Useful Information

[Blacktank]

If you would like something in the thread make a post here to be vetted by the members and then i or a mod will move it

[Snikwahjm]

www.tripleblaze.com

[Optimistic Paranoid]

In my first post, near the bottom there are a few words surrounded by [I] and [/].  That was supposed to be /I inside the brackets so the words would be italicized.  Would appreciate it if you could correct that for me.  Thanks.

Here's another submission.  If Sternwake disagrees with any of it, by all means let him edit or change it.  I will always bow to the master.

Battery Basics

We’re going to discuss conventional Lead-Acid batteries.  More exotic stuff like Lithium batteries will need a different post from someone who knows more about them than I do.

First, let’s talk about cycles.  You start out with a fully charged battery, you run various stuff – lights, fans, a 12 volt fridge, maybe recharge a laptop computer – and eventually you notice that it’s getting low, so you recharge it.

THAT is one cycle, from charged to discharged, back to fully charged.

Hold that thought – we’ll come back to it.

Lead-acid chemistry cells each produce 2.1 volts.  So a 12 volt battery has 6 of those cells, and a nominal “12 volt battery” is actually 12.6 volts or a fraction more when it is fully charged.

Moreover, in order to recharge a battery, the charging source – a battery charger, the vehicle alternator, a solar panel controller – must be at a HIGHER voltage in order to force electrons back into the cells.  Most of them operate at 13 to 15 volts.  So “12 volt stuff” – lights, fans, etc. are actually designed to run on anything from about 10.5 volts to about 15 volts.

Regular lead-acid batteries have liquid acid in them.  They are often referred to as Flooded Lead Acid or FLA for short.  There are three types of them.

Regular car batteries are sometimes called “engine batteries” or “starter batteries” or “Starter-Lights-Ignition (SLI for short)”.  Because the starter needs a lot of amps for a very short period of time, they are designed with many thin plates in each cell.  The idea is to MAXIMIZE the amount of surface area of lead exposed to acid.  This maximizes the amount of amps the cell can provide to the starter when you turn the key. (Surface area controls the amount of amps, the chemistry controls the amount of volts, the fully charged cell will always be 2.1 volts regardless of how thick or thin the plates are.)

Starter batteries are rated by something called Cold Cranking Amps (CCA). This is the number of amps it can deliver at 0 degrees Fahrenheit.  The higher the CCA rating, the more likely it is to start your car when it gets really cold out.

BTW, diesel engines, because of their much higher compression compared to gasoline engines, require a LOT more amps to power their starters, so much so that most diesel trucks have TWO batteries wired together in parallel to double the CCA available to their starter.

We are not interested in Cold Cranking Amps on house batteries, we are interested in how much total power we can get out of it, which is something called “Amp-Hours”.  Amp-hours can be measured at different current rates, but we are interested in the industry standard, which is the 20 hour rate.  If a battery can deliver 5 amps for 20 hours before it is discharged, it is said to contain (5 X 20 = 100) 100 amp hours.

Now, once your engine starts, the alternator immediately begins powering the ignition, lights, radio and everything else as well as recharging the starting battery.  Ordinarily, it would not use more than 5 to 10 percent of it’s capacity before the alternator recharges it, and it can survive thousands of these 10% duty cycles.  But if you discharged it down to 50% every time before recharging it, it would only survive about 40 or 50 of such cycles.

True story:  I once had a landlord who worked nights at a place only a few miles away from his house.  His wife drove the “good” car and he drove an old beater back and forth to work.  His alternator died, but he had access to a garage with an outlet where he worked, so rather than buy a new alternator, he decided to drive to work and plug his car into a battery charger for eight hours.  Next morning, he’d drive home and plug it back into the charger until it was time to go to work again.

His battery lasted a little less than a month before it was completely dead.  Driving at night, with the lights on, he probably pulled the battery down to 50% or less every cycle.

