Comparing Batteries - need to replace 16

fooddiva

We have been off the grid for 20 years and have a 24volt system. We have been using 16 Trojan T105's, 6 volt, wired in series/parellel and now are in need of replacing them. This will be our third bank to date. We got an unbelievable amount of life out of that last bank of Trojans (11 years). We are now considering AGM amongst the others. Have been researching Deka, Surrette and others. Does anyone have any recommendations? We like the idea of less maintenance with the AGM's. Any idea on life span of those batteries?

mike95490

Re: Comparing Batteries - need to replace 16

AGM's work fine till the first overcharge or equalize. No forgiveness allowed. They cost a bunch too.

Windsun

Re: Comparing Batteries - need to replace 16

There is really no advantage to AGM's in your case I suspect. The advantages of AGM's are no maintenance, totally sealed so no gassing or spillage.

But most of the advantages of AGM don't do much for you in a larger fixed system like yours.

You might want to look instead at something like a forklift battery, or the larger Surrette's.

crewzer

Re: Comparing Batteries - need to replace 16

I’m a big fan of AGM batteries. I installed my small bank (24 V x 400 Ah) two years ago and so far, so good. I like the virtually no maintenance feature, and I also like their high recharge efficiency (Wh out / Wh in), which is ~90%. Flooded-cell batteries are ~80%.

Life expectancy (number of cycles) of AGM batteries can be a hotly debated topic. Deka / MK’s specs are only so-so, but Concorde’s are quite good, and Exide/GNB’s AGM specs are excellent.

As Mike noted, there are drawbacks. One is that VRLA batteries (both AGM and gel) don’t take well to overcharging. Basically, water that is outgassed can’t be replaced. But, modern chargers with temperature compensation adequately address that issue. I have my MX60 controller’s temperature compensation feature set to a limited value.

I also had a problem with un-equal voltages in my bank’s series pairs. I solved that using a pair of PowerCheq “equalizers”. Another issue is that AGM batteries can be fairly expensive. But, it can pay to shop around. Battery warehouses seem to have better prices that the solar equipment dealers. Two years ago, my four size 4D batteries were $220 each.

For your application, a comparable bank of AGM batteries would be eight size 8D batteries wired 2 (series) x 4 (parallel) to make 24 V x ~1,000 Ah.

HTH,
Jim / crewzer

System2

Re: Comparing Batteries - need to replace 16

I can't speak for the overcharging issues, or the lifespan of the AGM's, but if they can't be equalized without wrecking them, I would stay with Trojan. I have heard only good things about 6V Trojans wired in series. Even more importantly, I think it would be a good idea to focus on the charge controllers if you are going solar. I got a great 20 amp CC from Cirkits.com, which uses pulse-width modulation to regulate the input charge incrementally. It doesn't do a bulk charge as fast as a battery charger for cars, but it does get there rather smoothly.

You can save money on Trojans by picking them up at a distribution source near you. They have regional distributors, so you might want to check with the company for details. I would go with a winning game.
DJ Dr. Disco

crewzer

Re: Comparing Batteries - need to replace 16

...but if they can't be equalized without wrecking them...

Therein lies something of an irony: AGM batteries don't need to be equalized at a high voltage. At worst, they just need an occasional freshening charge for a couple of hours at the high end of their safe absorption voltage range.

Hey, niel! How old are your Concorde batteries, and how are they doing?

Regards,
Jim / crewzer

Solar Guppy

Re: Comparing Batteries - need to replace 16

I Vote AGM, Much better batterys, thats why they cost more.

System2

Re: Comparing Batteries - need to replace 16

Interesting note, when I spoke to my battery supplier last year, simply just to ask price and availability of AGMs to consider sometime in the future as possible replacement for my flooded L-16's, his reaction was instant and negative. Precisely because of the AGM inability to accept any abuse at all. His reaction really surprised me. Looking back over the last 4 or 5 years, I now know that my flooded L-16 bank has undergone considerable, but unintentional abuse, and kept on ticking. I've learned a lot during that time, and I'm still learning.
Just recently I received the following from my supplier (East Penn Canada) and I'm including it for anyone who might not know any more that I did re the flooded L-16.
Keep in mind that I have 6 of these in my bank, wired for 12 volts.

"Max Current would 111 amps
Float 13.8 – 14.1
Absorb 14.4 – 14.7
Equalize 15.0 – 15.3

Cut-off parameters per charge and equalize intervals are application specific and will vary dependent upon site specific characteristics such as temperature, days of autonomy, array to load ratio, etc, for this reason it is best to monitor the specific gravity reading on a regular maintenance interval and with this data the equalize frequency will be determined it is recommend that at least once per month the system be returned to 100% state of charge.

Specific Gravity reading values
1.265 - 12.75 indicates full charge
1.225 = 75%
1.190 = 50% system should never go below this value.

Variation in specific gravity readings from one cell to another of .20 indicates equalizing should be performed.
Example:
Cell 1 at 1.265, cell 2 at 1.260, and cell 3 at 1.255
I hope this helps Wayne but should you require any additional information please feel free to contact me directly.
Jim DeCoste"

niel

Re: Comparing Batteries - need to replace 16

jim,
doing great. no problems.
fooddiva,
i'm adding here that there are some agms that do have very high capacity and due to the size and weight they shrink down the battery to 3 cells or even just 1 cell as many standard batteries have come in due to their physical size. if the system is really that large in making eq a problem then simply rearrange the batteries in their electrical connection every so often. this is good to do with any large battery bank regardless of the type you go with and eq isn't just achieved by electrically frying batteries. very large interbattery connections are a great help in keeping the batteries equalized as is cross wiring. all batteries will work and is a matter of preference or ability to pay for. each also have their advantages and disadvantages

fooddiva

Re: Comparing Batteries - need to replace 16

Wow, I had no idea that I would get so many responses to my inquiry on batteries. Thanks to everyone who posted. Still doing our research, but now have alot of information to make, what I hope, will be an intelligent decision.:-)