Hwere we go again: Low Voltage on Stb Engine

[bobk]

We just returned from a visit to Miles River YC. We normally run at 1000 rpm, 8 knots. Today I ran it up to 15 knots for about five minutes to blow the engines out and the voltage on the starboard engine (both helms) dropped to 10-11 volts. We started the generator because this engine ties to the inverter bank via a combiner. The lower helm came up to 13 volts, the upper showed 12. After idling waiting for a bridge opening the meters began reading as usual, and continued to do so after turning off the generator. A half hour later at 1000 rpm, the synchronizer quit.... wouldn't engage. We shut both engines down and restarted and voltage was OK, but the synchronizer still didn't work.

Any ideas? I need to get this fixed before we start south. We had a similar situation this spring, but in that case the starboard ignition switch also got hot, then returned to normal but the synchronizer worked OK. Boatsb replaced the starting batteries and ignition switch and all was well until this morning. Dontcha hate intermittent problems?

Bobk

PS, 1981 Series I 48MY, 6V92 TA 425 HP

 

[bobk]

I just had a chance to start checking. Found the synchronizer fuse was blown. Replaced it and the synchronizer is now working..... but the blown fuse was 20 amp, the book calls for 10 amp. Something must have pulled a lot of amps?? Anybody??

Bobk

 

[Reefgeorge]

Which engine/battery bank does the synchronizer gets its power from?

If it's the stb side which has the voltage problem then if the synchronizer does not tolerate low voltages well, it could have started over heating and/or drawing too much current. If it's failing and given the improper fuse value, it may have pulled down the bank voltage if that side has any marginal problems. Can you run without it to see if the problem is gone?

If it was an independent low voltage problem then of course we have all the usual charging/battery suspects. I would start with checking all grounds at the engine block, batteries, alternator, etc. How old are the batteries? The fact that it appeared with the rpm change makes the alternator and its regulator a prime suspect. Is that belt OK?

 

[bobk]

Which engine/battery bank does the synchronizer gets its power from?

If it's the stb side which has the voltage problem then if the synchronizer does not tolerate low voltages well, it could have started over heating and/or drawing too much current. If it's failing and given the improper fuse value, it may have pulled down the bank voltage if that side has any marginal problems. Can you run without it to see if the problem is gone?

If it was an independent low voltage problem then of course we have all the usual charging/battery suspects. I would start with checking all grounds at the engine block, batteries, alternator, etc. How old are the batteries? The fact that it appeared with the rpm change makes the alternator and its regulator a prime suspect. Is that belt OK?

It is the starboard side and that is the slave engine. The on off switch is wired to that ignition switch. The two 8D's on that side are new and in parallel and have been on the charger all week as we were 'plugged in'. When I start the engines I always look at the volt meters for signs of trouble but all was OK.

No belts on the 6V92.... gear driven.

I just spoke with the Glendenning synchronizer tech and he offered much the same advice. If the low voltage is due to the engine charging system, the solenoid may have pulled more amps than normal and blown the fuse and it is not part of the 'problem'. If there is some issue in the solenoid, it 'might' have pulled the voltage reading down and caused the blown fuse. One possibility here is the spring tension on the engine governor may be too high and overloads the solenoid. But nothing there has changed for 2000 hours at least. I need to get a clamp-on DC amp meter to see what the Glendenning draw is.

What is weird is the similarity to my problem this spring on the way north.

Ideas??? Keep 'em coming.

Bobk

 

[Reefgeorge]

It is the starboard side and that is the slave engine. The on off switch is wired to that ignition switch. The two 8D's on that side are new and in parallel and have been on the charger all week as we were 'plugged in'. When I start the engines I always look at the volt meters for signs of trouble but all was OK.

No belts on the 6V92.... gear driven.

I just spoke with the Glendenning synchronizer tech and he offered much the same advice. If the low voltage is due to the engine charging system, the solenoid may have pulled more amps than normal and blown the fuse and it is not part of the 'problem'. If there is some issue in the solenoid, it 'might' have pulled the voltage reading down and caused the blown fuse. One possibility here is the spring tension on the engine governor may be too high and overloads the solenoid. But nothing there has changed for 2000 hours at least. I need to get a clamp-on DC amp meter to see what the Glendenning draw is.

What is weird is the similarity to my problem this spring on the way north.

Ideas??? Keep 'em coming.

Bobk

Please explain "slave" engine, I don't understand that term for propulsion engines.

