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The 12-volt Newbie

If you're new to the world of 12 volts, check out these sites, then read my 2-cents worth below.

You need a multi-meter.  That's #1.   Here's a really cheap one - as long as the sale lasts.   You can also get one at Radio Shack for about $20.

If you want to install a panel meter later, Radio Shack or All Electronics have them for about $10.

Camping World has one that plugs into your cigarette lighter for about $15.  The only problem with that is that you must have the key on for it to work, unless you have a cigarette lighter mounted somewhere else.

Backwoods Solar in Sandpoint, ID. has really good information on batteries and chargers.  Be sure to read it all.  Check out the Schauer 30-Amp automotive battery charger about half-way down the page.  They claim it to be continuous output, whatever that means.

We can't forget solar power.  I don't have that; but good information from a trusted friend is to contact Mike at Solar Electric, Inc.  He'll give you the straight scoop.  All the rest of this still applies to solar as well.

Now, my 2-cents worth:

After you've checked out all of the above, and are not as confused as when you started, here's what I suggest:

1.  Buy that cheap multi-meter, no matter what.  If you feel that you want a panel meter sometime later, you can always get it.   But you need a multi-meter anyway, and you need to know how to use it.

2. Buy Trojan T-105 batteries - period.  They are the best.  They have dealers all over the place and the prices can vary a little; so check around. 

3. Get a battery charger, or an inverter that acts as a battery charger; one that you can control the output. "Automatic" is not a good word, unless you're stupid.  If you're stupid, get an automatic battery charger. Here's how that works.  When you can control the output, you can get it over in a reasonable time, and then shut off your engine.  If you've used 100 amps in the last day or two, you need to put in about 120 amps. There is no perfect!  You must allow for inefficiencies. Use the following table as your guide.

How "charged" is your battery?

Here is a table to help you determine the state of charge of a 12-volt battery:

Add .17 volts for every 10 degrees below 80F.
Subtract .17 volts for every 10 degrees above 80F.

The only accurate measurement of open-circuit voltage is after the battery has rested for 24 hours, with no charge, recharge, or load of any kind on the battery.  However, there is a shortcut.  Turn your headlights on for about 5 minutes, turn them off and then check the voltage.  That works just about as well.

When to stop charging your battery.

Forget the above table.  We're talking about charging voltages now, not stagnant voltages.  They're different!

First of all, you should only charge at about a 10% rate. That means, if you have a 240AH battery, you should charge it at 24 amps or less.   Depending on the battery (they all have their maximum voltage), that changes slowly as they get older; so do this test about once a year.

Start your 10% charge and keep it at a constant amperage.  Take pencil and paper and make a chart. Write down the time and the voltage every half hour (exactly).  When the voltage quits climbing, you're finished.  Mark that voltage down.  That's fully charged for that battery - for the next year.  For the future, it doesn't hurt to taper that charge off to about 5% when you get near the end of the charging cycle.  We're assuming here that we are running an engine and burning up fuel.  If you're plugged into the grid, it's a whole other matter.  NOTE: There is nothing "stupid" about this procedure.  If you walk away and leave it alone, it will burn up your batteries.  So, beware!  That's why I use the term "stupid" - - to get your attention.

Click here for more info on the care of batteries.

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