MPPT SCC stacking

[ericfx1984]

I am curious about stacking SSC

My experience so far has been this

Originally I had a Victron 100/50 with a pair of 300 watt bi facial mono panels in series... it would pump as much as 55 amps into the batteries yeah, more than the rated power output of the panels... (when conditions are right)

Then I added an EPEver 40a MPPT with 3x 200w mono panels in series

The pair of these would pump a little south of 100 amps into the batteries

Then I added three(3) EpEver 60 amps SCC, each with 3x, 250w Santan Solar panels, However I rarely see more than 35a on these controllers... in addition, the other controllers are now quite limited I rarely see more than 170a coming off the collection of SCCs... I rarely see more than 2500w coming in... BUT the overall daily power production is hugely increased...

If you are keeping track, I have 3450w worth of solar panels... and 270a of potential charging capabilities

I SHOULD be able to hit as much as 250a on peaks with these panels...

I was able to make some adjustments to the SCC settings that helped quite a bit...

Would it make more sense to swap out these units for LARGER controllers such as 100a or 120a? I get it, my primary limitations here is the 12v system... I COULD convert to 24, or even 48v, its a thought

 

[sunshine_eggo]

Multiple chargers only benefit during bulk phase. Too much current going into a battery and/or marginal wiring can cause a notable voltage drop where the chargers see an artificially high voltage. If that measurement hits absorption, they will taper. The way to counter this on a Victron is to get a smart battery sense (or smartshunt/BMV 712) that feeds it the actual open circuit voltage.

IMHO, 270A of charging (or discharging) on 12V is at the ragged edge of practicality, and you're very susceptible to wiring losses. 3450W/48V = 72A - almost trivial if you go to 48V. Given your cell counts, 24V might be more practical as you could adapt both to 24V... unfortunately, new inverter and two new BMS are needed.

 

[ericfx1984]

Multiple chargers only benefit during bulk phase. Too much current going into a battery and/or marginal wiring can cause a notable voltage drop where the chargers see an artificially high voltage. If that measurement hits absorption, they will taper. The way to counter this on a Victron is to get a smart battery sense (or smartshunt/BMV 712) that feeds it the actual open circuit voltage.

IMHO, 270A of charging (or discharging) on 12V is at the ragged edge of practicality, and you're very susceptible to wiring losses. 3450W/48V = 72A - almost trivial if you go to 48V. Given your cell counts, 24V might be more practical as you could adapt both to 24V... unfortunately, new inverter and two new BMS are needed.

I completely agree... One of the big issues is that I never intended to be in this RV for this long The plan was to have the house Shell up and the new 10,000 w worth of solar panels 48 volt system up and running and then to bring this system down to a more realistic power range

As far as converting it to 48 volts it would actually be a fairly simple affair... A 5000 w all in one unit with 80 amp charger would be about $800 I already own a pair of 48 volt BMSs and they will work 7S up to 20s battery configurations

I suppose then it would just be a simple matter of getting a 40 amp or so DC to DC converter to run the 12 volt systems of the RV

The other possibility is that I could just wait... Even if I convert over to 48 volts I'm not going to leave 3400 Watts of panels running on this RV I'm only going to leave about 1200 Watts when I sell it

It is serving the purpose pretty well and honestly there may be ways to manipulate everything

As for the wiring, both of my batteries go to a blue sea 350 amp continuous battery switch... One battery is on side one the other battery on side too and those are fed with 1/0 wiring

After the switch there is 4/0 wiring going to the inverter... All of the charge controllers meet up on a bus bar on the inverter side of the switch

I make sure to check all my wiring about once a month sometimes a little more often

According to temperature sensors, infrared thermometers and a good old fashioned finger touch everything seems to run reasonably cool... There is a measurable increase in temperature of course when the sun is giving all it has to give

 

[ericfx1984]

24V might be more practical as you could adapt both to 24V... unfortunately, new inverter and two new BMS are needed.

That's a good point I only plan to leave eight x 230 amp hour cells behind when I no longer need to live in the RV... I plan to take the 16x 304 amp hour cells and convert them to a 16s battery

 

[sunshine_eggo]

I forgot your circumstances. I don't know how far I'd go. If what you have is getting you by, it may fall into the "ain't broke, don't fix" column.

If something needs to be done, 24V makes the most sense. That would be able to carry forward to the future RV config. I treat a non-12V system as "on board shore power," i.e., conceptually simply "plug" your RV into the inverter output and let the converter keep an existing 12V charged. This provides another layer of backup for 12V. The 24-12V converters are 80-90% efficient and typical 24VDC-AC-12VDC conversion is about 75% efficient, so you don't lose a lot keeping the 12V floated on the converter.

If you rely on the surge rating of the AIMS, an AiO might disappoint.

 

[ericfx1984]

I forgot your circumstances. I don't know how far I'd go. If what you have is getting you by, it may fall into the "ain't broke, don't fix" column.

If something needs to be done, 24V makes the most sense. That would be able to carry forward to the future RV config. I treat a non-12V system as "on board shore power," i.e., conceptually simply "plug" your RV into the inverter output and let the converter keep an existing 12V charged. This provides another layer of backup for 12V. The 24-12V converters are 80-90% efficient and typical 24VDC-AC-12VDC conversion is about 75% efficient, so you don't lose a lot keeping the 12V floated on the converter.

If you rely on the surge rating of the AIMS, an AiO might disappoint.

I don't think that I would float a 12 volt battery... Rather use the converter to operate the furnace blower, the lights and a few other minor items

I do not rely on the aims power surge capability... My highest load is a 12,000 BTU mini split on 120v as well as an RV microwave... Everything else is small things like TVs and laptops

 

[sunshine_eggo]

I don't think that I would float a 12 volt battery... Rather use the converter to operate the furnace blower, the lights and a few other minor items

For me, it's about another layer of backup. If any of the 12V loads have a surge (slides/jacks), you'll need an oversized converter rated for the surge. The presence of a 12V battery serves as a buffer for the surge. An oversized converter will be no more efficient than DC-AC-DC.

I do not rely on the aims power surge capability... My highest load is a 12,000 BTU mini split on 120v as well as an RV microwave... Everything else is small things like TVs and laptops

Then the typical Growatt 24V/3kW w/80A MPPT should get you by.