First, let me apologize to all.
Hey Turtle !!
Need your battery knowledge for a sec.
I've run a 12V A/C system since late Sept of last year. With the 4 PowerRush Platinum AGM batteries, I am currently almost doubling what Arctic Breeze says is run time 8-10 hrs off full charge.
I think the Arctic Breeze 8-10 hours of running time is for a 50% DoD. If you're doubling that, then your battery bank is twice the amp hours of the base system, or you're running the batteries down too low.
In any event...
Now , if I were to invest in another oposing side battery tray, and run eight batteries, would that mean I could go double my current 14-17 hours ?
Yes. Doubling the amp hours will double the available amps. Actually, taking the Perkuet Effect into account, if the amp draw stays basically the same, you'll actually have more than double the amount of available amp hours.
Im no artist, which drawing do you think's the correct way to wire the eight ?
Neither. Wiring Positive to Negative increases voltage. If you have eight 12-volt batteries, and wire them Positive to Negative (in a series, as with the second drawing), you wind up with, in effect, a single 96-volt battery.
Let's assume 6-volt batteries, however. In the first drawing, you have two sets of four, with each set being wired in a series so that each set of four is a single 24-volt battery, and then those two sets are wired in parallel to double the amp hours, giving you one large 24-volt battery.
What you want to do is wire them Positive to Positive, and then Negative to Negative, which is a parallel configuration, which doubles the amp hours, but keeps the voltage the same. Every time you add another battery in a parallel configuration, the voltage always stays the same, but the amp hours of each battery gets added together.
If you have a bunch of 6-volt batteries, you'd connect one pair in series as positive to negative, to turn the pair into a single 12-volt battery, and then do that for all the other 6-volt pairs, then connect each of the 12-volt series batteries in parallel to start adding up all the amp hours of the batteries, while keeping the voltage to 12-volts.
There are four basic ways to wire up multiple batteries:
Method 1
Notice that the connections to the main installation (Main Installation being either the charging source, or the draw connection, i.e., inverter or busbar distribution) are all taken from one end of the battery. The interconnecting leads will have some resistance. It will be low, but it still exists, and at the level of charge and discharge currents we see in these installations, the resistance will be significant in that it will have a measurable effect.
You can use really large cable, which will have a resistance of as low as 0.0002 Ohms, so the 6-inch length between each battery will have a resistance of 0.00012 Ohms. Practically nothing, I know. But add onto this the 0.0002 Ohms for each connection interface (i.e. cable to crimp, crimp to battery post, etc.) and you end up with the resistance between each battery post is around 0.0015 Ohms. Four batteries with 8 terminal posts, and you have .012 Ohms, and that's just to interconnect them. It doesn't include the resistance of the connections to the alternator, fuses, inverters and/or busbars.
So, the key is to use cables large enough to handle not only the amp draws expected, but also to minimize resistance, since resistance increases heat and decreases voltage, thereby making the batteries work harder and thus giving you less amp hours to work with.
The Method 1 above shows the installation connected at one end of the bank. If you pulled 100 amp hours out of the batteries, one would think we're pulling 25 amp hours from each battery. And that would be wrong.
In actuality (and I can provide the mind-numbing, nap inducing mathematics if you like), what's happening is this:
The bottom battery provides 35.9 amps of the 100 amps.
The next battery up provides 26.2 amps.
The next battery up provides 20.4 amps.
The top battery provides 17.8 amps.
So, the bottom battery provides more than twice the current of the top battery. When charging, the reverse is true, where the bottom battery is subjected to more current and voltage, and the top battery gets the leftovers. The bottom battery is being worked over twice as hard as the top battery. The effects of this are rather complex and do not mean that the life of the bottom battery will be half that of the top battery, because as the bottom battery loses capacity quicker (due to it being worked harder) the other three batteries will start to take more of the load. But the net effect is that the battery bank, as a whole, ages much quicker than with proper balancing.
Now on to Method 2
Method 2
All that has changed in this diagram is that the main feeds to the rest of the installation are now taken from diagonally opposite posts, from battery #1 and battery #4.
It is simple to achieve but the difference in the results are truly astounding for such a simple modification. The connecting leads, in fact, everything else in the installation remains identical. Also, it doesn't matter which lead (positive or negative) is moved, whichever is easiest is the correct one to move.
The results of this modification, when compared to the original diagram are shown below. Only that one single connection has been moved. After this simple modification, with the same 100 amp load:
The bottom battery provides 26.7 amps of the 100 amps.
The next battery up provides 23.2 amps.
The next battery up provides 23.2 amps.
The top battery provides 26.7 amps.
Such a simple and effective change, but one that hardly anyone employs. Drives me crazy. The batteries are much closer to being correctly balanced.
However they are still not perfectly balanced. How far is it necessary to go to get the matching equal? It depends. In a massive installation, like in a home that's off the grid, or in some ultra critical installation, it's very important to have the batteries all perfectly matched. But in a 4-battery setup, Method 2 is fine. In an 8 battery setup, I'd split it into two connections, where you'd connect the four batteries together as in Method 2, then do the same for the other four, and then connect those two together.
Now on to
Method 3
Method 3
This looks more complicated, but it's not. And it's very similar to how you'd connect 8 batteries, in sections of 4 each, actually.
It is quite simple to achieve and requires only two extra interconnecting links and two terminal posts. It is important that all 4 links on each side are the same length otherwise one of the main benefits (that of equal resistance between each battery and the loads) is lost.
