinks he knows all. Ok, so just because there is one piece showing, it does not mean that it's one diode. Thanks.

 

[jicman]

A 9V battery may not provide a high enough voltage to test all microwave oven diodes. The NTE517 diode, for example, has a rated Vf of as much as 14V, so would not conduct appreciably with only 9V applied.

Hmmm... So, why are there so many videos showing "how to test" with a 9V battery?

 

[Alec_t]

Because some diodes obviously have a Vf less than 9V.

 

[jicman]

Because some diodes obviously have a Vf less than 9V.

Thanks. What is the correct way, then, to check a diode? Do I have to get a proper test meter and be absolutely sure? When I place the +(red) and the - (black) to the tester, I get a 9V read. When I place the diode, in sequence, I get close to 3.5V. If I reverse it, it goes to the negative side. Thoughts? And I will leave this alone. It's just that I have a microware that does not heat. It works as if it was working, but it's forgetting the heating part. So, I am testing what is broken here. Thanks for all the replies...

josé

 

[duke37]

A high voltage 'diode' should pass current in one direction with some voltage drop..
In the other direction it should appear as open circuit with no current passing. The only way to test this open circuit is to provide a high voltage source such as a Megger which can give 1kV.

If the 'diode' appears to be correct at low voltage, it probably is correct at high voltage. A faulty 'diode' which leaks at high voltage would be expected to explode or blow a fuse.

The voltages in a microwave oven are extremely high and will jump. The capacitor may hold voltage even when the oven is unplugged from the mains.