Greetings to the forum
Recently the tachometers(Motorola) on the bridge and cabin have been fluctuating a couple of hundred RPM periodically. As they would eventually come back it slipped my mind as being serious.
On this trip about into it a couple of hours, the tachs began in earnest to drop RPMs in an increased amount till around 500 RPM or so. As I was at sea, I called a local Ketchikan alternator/generator shop (White Marine).
The tachometers are run through the alternator so the call seemed correct, The technician gave me a question. ‘Did I have anything in line that called for amp usage? Well, yes, I have an inverter that runs our 110 fridge underway and if called for, a coffee pot, toaster, and micro oven, outside of the fridge, not run together.’ ‘What amperage is your alternator?’ ‘60 amp, I responded. ‘Well, the shop said, I am going to guess that you have pretty much fried your alternator as it is too small for coffee pots and such. When your tachometer dies, Johnson, your alternator is as well!’
When you return home bring your alternator in for review to confirm and by the way, plan on a larger alternator.
Okay, that is the first chapter of this adventure
By the time I arrived at the destination, Wrangell, AK. the tachometers had in fact ‘Died’.
I removed the alternator, went to NAPA and purchased the same make, Delco, in 90 amp capacity and installed.
Now this is a simple four wire system, Ground connection Positive connection, Diodes two prong connector and rectifier (Tachometer connection). I re-installed all wires and connections, double checked and fired up the engine. NO TACHOMETER! What the heck. thought about it, double triple checked connections and out of whim, turned on the inverter system and activated the toaster. VOILÀ!! The tachometer came on and held RPM. What happened?
Call into my heavy duty mecanic son who at once went into a complicated explanation regarding AC/DC science which is all Greek to me. I understand 12 volt and 110 but in separate capacity, not when the integrating conversion of it comes into play.
I had also text my young marine mechanic who responded with confirmation of what had been told to me and the end result is: The new alternator will have to be opened up and something with the rectifier has to be reversed or something.
The point of all this is to lay out a situation that may not be common yet common enough that a seed of what happens in our case will prove helpful.
The new alternator is providing charge to the system. the system currently is at full capacity, reflected in the tachometer not registering. How ever, were our batteries low and we start the engine, the tachometer will register dropping to zero again as the batteries become fully charged.
It is all magic that is what it is, magic!!
I do not pretend to understand it.
Al-Ketchikan Marben 27’ Pocket CRUISER