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

[J.P.M.]

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.

Nothing beats measurements on a working system. Hard to argue with reality when it slaps you in face.

[Falsa_Nominis]

I didn't know you couldn't parallel batteries.

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.

[Falsa_Nominis]

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.

Natural manufacturing variances. The current in each series branch is determined by the least capable cell.

[Mike90250]

Natural manufacturing variances. The current in each series branch is determined by the least capable cell.

This is a parallel install being talked about. And if a series string of cells, in a parallel array, has a high impedance cell, that forces the other strings to work harder to carry the slacker's load, and ages the other strings till they are all as bad as the worse one, which usually continues to get worse, and then the race to the bottom is on.

[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?

[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.

[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.

[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.

[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.

[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.

[littleharbor]

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

[Sunking]

I know exactly what I talking about.

You do not know chit from shinola.

[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.

[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]

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.