mickey48
cincinnati
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Looking at a trailer with a 12 volt fridge and solar panel mounted on the roof. not sure of the size of panel. My question is this. how can i tell if the panel is charging the battery?
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CA Traveler
The Western States
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Size of solar depends upon your usage. For storage only and battery maintenance then 100W might be OK. Otherwise do an energy audit to determine what you need for solar. Info/calcuators available on line.
The better question: "Is the solar large enough for my needs?"
Being critical: Salesman "Comes compete with solar" ie Total nonsense until you know it's capability and YOUR needs.
Measure the battery voltage, turn the solar controller on and the voltage should start for rise. Assumes battery a little discharged. Even better if you have a battery monitor that measures voltage, amps and battery charge state.
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Boomerweps
Hills of PA
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Does your TT have a battery disconnect?
Most solar charging bypass the battery disconnect to keep the battery charged in storage.
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valhalla360
No paticular place.
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Most controllers have an screen that shows the voltage. It should be north of 13v if charging. That or just check the battery voltage on a sunny day and it should be north of 13v.
If its just the fridge and you run almost nothing else 12v, it's likely OK for a night or two of boondocking with 100w. A second battery would be more useful than more solar. This assumes a 12v compressor fridge...an absorption fridge (also runs on propane) will easily use 10 times as much when running on electricity. It also assumes it's not killer hot out and you leave the door open a lot.
If you want to run more 12v stuff (lights, fans, furnace, etc...) and boondock for multiple days, an energy audit is the way to go. Simplified a bit:
- How long will each 12v device be run per day, then mulitply the wattage by the hours it is on to get total amp-hours @ 12v.
- How many "usable" amp-hours does your battery bank have (lead-acid batteries should only use 50% of the rated amp-hr and lithium should only use 80% of the rated amp-hr...using more can prematurely age the batteries). Convert to watt-hours by multiplying by 12.
- Divide usable watt-hours by how many watt-hours you estimate you will use. This will give you an estimate of how long the batteries will last in days. Discount this by 20-30% to cover items you missed or aging of batteries eventually reducing usable amp-hr.
- Solar is really about longer term boondocking. If you are stopping for a night or two, solar is mostly a bonus. If boondocking longer term, you want enough solar to cover your daily consumption. Take the rating of the solar panels and multiply by 4 to get an estimate of how many watt-hours it will generate (100w panel would be 400watt-hour generated each day). In reality it will vary based on time of year and weather (clouds are a big impact) but 4 times the rating is a good starting point.
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Boomerweps
Hills of PA
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valhalla360 wrote:
- How many "usable" amp-hours does your battery bank have (lead-acid batteries should only use 50% of the rated amp-hr and lithium should only use 80% of the rated amp-hr...using more can prematurely age the batteries). Convert to watt-hours by multiplying by 12.
Where is the reference about “only use Lithium to 80% rated amp hour” stated clearly by a battery maker? I’ve never seen it referenced except on this forum. I’ve read where a LiFePO4 retains 80% capacity after its expected recharge cycle life is exceeded. I’ve also read where you can fully discharge them and then fully recharge them with no damage.
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ScottG
Bothell Wa.
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While technically true, there's really no reason to worry about the 80% thing. The spec that all quality manufacturers (those that use grade A cells) state is that you can discharge their battery 100% and then recharge fully on a daily basis and still have 80% of the overall capacity left after 10+ years. So with this kind of service life, who cares about trying to keep them between 20~80%? Most of us wont use them that hard and can probably expect something more like 20 to 30 years of life.
I think that's a lifetime of camping for most of us and after that much time something better will have come along anyway.
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edited 07/16/23 11:25am by an administrator/moderator *
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Boon Docker
Mountain Foothills of Southern Alberta
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Wow, this thread sure went off the rail quickly. ![[emoticon]](http://www.coastresorts.com/sharedcontent/cfb/images/doh.gif "doh")
To the OP.
The charge controller should indicate the charge going to the battery.
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valhalla360
No paticular place.
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Boomerweps wrote:valhalla360 wrote:
- How many "usable" amp-hours does your battery bank have (lead-acid batteries should only use 50% of the rated amp-hr and lithium should only use 80% of the rated amp-hr...using more can prematurely age the batteries). Convert to watt-hours by multiplying by 12.
Where is the reference about “only use Lithium to 80% rated amp hour” stated clearly by a battery maker? I’ve never seen it referenced except on this forum. I’ve read where a LiFePO4 retains 80% capacity after its expected recharge cycle life is exceeded. I’ve also read where you can fully discharge them and then fully recharge them with no damage.
They don't officially state the 50% for LA either (they do often provide charts of depth of discharge vs life cycles) just when you abuse them, they don't last as long.
Some would argue Lithium is OK down to 10% just depends how long you want them to last. So even at 80-90% usable, it's still a lot more than you get out of the same amp-hr rated LA. If you are going to boondock a lot for long periods of time while running a lot of 12v stuff, that can be worth the cost of upgrading to Lithium for the weight & space savings. If just running the fridge and a few lights for an occasional overnight, a couple of LA batteries makes more sense.
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ktmrfs
Portland, Oregon
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Trojan DOES show life curves for there deep discharge FLA GC and 12V batteries. for the GC2, life is >500 cycles discharge to 25% SOC/ 75% DOD. Probably representative of golf cart use. Pretty hard for us TT folks, even with lots of dry camping to hit 500 cycles to 70% DOD in a reasonable time. For the 12V FLA true deep discharge, life is about 1/2 that. Likely the result of having to use thinner plates to get 6 cells in a battery instead of 3.
And if you want to spend the bucks, trojan has a line of GC2's that have double or more the above mentioned cycle life.
to back up the Trojan spec's, I've gone through two sets of Trojan batteries in the last 20 years on one trailer. that trailer saw at least 50 deep discharges to anywhere from 50%DOD to 75% DOD every year. After 10 years I gave the batteries to a buddy who occasionally dry camps and they lasted him another 4 years. The second set had similar use, and last year one cell on one battery went dead.... so the second set ONLY lasted 10 years and only somewhere in the neighborhood of 500 charge/discharge cycles to 50% or more.
My other trailer was new in 2011 and it sees not as much deep discharges, I run 4 GC2's, but many down to 50%, probably on the order of 30/year, and those batteries are now 12 years old and SG test is similar to new. I'll probably replace them later this year before our annual two week dry campout.
The key to longevity IMHO is (a) don't let them sit to long at deep discharge before getting a FULL charge, that means getting the voltage up to 14.4 to 14.6V, which also means a typical WFCO charger is going to kill them and (b) keep them watered.
This is probably the last set of FLA I'll be getting, I figure when these are done lithium will be low enough cost premium to FLA to make the switch and get new charger as well.
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mickey48
cincinnati
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when parking trailer for extended period of time can i just turn 12v fridge off inside and battery disconnect switch off , will my battery hold a charge?
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