24 Volt Solar

[MambaJack]

Yep, I was referring to this comment, but just realized the op didn't post it.

At any rate, I have room for two automotive-starter-sized AGM batts in the batt box, and room for 2 or maybe 3 "average" sized panels on the roof

[MambaJack]

how many volts are those cells?

[john61ct]

What cells?

[dzl_]

Originally Posted by john61ct

Only if you think one big expensive SC with multiple panels is a good idea.

Whereas Victron's model lines allow for much greater efficiency, more flexibility and better value, enabling a 1:1 ratio between SCs and panels.

So 36+Voc panels, up to 65V, rated 240-280W (up to maybe 300W if you find a super bargain) pairs perfectly with a SmartSolar 75/15, at only ~$120 each.

Each pair optimizes its own MPPT independently of the others, so greater conversion efficiency, especially with partial shading, slightly differing angles to the sky, bit of bird poop etc.

Yes you'll save a few hundred just on the SCs going to 24V, but that would not justify the decision on its own, unless the other factors discussed above were in alignment.

All this assumes energy efficiency is a priority. Those running mains household appliances off big inverters, I agree no big difference, any savings lost in the noise.

John, I'm curious to know more about this solution (individual 75/10 or 75/15 SCCs per panel). Have you seen any data on how much more efficient we are talking about with individual SCC's.



If it made enough of a difference I might go this route, as better partial shade performance is a huge advantage for a mobile system, but if we are only talking like 10% more efficient it probably isn't worth the extra expense to me.


Also can you comment on how the Victron controllers work together? Is there any sort of centralized monitoring/control or does each SCC have to be monitored individually?

[john61ct]

The more conditions vary from one panel to the next the greater the efficiency gain. Especially good for portable units laid out away from the vehicle while you park in the shade.

Not much added expense the way Victron prices, more the extra mounting space needed and some wiring.

They have have the Venus or Color GX central units but expensive and little added value IMO. Unless you go DIY with their FOSS.

No coordination is needed.

[Doktari]

I’m not sure if all the newer Victron charge controllers come with Bluetooth built in now?. It used to be only the upper end Victron CCs had built in blue tooth. There’s a Victron Bluetooth dongle available if the Victron CC does not have built in Bluetooth. They keep coming out with new stuff so it’s confusing.
The Victron control panel I have is the Color Control GX. It’s dang expensive and I haven’t had a chance to use it yet. But I think multiple CCs can be monitored with it.
I’m going to change out my Midnite solar Kid CCs for Victron CCs to go with the other Victron Stuff I have: Inverter, CCGX, Battery Equalizer, Battery Meter , ...
I never thought seriously about having one CC per panel. It’s a interesting concept. If I had the big 435 watt panels I’d consider it. I’m not sure for smaller panels. That would be a lot of wiring.

[john61ct]

The older BlueSolar line the dongle was optional.

SmartSolar is current with BT built in much better idea.

Yes the CCGX is for centralizing comms and logging, also Venus and VenusOS.

Victron has excellent user forums.

Originally Posted by Doktari

That would be a lot of wiring.

Yes for very big setups that is a downside.

[john61ct]

Note Victron afaik does not support dropping to Float based directly on reading endAmps from a shunt

as you can rig via MidNite's Whizbang Jr

For some reason removed via non-optional firmware update

[Doktari]

Originally Posted by john61ct

Note Victron afaik does not support dropping to Float based directly on reading endAmps from a shunt

as you can rig via MidNite's Whizbang Jr

For some reason removed via non-optional firmware update

Victron actually removed the endAmps setting? I do think that setting confuses a lot of people and they may have gotten many emails about how to set it. I think the Outback literature I read said it is largely ignored if I remember correctly. Is it all done by a algorithm by Victron CC? Now, I’m confused and need to study it again. I will start reading the Victron forum again. Thanks for the clarifications.
I have four @200 watt panels in series on the roof of my trailer. They are 12 volt panels so it came to around 80 volts input to a Kid CC. Then there’s 3@190 watt panels in series hanging on hinges on the side of the trailer. They are 24 volt panels so it comes close to 80 volts input to another Kid CC. There’s a Whiz Bang Jr and the Kids are linked so one follows the other. I need to check all the settings as it’s been sitting for a while and I forgot what I set it to. It’s a 24 volt battery and early Multiplus inverter.

[john61ct]

Victron's AHT algorithm is a bit obscure, but much better than a dumb eggtimer, recently improved with an update.

But if you measure trailing amps and see the SC goes to Float prematurely, just increase the minimum AHT setting until you see it's getting to endAmps "most days".

With FLA can go way long no worries.

With GEL be more conservative, AGM in between.

LFP I do Absorb at 3.45Vpc and **minimum** AHT, for good longevity. CC-only would be even better at such a slow C-rate.

[Doktari]

Originally Posted by john61ct

Victron's AHT algorithm is a bit obscure, but much better than a dumb eggtimer, recently improved with an update.

But if you measure trailing amps and see the SC goes to Float prematurely, just increase the minimum AHT setting until you see it's getting to endAmps "most days".

With FLA can go way long no worries.

With GEL be more conservative, AGM in between.

LFP I do Absorb at 3.45Vpc and **minimum** AHT, for good longevity. CC-only would be even better at such a slow C-rate.

Interesting. My DC clampmeter has vanished. I was going to use it to measure end amps in my system and in my friends converted Greyhound bus. I’m waiting to buy another clampmeter hoping mine will turn up. Does “AHT” stand for Absorb Hour Time? Is there neither way to check end amps? Thanks

[john61ct]

Some sort of ammeter is required to watch amps decline toward the end of Absorb / CV stage.

Rather than duplicating your clamp style one, an Ah-counter (coulometer, cumulative wattmeter, Wh meter) is generally very useful and also shows amps, i.e. instantaneous current

Some are inline, better ones have a separate shunt.

Best of all, a good BM like Victron BMV-712 does too, but those cost more.

AHT = Absorb Hold Time, some chargers just use a dumb eggtimer approach, but better that than non-adjustable.