If an alternator voltage regulator is not connected to a shunt, it's not smart.
One of the biggest snow jobs in boat gear sales is the myth of the smart three-stage alternator regulator. In fact, the alternator voltage regulators that have been available to us cruisers for about the last 15 years are not that bright...OK, they're downright stupid.
They're so stupid that they can't even perform their primary function of charging our batteries properly until full.
I know what you're thinking:
John is saying that a piece of gear with tens of thousands of units installed (that's a guess) in boats, and thousands more sold every year, that's so fundamental to comfortable live-aboard life, does not even work. Clearly he has lost his grip.
I totally get your scepticism. Heck, when our old, and sadly no longer made, Link 2000-R regulator died—the last cruiser's alternator regulator that was actually smart—I bought the then, and now, most popular "smart three-stage regulator" thinking that it would work, too.
I settled down and read the whole manual looking for the fundamental capability that would make it usable on a liveaboard cruising boat, and got to the end to find...nada. So I figured there were pages missing...nope.
What Matters in Alternator Regulators
What's that fundamental capability? The ability to measure when our batteries are full and reduce the voltage output by the alternator to float.
Sounds pretty simple, right? And it is. All you need is a shunt in a cable to the house battery to measure that current—often already there on a cruising boat to support a battery monitor—and a bit of simple logic in the regulator to turn the charge voltage down to float (typically 13.4 volts) when the above threshold is reached, but not before.
Easy peasy. But since the death of the Link 2000-R, and a rather complicated regulator from Ample Power (no longer in business), there has been no alternator regulator available, at least that I have found, that could do that simple fundamental thing.
How Could This Be?
Why? Beats the crap out of me. Maybe because few boat owners really understand how batteries charge and, even more distressingly, very few technicians in boatyards do, either, so the industry got away with selling stupid regulators for years, and they even had the nerve to call stupid smart—the power of marketing.
Stupid Is As Stupid Does
Rather than making that simple required measurement, these stupid regulators guesstimate using a combination of time and how much the regulator needed to juice the alternator field coil to maintain the acceptance voltage. That's bad enough, since different alternators have different relationships between field and output current (amperage) and, of course, how long a battery will take to charge will depend on how much it was discharged...duh.
Making Stupid Worse
The way the manufacturers of stupid regulators get around this fundamental weakness is by shipping the regulator factory programmed to chronically undercharge the batteries, to the point that the regulator will typically cut the charge current back to float in less than two hours, even though a lead acid battery bank discharged even just 25% will typically take at least four hours to fully recharge, no matter how big the alternator—if you don't believe that, see Further Reading.
Now this can be kind of fixed, in a klugy way, by reprogramming the regulator, which is what I did, and then wrote an article about it to help others, recently deleted since this new regulator makes it obsolete.
At Last, Real Smarts
But now, finally, we have, once again, a truly smart regulator. Let's take a look:
