battery setup for alt delete. 2 6v or 2 12v

[mans]

Hi folks,
I'm looking to have about 200 ah of available battery power for an alt delete.
after much searching what is available out there in the battery world, I've come to two options. I've weeded out the junk, and I unfortunately had to weed out the best (trojans) due to their heavy price tags. but I have some very good and affordable inbetweens, now it's just a choice between the two options.

Route #1 is a pair of 100ah (@20amps) 12v marine deep cycle batteries from the batteries plus store. Wired in parallel.
this should give 12v and 200 ah and will cost $220+tax. (from the outside they are the size of car batteries.)

Route #2 is a pair of 6v 220ah (@20amps) golf cart batteries wired in series to provide 12 volts and 220 amp hours. this will be a little cheaper at $190+tx for the pair. (these are manufactured by "crown" battery company for another company and have a different label, but i'm told it's identical to the crown battery except for the label). they should be 92%-95% as good as the famous trojan T105 as far as capacity, without the T105 price tag. (they look like a typical 6v golf cart battery.)


I can go either way.
any reason to go "wired in parallel" over "wired in series"?
which way would we be better off?
someone mentioned earlier that when u wire batteries in parallel they attempt to charge each other till there is no power left, but how can that be true, aren't there large battery banks in parallel for off grid housing etc. etc. wired in parallel?
M.

[deathtrain]

batteries for off the grid banks are usually in series-parallel.

for cars you want all of the aH as you can hold for an alt. delete.

[Tesla]

I mentioned the issue of parallel connections, read that many years ago and there are numerous issues as even "equal" batteries are never truly equal.
Below is a quote from a thread I just looked up, someone elses explanation of one of the problems:

"mrebmen,
you can hook Pb in parallel, but you should be aware of some limitations.

In the RV arena, none of the coach makers put PB in parallel any more. They found out after years of testing that while charging in parallel is fine, in discharging one battery gives its "all" first and the other "loafs". The two batteries have different internal impedences, so one battery is always being discharged more than the other. As the battery ages, the lower impedence battery is always giving max current and therefore its PB plates are undergoing sulpharization more rapidly than the other. So one battery dies of "old age" while the other has only given half of its life cycle. And the problem is that the dying battery now starts to pull down the "loafing" battery. In short, the two batteries do not yield anything like twice the lifetime of a single battery. That is why the RV coach batteries have two marine 6 volt cells in series rather than cheaper 12 volt deep discharge in parallel. You get longer battery life with the two in series.

Some people have negated this problem with the following. They put knife switches on both batteries in parallel. They always charge in parallel. When its time to use the coach battery, they shut off one switch. When that battery starts to get low, they reverse the switches and keep going. This tends to give equal use to both batteries and gives a longer service life. The only problem is remembering to set the switches.

Hope this helps.
Crazy Ted -- a battery junkie "

Link:Can I hook up Lead Acid batteries in Parallel? - RC Groups

Every traction battery, remote power supply, house supply I have ever seen has been individual 2V cells connected in series, if more power is required they use a larger 2V cell, or alternate between 2 banks of batteries.
Good luck with it.

[brucepick]

FWIW, I think Tesla is right on the money.

[Ryland]

The only time I've seen off grid houses run batteries in parallel is when it was due to poor planing and they needed to add more batteries in a pinch, Tesla is right, most people with off grid houses use large 2v cells, more or less forklift batteries.
I would opt for the golf cart batteries because they are a traction battery, they have much heavier plates and can handle a deeper discharge, I haven't priced Torjan T105's in a while, but when I bought my set for my electric car they were $110 each, the thing is, Trojan makes a T105 RE (Renewable Energy) that is designed for deeper cycles at a lower discharge rate I believe, it might be worth doing your own research on those to see if they might last longer.

