I posted an epistle to this topic a few days ago - here it is again.
Voltage is not what you are looking for - to charge batteries, you need amperage. The voltage can read 14. 1 but you still can
have very little amperage flowing to the trailer due to small factory wiring in the truck. Here's what I did. Run 8 guage
wire from the battery through a 30 amp automatic resetting breaker, then through an isolator, back to the trailer plug. With
my batteries down 50% (around 12. 1 volts or 100 amp hours) I can get an initial charge of around 15 amps which will restore
most of what I lost over the past night in 6-8 hours of towing.
I do a lot of dry camping and I use 2 6 volt golf cart batteries which provide around 210 amp hours of capacity.
If you are using the batteries hard, you will need to charge the trailer directly from a generator hooked to your shore
power. Your trailer power convertor should be capable of charging the battries at around 40 amps. I can recover 95% of a 50%
- 60-% drain in around 4 hours of charging.
For charging, I use a 1800 watt Coleman Powermate generator which is excellent for battery recovery. Do not try to run an air
conditioner or microwave oven on a generator this small.
If you are a serious dry camper, you need a computer in the trailer that will tell you exactly what is going on with your
batteries. I use the Trimetric from Backwoods Solar. You can get information on this device at:
http://www.backwoodssolar.com/Catal...#Meter Basics
This web site has a wealth of information on living independent of shore power. I have found their products, service and
expertise to be among the best. Check them out and happy dry camping.
I charge on the road when I am travelling. When I am dry camped at a race, I can run my system fairly hard (furnace, power
vent and inverter for TV/VCR) over a 24 hour period then charge for 4 hours daily with the generator.
To keep your batteries in top shape and to maximize their life, you will also need to equalize them regularly.
One final thought - I expected to receive more amperage to the trailer when the truck was running after my direct wiring
upgrade. After all, the alternator is capable of producing 200 amps of DC power. I thought my wire size was adequate to the
hitch plug - I've since found per wiring specs, it could have been 1-2 sizes larger. However, the mechanic at the RV dealer
told me that larger wiring in the truck would have been a waste of money because of the size of the wiring in the trailer.
Like everything else, you are always limited to the strength of the weakest link in your chain. Kind of like a big garden
hose carrying high pressure connected to a small nozzle.
Fact is that neither the truck or trailer manufacturer anticipated many dry campers trying to use their trucks to charge
seriously depleted trailer batteries. Just look at the size of the wiring to your truck batteries compared to the size of the
DC supply in your trailer.
With large enough wiring thoughout the system, you cold just hook the trailer to the truck and allow the truck alternator to
do the work while you sat back and enjoyed the sweet idle of the CTD.
Good luck and happy dry camping