diy solar

diy solar

after 2 years of dependable use my lead acids have died. can i do better ?

I just bought a 140ah 12v battery for $400 on amazon, because i waited a little too long and let the discount to $370 expire. I would recommend going to lithium and making the minor accommodations to keep it functioning in your climate.

Honestly, unless your battery bank was functioning one day and not functioning the next, i suspect what happened is you were 'away' from the setup (or not watching it) during a period where it sat at low soc AND endured cold temps and it put a quick end to what was already an 'aged' pack. It's possible if it had not gone through that, they would last longer.

I think going to true deep cycle lead acid would be an improvement, but as mentioned that doesn't change anything about them not liking to sit at partial SOC, so it may be more prudent to focus on keeping them full (i.e. reliably fully replacing the energy you used, preferably quickly) than buying a slightly more tolerant or higher capacity lead acid design.

But, all of the above would be good, with an upgrade to lifepo4 and some protective measures against the temp, being the optional but ideal capstone.
 
Last edited:
Jack Rabbit Off Grid said:
I was also going to recommend Costco cart batteries. that why I asked what 12v he currently had to see if he had the room. I have a set of them That I removed from my RV that is currently running my container/shop. They are 5 years old and still working. But they are 58lbs each so he may not want that extra weight.
Click to expand...

Vigo said:
I just bought a 140ah 12v battery for $400 on amazon, because i waited a little too long and let the discount to $370 expire. I would recommend going to lithium and making the minor accommodations to keep it functioning in your climate.

Honestly, unless your battery bank was functioning one day and not functioning the next, i suspect what happened is you were 'away' from the setup (or not watching it) during a period where it sat at low soc AND endured cold temps and it put a quick end to what was already an 'aged' pack. It's possible if it had not gone through that, they would last longer.

I think going to true deep cycle lead acid would be an improvement, but as mentioned that doesn't change anything about them not liking to sit at partial SOC, so it may be more prudent to focus on keeping them full (i.e. reliably fully replacing the energy you used during the day, preferably quickly) than buying a slightly more tolerant or higher capacity lead acid design.

But, all of the above would be good, with an upgrade to lifepo4 and some protective measures against the temp, being the optional but ideal capstone.
Click to expand...
so what i am getting from all of your valuable and greatly appreciated responses is that i should upgrade my scc to 30 amp so i can have 400 watts of panels. get 200 watts more in panels. get 4 6volt costco batteries and go through my system much closer so i know what my actual usage is and figure out watt hours per day. pretty sure it is astronomical somewhere close to 4k is my guess.
 
I like the idea of flooded lead acid batteries maintained with measurements from a hydrometer to know when you are supposed to equalize these batteries. For my area of Arizona, I found that I used 1000 watts of panels to reliably charge those four golf cart sized FLA batteries, which gave me 2.5 kwh of power, about 220 ah of usable power. The panels may seem overkill, but helped much for cloudy days.

I even had 400 watts of ground panels I angled at and moved with the sun that outperformed the 1000 watts of roof panels.

Lead acid batteries will need to be limited to charging to whatever the battery spec said, in my case 60 amps or 13%.
 
Vigo said:
Since you are already incorporating a new charge controller, i would just try to get one that will track the usage for you so you can skip most of the math.
Click to expand...
While this approach does work, doing the math becomes a whole lot more important the bigger a system gets.
 
chrisski said:
While this approach does work, doing the math becomes a whole lot more important the bigger a system gets.
Click to expand...
future mods should also be taken into consideration. that worries me that it takes 1000 watts of panels to completely charge four 6 volts. wow
 
i get it. just dont know how reliable any lithium variety will be where you get winter conditions 6 months a year. that is why i am leaning in the 6 volt direction
 
Fan for propane heater could be much less power than fridge.
Other model refrigerators may use less than the one you've got.

If heater is needed, refrigeration probably isn't.
Maybe a light sensor to disable fridge at night.

Lithium should be quite reliable in winter conditions. Less so in Mojave Desert conditions.
Just need to disable charging below 32F (also charge slower near 32F). I would suggest a heater and disable charging below 40F, look up what current is acceptable at that temperature. We don't have SCC that will vary current, so select parameters for simple on/off control.

