Tiny Cabin - What To Do

[sunshine_eggo]

Yes cooler than 25C ,,, this screenshot shows 17C;

Ah... missed that.

VE Smart Network; I do not know what that is, but they are “networked together” so the MPPT reads the BM712 for temp, volts, & whatever else that software does. No “Internet” @ the Cabin other than our phones.

VE.Smart network is the means by which the BMV feeds the MPPT the voltage, current and temp data.

“Expert Mode” settings I will screenshot next time I am @ the Cabin & post them.

Want to check your absorption method/time. Since you leave it unattended for days at a time, adaptive is probably appropriate, but for days you're there using it more heavily, you probably want to go to a manual absorption time based on the Rolls calculation and/or tail current.

Regarding Utilization / Harvest; So much depends upon the weather & the last few days have not been Stellar for Harvest. Still, I think you are correct & the solution will be as you suggested @ the start of this thread;

1) Twin the battery bank in Parallel 2S2P ( 12vdc @ 500Ah )

I would do this as step #2.

2) Over panel to boost amps not volts; If the Sun is shining best harvest is 10am to 2pm, but I might be able to morning face & afternoon face a couple of added strings. I currently have 6 ( slightly mismatched ) 100W panels 600W 3S2P ( 60v @ 10a ). If I add panels, would I be better off with new 6 350W? 2S3P east south west. So 700W each string hoping for 70v @ 10a & 3 strings ?

If you're adding to the same MPPT, you need to match Vmp. If you're adding to a new MPPT, or completely replacing all the panels, whatever works best. Since you're on 12V, there's no need to drive the PV voltage any higher than you are as long as you stay within PV input current limits.

If those 350W are readily available, that's the way to go.

Then I would use those 6 - 100W on something else.

Of course, I could buy a new MPPT that handles bigger volts, watts, amps if I twin the batteries & consider Rolls 50amps “recommended” 50x2=100amps “recommended” ,,, or 87.5x2= 175amps max.

The rolls manual also mentions a minimum of 10% of the C20 rate:



(also noted the tail current)

So for 500Ah, I'd make sure you can deliver 50A or more earlier rather than later, so the staggered E S W strings would help you work towards that.

Now I understand that Farmer’s Quote;

Make Hay when The Sun’s Shining !!

********

Them farmers are smart.

On another note - Economics (Canadian Version)

I paid about $400 for that new Fridge. A same size 12vdc “solar” Cabin Fridge would cost me $2,000 to $3,500 approximately. It already had the inverter ( albeit I could have sold it ,, not my favourite activity - selling off my stuff ). Solar “tech” seems to keep getting better & cheaper.

If my 120vac Fridge craps out after a 2 year warranty, chances are I can buy another for $400 rather than another $3000 for a 12vdc. I am more of a 12vdc purest, but the economics don’t support that ( in my case ).

You're preaching to the choir... I'd never spend that kinda money for the "advantage" of 12V. We paid about $400 for a 10cu-ft Magic chef that uses about 0.8kWh/day @ 60W.

 

[RV8R]

Ah... missed that.



VE.Smart network is the means by which the BMV feeds the MPPT the voltage, current and temp data.



Want to check your absorption method/time. Since you leave it unattended for days at a time, adaptive is probably appropriate, but for days you're there using it more heavily, you probably want to go to a manual absorption time based on the Rolls calculation and/or tail current.



I would do this as step #2.



If you're adding to the same MPPT, you need to match Vmp. If you're adding to a new MPPT, or completely replacing all the panels, whatever works best. Since you're on 12V, there's no need to drive the PV voltage any higher than you are as long as you stay within PV input current limits.

If those 350W are readily available, that's the way to go.







The rolls manual also mentions a minimum of 10% of the C20 rate:

View attachment 225091

(also noted the tail current)

So for 500Ah, I'd make sure you can deliver 50A or more earlier rather than later, so the staggered E S W strings would help you work towards that.



Them farmers are smart.



You're preaching to the choir... I'd never spend that kinda money for the "advantage" of 12V. We paid about $400 for a 10cu-ft Magic chef that uses about 0.8kWh/day @ 60W.

Thanks @sunshine_eggo

So I guess I did setup the VE.Network

Funny - I had 3% tail current prior to swapping it to the 4% per your post ,,, but my other charge settings was way off;




Expert Mode;

Absorption Method, IIRC I left it on “Adaptive”. I know I did 2 things on the Equilization lowered the voltage to some useless value & made sure it was on manual start.

I will bone up on the manual absorption vs adaptive for absorption.

Rolls charge currents (% based upon C20 capacity);
10% min
20% recommended
30% max

 

[sunshine_eggo]

This says that if you ever drop below (0.03 * 250Ah) 7.5A while above 13.2V for 3 minutes, the unit will sync to 100%.

With PV charging and poor conditions, that would be very easy to accomplish yielding a fake 100% when you could be at a notably lower SoC.

