diy solar

diy solar

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

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.
 
Technically you have a generator. It’s not very efficient but would work in a pinch since you run a 12v system. Jumper cables and a Dodge.

Back in the day when I built my very first system in a 1973 Dodge class C. I used a 8d battery I got for free out of a friends boat. Mounted some real cheap solar panels on the roof and some cheap controller. I found my self in the same spot. The panels couldn’t keep up. Being I was a Diesel technician at the time. I replaced the factory Dodge alternator with a 160 amp one out of a KW T600 tractor. Couldn’t afford any fancy generator back then. In the morning if the battery was dead just fire up the gas guzzler 440 and let it idle. I even had the for thought to over drive the alternator so it would put out full power at idle.
 
Hedges said:
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 syst
Click to expand...

Jack Rabbit Off Grid said:
Technically you have a generator. It’s not very efficient but would work in a pinch since you run a 12v system. Jumper cables and a Dodge.

Back in the day when I built my very first system in a 1973 Dodge class C. I used a 8d battery I got for free out of a friends boat. Mounted some real cheap solar panels on the roof and some cheap controller. I found my self in the same spot. The panels couldn’t keep up. Being I was a Diesel technician at the time. I replaced the factory Dodge alternator with a 160 amp one out of a KW T600 tractor. Couldn’t afford any fancy generator back then. In the morning if the battery was dead just fire up the gas guzzler 440 and let it idle. I even had the for thought to over drive the alternator so it would put out full power at idle.
Click to expand...
i actually have a dual alternator on that wagon stock. helps when winching, with extra lights and any additional current draws
 
Only use wet batteries if you can look at them every day and check the water levels. Your batteries died as you were away for months yet they were continued to have charge applied. If you don't want LFP, then your only option is agm. But in your cycling even AGM likely won't last any longer as the cycle count isn't a good match for this use case.
 
roaming ram said:
i am seeing i really do not have many realistic options for my consumption other than LiFePo4's
Click to expand...
I agree with this statement. If you can control heating and cooling for your lithium batteries, then there is only a very narrow set of circumstances where lead acid is better. Where lead acid works out better is for extreme cold where you can't reliably provide heating or cooling to your lithium battery pack.

Earlier this year, I switched from lead acid to lithium, and I enjoy the added capacity with less space and weight, along with the batteries lasting longer than a lead acid pack. Researching and building this heater could take weeks but could be worth it. I am not in an extreme cold area and won't charge my batteries if the battery temps get below freezing and I have two different thermometers to automatically shut off charging. One single thermometer shuts off the SCC, another two sets of two thermometers will trip the BMS. I forget what the max discharge temp is on my lihiums, but it's well below both freezing and record cold temps.

People make heaters to keep there battery packs above freezing in RVs that are stored for months at a time, so they can be reliable. If the heater fails, that causes the BMS to trip and stop charging.
 
Solar Guppy said:
Only use wet batteries if you can look at them every day and check the water levels. Your batteries died as you were away for months yet they were continued to have charge applied. If you don't want LFP, then your only option is agm. But in your cycling even AGM likely won't last any longer as the cycle count isn't a good match for this use case.
Click to expand...
so you do not believe heated LiFePo4's would be a good fit if i stored them each winter and kept them trickle charged ?
 
chrisski said:
I agree with this statement. If you can control heating and cooling for your lithium batteries, then there is only a very narrow set of circumstances where lead acid is better. Where lead acid works out better is for extreme cold where you can't reliably provide heating or cooling to your lithium battery pack.

Earlier this year, I switched from lead acid to lithium, and I enjoy the added capacity with less space and weight, along with the batteries lasting longer than a lead acid pack. Researching and building this heater could take weeks but could be worth it. I am not in an extreme cold area and won't charge my batteries if the battery temps get below freezing and I have two different thermometers to automatically shut off charging. One single thermometer shuts off the SCC, another two sets of two thermometers will trip the BMS. I forget what the max discharge temp is on my lihiums, but it's well below both freezing and record cold temps.

