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Off-grid solar shed 24v project layout
#1
I have most of the components (waiting for the panels to arrive)  *see Image with the exception of a Victron low voltage battery disconnect.  
1) Does anyone think a Low Voltage battery disconnect would be crucial? 
2)  My ground is 4ft grounding rod, with 6 AWG copper wire connecting to the Negative Bus.. Is this the suitable position?  
I do use a 12v converter for lights, which will have a parasitic draw and consider this to be non issue.   

The purpose of this setup was to run lights and charge tools in a small workshop, with a emphasis on making future upgrading as safe/easy as possible, adding additional solar panels, larger AC inverter, and increasing the capacity of the lipo battery bank.  Eventually run a small window AC unit to the shed.   I'm building custom batteries from 18650's salvaged from modem battery packs.       

Any recommendations? 

Thanks 
-Tony

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#2
Nice drawing - very helpful for discussion and implementation Smile

>2)  My ground is 4ft grounding rod, with 6 AWG copper wire connecting to the Negative Bus.. Is this the suitable position? 
In my jurisdiction, the recommendation is to use the house ground instead of adding a 2nd grounding rod - so you don't setup a potential between the 'rod' and the 'house'...  but not sure it's a big deal.   Maybe if you have house power (with grounding wire) you might consider using it.    Just laymen comment for you to possibly research Smile

Grounding to the negative bus-bar?   I'll be interested to see comments on this.   
My electrician grounded the Midnite Classic Charge Controller (it has a connector for a ground), the inverter (it has a connector), and the metal control boxes/conduit but not the battery/negative-bus itself.   You might consider surge protection (lightnihg arrestor) on the PV input - https://www.altestore.com/store/enclosures-electrical-safety/lightning-protection/midnite-solar-solar-surge-protection-device-600v-p9043/?gclid=EAIaIQobChMI69fV_pz46gIVxBx9Ch2NEgv6EAQYAyABEgJ2hvD_BwE - and it uses a ground connection.  

>1) Does anyone think a Low Voltage battery disconnect would be crucial? 
It looks like you have a "10 Breaker" on the diagram for this?   (good idea)
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#3
thanks for comment.  

Shed location is (150ft or 45m) from the house ground, on the opposite side which is a huge bummer.  The PX60 Charge Controller does have a ground connector, would require a connection (good catch) but I wasn't sure about AC inverter when tied to an off-grid DC system ground, seems I've read it may need its own dedicated ground?   I ran this past our Company maintenance guy, who's no electrician but immediately thought that the bus bar would work, but seems wrong.   Panels will be mounted on a metal roof, I need to plan on attaching the ground to it as well.   Im looking into a surge arrest, if not immediately... eventually. 

My battery disconnect main concern was that it may be redundant, the Daly3.7 7s 24v Li-ion 100amp Bms  has low voltage discharge protection. I'm guessing if I did decide to use a Victron, I'd need to somehow set it a bit below the lowest activation level of the Bms.   I wonder if/when BMS's fail, if its a coin toss if failures result in the load side being left fully open or closed.
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#4
Grounding looks good to me.
Check into adding earth leakage breakers on the AC output of the inverter for safety.
The mains there should have a ground pin (tied to battery- busbar & ground stake) as normal (check the inverters output is floating & not tied to the battery somehow).

With the BMS charge input cut off, to protect from blowing the charge controlller, you might rig it so the solar panel input is disconnected by the BMS using a suitable relay or MOSFET.

Tip: regular house solar panels (eg approx 37V ish) will work nicely with a 24V system & a proper MPPT charge controller (not a PWM one).
Running off solar, DIY & electronics fan :-)
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