Give me feedback on my battery set up

[Dee Bee]

The DC system is powered when I am away from shore power by two gel batteries. The reason I am starting with these is that they were given to me. I wired them in parallel (red to red and black to black). This keeps the voltage at 12 v DC and yields about 75 amp hours. This should be enough for a weekend and probably a few more days of careful use. All wires are 10 gague. All wire harness connections used soldered terminal lugs, these were connected at the terminal with bolts. I added protective plastic wire loom to guard against friction chaffing.



Let me know if you see any weak parts in this set up. Thanks!

DEE

[webbedouin]

One problem you're going to have is that the batteries are going to use the bulk of their power charging each other when wired in parallel, as bat A's voltage drops lower than bat B, Bat B will charge Bat A until it's voltage drops lower than bat A. Then Bat A will charge Bat B. This will go on forever discharging both batteries as the total charge dissipates in the form of heat. You need a battery isolator, on the plus side. Charger goes to the isolator and isolator legs (Input across two big diodes) then to both batteries. That way the two don't see each other's load. The diodes will drop the charger voltage .6 of a volt. It just what diodes do. Don’t know where your 12 volts go from there, but be careful the rest of the wiring does not allow the two batteries to talk to each other.

[asianflava]

You can get away with this setup without an isolator (at least for a little while) if the batteries are: the same make, model, age.

[Dee Bee]

One problem you're going to have is that the batteries are going to use the bulk of their power charging each other when wired in parallel, as bat A's voltage drops lower than bat B, Bat B will charge Bat A until it's voltage drops lower than bat A. Then Bat A will charge Bat B. This will go on forever discharging both batteries as the total charge dissipates in the form of heat. You need a battery isolator, on the plus side. Charger goes to the isolator and isolator legs (Input across two big diodes) then to both batteries. That way the two don't see each other's load. The diodes will drop the charger voltage .6 of a volt. It just what diodes do. Don’t know where your 12 volts go from there, but be careful the rest of the wiring does not allow the two batteries to talk to each other.

Where can you purchase or how can you make battery isolators?

DEE

[webbedouin]

IMHO you can not get away with anything with your batteries. Oh, it may work for a while, sure, but the only reward you'll ever get is a shorter batter life.

Battery isolators aren't too hard to find, JC Whitney, RV suppliers, good auto parts stores, solar & wind power dealers, even a good electronic shop might have 'em or can get them.

They are rated in amps, if you're using a 15 amp charger get at least a 30 amp isolator. Always double what you expect use for a nice safety margin and durability. A general rule of thumb in electronics. You might expect to spend 30 to 60 bucks for one.

BTW, once you drain your pet batteries, charge 'em up again ASAP. They like to be fully charged (but not over charged) and they'll live longer.

[engled]

Or if your from the school of "Cheap" (like me) just seperate the batterys and save your self the 30-60 bucks. With this method you will know when "half" of your power is gone.

[webbedouin]

That'll work, a switch is a cheap easy solution also...

[asianflava]

IMHO you can not get away with anything with your batteries. Oh, it may work for a while, sure, but the only reward you'll ever get is a shorter batter life.

True but this is relative, you are not camping 365 days a year. If someone was using this setup under the hood of their car, then longevity is definitely a factor. In a camper, it is only used for a few days then back home to be stored. I hope that when the trailer is stored, the batteries are disconnected (or removed). They will probably be charged before and/or after use.

By saying "get away with it for a while" I'm talking about a season or two. Of course unless they were overcharged, that only takes one time. I'm also not saying that this is the ideal setup, I'm just saying that it will work.

Your post got my doubting myself. The practice of connecting batteries in parallel is common in competition car audio and lowriders. I've seen the entire bed of a truck filled with batteries and several farads worth of capacitors. I knew that it was done but I haven't installed stereo for a dozen years.

I started poking around the net and found pretty much the same info in the
Optima site:
http://www.1st-optima-batteries.com/faq.asp#10
10. Can I hook an OPTIMA in parallel with a different battery?

No, when hooking batteries together in parallel, they should be of the same type and similar age.

