Alternator help on DD 8V92 ta's needed

[Bill Root]

As we were returning from a three day cruise this week, the needle on the alternator gauge for the port engine began slowly dropping from it's normal reading of 34-36V all the way down to 12. I assume that means the alternator is no longer putting out the required voltage to mainatain that battery bank.

Is there a way to test the alternator output to make sure that it really is bad and not some other wiring problem? If I do need to remove the alternator to have it rebuilt, is there anything I need to know about taking it off? It looks pretty straightforward to me, but I do want to be sure before I start putting a wrench on it.

Advice from the experts would be much appreciated.

 

[SKYCHENEY]

Is that the gear driven unit on the back of the engine? If so, you'll what to get a seal kit for when you reinstall.

 

[Bill Root]

Is that the gear driven unit on the back of the engine? If so, you'll what to get a seal kit for when you reinstall.

Yes, it's the gear driven unit. Thanks for the tip. It looks like three bolts hold it on.

 

[bobk]

My mech pulled mine for rebuild when I bought Chateau de Mer six years ago and I seem to recall there were two seals to be concerned with???? Pretty heavy too and in an akward place to retrieve it from.

Bobk

 

[Genesis]

Couple of things on those flange alternators.

They're nothing special internally. Before you pull it stick a voltmeter across it while the engine is running and make sure you don't have a bad connection somewhere else. Be careful doing this -- you're across an UNFUSED energy source while the engine is running and more than enough VA to cause big trouble. If it's bad pull it and take it to an alternator shop -- just swapping it is going to be more expensive than you care to know but they're very rebuildable.

Assuming the alternator is bad there are two issues with regard to seals and oil leaks:

1. The hub drive itself is a phenolic disc that goes on the engine's tanged adapter, then the tangs on the drive for the alternator (bolted to the shaft) engage that. The alternator's drive goes through a hub with a teflon-style seal. That seal is easily damaged and once you remove the drive hub you should replace it or it is likely to leak. Many people just buy a hub kit (containing the hub plate and seal already in it) as if you press in a new seal (which is not very expensive) and do not get it in straight it will definitely leak. Pay particular attention when installing the drive through the seal and make sure (1) you don't nick it and (2) you don't roll it over. If the alternator drive (the tanged metal cylinder that bolts to the alternator and engages the disc on the engine's drive point) has any detectable ridging on its surface the seal will definitely not keep the oil in and it should be replaced. Note that these seals and the drive going through it should be installed clean and dry; use of lubricant is asking for trouble. If I recall correctly the torque on that bolt that secures the drive to the alternator is 80ft/lbs but check the manual to be sure. Having that come loose will ruin your day; don't guess.

2. There are a number of NOT-blind bolts in the adapter that is on the back of the bell-housing and to which that plate (and alternator) bolt up. Those frequently seep oil as well. When you go to re-mount the alternator run a thin bead of RTV around the outside of each of those recessed bolts' holes (you'll see them once you dismount the alternator) so there is no realistic way for oil to get out of there.

If you have some leakage now but there's none on the fan disc then it's almost always coming from the not-blind bolts in the mount and not the center seal. If it's on the fan disc then it's probably coming from the center seal.

 

[Bill Root]

Couple of things on those flange alternators.

They're nothing special internally. Before you pull it stick a voltmeter across it while the engine is running and make sure you don't have a bad connection somewhere else. Be careful doing this -- you're across an UNFUSED energy source while the engine is running and more than enough VA to cause big trouble. If it's bad pull it and take it to an alternator shop -- just swapping it is going to be more expensive than you care to know but they're very rebuildable.

Assuming the alternator is bad there are two issues with regard to seals and oil leaks:

1. The hub drive itself is a phenolic disc that goes on the engine's tanged adapter, then the tangs on the drive for the alternator (bolted to the shaft) engage that. The alternator's drive goes through a hub with a teflon-style seal. That seal is easily damaged and once you remove the drive hub you should replace it or it is likely to leak. Many people just buy a hub kit (containing the hub plate and seal already in it) as if you press in a new seal (which is not very expensive) and do not get it in straight it will definitely leak. Pay particular attention when installing the drive through the seal and make sure (1) you don't nick it and (2) you don't roll it over. If the alternator drive (the tanged metal cylinder that bolts to the alternator and engages the disc on the engine's drive point) has any detectable ridging on its surface the seal will definitely not keep the oil in and it should be replaced. Note that these seals and the drive going through it should be installed clean and dry; use of lubricant is asking for trouble. If I recall correctly the torque on that bolt that secures the drive to the alternator is 80ft/lbs but check the manual to be sure. Having that come loose will ruin your day; don't guess.