Since you charge primarily with PV, you need to set the "charged" parameters according to that method - target absorption voltage and actual tail current. Per Rolls, full charge is 14.7V @ 3% tail current, so you want to be a little under 14.7V (14.5V) and a little over 3% (4%) to ensure you can capture that moment relatively accurately. Yes. You might trigger a premature 100%, but it's going to be when the battery is already nearly at 100% anyway.

This is discussed in 10.3.11:

10. Troubleshooting

www.victronenergy.com

In most cases, due to the inefficiency in lead-acid charging, it counts back up to 100% before 100% is actually triggered, so it just says 100% for awhile.

 

[RV8R]

View attachment 225099

This says that if you ever drop below (0.03 * 250Ah) 7.5A while above 13.2V for 3 minutes, the unit will sync to 100%.

With PV charging and poor conditions, that would be very easy to accomplish yielding a fake 100% when you could be at a notably lower SoC.

Since you charge primarily with PV, you need to set the "charged" parameters according to that method - target absorption voltage and actual tail current. Per Rolls, full charge is 14.7V @ 3% tail current, so you want to be a little under 14.7V (14.5V) and a little over 3% (4%) to ensure you can capture that moment relatively accurately. Yes. You might trigger a premature 100%, but it's going to be when the battery is already nearly at 100% anyway.

This is discussed in 10.3.11:

10. Troubleshooting

www.victronenergy.com

In most cases, due to the inefficiency in lead-acid charging, it counts back up to 100% before 100% is actually triggered, so it just says 100% for awhile.

Very Very Helpful “Catch” @sunshine_eggo

Much Appreciate !!

Honestly, I look at the SOC the same as an “ASI” ,,, Airspeed Indicator or the nickname Pilots call it by “The Gauge That Lies”

Regardless, with your help here, I can probably get that BM712 to stop lying to me . FLA & AGM, I really look at the voltage & if the system has a shunt the current & capacity (plus or minus).

You have helped me out here on this thread huge ,, Many Thanks.

RTFM (manual), could apply here towards me . But some of this stuff is not that straight forward to a novice inexperienced with “Team Blue” & Rolls.

Further, I had to think back a few years when I 1st set up that BM712 “shunt” @ my Cabin ,,, I am sure you will get this ,,, Because I am basically lazy, I copied a BM712 file from my Van which is “Alternator charged only” & changed the name of the device ,,, same Rolls batteries in the Van but different charger ( Alternator vs Solar ).

 

[sunshine_eggo]

Very Very Helpful “Catch” @sunshine_eggo

Much Appreciate !!

Honestly, I look at the SOC the same as an “ASI” ,,, Airspeed Indicator or the nickname Pilots call it by “The Gauge That Lies”

LOL... I flew a Musketeer for a few years... Well aware of how ASI lies... The LORAN was more truthful.

Regardless, with your help here, I can probably get that BM712 to stop lying to me . FLA & AGM, I really look at the voltage & if the system has a shunt the current & capacity (plus or minus).

Yes. Shoudn't be more than ~5% wrong and that's mostly due to inefficiency of AGM charging. You'll need to sync at least once every 1-2 weeks to maintain accuracy.

You have helped me out here on this thread huge ,, Many Thanks.

RTFM (manual), could apply here towards me . But some of this stuff is not that straight forward to a novice inexperienced with “Team Blue” & Rolls.

That wasn't my intent. I often try to prove that what I'm saying doesn't just fly out from betwixt my cheeks.

 

[RV8R]

LOL... I flew a Musketeer for a few years... Well aware of how ASI lies... The LORAN was more truthful.



Yes. Shoudn't be more than ~5% wrong and that's mostly due to inefficiency of AGM charging. You'll need to sync at least once every 1-2 weeks to maintain accuracy.



That wasn't my intent. I often try to prove that what I'm saying doesn't just fly out from betwixt my cheeks.

RTFM, my words ,,, not at all what I was getting from your posts.

Regarding the SOC ,,, I simply look at consumed capacity Ah & manually calculate it. Easy to do in my head if -50Ah & 250Ah capacity. I know that is a gross method, but the BM712 (not setup correctly by me) was out reading high SOC & out by more than 5%. But your post above “dropped the penny for me”. I will also review my Van BM712 & attempt to tweak the “ASI” outta them .

A married couple go to a private party where they know a Pilot they have never met will be attending. The wife asked the husband, how will I know which one the Pilot is. The husband responded “About 5 or 10 minutes after we get to the party, some random guy will approach us, introduce himself & tell us he is a Pilot. That will be the Pilot”.

LORAN & now GPS. I once approached small vacant, remote rough strip in WA up high in summertime , & on final ASI vs GPS did not agree ,,, substantial tail wind ,, no wind sock ,,, low & over, tear drop & approach from opposite end ,,, same tail wind ,,, ASI & GPS & high density altitude & zero wind. As a mostly sea level pilot, I learned a little that afternoon in the WA Mountains.