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large battery bank solutions

offgridjoeandpeg

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I currently run 900 amp-hr bank- 24 volt- agm batteries. Looking to replace as we have gone from vacation use to full time living off grid and find the batteries just don't have it anymore (more than 7 years old). I never tried the forklift style industrial lead acid batteries and now am tempted. All this discussion on lithium is great and I may go down that road but I want to air out the older tried and true technology first. I really don't need help with sizing or totaling loads, rather need to look globally at my ability to keep them charged with minimal sun in winter (Pacific NW) using occasional diesel generator power source. Either way the battery will be expensive and I am aged such that do-overs are not an option. I understand the LI bank can be smaller based on depth of discharge characteristics so that may come into play if I rule out lead-acid. Mostly, I want to get back to not having to service the system on a daily basis.
Any nods towards a 600 amp-hr 24 volt battery and up will be appreciated.
 
My grid-backup system uses SunXtender AGM, 8x 405 Ah 6V for 48V.
Consider 2V 648 Ah or larger, or 2 string 6V 305 Ah in your case.
These days some lithium are actually cheaper per kWh.
Forklift batteries and Rolls batteries give more cycle life, same or cheaper per kWh.
My bank is as small as possible (one night's consumption) and I went with AGM for zero maintenance.
But they can deliver high surge current (start motors, carry the entire house for a few minutes until grid-tie inverters come back online.
If I cycled it 70% every night it would wear out in a few years, but grid failure is rare here.
If you sized for 3 days, then typical nightly cycling and occasional deep cycling over multiple days might allow 10 years life.
Lead-acid of course wants to get full recharged soon and kept floating.
Lithium is best partially discharged.

Here's what I saw for Rolls:


This guy uses forklift battery:

 
Having done AGM, Trojans and now on a forklift pack I’ve had enough of lead. Too in efficient and slow to charge. I’ve got 30kW of lifepo4 on order. Cannot wait. So much wasted time on absorption.
 
thank you for the comments. I being jack of all trades in background am slow on the uptake as far as the charging character of LI goes. My 10 + year old magnum inverter will throw 100 amps into charging when given external ac power. Now wondering if since this is not configurable with this model inverter whether to go with LI and have a separate generator set to send 5kw 120 ac to yet another charging source to maintain the bank. I have a good, quiet gas generator to do this and will look for the charger based on having a Lithium Ion bank to charge. Great time to be looking for these batteries; every source I have looked at is out of stock for at least 2 weeks. by the time this all comes together at my speed the season will be half done....
 
Our lithium ion battery bank was made using cells destined for the Chevy BOLT EV. Its 48v (14s8p - 51 volt nominal) and 480 amp-hours (25.5kWh). It will take a 100 amp charge and not even rise 2°F, if even that much. I've seen the 10.7kw solar array pump 150 amps into it without even getting warm to the touch.

Lead Acid is horribly inefficient (70%?) when charging and you need more sunlight or more array to harvest the same energy as lithium (>96%).

If you buy lithium batteries from a retailer, you're going to get a much better battery than what you would with lead acid.. but you're also going to pay a lot more for it.

Lithium Phosphate batteries are the king of safety and have a very high cycle life, but they are also (by far) the most expensive.

Lead Acid batteries are the simplest and most reliable, but they (usually) require maintenance, have a short life cycle count, emit fumes, and are inefficient.

Lithium Ion (like what electric vehicles use), have the highest energy density, can be found cheaper than lead acid (do it yourself project) and far cheaper than lithium phosphate, but are the least safe of the options and almost demand they be housed in a steel enclosure.

If you decide to build your own lithium battery bank, remember to factor in the cost of a quality BMS and associated hardware for it. A good BMS setup can run almost $1000.

Here's a photo of mine:

Just my 2 cents, some may have a different opinion.
 

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I went from 856AH (428AH useable) of Rolls Surrette Heavy Lead to 910AH of LFP and wowzers what a difference. 2x 280AH & 2x 175AH 8S LFP packs,. The Midnite Classic-200 Solar Controller can charge the bank nicely. I've pulled 200A+ and pushed 150A charge (solar + charger combined) without a blink. I'm actively allocating 85% of my LFP Capacity to use, reserving 15% to maximize lifecycles. I just finished a Thrash Testing Run of 150A Charging for 6 hours (taking packs to the edges) and quite tickled. Hard testing is going on for another week yet.
LFP requires no babysitting, no watering, no maintenance one assembled & running.
LFP charges FASTER than Lead Based batteries.
LFP Charge / Discharge profile is the closest to Lead Acid profiles and therefore more compatible with equipment on the market, including older equipment. This does NOT apply to other Lithium Chemistries, as they have different voltage curves & power knee's.
LFP does not explode or catch fire and can be stored in your house, where other Lithium Chemistries cannot be in a residential building for safety reasons. Rule vary by district & nation and of course there is always the "insurance companies" to think on.

To replace my Lead would have cost me $3400.00 + Govt Hostage Fees (taxes) and that would have only provided 428AH useable !
I built my LFP in two batches hence the different sized packs.
To build 1120AH using 280AH cells in 8S configuration for 24VDC means 4 battery packs.
  • 32x 280AH cells Total US $3,324.64 shipped to USA Duty & Taxes included. LINK to Luyuan Tech 280AH cells.
  • 4x MRBF Fuses @ 225A each. $100 USD Link to MRBF Fuses from BayMarine (EBay)
  • 4x 8S 24V BMS (Battery Management Systems) FET BASED 250A minimum approximately $200 USD+ each. OR Relay/Contactor based where the relays handle the amperage & control cutoff of power for protection. can vary, starting from $200 and up to infinity.
  • 4x Boxes Casings or ? This really depends on the individual as to how they want the battery setup to be. Most people actually use End-Plates & Threaded rods to make a pack that can keep the cells under slight compression and yet accessible. So cost is ??

Dangerous vs. Safe batteries, Explosion and fire test! - YouTube

Hope it helps, Good Luck.
Steve
 
I went from AGM to LiFePo4 at our cabin and whish I'd have done it sooner. We have a 800 AH 24V Specialized Power Systems bank.
 
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