Charging House Batteries while Driving

cewillis wrote:
The warnings about a small charge line are important. To get a full charge, heavy gauge wire and a non-limiting solenoid/relay are needed. You said you have a diesel, but not which brand. Here's what I did in my GMC (charge wire is 2 gauge). Something similar would probably work in other trucks.

cewillis wrote a good common sense article at Truck Camper Adventure on this subject.

The thing I am most curious about is how you got that percent sign in the last sentence past the censors :).

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%).

rickst29 wrote:
This Thread contains several misconceptions. For simplicity, I'll discuss SLA Batteries in a typical "Trailer"...
{snip}
... there's another scheme which works really great. (I will write up my configuration, and insert a link from here when my new Thread is finished).

Good lead in- I'm on the edge of my chair....:R

I'll add to a OPs several month old question, that pretty much was already answered by others. Our truck does just fine, ok minimally, but recharged 2 group 29s in the camper and its own 2 batteries with a few hours on the road.
And that was using factory auxillary charge wiring-but it all depends. Ive since added an auxillry charge line to offset 12v refer use, plus solar which is also adding.

rickst29 wrote:

13.8V is basically a "float charge" Voltage, incapable of pushing significant power into discharged batteries.

If you get 13.8V at the camper battery terminals, and the camper battery is at a low State Of Charge, it will accept plenty of current. From about 80 percent SOC up, it will be significantly slower than if it were 14.4V, but it will still get there.

If you have solar (and sun), you are well served by providing the bulk charging with the truck or line charger, then letting the solar finish up the long low current tail of the charge curve.

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

I don't know ... why? :) It seems to me that his good information will be forthcoming in a new thread.

I was curious since the post came out of nowhere as a driveby. It's the poster's 5th post in the last 3 years. Maybe he'd post more if people hadn't been giving him a hard time, or maybe he hasn't been given a hard time and is selling something.

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

jimh425 wrote:

rickst29 wrote:
This Thread contains several misconceptions.

It was also finished a few months ago. ;)

Why give someone a hard time when they are providing good information?;)

rickst29 wrote:
This Thread contains several misconceptions.

It was also finished a few months ago. ;)

This Thread contains several misconceptions. For simplicity, I'll discuss SLA Batteries in a typical "Trailer", combined with a fairly capable TV "Pickup Truck" which contains typical "towing package" wiring.

Here's what the Batteries need: Voltage. Without sufficient Voltage to push power into the Trailer Batteries, it will take too long to charge them. But, from our "capable Pickup Truck", even with "50A wiring" and a big alternator spinning at highway speeds, the voltage will usually be too low to have much effect on the Trailer Batteries.

Vehicles "Sense" the Truck Battery Voltage by using an alternator-mounted charge controller, or by using a computer external to the Alternator (which sends an adjustment signal to the Alternator).

Just a minute or two after starting the truck and running the Alternator at high output Voltage and Current, the starting battery becomes fully recharged - and the "Sense" logic will detect this, reducing generator output to create an operating Voltage of 13.5-13.8 Volts. The Trailer problem is this: the TV "Voltage Sense" process is dominated by the situation under the hood of the Truck, with hardly any awareness of Trailer Battery State.

13.8V is basically a "float charge" Voltage, incapable of pushing significant power into discharged batteries. Unless the cables are made large enough to drag then entire TV electrical system down to Trailer Battery Voltage, TV Voltage Sense will "see" no need to increase this Voltage. (Such wires would be huge and costly, and better workarounds for towing situations.) But you CAN use this method in camp, if you can move your truck into a "jump with booster cables" distance from your Trailer House batteries: With really good, thick booster cables, your Truck's electrical system will get dragged down to the Voltage of the Trailer batteries - and the Alternator will respond appropriately.

You can also try to improve matters, on the road, by creating big electrical loads in the Truck. Turning on the Stereo, AND the headlights, AND running a 12V Fridge (all together) will typically create a Voltage Drop which provokes "Sense tuning" to reconfigure the alternator into a high Voltage, high Power configuration. And the Trailer will benefit from the increased Voltage.

(Short aside: Alternators adjust output power by moving the non-spinning magnets slightly up or down near the spinning armature, causing a bigger magnetic field, which creates more resistance to armature rotation. More "work" done by the armature == higher power generated.)

Another low-cost alternative, if your alternator contains the Voltage Measurement in its controller (and does not depend on an external computer), is to clip a Diode (A ceramic diode, not a Shotke) into the Voltage Sense wire. The Diode will cause a Voltage Drop of about .5V along the wire, and the Alternator will imagine your Truck Battery to be significantly discharged - al the time. (But obviously, this will cook your Truck battery if left in place all the time.)

Actual "Solutions" use Voltage Boost, and (sometimes) Solar Charge Controllers to convert the boosted Voltage back downwards, according to the Trailer Battery SOC. Purpose-Built devices by Redarc and Ctek, installed just in the Trailer, do a good job of charging Trailer batteries (with proper Voltage levels), with no mods to the Truck. 13.5 Volts, or even less, comes in on the Bargman cable and gets boosted for battery charging. The only problem? They are quite expensive.

But for cheapskates who already own a good Solar Controller, there's another scheme which works really great. (I just wrote up my configuration, and here's the link: http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/28839758.cfm

This thread has a ton of good advice, but not much you can use until you first try it with *your* rig.

Let me put it this way... You *should* be just fine. Running the furnace overnight should not deplete the battery so much that the next day's driving doesn't bring it back up to full. If, however, you have problems on the trip, then there is a bunch of good info on this thread with which to start troubleshooting.

The only advice I have is separate from your question, but related: If you bought your camper used, take a good check at the battery. When we bought our camper used, the dealer assured us the battery was in tip top shape. It barely made it one night in cold weather. I replaced it with a Trojan battery in 2007, and it has been rock solid ever since. I credit annual maintenance and storage in a heated shop to its longevity. If it is used-new to you, well, no one sells stuff because it works 'too good'.

HTH!
-Eric