alternator output

[sail4dale]

I have a hypothetical question regarding what if?

The switch under the chart table is an engine on switch and without it being in on position, the engine won't start.  Also we know that  we don't turn the main electric switch to off while the engine is running as the alternator just may burn up the diodes.

So, what could happen it someone accidentally turns the engine switch to off when the engine is running?  Does it disconnect the alternator output to the batteries.  I've not been able to isolate the wiring for that in the diagrams I have in the manual.

I don't intend to try that trick te see what would happen but I would love to have the detail of the engine on/0ff switch explained.  We have such a wealth of "experts" on this web site I know I'll get some good answers.

[Ron Hill]

Dale : Great Question!!
If your voltage reg/alternator is sensing the battery voltage at the key switch, you'll fry the alternator!  Some early regulators did this!!
If your battery voltage is sensed at the battery/s, then the on/off of the key switch matters not!!   
Guess you need to know YOUR charging/sensing system and how it works !!!!!!!   

[Stu Jackson]

Yes, Dale, good question, and it's NOT hypothetical.  It's VERY real.

Please see update further down this thread (June 19)

Basic answer: MAYBE [/size]

What do you mean by "engine on switch?"  The 1-2-B or the key switch?  (I guess you mean the 1-2-B by "under the chart table," but most of the C34s have the switch in the panel above the nav station.)

Discussed in many previous posts, but try this one:  Connecting Batteries in Parallel:  http://c34.org/bbs/index.php?topic=2347.0

It's very long, but read the whole thread, please.

The majority of the boats until just recently were factory wired with the alternator output to the "C" post of the switch.  This means that the switch is actually used for two purposes:  which battery bank(s) the alternator charge goes to when the engine is running, and which bank is chosen for use for DC power.

Only YOU know how your boat is wired.  As mentioned in the reference, on our boat I deliberately MOVED the alternator output from the C to the 2 post to charge my house bank THROUGH the switch, which can only be done with a combiner or some serious bypass wiring.

YOU have to understand how this all works on your boat.  DC wiring is red and black, + and -, flows one way, except for my example ( ), which is how they wired the boats.  Learn to follow the wiring and make sketches of your own.  Many more discussions are on the Message Board, try searches on alternator, electrical, regulator, batteries, etc.

Projects has some very good electrical articles, see Jim Moe, John Gardner and Mark Elkin's fine descriptions, print out the wiring diagrams and get to it.

Good question, lotsa ways for YOU to control how it works on each of YOUR own boats.


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IF your alternator is wired through the C post of the 1-2-B switch,  FOGETTABOUT ever turning your switch to OFF if you want to keep your alternator working.  Keep your brother-in-law off the boat.  Don't move the switch, from whatever position it was in when you started, when the engine is running.

IF your alternator is wired directly to your house bank, AND you have a 1-2-B switch for the output only of your banks, it shouldn't be a problem.

If you have two separate switches, one for house and one for start bank, it doesn't matter, because you don't have a 1-2-B switch that cuts over the alternator.  BUT, don't turn off the switch when the engine's running.

You asked: "So, what could happen it someone accidentally turns the engine switch to off when the engine is running? "

DON'T DO IT, IT WILL MOST LIKELY FRY YOUR DIODES, AND WILL IF YOUR ALTERNATOR OUTPUT IS WIRED THROUGH THE C POST OF THE 1-2-B SWITCH

IS THAT CLEAR ENOUGH?   

Also, what could "accidentally turn off" mean?  It's a BIG switch.  DON'T TOUCH would be a good idea to mean not turn off accidentally.  I have a great deal of difficulty understanding how someone could do this without it being deliberate.

However, you could turn off your cockpit key switch.  Depends on what you mean by "engine switch?"  And I DO mean COULD, because it depends on how your boat is wired.

Sorry to be an engineer about this, but English is an imperfect language...

BUT, (OK, here's that damn but), IT'S YOUR BOAT and we can tell you how to wire it to make it work better, but really, it's a matter of safety and it's YOUR choice.

Sorry about the disclaimer, but it's personal here, beyond the C34 IA and website stuff.

