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Old 06-06-2016, 11:29   #16
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cwyckham's Avatar

Join Date: Apr 2011
Location: Vancouver, BC
Boat: Niagara 35
Posts: 1,876
Re: How high can I safely charge 12 V batts?

Originally Posted by PPLepew View Post
When batts are down to 12V, they are basically "empty".
Charger/inverter/regulator bring them up to around 13.2 to 13.4V.

I have solar panels that I can set to higher than that. I tested them on an old battery and can get up to 16V. Silly I know, but it started me thinking.

How high can my house batteries be charge safely (14V, 14.5V)? And what advantage do I get when they get that high?

I have 6 AGM 100AH (8G31DT) gel house bank and a second bank of 2 Marine Deep Cycle (24DC-1) for cranking my engines (catamaran).
It sounds like you have a really nice (and expensive) battery bank. You are at a high risk of killing it, though, unless you learn more about how it works and buy yourself some better diagnostic tools.

First, the learning: Very few sailors seem to really understand how batteries work and how they charge. You never have to understand such things in "normal life," so this isn't surprising. It's well worth reading up on.

If you don't already have it, Don Casey's Illustrated Sailboat Maintenance manual is a gold mine for really simple to understand and follow maintenance instructions for all you boat's systems. I love mine (even more than the old standard from Nigel Calder)

Second, you need to have the tools to understand what's going on in your battery. If you let the charge get below 50% too often you'll kill the battery.

A voltmeter is next to useless. Volts only tell you the charge state of your battery if the battery has been "at rest" for a couple hours. That means no current going in or out. That NEVER happens on a sailboat in real life.If y

The state of charge of your battery is measured by how many Amp hours (Ah) are in it. You can only really know what's going on if you invest in a battery monitor that counts how many Amps are going in and out of the battery and keeps track of how many Amp hours are left.

The added benefit of a battery monitor is that you will be able to see how many Amps you're using at any given time and how many each electrical appliance uses.

The major downside of a battery monitor is that you will become obsessed with the moment to moment electrical flow and your family will hate you for being an "Amp Nazi."

You should also never hook up any charging source to your batteries unless there's something in-between that will control the voltage (a charge controller) or you really know what you're doing. You can burn down your boat.

I highly recommend using a 3 stage controller which has a setting for AGM batteries. You'll charge faster and protect your batteries all at the same time.

Chris - Become the Confident Skipper of Your Own Sailboat
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Old 06-06-2016, 12:14   #17
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Location: Cowichan Bay, BC (Maple Bay Marina)
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Re: How high can I safely charge 12 V batts?

Man o man.

Buy a book about boat electrical systems. And read it.

Good luck.

Stu Jackson
Catalina 34 #224 (1986) C34IA Secretary
Cowichan Bay, BC, (Maple Bay Marina) SR/FK, M25, Rocna 10 (22#) (NZ model)
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