What on/off switch is connected to the ignition switch? Is it the one for the synchronizer? What was happening to the voltage when that switch got hot earlier?

One diagnostic approach is to move the synchronizer power over to the port engine and observe.

Another as mentioned is disconnect synchronizer power temporarily.

When the voltage starts misbehaving is the generator/shore charger ever on or did you only turn those on to temporarily solve the problem. If so and it always solves the problem then that indicts the stb engine charging system. Does the genset have a charging alternator and which bank does it charge when started?

 

[Reefgeorge]

Two more thoughts.

Do you alternators have temp probes at the alt case or the batteries to derate voltage with high temp?

Which engine/bank is the house bank?

 

[MikeP]

Of course, the 20A fuse in a 10A's position is a very bad thing so put the 10 back in. You are lucky there wasn't a wiring fire!

Since nothing has changed in the throttle liinkage/spring on the slave engine , I can't see how anything there would affect the solenoid power draw. Though it's certainly worth checking and adjusting if necessary.

Until the time that the fuse blows, does the synchronizer keep the engines in sync or does it kick itself "off?" It will do that if it can't bring the slave motor to match the lead.

Did this problem begin after some sort of change/maintenance to the boat's DC electrical system?

 

[bobk]

Two more thoughts.

Do you alternators have temp probes at the alt case or the batteries to derate voltage with high temp?

Which engine/bank is the house bank?

I do not know if there are temperature sensors. I just checked and my generator does have an alternator linked to the starboard battery bank. The house bank is the port pair of 8D's.

Bobk

 

[bobk]

Of course, the 20A fuse in a 10A's position is a very bad thing so put the 10 back in. You are lucky there wasn't a wiring fire!

Since nothing has changed in the throttle liinkage/spring on the slave engine , I can't see how anything there would affect the solenoid power draw. Though it's certainly worth checking and adjusting if necessary.

Until the time that the fuse blows, does the synchronizer keep the engines in sync or does it kick itself "off?" It will do that if it can't bring the slave motor to match the lead.

Did this problem begin after some sort of change/maintenance to the boat's DC electrical system?

Mike, yes, 10 amp fuse goes back in. I checked the associated wiring and solenoid and all looks good.... no charring. Glendinning thought no harm would be done but of course recommended the proper fuse.

The synchronizer is working properly. I've had it kick off for the reason you describe but that doesn't blow the fuse. A simple throttle adjustment fixed that issue years ago. And I can't relate the problem to any maintenance unfortunately.

Bobk

 

[bobk]

Please explain "slave" engine, I don't understand that term for propulsion engines.

What on/off switch is connected to the ignition switch? Is it the one for the synchronizer? What was happening to the voltage when that switch got hot earlier?

One diagnostic approach is to move the synchronizer power over to the port engine and observe.

Another as mentioned is disconnect synchronizer power temporarily.

When the voltage starts misbehaving is the generator/shore charger ever on or did you only turn those on to temporarily solve the problem. If so and it always solves the problem then that indicts the stb engine charging system. Does the genset have a charging alternator and which bank does it charge when started?

"Slave" engine (starboard) is the one who's throttle is moved by the synchronizer in response to moving the "master" (port) throttle.

The synchronizer on/off switch is connected to the starboard ignition switch.

When the fuse blew, the synchronizer power was disconnected.

I turned on the generator after seeing the voltage readings drop and I didn't know what was happening. I don't remember the result from the first incident, but yesterday the voltage reading increased a little but not up to normal when the generator and battery chargers were engaged. I don't recall if there is an alternator on the generator.

The problem with any of these diagnostic tests is the problem has only occurred twice and those incidents were separated by 1500 miles and several months of operation. It will be hard to learn anything much in that kind of situation.

Bobk

 

[Reefgeorge]

I feel your pain on electrical problems that wont stay broken long enough to diagnose. I have one of those right now.

Synchronizer slave, got it.

If I understand the "clues" that we have so far, the voltage drops when the stb rpm increases and is normal after rpm decreases. The generator and shore chargers are turned on in between so they may or may not be material to the main problem. You went from normal voltage to low voltage to partial voltage recovery (generator and shore charger) and ultimately normal volatage. Then the synchronizer quit.

Since this problem is intermittent, you need to get the most valuable info possible when it happens again. I suggest that you get your hand held volt meter handy, reproduce the same conditions and when the voltage drops again, run down to the engine room and measure the voltage at the batteries. This way you will know if you have an alternator/regulator/battery/cable problem, or a problem that is on the way up to or at the helm. Even though both helm stations show a low voltage I would verify the voltage at the helm where the synchronizer is connected on both sides of the ignition switch. The fact that the switch was once hot to the touch suggests that it could be failing and not just a symptom of excessive current. If the other helm gauge is downstream then both helm meters would be affected. If it is the switch just wiggle it and you might see the helm voltage meter flop around. You might want to replace that switch as a starting point.

If the battery voltages are normal then at least you know that the problem is beyond that and you can start looking at everything that is tied to the stb bank such as the inverter that you mentioned, etc. You could then also relax a little because you wont lose that bank or comprimise the starting process.

The fact that it happened with changing rpm does suggest that the alternator/regulator may be the cause. As mentioned before, check the wire connections involved. If having the alternator/regulator removed and bench tested is not desireable than you can at least swap regulators between the alternators if they are easy to remove on the back of the alternators. If the problem does/does not follow the regulator then you have cleared one possibility.

The fact that the generator and shore chargers coming online only partially fixing the problem does not help much because either 1) there is not really a battery/charging issue or 2) if there is and the batteries were almost dead then proper charging will not restore the voltage until the batteries start recovering. Full recovery appears to be associated with a return to low rpm so once again the alt/reg must be considered.

Now that the synchronizer has a proper fuse value it will be interesting to see if it starts blowing fuses regularly.

 

[bobk]

I feel your pain on electrical problems that wont stay broken long enough to diagnose. I have one of those right now.

Synchronizer slave, got it.

If I understand the "clues" that we have so far, the voltage drops when the stb rpm increases and is normal after rpm decreases. The generator and shore chargers are turned on in between so they may or may not be material to the main problem. You went from normal voltage to low voltage to partial voltage recovery (generator and shore charger) and ultimately normal volatage. Then the synchronizer quit.

Since this problem is intermittent, you need to get the most valuable info possible when it happens again. I suggest that you get your hand held volt meter handy, reproduce the same conditions and when the voltage drops again, run down to the engine room and measure the voltage at the batteries. This way you will know if you have an alternator/regulator/battery/cable problem, or a problem that is on the way up to or at the helm. Even though both helm stations show a low voltage I would verify the voltage at the helm where the synchronizer is connected on both sides of the ignition switch. The fact that the switch was once hot to the touch suggests that it could be failing and not just a symptom of excessive current. If the other helm gauge is downstream then both helm meters would be affected. If it is the switch just wiggle it and you might see the helm voltage meter flop around. You might want to replace that switch as a starting point.

If the battery voltages are normal then at least you know that the problem is beyond that and you can start looking at everything that is tied to the stb bank such as the inverter that you mentioned, etc. You could then also relax a little because you wont lose that bank or comprimise the starting process.

The fact that it happened with changing rpm does suggest that the alternator/regulator may be the cause. As mentioned before, check the wire connections involved. If having the alternator/regulator removed and bench tested is not desireable than you can at least swap regulators between the alternators if they are easy to remove on the back of the alternators. If the problem does/does not follow the regulator then you have cleared one possibility.

The fact that the generator and shore chargers coming online only partially fixing the problem does not help much because either 1) there is not really a battery/charging issue or 2) if there is and the batteries were almost dead then proper charging will not restore the voltage until the batteries start recovering. Full recovery appears to be associated with a return to low rpm so once again the alt/reg must be considered.

Now that the synchronizer has a proper fuse value it will be interesting to see if it starts blowing fuses regularly.

Let me clarify, the first time this happened we had been running only an hour or so at 1000 after a lunch break. I can't say that increasing speed is involved. In the recent case, we may have been at 2000 rpm for 3-5 minutes. I can say it was not immediate because I always watch the instruments as I crank her up.

Good point about checking battery voltage. My admiral is not comfortable running the boat unless it is in really open water so that will cut the chances of detecting it even further. Most of our time is in rivers and AICW.

We know the starboard bank is good... it's new and started the engine very fast with normal voltage drops when I restarted it several times with in 10 minutes of all this. If it had died, it could not have recovered that fast.

Again, I can't associate recovery with return to low rpm. In the first case we were never at a higher rpm. That would have been a very valuable clue if the case.

