Need some grounding advice for a simple off-grid setup

ntinker

Hello!

I am currently using a system consisting of twelve 6v golf-cart batteries connected in series and parallel for a 24v system. I am not currently using solar panels or anything (although planning to in the near future), the purpose of the batteries is just so that I won't have to run the generator as often.

The battery bank is currently indoors in a wooden enclosure with an exhaust vent that runs when it is charging.

I am using two Iota DLS27-40 24v 40 amp chargers in parallel to charge the battery bank. It is being charged with a "Blackmax" 7kw generator.

The inverter I am using is a Samlex SA 1500w PSW inverter. We live in a small 500 sqft. cabin so our electricity (only lights, computer, and some small tools once in a while; bigger loads go directly to the generator) is just connected to a power strip plugged into the inverter. We don't have any breaker panels or anything yet.

My question is, would it be necessary to ground these components (the battery bank, inverter, chargers, generator)? How should I run the grounding connections?

I am assuming that the battery bank will need to be grounded on a separate grounding rod. Then, the inverter, chargers, and generator will all share another grounding rod? How far apart do I space these rods?

Any advice will be appreciated, thank you.

Organic Farmer

Re: Need some grounding advice for a simple off-grid setup

ntinker
This sounds like a large UPS. Do you experience frequent power-outages of mostly short-term duration?

We have that in our township. We have outages every month, though most of them are less than a day in duration. Rarely do we see outages of greater than 4 days [maybe only once or twice a year].

The reason I ask is that the maintenance cost and replacement cost of your battery bank will be significant.

waynefromnscanada

Re: Need some grounding advice for a simple off-grid setup

Sounds like you're totally off grid. Yes, these things should all be grounded and all to the same ground rod, or at the very least, if different ground rods are used, the rods should be bonded together so electrically they appear as one single ground rod. This hopefully will prevent possible large and dangerous voltage differences between the different ground rods in the event of a nearby lightening strike.

Cariboocoot

Re: Need some grounding advice for a simple off-grid setup

It is not necessary to ground anything; it is done for safety reasons in case something goes wrong.

Normally the negative of the DC as well as metal casings of components and the neutral line of the AC will be grounded, all to the same rod. But you need to investigate to see if any neutral-ground bonds exist on the AC side and where they are. There should be one, and only one.

I can't remember if the Samlex has an N-G bond built in or not. One with outlets on it probably does. You can test this with a simple plug-in outlet tester available at hardware and electrical supply stores. If it is bonded then the case grounding lug should suffice to supply ground.

Generators usually do not have N-G bond built in. It should be labeled "floating neutral". In that case simply connect its ground lug to the other grounds and leave the AC side alone if it also feeds loads when in use.

The least important is grounding the DC negative as it has the lowest danger potential @ nominal 12 Volts. The AC side is 10X the Voltage and far more dangerous.

Sorry, but grounding is not a simple issue.

BTW your three parallel battery strings are a potential problem for current sharing, even if wired correctly (to bus bars with individual string fuses). That is quite a large battery bank at 660 Amp hours and 24 Volts: almost 8 kW hours. If your loads are small and you run them down low before recharging you may be spending too much time below 75% SOC and shortening battery life. It is better to discharge and then recharge ASAP rather than leave them in a partial SOC for, say, three days. You may actually benefit from a smaller battery bank and an inverter-generator for this type of system (to say nothing of adding solar; about 2kW array and 80 Amp MPPT controller).