SiO2 Batteries

HMS Beagle wrote:
One question on the SiO2 to which I cannot find a good answer

I think that greatly depends on state of charge. All I have read suggests .25 C as the charging rate. None of the literature suggests it tapers--but BFL13 has measured tapering. I have no reason to doubt his inestimal results.

SiO2 charging spec says 27 amps for 100 AH batt, but some write-ups say you can go way higher if you don't do it for too long or maybe too often, it is really unclear. I have no reason to try and find out how high is too high, so 27% charging rate is fine with me.

I find it strange that the SiO2 has such a high discharge rate allowance, but they don't specify a higher charging rate. With FLAs it is the same each way, around 25% most seen as recommended (but 10% for most cycles "lifetime"--which is fine on shore power, but no good for generator time that you want to keep to a minimum while restoring the most AH)

With any FLA, your SOC when Bulk ends and amps start to taper depends on the charging rate of course. So with a very high charging rate, amps would taper at a low SOC anyway.

There was a graph somewhere in one pf the LFP write-ups that gave the SOC when amps tapered using 1C charging rate. ISTR it was in the 70s or 80s. So the claim you stay in Bulk up to near full must be with a lower charging rate. Don't have any info on that.

(Been trying to work Darwin's Law into this somewhere, but no luck)

One question on the SiO2 to which I cannot find a good answer: What is the charge current limit? On good quality AGM (Lifeline) you can bulk charge, voltage controlled, with no current limit. Practically for Lifelines it will take about 0.5C for about 1/2 an hour, then go down to maybe 0.3C for a couple of hours, then taper slowly to 0.02C at the end of charge. Much of the SiO2 advertising says "charge faster than AGM" yet their charge limit seems to be 0.3C. That is not faster than AGM, and requires the charger be current limited which leads to power management problems.

HMS Beagle wrote:
SiO2 appear to have a similar slow charge tail, but are claimed to not suffer from sulfation, and may not require that periodic full charge.

SiO2 sellers recommend a full recharge once every 30 days. As others have pointed out, they do charge faster than flooded and apparently, faster than agm. Just how much faster is not a known number yet.

The selling point for me is the ability to charge and use at -40.

I've been used to a large bank situation--and weight is not an issue for me.

There are no perfect batteries, but for my use pattern, SiO2 or Lithium Titinate work. SiO2 are less expensive than Li, unless you wish to "roll your own" (I don't want to do that).

HMS Beagle is correct. In my testing, the SiO2 G27 held constant amps (Bulk stage) longer than my regular AGM at the same charging rate, but only for the 78-88% SOC range. Amps tapered after that.

So doing a "50-80" is the same time, but you save some generator time if you go to 90 and have the SiO2. Another thing with the SiO2, like LFP, is you can safely run them down to a low SOC and they hold voltage up enough, and thus get more AH useage than regular batts where you try to stay above 50% SOC.

That is not so much a faster charging advantage, but you can do a "17-87" for 70% of AH at 27% charging rate, compared with a "50-80" or 30% of AH before tapering amps begin.

I found having the one SiO2 was awkward for charging at 27 amps limit, same as one regular AGM or FLA. The RV converter does not go that low!

To use my 55 amp converter, I need more like 200AH of battery bank. But LFP does let you recharge at 50% or even higher depending on brand recommendation, so you could use the 55 amper on one 100AH LFP.

The problem is that 100AH is not enough to go camping with in many/most scenarios, so you need 200AH anyway, so you get to use your 55 amper either way.

It is a special scenario thing to figure out. I think most RVers don't have the charging times info they would need to do that figuring, so they might spend a lot of money they don't need to if they want "faster charging".

IMO, there is a lot of LFP advertising that resembles the late 1950s when cars got new styles. "The Forward Look" did make those Dodge cars look much better than the previous "look", but it didn't get you to the store and back any better. :)

BFL13 wrote:
The "fast charging" advantage is mostly bogus in real life, because your charger can't go any "faster" no matter what kind of battery you have. People can't seem to get their minds around what "faster charging" really means.

"Fast charging" is a complicated issue, especially with AGM and perhaps SiO2. I can't find a lot of good charging information on SiO2, but they appear to mirror AGM in charge characteristics. An AGM must be recharged fully, periodically (say once a week) or it will lose capacity. The problem is the acceptance rate reduces as you approach full, consequently you cannot fully recharge an AGM in less than about 6 hours regardless of source. You can get it to 80 or 90% pretty quick, but the last 10 or 20% takes a long time. SiO2 appear to have a similar slow charge tail, but are claimed to not suffer from sulfation, and may not require that periodic full charge. The claims on that are mixed, some of the literature suggests that they need to be cycled periodically and charged at fairly high current or they will degrade due to moisture locking up in the plates.

In contrast LFP batteries will take full charge current right up to 100%, and don't care how much current, high or low. The tail on the acceptance rate in absorb only lasts a few minutes. Their recharge time depends mostly on the capacity of your charge source. So with a current limited charge source, AGM and LFP may get to 80% at just about the same time, but the LFP will get to 100% much faster. Whether this matters or not depends on your useage.

IMO, most RVers can get the job done perfectly well with "ordinary" batteries, and can spend their money on something else besides SiO2 or LFP.

I agree and I also agree with the weight comment..Assuming two 100ah batteries saving 100# combined..That's know big deal or atleast shouldn't be...I was thinking Lithium or SIO2 but I just can't pull the trigger on such spendy batteries for some reason when you can get for less than $200 batteries that will last 6-7 years as mine have the last two times(different rigs)..Then there are the chargers for and other items some feel are needed and the price goes up and up..

To each his own..Good luck op..

Trade-offs for everything! It is sad when the extra weight of a couple of batteries in a TC is such a concern that owners would consider spending a couple thousand dollars for 200AH of lighter-weight batteries.

In some cases, you might do better by getting more of a truck, those LFPs cost so much ! :)

Around here the usual LFPs are twice the price for a 100AH than for an SiO2. But they are twice what a regular AGM costs. (so an LFP is four times what a regular AGM costs) Weight was not an issue with our set-up, but I needed the high discharge rate compared with regular AGMs.

Getting a lower price for LFP makes things more of a comparison for choosing by "features". You have that cold temp issue with LFP to resolve for RVing, but a weight saving advantage.

The "fast charging" advantage is mostly bogus in real life, because your charger can't go any "faster" no matter what kind of battery you have. People can't seem to get their minds around what "faster charging" really means.

IMO, most RVers can get the job done perfectly well with "ordinary" batteries, and can spend their money on something else besides SiO2 or LFP.

Geewizard,

There is a company in northern Alberta that is selling LI of various types for extremely low prices. Plan a trip?

https://ablithium.com/

You want to make sure you use LiFePO4 cells, not lithium cobalt (which is what Tesla uses).

I can't speak to these specific cells as I haven't used them, but many other folks have with good luck:
EVE 280Ah LiFePO4 Cells

I use this BMS:
Bluetooth BMS

Which is also resold in the US by these folks:
Overkill Solar BMS