There are lithium chemistries for extreme cold, but they cost more.
 
roaming ram said:
i get it. just dont know how reliable any lithium variety will be where you get winter conditions 6 months a year. that is why i am leaning in the 6 volt direction
Click to expand...
Honestly, over-panel slightly and put a heating pad on it for daytime. As long as it is in an insulated box/cooler it should be enough in night time ambients down to ~0°F.
 
no generator to top off LA batteries when the sun don't shine is like drinking and smoking in bed
It will definitely lower lifespan
LA limits you to basically half the usable capacity
as noted, discharging to deeply will shorten their life

Lithium is a better choice IMO
They like not being held at a constant full charge
DOD is far greater, there's more usable capacity
I'd rather deal with the cold than to constantly baby a lead acid battery

Dealing with the cold will really depend on how cold it gets
I can see -40F and mine are in the garage in an insulated box with a seed starting heat pad
Mine runs a constant 25w load but I've got enough juice in the battery bank to not really notice
600wh a day to keep the pad running is a big draw on a small system
Shimmy said:
Honestly, over-panel slightly and put a heating pad on it for daytime. As long as it is in an insulated box/cooler it should be enough in night time ambients down to ~0°F.
Click to expand...
your mileage may vary, there's a lot of thermal mass in the battery, just how fast they get cold depends
Maybe build a bigger insulated box with space to put in a heated rock wrapped in a towel. a few firebrick would be better


The other option is to have a "heated" battery.
They will have a low temp charging cutoff to prevent charging at damaging temps
When they're too cold to charge they will divert power from the solar panels to a heating element until the battery is warm enough to charge
https://www.currentconnected.com/product/sk12v206h/
The problem I see with a heated battery is they can take a couple hours to heat and by then most of the charging potential is lost in the short daylight of winter

Either way it's best to have a well insulated battery box

and more panels, be good to have enough to run daytime loads while charging the battery
 
So here's a quick & dirty way to guesstimate how much solar & SCC you need with some napkin example numbers:

Total AH of the batteries (3x 120Ah batteries in parallel)
Total nominal voltage ( WallyWorld deep cycles are 12v, in parallel it stays 12v)

FLA batteries on average like a 0.2c rate (120Ah * 0.2 = 24a, and I have 3 batteries so 72a is the most they will take)

Calculate your usable watt hours with Volts(12) * Amp Hours (360) divided by 2 (50% DoD) and that tells you how much you can use (12 * 360 * 0.5 = 2160Wh usable power).

Ok, so you want to be able to replace that much power in a day. National average rule of thumb is 4 hours of usable sun, so power used divided by 4 (2160Wh ÷ 4hours = 540 watts of panel) rounded up to convienent panel size. In this case I'd go for 600w of panel.

Now, if ypu had 600w of panels divided by your 12v nominal voltage (600w ÷ 12v = 50a) to get the size of the SCC that makes your panels fit your battery bank.

Does that math and example make sense? Let's try going the opposite direction with what you've posted so far, which is 400w of panels and a 30a SCC...

400w ÷ 12v = 33.3a so slightly overpaneled for your SCC so you're fine there.

12v * 30a = 360w * 4hrs = 1440wh a day generated.

1440wh ÷ 12v = 120Ah you can pump into your batteries in a day,

Your goal with your current setup is to keep your total load per day well under that 1440Wh a day. That assumes you get that sweet 4 hours a day of good sun. One day of overcast and you'll always be playing catch-up trying to refill those batteries, which will damage the batteries.
 
Rednecktek said:
So here's a quick & dirty way to guesstimate how much solar & SCC you need with some napkin example numbers:

Total AH of the batteries (3x 120Ah batteries in parallel)
Total nominal voltage ( WallyWorld deep cycles are 12v, in parallel it stays 12v)

FLA batteries on average like a 0.2c rate (120Ah * 0.2 = 24a, and I have 3 batteries so 72a is the most they will take)

Calculate your usable watt hours with Volts(12) * Amp Hours (360) divided by 2 (50% DoD) and that tells you how much you can use (12 * 360 * 0.5 = 2160Wh usable power).

Ok, so you want to be able to replace that much power in a day. National average rule of thumb is 4 hours of usable sun, so power used divided by 4 (2160Wh ÷ 4hours = 540 watts of panel) rounded up to convienent panel size. In this case I'd go for 600w of panel.

Now, if ypu had 600w of panels divided by your 12v nominal voltage (600w ÷ 12v = 50a) to get the size of the SCC that makes your panels fit your battery bank.

Does that math and example make sense? Let's try going the opposite direction with what you've posted so far, which is 400w of panels and a 30a SCC...

400w ÷ 12v = 33.3a so slightly overpaneled for your SCC so you're fine there.

12v * 30a = 360w * 4hrs = 1440wh a day generated.