Now, TRUE Deep-Cycle Batteries – such as are used in golf carts and industrial equipment like pallet trucks and floor sweepers, are designed with extremely heavy, THICK lead plates.  You will probably not get as many amps out of each cell as you will from a starter battery.  But what you will get is cycles.  On a 50% cycle, you will get anywhere from 1,000 to 1,500 cycles out of these bruisers.  If you are only pulling them down to 60 to 70 percent, it may well exceed 2,000 cycles.

Notice that I said that you probably won’t get as many amps out of each cell.  But if the battery were physically big enough so that as many square inches of the much thicker lead plates would be exposed to the acid, you would get that many amps.  But the battery would be a lot bigger, a lot heavier, would have a lot more lead in it, and would therefor cost a lot more money than a starter battery would.

But for house batteries, we’re not - usually - interested in drawing large amounts of current (amps) out of it.  But if we were trying to power a large inverter, say 1500, 2000, or even more watts, that WOULD require a lot of current, and it would need it for a lot more time than the 20 seconds or so that a starter draws a lot of current.  So for that, you need a large battery bank – lots of batteries – or the large inverter will cause the battery’s voltage to drop WAY down, and the inverter will shut down due to insufficient voltage.

Anyway, we need to keep in mind that we’re not usually concerned so much with amps as we are with amp-hours.  The thing to keep in mind is that we DON”T want to draw the battery down below 50%, because even deep cycle batteries will fail quickly if they are drained too much.  Run them down to only 20% every cycle (That is, use 80% of their stored power) and you may only get 100 cycles or less out of them.

The take away here is that if the battery says it holds 100 amp-hours, it really means there are only 50 USEABLE amp-hours in it.  So if we need to use 100 amp-hours every day, we need a battery bank with two or three 100 amp-hour batteries in it.

Now let’s talk about the third kind of FLA battery, the Marine/RV “deep-cycle” battery.  This is not a TRUE deep-cycle battery.  It is a hybrid battery, midway between a real deep-cycle and a starter battery.  It was originally developed for boats.  They not only need to start their engines, but if they are anchoring somewhere instead of being tied up at a dock, they are required by law to run certain bright “anchor lights” at night, all night long, to avoid collisions with other boats.  So they needed batteries that could stand being discharged a lot more than the 10% that starter batteries are designed for.

The commercial motor home and trailer manufacturers use these batteries because they are a lot cheaper than the true deep-cycles.  They are usually good for 400 ton 500 cycles.  The average new RV buyer doesn’t know any better, and by the time these “RV” batteries die, the smarter RV owners will replace them with golf cart batteries, which ARE true deep-cycle batteries.

In addition to FLOODED lead acid batteries, there are also GEL batteries and AGM batteries.

GEL batteries have the acid between the plates suspended in a gelatin.  They are very finicky about how you charge them, and you can damage them or even destroy them if you charge them wrong.  They are still used in certain specialized fields, but they really have no place in our world.
 
AGM stands for Absorbed Glass Mat.  These batteries were developed to be a better replacement for the GEL batteries.  Instead of liquid acid, a fiberglass screen (the Glass Mat) soaked in acid is held tightly in place between the lead plates.

Like the GEL batteries, it is a sealed battery that cannot leak, and it can be mounted sideways as well as the more usual way if it will fit better like that.  It’s being used more and more in commercial RVs, especially truck campers, because the designers can bury them down in nooks and crannies that are almost unreachable.  They require almost no routine maintenance and you don’t have to check the cells or add distilled water like you do the flooded batteries.  They are also very rugged.  The 4X4 crowd loves them because they can survive shaking on rough terrain that would damage the plates on regular FLA batteries.

There is really no practical distinction between starter and deep-cycle in the AGM world.  Their only disadvantage is that they are more expensive than Flooded Deep-Cycle batteries.

If money is really tight, you will get the most bang for your buck by buying golf cart batteries from Costco or Sam’s Club.

[AbuelaLoca]

First post where, John?

[AbuelaLoca]

I found it and corrected it, John. I don't know why that post didn't show up in my search for "view today's posts"!! Oh well, I'm catching up!