In many cruising grounds, at least a couple of times a month, the wind won’t blow and a passage will be made, at least partially, under power. And, as long as the engine runs continually for 6-8 hours, this will be a perfect opportunity to charge the batteries to 100%.
But even if you have the biggest and best alternator in the world, if you don't have a good regulator and, in most cases, reprogram it from the factory default settings, your batteries are not going to get that full charge they so desperately need.
The Regulator And Its Dirty Little Secret
Of course most cruisers know that you need a good three stage regulator to control the alternator. But sadly…it’s dirty little secret time:
Most, perhaps all, alternator regulators have no way to know how many amps are actually going into the battery, as opposed to powering loads. In fact, they can’t even tell how many amps the alternator is actually putting out.
Wait, it gets worse (you knew I was going to say that, huh?). The regulator manufacturers are so concerned about overcharging batteries that they ship their products programmed to horribly undercharge, at least when installed on a cruising boat with high battery usage.
Let’s take our Balmar MAX CHARGE MC-612 regulator as an example. Installed in our boat as it comes from the factory it will typically supply full amps from the alternator for just one hour after the engine is started.
Wait, it gets worse (I can’t help myself). Regardless of the charge state of the batteries, our regulator will drop the voltage to a lower level than proper acceptance as soon as the bulk phase is finished. And it will typically drop the voltage to float level (about 13.5 volts) about two hours after engine start.
This regardless of the fact that our batteries should be receiving the full current that our alternator can supply until the voltage reaches 14.4 volts and continue to be charged at that voltage until the current accepted by the battery reaches 0.5% of total capacity. Only then should the voltage be reduced to the float level.
Even if the batteries were only 25% discharged when charging started, this will typically take 5-7 hours.
By the way, my purpose here is not to beat up on Balmar. Rather this seems to be an industry problem. At least our MC-612 regulator is adjustable, which many are not.
So what can we do about this dirty little secret that will lead to premature failure of our batteries from undercharging?
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