alternator and tach problems

[Bobg]

Hi everyone, just got done reading the archievs to try determine what may be wrong with my alternator, this weekend I looked down and saw zero rpm reading and around 10volts on the voltage meter, I checked the output on the alternator and couldn't get a reading, checked my batterys and they were down to 11 volts, usualy I get at least a 13 plus reading when the motor is running.  according to the archeives, I should check for loose connections, belts, excessive heat build up ect.  

here is my question, after a while the tack started to work again, but still no output from the alternator.  Can this be so?, if the alternator is bad, should the tack still work? I didn't have time to go through the checks, had to go home as soon as we docked, so I have some time to ask these questions before I go back to the boat for the trouble shoot.  Could it be that the alternator simply went out and I have to replace it.  Seems odd that the tack and alternator were both out, then the tack kicks in. but not the alternator output. Thanks guys

[Stu Jackson]

What'd be helpful is a bit more info on what you have.  What alternator, how old, external or internal regulator - that stuff.

Tach working and no alternator output is suspicious, since, as you most likely already know, the tach only works when the alternator is outputting.  So, if the tach was working, what led you to believe that the AO was zero, or did you measure it?  Just askin'...  Many folks complain about no tach operation, but their batteries are full and the regulator says "don't need any power" when they startup their engines.  I understand from your post that may NOT be your issue.

Answer to your ? is: NO.

BUT, if YOU didn't have time to do the checks, then until you find out whether or not you have a loose wire, we're all just guessin'.  Might be better to find that loose wire before we all go huntin'.

Do you know Jim Moe? Have you asked him?

[Ken Juul]

Might not be a loose wire.  Could also be a corroded connection.  Anything else that runs on 12v acting up?  If yes could very well be the ground wire connection at the rear of the engine.  If the engine harness upgrade has not yet been done, the trailer plugs at the engine and the engine panel are also good culprits.

[Bobg]

I have a motorola, I do believe it is original equipment, I have what looks like a external regulator mounted on the engine.  When the Tack started working again, I went to the batterys with my digital voltmeter and didn't see where a charge was coming in, and clearly the batterys were down.  maybe when I look it over again I'll find something.
Is it true, that when your batterys are full, like when you just leave the dock after having been plugged in and the on board charger has filled the batterys, and the alternator shuts down or goes into the "sleep mode", that the tack should stop also?  5 years with this boat and have never seen the tack go to zero like that.  thanks guys  Bob

[reedbr]

Bob-

If the tach came back but you didn't see 13 volts at the battery, it could just be that the batteries were still significantly discharged.  I usually see 13-14 volts when my engine is running too, but the batteries are usually between 12 and 12.5 volts to start.  As Stu said, a little more diagnostics is necessary.  Either way, no tach usually means a failure, even if intermittent, in the charging system. 

[Stu Jackson]

Is it true, ... and the alternator shuts down or goes into the "sleep mode", that the tack should stop also?  5 years with this boat and have never seen the tack go to zero like that.  

Essentially it is true.

There is NO "sleep mode" although I know what you mean and agree with your suggestion as a better way to describe the actual "symptoms" but we already have so many engineering terms with these pieces of equipment, it may be prudent to reduce the addition of any more terms, as much better as yours actually is!

You could leave your shorepower charger on with full banks and start your engine (not recommended for daily use!) and see what the tach does.  One of our members did just that and asked about it years ago.   One is Reply #8, here:  http://c34.org/bbs/index.php/topic,4972.0.html  Another is here:  http://c34.org/bbs/index.php/topic,3881.0.html  This is the one I had in mind, took a few minutes to find it ("batteries and the fridge"): http://c34.org/bbs/index.php/topic,973.0.html

\Where'd I find all this?  Search on "tach" with lots of experiences to share.

You can learn how regulators, both internal and external, work, and about battery acceptance (see:  http://c34.org/bbs/index.php/topic,4787.0.html) which are subjects beyond the scope of this board to explain and is much better done by books.

Sometimes the tach will stay at zero until you turn on a load.  If you start your fridge before your engine, then that load will drop the house bank down just enough to have the regulator say "let's charge" and at the same time, the battery acceptance level has dropped a tad, too, so an amp or so can go back in.  While a regulator may be sending a  "putting out" signal, the battery bank may not be accepting and the ONLY way you're gonna know is by either a) trusting me completely about this stuff  ; or b) installing and using a battery monitor.  Amazing how much you can learn with one of those puppies.  

We've had many conversations about these, and searches on "battery monitor" and "Link" will provide you with hours of fun reading.

Like this one: Link "Gotcha Algorithms" - for those of you who have them or are getting one, you NEED to know this:

http://c34.org/bbs/index.php/topic,4922.0.html

[Ed Shankle]

Bob,
I've had the same symptoms, first started end of last season. Periodically the tach would drop to zero, the volt meter drops to 11.5 and a separately wired amp meter drops to zero. After a while everything would resume normal function. This year, sometimes I've been able to get it going again by just changing speed! Turning the engine off and restarting also got it going again.
I had the alternator rebuilt over the winter, I tinned the engine compartment wires and reconnected, I cleaned the engine grounding points, checked all connections on the engine panel. My external regulator is about 8 years old, and passes the diagnostics.
This season it hadn't happened, until last week. Came back after a few minutes and happened a 2 more times. Ok this weekend.
I don't suscribe to the "full battery" theory. It hasn't happened after spring commissioning when the batteries are fully charged before re-installing. I would think that would be the most likely time for me since I'm on a mooring all season. However, I am not anywhere near an expert on electrical systems, 12v systems or the wiring of our boats. It's just that after owning Tail Wind for 12 years and not having seen that happen until last season, I think it's more in the loose wire, rusted connection category. So, I'll methodically start going over all the connections again. 
Good luck,
Ed

[Bobg]

Reedbr, thank you and to you all for the help, when the tach came back,  the batterys still showed they were down, however, the volt meter still showed the alt wasn't charging, I didn't read it close but the needle was significantly to the left of top on the guage.  I usually show around 14 volts when I cruise, with occasionally 12 volts, which I assumed drops when the batterys were fully charged.