2. There are a number of NOT-blind bolts in the adapter that is on the back of the bell-housing and to which that plate (and alternator) bolt up. Those frequently seep oil as well. When you go to re-mount the alternator run a thin bead of RTV around the outside of each of those recessed bolts' holes (you'll see them once you dismount the alternator) so there is no realistic way for oil to get out of there.

If you have some leakage now but there's none on the fan disc then it's almost always coming from the not-blind bolts in the mount and not the center seal. If it's on the fan disc then it's probably coming from the center seal.

Thanks for all the great advice. It's much appreciated. The plot is getting thicker, though. I went to the boat today to check the alternator power output with a multi meter. When I started the engine, the voltmeter on the instrument panel went right up to 36V and stayed there. I tested the output at the alternator and at the input to the battery bank - 36V at both. So what the heck caused the voltage output to drop off the other day while we were under way? My son suggested it could be the "rectifier assembly" on the alternator. He said that it's a common problem on motor cycles. What do you all think?

 

[captddis]

Thanks for all the great advice. It's much appreciated. The plot is getting thicker, though. I went to the boat today to check the alternator power output with a multi meter. When I started the engine, the voltmeter on the instrument panel went right up to 36V and stayed there. I tested the output at the alternator and at the input to the battery bank - 36V at both. So what the heck caused the voltage output to drop off the other day while we were under way? My son suggested it could be the "rectifier assembly" on the alternator. He said that it's a common problem on motor cycles. What do you all think?

Was the charger on??

 

[Genesis]

Thanks for all the great advice. It's much appreciated. The plot is getting thicker, though. I went to the boat today to check the alternator power output with a multi meter. When I started the engine, the voltmeter on the instrument panel went right up to 36V and stayed there. I tested the output at the alternator and at the input to the battery bank - 36V at both. So what the heck caused the voltage output to drop off the other day while we were under way? My son suggested it could be the "rectifier assembly" on the alternator. He said that it's a common problem on motor cycles. What do you all think?

The rectifier and regulator on those as they are originally built are both internal. They're also surprisingly robust; I had one develop a bad connection offshore and burn the wire literally off the terminal bolted to the stud (it was bad up inside the terminal itself.) That (an open circult on an alternator) usually winds up destroying the diodes and/or rectifier but mine was fine once I replaced the damaged cable (there wasn't enough extra to cut it back and put a new end on it.)

If it is bad I assume the diodes and regulator can be replaced; an alternator shop would know if parts are available (they should be.)

How's your AC charger wired and was/is it on? (I see captddis got to this while I was typing) If you only had 12V while running how'd that bank get enough charge in it to be able to start the engine? If the AC charger was not on in the interim that's real solid evidence that the fault is in the gauge wiring and not the charging system.

If your charger is original and is like a lot of the ferroresonant ones that were put on Hatts there are multiple outlets but only one sense line to disable the charger when the engines are running. If the engine that has the sense line on its starting bank is not running the AC charger will continue to put out power so you would see "charge" even though the alternator is not putting out anything.

Add all that up and what I'd do to isolate this is first to make sure the AC charger is off (breaker open) and see if you still see charging with that engine running at the dock.

If you still see charge knowing the AC charger is disabled then check the wiring carefully -- you may have a loose connection somewhere; there's a high-amperage (was 80A on Gigabite) ANL fuse in the main engine room panel between the alternator feed and the DC bus so you have the connection at the alternator itself that could be loose and also the ones in the panel, along with the wiring to your gauge on the panel. Be extremely careful working around the main DC panels as the primary side of those connections go directly to the battery with no current protection and there's plenty of grounded things in and around there. In addition my boat was wired with the master disconnects on the panel leaving the alternator circuit hot even when they were in the OFF selector position! That's good for preventing an accidental destruction of the diodes but bad if you think all those ANL studs are "dead" with the switch set to OFF -- they're not! Best practice is to pull the battery cables before opening those main DC panels up.

 

[krush]

And as I said before. VA is mentioned but that is a unit of measurement not used in DC circuits.


But for the problem of dropping volt meter to 12V: I would first carefully check all your connections. 12V would be dead flat on all the batteries and though possible, not really probable. I'd make sure you didn't have a poor connection that caused a large voltage drop. Test, don't guess.

 

[Bill Root]

And as I said before. VA is mentioned but that is a unit of measurement not used in DC circuits.


