Checking alternator diodes while car is running

[pmureika 31]

How do I do it. Just set the meter to ac and see if I have any ac current.

[Kangaroux 47]

What diodes?

[pmureika 31]

What diodes?

In the alternator.

[Kangaroux 47]

What diodes?

In the alternator.

Oh I thought you meant diodes outside of the alt lol. Yeah just switch it to AC I guess. Make sure you use a clamp meter if it's anywhere over like 500 mA or whatever your DMM is rated for..

[pmureika 31]

What diodes?

In the alternator.

Oh I thought you meant diodes outside of the alt lol. Yeah just switch it to AC I guess. Make sure you use a clamp meter if it's anywhere over like 500 mA or whatever your DMM is rated for..

I was told to set it to ac volts and measure at the bat. Which I did and got .05vac

[Kangaroux 47]

What diodes?

In the alternator.

Oh I thought you meant diodes outside of the alt lol. Yeah just switch it to AC I guess. Make sure you use a clamp meter if it's anywhere over like 500 mA or whatever your DMM is rated for..

I was told to set it to ac volts and measure at the bat. Which I did and got .05vac

You measured at the battery? Your alt puts out DC volts not AC.

[pmureika 31]

What diodes?

In the alternator.

Oh I thought you meant diodes outside of the alt lol. Yeah just switch it to AC I guess. Make sure you use a clamp meter if it's anywhere over like 500 mA or whatever your DMM is rated for..

I was told to set it to ac volts and measure at the bat. Which I did and got .05vac

You measured at the battery? Your alt puts out DC volts not AC.

Not if a diode is going bad. Alternators put out ac voltage the diodes turn it into dc volts.

[MrBrooks 0]

What diodes?

In the alternator.

Oh I thought you meant diodes outside of the alt lol. Yeah just switch it to AC I guess. Make sure you use a clamp meter if it's anywhere over like 500 mA or whatever your DMM is rated for..

I was told to set it to ac volts and measure at the bat. Which I did and got .05vac

You measured at the battery? Your alt puts out DC volts not AC.

Not if a diode is going bad. Alternators put out ac voltage the diodes turn it into dc volts.

[MrBrooks 0]

That's why it's called an ALTERNATEor ..............the rectifier(diodes) turns the AC to DC

[Tirefryr 1,742]

YOu won't be able to test, unless you have an outboard rectifier.

[shizzzon 461]

if the sole purpose is to see if part of the 3 sets of diodes have burnt out of the rectifier, then that's easy..

Get a clamp meter(ammeter), clamp it around your charging cable at the alternator.

Now would be a good time to know what your alternator's rated specs are.

I would primarily test maximum output potential.

Most alts, unless otherwise stated, are rated COLD and most alts will reach peak at engine rpm of 1800-2500.

So.. just to make sure you get there, rev to about 3000rpm, put an ENORMOUS load on the vehicle. Something you know the alt just can't handle.

Obtain reading...

if an alt is rated for 250A cold, it's hot reading could be anywhere typically between 195-230A due to variables(belt, engineering, resistance, wiring configuration, etc)

If one set of diodes go out, 13 of the output would be lost so it should be quite noticeable.

[pmureika 31]

if the sole purpose is to see if part of the 3 sets of diodes have burnt out of the rectifier, then that's easy..

Get a clamp meter(ammeter), clamp it around your charging cable at the alternator.

Now would be a good time to know what your alternator's rated specs are.

I would primarily test maximum output potential.

Most alts, unless otherwise stated, are rated COLD and most alts will reach peak at engine rpm of 1800-2500.

So.. just to make sure you get there, rev to about 3000rpm, put an ENORMOUS load on the vehicle. Something you know the alt just can't handle.

Obtain reading...

if an alt is rated for 250A cold, it's hot reading could be anywhere typically between 195-230A due to variables(belt, engineering, resistance, wiring configuration, etc)

If one set of diodes go out, 13 of the output would be lost so it should be quite noticeable.

I have a mechman 300amp in a jeep liberty. With clamp meter I was getting 250 plus with the stereo cranked up and ac running. Also the voltage was at 14.1.

[shizzzon 461]

then ur diodes are fine.

[pmureika 31]

then ur diodes are fine.

Thank you!

[pmureika 31]

YOu won't be able to test, unless you have an outboard rectifier.

Built into the 300amp mechman.

[jonbearsmt 919]

a lot of people have no clue that the alternator is a AC generator but its true.

[pmureika 31]

a lot of people have no clue that the alternator is a AC generator but its true.

Not like when I learned, they were generators.1962 mercury comet.