Batteries

[John61CT]

Are you sure you'll be able to recharge to true 100% at least a few times per week? This means frequent overnight stays on shore power, or solar+gennie backup if boondocking.

Solar alone or the alternator won't do it?

Above was for normal lead banks, FLA or AGM.

Only situations where alt or gennie is running all day or night anyway will get to 100%, the last 5 hours is tiny current, not worth burning fuel.

Solar alone is fine to get to 100%, as long as over-sized proportional to bank, unless you live where clear skies are the norm year round, have to size for worst-case weather + heavy usage.

Usually better to have a small gennie + big charger to help with the worst case times.

Especially where space for panels is limited.

[rruff]

Solar alone is fine to get to 100%, as long as over-sized proportional to bank, unless you live where clear skies are the norm year round, have to size for worst-case weather + heavy usage.

Hmmm. Hadn't even thought about the difficulty of getting to max charge. I was planning on a pair of ~225A 6V AGM batteries (ditching the starting battery) and a 160W panel flat mounted on the roof. Power use should be pretty mild relative to capacity, just a couple laptops and some led lights. No fridge, microwave, etc. I figure ~30A-hr per day max, which the solar will supply on a sunny day even in winter. And even if I get no sun at all (I'll be in the SW desert), it's only 13% of capacity per day. Once a week figure ~3 hrs of driving, going to town for supplies.

From what I've been reading the AGMs like .4C to get to 100% if they are deeply discharged. That's 90A. That definitely won't happen with the solar panel. Would the truck's alternator adequately top off the batteries to 100% once a week? Seems like it should have the capacity to anyway, with >100A. Once a week would be better than never.

And I'm unclear on what "deeply discharged" means and how the state of discharge effects charging. If I typically only use 10% of capacity at night, will I get to 100% with the solar panel on a sunny day?

[John61CT]

High amps only helps you get to 80-90% quicker, that's your trip into town, the last 10-20% needs like overnight on mains, maybe 10 hrs. Or lots of solar and sunny days.

Hard to predict, but seems likely to me you'll murder those pricey batteries much quicker, even weekly's pretty infrequent.

Can you just get Sam's Club GC2s instead?

Or a little quiet genny with a high-amp charger, run every other day, ideally between end of use and start of solar, which is fine for the long tail low current.

Drawing less off the top will help a bit, implies more storage, but bottom line you should put back what you take out, + a bit more, ASAP for longevity.

Or go to Firefly Oasis, they're happy in PSOC situation will last for years, but $500 for 100AH.

[rruff]

If I typically add more each day in solar than I take out, will it charge to 100%? Or will the charge cycle be relatively inefficient because the amps are too low?

No generator for me. My main reason for wanting AGMs is so I can put them inside the living space and won't have to service them. LiFePo is starting to look better, and the weight savings is always nice as well.

[John61CT]

You'll find LFP crazy expensive per AH, and very high risk IMO involved not automating low/high voltage shutdown protection, if you don't go full BMS.

Reconsider FLA GC2s, nothing wrong in the living space, less venting than a fridge, and as long as you're not overcharging maintenance is hardly any bother, in fact being able to get an Accurate SoC with a cheap hydrometer is a huge advantage!

You do check and replenish your vehicle's fluids right?

Cheap up front, learn your usage / recharge routines, maybe they'll last 7-8 years, then you know you're ready to spend big buck$ on fancy chemistries.

Otherwise Firefly gives you the longevity in PSOC context at much lower up-front cost vs LFP, and MUCH lower risks, mainstream well-understood care & feeding.

[John61CT]

If I typically add more each day in solar than I take out, will it charge to 100%? Or will the charge cycle be relatively inefficient because the amps are too low?

With any lead bank but Firefly, it will last longest the shorter the time they spend under 100%.

If regularly drawn down 30-50% and only get back up to full 100% couple times a week, lifespan will be a fraction of a bank with 10-20% draw down and getting back to full 100% (not 95%, not 98%) most cycles.

With minimal days of alt input, rare overnights on shore power and no genny (why no genny again?), your only regular energy source is your solar.

So your choices become A find a way to expand your panel area (portables on the ground?), B live within your input budget or C buy cheapest GC2 batteries, expand your bank size and accept you'll be replacing them often, maybe every 1-2 years.

Fossil fuel for fast hi-amp bulk phase charging, solar for long slow finish. Or lots and lots of panels in a sunny place.

[rruff]

I've been researching AGM and solar, and haven't seen any mention of needing high current to get to 100%. Seems like it would be a common issue with an off grid system if that is in fact the case.

I don't want a generator because it is a gas powered and noisy contraption I have to carry around. Plus the small and cheap ones I've seen are designed for 120v and only put out ~8 amps which isn't enough.

I have plenty of room on the roof for more solar. I just didn't think I'd need it. But if a decent excess capacity over my nominal usage will do the job, that seems like the easiest solution.

[John61CT]

I don't think anyone said high current needed to get to 100%.

The last 20% at LOW current just takes a long time. Doing the high current bulk stage quickly before solar starts lets fewer panels finish up a bigger bank.

The little 2000w units aren't that big nor noisy, and of course you don't use their little built in DC charging, you put the bank on a big (.4C) AC-DC charger until volts are up to spec, plus maybe 30 min absorption, maybe a bit longer on cloudy days until current drops. Sunny days maybe shorter or no gen needed, trial and error as you get to know your needs.

I hate fossil fuels myself, just helping you understand your choices within realistic boundaries.

[dancam]

https://handybobsolar.wordpress.com/the ... -puzzle-2/

Sent from my SM-G920W8 using Tapatalk

[John61CT]

Yes Bob's great, very entertaining but valuable learning resource, just let some overly dogmatic fixations slide. . .

[John61CT]

In researching Firefly Oasis some more, I came across this very relevant post:

http://www.cruisersforum.com/forums/f14 ... ost2219754

Reading Maine Sail's immediately above (anything by him on these subjects) is also very enlightening.

[defjr333]

Lots of great info here. Yet the info has now left me more undecided than before. I have already purchased the entire electrical system except batteries, solar panels, and MPPT. Any help deciding these components would be greatly appreciated. Thanks for all the replies

[rruff]

Lots of great info here. Yet the info has now left me more undecided than before. I have already purchased the entire electrical system except batteries, solar panels, and MPPT. Any help deciding these components would be greatly appreciated. Thanks for all the replies

You listed the equipment you have, but what does your daily use come to? How much sun will you get? 800-1000 A-hr is pretty huge BTW. Doubt you need that much.

[defjr333]

After reading all the replies and skimming over a few other battery threads, I THINK(lol) I have found the batteries I am going to use. Would like to run by those of you with a little more "real life" experience with 1st. Thinking of 4, maybe 5 of these:

https://www.mightymaxbattery.com/p34882 ... boats.html

Seems to be best ah per dollar and AGM which i like due to less maintenance. Feel free to reply with any info would be helpful. Looking to hear if anyone has used or heard of this brand, any better choices for similar money(cant afford lithium), or ANY info to help me finalize the decision on batteries to purchase as I want to get them within next few weeks. Thank you all for your knowledge and time.

[rruff]

Seems to be best ah per dollar and AGM which i like due to less maintenance

I don't think I'd use AGMs unless venting of gases is an issue (which is why I'm considering them). Flooded batteries are cheaper and will last longer.