Alternator diode query

[what2do]

A bit of a specific question this but who knows, we may have an alternator specialist amongst us. When testing the diodes in a rectifier, does anybody know where I can find the acceptable values? I believe mine is reading high and would like to check. From what others have said it appears to need replacing regardless.

Thanks.

[Oldiebut goodie]

Give me the part no on the diode and it can soon be found out. Generally if they are all the same value they will be ok, it is when 1 is different that it will need replacement.
If I get chance I'll rip an alternator apart and check them.

[what2do]

I don't have the alternator apart, I just did the simple test of putting the meter on the 2 posts at the rear (D and B+). With the meter probes one way I get 0L and the other way I'm getting over 1600 with the meter set to 'diode'. I've read that it shouldn't be more than 800. That's the extent of my knowledge at this point. Thanks.

[Oldiebut goodie]

The diodes need checking individually.

[CovKid]

Yep, need desoldering, by which point you might just as well change the rectifier anyway.

[what2do]

I hear you, I'm just trying to understand each process individually. Would the meter reading indicate a fault that you can relate to? The actual symptoms that I've mentioned have given you reason to suggest that the rectifier needs replacing, it will be replaced but I'm just trying to further understand what the figure of 1600 means.

Thanks.

[bigbadbob76]

The figure 1600 is millivolts drop across the two points you are measuring.
If you remove the diodes and check them individually I'd expect round about 700mV one way and open circuit (ol) the other way.
Measuring them in circuit with the other diodes and alternator windings gives confusing results.
Hope that helps.

[what2do]

The figure 1600 is millivolts drop across the two points you are measuring.
If you remove the diodes and check them individually I'd expect round about 700mV one way and open circuit (ol) the other way.
Measuring them in circuit with the other diodes and alternator windings gives confusing results.
Hope that helps.

No, it doesn't really help but that's because it's gone beyond my level of comprehension!!!! Perhaps, it's too much to ask to become an 'expert' just by watching a few youtube videos...

I've found a local guy that refurbishes alternators so I'll be dropping it off soon. Ta.

[what2do]

The diodes need checking individually.

Searush by any chance????

[Oldiebut goodie]

Above does not compute in my brain! Searush?

[what2do]

Above does not compute in my brain! Searush?

Not one of your other usernames on a boating forum?

[Oldiebut goodie]

You wouldn't catch me on a yellow welly brigade's forum!

[what2do]

You wouldn't catch me on a yellow welly brigade's forum!

He has the same avatar as you, just wondered.