People make heaters to keep there battery packs above freezing in RVs that are stored for months at a time, so they can be reliable. If the heater fails, that causes the BMS to trip and stop charging.
Click to expand...
not sure i can really afford it but battleborn has LiFePo4's that are heated and have a bms as well. i would like to know more about the thermostats you are using. i assume they just break the ground loop ?
 
Hedges said:
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.
Click to expand...
i saw they have some advantages over lead acid. no water requirements, but almost double the weight. not a deal breaker, but a concern. my goal is to only use 400 watts of panels and find a battery or combination of batteries that can be fully charged or can handle a partial charge yet still handle daily requirements for a long weekend. i would think with me being a long weekend warrior i could get the charge state back to full during the week especially if i shut down the fridge when not in use.
 
roaming ram said:
so you do not believe heated LiFePo4's would be a good fit if i stored them each winter and kept them trickle charged
Click to expand...
Unlike LA batteries a lithium doesn't need to be kept at full charge. They can be stored for long periods at a lower charge (60/70% ?)
I bought cells to build my own battery, they sat for a at least a year at 30% before I got them
( it was a bargain deal, no warrantee, but they turned out to be just fine)
roaming ram said:
not sure i can really afford it but battleborn has heated LiFePo4's that are heated and have a bms as well.
Click to expand...
BBs are over priced IMO, I go with the SOK if I wanted a heated battery.
But really. you're going to want an insulated battery box anyway and adding a heating pad to use 'as needed'
roaming ram said:
my goal is to only use 400 watts of panels and find a battery or combination of batteries that can be fully charged or can handle a partial charge yet still handle daily requirements for a long weekend. i would think with me being a long weekend warrior i could get the charge state back to full during the week especially if i shut down the fridge when not in use.
Click to expand...
So in all of this I haven't actually seen what your actual use is
I've gleaned
you had appx. 300ah at 12v or 3600wh of capacity
You may have used nearly the full capacity over a 3 day trip (not entirely since you didn't say they went dead)

Recommending a battery capacity is a wild guess at this point without knowing just how much power you use.
also it would be good to know what the max power/load you have
the 3 old batteries could deliver a sizeable amount of amps at a time
a single lithium battery is limited to commonly 100 amps (some higher some lower)
I'm assuming you don't need to draw a 100 amps at a time while camping although your 2000w inverter is capable of pulling about 167 amps
As long as your loads stay below 1100w at a time you're fine with a single battery

If the 3 old batteries saw you through a 3 day trip then a 300ah lithium should do you good
No heating but a chins 300ah, 12v battery may be the cat's pajamas
https://www.amazon.com/CHINS-LiFePO...ocphy=9005349&hvtargid=pla-1106935315637&th=1

---
EDIT: there is a heated model
https://www.amazon.com/dp/B09SX4NGDJ/ref=twister_B09T2QSBV3?_encoding=UTF8&psc=1
but I think think doing your own heating is better
---

of course that's back to an insulated battery box (easy enough to rough out with 2" foam board and some duct tape to seal cracks)
a heating pad used as needed (turn off fridge at night and plug in heating pad)
I mentioned I use a seed starter heat pad (25w, if used overnight it would be less than the fridge so there's no real net loss using it)
and not to forget, using some heated fire brick could go a long way in keeping the battery box warm)
 
Last edited:
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...
Don't necessarily need to store the batteries for the winter, just store a couple extra solar panels in the summer when you get plenty of sun. With LFP you have a higher charging uptake rate, so you can increase the winter array size.
 
There is one other option that I don't believe that has been mentioned. If you buy lifepo4 batteries you could keep them in the heated space with you. Just find a suitable place like under a dinette bench or something like that and as long as you are at a comfortable temperature they will be fine. And when you are not camping and they get cold just don't charge them.
 
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