Battery Selector Switch

That ASE quote is badly written and too dumbed down to be of any use even for an automobile. It's so off base, even the spirit of what it is trying to convey gets lost. Referring to ASE as the experts on alternators is like referring to a pot smoker as an expert in gardening.

The best thing you can do with your battery switch is to replace it with something more automated. If you run on "All", you charge both batteries, but lose the benefit of isolating starting and house loads. If you run on 1 or 2, you fail to charge one of the two banks.

The only benefit of these switches is low cost. Everything else is downside.

Here's what you want to achieve.

1.) Isolate starting and house loads so you don't drain both batteries and can't start the boat.
2.) Keep both batteries charged.

Study 1&2 and I'm sure you can come up with a good plan for using that switch to optimize the outcome. It takes a lot of discipline though and eventually it will bite you.

Get one of the blue sea switches that has a combiner built in.
 
Mike is right that an alternator is not a charger...this is from Arco's website....notice the first few lines...[http://www.arcomarine.com/xhtml/Tech%20marine%20charging%20systems.pdf]
 
Two comments you may/may not be interested in..
First, and only FYI, little reminder, those little red "Perko" (there may be other brand) battery switches have a service life of their own and have been found, on this forum, to be trouble sources that OPs were ignoring, just taking the switch for granted. Also, those red "Perkos" don't have all that high a current capacity, definetly not for diesel applications.
Second, in the interest of keeping things simple, I store the boat with the Perko OFF, go out on Battery One, go back on Battery Two, and use Both if I shut the engine down hot and it's balky on the restart. Once it starts, I go back to One or Two. Both batteries are Start type, and I rarely anchor out. If I did, I'd use one for lights, radio, etc. and save the other to start and go home, like so many do.
 
It is my understanding that the boat's typical alternator will never charge a battery past 85% of full. The only way to get up to 100% of the battery is to use a charger. Since I have been topping off my batteries with a charger, they now last 6-7 yrs instead of 2-3. These are two typical marine 27 start/deep cycle batteries with a Perko switch. I never use the ALL postion. I always charge one battery at a time whether by running the boat or with the charger.

IMHO
 
Flutterby
Not sure of your charger, battery and switch setup. My charger has to positive leads. They attach to the battery posts on the switch. As long as the switch is in off, 1, or 2, it will cahrge the batteries independenly. If the switch is in the both position, then they are charged as one battery which is not the perferred way.
 
"It is my understanding that the boat's typical alternator will never charge a battery past 85% of full."

Again the devil is in the details. That statement is not true IF the the alternator output is higher than the electrical load and the run time is long enough. Maybe the 85% figure you heard has to do with the typical cruisers situation. Since the charge slows as a battery charge increases the time to bring a battery from 85 to 100% charge is long VS the amount of capacity you gain. Many who run batteries down while on the hook for extended periods and recharge them running an engine alternator only bring them up to 85 or 90% charge instead of running the engine longer to bring the batteries to 100%.
 
Regarding my earlier point about alternators and engine speed.

Just because the alternator looks like it’s turning, doesn’t mean it’s turning fast enough to charge. Most alternators do not start charging until they reach 1,000 RPM alternator shaft speed. 5,000 RPM alternator shaft speed is normally required to reach maximum output.
If you’re not sure what the alternator shaft speed is,you can determine this with the pulley ratio.
Measure the diameter of the crank shaft or drive pulley and the alternator pulley. Divide the crank shaft pulley diameter by the alternator pulley diameter. This figure would be the engine-to-alternator RPM ratio. A normal ratio would be 2.5 to 1.
For example, let’s say we have a 7 inch diameter crank shaft pulley and a 2.75 inch alternator pulley. We would divide 7 inches by 2.75 which equals 2.54 to 1. If the engine was turning 1,000 RPM we would
multiply 1,000 by 2.54 which would give us 2,540 alternator RPM.
 
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