If your Using lithium keep in mind the very high charge efficiency increases the feasibility of using the tow vehicle to help in a pinch. Not sure where you camp, but also keep in mind that you cant charge lithium if the battery bank is below freezing... dont see that mentioned much...
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Solar + battery system design (help head spinning!)
- Thread starter polomasta
- Start date
Hey I just did a similar calculation and got even higher AH/day than you
(calculated highest usage day + winter)
Water pump, 15 min/day @90w = 22.5Wh
10 LED lights, 8hr/day @20w = 160Wh
Fridge, 8hr/day @45w = 360Wh
Laptop, 3hr/day @70w = 210Wh
Induction hob, 1hr/day @1000w = 1000Wh
Maxxair fan, 8hr day @53w = 424Wh
Sound system, 5hr day @10w = 50Wh
Misc/(laptop2), 3hr/day @70w = 210Wh
2500w = 208A/day
Winter +
Espar D2 8hr/day @34w = 272Wh
Espar D4s 8hr/day @40w = 320Wh
3100w = 258A/day
3x C20- 215AH 12v AGM batteries = 645AH, not discharging more than 50% = 322.5AH usable battery
6x100w solar panels running at 70% for 5hr/day = 2000w @12v = 166a
166amps/day would probably cover the average day at average usage. At max power in winter, draining say 250A/day, charging 166A/day @ 70% efficiency from solar, I'd be losing 84a per day if the batteries couldn't top up. With 322A usable, that would give nearly 4 days before the battery bank hit 50% and it'd need a full top up.
Anyone want to school me and/or make me feel better by saying I wouldn't use anywhere near that?
By the way, if my vehicle had a 150a alternator with an ACR to the house batteries, how much charge would go into the house batteries while the engine is running? (obviously not the full 150a?). The battery specs state that constant current charge can be at 0.1-0.2 C10 Amps, so C10 = 190AH/0.2 = 38. I assume this means each battery can handle a charge of 38 amps. If the battery system is at 50% and needs to be charged 322.5amps, does this mean that 38a/hour can be spread across 3 batteries, charging at 114amps per hour total and recharge the system in 3 hours, or can the whole system only be charged at 38a meaning 8hr to charge? Not sure if I understand all this correctly
(calculated highest usage day + winter)
Water pump, 15 min/day @90w = 22.5Wh
10 LED lights, 8hr/day @20w = 160Wh
Fridge, 8hr/day @45w = 360Wh
Laptop, 3hr/day @70w = 210Wh
Induction hob, 1hr/day @1000w = 1000Wh
Maxxair fan, 8hr day @53w = 424Wh
Sound system, 5hr day @10w = 50Wh
Misc/(laptop2), 3hr/day @70w = 210Wh
2500w = 208A/day
Winter +
Espar D2 8hr/day @34w = 272Wh
Espar D4s 8hr/day @40w = 320Wh
3100w = 258A/day
3x C20- 215AH 12v AGM batteries = 645AH, not discharging more than 50% = 322.5AH usable battery
6x100w solar panels running at 70% for 5hr/day = 2000w @12v = 166a
166amps/day would probably cover the average day at average usage. At max power in winter, draining say 250A/day, charging 166A/day @ 70% efficiency from solar, I'd be losing 84a per day if the batteries couldn't top up. With 322A usable, that would give nearly 4 days before the battery bank hit 50% and it'd need a full top up.
Anyone want to school me and/or make me feel better by saying I wouldn't use anywhere near that?
By the way, if my vehicle had a 150a alternator with an ACR to the house batteries, how much charge would go into the house batteries while the engine is running? (obviously not the full 150a?). The battery specs state that constant current charge can be at 0.1-0.2 C10 Amps, so C10 = 190AH/0.2 = 38. I assume this means each battery can handle a charge of 38 amps. If the battery system is at 50% and needs to be charged 322.5amps, does this mean that 38a/hour can be spread across 3 batteries, charging at 114amps per hour total and recharge the system in 3 hours, or can the whole system only be charged at 38a meaning 8hr to charge? Not sure if I understand all this correctly
Last edited:
No, you need some 101 batt charging.
First off what batt chemistry?
Any lead, dino juice only gets you to 80-85% SoC, unless you're driving all day long.
The remaining long tail at very low amps is at least 3-5 hours to get to 100%.
Failing that shortens life drastically, except Firefly Oasis, expensive.
LFP has no such issue but super expensive.
First off what batt chemistry?
Any lead, dino juice only gets you to 80-85% SoC, unless you're driving all day long.
The remaining long tail at very low amps is at least 3-5 hours to get to 100%.
Failing that shortens life drastically, except Firefly Oasis, expensive.
LFP has no such issue but super expensive.
First - your numbers are way too high (feeling better already?)
Second - and I have said this many times before - don't budget for happens 1% of the time in a worst case scenario! You are a sentient being, and you can make a minor modification to your behavior based on power availability. Maybe if your batteries are low you could decide NOT to cook that big pot of stew for dinner that requires 2 hours of boiling, or start your engine while you cook. Secondly, if you do find yourself in a bad situation where you need more power, there is no problem running your batteries down to 25% SOC on occasion. Also realize that certain actions are either/or not and. If you are running your heaters 8 hours a day, you won't be running your fans 8 hours a day, and your fridge won't be drawing much.
Third - build in the capability for expansion, but start at the low end of your requirements and see how things go. If you realize you are always negative on your power budget at the end of the day you can add more solar or more batteries.
Second - and I have said this many times before - don't budget for happens 1% of the time in a worst case scenario! You are a sentient being, and you can make a minor modification to your behavior based on power availability. Maybe if your batteries are low you could decide NOT to cook that big pot of stew for dinner that requires 2 hours of boiling, or start your engine while you cook. Secondly, if you do find yourself in a bad situation where you need more power, there is no problem running your batteries down to 25% SOC on occasion. Also realize that certain actions are either/or not and. If you are running your heaters 8 hours a day, you won't be running your fans 8 hours a day, and your fridge won't be drawing much.
Third - build in the capability for expansion, but start at the low end of your requirements and see how things go. If you realize you are always negative on your power budget at the end of the day you can add more solar or more batteries.