diy solar

diy solar

All At Once With LiFePO4?

Rabbit

Rabbit

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Joined
Nov 19, 2019
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85
I currently run a small (1220 watt) home solar plant with golf-cart type lead acid batteries as my power-bank. When I bought these batteries-- there are eight of them, and from time to time I've wished for a bit more capacity-- I learned that I had to buy all the batteries at pretty much the same time, so that the older and therefore weaker batteries wouldn't limit the total capacity of the bank. I'm now considering buying two high-quality 12-volt 100AH batteries for another non-related low-use purpose, but may want to include them as part of a replacement LiFePO4 bank later, when my lead-acid bank inevitably dies and needs to be replaced. So... With high-quality LiFePO4's, can I buy two now, use them (lightly and gently), and then add two or three more of the same brand/model/etc to make up a larger bank in probably about two or three years without significant age- or use-cycle related issues? Or do I need to buy all four (or maybe five) now, all at once, and just let two (or three) pretty much sit around doing little or nothing in the meantime? Or, perhaps worst of all, should I just grit my teeth and rip out a perfectly-functional, paid-for, and satisfactory lead-acid bank, sell it for what I can, and go LiFePO4 today? (If I do this, I'll have to dis-assemble the new bank several times a year to pull two of the batteries for the special, non-solar purpose I mentioned earlier. A pain in the ass, yes. But not an impossibly huge one.)

What would you folks do? I'm going to require those two LiFePO4's for the non-solar purpose fairly soon now, so this isn't merely a theoretical question.
 
This is very good question, thank you for asking it, I hope that others who know the answers will chime in. I think you should be ok to do the lifepo's upgrade sequentially over a couple of years with no major problems but I could be wrong.
 
I'm in a similar situation. I have Twenty 6V flooded lead acid golf cart batteries in a 24V configuration at a recreational hunt camp used about once a month for 3 days or so at a time. I decided to go rogue taking the risk of buying 2 flooded lead acid batteries periodically over the years (originally used a 12V configuration) building up the bank. Oldest batteries are Jun 2013, newest are Aug 2018. Since the batteries aren't regularly discharged I've not had a problem with older batteries mixed in with newer batteries. Last month, the battery hydrometer still shows green (good) on all the cells. I'll simply remove any batteries from the bank as they go bad. The bank is big enough now where we can afford less capacity in the short-term. I plan to use them up until they're no longer usable and recycle them, maybe possibly even get my core-charge deposits back.

I'll likely do a gradual replacement with LiFePO4 batteries like what you're thinking of doing. If I get another year or two outta the lead acid batteries, perhaps LiFePO4 batteries will be cheaper than they are today. I'll likely do the same gradual implementation of adding more batteries over time as it's not as big of a pill to swallow dropping thousands of dollars in up-front costs compared to a few hundred here, a few hundred there as funds become available.

I've heard you can gradually add LiFePO4 batteries to a bank over time as long as each battery has it's own BMS. Would need to double-check with the manufactures on how they can be wired in series/ parallel. Apparently, they're not as sensitive to calendar age/ cycle usage compared to lead acid.
 
Delta-V said:
I'm in a similar situation. I have Twenty 6V flooded lead acid golf cart batteries in a 24V configuration at a recreational hunt camp used about once a month for 3 days or so at a time. I decided to go rogue taking the risk of buying 2 flooded lead acid batteries periodically over the years (originally used a 12V configuration) building up the bank. Oldest batteries are Jun 2013, newest are Aug 2018. Since the batteries aren't regularly discharged I've not had a problem with older batteries mixed in with newer batteries. Last month, the battery hydrometer still shows green (good) on all the cells. I'll simply remove any batteries from the bank as they go bad. The bank is big enough now where we can afford less capacity in the short-term. I plan to use them up until they're no longer usable and recycle them, maybe possibly even get my core-charge deposits back.

