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Lead acid isn't that much cheaper. You can get LFP 12v 100AH batteries for $290, with a 10yr warranty. You also don't have to worry about discharging them t

Lead acid isn't that much cheaper. You can get LFP 12v 100AH batteries for $290, with a 10yr warranty. You also don't have to worry about discharging them too low.

Gibbon1 3y ago
Last time I tried spec'ing a lead acid battery in a product I found you have to derate the lead acid battery a lot more than would expect if it has to deal with constant deep charge discharge and temp extremes. Where you don't need to derate a LFP battery much at all. So lead acid is okay at lower temps and with only occasional deep discharges.
- ianburrell 3y ago
  Lead acid battery can only use 50% of rated capacity. Also, they are heavy. Not a problem in fixed install or vehicle but pain if need to move.
  - dragontamer 3y ago
    We're talking about Rasp. Pi batteries here. 15lbs (6kg) of Lead-Acid is probably the biggest, oversized battery that'd be needed (Assuming PS-12200 a 12V 20Ah Lead-acid or 240 Watt-hours of battery life) > Lead acid battery can only use 50% of rated capacity. That's definitely wrong. Lead Acids lose durability when you deeply-discharge them, but all Lead-Acids have *hundreds* of deep-discharge cycles supported. The question is one of frequency. Li-ion is great because it has high-durability through deep-discharge cycles. But is this the use case of a UPS or Solar Backup? I argue no, it isn't. --------------- The key advantages of Lead Acid are its cheapness and simplicity. If you can overlook its size and weight (okay, 15lbs is heavy if you're used to Li-ion... but is it really a *problem*? I argue no), and also know that deep-discharges would be rare (ie: UPS style "backup battery" usage), then LeadAcid suddenly rises to #1 choice due to gross simplicity you can have when designing circuits. As I described earlier: two diodes and a constant 13.5V source are pretty much all you need to create a minimally viable Lead-Acid battery backup solution. None of this "LiFePo4 charge controller" crap or CC-CV charging circuits (Lead Acid _prefers CC-CV especially if you want to charge it in 20 hours or less, but it doesn't _need_ CC-CV circuits) A long-term trickle charger over days (~72-hours of charge) of use is perhaps a non-obvious usecase. But that's called "Always plugged in UPS" and is IMO, the kind of use-case that's best suited for "SolarPi". -------- You might laugh at "hundreds" of deep discharge cycles or counter with the "thousands" that LiFePo4 can support. But seriously, think about it. A 240 W-hr battery (12V and 20Amp-hours) hooked up to a 3W Rasp. Pi will give you 80-HOURS of life per cycle, that's over 3 days. Assuming ~500 Deep Cycles of durability (which is in-line with Lead Acid specs), that's 1500 days of worst-case deep-cycles, or 4 YEARS of life. And that's deep-cycling every 3 days, then fully charging on the 4th day instantly (it takes 20 hours to charge Lead-Acid in practice), so really you're looking at closer to 2000+ or 5+ years of worst-case life from something like the PS-12200. Do you _really_ need the thousands of deep cycle charges? The damn chemistry is going to fail for other reasons (temperature / humidity issues) after 5 to 10 years, rather than from the cycles. Especially in a UPS situation where you've got oversized Solar Panels keeping the Lead-Acid at near-100% charge for most of its life.

Lead acid isn't that much cheaper. You can get LFP 12v 100AH batteries for $290, with a 10yr warranty. You also don't have to worry about discharging them too low.

Gibbon1 3y ago

Last time I tried spec'ing a lead acid battery in a product I found you have to derate the lead acid battery a lot more than would expect if it has to deal with constant deep charge discharge and temp extremes. Where you don't need to derate a LFP battery much at all. So lead acid is okay at lower temps and with only occasional deep discharges.

ianburrell 3y ago
Lead acid battery can only use 50% of rated capacity. Also, they are heavy. Not a problem in fixed install or vehicle but pain if need to move.
- dragontamer 3y ago
  We're talking about Rasp. Pi batteries here. 15lbs (6kg) of Lead-Acid is probably the biggest, oversized battery that'd be needed (Assuming PS-12200 a 12V 20Ah Lead-acid or 240 Watt-hours of battery life) > Lead acid battery can only use 50% of rated capacity. That's definitely wrong. Lead Acids lose durability when you deeply-discharge them, but all Lead-Acids have *hundreds* of deep-discharge cycles supported. The question is one of frequency. Li-ion is great because it has high-durability through deep-discharge cycles. But is this the use case of a UPS or Solar Backup? I argue no, it isn't. --------------- The key advantages of Lead Acid are its cheapness and simplicity. If you can overlook its size and weight (okay, 15lbs is heavy if you're used to Li-ion... but is it really a *problem*? I argue no), and also know that deep-discharges would be rare (ie: UPS style "backup battery" usage), then LeadAcid suddenly rises to #1 choice due to gross simplicity you can have when designing circuits. As I described earlier: two diodes and a constant 13.5V source are pretty much all you need to create a minimally viable Lead-Acid battery backup solution. None of this "LiFePo4 charge controller" crap or CC-CV charging circuits (Lead Acid _prefers CC-CV especially if you want to charge it in 20 hours or less, but it doesn't _need_ CC-CV circuits) A long-term trickle charger over days (~72-hours of charge) of use is perhaps a non-obvious usecase. But that's called "Always plugged in UPS" and is IMO, the kind of use-case that's best suited for "SolarPi". -------- You might laugh at "hundreds" of deep discharge cycles or counter with the "thousands" that LiFePo4 can support. But seriously, think about it. A 240 W-hr battery (12V and 20Amp-hours) hooked up to a 3W Rasp. Pi will give you 80-HOURS of life per cycle, that's over 3 days. Assuming ~500 Deep Cycles of durability (which is in-line with Lead Acid specs), that's 1500 days of worst-case deep-cycles, or 4 YEARS of life. And that's deep-cycling every 3 days, then fully charging on the 4th day instantly (it takes 20 hours to charge Lead-Acid in practice), so really you're looking at closer to 2000+ or 5+ years of worst-case life from something like the PS-12200. Do you _really_ need the thousands of deep cycle charges? The damn chemistry is going to fail for other reasons (temperature / humidity issues) after 5 to 10 years, rather than from the cycles. Especially in a UPS situation where you've got oversized Solar Panels keeping the Lead-Acid at near-100% charge for most of its life.