Alternator Diode Rectifier Woe

[ndutton]

Would I be correct in saying that, at rest, no charger on, engine not running, but batteries and alt+ connected to the main buss bar, there should be zero current flow thru alt+?

Of course. The alt isn't connected in series and doesn't feed-thru.

[hanleyclifford]

Of course. The alt isn't connected in series and doesn't feed-thru.

If I were to place an ammeter between alt+ and the #4 cable going to the main buss bar, using a shunt and a digital gauge, I should get a zero reading even if the battery charger is connected. Do you agree?

[ndutton]

If I were to place an ammeter between alt+ and the #4 cable going to the main buss bar, using a shunt and a digital gauge, I should get a zero reading even if the battery charger is connected. Do you agree?

Yes, as long as nothing else is connected to alt+.

[hanleyclifford]

Yes, as long as nothing else is connected to alt+.

Thanks for considering and replying on this matter. It's too late to do anything about solving the mystery now, but the game plan now is to set up another ammeter right at alternator plus so that in the future I will always know what is happening there, especially when the the engine is not running. As a bonus when the engine is running I will get a reading on the raw amperage being produced by the alternator. My other ammeter gets the "net" amperage at the main buss bar.

[hanleyclifford]

Hanley, are the batteries good? And how/where was the charger hooked up?

I used a std 6/12V 2/10amp battery charger. I hooked it up to the output feed from the alt for the positive and to the main ground buss for the batteries, not the best way but most convenient due to access. The batteries were under a bunk and the engine was too and with the engine cover off both were exposed. I left the power switch to both and did this for 34 years. I also keep my battery in my hot rod hooked in the same fashion as the battery is under the seat. I clip to the output of the alt and an engine mount as both are exposed the the engine is not fully covered. No issues so far there either.

I would talk to another alt shop repairman to hear his opinion then tell him what you were told.

I kinda think the guy was trying to be impressive above his "paygrade" and knowledge. I've blown a few diodes in my time but never with a charger. This has peaked my curiosity.

Dave Neptune

Dave, I did replace a couple of batteries during the years the boat was in the barn but those events did not coincide with the problem. My charger is wired to the main buss bar which is the same as alt+ for all practical purposes. I am going to continue to talk to alternator shop technicians as I get the chance. Meanwhile I have ordered a new diode rectifier bridge to get the alternator back to work. BTW, this is the second time this has happened. The first time was in Titusville while I was wintering in the marina, again connected to a charger. There is an alternator shop there within walking distance of the marina. I had them do the job and did not investigate further. But now I'm suspecting that I have something wired wrong.

[ndutton]

The ammeter I prefer and have onboard is a Gauss loop rather than a shunt. Its main advantage is zero added connections so therefore zero added failure points due to corrosion, vibration or looseness.

https://www.amazon.com/bayite-Digital-Current-Voltage-Transformer/dp/B01JIK8J3C/ref=asc_df_B01JIK8J3C/?tag=hyprod-20&linkCode=df0&hvadid=642135191713&hvpos=&hvnetw=g&hvrand=2229951262329766552&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9060629&hvtargid=pla-1948309956361&psc=1&mcid=13e6c6e7c43c36cea15c0a8d965199e6

Waiting for the information this ammeter provides but I'm getting an idea what happened. More data first however.

[Dave Neptune]

Hanley, how old is your battery switch? Is it possible that a contact could be corroded or malfunctioning? Most of the time a diode blows is due to a surge from a quick off/on and usually from switching under alternator charging loads. Good switches have surge protection but it does not mean they can't fail.

Dave Neptune

[Al Schober]

I think it more likely that the alternator failed due to corrosion of one or both slip rings, preventing current from getting to the rotor. Not a big deal to crack it open and clean the rings.
edit: Might as well replace the brushes while you're in there.

[joe_db]

Another possible issue: If there is a problem with the regulator or how it is wired, it can end up always being on and thus drawing power and possibly causing damage.

[hanleyclifford]

Another possible issue: If there is a problem with the regulator or how it is wired, it can end up always being on and thus drawing power and possibly causing damage.

I am aware of that possibility but it is unlikely in my case where I have a solid state regulator (Transpo V1500) which has pilot lights for all functions. Also my ammeter is always on since the system is live at all times. On the mooring there is no problem but on a dockside charger even if you are showing no amperage at rest the possibility still exists that a parasitic draw is being balanced by the charger and concealing the problem. Both failures have occurred while on charger dockside or in the barn. As Neil has suggested I am going to start monitoring amperage at alt+.

[hanleyclifford]

The ammeter I prefer and have onboard is a Gauss loop rather than a shunt. Its main advantage is zero added connections so therefore zero added failure points due to corrosion, vibration or looseness.

https://www.amazon.com/bayite-Digital-Current-Voltage-Transformer/dp/B01JIK8J3C/ref=asc_df_B01JIK8J3C/?tag=hyprod-20&linkCode=df0&hvadid=642135191713&hvpos=&hvnetw=g&hvrand=2229951262329766552&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9060629&hvtargid=pla-1948309956361&psc=1&mcid=13e6c6e7c43c36cea15c0a8d965199e6

Waiting for the information this ammeter provides but I'm getting an idea what happened. More data first however.

Thanks Neil, I am going to get that very meter ASAP.

[hanleyclifford]

Hanley, how old is your battery switch? Is it possible that a contact could be corroded or malfunctioning? Most of the time a diode blows is due to a surge from a quick off/on and usually from switching under alternator charging loads. Good switches have surge protection but it does not mean they can't fail.

Dave Neptune

I do switch batteries while running and charging but always of course making sure at least one battery is on line. I never considered the scenario you describe.

[hanleyclifford]

I think it more likely that the alternator failed due to corrosion of one or both slip rings, preventing current from getting to the rotor. Not a big deal to crack it open and clean the rings.
edit: Might as well replace the brushes while you're in there.

I will be taking the alternator apart soon and check where you have advised.

[joe_db]

I am aware of that possibility but it is unlikely in my case where I have a solid state regulator (Transpo V1500) which has pilot lights for all functions. Also my ammeter is always on since the system is live at all times. On the mooring there is no problem but on a dockside charger even if you are showing no amperage at rest the possibility still exists that a parasitic draw is being balanced by the charger and concealing the problem. Both failures have occurred while on charger dockside or in the barn. As Neil has suggested I am going to start monitoring amperage at alt+.

There are only two ways for current to go IN to an alternator. Either some diode issue allows current to flow the opposite direction it usually does or the regulator is feeding current into the field.
OK, there is another way - a charger with a substantial AC component to the output might possibly do this. One would think the battery would smooth this out or the charger would just burn up, but in theory it might happen.
Jut thought of another way - if there is an AC tap for a tachometer or regulator signal, current might possibly go back in that way if there is some odd miswiring.