1440wh ÷ 12v = 120Ah you can pump into your batteries in a day,

Your goal with your current setup is to keep your total load per day well under that 1440Wh a day. That assumes you get that sweet 4 hours a day of good sun. One day of overcast and you'll always be playing catch-up trying to refill those batteries, which will damage the batteries.
Click to expand...
 
so your quick math tells me i really have no choice other than to go with heated LiFePo4's, store them for the winter, get another set of panels, a new 30amp scc that records all my usage so i can get real time data and become a guru at this. haha
 
wiseacre said:
no generator to top off LA batteries when the sun don't shine is like drinking and smoking in bed
It will definitely lower lifespan
LA limits you to basically half the usable capacity
as noted, discharging to deeply will shorten their life

Lithium is a better choice IMO
They like not being held at a constant full charge
DOD is far greater, there's more usable capacity
I'd rather deal with the cold than to constantly baby a lead acid battery

Dealing with the cold will really depend on how cold it gets
I can see -40F and mine are in the garage in an insulated box with a seed starting heat pad
Mine runs a constant 25w load but I've got enough juice in the battery bank to not really notice
600wh a day to keep the pad running is a big draw on a small system

your mileage may vary, there's a lot of thermal mass in the battery, just how fast they get cold depends
Maybe build a bigger insulated box with space to put in a heated rock wrapped in a towel. a few firebrick would be better


The other option is to have a "heated" battery.
They will have a low temp charging cutoff to prevent charging at damaging temps
When they're too cold to charge they will divert power from the solar panels to a heating element until the battery is warm enough to charge
https://www.currentconnected.com/product/sk12v206h/
The problem I see with a heated battery is they can take a couple hours to heat and by then most of the charging potential is lost in the short daylight of winter

Either way it's best to have a well insulated battery box

and more panels, be good to have enough to run daytime loads while charging the battery
Click to expand...
i am seeing i really do not have many realistic options for my consumption other than LiFePo4's
 
roaming ram said:
i am seeing i really do not have many realistic options for my consumption other than LiFePo4's
Click to expand...
That's my opinion based on my experience with Gel vs LiFePo4
It was good not to worry about getting out the charger and topping off the batteries when the sun refused to cooperate
for me it was just a hassle, but for you out camping it's not an option

either way, more panels are needed
I'd get as many as you can pack (assuming you're pretty well packed and space limited already)
 
roaming ram said:
so your quick math tells me i really have no choice other than to go with heated LiFePo4's, store them for the winter, get another set of panels, a new 30amp scc that records all my usage so i can get real time data and become a guru at this. haha
Click to expand...
Nah, just need to make space for batteries and panels. If this is for a trailer to connect to, there's no reason you can't leave the batteries and panels on site and just plug your trailer in when you get up there. A shed or container or basically any kind of weather resistant box to hold everything in.
 
wiseacre said:
LA limits you to basically half the usable capacity
as noted, discharging to deeply will shorten their life
Click to expand...

The AGM technical document I linked indicated anything from about 10% DoD to 80% DoD would yield similar total Ah of cycling over life of battery. Deeper cycles mean you get your money's worth sooner and replace it sooner.

I think shallow cycling of lead-acid makes sense if you want enough storage for 3 days without sun; most nights, only cycles 15%. At that, quality FLA could lasts 20 years or AGM 10 years.

For Lithium, nightly deep cycling could last 8 to 16 years. Size for 3 days without sun, it is likely to fail of old age before you get your money's worth. So I wouldn't want to size for more than 1 day without sun. Optimum usage might be multiple cycles per day.

My preference is to oversize PV, which costs about $0.025/kWh over 20 years. Size battery to barely last one night. In this case, optimal system delivers target charge rate to battery, additional current only if loads are drawing power.
Some other tradeoff might be better fit for mobile system.
 
You must log in or register to reply here.

Similar threads

O
Update from Lead Acid to LFP Batteries
Replies
11
Views
510
robbob2112
robbob2112
JeremyG
Are lithium ion batteries better than lead acid?
2
Replies
27
Views
1K
JeremyG
JeremyG
DXHum
So I am going to try my hand at reconditioning lead acid batteries...
2 3
Replies
51
Views
3K
DXHum
DXHum
J
From Harbor freight special 12 Volt Off Grid learning system, to new ground up build off grid solar build plan.
2
Replies
22
Views
2K
Doggydogworld
Doggydogworld
D
Please review my off-grid 24v setup to suggest best Lithium Battery upgrade
Replies
7
Views
814
Raymond Enriquez
R
Back
Top