I'll likely do a gradual replacement with LiFePO4 batteries like what you're thinking of doing. If I get another year or two outta the lead acid batteries, perhaps LiFePO4 batteries will be cheaper than they are today. I'll likely do the same gradual implementation of adding more batteries over time as it's not as big of a pill to swallow dropping thousands of dollars in up-front costs compared to a few hundred here, a few hundred there as funds become available.

I've heard you can gradually add LiFePO4 batteries to a bank over time as long as each battery has it's own BMS. Would need to double-check with the manufactures on how they can be wired in series/ parallel. Apparently, they're not as sensitive to calendar age/ cycle usage compared to lead acid.
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I'm slowly adding lifepo capacity, even when lifepo's get old, they will still go for years at 80% capacity, which still blows the doors off of the capacity of new lead acids. Yes it's good to make sure that your batteries and BMS's are series compatible, some are only good for parralel connectivity.
 
The potential to add-as-you-go that LiFePO4 banks offer is one of the greater selling points of the chemistry IMO... I'm a big fan of expandability. Sure, if you're running one set hard and then add another set later, there is a bit of imbalance to be expected, but I would consider it negligible unless we're talking hundreds of hard cycles. I say go for it -though, as others have noted, just pay real close attention to BMS limitations as far as series/parallel connection and throughput. Throughput limitation differences should be negated as long as you stay with the same manufacturer, but just pay very very close attention to the specs when you go to add more batteries.

...I wouldn't hold my breath on LiFePO4s getting cheaper with time, however... unfortunately, lithium supplies are extremely finite and mostly in countries that we're "punishing" with tariffs, so until someone realizes that's not how tariffs work, we're going to keep paying more for them. So far, most manufacturers are trying to shield the end user from those price increases (perfect example is Battle Born, who raised prices to their distributors by $45 per battery due to the cost of the tariffs, but strongly encouraged all of us not to pass that along to our customers) but that can only hold out so long.
 
Justin Laureltec said:
The potential to add-as-you-go that LiFePO4 banks offer is one of the greater selling points of the chemistry IMO... I'm a big fan of expandability. Sure, if you're running one set hard and then add another set later, there is a bit of imbalance to be expected, but I would consider it negligible unless we're talking hundreds of hard cycles. I say go for it -though, as others have noted, just pay real close attention to BMS limitations as far as series/parallel connection and throughput. Throughput limitation differences should be negated as long as you stay with the same manufacturer, but just pay very very close attention to the specs when you go to add more batteries.

...I wouldn't hold my breath on LiFePO4s getting cheaper with time, however... unfortunately, lithium supplies are extremely finite and mostly in countries that we're "punishing" with tariffs, so until someone realizes that's not how tariffs work, we're going to keep paying more for them. So far, most manufacturers are trying to shield the end user from those price increases (perfect example is Battle Born, who raised prices to their distributors by $45 per battery due to the cost of the tariffs, but strongly encouraged all of us not to pass that along to our customers) but that can only hold out so long.
Click to expand...
Well Said, and yes, the ruling lowest common denominator minority of the partnership of government and free enterprise can well afford tariffs, therefore, have no problem with the concept of course. The masses, of which you and I belong to, are for the most part common core brain damaged, distracted by sports, judgementally clouded by legal head meds, therefore, never even know enough to even begin to wonder or care about why all the tariff money that the wealthy government extorts from us doesn't go towards paying down to he staggering national debt, that no one cares about.
 
Justin Laureltec said:
The potential to add-as-you-go that LiFePO4 banks offer is one of the greater selling points of the chemistry IMO... I'm a big fan of expandability. Sure, if you're running one set hard and then add another set later, there is a bit of imbalance to be expected, but I would consider it negligible unless we're talking hundreds of hard cycles. I say go for it -though, as others have noted, just pay real close attention to BMS limitations as far as series/parallel connection and throughput. Throughput limitation differences should be negated as long as you stay with the same manufacturer, but just pay very very close attention to the specs when you go to add more batteries.
Click to expand...

