12v 101 For Dummies

Q:  How do I know how much power I’m generating and how much I’m using?  

A: Batteries hold juice and everything else uses that juice.

Look on your batteries and see if you can find a sticker that says something like 120 AH or amp hours.  Add them all together on your house batteries.  Amps are like measuring cups for electricity. Maybe a lightbulb draws 1 amp. That means that in one hour, it will use up 1 amp from the batteries. 10 hours = 10 amps etc.

Some things list the watts they use.  It’s just another measuring thing, but not much help cuz you have to convert them to amps.  Sigh.

Here’s how to convert: watts divided by 12 (12 volts – some folks have 24 volts and other weird things) equals amps.  So a 75 watt bulb draws 6.25 amps if it’s on for an hour. Yikes!!!

Now add up the amps for all the stuff you use.  Running lights might be on for 12 hours, but your fridge might cycle on and off and only use 7 amps in an hour.  You will have to pay attention to how long things are turned on.  Auto pilots use a lot and so do SSB radios when you are transmitting.

There should be a label on each light, pump, fridge, whatever – that states how much juice it uses.  Convert them all to amps and add them up. To be safe, round fractions up.

So lets say that your total is 80 amps in 24 hours, and your battery bank, all together holds 360 amps. You can only use half the amp hours in the batteries or it screws up the batteries, so you have 180 amps to work with. Woo Hoo! Your batteries can manage that!

Now, how do you put amps back in the batteries?  Run the engine, solar, battery charger (if you are plugged into a dock) etc.  What size alternator is on your engine? 50 amps, 80?  Look and see. Alternators charge fast when you first turn on the engine, but then taper off so you don’t fry the batteries.  Run the engine hard for about 20 minutes, then slow it down and charge them up!

Solar panels are rated in watts.  A 100 watt panel would crank out 8.3 amps every hour in perfect conditions, but not for more than maybe 4 or 5 hours every day, depending on where you are.  You still need to come up with 50 more amps…. does that make sense?  There is a doohickey called a Link Monitor, which you can install and it tells you how much you are using, how much you already used, how much you need back and how fast you are charging.  I put one in my boat and LOVE it.  No more worries.  Totally worth the time and money.

There’s a bunch of other technical stuff, but that’s the basics of what you need to know to figure this all out.  It’s kinda fun if you don’t get freaked out.

Smile and good luck!!!

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