I think your shunt is, indeed, of the usual type.....metal....but incorporates additional circuitry to calculate certain parameters, then converts these results to signals sent to the monitor
A few thoughts which might help:
1. If you have 520AH capacity, then the 20-hour discharge rate is 26 amps. Any average draw more than 26 amps would reduce the effective capacity below 520AH, while any draw below 26 amps would increase the effective capacity above 520AH.
From the remarks you provided, it's clear that your average load is way below 26 amps (since 26 amps x 24 hours would equal 624AH per day). Thus, your effective battery
capacity is more than 520AH...maybe as much as 600AH or more.
2. The only effective way to test the real capacity of your batteries is to do a controlled 20-hour test. A sophisticated internal inductance/resistance tester like the Midtronics series ($700 or more) is a quick way and is pretty accurate, but few cruisers have these. Maybe you can find someone nearby who has one and can test the capacity of each of your batteries.
Sulfation can occur if batteries are left below full charge or even if they are left on a float charge 24/7. They need to be bumped up to 14.8VDC or more periodically. And, as MaineSail said, they won't reach full capacity when new until they've been cycled a few dozen times.
I don't agree at all with the fashionable notion these days that voltage is not useful. If you know what you're doing and you know your boat, voltage is a very good way to estimate state of charge, and to guage how well your batteries are doing. I do research
on batteries, I install marine
power systems professionally, and have over 30 years experience with marine
batteries on my own boats. I don't have a battery monitor
on my boat, and I don't want one....though I've installed a number of them for clients who've drunk the Cool-Aid and think they're the cat's meow.
What I DO have is a good digital voltmeter, mounted where I can see it from anywhere in the cabin
. At a single
glance I can get a good estimate of the SOC of my house batteries (six golf-carts), because I know in my head
what I should be seeing before I look. I know what to expect in the morning upon waking, when motoring or charging from the diesel
genset, when retiring at night, etc. I can see how long it takes to get to 14.8VDC charging, and how long the DC ammeter remains at 80A when running the engine
. This is all the info I need.
Don't be seduced by what your monitor is saying. As the retired process engineer
said above, use independent tools to measure what's really going on. A good multimeter and a good clamp-on AC/DC ammeter is all that's necessary. You do need to inventory your boat, though, and calculate closely what each piece of equipment
draws. Develop your own energy budget
on a spreadsheet.
Most promising thing I've seen in all the above discourse is your statement of intent to fit solar panels
to your boat. GREAT. That's the only real solution to keeping your batteries fully charged.
with at least 270-watt total capacity and don't skimp on a good MPPT
controller. Forget the wind
genny....too much trouble, too much noise
, and the solar panels
alone, properly installed, will likely do the trick.