If I understand correctly, you have the Victron setup to turn off the charger (interrupt the AC line?) based on state of charge, rather than the volt and amps thresholds? I will be very interested to see how that works out over time, if that is how it is. I mention this only because I have been perpetually curious about how the manufacturers are actually controlling their systems. We read lot about getting to 100% state of charge, or something less in units like the ARV setups, but it is always sketchy of how it is being done. Are they measuring amps in and out to get a SOC directly, or inferring it from the voltage, for instance.
I think I would rate the voltage reading as kind of a moving target as things are changing quickly near the end of charge, as we talked about earlier. The SOC off amp hour counting is going to be nearly dead on accurate in what it read, but there is the nagging possibility of cumulative error if the charge efficiency is anything other than 100% or exactly repeatable to a programmed charge efficiency. I have read several places that claim the charge efficiency is "very high", "near 100%", etc, but have never seen any details. If you are off even a small amount on the actual charge efficiency and are using the amp hour counting you will progressively more error in every charge cycle over time, unless there is a recalibration. This is the same thing that happens with the lead acid batteries and meters, on with lithium the error will likely be much smaller. On most monitors, the SOC will reset at 100% once charging reaches the volt and amp thresholds for full batteries. It will often be several % off when it does that.
I hope I'm remembering this right - I've changed things around so many times <g>...
You're right, I'm working now just on SOC. I define 100% as up to 13.4 and down to C/10. I cut charging off at 99% SOC because they won't let me set it to 100%. I'm also concerned about cumulative error - there are correction factors both for discharge and recharge, and I'm not correcting for temperature either.
But on both my alternator relay and my charger relay I'm placing a toggle switch that forces charging ON. I'm thinking that every so often when I have the time to pay attention, I'll just turn the relevant switch on after auto-charging has shut off - it should take just a few minutes to go up to 100%, and that'll reset the monitor.
I was surprised again last night at how long it took to recharge - not as fast as expected "by the numbers". I also noticed that I never saw more than 45A from the charger, even though it's rated at 60A, and this time I didn't see the voltage climb up to 14 (though I have before). I'm thinking that my charger->battery wiring may be slightly undersized, as the original charger was a 45A charger - that may be slowing things down a bit. I did look to see what size the wiring from the charger was, but don't remember offhand - I'll have to dig in my notes or look again.
I'm back from a week's trip so I've finally had more time to watch and graph my charging. I'm still switching both the charger and alternator off manually - I've tested hooking both up to my Victron monitor, but haven't yet done the final wiring.
Both alternator and charger look similar, and like the earlier graph I posted. On this trip I was usually down to somewhere between 60 and 75% SOC when I started charging. I'd see initial high current - up to 70 amps from the alternator, up to 50 amps from the charger. Then I'd see the voltage slowly climb and the charge current slowly fall. As I approached my 100% SOC setpoint (13.4v and 20A charge rate), I'd be over 13.4 by a good bit, usually just around 14.2-14.1. I'd let the current drop a bit below 20A - at that point I'd be into that "upper knuckle" on the graph, and the current rate would be dropping fast. So practically speaking, the question of whether charge rates of up to 14.6v are OK or not is a bit moot - neither my charger nor the alternator takes the voltage that high if I switch charging off at 20A.
As for what the Victron will do when it controls charging - the one unexpected thing about the relay control is that the highest SOC I can enter is 99% as it only accepts 2 digits. So if I use SOC to control the charging, that's the highest I can go. That may be just fine - it should make a nice conservative charge algorithm. If I want to goose it up higher later, I can lower the current for my definition of 100% SOC.
Finally, I was surprised to see that the stock alternator charges faster than my charger on shore power. If I average over the whole charge, I replace about 50 Ah per hour via alternator and about 39 Ah via the charger. This was a surprise - I thought I'd get more from the charger and less from the alternator.
The final thing is the issue we've already discussed, about turning off the charger at full charge when on shore power, so that we don't run the RV off the charger when plugged in, once the batteries are up. I'm not seeing a way to do this any other way, if we believe it's best for the batteries not to float after full charge has been reached - do you see any other way?
