Which batteries to get?

pabloesguapo · September 2020

Time for new batteries. (48v system)

Price is a HUGE issue, I'm not interested in paying $300+ each for Rolls, etc...

Which would you prefer, Interstate GC2, for $98.99 each (210Ah), or Trojan T105 for $125.00 each (250 Ah)?

mountainman · September 2020

Id go for the trogen t105 I think they are 225 ah
$125 great price.
I've read there's often issues with
Hydrolink systems.

BB. · September 2020

Only turning on the auto-watering system main valve when you are there to monitor everything... At least until you are sure everything is OK.

There have been (a few?) reports of the system/per cell float hanging up and dumping your distilled water into the cell and flooding electrolyte/water on the floor. Causing a mess, and having to fill the cell(s) with new electrolyte.

-Bill

Dave Angelini · September 2020

Price may be your driver but size matters. What do you need to store and for how long. Details do matter.....

pabloesguapo · September 2020

Update. I'm going to nix any automation. I'll just give the pump a little squeeze once in a while, of course, after noting SG, etc.

Here are new options I have found:
-Interstate GC2 (215Ah) 6v x 8 = $800+tax from Costco
-Trojan T105 (225Ah) 6v x 8 = $1000 +tax from a local company
Trojan T1275 (150ah) 12v x 4 = $756 + tax - from a local company. I would get 2 strings for 300Ah, $1512
-Unigy Hr5500 AGM (150Ah) 12v x 4 = $600 no tax from another local company. I would get 2 strings for 300Ah, $1200

Is it OK to use four 12v batteries instead of eight 6v batteries? Are there things I need to be aware of or consider?

Are there any things I need to consider using AGMs instead of FLAs?

Finally, how do I figure out the necessary size of my solar array? Currently, I have 6,500w. One salesman says I don't have enough, one says its too much, one says its just right. My average daily (24hr) usage is 24kwh in summer, 16-18kwh during winter. Overnight usage year round is about 7,200wh (600w average for 12hrs a night)

Marc Kurth · September 2020

If I am understanding correctly:

You are putting together a 10 to 14 kWh battery bank.

You plan to draw about 7.2 kWh from the battery bank nightly.

I would respectfully suggest that you are setting yourself up for a reduced battery life. Have you researched the DOD vs. Cycle life ratings for these batteries?

Marc

pabloesguapo · September 2020

That's the stuff I'm trying to figure out

If my overnight requirement is 7200wh, my battery bank capacity would need to be minimum 14,400wh, for a 50% TOC discharge, right?

I'm leaning toward getting the Unigy AGMs. 300Ah would get me exactly 14,400wh. 450Ah would get me 21,600wh, which would bring me to (in theory) 66.67% SOC.

But how much panel would I need?

mike95490 · September 2020

> things I need to consider using AGMs instead of FLAs?
Difficult to properly parallel AGM compared to FLA, as their internal resistance is lower and you are more likely to have one string hog all the load and charging.

12V batteries are less amp hours than 6v batteries in the same size case, so you would have to parallel them instead of series.

I see you are undecided, and I would push you to use the simple GC2 batteries, if you can keep from deeply discharging them, but if you need more capacity...

Image: https://us.v-cdn.net/6024911/uploads/editor/st/hykce64bpemx.jpg

BB. · September 2020

More or less, for lead acid batteries I would suggest that if you are full time off grid/daily(nightly) cycling, that you size for 25% discharge per night... Or, basically 2 days storage and 50% maximum discharge, or battery bank 4x the daily/nightly load.

Lead Acid batteries need a lot of time on charge (6-10+ hours) if deeply cycled. There is a good chance (especially in winter) that you would need 2 days of sun to recharge a lead acid bank from 50% to 100% State of Charge... You not only have "bulk" maximum charging current from 20% to 80% State of charge, you have the absorb cycle (charge holds voltage set point) for another 2-6 hours or so--And closer to 6 hours for deeply cycled batteries.

If you are down in Arizona (southern US), then winter hours of sun (sun above horizon) is not bad... If you are in the northern US towards Canada, not many hours of sun (above horizon).

There are other chemistry batteries such as LiFePO4 where they charge pretty much at maximum current until 100% state of charge--And those batteries would be better if you wanted to cycle deeper and quickly recharge the next day...

-Bill

pabloesguapo · September 2020

What are your thoughts on AGM batteries for a full time house in Central AZ? Shorter recharge time than FLA, I hear, but if I ride them too hard and lose fluid, I can't just add water.

Marc Kurth · September 2020

pabloesguapo said:

That's the stuff I'm trying to figure out

If my overnight requirement is 7200wh, my battery bank capacity would need to be minimum 14,400wh, for a 50% TOC discharge, right?

I'm leaning toward getting the Unigy AGMs. 300Ah would get me exactly 14,400wh. 450Ah would get me 21,600wh, which would bring me to (in theory) 66.67% SOC.

You need to understand how different battery types and brands handle discharging to various levels. In the lead-acid world, some batteries are rated for 500 charge-discharge cycles at 50%. Others are rated 2-4 times more. If you cannot find published data, the numbers are likely quite low - like 200 to 300. Lithium takes it to a different level.

Mike brought up Carbon-Foam AGM and they publish around 3600 cycles at 50%. That's about ten years of daily 50% DOD, but I have a hard time wrapping my head around that.

Whatever the number, you need to know what you are buying.

Marc

Dave Angelini · September 2020

All you really need is alot more money or alot more conservation.

I take it this is new and good to learn this. I think you could do alot more towards getting a real number for your storage. Most offgrid folks can do with a 48v 20 kwh 6v L16. One uses less than 10 kwh to stay above 50%.Even less to get longevity.

Many can use less than 5 kwh with a mini-split backed off to 77 at night. Can't do this with your golf carts for very long. Your $300 Rolls in the first post start looking good, especially if you are not living offgrid now and can learn the maintenance.

Which batteries to get?

Comments

Categories