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Off-grid shed question...

JTC

JTC

PFM Villager...
Very quick one. I'm adding a solar panel, MPPT charger and a spare leisure battery to build a simple off-grid shed power system. I just wondered how this should be earthed. For info, the shed also has 230v AC but I had the spare charger and battery and am picking up a solar panel. The plan is to power some garden lights and additional lighting in and around the shed, more for the fun of the project than to save money or be green. It just occurred to me that such a system doesn't have a natural 'earth' to which to tie the neutral, e.g. where you'd attach to the chassis of a car, or a dedicated earth leg such as in the house wiring.

thanks.
 
So you are saying that the 230 Vac is a stand alone supply that you are generating in house? If so, then the Earth should be literally that, a spike in the earth that you connect to and keep moist. Some hifi enthusiasts are into dedicated earths like this in addition to the one in the house.
 
Nit-picking - a car earth is not, it is one pole of the 12V circuit. It is just a misleading name.

There are legal requirements about how close seperate earthing points/stakes can be.

Will anything that you attach to the solar system actually require an earth? Very many lighting systems do not.
 
I assume your lighting is 12v, and by "leisure battery" you mean a 12 v unit from a camper? If so, simply attach the lights across the terminals of your battery. No need for a separate earth. Be aware though that 12V DC doesn't travel very far: voltage will drop significantly after 5 metres. For longer distance, you may be better to use an AC Inverter off your battery, but that does reduce efficiency too.

Assuming the charger and panel are intended for 12 V batteries, just connect the charger across the terminals as per the manufacturer's instructions.

A friend of mine used a very similar setup (but with a large bank of batteries) to power a Ham Radio station, so if you need details I can ask him...
 
Talk to a fully qualified electrician. As the shed already has 230v AC any solar power may need to be tethered to the same earth whether the light fittings it is supplying are double insulated or not.
 
KrisW said:
Be aware though that 12V DC doesn't travel very far: voltage will drop significantly after 5 metres. For longer distance, you may be better to use an AC Inverter off your battery, but that does reduce efficiency too.
Click to expand...

Ohm's law doesn't apply?

Interesting!
 
For clarification, the 230v AC is mains, via an armoured cable from the main house consumer unit. The 12v system is just a simple project, no intention to be used for anything beyond lighting, as there's no need (230v AC available). This is not by any means a project of 'necessity', just a 'I happen to have most of the bits and fancy a summer project, so why not?' type deal. I gather thicker gauge wire for the 12V lines (for garden lights) will have a lower resistance and therefore make the 12v go a bit further, within reason.
 
It does. Just wasn't sure if it was allowed to connect a separate 12v system to a mains earth, at least in the way that I think you mean. Though I'm struggling to think of a good reason why not.
 
1.5mm mains cable/flex has a resistance of 29 milli-ohms/metre. (0.029 R/m) - half each in positive and return. 20% more for 1.0mm

Nice round figure - 60W, so 5A, that is a loss of 25 x .029 for 1.5mm - 0,725W over a metre, which is 5 x 0.029 - 0.145V drop per metre.
 
JTC said:
Though I'm struggling to think of a good reason why not.
Click to expand...
Like many here, I'm not an electrician but I can't see any reason whatsoever that you would join (what and how?) an independent, 2 wire, 12volt system to the mains Ground - any more than you would a flashlight.
 
If it is lighting, it is very unlikely that will be anything to connect to an earth - it is that simple.

Would anyone be seriously worried about 12V? If they are, then a lot of torches need an earth, presumably.
 
Vinny said:
Ohm's law doesn't apply?
Click to expand...
Of course it does... the cable has resistance, so your DC circuit looks like the out and back cable runs as resistors above and below the load in a three element potential divider.

Low voltage DC isn't a good idea over long distances because the cable resistance, although small, can become electrically significant very quickly.
 
Those were my thoughts too, but I wanted to check I wasn't missing something fundamental.
 
KrisW said:
Of course it does... the cable has resistance, so your DC circuit looks like the out and back cable runs as resistors above and below the load in a three element potential divider.

Low voltage DC isn't a good idea over long distances because the cable resistance, although small, can become electrically significant very quickly.
Click to expand...

Go away and read up on pre O-Level physics. Get educated.

AC or DC - they both obey Ohm's Law, indeed RMS AC value is the voltage figure for equivalance in DC. (If you want peak AC voltage, multiply by square root of 2)

AC or DC, same voltage, makes not one single solitary, minutest jot of a difference.
 
You are getting mightily confused about AC power distribution and this VERY simple problem.

Mains is AC for a multitude of reasons, not least transformers.
AC voltage for grid transmission is HUGE because it loses less power.

Put 100kW through 10R at 100V and 10,000V and work out the losses - losses are I^2R.
 
Vinny said:
Go away and read up on pre O-Level physics. Get educated.

AC or DC - they both obey Ohm's Law, indeed RMS AC value is the voltage figure for equivalance in DC. (If you want peak AC voltage, multiply by square root of 2)

AC or DC makes not one single solitary, minutest jot of a difference.
Click to expand...

I think you might have missed the "low voltage" bit.
 
It doesn't help that high voltage AC and low voltage DC circuit diagrams use the same symbol for 'ground', even though they are implemented differently.

65f854814fd223fc3678f2c9_What-is-Ground.jpeg
 
Your 12V DC system should be fine and doesn't need to be grounded for any reason. Its just a battery that you are charging from solar energy to which you can connect your 12V lights. Its also an isolated circuit.

Unless you have other things in mind..........

Have fun,

DV
 
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