How to ground a mobile off-grid back-up battery generator

pmac · 08-29-2012, 06:22 PM

I have a 1000 watt power inverter that I want to connect to a marine battery to make a portable off-grid back-up generator. I was planning on using a small dolly to transport the generator unit. How should I go about grounding the inverter to minimize the chance of electric shock?

The instructions for the inverter state:

"The Chassis Ground screw must be connected to
a grounding point, which will vary depending on
where the unit is installed.Use a #8 AWG copper
wire (preferably with green/yellow insulation) to
connect the chassis ground screw to the grounding
point.
� In a vehicle, connect the Chassis Ground to the
chassis of the vehicle.
� In a boat, connect to the boat grounding
system.
� In a fixed location, connect the Chassis Ground
screw to earth ground by connecting to a
ground rod (a metal rod pounded into the
earth) or other proper service entrance

ground."

mpoulton · 08-29-2012, 07:32 PM

It pretty much doesn't matter. If you really wanted to, you could connect the chassis grounding screw to the dolly frame and also to the negative battery terminal. But completely ignoring this probably won't hurt anything.

jbfan · 08-29-2012, 08:13 PM

Yopu do know that that 1000w inverter will kill that battery pretty quick, so don't depend on anything critical running on it.

joecaption · 08-29-2012, 11:38 PM

What do you plan on powering with it?
How do you plan on recharging the battery once it's dead if there is no power?

And it's not a generator. A generator would produce power.

pmac · 08-30-2012, 12:13 AM

Thanks for the responses. The battery is being charged with a 100 watt solar panel. I will ground the inverter to the dolly frame as suggested.

joecaption · 08-30-2012, 12:27 AM

Where all still wondering what do you plan on running off of this?
Just one batterys not going to last that long.
May want to have concidered an AGM battery. They will charge up to 50% faster and hold a charge longer when not being used and no off gasing. Also no way for them to spill.

mpoulton · 08-30-2012, 12:55 AM

Just remember not to let the battery discharge completely. That severely and permanently damages them. A completely discharged lead acid battery is usually unsalvageable. Make sure your batteries are big enough that you don't discharge them below 50% regularly (or 60-75% if they are not deep cycle batteries). Of course, you also need to use a proper charge controller with the solar panel, set to a proper cell voltage for the specific batteries you are using. A 100W panel is plenty large enough to kill the batteries by overcharging.

pmac · 08-30-2012, 02:48 AM

Thanks for the great advice. I have a charge controller to protect the battery. I built the solar generator so I could learn more about solar electricity. At this point the solar generator is more just for emergency back-up power (so I can run some lights or maybe a fridge for a few hours). The battery is 110 AH. If my calculations are correct then I should get about 650 watt hours out of the battery before I need to recharge it.

mpoulton · 08-30-2012, 03:50 PM

Quote:

Originally Posted by pmac

Thanks for the great advice. I have a charge controller to protect the battery. I built the solar generator so I could learn more about solar electricity. At this point the solar generator is more just for emergency back-up power (so I can run some lights or maybe a fridge for a few hours). The battery is 110 AH. If my calculations are correct then I should get about 650 watt hours out of the battery before I need to recharge it.

650WH would discharge the battery to about 50%, if the discharge is very slow (like 20 hours or so). Fast discharge results in huge efficiency losses. At a 5-hour discharge rate, that battery's capacity is probably only 50AH or so. Keep in mind that this efficiency loss at high discharge rates applies on an instant-by-instant basis, not to the average discharge rate. So if you are using it to run a 1000W microwave, but only for 30 seconds at a time every few minutes, the applicable discharge rate is still the 1000W rate (about 45min discharge, should give you about 15-25% of the battery's 20-hour rated capacity).

Also remember that the inverter is inefficient. Whatever load you put on the inverter, the load on the battery is about 20% more.