Rockcrawler.com
http://www.rockcrawler.com/techreports/kilby_dual_battery_TJ/index.asp
A third option, which I chose, was to simply wire both batteries together in parallel – positive to positive, negative to negative. Though you lose any sort of battery management, this method is the least expensive, and gives you double the cranking power and double the reserve capacity. The only absolute requirement is that both batteries be the same (identical) capacity and age. You cannot mix and match or the weaker battery will drain the stronger and could cause both to fail.

[DestinDave]

Why not use a battery selector switch such as this one? All marine stores will carry these.


http://www.westmarine.com/webapp/wcs/st ... storeNum=9[url]

[denverd0n]

People who run solar powered homes almost ALWAYS wire batteries in parallel and charge the entire bank from a single source. I see no reason why this should be any problem at all, as long as the batteries--as was said before--are the same size and age, and you're using the correct voltage for charging them.

[webbedouin]

Yeah but of course solar systems are very different concept. The batteries are getting their charge from a third source half the day and under load the other half of the day. Less time for the batteries to rely upon each other and under load, they're both giving. The batteries will spend much less time charging each other under those circumstances.

That's really different than charging up a pair and heading out for a weekend and trying to conserve every last bit of juice. And to conserve every last bit of juice, you need a battery isolator. Even a matched pair of batteries will always display a slightly different voltage, when wired together you can't even detect it, but the batteries know what’s goin' on. Separate them and you can detect it. It's likely to be only be a piddling few millivolts (thousandth of a volt) difference, but as long as there is a difference and they aren't under load, the batteries will see each other as the load and the lower one will take from the hotter one. And they'll be forever switching roles.

By way of example, my expectations for battery life is three to five years. And i'm using a big Sears diehard that has been in a dual battery situation for 7 years!!!

Have seen some of those banks of batteries and capacitors. When used on a stereo those capacitors can provide that extra punch for reproduction of very loud quick transients. Of course those systems, too, have a charger available, just turn on the engine. And with the monster stereo and the hydraulics, quite the load.

The part that cracks me up is, a battery is essentially a huge large very big assed capacitor. So once you've set up the large bank of batteries, Whatdaya need more capacitors for anyway??? It's like spreading a handful of sand on a boulder field. They sure look Kewl though. But then those displays have a certain amount of conspicuous consumption function built in.

[webbedouin]

Oh, by the way Dee, very nice wiring...

[Auszooker]

Batteries wont kepp discharging into each other, they will equalise a bit and then stay matched to each other
the only time this wont happen is when
a one battery is faulty and wont hold its charge
b batteries arent the same model, the smaller one will discharge quicker and the larger one will equalise with it but that capacity will still be there to use just at a lower voltage

[asianflava]

By way of example, my expectations for battery life is three to five years. And i'm using a big Sears diehard that has been in a dual battery situation for 7 years!!!

With the heat we have 2 or 3 months of the year and add to that the 2 or 3 weeks of freeze warning weather. Batteries don't last that long here even my Die Hard "Heat Handler" (had the "Weather Handler" in NC) doesn't make it out of warranty.

Have seen some of those banks of batteries and capacitors. When used on a stereo those capacitors can provide that extra punch for reproduction of very loud quick transients. Of course those systems, too, have a charger available, just turn on the engine. And with the monster stereo and the hydraulics, quite the load.

The part that cracks me up is, a battery is essentially a huge large very big assed capacitor. So once you've set up the large bank of batteries, Whatdaya need more capacitors for anyway??? It's like spreading a handful of sand on a boulder field. They sure look Kewl though. But then those displays have a certain amount of conspicuous consumption function built in.

Yeah, there has to be a point of diminishing return on some of those systems. I guess like you mentioned, it's to look cool.

[webbedouin]

What can i say, here where i live, in the Southern Sierra Mountains, we get into the 20's and snow in the winter, it usually hits 105 in June and stays there 'till Labor Day. This year has been pretty cool so far, just upper 90's. It just might not the weather conditions killing your batteries, it might be the amount of time they're spending charging each other. I'n not trying to sell you batteries every couple of years, just how to conserve 'em. Big difference!