Are you keeping your regular starting battery? it seems like it would be a good idea if you have the space, an isolation diode will let you charge all of the batteries at the same time but will keep the starting battery from discharging as you run the lights.
You might also check in to getting a DC to DC converter and have your deep cycle pack at a higher voltage then drop it down to 13.7v, you'r lights will be brighter and you will be less likely to burn out any electronics, because as the voltage drops the amp draw goes up, for my electric car I'm planing to hook my DC to DC converter up to a small motorcycle battery that I had to act as a buffer, that way I can push the limits of the size of the converter without having to worry about flipping on the wipers and defrost fan while driving at night, and when I do that my head lights will still be full brightness.

[3dplane]

Hey guys!
I read this thread and I feel I have to chime in because of my experience using parallel connections disagree with the RV article.

Key word in that article is "CHEAPER"
Quote:
"That is why the RV coach batteries have two marine 6 volt cells in series rather than cheaper 12 volt deep discharge in parallel. You get longer battery life with the two in series."

When you have two similar batteries parallel connected and they are being discharged,the article says that the one with lower internal impedance will give it's max current and basically die sooner than the other...
Let's think about this for a second.

What happens to a battery's voltage when you load it to make it produce large current flow? .... Correct! It's voltage drops or sags! Right?

Now how far can that voltage sag RELATIVE to it's buddy pair who is parallel connected to it? Not very far since they are "clamped" together so as soon as the stronger battery is trying to give it's all and it's voltage tries to sag,the other one with now slightly higher voltage will be forced to "help out" and equalize or even out the current flow.

If we look at the other example with two batteries that are also not exactly equal in regards to internal resistance and now they are connected in SERIES.

When we put an electrical load on this circuit, the batteries "see" or share or in other words have to produce the same current! The one with higher internal resistance will work harder /tries to get hotter than the other one.

How is that supposed to be better when over time they could get out of balance if not monitored?

I don't know but in reality using quality batteries that are pretty close match and are cared for,will not cause a problem.

I've got a couple of real world personal examples:

#1: I have a golf cart that I run on (big no no) car batteries! Not new car batteries but used/failed ones. All different age and size. Ranging from 55A/h to 74A/h.
I parallel connect two to make a pair,and then I series connect more of these pairs to get my desired system voltage.

After three years of use I only replaced the weakest pair because I was trying to set new personal speed records with it.

#2: Alternator disable switch in my car... first I added two 7A/h little sealed lead acid batteries parallel to the existing battery in my car! (no they did not explode).
Monitoring my system voltage showed improvement daytime driving but at night with the headlights on, voltage sagged close to 12.0V by the time I got home.

So I added another 55A/h car battery mounted in my trunk and now I can make my 58 mile round trip day or night without voltage sagging below 12.2V (under load of fuel pump,ignition,accessories etc.)

So I have a 55A/h ,60A/h, and two 7A/h batteries ALL parallel connected in my car for the past two months with no problems.

Sometimes a few hours after the trip home from work,the voltage recovers to 12.7V and I have to trick my automatic charger by turning on the headlights so it will start charging.

The key is to know your voltage in all situations , learn the limitations of the system so the batteries don't get abused.


Just my opinion.
Barna

[IsaacCarlson]

It is fine to run batteries in parallel. I have run batteries in parallel for a while and never hurt them. I do try to keep them equal in capacity, just to be safe.

[Ryland]

Making sure your connections are good and clean is also very very important, if you have batteries in parallel and your connections are not good, then you are going to wear down the battery with the best connection, that is why when I store my 6v batteries, I wire them up in a parallel string, but instead of connecting the charger to the first battery in the string, I connect it to the + post at one end and the negative post at the other end, each connection no matter how good, and each inch of cable no matter how large, has resistance.

[Gasoline Fumes]

A lot of diesel trucks run parallel 12v batteries. Mine lasted 7 years with a lot of abuse. But they were a matching pair.

What about 3 6v batteries in series with a regulator? I like my headlights much better at 14.5v than at 11.5v.

[brucepick]

Originally Posted by Gasoline Fumes

A lot of diesel trucks run parallel 12v batteries. Mine lasted 7 years with a lot of abuse. But they were a matching pair.

What about 3 6v batteries in series with a regulator? I like my headlights much better at 14.5v than at 11.5v.

I'd love that. Where do you get a regulator at a reasonable price?
And are there efficiency losses when you use one?????