....CONTINUED FROM ABOVE.....
Why? Several reasons:
1) it's plug-and-play. You mount it to the wall, connect the wires, and you are done. No rewiring the TV or TM
2) It's a 3-stage charger, and thus a more elegant charging solution. It seems silly to spend $400 or more on batteries only to abuse them by ramming power into them.
3) It's basically the same price
4) If I switch TV's, it remains in place. No need to rewire the new TV.
5) If I purchase a new TM, I simply disconnect the wires, unmount it from the wall, and reinstall it in the new TM. No need to rewire the new TM.
6) No extra connector to connect when hooking up the trailer
The only disadvantage I could think of is that the charging rate would be significantly less than 23-28 max rate I was using in the above calculations. A big disadvantage, but I decided it was worth the tradeoff.
DC-powered 12v battery chargers that supply any decent current (> 10 amps) are hard to find. I eventually found one made by a company in Australia. It had a max output of 20A, which meaned the max rate I could expect to charge the batteries at was 10A with the fridge on. One of their techs also said many of these units can also put out up to 22A, so my charging rate could perhaps be as high as 12A. It also had a fused input at 30A, which was good because that the charging circuit in my TV also happens to be fused at 30A, and that meant I did not need to modify the TV wiring at all.
Before I installed it, I inspected the wiring running from the fridge to the DC distribution panel -- as suspected, it was only 12 AWG. With the batteries fully charged, I was getting a 1.2v drop at the fridge. To maximize current flow to the fridge, I ran 8 AWG wire (positive AND negative) parallel to the factory wiring, which runs under the kitchen sink and bathroom floor. That reduced the voltage drop to 0.5v, which I think is a significant improvement. Interestingly, it still draws the same amount of current, so I presume that means it is consuming more power, and thus will get warmer and make the fridge cooler. Time will tell. I have a Dometic fridge, but for those with newer TMs who may have the Norcold fridge, take note: the Norcold service manual provided by forum member Rickst29 and posted here:
http://www.trailmanorowners.com/foru...ad.php?p=67910
...specifically states on page 5 that the minimum input voltage is 13.5v and that "Operation out of these limits may damage the refridgerator's electrical circuit parts and will void the warranty."
I have no idea how they can reasonably expect that kind of voltage in a trailer, even when connected to a vehicle with a charging circuit. I am not aware of a 12v battery that has a voltage of 13.5v, especially under a 10A load.
I haven't used the charger much in our typical camping routines yet, but from my initial testing, it works ok, but not quite as well as I had hoped. With the fridge off, the max charger output I have measured is 17A. So with the fridge on, I should be getting 7-8 amps to the battery when the charger is in bulk charging mode, but I need to do more testing. I'm not positive why it isn't at the full 20A output, as the batteries were at ~50% state of charge....unfortunately, I didn't measure the input current at this point, but my guess is I was close to the input max. I had taken a reading at one point where the output was 13A and the input to the charger was 19A -- that's roughly 70% efficient overall taking wire resistance into account, so a 17A output may mean it was drawing 24A (@ 70% overall efficiency). With a 30A fused input, the input max is probably real close to 24A, so wire resistance is again probably the ultimate limit here, as the unit's efficiency is supposedly ~95%. Once I have more time to work on it, I'm going to consult with their tech, who is responsive to both emails and phone calls, and make sure there isn't something amiss with the unit's sense wiring or anything else.
More info on the charger is available on their website:
http://www.redarc.com.au/products/pr...rt-start-bcdc/
The AUD$495 price listed on their website is for Australia customers. They charged me AUD$300 + AUD$80 shipping, and delivery only took 3-4 days. With the 3% currency conversion fee on my credit card ($10), the total cost was ~USD$340. The unit is small -- about the size of a regular pack of hot dogs (the ones pictured are bun length -- I hate short dogs), and weighs about a pound. I have it mounted to the side wall in the rear compartment directly on the aluminum, as it does get rather warm during operation.
It also appears weather resistant. Being a gadget guy, I took it apart as soon as I got it and immediately noticed that the entire circuit board was dipped in some sort of soft squishy plastic. There are no exposed electrical components. It is in fact designed to be installed in an engine compartment, so it should be fine installed on the exterior of a TM for those folks with batteries on the tongue.
Dave