Thanks!
 
I hate to be the dissenting vote, but IMO it's not a good idea. If you dont stay fairly identical w/ capacities and chemistries you'll end up working one bank of batteries harder than the other bank and wearing them out. Since the internal resistance of LFP batts is so much lower then lead acid they'll be doing most of the work. The two chemistries don't play well with each other.

You can kind of mitigate this with a relatively high amperage active balancer but it's like putting a bandaid on a sucking chest wound.

Battery banks, even LFP banks arent all that expandable, you need all parts of the bank to be as close to identical as you can get it or one part will simply wear out faster. The higher cycle life of LFPs will hide this for a while but it'll still show up in time.
 
Maast said:
I hate to be the dissenting vote, but IMO it's not a good idea.
Click to expand...
Always appreciate a dissenting opinion! A different set of eyes is always valuable. My impression of the OP is that the switchover would be entirely LFP, with just additional LFP being added down the road, but if the plan is to run LFP in parallel with FLA, I concur with you - that would be a bad idea.
 
Yes, that's my thinking as well in my situation. I have a good sized Flooded Lead Acid battery bank. When these batteries start to fail and dwindle the bank capacity, I'll start a 2nd new LiFePo4 battery bank to gradually transition over to. I already have 2 solar arrays and two 3000 Watt pure sine wave inverters. I'll just have 2 independent solar systems or 2 power circuits to power our camp.

I have no intention of mixing Lead Acid batteries and LiFePO4 batteries in the same bank for the very reasons Maast pointed out.
 
Rabbit said:
I currently run a small (1220 watt) home solar plant with golf-cart type lead acid batteries as my power-bank. When I bought these batteries-- there are eight of them, and from time to time I've wished for a bit more capacity--
Click to expand...

Are you sure they are getting charged? 8 typical golf cart batteries (6v 225ah) makes a 10.8kwh battery (equal to two tesla batteries). That's a lot to charge with a small solar array.....are these cycled daily or do they get days to charge?
 
SolarRat said:
Are you sure they are getting charged? 8 typical golf cart batteries (6v 225ah) makes a 10.8kwh battery (equal to two tesla batteries). That's a lot to charge with a small solar array.....are these cycled daily or do they get days to charge?
Click to expand...


Yes, they're getting full charges most days-- in the summer, every single day usually topping off sometime around noon or one-ish. I deliberately overbanked to keep the cycles shallow, so the bank would last longer. Also, I live in hurricane country (Florida). In an emergency I can draw them down much further if I really must. In normal day to day usage powering my computers, internet modem and big-screen TV, however, it's rare for me to discharge them more than 30-40%. In summer I produce considerably more power than I use, to the point that if I could work out a cost-effective grid-tie setup (the fly in the ointment is installation costs) I'd go for it. In winter, I almost exactly break even in November, December and January and then do sometimes-- rarely-- have to unplug and transfer to shore power for the good of the batteries for a single day. The bank is monitored daily, and my system is over a year old. So far, I've been entirely happy with this configuration. (I probably won't ever add any more panels because I live in a very old trailer that has a limited life expectancy, and I'm not physically able to climb up on roofs anymore so additions would be pricey. Therefore, the extra-large battery bank is the way I went.)

For what it's worth, I gritted my teeth and bought five of the old-style Renogy 100AH lithium-irons on sale plus 20% off. (In other words, in regard to the thread's title I've decide to go all-at-once.) Eventually, after doing more research so I can understand the answers better, I'm probably going to be asking questions about trying to tie both banks together via some sort of isolator-- after all, the perfectly-good lead acids are essentially free and surely someone somewhere has worked out a safe, effective way to do this. But for now...

Thank you all again, very much!
 
So...you had no problem with the capacity or function of your LA's...but you bought the lithiums anyway? I'm confused. I would have used those LA's for the next 5 years and then bought some lithiums much cheaper than today's prices.
 