The difference in results between this and the 2nd example are much smaller than the differences between the 1st and 2nd (which are enormous) but with expensive batteries it might be worth the additional work. Most people don't consider the expense and time to be worthwhile unless expensive batteries are being fitted or if the number of batteries exceeds 8. Plus, this method isn't always so easy to install because of the required terminal posts. In some installations there is simply no room to fit these
To achieve the same results in a much easier to install configuration, we have
Method 4:
Method 4
Again, it looks odd, but it's actually quite simple. What has been done here is to start with 2 pairs of batteries. Each wired in the proper "cross diagonal" method. Then each pair is wired together, again in the cross diagonal method.
Notice that for each individual battery, the current always goes through a total of one long link and one short link before reaching the loads.
This method also achieves perfect balance between all 4 batteries and may be easier to wire up in some installations. It costs more, obviously, because of the additional cables and cable lugs.
There really is no excuse whatsoever (except perhaps incompetence or laziness) for using Method 1 given at the top.
The other three methods achieve much better balancing with the final two achieving perfect balancing between all four batteries.
Interconnecting batteries is just one of those rare things where doing something the correct way actually looks less elegant than doing it the wrong way.
Of course, if you only have 2 batteries, then simply linking them together and taking the main feeds from diagonally opposite corners cannot be improved upon.Method 2 is to be used for 3 or more batteries. With a large number of batteries it may be necessary to go to the 3rd method or 4th method. But even with 8 batteries it is possible to get reasonable balancing by placing the main "take off" feeds from somewhere down the chain instead of from the end batteries. Remember, count the number of links each battery needs to run through to reach the final loads and get these as equal as possible.
If your battery bank has various take off points on different batteries, where you have this 12-volt thingy connected to one battery's terminals, and another 12-volt thingy connected to another battery's terminals, stop doing that. Change it now! Not only is it is extremely bad practice, it's retarded. Not only does it mess up the battery balancing, it also makes trouble shooting very much more complicated, and it looks just awful.It truly looks like it was installed by someone who doesn't know what they are doing. Be a man and get a busbar. Do it right.
Finally, the charging source should always be connected to the same points as the loads, a.k.a., the inverter or the busbar. Without exception.
And i'd probably need to re-invest in an upgraded battery isolator ? And battery management control panel ? Just wondering how you'd do it ? I wired up the current supply bank with a bunch of #2 to batteries and #0 to alternator.
Upgraded battery isolator? I dunno, what kind do you have now? A 100 amp isolator will probably work, although a 200 amp isolator would be better.
As for a battery management console, a Xantrex Battery Monitor is the way to go. It monitors all amps in, all amps out, voltage in and out, depth of discharge, battery temp (if you add the optional temp sensor), and time to discharge at the current draw. There are more expensive battery monitors, and the Xantrex isn't cheap, but thy won't tell you anything more than what the Xantrex will.
I've got #2/0 Cobra brand (no, not
that Cobra) Ultra-Flex cable (way more flexible than welding cable) with Panduit cable lugs made specifically for that Cobra cable. The cable from the alternator to the batteries could have been #2 cable, or smaller, but to keep the voltage drop to a minimum on that length of cable, I went with the #2/0. The interconnecting cables, and the cables to the busbars and the inline fuses, are also #2/0 cable. I'd have gone with #4/0 cables and lugs just to further minimize the voltage drop (Ohm resistance), but the lugs alone were gonna be like $9.00 each, and I'd need like 30 of them.
The busbars I use are thicker than I need, but again that's to minimize resistance. I use the one with the four stud bars, but if you have a lot of 12-volt loads, they have an 8 stud bar as well. Two or three connections can be made at each stud, so 4 was enough for me. It also has four #8 screws for connecting smaller loads. (
PowerBar 600 Ampere Common BusBars - Blue Sea Systems)
100 amp busbars would work for most people, 250 amp busbars would further reduce the resistance, mine is the 600 amp busbar.
Fuses are Class-T
(Class-T Fuses - Blue Sea Systems) with heavy duty fuse blocks
(Class T Fuse Blocks - Blue Sea Systems)
Some people use SEA or ANL fuses, and that's fine, but in a multiple battery installation with an inverter, Class-T is what you want, because of their extremely fast short circuit response and smothering capability. SEA fuses are OK in lower amperage situations, but they are known as the "economical" alternative.
Here's the thing about "economical" alternatives in a situation like this. Look at all of the batteries in the bank, and then add up the Cold Cranking Amps of each. If you have four batteries, each with 800 Cold Cranking Amps, if there's a short circuit, like a cable that ends up rubbing on the vehicle frame, then that's a cool 2400 amps that gets fed into the short. That's enough to blow the bottom out of the truck.
What you want is a fuse that has microsecond response time, and that means a Class-T fuse. ANL is OK, but it won't have nearly as fast of a response time. In a situation where a short causes a 600% load over rating, an ANL fuse will blow in about 1/10th of a second. A Class-T fuse will blow in less than 1/100th of a second.
At lower currents, like 200% above rating, which can occur in some inverter load start ups, you don't necessarily want the fuse to blow as fast, and the Class-T fuse won't blow at 200% until after about 50 seconds, whereas the ANL fuse will go ahead and blow at about 2 seconds. So basically, Class-T fuses will blow exactly when they need to, and won't give you a lot of annoyance blows like ANL fuses will. After a couple of annoyance blows, the cheaper ANL fuses suddenly cost more than that Class-T.
