trojan battery solar spre 06 255

[chrisski]

For solar batteries in a fifth wheel, thoughts on trojan battery solar spre 06 255, a 6 volt 229 AH battery with two in series two in parallel for 12 Volts 458 AH? Want to get the batteries ordered.

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After about a month of consideration, I want to purchase four Tall Golf Cart Batteries Which are GROUP GC2H, trojan battery solar spre 06 255. THese batteries are suppposed to have 229 AH, 6 Volts. At the 20 hour rate. They’re spec’d for 2000 cycles at a DOD of 50%, 4000 cycles at a DOD of 25%. These are about an inch. Taller than the standard Golf cart battery and the inside dimensions of some battery cases leave an inch of room on top fo emu venting system if I go with an off the shelf.

These Trojan 6V 229 AH are slightly less expensive than the AGM batteries I was considering. Also, the AGM batteries I was considering did not have the spec sheet that Trojan publishes for DOD. All I can go with is things off the stickies and the battery university that say you get significantly less charging cycles for AGM compared to FLA Batteries.

I’d also considered a set of 6V 440 amp trojan batteries, but these are too tall for an off the shelf battery box, and also twice as heavy. Advantage of those would have been able to hook up in series.

Too early for me to put down 4 times the price of lithium batteries, especially since this is not a full time RV.

[secessus]

> thoughts on trojan battery solar spre 06 255,

My conclusions:

* RE may be worth the premium over plain Trojan flooded for batteries that are not charged daily to charged to mfg specs (including current minimums, 46A in this case). Lithium or carbon-foam would be a better chemistry for PSoC use, but I too am sensitive to the $$$.
* RE is not worth the cost premium when batteries are fully charged their batteries to mfg specs [nearly] every day.

Of course, if replacing the batts is especially difficult (bank location, remote geographic location, disability, etc) then time-between-replacements factor may outweigh the economic concern.

I tend to boondock in areas with good insolation and have a good panel:bank ratio (2.6A:1A). Since charging to spec is not an issue in those conditions I will replace the present bank with plain flooded again when needed. If I find myself hanging around the Pacific NorthWet or similar and struggle to get the bank charged to spec daily I'd spend the extra money on RE.

[chrisski]

What is your panel to bank ratio mean? I’m using advertised panel wattage to Battery Amp Hour. So, about 600 watts of panels to 400 amp hours of batteries, at my case parallel series to 12 Volts. So if that’s the same ratio you’re using, for a 12 VDC Battery bank at 400 AH, that would mean you have 1200 watts of panels.

My 1.5 to 1 ratio is something I came up with based off what I’ve found for successful systems that gave their panel wattage to Battery Bank AMp Hour. I got this off YouTube, some websites, and various forums. It would be nice to know if this is a decent measurement or not.

With the MPPT charge controller, I may be able to hit or come close to 10% the amperage from the MPPT to the battery bank in rather good, but not quite ideal conditions.

[secessus]

What is your panel to bank ratio mean?
I’m using advertised panel wattage to Battery Amp Hour

Yes, that's what I mean.

So, about 600 watts of panels to 400 amp hours of batteries, at my case parallel series to 12 Volts. So if that’s the same ratio you’re using, for a 12 VDC Battery bank at 400 AH, that would mean you have 1200 watts of panels.

2.6 * 400 = 1040w, but yes that's the idea.

My 1.5 to 1 ratio is something I came up with based off what I’ve found for successful systems that gave their panel wattage to Battery Bank AMp Hour. I got this off YouTube, some websites, and various forums. It would be nice to know if this is a decent measurement or not.

The commonly-repeated rule of thumb is 1.1, although you and I would might say that is insufficient for solar-only charging lead. I think of it as an absolute minimum, a sanity check.

1:5-to-1 is certainly much better, and will be sufficient under good sun like you get in AZ (see below). And of course adding in another source of charging (generator, shore, alternator) can greatly reduce the amount of panel required.


Don't trust me on any of the math below; I could be insane/drunk/stpuid/caffeine-deprived. Submitted for the sake of discussion of panel-to-bank ratios:


I did some back-of envelope calculations and came up with a ratio very much like yours for solar-only charging 50% DoD-cycled flooded batteries: On average (annual) about 1.5-to-1 for abundant insolation, 2.5-to-1 for average insolation, and 3.75-to-1 for poor insolation like the PNW. Of course, this doesn't include loads, and yield will be ~50% higher in July and ~50% lower in December. To keep the batteries healthy we can overpanel for the winter (2.25-to-1 under abundant insolation), reduce our depth of discharge, or augment with another charging source.

A more specific estimation for any particular location and a 400Ah bank would involve something like:

* replacing 200Ah fropm 50% DoD + ~15% lead-acid charging inefficiency = ~230Ah
* checking insolation averages (hours of Full Sun Equivalent), 5.38hrs for Phoenix means we need to collect 42.75A per hour of FSE on average
* which is about 535w of panel @ 12.5v
* derating MPPT for 5% inefficiency
* heat derating panels 14.47% at the annual average high temp of 75F

Assuming everything goes right (including negligible wiring losses), on (yearly) average in Phoenix it would take 639W of panel to fully charge 400Ah of flooded battery from 50% DoD daily, or 1.6-to-1. Aligns nicely with your numbers.