See my original post. I immediately require two LiFePO4's (to be used only occasionally, but the need is urgent when it happens) for a non-solar purpose, and wanted to know if I could effectively buy just these two now and then add on to them several years later to create a new, complete bank when the lead-acids eventually need replacement. (I'm aware it's bad practice to add on later with lead-acid, but didn't know RE LiFePO4's.) A combination of the replies here and the fact that the old-style Renogy's are extraordinarily cheap right now but won't be available at all later (so that everything in my new bank would match) persuaded me to buy an entire new bank immediately. Given these facts and that I _must have_ those two LiFePO4's within sixty days (sooner is better) and therefore absolutely had to buy 40% of a new bank immediately, no matter what, this seemed to me to be the best plan in terms of overall long-term money-wastage. So, yes. I now have a large surplus, fully-functional and trouble-free lead-acid battery bank that I currently have absolutely no use for-- or at least won't have any use for, once the new cells arrive. The ideal outcome, of course, would've been for me not to immediately need the two new lithiums or for the battery sale and availability of the old model to continue indefinitely. But, sadly, we don't inhabit an ideal world where ideal solutions are always available. Physics and reality sometimes force compromise on us.

So I compromised as best I could, after coming here to seek expert advice. Which I got, and am thankful for.
 
Last edited:
Delta-V said:
I'm in a similar situation. I have Twenty 6V flooded lead acid golf cart batteries in a 24V configuration at a recreational hunt camp used about once a month for 3 days or so at a time. I decided to go rogue taking the risk of buying 2 flooded lead acid batteries periodically over the years (originally used a 12V configuration) building up the bank. Oldest batteries are Jun 2013, newest are Aug 2018. Since the batteries aren't regularly discharged I've not had a problem with older batteries mixed in with newer batteries. Last month, the battery hydrometer still shows green (good) on all the cells. I'll simply remove any batteries from the bank as they go bad. The bank is big enough now where we can afford less capacity in the short-term. I plan to use them up until they're no longer usable and recycle them, maybe possibly even get my core-charge deposits back.

I'll likely do a gradual replacement with LiFePO4 batteries like what you're thinking of doing. If I get another year or two outta the lead acid batteries, perhaps LiFePO4 batteries will be cheaper than they are today. I'll likely do the same gradual implementation of adding more batteries over time as it's not as big of a pill to swallow dropping thousands of dollars in up-front costs compared to a few hundred here, a few hundred there as funds become available.

I've heard you can gradually add LiFePO4 batteries to a bank over time as long as each battery has it's own BMS. Would need to double-check with the manufactures on how they can be wired in series/ parallel. Apparently, they're not as sensitive to calendar age/ cycle usage compared to lead acid.
Click to expand...
This past summer I transitioned from lead acid to Lifepo's and I will never look back. One MAJOR drawback of lifepo's is that they cannot be charged below 32 degrees Fahrenheit or exist in a below zero farenheit situation or they will be ruined. One way around it us to build a huge enough system to run battery heaters, which to me is insane. Instead, I have my lifepo's in a insulated box in a root cellar that never drops below 32.
 
offgriddle said:
This past summer I transitioned from lead acid to Lifepo's and I will never look back. One MAJOR drawback of lifepo's is that they cannot be charged below 32 degrees Fahrenheit or exist in a below zero farenheit situation or they will be ruined. One way around it us to build a huge enough system to run battery heaters, which to me is insane. Instead, I have my lifepo's in a insulated box in a root cellar that never drops below 32.
Click to expand...
12v snowmobile handgrip warmers stuck to the outside of the batteries... Cheap, efficient, and works remarkably well. It's still a PITA, don't get me wrong... Would far prefer that we didn't have to worry so much about temperature... But when you can solve the problem for roughly $10 a pair, I still count it well worth the hassle.
 
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