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Added June 9th

Re: Key switch.  In most cases, the key switch is the connection to the alternator's regulator.  That means when you turn on the key switch, the ignition wire to the regulator is energized, turning the regulator on.  In the case of OEM regulators, which are internal, it just tells the regulator to work once the engine starts and the alternator is turning.  It does the same for externally regulated alternators, turning the circuit ON to the regulator, essentially waking it up and saying: "Next step the engine's gonna start and you need to start working to regulate the alternator."  It has nothing to do with the alternator electrical output itself, which should go to the batteries, either though the 1-2-B switch or directly to the house bank and combiner or echo or duo chargers.  So, with the caveats still in place mentioned above, turning off the key switch when the engine is running normally shouldn't affect the alternator -- it just won't put any current out, since the regulator is OFF.  The issue with turning the 1-2-B switch off is that you are interrupting the 12V output of the alternator, which would fry the diodes.  The diodes will fry whenever you interrupt the ability of the alternator to send power to the batteries when the alternator is running. I also recommend that you buy and install a ZAP STOP across the + & - terminals of your alternator.  This will save the diodes in case that switch accident actually does happen.  Very cheap insurance.

Please see update further down this thread (June 19)

[Craig Illman]

Just to be a little picky, but DC negative can now be yellow as well, to eliminate the potential mix-up with AC hot.

I agree with all Stu & Ron have said. One of the best things one can do is clearly understand how your individual boat is wired. It's a SAFETY thing!

- Craig

[Ron Hill]

Guys : With all of the HOOPLA side, it still depends WHERE the voltage regulator is sensing the battery voltage.  If the regulator senses the battery's voltagare is OK there's no problem.  If the regulator senses "0 voltage at the batteries then it'll fry the alternator diodes!!!

KNOW YOUR SYSTEM !!  Any question, then you should install a "ZAP Stop" on your alternator.   

[Fuzzy]

Dale:
Is the switch that you're talking about OEM or did the PO install it?  I wonder if it may be
a starter batter on/off switch.  If the placement is under the chart table it surely has me
stumped.
Let us know what you find out.
Larry

[sail4dale]

The switch in question is along side of the three-position battery switch under the chart table facing aft.

It is an "engine" on /off switch and with out it being turned on you can't start the engine

it's position is inboard of the two circuit breakers (windless and control panel)

[Ron Hill]

Dale : It sounds as though that switch was installed by a PO.  You'll have to drop the panel open and trace the wire. It almost sounds as though the PO wired the + wire to the engine instrument panel, so it could be switched on/off ?   

[sail4dale]

a heavy wire goes from the three pos batery selector switch common to the Engine on off switch (same arrangements on the newer Cat 36's) and from the engine switch aft to ???? 

It is factory installed and in the manual except it doesn't show where it ends up   

[Ron Hill]

Dale : As a last resort - ask the factory, as we on the message board are guessing and haven't seen your wiring!! 
Would think that they ought to be able to answer your question!!   

[Stu Jackson]

Ron's right, but why not try to answer your own question: from the engine switch aft to ????   

You're on your boat (and we're not), follow the wire(s) and find where it (they) go(es).  When we bought our boat (albeit an older one) we still had ALL the documentation (plus this website), but I traced and labeled most of the wiring so I could figure out how it worked by knowing the wire's starting and ending positions.  Some places required some very inventive bodily positions, most, if not all, that I could get myself out of without help.   

I also looked into the C34 Mk II manuals, available at www.c34.org, left index: Manuals, and could not find the wiring you are describing on your boat in the factory wiring diagrams.

[Stu Jackson]

OUTPUT Question Redux to reply #2 above

WHY RISK IT?

I asked Jim Moe, a C34 owner and a professional electrical expert, the following question, with his reply:

Jim

Re alternators and regulators.  I've always been under the impression that if the 1-2-B switch was turned off when the alternator output was wired through the C post of the switch that the diodes would fry.  I also thought that if the regulator was turned off no damage would occur since the alternator output is still connected, just that the field isn't getting excited for output.  In reading this thread, Jeff Tancock, another C34 owner, reported to me that he had OEM alternator output to the C post, his guests turned off the switch, but the alternator survived.
 
Stu

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Jim's reply:

Generally speaking the determining factor is just how hard the alternator is pumping at that moment.  If it isn't working too hard the magnetic flux in the rotor isn't so great that you get a huge voltage pulse which back biases the diodes to the point they fail.  If it is, the flux may be so great that even though the regulator says "cut back, the voltage is too high" there's enough residual flux to cause enough voltage to kill the diodes.  Thus it's the luck of the draw.

Some of the later alternators have suppressors which limit the voltage spike which occurs under these adverse conditions and some use avalanche breakdown diodes (which are somewhat pricier) that are more or less self protecting.  There's a possibility that what he has as well.

So far as the regulator being disconnected, you're quite right.

Jim