TV charging for T@B 320 12v battery

scaup

We just got back from dry camping with our T@B 320. Really sunny and hot so the Zamp solar kept up with charging the single 12v RV battery. When we left the battery meter in the T@B read 11.7 v. On previous trips without sun we had thought the TV, 2015 Ford F150, would recharge the battery. On this trip we looked at the T@B battery meter when we got home and it was basically unchanged. The last time in I had the TV in the shop I asked them to verify that the charging pins on the 7 pin connector were working. They said it was working.

We checked on the internet about TV charging and they said because of the distance between the TV alternator and the T@B battery, it was useless to expect the TV to charge the T@B battery. The best we could expect was maintenance, not recharge.

Looking on the internet we saw a DC/DC charger, the Redart In-vehicle BCDC single input battery charger. Does anyone have experience with these after-market TV chargers?

Another question.......why is the consensus to change to 2 6v batteries instead of just adding another 12v battery?

Thanks and please be explanatory with your answers and I know nothing about DC power.

Gene 

webers3

I think before you decide to swap out batteries you need to find out why your TV is not charging the battery you have. The internet post about alternator being to far is false, unless you have a wiring issue from the alt to your 7 pin. I have a 320 and never had an issue with my TV recharging the T@B battery. Get a 7 pin tester to verify, but even before that your battery meter should show 13+ volts when you have the TV running and T@B connected via 7 pin, if not then you need to troubleshoot your 7 pin and or the converter

pthomas745

Not every vehicle is capable of charging the trailer battery. Some do, some don't, some do a little, some a lot.  There is no one single answer.

We need to know: what trailer?  What year? What size battery?  What fridge?

And: what other device do you have to monitor your battery?  Any device that measures voltage will always (always always always) produce false readings if: the battery is being charged.  Or the battery is "in use".

The only way to get a relatively accurate reading of voltage is with the battery switch off.  Which rules out the battery monitor in the trailer. 

Your battery voltage may be better than you think.  Have a multimeter?

pthomas745

Threads about the tow vehicle and battery charging.

https://www.google.com/search?q=vehicle+charging+battery+site:tab-rv.vanillacommunity.com&client=firefox-b-1-d&sxsrf=ALiCzsZ3Na7haruxk3FKul_zx5I2-o8fDA:1660321566009&ei=Hn_2Yv8OoM6Q8g_ttJfoAQ&ved=0ahUKEwj_lZ7p28H5AhUgJ0QIHW3aBR0Q4dUDCA0&uact=5&oq=vehicle+charging+battery+site:tab-rv.vanillacommunity.com&gs_lcp=Cgdnd3Mtd2l6EANKBAhBGAFKBAhGGABQuQlY4TlgwUFoAXAAeACAAZMBiAGrGZIBBDM1LjOYAQCgAQHAAQE&sclient=gws-wiz

Grumpy_G

Before you go all out and throw money at the problem make sure all the basics work: Power from the tow vehicle, wiring from the plug to the trailer battery (both positive and negative side), do all the trailer lights and the trailer brake work. 

Voltage drop over longer wire runs can cause slower charging but rarely no charging at all. A DC/DC converter can't defy the physics of the wiring limitations, voltage x current is the same on both sides (minus losses in the DC/DC converter). 

Denny16

Also, most newer vehicles, SUVs, PU trucks, etc, have alternators that reduce their charge rate at higher engine rpm’s normally encountered with towing a RV trailer.  I discovered this with my new Jeep Gladiator truck, the alternator reduces its charge output at higher rpm’s, and has the higher charge rate a lower rpm’s.  My mechanic said most newer vehicles work this way now.
 Cheers 

JeffroNC

My 2017 F150 smart alternator was outputting 13.2 volts after the battery was charged. Not enough to charge the trailer batteries.

I installed a Victron DC DC charger in the bed of my truck wired to the vehicle battery with 8ga. Ran a pigtail out to the bumper with an Anderson connector. Next, I removed the wire from the 7 pin at the junction box in front of the trailer and ran 8 ga power and ground to a pigtail which I plug into the truck.

The weak link is the run from the junction box to the batteries in back of my 400. One day I will complete the run with 8 ga to the battery terminals. (Maybe :-))

I went from 2-3 amps up to 20-30 amps trailer battery charging according to my shunt. The DC DC takes in the 13.2 volts and boosts it to 14.7 to charge my lithiums. The other day I went from 60 to 92% SOC after a three hour drive. I’m happy with that.

MarkAl

I hesitate to add to the above as it gets into a rabbit hole but the alternator output is designed to charge the TV battery in a very simplistic manner: to recharge the lead-acid battery from the starting load then maintain voltage for the accessories. On the trailer our converter and solar controllers have a more sophisticated charging scheme of (for lead-acid): 3 charging states: bulk, absorption and float. DC to DC converters generally can supply lots of current at a higher voltage ... always. On a long trip this may hurt your battery by overcharging. The problem is different and simpler in the case with a Lithium as they have a built in monitor that limits the damage if higher voltages are delivered. BUT remember the higher charging voltage with lithium and solar charging and if driving it will attempt to charge your TV's lead acid to higher than desired voltages...

A solution I've considered but requires some rewiring of the trailer is to disconnect the TV to Trailer battery 12V connection on the 7 pin.  Then use a DC-DC converter set to 20V and run it directly into a solar controller THEN to the trailer's battery bus. Since my solar is managed by the Victron Smart Net, this would allow maximally efficient charging while driving and getting solar input and TV input. This also isolates the TV's lead acid battery from the state of charge and chemistry of the trailer system.

(updated) I got off my butt and ordered the Victron Orion 12/24-8 DC-DC which is 12V in and 24 out at 8 amp max. I have a remote solar port that I sometimes use while driving and the panel in the rack on back. I decided it was easier to limit the remote use to camping and use the controller or this application. Since my controller is limited to 16 Amps into the battery it will max out my controller. Also since I'll plug this in only when not using the remote panel, there will be no conflicts. This may work well enough if not I'll get a larger capacity DC-DC and a separate, higher current solar controller to really pump out current. My Jeep has a 225 amp alternator so I can go up a ways. When I move to Lithium, I'll need to isolate the TV output and the trailer.

(updated again) RIGHT BEFORE I started to wire this in I found a possible wiring problem and to check for a solution (where else) TaDa the internet! Duh, the Victron site doesn't clearly describe a class of DC-DC converters that also have a battery charger - I returned what I bought and got a Orion "TR Smart" Non-Isolated DC-DC converter. This eliminates the issues I had with a straight only DC-DC converter. In addition can be configured for Lithium or conventional and isolates the two system's potentially different charging states. Now it's only find a place to put this in series with the TV output 12V and into the J box. This will now combine with the Victron BT network and give me status while driving (I hope).