An update on where I’m at with the solar PV system batteries…
I’ve reconditioned all four of the Exide EP800 batteries using the Victron IP22 charger, two show little change, after charging they drop to ~10.8v within an hour or so with a 5W LED lamp load, the third is improved and lasts quite a bit longer with a 1 amp load, but still drops to ~10.8v after several hours, the fourth is showing no problems. The best two batteries are in the system at present and are lasting from sundown at ~5pm till around midnight before showing the sudden drop in voltage. Is it worth, or sensible, to try reconditioning the poor batteries more than once ?
One thing I have noticed, when the ‘good’ batteries have been run down for a while and the solar charger comes up in ‘bulk’ charge mode it applies 28.3v across the two batteries for a short period (usually 30-40 minutes) before dropping back to ‘absorption’ mode on 27.1v. During the ‘bulk’ charge mode the good battery has up to 16v or more across it for a short period before the voltages across the batteries stabilise at about the same level. Once charged the two batteries are within 3-400mV of each other. I assume applying 16v across the good battery is effectively ‘reconditioning’ it as that seems to be what the Victron charger does in recondition mode ?
I’ve dismissed using Lithium batteries for now, I can’t justify the expense at present for decent quality, non Asian, batteries. I’ve opted to purchase four ‘wet’ leisure batteries, locate them in an outside cabinet and re-locate the solar gear onto the inside of the wall behind the cabinet. I can purchase ‘wet’ batteries with a four year guarantee quite cheaply and replace them several times for what I’d pay for Lithium at present. Hopefully in four years the price of Lithium may have dropped considerably and I’ll have had a chance to get to grips with the diyBMS system.
Thanks to all who have replied to my original post, I’ve learnt quite a bit from you all.
In my opinion, the core issue lies in the inefficiencies of lead acid charge. I’m not absolutely up to date with my understanding, but afaik the charge efficiency is something like 1/10. And the slow charge efficiency is what causes the lead plates to oxidize.
Cody’s lab on YouTube has some interesting chemistry videos about the issue. I think he also talks about the welder thing and why that works. (I’m not saying you should)
If efficiency is what we are after, with the price of raw lithium cells being about 2* the price of lead acid variants, but efficiency being 10*…the math says the price is valid.
The issue then becomes the monitoring of lithium, over the “stupid” resilience of lead which from what we’ve seen historically cause the issues you are facing.
The issue with Asian batteries is how they are built. If you get those 280ah eve cells, with no extra logic and build your own, the reports I’ve seen are quite acceptable.
If you get a generic all in one sealed battery with a cheap BMS installed for quite a high price, those can be less reliable because of how the factory builds them.
So if you want good and cheap, build your own BMS with Asian cells. for about 4-600 exchange units you can get a good set of good quality eve cells.
And there are reliable projects out there that you can just buy, the 123bms is a bit pricey and are pretty similar to the super-b nomina bms and pre epsilon v2 range. Theres electrodacus who builds and sells a few different bms variations in canada, Ive personally used these and was quite happy with how they worked, though youd have to wait till he gets around to your batch. Or as Ive mentioned the diybms, which is by far the most stellar starter project out there that I know of and has branced into a few different variants.
If you want reliable, you will pay for RnD and the testing required to project high cycle count.
If you want something midrange, it’s not going to last and will be designed for mass production and high turnover.
I think the price for lithium won’t really drop soon, if anything it’s going to increase.
Sorry, but a charging efficiency of only 10% for lead-acid batteries is far from reality. The charging efficiency is typically around 80-90%.
That’s a thing of the past. Here in Germany, we as end customers can buy Chinese LFP cells for around €80/kWh. That’s far less than we would have to pay for lead-acid batteries, especially since lead-acid batteries only have half the usable capacity.
One can also look for used car batteries like these VW/ID 8s 6.85kWh and with a decent BMS. Some times one can find some cheap ones.
I use them in my project @How sustainabile an ESS can be? and after 2Years i can see no degradation at all. These high quality packs much more safe as an DIY pack off 18650. The two internal temperature elements fit to JK BMS or Dali (others i have not checked).
There is a ‘1/10’ rule involved with lead-acid, it applies to charge speed (C-rate) rather than energy efficiency. To keep a lead-acid battery from overheating or gassing, you typically charge it at 10% of its capacity (C/10). Lithium can handle 1C (or 100% of its capacity) in current. So, while lithium isn’t 10x more efficient, it is roughly 10x faster to charge making it effectively 10x more efficient than lead acid cells.
Thanks Tom, yes like I said I wasn’t entirely sure if I was up to date, so you are correct that the efficiency is something like 80-90%
But apparently it was charge rate I was thinking of and that does effectively make lithium 10x more effective for charge speed especially if you only have 1 hour of sun.
No, it makes it 10 times faster. Again: efficiency has nothing to do with it. Your car is not more efficient than others when it can drive faster
But probably just as important: you should not charge a 48V-100-Ah-lead-battery faster than with 10 to 15A which is around 500 to 600 W. So you can’t use it with a larger PV array.
Ich glaube, hier liegt ein Missverständnis bezüglich des englischen Begriffs ‚efficiency‘ vor. Im Englischen ist Schnelligkeit (velocity/speed) ein integraler Bestandteil von Effizienz, kein Gegensatz dazu. Die Verwirrung entsteht also nicht durch meine Wortwahl, sondern durch eine zu enge deutsche Interpretation des englischen Begriffs.
Danke für den Input, aber das glaube ich nicht. Es gibt zwei englische Begriffe, die häufig verwechselt werden: efficiency und effectiveness. Die gleiche Verwirrung gibt es auch bei den deutschen Entsprechungen “Effizienz” und “Effektivität”. Bei letzterem geht es darum, ein gesetztes Ziel zu erreichen, und wenn das Ziel darin besteht, einen Akku möglichst schnell zu laden, dann ist ein hoher Ladestrom effektiver als ein kleinerer, aber er ist nicht effizienter.
Da wir hier Lithium mit Blei-Säure-Batterien vergleichen, liegt der Knackpunkt genau in dieser sprachlichen Generalisierung. Im Englischen werden die Begriffe oft synonym verwendet, wobei ‘efficiency’ meist als Oberbegriff fungiert.
In diesem Kontext ist Lithium schlicht beides: effektiver und effizienter als Blei-Säure.
Ich schätze die Präzision Ihrer Definitionen sehr und bitte erneut um Nachsicht, dass ich die Begriffe aus Ihrer Sicht nicht trennscharf genug verwendet habe.
This is no joke. Look up the Japanese word “mokusatsu”. This word is what determined the fate of Nagasaki and Hiroshima in WWII and may have been interpreted incorrectly.