  Ed, when you say the tach would drop to zero, and then everything came back, does that mean the voltmeter showed charging also?, I would certainly subscribe to the loose/corroded wire theroy.  From what I have learned, if the alt is bad, the tach shouldn't work.  In that my tach comes back but the alt shows no charge, and the batterys are down, I must have a different issue to ferret out.   Or am I overeacting and it is just the nature of the system that revealed itself after 5 summers.  I have 4 trojans and a dedicated isolated start battery and a combiner.  I leave the battery switch on all and have a referigerator, thanks guys, just trying to be armed with some info for when I go back to the boat for trouble shooting.  talk to ya later.   Bob

PS:  what is a simple way of seeing if the alt is good with a multi meter   thanks

[Stu Jackson]

It's a loose or corroded wire connection, a bad alternator or, I just thought, a loose and slipping in a major way belt.

Bob, alternator output is most easily checked with a DVM, voltage is the clue.

For those who claim "I dunno anything about electrical" I strongly urge you to start reading.  I recognize that some folks don't have the time, can't make the time, or like our classmates in school some folks don't get math & science, while I never "got" art.  That said, I still believe it is an important safety issue.  No one says you need to know everything or be Mr. Toolman, but you can learn the basics to be able to work on the system you have on your boat.  It's wires and connections, and safety if things don't work.  So, consider buying a simple book about boat electricity and read it every once in a while, and sooner or later some of it will get through.  

If you do a search on "wiring diagrams" and print out some of them, start tracing how the power works.  Wiring diagrams, while daunting to some, are actually the easiest way to start to understand how boat electrical systems work.

I did NOT know any of this stuff when we bought Aquavite in 1998.  I read a lot, learned as much as I could, and feel safer for it.

Bob wrote: I leave the battery switch on all...   When and why?

[Ed Shankle]

Bob,
When it comes back up, that includes the voltmeter returning to the 13.5 - 14 volt range.

Ed

[jmnpe]

Hi All,

A few more things to think about when you have strange things going on in your alternator and/or tach. First, some alternator basics.

In typical diesel applications such as our C34 engines, the alternator provides both 12 volt power output and a tach signal output. The power output has effectively 3 pairs, or 6, high power output rectifiers to rectify the 3 phase output from the stator winding. The tach output is a halfwave rectified output of only one leg of the 3 leg stator output, meaning it has a dedicated low power diode. The tach diode and the power output diodes are independent ( something to remember  ).

In the case like Ed was describing where the tach and alternator output both failed at the same time, there is really only one root cause that can produce such a simultaneous failure ( if you don't count having the alternator intermittently stop turning.... ), and that is loss of field current. The loss of field current can be produced by: (1) a bad field current circuit, including a failed voltage regulator or bad connection in any field current wire; (2) a bad slip ring or rings in the armature circuit ( this winding is the field winding; (3) loss of DC power input to the voltage regulator. There may be a few more specific combinations of things, but they will all be some variant of these 3 general classes.

If the alternator output and tach outputs do not fail together, then there are a few specific combinations of failures that can produce the problem depending upon what works and what doesn't work. (1) If you have a smart voltage regulator and the tach quits after the regulator goes into float mode, that just means that your batteries are still floating down from the absorption charge voltage ( ~ 14.4 volts ) to the float voltage ( ~ 13.4 volts ) and the problem will generally go away if you have a modest load on the 12 volt system to get the battery back to the normal float voltage. (2) If your battery voltage falls obviously below your normal "cruise" charging voltage but the tach still works, you have lost some or all the power output from the alternator. If it is permanent, you probably have had output diodes fail or had an output circuit wiring failure. If it is intermittent, look first for output circuit path problems. It is possible under the right circumstances to experience intermittent output diode failures, but it would probably be a problem in the mechanical mounting of the diodes into the alternator case. I have also never actually seen intermittent output diode failures, but it is still possible. (3) If the tach quits but the alternator power output is normal, the problem almost has to be either in the wiring from the alternator tach output to the tach instrument; a failure in the the tach unit itself; a failure of the internal isolation diode on the tach output; or an internal alternator wiring failure in the tach output signal circuit.

If this posting doesn't go into enough detail for anybody about how exactly to perform the troubleshooting with normal "boat" tools, I'll try to add more detail in a follow up post if it's needed.

Regards, and happy troubleshooting.

John

[Roland Gendreau]

Check for corrosion at the engine harness connector, if you have not yet done the upgrade to terminal blocks.  It is a common source of issues that show up at the engine panel.

Roland Gendreau
Gratitude #1183

[Stu Jackson]

Good point, Roland, I keep forgetting about that.

We have, as many may have noticed, included a new feature called "Critical Upgrades" both here and on the wiki.  http://c34.org/bbs/index.php/topic,5078.0.html

One of the "most popular" is the wiring harness and connector upgrade, you know, that FIRE hazard just waiting to bite you in the you know where.

But I'm sure Bob has done that, right Bob?

[Hawk]

Bob,
As mentioned above, really check the connections to the alternator. I had a similar intermitant problem. Then in July as I was motoring the tack and volt meter dropped to zero. Finally located the problem to be at the alternator where the lug crimped to the wire had broken. A new lug crimped on the wire and back on the alternator...all well.

Hawk

[Stu Jackson]

Hawk's right, connections:  see "Regulator to Alternator Wiring" : http://c34.org/bbs/index.php/topic,3398.0.html