Also I did wiggle the stb ignition switch several times but it had no effect. In the first instance, when the switch heated up, the switch continuity checked OK after the fact. Maybe Scott will remember if he measured actual resistance. I could see a case where there was a heavy draw on the switch and if it was somewhat corroded it might have heated up. Now I have a brand new switch with no resistance so perhaps the problem passed to the synchronizer? And then the synchronizer failed because the fuse blew. I'll need to get a clamp on DC amp meter and see if it is drawing too much. I just wish I knew more about things electrical.

Bobk

 

[Reefgeorge]

RPM's not necessarily important. Check.

Given the issues with being in two places, a dedicated voltage monitor wired directly to the batteries is helpful (thats what I did because my analog ignition voltage gauges suck). If not run a wire up from the batteries/main breaker (fused) and have it available as a measurement point at the helm while trying to catch this. Another approach is wire a voltage meter to the ER point and ask the Admiral to go down to the ER and tell you the battery voltage. You can use a DVM or buy a $5 digital on eBay.

Once you know if battery voltage is solid during an event then we/you can start picking apart the problem further.

As far as electrical knowledge, thats what we are here for but keep asking and we will get you smarter. The bigger skill is problem solving anyhow so lets keep dissecting this until we find the problem.

Has this happened since the ignition switch was replaced?

 

[bobk]

RPM's not necessarily important. Check.

Given the issues with being in two places, a dedicated voltage monitor wired directly to the batteries is helpful (thats what I did because my analog ignition voltage gauges suck). If not run a wire up from the batteries/main breaker (fused) and have it available as a measurement point at the helm while trying to catch this. Another approach is wire a voltage meter to the ER point and ask the Admiral to go down to the ER and tell you the battery voltage. You can use a DVM or buy a $5 digital on eBay.

Once you know if battery voltage is solid during an event then we/you can start picking apart the problem further.

As far as electrical knowledge, thats what we are here for but keep asking and we will get you smarter. The bigger skill is problem solving anyhow so lets keep dissecting this until we find the problem.

Has this happened since the ignition switch was replaced?

Yes, the switch was replaced in May. the last occurance was yesterday.

I'm going to attach a clamp on voltmeter to the Glendinning control wires as soon as I can buy one and see if the unit is drawing too much, but it strikes me as unlikely as the wires are fairly heavy. I'll also tie in a volt meter to the batteries to try to catch the event. The admiral is happy to do ER checks underway, so I' try to get her to check it if we can catch it. A recording volt meter would be really nice.

Bobk

 

[Reefgeorge]

If you have no other use for a clampon ammeter, put a high watt one ohm resistor (shunt) in series with the wire. The voltage reading equals the current with minimal effect on the circuit.

 

[Boatsb]

Bob how long since the alternators were rebuilt? Is it easy enough to get them tested to see if they're the cause. The regulators and alternators seen to be a constant part of my thoughts about the cause.

The syncronizer may not be related to this at all.

 

[MikeP]

FWIW - many electrical problems are connection-related, not component related. Intermittent problems could easily be due to corroded/faulty connections/switches.

 

[bobk]

Bob how long since the alternators were rebuilt? Is it easy enough to get them tested to see if they're the cause. The regulators and alternators seen to be a constant part of my thoughts about the cause.

The syncronizer may not be related to this at all.

Scott, no idea about last rebuild. They were tested several years just for S&G. One got new bearings if memory serves. But how could a mall functioning charging system drop the voltage to 10 volts, and not have the battery go down?

Mike, the switch on the bridge was replaced a few years ago, so assume those connections are OK. The Synchronizer it self was new in 2007 and the ER is dry in that area. Connections look good. I did look at the alternator wiring today and the cable ends look clean but I didn`t break any connections.

I`m trying to get my Detroit guy to check this out. We are off to Maui in the morning. More to follow. Thanks to everyone for all the advice .

Bobk

 

[Boatsb]

Alternators do short. Diodes go bad over time. Maybe it's as simple as a new regulator and your golden.

 

[Reefgeorge]

Alternators do short. Diodes go bad over time. Maybe it's as simple as a new regulator and your golden.

I have been trying to lead you down the path of confirmation of the source of the problem before replacing parts but i can understand it if you want to start diving in and not wait for a complete set of answers. The only problem is it will be intelligent guessing and may result in wasted money if that matters to you. To that end, about the only two devices that can draw the actual battery voltage down that much on a perfectly good set of batteries without blowing a fuse, a breaker or starting a fire are the alternators and the starters. They have the cabling and windings to handle it so in fact a faulty alternator/ regulator or starter could be the cause. Just remember that low voltage at the helm guage does not guarantee low voltage at the batteries.