Back-feeding a portable power bank into the 12V system

GulfCoast

I've seen several references to people "back-feeding" a 12V portable power bank into a small camper's 12V system via a cigarette lighter outlet. The intent is to provide the camper's 12V needs without dipping into the house battery, or meeting basic needs like lighting when the house battery is depleted. On the surface, it seems like a workable thing as long as loads are kept within reason and the house battery switch is in the off position.

Experiences? Thoughts? Warnings?

The_Rigger

APPROACH WITH CAUTION!

(yes, I'm yelling. Electrical fires are no fun. DAMHIK,IJK,OK?)

Long as you are keeping your loads low, and it sounds to me like you're aware of that, the only thing I can think of that gives me pause is that because you're back-feeding the DC system you will have no fuse protection for the circuit, unless the power bank itself is fused.

And really, the camper's load center isn't really designed to be fed that way, so in addition to lack of overcurrent protection, you might damage the DC/AC interface.

GulfCoast

Regarding "APPROACH WITH CAUTION!", AMEN! and yes indeed.

I think that a 10A fuse on the circuit from the power bank ought to be a given. That's a simple thing to do.

I agree that the potential effect on the load center is a concern. I'll wait for input from someone who has done this before proceeding.

I suppose another option would be tapping into the load side of the house battery switch with a receptacle to plug in the power bank, being sure not to have the switch on when the power bank is plugged in.

MrGneissGuy

Stupid question, but assuming you're speaking of something such as a Jackery pack why not just plug it into the shore power outlet on your T@G? Most of those have 110 plugs and you can get a 110 to 30 amp adapter. I actually hooked one up that way briefly to see if that would provide 110 power if needed and I'm at a site without electric hookup. It worked for the interior 110 outlet (I was testing for the Fire TV stick power). Out of curiosity, I also turned on the AC, which worked, but only left it running long enough to see if it would blow out cold air (it did). I believe I had the house battery off when testing, just to be safe. I've considered doing more testing with the house battery on, to see if it would charge as if it were hooked up to shore power. It would make a nice backup if there's a day without enough sun for the solar panels to keep it charged up.

I doubt one would last very long running AC like that. But if you're just using it for lights, I imagine it would work quite nicely. But I'm not an electrician and could be overlooking something important.

GulfCoast

@MrGneissGuy, that doesn't seem to me to be a stupid question at all. What you describe is a simple and reasonable way to use a portable power bank with a T@G.

Unless the power bank was very large, there would not be enough capacity to run the air conditioner, heater, or other such 120VAC loads for long. I'm looking at 12V loads - lighting, fans, stereo, and USB charging of phones and such. What you described will work for 12V loads, too, but there are significant losses converting the 12VDC power stored in the power bank into 120VAC output to supply the T@G and converting from 120VAC to 12VDC in the onboard converter. But, lossy or not, it's easy to do and doesn't create any significant concerns.

I'm wondering about an equally simple solution to meet 12V loads in the T@G directly from the power bank's 12V output without conversions and losses.

You wouldn't happen to be a geologist by any chance? Rockhound?

MrGneissGuy

@GulfCoast said:

You wouldn't happen to be a geologist by any chance? Rockhound?

Yes, I do happen to be a geologist.