Grounding Battery Bank and Inverter

bunker80 · July 2018

I have what seems like a relatively simple question; however, I have yet to find a simple answer. I’m by no means an electrician so be patient with me. I have set up the following system in my van.

(2) 100W Renogy Solar Panels hooked up in parallel.
(1) Renogy wanderer charge controller.
(2) 33 ah deep cycle sealed 12V batteries.
(1) 1000 W AC inverter with grounding provisions on case.

Question 1. Should I negatively ground the 12v batteries to the frame or chassis of the van. If so, what size wire and what’s the best mounting option.

Question 2. Should I also ground the inverter the the frame/ chassis. If so, what’s the best wire size and attachment.

Thanks for your help in advance!

BB. · July 2018

Don't feel bad... "Grounding" is huge and complex issue--peppered with many "opinions" too.

I will try to answer quickly/simply--But feel free to ask questions/have me/us justify answers.

Yes, ground the negative 12 volt battery bus to chassis of vehicle. Note that some vehicles have less than optimum grounding (for example chassis of vehicle may be noise isolated with rubber mounts to sheet metal. In HAM Radio world, adding "bonding straps" (flexible braided wire with terminal ends between frame/sheet metal/etc. is common).

For your needs, grounding to the sheet metal of the body of the vehicle is a good start. If you eventually have a larger battery bank and/or connect to vehicle alternator (via a battery isolator), you may need to add a bonding strap(s) between sheet metal, frame, and possibly engine to get alternator charging to work correctly (higher currents, better bonding needed).

I would suggest 6 AWG for your battery to body grounding strap would be a nice. If you only have 14 AWG, it will work with this small battery bank.

You say you have ~66 AH @ 12 volt battery bank and a 1,000 Watt AC inverter.... Nominally, I would be suggesting a maximum inverter size of C/5 to C/10 discharge rate for battery bank (drawing more current than batteries can cause battery voltage to collapse or even damage the batteries:

12 volts * 66 AH / 5 hour discharge rate = ~158 Watt maximum inverter rating
12 volts * 66 AH / 10 hour discharge rate = ~79 Watt nominal inverter rating

It does depend on battery type (flooded cell, deep cycle, Sealed, AGM, Li Ion, etc.)... But at a first guess, I would say your battery bank is too small to "reliably" support a 1,000 Watt AC inverter... Such an inverter would draw a maximum current of:

1,000 Watts * 1/0.85 inverter eff * 1/10.5 volts battery cutoff = 112 Amps (or ~56 amps from each battery)

Anyway, will stop here and see if you have more questions.

Best wishes,
-Bill

Grounding Battery Bank and Inverter

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