Charging House Batteries while Driving

jimh425 wrote:

Bob B wrote:
Why give someone a hard time when they are providing good information?;)

Time will tell, and if the poster feels I was giving him a hard time, then I apologize to him.
Oh, and this is the thread he was referring to. https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/28839758.cfm

Thanks! I feel that your points ("thread is old", "he doesn't post much") are both valid. I hang out, fairly often, at a forum dedicated to the specific "hard-shell pop-ups" of the type I own, and hardly ever visit here.

(Long and slightly OT reply mixing multiple topics).

But I feel that this "new invention" scheme (charge batteries using Boosted TV Voltage, later cut back by the Trailer's Solar Controller) is appropriate for a much wider audience, so I visited here again. My design is a bit like running a 120VAC line from a TV-mounted Inverter, back to the Trailer's inverter: But it involves the Bargman cable you already have (rather than stringing a new cable at dangerously high Voltage), and it has extremely low power loss (compared to at-least-slightly losses inverting to 120VAC, and big losses converting back to "12VDC"). And finally, the battery management capabilities of many Solar Controllers are superior to those found in most (not all) Power Converters. Heck, my own Converter doesn't even have a battery-mounted BTS.

I'm not sure how "charging house batteries" ended up inside of "Truck Campers", but a lazy search popped up this Thread, rather than others, and some of the earlier comments are incorrect. If you've got a Trailer Fridge running 12V electric during your travels, and temps are high (causing the Fridge to run the heater almost continuously, then the "house batteries" will typically get pulled down to about 12.6V before "significant" power gets pulled form the TV.

The wire distance back to the TV hood is very long, OEM wires are very thin, and Voltage Drop on that path makes it less attractive (electrically) than pulling from the "local batteries" - even if they have lower Voltage readings at the terminals. The lower Voltage Drop along the "local" path enhances the attractiveness of the less-charged Trailer batteries, even with just a small proportion of the 11-13A amps used coming from the TV. (Norcold N300 as the example, and unit I worked with in the past.)

A no-load Trailer can charge batteries, very slowly, from a "13.8V" TV. But put in the big electric load of the Fridge, and it becomes a losing proposition - the TV electrical path won't protect the house batteries from discharge until they've reached fairly low SOC (for SLA, around 60-65%).