About to buy an AGM battery bank. Anything new or economical I should consider?

[sdold]

It depends. If the cable lengths are symmetrical from the midpoint to both end points, It will be OK. If the cable lengths are asymmetrical from the midpoint to both end points, there will be a voltage imbalance across the batteries. Keep it as symmetrical as possible and the shortest possible lengths best results.

Why would it matter? The current is the same in all batteries in a series string.

[Falsa_Nominis]

Oh, I've been wondering this, can the cables connecting the batteries in series be different lengths?

It depends. If the cable lengths are symmetrical from the midpoint to both end points, It will be OK. If the cable lengths are asymmetrical from the midpoint to both end points, there will be a voltage imbalance across the batteries. Keep it as symmetrical as possible and the shortest possible lengths best results.

[Withalligators]

For my last series bank, I used 2/0 cable, with copper terminals that I crimped at West Marine, soldered afterwards, and then used heat shrink tubing on to cover as much as possible. Is that enough?

Oh, I've been wondering this, can the cables connecting the batteries in series be different lengths?

[Falsa_Nominis]

Your point being ?
A massive parallel bank (3 strings) containing series batteries (6v x 2)

The point is: Even with the best of engineering, one cannot factor out manufacturing variations. In a parallel array of batteries there is going be some imbalance because of manufacturing variations in the cells that compose a battery. For this reason, if one can do a one series string battery bank, one would be better off doing a one series string battery bank instead of a parallel battery bank. A one series string battery bank produces the longest life span and the lowest required maintenance ... better ROI and lower overhead.

[Sunking]

I will be working in the field most of the time and almost never have access to shore power. So, I won't be able to do that. I'm going to follow your advice and do a series of 6 x 2V batteries, of the Sun Extender variety. Thanks, guys!

Based on your other thread for your safety sake get a Marine Shop to make at least your battery cables. Have them make the Inter-Cell cables and the cables between the CC/Battery, and Battery/Inverter. Also please please use Dual Fuses installed directly on the Battery Term Post. Again the Marine Shop can do that because they have the product in stock from Eaton Bussmann. Pictured below. They are called MRBF (Marine Rated Battery Fuse) Blocks. One fuse of appropriate size to the CC, and the other to the Load. Your life depends on it.

Those batteries pack a lot of punch and can easily pump 10,000 amps into a dead bolted fault which is more than enough to vaporize 1/0 copper wire. Hot enough to burn your flesh to the bone in an instant and set steel on fire. God cannot help you if there is any aluminum or magnesium around.

[Withalligators]

I will be working in the field most of the time and almost never have access to shore power. So, I won't be able to do that. I'm going to follow your advice and do a series of 6 x 2V batteries, of the Sun Extender variety. Thanks, guys!

[Sunking]

Some other engineers here recently installed several new AGM batteries at a solar site. They tried hard to make the wiring to all batteries equal. For fun I went up and measured the charge currents to each battery on a sunny day. The currents were (rounded to the nearest quarter-amp) 6.5 A, 6A, 8A, 6A, 4A, 8A, 3A, 8A, 5A, 8A, 8A, and 7A. These are all new batteries wired in a way that they thought would make the currents equal. It showed me first hand why parallel cycled batteries is a bad idea.

Steve I think you and I have discussed this in another lifetime. In Telecom and Data centers paralleling batteries is a common practice. Mostly to obtain the huge Amp Hours capacities required. Even with 2 volt cells a 20,000 AH cell would be almost impossible to lift and move around in confined spaces. Such a cell would weigh 2500 to 3000 pounds. However what must realized by others is Telecom and Data DO NOT CYCLE batteries. They are used in Emergency Stand By Float Service. They rarely ever get used and batteries in Float Service made from Pure Lead like the Round Cells can have a service life in excess of 30 year while AGM are toast in 10 years.

In Float Service, the batteries will equalize in 24 hours. You do not have that luxury of time with a daily cycle battery, and you get the double whammy with solar as you only have a few precious hours to try to get fully charged which you can never really do anyway. So parallel batteries in solar just compound the problems.

Now having said that an RV is a bit of different application. As long as you do not use the RV on a daily or regular basis, you can get away with parallel batteries without a huge hit on cycle life. That is providing when the RV is parked at home in between trips you put the batteries on a commercial AC charger with a Float voltage setting and disconnect solar. A lot of people do not understand the so called smart chargers (Multi-Stage) are hard on batteries. They are used to speed up charging which is required for daily cycle applications. Float Chargers aka CC/CV are the gentlest charging algorithm, and put the least amount of stress on a battery. They never go above gassing voltage.

[Sunking]

I know exactly what I talking about.

You do not know chit from shinola.

[littleharbor]

17 posts and gone, might be a new record. It seemed from his opening post he had a chip on his shoulder.

[Mike90250]

Observe "Least capable cell"

All batteries are a series of cells. Two batteries in parallel is two series strings of cells in parallel. This is elementary.

Your point being ?
A massive parallel bank (3 strings) containing series batteries (6v x 2)

What steps can I do to maintain a 6 battery bank (3 parallel in 2 series) at 660AH?

As told to the OP, it's difficult and doubly so with low resistance AGM cells. Then sdold in post 15, relayed his measured experience with a parallel AGM bank that had been given care and attention to the cabling, and found wide variations within the battery bank

If you are unable to contribute meaningful input, but just want to type and raise the noise level, we'll oblige you with vacations from the forum.

[Falsa_Nominis]

a parallel install being talked about

Observe "Least capable cell"

All batteries are a series of cells. Two batteries in parallel is two series strings of cells in parallel. This is elementary.

[Falsa_Nominis]

Ignore this guy. He is dangerous and does not know what he is talking about.

I know exactly what I talking about. Your just scared of the new guy.

[Sunking]

This is all good info, I wish I had known.

So, what do you guys think of a bank of 6 of these? http://lifelinebatteries.com/product...es/gpl-4ct-2v/

They're expensive and heavy. But lifeline is a good brand. How would I maximize their health with my current setup?

Lifeline is a Concorde product line. Concorde invented the AGM battery for military aircraft. Lifeline is a mid range product made for the Marine marker. Fine if that is what you want but they make a line just for solar called Sun Extender PVX line. Nothing wrong with Lifeline, but PVX is a step up closer to military grade.

[Sunking]

It can be done but one needs to know how to wire the loom and understand the why in detail. If ones does not get the loom correct, some batteries in the bank will receive more charge, others will be discharged harder, resulting in a unbalanced battery bank. Without going into protracted detail, a unbalanced battery bank is self-destructive. Then there are variables that the best loom cannot factor out. The only way to deal with the variables is higher battery maintenance or accepting a shorter battery life span.

On the other hand, a series loom is almost .. almost idiot proof.

Ignore this guy. He is dangerous and does not know what he is talking about.

[Withalligators]

This is all good info, I wish I had known.

So, what do you guys think of a bank of 6 of these? http://lifelinebatteries.com/product...es/gpl-4ct-2v/

They're expensive and heavy. But lifeline is a good brand. How would I maximize their health with my current setup?