But for the problem of dropping volt meter to 12V: I would first carefully check all your connections. 12V would be dead flat on all the batteries and though possible, not really probable. I'd make sure you didn't have a poor connection that caused a large voltage drop. Test, don't guess.

Thanks again for the great advice. Let me clarify a couple of things. I was not looking at the gauge when I sent the original post. When I looked at it yesterday while on the boat, I realized that the low end is actually 26V, not 12. The gauge did go down to just above the bottom peg. When it did that I checked the second gauge on the fly bridge. It read the same, so it definitely isn't a gauge problem. Sorry for providing inaccurate info in the original post.

The charger breaker was on and the generator was running. I have the original Lamarche charger.
Does the alternator output run through the charger to the batteries, or does it go direct to the battery bank through the main DC panel?

At some point as we approached the marina I ran across some low water and sucked mud up into the generator intake, causing it to shut down. Unfortunately, since I couldn't hear the generator over the engine noise, I didn't realize it had quit until I notice that the AC was no longer running. I don't know for sure if that all happened just before or just after the alternator voltage output drop.

At this point, based on the advice so far, it sounds like a bad connection, wire or fuse is the most likely culprit, so I plan to start by tracing all the connections from the alternator to the battery bank, cleaning them up and re-tightening them.

Thanks again for the helpful input. I'll keep the forum posted on how I make out.

 

[Genesis]

The charger is a separate energy source.

Most of the original chargers (ferroresonant type) have a "cut out" board in them but only one sense line. The purpose of that is to inhibit the charger when there's another charging source (alternator) supplying current, but since it only senses one bank but the charger has multiple bank outputs it will not shut down with only one engine running (e.g. at the dock) unless the correct one is running (the one with the sense wire.)

Disable the AC charger by opening the AC breaker for it and then see if you have charge showing up now at the dock. If so it's probably a bad connection somewhere; if not the odds are higher that the alternator is bad, but you still need to check connections before removing it since it's somewhat of a pain to get out and there's no point in removing it and taking it to a shop to be rebuilt if it's not defective. The most-likely bad connection is at the alternator itself simply because that's where vibration is greatest, but it could be anywhere between the alternator and main DC bus. Just be careful working around the main DC panels and alternator since those are large-wire connections and either fused with high-amp (ANL) fuses or not fused at all and connected directly to the battery banks -- disconnecting the batteries is the best choice before opening the main panels and when working on the alternator connections themselves. Don't rely on the disconnect switch; mine were wired to not shut off the alternator feeds and thus it was very possible to get a nasty surprise if you grounded the positive alternator wire out by accident.

 

[Bill Root]

The rectifier and regulator on those as they are originally built are both internal. They're also surprisingly robust; I had one develop a bad connection offshore and burn the wire literally off the terminal bolted to the stud (it was bad up inside the terminal itself.) That (an open circult on an alternator) usually winds up destroying the diodes and/or rectifier but mine was fine once I replaced the damaged cable (there wasn't enough extra to cut it back and put a new end on it.)

If it is bad I assume the diodes and regulator can be replaced; an alternator shop would know if parts are available (they should be.)

How's your AC charger wired and was/is it on? (I see captddis got to this while I was typing) If you only had 12V while running how'd that bank get enough charge in it to be able to start the engine? If the AC charger was not on in the interim that's real solid evidence that the fault is in the gauge wiring and not the charging system.

If your charger is original and is like a lot of the ferroresonant ones that were put on Hatts there are multiple outlets but only one sense line to disable the charger when the engines are running. If the engine that has the sense line on its starting bank is not running the AC charger will continue to put out power so you would see "charge" even though the alternator is not putting out anything.

Add all that up and what I'd do to isolate this is first to make sure the AC charger is off (breaker open) and see if you still see charging with that engine running at the dock.

If you still see charge knowing the AC charger is disabled then check the wiring carefully -- you may have a loose connection somewhere; there's a high-amperage (was 80A on Gigabite) ANL fuse in the main engine room panel between the alternator feed and the DC bus so you have the connection at the alternator itself that could be loose and also the ones in the panel, along with the wiring to your gauge on the panel. Be extremely careful working around the main DC panels as the primary side of those connections go directly to the battery with no current protection and there's plenty of grounded things in and around there. In addition my boat was wired with the master disconnects on the panel leaving the alternator circuit hot even when they were in the OFF selector position! That's good for preventing an accidental destruction of the diodes but bad if you think all those ANL studs are "dead" with the switch set to OFF -- they're not! Best practice is to pull the battery cables before opening those main DC panels up.

Thanks for the tip about disconnecting the batteries.