But this really doesn't seem to be any big deal either. I usually assume that I use about 95-110 Ah on a typical day, but this trip I really wasn't even using 50. So perhaps I'm recharging once every day or two. Even if I'm full-timing and I recharge more than 300 times a year, we're talking about 8-10 years before we get to 2000 cycles, even if we count partial cycles. And my research last month indicated that when the battery companies give those figures, they're talking about full cycles - so 2 charge cycles that replace 80Ah is identical to 1 charge cycle that replaces 160 Ah. So we're still talking about very long battery life.
So all in all, considering all that I didn't know when I started, I'm happy that this is starting to look like a pretty seamless integration <g>...
Since you have the fixed voltage charger, there is not much else you can do to stop the charging earlier other than raise the amperage requirement. I think that would work well. I think the best test will be where the batteries settle after various cutoffs. I think you were wanting 13.4v?
I think we all have found the alternator to be faster than shore charging. Our stock Chevy 145 amp unit would do over 75 amps to the batteries if they were low enough, shore charger was only 40 amps. Now we can do near 200 amps from the alternator and 95 from the shore charger.
The shutting off of the charger when the batteries are full is a catch 22 as we have mentioned before. Probably better for the batteries, but you could wind up leaving from shore power with less than full batteries. Your Victron probably has a recharge voltage or even better SOC setting that could turn the charger back on when you were down a bit on charge, so you could limit have far you could actually wind up down on SOC.
We did have the discussion about whether of not batteries had a relatively fixed amount of energy they could store and give up over their lifetime. It is in the earlier pages of this thread. Surprisingly, wet and AGM batteries appeared to be closer to having constant total lifetime energy capacity than the lithium did, which was shown be the lithium losing substantially more life total energy life with deep discharges that wet or AGM batteries. It was very surprising.
We will all be watching how your batteries hold up over time, as there is very little real world information out there currently, just manufacturer's claims.
I've also found the same thing - the alternator charging is a bit more than the onboard converter/charger. On The Travato, the alternator charging is hardware limited to 50 amps anyways. The Stark Battery also is limited to 50 amps input (each). I really don't see slow charging as a problem 99% of the time, as drive time between destinations is usually several hours, if not all day.
I've pretty much not concerning myself over isolating the batteries from charging if I'm using the van. If you are constantly "working" the batteries by charging and discharging, then it may be of no benefit to isolate them. This last weekend, I was showing maxed out at 14.5 volts, and the solar controller was showing 0 amps going in. Unplugged from shore power, the batteries would settle to 13.5 volts fairly quickly.
When in storage, I'm not plugging in and the solar is inactive as I have inside storage. That will be the bulk of the time unfortunately. My use is primarily as a weekender.
We'll see how our results compare. I'm still expecting these batteries to be perfectly sufficient for 4 or 5 years, even if I'm abusing them. What I am finding is that I'm not deeply discharging them each day. My daily power consumption is 40-50 amps at most over 24 hours (crediting solar output) - which is only about 20% of my capacity. If I was using an inverter, I'd be more concerned probably. There will most likely be better (and cheaper) batteries and better charging equipment in that time anyways.
I am finding that not being concerned with the SOC is pretty liberating. Since this kind of battery doesn't need to be topped off, and the capacity is far above several days use, then monitoring where they are at is not that important, at least to me anyways. I have no anxiety about the refrigerator or the Truma depleting the batteries as I was expecting initially. Solar easily displaces the consumption of the refrigerator and adds significant charging most days.
Interesting vid. What about his claim that lith phosphate batteries are happiest around midrange with a limited range of charge/discharge - so they'd be happiest if they were around 40-60% most of the time (or whatever midrange he mentioned - not sure if I remember it exactly)? Where's the evidence for that? I've never heard anything of that nature, though for normal travel when not planning to dry camp for several days, it would be easy enough to do it...
I calculated around 600AH for my needs, I have 900AH which will extent the life due to less cycles, no need to charge to 90-100% and will still be enough when they degrade 20% in a few years to 720AH. The 360 extra AH cost around $1800 for the extra cells.
Linear Mode
