Another Rectifier Question - with a twist..

[Romaine]

I am battling some electrical gremlins and I am trying to figure out if the issue is my rectifier.

Without a battery - just running a 12V source (CTEC charger) I would start the bike and as it runs I have blown out the bulbs in the headlight and the taillight (and the gauge cluster) when I rev the engine. I have blown out the rear twice and the gauge bulbs twice..

A friend of mine hooked up and multi-meter to the battery terminals (after the bike was running) measuring AC volts and seeing 7 -10 volts but shut it down without an extended run.. So I am assuming this is why I am blowing bulbs? I should only be getting DC back to the terminals correct?

I did a search on rectifiers in this forum and KARL states:

To check the rectifier:

There is a simple check on page 59 of the 350 service manual .PDF. That quick check will tell you if it is shorted. However, generally, I've found they have an open section or two. A digital multimeter doesn't work well to check those old selenium rectifiers as the meters don't provide enough current to distinguish well between good and bad junctions. You need an old analog meter or a battery and test light. To fully check the rectifier (with all wires disconnected) using a battery and test light:

1. Connect battery Negative to rectifier Black: test light connected to battery Positive should NOT light when touched to each of the other four terminals.

2. Connect battery Negative to rectifier Red: test light connected to battery Positive should light when touched to each of the other four terminals.

3. Connect battery Positive to rectifier Black: test light connected to battery Negative should light when touched to each of the other four terminals.

4. Connect battery Positive to rectifier Red: test light connected to battery Negative should NOT light when touched to each of the other four terminals.


Will this test confirm my rectifier is bad?  Can the rectifier be bad without being shorted?

Im a bit confused on this .. Its not like Im getting low volts - just AC volts.. or maybe that is the problem?


https://bridgestonemotorcycleparts.com/index.php?topic=619.msg2771#msg2771

[OldSwartout]

If you are seeing AC voltage at the battery, the rectifier has at least one shorted junction, letting current flow both directions. The battery is effectively the voltage regulator in that charging system (just like on the singles), without a good battery, you will blow bulbs.  The 350 was the only BS with an effective voltage regulator.

Search the forum for rectifier replacement, you'll find suggestions on using an aftermarket three phase bridge rectifier.  Don't bother looking for a good used OEM one, they are very likely bad.

[Romaine]

Ok - thank you..

I'm still confused as I pulled the unit off and bench tested it with battery and test light.. Of course it did pass the test - but when re-installed it still showed AC voltage to the battery when revved.


I ordered this:

https://www.ebay.com/itm/SQL-100A-Amp-1200V-3-Phase-Diode-Metal-Case-Bridge-Rectifier-5-terminals-CE/171796020110?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649

I think that is what you recommended to someone else in the forum.

Thank you so much for your feedback..