After earlier this year installing a pair of Battleborn batteries in my TT I have been less than satisfied with how they charged from my Tow Vehicle. At first I just tried to charge them from the Charge wire incorporated into the 7-pin connector. Results were disappointing at best. 5-6 amp charge current even if batteries well discharged.
Second attempt, I bough a DC to DC Charger from Renogy (DCC-1212-20) which boosts charge voltage to the 14.6 required to charge the LiFePo's. Not terribly expensive ($127) and I had high hopes. Based on the wire size in the "Pigtail" I figured it would handle the current necessary to deliver a full 20 amp charge rate to my depleted batteries. Result? About 12-13 amp while cruising down the road (as shown on my Smartpone App for my Victron Battery Monitor. Still not seeing the full 20 amp advertised by Renogy.
At this point I had a cruel fact revealed to me. I crawled under the truck and looked at the wires feeding the trailer connector receptacle. IF the largest wire is 12 ga I'll be greatly surprised. If they followed the same wire sizes used in pigtails, the charge and ground would be #10, the Brake line #12, and the rest of the lighting wires would be #14. The supply wires in mine look more like they are all one size smaller.
Obviously my DC-DC charger was being starved of power.
Here are a series of pictures of what I did to solve the issue:
First, some new wiring in the truck----
Wire size -- #8 AWG and Circuit breaker -- 30 amp. Wires encased in some "Wire Loom" and zip tied to the main loom that runs from just behind the battery, along the frame, to the back of the truck. #8 wire was largest practical size for my application.
Next, some new wiring for the Trailer:
A 15 foot length of #8-2 Marine wire (heavier insulation than most other paired wires as well as fine stranded for flex)
Terminated with a 50 amp Anderson Connector at wire end with some liquid electrical tape to keep out dirt and as much water as possible. Other end of Anderson connector is secured right next to the regular trailer receptacle so I just plug them both in at the same time.
Wiring inside my "Electrical Compartment" needed some changes too:
The Compartment----
Added larger wire feed to the DC-DC charger:
Output from DC-DC Charger showing "control wire":
Control wire is wired directly to old 12V feed from receptacle which is only hot when engine is running. This turns on or off the Charger, depending on whether engine is running, even though Charger is being fed directly from TV battery. Without this control it would be possible for the DC-DC Charger to run the starting battery down even without the engine running. This way everything works when I run the engine and when stopped, all is off, even if i leave everything plugged in.
I also added a "cheap Chinese" panel mount meter to monitor the input voltage and current to the Charger. It works independent to the regular shunt for my Victron and merely measures the input power so I can compare with the output as shown on my Victron. Only $14 on Amazon so I said "why not". Only need simple voltage/amperage readings with none of the fancy battery monitoring functions so it's adequate.
And now for the results. After all the wiring etc, I backed the truck up, hooked everything up, started engine, closed circuit breaker, and after making sure there was no smoke, read the input meter.
26.7 Amp of Input current at 13.1 volts. or 349 watts.
Actual charging current shown on the Victron Monitor was a full 20 amp which is the max for the unit and wattage was shown as 250 which again is max for the unit. The LiFePo batteries will continue to suck up the power at the 20 amp rate until the internal voltage climbs and it will eventually drop to zero. Voltage at the battery will vary from a low in the 12 volt range until it rises to 14.6 just before current drops to nothing.
It appears that the process of boosting voltage is about 75% efficient but I can live with that. Since most of my driving days are around 4 hours average I will arrive at my next location with fully charged batteries and not have to worry about starting generator or whether or not there will be enough Sun the next day to do the job.
Some notes:
I chose the 20 amp model as my vehicle alternator is a little small by today's standards. Only 130 amp and I didn't feel like paying $600 for a larger, 225 Amp one. Renogy does offer a 40 amp unit that would be ideal for those with larger alternators and larger battery banks.
This work was done on a Tow Vehicle and Travel Trailer. For those who have Motorhomes the principle is the same, just the wiring is easier as no Anderson Connectors and extra wiring would be needed. A simple pair of wires from Starter Battery to charger location (Renogy specifies not using chassis ground for a common/neg connection).
Remember, this was done for LiFePo batteries but similar benefits can be obtained by those who want to fully charge their batteries from a Tow Vehicle or Motor Home Alternator. Newer vehicles are especially difficult to have them charge "Auxiliary" batteries as many incorporate a current sensor (shunt) in the battery's negative connection on the starting battery. Once the starting battery is fully charged, the alternator's output if reduced to prevent overcharging and also free up horsepower that would ordinarily be used to turn the alternator under load. This is the main reason these DC-DC Chargers are becoming popular in the RV industry. (For those who need a regulated power supply with steady voltage output, these work great for that as well. Output voltages can be set with various DIP switch settings to keep electronic gear from being exposed to low voltages from a battery or high voltages from an alternator)
I chose to re-purpose the small compartment at the front of my Travel Trailer as a dedicated electrical compartment. Batteries are inside and out of the hot/cold environment. Connections to many of my added accessories are made to Bus Bars and ALL power can be disconnected with the turn of one switch. Compartment was pretty much useless before as it was too small for a tool box but is proving to be just right for what I'm using it for.
Now that this project is done I'll have to think about what next. Who knows, maybe I'll tackle the "Spaghetti Bowl" of wires behind my power distribution panel and make it look more like the wiring on my old boat. Everything to a series of terminal strips with labels, then into the power distribution panel. Right now it looks more like a wire scrap box in the back of an Electrician's van.
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2018 Surveyor 264RKLE
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