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Position: 41°42’26.3″N 70°45’29.6″W
Aleta’s been a bit reluctant to start recently. I am certain it is related to an electrical problem that we have had since we bought her: the notorious ‘wacky tachy’. The tachometer, as you know, is connected to the alternator, which is connected to the voltage regulator, which is connected to the starter, which is connected to the voltmeter. Hear the word of the Lawd! And when the tachy goes wacky and things ain’t quite right with Aleta’s currents and flows, the batteries grumble. Then I grumble and start rooting around in search of solutions.
Now, I’ve heard all kinds of metaphors and similes for chasing down electrical faults. Electricity is like water, they will tell you. It follows the path of least resistance and you just keep following leads until you find the cause of the trouble. Well that’s all fine and dandy until you’re dealing with miles of wiring in spaces too tight for a hamster to squeeze into. I swear there are black holes in the fabric of space time swallowing all energy from our batteries right here under Aleta’s cockpit.
Who’s Fault?
Worse, and I learned this from years of working in the computer industry, is that nasty little gobshite – the intermittent fault. If you get one of those you’re really stuck. All the leads will check out, great continuity, clear voltages and still things don’t quite work properly. Computer companies solved the intermittent fault problem by simply chucking your cranky old printer in the dumpster and giving you a new one. It’s a little more difficult to do that on a boat. Is it aggravating? Yes! A learning opportunity? Yeah, well okay. You could argue we have all the time in the world to sit around learning about and troubleshooting this stuff. That would be true if it weren’t for the wind and the weather and old man winter breathing down our necks. Living a life of leisure? Not bloody likely!
Yes, No?
Short-circuiting the electrical learning curve seems like it should be relatively straightforward. Get on the cellular horn and call around until you find a boatyard capable and willing to undertake a little diagnostic work. After which they will propose a gigantic bill to fix things. It’s a well-worn path that should be simple to follow. Hah! I say again – Hah!
From the borders of Canada to Rhode Island there isn’t a free hour from a technician, of any kind, that’s available on short notice. If you know of someone, please call me, because I’ve had a healthy round of calls that go something like this: “Hi this is Mike, (I explain the issue)”, other guy (it’s always a guy) says, “well we’re really slammed right now, but I’ll write up a work order and will give you a call when someone frees up.” Translation: “you’ve got an intermittent fault that’s horrible to deal with and, yes, we’re truly busy, but no amount of money will persuade me to tie up one of my techs to fix your problem. Besides, you’re cruising and I’m betting you’ll move on or fix it yourself before you hassle me to the point of actually trying to chase someone down.”
When I worked in Asia I became familiar with the ‘Japanese Yes’, which was a very polite way of saying No. Writing up a work order and hoping for a technician is a long-winded American version of saying ‘No, now please go away.’
Well me hearties, there be only one answer: Arrgh! It’s time to break out the multimeters, splice the connections, and ground the faults! We’re quitting piracy and becoming electricians! Our fortune is made! Arrgh! Har har har! (Fade out)
Shocking!
Sounds like a job for Sherlock Ohms!
Perhaps a trip to The Ohm Depot is in your future.
Try not to get too amp’d up… but if you do, I recommend meditating to calm down… ohhhmmmm.
I’m going to switch to something else now.
Zzzt! Zzzt! Dude – watts happening? Retirement hann’t dimmed your sense of humour!
A good little puzzle in de-buggering! I’d like to know a lot more detail about the wackiness of the tachy. Does it intermittently indicate zero? Does it overstate the RPMs ever? Under what circumstances? That sort of thing. (Think of the questions Click and Clack asked their callers.)
Notwithstanding your devout hymn, I’d expect a tach to be connected to nothing much but the rectified output of the alternator, assuming that the tach itself is basically a DC voltmeter. Or perhaps to the unrectified output if it’s basically a frequency meter. But either way, it must tap in before the regulator, since regulated filtered DC voltage would make a rather boring tach.
Going with the voltmeter model for a moment, let’s focus on the six mighty diodes built into the alternator, that rectify its AC output to a ripply DC. The wisdom about those diodes is that if the main power switch is turned off while the engine is running, the sudden removal of load is very bad for the diodes. So maybe you didn’t commit this ghastly sin, but maybe somebody (previous owner?) did, or, perhaps more likely, something did.
If you can disconnect the tach from the alt and substitute a regular voltmeter, and do whatever it is that makes the tachy go wacky, see if that makes the VM go wacky. That would suggest a dicey connection in the diode subsystem, perhaps due to an occasion of sin. Replace alternator?
Or if, while everything except the bilge pump is off, you can disassemble the OFF-1-BOTH-2 main power switch, see if its connecting strips fulfill the design intention of maintaining contact with some load during all transitions between the BOTH state and either the 1 or 2 state. Replace switch?
Nothing guaranteed, but can’t resist having a go from my nice stable desk chair.
Thanks Unk. This all makes sense and I would love to discuss further.
In reference to all this buggering about, do you remember doing one of those interminable 24 hour runs from Chicago to the Cape? It was early on in the history of such events and there was a programme about the wonders of computing. Totally incomprehensible except when the word ‘bugger’ was tossed in amongst too many twenty syllable words. We (kids) looked at each other and wondered if the parents had noticed this breach of etiquette. The rest of the programme carried on as though nothing had happened, but I was able to work out that ‘bugger’ referred to glitches to the system. I was very disappointed, needless to say. It obviously affected my interest in computing for many years! (and that is why all the family despair when I contact them with a problem such as ‘how does one open this b****y attachment?’ I missed my calling when computers were cured by pulling the plug, counting to ten or making a cup of tea, and then reconnect the power supply!