krby
Solar Enthusiast
I haven't been able to find this info anywhere so I thought I would ask here.
I'm trying to spreadsheet out various battery costs, comparing different sizes, LFP vs AGM vs SLA as well as comparing different discharge depth. What I'd like to be able to do is know something like:
a LiFePO4 4 cell (the common config for 12V systems) 100Ah battery has X watt-hours total. So if I set my discharge limit at 80% discharged then I get roughly X * 0.8 watt-hours total in DC (assume I account for various losses somewhere else in my spreadsheet). This should be easy, right? But what voltage do I use for Ah * V = Wh? 3.3V per LFP cell? Something else? Why?
I want to answer the same question for SLA batteries (specifically AGM or Gel). It seems even harder to guess a V for SLA chemistry as the voltage range is larger from 100%-0% than it is for the very flat LFP discharge curve.
I understand the trade-offs between depth and number of usable cycles, I'd like to be able to compare various discharge depths and then cost out what I would need for a particular application. It's going to be a fairly low load, 60W AC with maybe spikes of 110W AC. So the current from "12V-ish" batteries will be in the range of 6-10A
I'm leaning towards SLA because I'm building a DIY UPS that will be plugged into mains AC nearly all of the time, with the batteries being left topped off for months at a time. I won't need to cycle them often. Also, wait isn't a concern. If I get 10 cycles out of them over the next 5 years, that would be awesome. But, I'm curious about the overall costs if I assume various depth of discharge .
I'm trying to spreadsheet out various battery costs, comparing different sizes, LFP vs AGM vs SLA as well as comparing different discharge depth. What I'd like to be able to do is know something like:
a LiFePO4 4 cell (the common config for 12V systems) 100Ah battery has X watt-hours total. So if I set my discharge limit at 80% discharged then I get roughly X * 0.8 watt-hours total in DC (assume I account for various losses somewhere else in my spreadsheet). This should be easy, right? But what voltage do I use for Ah * V = Wh? 3.3V per LFP cell? Something else? Why?
I want to answer the same question for SLA batteries (specifically AGM or Gel). It seems even harder to guess a V for SLA chemistry as the voltage range is larger from 100%-0% than it is for the very flat LFP discharge curve.
I understand the trade-offs between depth and number of usable cycles, I'd like to be able to compare various discharge depths and then cost out what I would need for a particular application. It's going to be a fairly low load, 60W AC with maybe spikes of 110W AC. So the current from "12V-ish" batteries will be in the range of 6-10A
I'm leaning towards SLA because I'm building a DIY UPS that will be plugged into mains AC nearly all of the time, with the batteries being left topped off for months at a time. I won't need to cycle them often. Also, wait isn't a concern. If I get 10 cycles out of them over the next 5 years, that would be awesome. But, I'm curious about the overall costs if I assume various depth of discharge .