Charging

[Learjet]

One of the factors to consider here... is that the ECM on the truck controls the charge rate, or charging voltage... Its common for a new truck to have batteries that are never fully charged... if you remember that charging voltage used to be 14.2-14.4 and you'd need to check the water level in the batteries at a regular basis... today's modern trucks with the ECM controlling the battery charge and a temperature gauge under the batteries assures that the batteries are never really fully charged, and in some cases batteries go years and you don't add water...

What this means for us that tow, and dry camp for a couple of days is that our trailer batteries are never really much more than 75% charged, at least that is the way mine are... I often run a static voltage test and have wired in a digital volt meter check that regularly..

I've worked hard to look for and repair any connection that won't pass a voltage drop test.. but I can't see where a 6 or 8 gauge wire from the alternators to the RV would help until I get the charging voltage up where it needs to be...

I've even gone so far as to look into a buck boost... a device that will raise the 13.5 vdc at the alternator to 14.4 at the trailer batteries...

Any thoughts would be appreciated...

You could put an inverter in the truck, then run a converter set to 14.4 volts to charge the trailer batters from the truck.

 

[ntsqd]

I've seen that done on the tiny trailer & tear-drops forum, but the inefficiency of the scheme is appalling.


OTOH, this is nothing different than the high voltage transmission lines. Step up the voltage to decrease the amps transmitted. Conductors can be smaller without heating them (further Voltage Drop inefficiency) due to the high current.

 

[Bob4x4]

Maybe in your world, or while the battery is being charged. I just checked 8 relatively new, good 12 volt batteries. The three in my two pickups, the three in my boat and the two in my RV. The highest any of them read is 12 volts, the rest were 11.8 or 11.9
However, if it makes you happy I changed my post to read 13.

You can do a web search and find the levels for a fully charged battery.Yours are all discharged below a good state of charge.

 

[Bob4x4]

I always thought that when my 2014 was attached to the 5th wheel and I was connected to shore power the truck batteries were being charged too.

Recently I decided to check it out. I put my meter on the trailer batteries and they read around 13.5 volts. The truck batteries read a little over 12 volts. I was disappointed because my older trucks used to get charged from the trailer.

There must be a relay or diode or something because I wasn't getting a charge from the trailer.

The oem wiring is too small to effectively charge in either direction.Most trailer convertors only allow a percentage of their rating for battery charging.In my trailer the oem convertor (45a) only allowed max of 15a.That is no where near enough to make a dent in over 200ah s worth of batteries 20 ft away through the small wiring

 

[Ozymandias]

The todays solution for Trailer or Camper Batterys is a B2B Charger, that is the only way to keep a Trailer Battery 100% fully loaded.
Every other solution will fail this goal because of the voltage drop.

I have a 90A B2B Charger in my camper, so even a short drive is enough to charge the batterys fully.
http://www.votronic.de/index.php/en/products/charging-converters

 

[Bob4x4]

The todays solution for Trailer or Camper Batterys is a B2B Charger, that is the only way to keep a Trailer Battery 100% fully loaded.
Every other solution will fail this goal because of the voltage drop.

I have a 90A B2B Charger in my camper, so even a short drive is enough to charge the batterys fully.
http://www.votronic.de/index.php/en/products/charging-converters

Interesting solution,but would require wasting fuel to charge while boondocking any length of time.For my application solar is the better solution

 

[ntsqd]

The todays solution for Trailer or Camper Batterys is a B2B Charger, that is the only way to keep a Trailer Battery 100% fully loaded.
Every other solution will fail this goal because of the voltage drop.

I have a 90A B2B Charger in my camper, so even a short drive is enough to charge the batterys fully.
http://www.votronic.de/index.php/en/products/charging-converters

Disagree. I've outlined what I did above. Camper batteries were always at 100%SoC (according to the TriMetric camper battery monitor) after the day's drive.

Interesting solution,but would require wasting fuel to charge while boondocking any length of time.For my application solar is the better solution

Not to mention an alternator's output at idle is rather dismal. Agree, adding solar made charging off the alternator only necessary in emergency situations. See the Handy Bob link above.

 

[RBridenbaugh]

I re-wired both the truck side and inside the slide-in camper (TC) with 2 AWG wire to have charging from the truck alternator to the TC while driving. TC converter / batteries could charge / jump the truck batteries with addtion of a jumper cable inside the TC, if the truck batteries got discharged by accident. Went with 2 AWG because of the size of my battery bank, 440 Ahr, for winter camping. The truck batteries are isolated from the TC batteries and vice versa using Power-gate, high current solid state relays after the alternator. No voltage drop, even at 80-90A of current during bulk phase of charging.

Only modification I made was the addition of on/off switch inside the TC to prevent over charging / ruining my AGM batteries by the alternator, when driving long distances in the winter. Found that with the fully charged TC batteries, inside the warm TC, the truck alternator would put out a temperature compensated 16.1 VDC due to the cold outside temperature, while the warm TC batteries where expecting 13.4 VDC during the float stage.

Pulled fuse 19 (truck battery power to the 7 pin connector) the first time truck batteries discharged due to TC loads when I just parked it in the garage and didn't plug in the TC.

 

[Loren]

I usually disconnect the trailer also, but more than once I forgot to pull the plug and never had the batteries discharge.
Larry

Interesting, Larry. I usually have done the opposite, which is worse. I unplug the connector and then forget to plug it in again when I leave the next day. I would catch my error the first time I stepped on the brakes.

I now take steps to prevent this, but I’ve done it several times in the past.

– Loren

 

[Ozymandias]

Sure Solar ist the way for boondocking, but i thought we talk about charging from the vehicle while driving. I got 500wp on the roof.

 

[Bob4x4]

With a good solar system,charging from the vehicle is pretty much a moot point unless you have really bad overcast conditions.

 

[Larry Willard]

Interesting, Larry. I usually have done the opposite, which is worse. I unplug the connector and then forget to plug it in again when I leave the next day. I would catch my error the first time I stepped on the brakes.

I now take steps to prevent this, but I’ve done it several times in the past.

– Loren

I have caught myself forgetting too, but I always do a walk around check each morning and at stops during the day checking lights, looking at all tires and underneath and apply brakes as I pull out to make sure all is working well.

 

[ntsqd]

With a good solar system,charging from the vehicle is pretty much a moot point unless you have really bad overcast conditions.

This! Although I think it worthwhile to build the alternator based charging part of the system to be capable just for those times. Belt AND suspenders.