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Old 07-05-2015, 11:05 PM   #1
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Westerbeke low voltage

My Westerbeke 12.5 KVA, brushless generator is only putting out 102 volts. I have checked the rpm which is fine at 1850 no load rpm. The rectifier also checked out. The guide suggests hooking up a 12 volt battery and a bulb to check the diodes in place. This test indicates 4 of the 6 are bad.

My questions are....
Is this possible? I would have thought 4 of 6 bad diodes would cause a much bigger voltage loss.
Has anyone changed these out before themselves or is it time to bite the bullet and get a tech to the boat?
What could have caused the diodes to blow?

Any advice is appreciated!
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Old 07-06-2015, 06:18 AM   #2
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"What could have caused the diodes to blow?"

Starting with loads already on the circuit makes some noisemakers very unhappy.

Best to start , let it operate for a min or two, no load , them put the load on slowly.
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Old 07-06-2015, 09:27 AM   #3
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I assume you are talking about the diodes on the exciter rotor. I have replaced those before and even with one out of six failed, volts were very low. To confirm, I would unsolder one terminal at a time and test in open circuit configuration. Testing within the circuit is not easily done.

Did unit make proper volts up until recently?
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Old 07-06-2015, 10:25 AM   #4
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Ski, yes it has performed perfectly until last weekend. The test for the diodes on the excitor rotor, using a 12 volt battery and bulb instead of a multimeter was meant to allow "in place" testing. I just think I must have been doing something wrong to have for out of 6 showing blown. Either something I did during startup or something in my testing procedure. These diodes are miniscule!
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Old 07-06-2015, 10:50 AM   #5
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Those diodes just plain fail. When I was deep in generators, I kept a box of them. It is delicate surgery to unsolder them through that little access, but can be done. I would test in place, then if one was suspect, unsolder one terminal and test it in open circuit. Sometimes it would test ok then, sometimes not. Often I would replace that one anyway. Be very careful with polarity, sometimes the paint ring on the old one is hard to read.

Also, have you double checked the voltage with a separate meter? Boat panel meters can be sketchy. Check with DVM.

Westerbeke electrical ends don't seem to hold up as well as other brands. I have replaced numerous westy stator/rotors, got another one this week. I have replaced one Onan stator for like 10 Westy's.

And FF is right- Start under no load, breaker open, apply load small things first. When shutting down, run unloaded for a few minutes, breaker open, then shut down.

You may have a fault in unit other than the diodes.

Has unit breathed salt mist or got dripped on?

Rewind exchange units are available from Broward Armature in Ft Laud.
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Old 07-06-2015, 11:04 AM   #6
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Dimer: Wish I could help, but it's beyond me...GOOD LUCK!
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Old 07-06-2015, 11:29 AM   #7
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Thanks Ski, I will give it a go. Can't break something that's already broke
Wyoboater, you could come drink a cold one and give me moral support!
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Old 07-06-2015, 07:24 PM   #8
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Wasn't able to make it to Bmt today, but, perhaps later this week. You had any luck yet?
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Old 07-06-2015, 09:35 PM   #9
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Yes and no. Checked with OEM and the diodes are $33.00 each plus shipping. Went to the little local electrical shop, $0.78 each including shipping and they will be here tomorrow. Felt so bad I bought yet another soldering gun, 4 cans CRC which should last me 4 years and a flashlight.
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Old 07-07-2015, 05:47 AM   #10
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That's too funny! Nice of you to keep local businesses going though.
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Old 07-09-2015, 11:19 PM   #11
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Ok, cannot find a local generator tech locally that is willing to come to the boat. So I unsoldered (those things were welded in!) one end of each of the 6 diodes. All tested fine. Now I guess I need to test the actual windings. Not looking good. I guess I will be pulling the generator out if I need an exchange unit as can't see doing major surgery in the hole it's in.
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Old 07-10-2015, 06:30 AM   #12
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That's really not looking good. Do you have a manual for it? Any other trouble shooting hints?
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Old 07-10-2015, 09:22 AM   #13
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Sounds very similar to my problem a few months ago but my output was 92 volts

Broward armature sent me a rebuilt head and then stayed on the phone with me while I installed it

Dan the former owner still works there and was great
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Old 07-10-2015, 09:39 AM   #14
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Thanks guys. I see a road trip in the very near future. I know of worse places than Ft L. Siestakey, roughly how much is an exchange unit?
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Old 07-10-2015, 09:42 AM   #15
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Quote:
Originally Posted by dimer2 View Post
Thanks guys. I see a road trip in the very near future. I know of worse places than Ft L. Siestakey, roughly how much is an exchange unit?
Mine was 1186.58

and that included shipping

and shipping back for my core
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Old 07-10-2015, 12:30 PM   #16
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Be certain of the voltage readings before you jerk it out. If rpms are good and volts confirmed low, I'd just do the Broward swap.

Besides the exciter rotor diodes and the bridge rectifier, not much serviceable in that thing. Even if you can find a tech with the proper test gear, that means you might find what the issue is, but the fix is the same.

Have you tried swapping the bridge rectifier cube? I think I had one that tested well but apparently was failing under load. Swapped and volts came back.
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Old 07-10-2015, 10:29 PM   #17
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Hi Ski, yes changed the rectifier cube and checked all diodes. I have a tech coming tomorrow to check winding (he says he has a special machine?) and will help with the removal if needed. I will know for sure tomorrow if/when he shows up but have resigned myself to a road trip to Florida next week. Took the Jarvis Newman out for the day to make me feel better. It's amazing how well that works
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Old 07-11-2015, 12:20 AM   #18
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Quote:
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Hi Ski, yes changed the rectifier cube and checked all diodes. I have a tech coming tomorrow to check winding (he says he has a special machine?) and will help with the removal if needed. I will know for sure tomorrow if/when he shows up but have resigned myself to a road trip to Florida next week. Took the Jarvis Newman out for the day to make me feel better. It's amazing how well that works
Amazing how a road, I mean boat trip will cure most of your blues! We are anchored out tonight waiting on the Blue Angles tomorrow. It's the best stress reliever there is!
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Old 07-11-2015, 01:12 AM   #19
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Capt, as a lowly private pilot, I stand in awe of the skills and reflexes those guys have. It is simply amazing. Enjoy the show tomorrow!
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Old 07-13-2015, 10:01 PM   #20
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How'd it go with the tech? Any progress? And I totally understand taking Rhino for a spin.....boating cures the soul.
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