Off-grid solar shed 24v project layout

Pronesis

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Jul 31, 2020
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I have most of the components (waiting for the panels to arrive)*see Image with the exception of a Victronlow 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 wireconnecting 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 andcharge 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 runa small window AC unit to the shed. I'm building custom batteries from 18650's salvaged from modem battery packs.

Any recommendations?

Thanks
-Tony


image_kuplbl.jpg
 

OffGridInTheCity

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Dec 15, 2018
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Nice drawing - very helpful for discussion and implementation :)

[size=small][size=small][size=small][size=small]>2) My ground is 4ft grounding rod, with 6 AWG copper wireconnecting to the Negative Bus.. Is this the suitable position?[/size][/size][/size][/size]
[size=small][size=small][size=small][size=small]In my jurisdiction, the recommendation is to use thehouse 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:)[/size][/size][/size][/size]

Grounding to the negative bus-bar? I'll be interested to see comments on this.
My electriciangrounded the Midnite ClassicCharge Controller (it has a connector for a ground), the inverter (it has a connector),and the metal control boxes/conduitbut 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.

[size=small][size=small][size=small]>1) Does anyone think a Low Voltage battery disconnect would be crucial?[/size][/size][/size]
[size=small][size=small]It looks like you have a "10 Breaker" on the diagram for this? (good idea)[/size][/size]
 

Pronesis

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Jul 31, 2020
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thanks for comment.

Shed location is (150ftor 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-gridDC system ground, seems I've read it may need itsown dedicated ground? I ran this past our Company maintenance guy, who's no electrician but immediatelythought 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 beredundant, theDaly3.7 7s 24v Li-ion 100amp Bms has low voltage discharge protection. I'm guessing if I diddecide to use aVictron, 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 resultin the load side being leftfully open or closed.
 

Redpacket

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Feb 28, 2018
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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).
 

Overmind

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Jan 16, 2019
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Grounding the negative...hmm...no.
Grounding should be separate, on the metal parts of whatever cases you will use for every piece on your setup.

I intent to do a very similar build in the future but I did not actually completely plan anything yet.

My initial thought was to use a high quality APC UPS in such a system, also using a 24V pack. I'll have to research a little the controller part. Got a good idea of how-to on everything else.

I'll follow your topic and progress with interest.
 

daromer

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You cannot ground the negative directly. Many inverters will bog out totally doing that! You must also read up on local regulations how you are allowed to ground equipment that is connected to grid in some way or another or is tied to an insurance. In your case it doesnt look like you have it connected to grid.
- And if so it should be on the AC side most likely. So look into this before starting. most batteries are floating due to not having grounding issues.

Where I live you are only allowed to ground in a certain way and get it tested and approved. For instance if i ground negative my inverter will beeeeeep like crazy and shut down.

Regarding LVDC.. No you dont need it if you have a decent BMS. The BMS should have such function built in. Its one of the BMS main functionality :) WIth that said if it disconnects the charger wont be able to charge anymore. In that case you might want to go with a bms with Charge and discharge port!.. Dont connect the inverter directly to the battery and bypass the BMS own built in system (If it is one that have disconnect that is). If it doesnt look into if it can be hooked up.


Nice drawing and it makes it so much easier to follow!
 

OffGridInTheCity

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I had forgotten until reading this thread again today - but one interesting feature that is rarely discussed is DC GCFI - which works via a proper ground. At 48v (nominal) I understand it not as likely as 120v AC to be serious risk (like a SPA) but there is some risk with 48v+ andis actually a requirement in my jurisdiction. The Midnite Classic Charge controllers come with this built-in... and is partly why they are hooked to a proper ground. You can buy stand-alone DC GCFI circuit breakers (e.g.https://www.solar-electric.com/mndc...MIrOf8qZ2q6wIVkxh9Ch3TWAgAEAQYBSABEgIQavD_BwE) if your controller doesn't have this feature. Maybe its worth some research on the protection it provides (or maybe required by your jurisdiction like it is in mine) - and this might lead to a better understanding of grounding requirements.

(To repeat @Daromer's warning -as I said above my electrician did NOT hook ground to battery negative)
 
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