krby
Solar Enthusiast
I'm would like to build a sort-of portable power bank. This idea started out as way to power the fridge for a few days during PG&E's scheduled blackouts. But now that I've decided to build one, I'm finding more and more things I would use it for both in and out of the house!
From my research, I think the components are basically an battery bank, an inverter, an AC charger, and some supporting electronics. No solar charging. Given what I'll be powering, I'd like to be able to deliver ~1600W for about 20-30min. I'm sizing for 2000W to give some headroom. I'd like at least 3-4kWh of usable capacity. This won't see every day use. Maybe a hundred cycles over a few years. I'm familiar with the tradeoffs between AGM vs LFE and I've decided to go with LFE because of the size, weight, and discharge rate. Because I'm not expecting a lot of cycles, I've been assuming a 90% DoD when sizing. I do want it portable, even if that means it's the size of luggage with wheels.
Reading the mobile-solarpower.com website's guides on building a LFE pack I recognized the concepts and gear from things I've been doing in the R/C flying hobby for years. About 15 years ago, I put together a 100W solar powered wifi access point with a AGM battery backup. Hopefully, my confidence isn't misplaced, but I think I can do this with help from you all.
Finally, the questions!
* Is this whole ideal reasonable? Is 2kW and 3-4kWh of capacity a reasonable goal? A 24V system 200Ah pack would do it (assuming 90% DOD).
* 12V vs 24V?
I understand the voltage drop and wire gauge vs current issues. Given this is all going to be in one box, how much does this matter? I'll have bars across cells to make series connections, and lets say no more than 2-4 feet of wire to the inverter, I'll use 2ga wire in either case. To me, the only reason not to build a 24V system is that I feel like there are more components choices in 12V. In general it feels more flexible but I can't put my finger on anything specific. Does this really matter?
* Inverter/Charger or separate items?
All the inverter/chargers I have seen seem built for a whole-home backup, with an automatic tranfer when the AC input goes down. I don't really need that feature, but I do like the idea of one less thing to wire up in my box. Is there a reason to get split these out?
* Dedicated LFE charger?
All the inverter/chargers I have seen seem to have their charging side built for lead acid batteries but many can be configured to work with LFE voltages. Is it better to get a charger that is dedicated to LFE? I'm used to the computerized mulit-chemistry chargers from the R/C hobby, where the LFE profile is a CC phase followed by a CV phase, no absorb or float.
One I get some feedback on the big questions above, I'll dig into specific questions about components for the battery pack, bms, balancing, etc (I'm thinking about two Sinopoly 12V 200Ah packs) Thanks!
From my research, I think the components are basically an battery bank, an inverter, an AC charger, and some supporting electronics. No solar charging. Given what I'll be powering, I'd like to be able to deliver ~1600W for about 20-30min. I'm sizing for 2000W to give some headroom. I'd like at least 3-4kWh of usable capacity. This won't see every day use. Maybe a hundred cycles over a few years. I'm familiar with the tradeoffs between AGM vs LFE and I've decided to go with LFE because of the size, weight, and discharge rate. Because I'm not expecting a lot of cycles, I've been assuming a 90% DoD when sizing. I do want it portable, even if that means it's the size of luggage with wheels.
Reading the mobile-solarpower.com website's guides on building a LFE pack I recognized the concepts and gear from things I've been doing in the R/C flying hobby for years. About 15 years ago, I put together a 100W solar powered wifi access point with a AGM battery backup. Hopefully, my confidence isn't misplaced, but I think I can do this with help from you all.
Finally, the questions!
* Is this whole ideal reasonable? Is 2kW and 3-4kWh of capacity a reasonable goal? A 24V system 200Ah pack would do it (assuming 90% DOD).
* 12V vs 24V?
I understand the voltage drop and wire gauge vs current issues. Given this is all going to be in one box, how much does this matter? I'll have bars across cells to make series connections, and lets say no more than 2-4 feet of wire to the inverter, I'll use 2ga wire in either case. To me, the only reason not to build a 24V system is that I feel like there are more components choices in 12V. In general it feels more flexible but I can't put my finger on anything specific. Does this really matter?
* Inverter/Charger or separate items?
All the inverter/chargers I have seen seem built for a whole-home backup, with an automatic tranfer when the AC input goes down. I don't really need that feature, but I do like the idea of one less thing to wire up in my box. Is there a reason to get split these out?
* Dedicated LFE charger?
All the inverter/chargers I have seen seem to have their charging side built for lead acid batteries but many can be configured to work with LFE voltages. Is it better to get a charger that is dedicated to LFE? I'm used to the computerized mulit-chemistry chargers from the R/C hobby, where the LFE profile is a CC phase followed by a CV phase, no absorb or float.
One I get some feedback on the big questions above, I'll dig into specific questions about components for the battery pack, bms, balancing, etc (I'm thinking about two Sinopoly 12V 200Ah packs) Thanks!
