Testing a alternator diode/rectifier pack

[MandM]

Hi experts how do you test a rectifier from a 18acr alternator to see if its fully working

Please be kind as I'm not good with electrics , I know that the diode should only pass a voltage one way , so do i just put a meter on the 3 small ones in this view?

P1100333.jpg

what about the others that look like spacers in the next view , how do you test them? where do you put the probes of the meter?



P1100335.jpg



thanks for your help, this is a original Lucas UBB110 diode pack

[Wheelz]

Heres a typical alternator circuit. The current flows in the direction of the diode arrows.

If you have disconnected the windings then you can test each diode individually with a normal multimeter using the diode test function. The band is the negative end.

Note that those banded diodes with wire ends are not the original ones which are those that look like spacers!

How to test a diode - YouTube

[MandM]

thanks Chris will have a play, the spacer type looks the hardest

martin

[marshman]

The little diodes are the "exciter" diodes. The main diodes that rectify the "power" output are the big ones between the two plates.

If you want a good quality replacement pack then try here. They are a good price and likely ex MoD stock so should be a quality item as opposed to a cheap knock off.

https://www.thexmod.com/item_detail.asp?id=9790&t=Rectifier_Metallic_Alternator_83842_UBB110

[MandM]

Ok thanks, I have just check the "exciter" Diodes they all see ok and give a valve of .472-.514, the next plate down with 3 spacer type diodes seem ok as well and give a reading of .389-.402,

The back plate with the other 3 spacer type only 2 give a reading the third does not , so can this be replaced or is it dead?

see reading below


1.jpg 2.jpg 3.jpg 4.jpg

[Wheelz]

A reading of 0.00 would suggest diode has failed short circuit. Theoretically replaceable, but without a part ID you would have to search for something suitable that is physically compatible, and has an adequate current rating (>45A continuous). Replacement diode packs are available for 18ACR or perhaps salvage one from an old alternator.

[MandM]

Thanks Chris just seems a shame to dump a original Lucas part, maybe I will see what's about from local members, or keep the small diodes and middle plate that might be of service to someone else , at least this thread gives others an idea how to test a rectifier , so they know.

just happy I keep learning from this forum

thanks all