Well, I ran a test with the new Tow Vehicle (TV) to Cargo Trailer Conversion (CTC) charging system which is basically a continuous duty relay to switch the TV Alternator circuit to the CTC Battery Bank through 6ga wires and automatically disconnect when the TV motor is shut off. Of course, all the proper fusing and etc. in place. (Note: TV is an F150 with a 225A Alternator and CTC Battery Bank is ~430Ah @ 12VDC).
Conclusion for my Truck and Battery bank: it works great, and I see no need to spend $278 on a DC to DC Charger since this is just a backup mode of charging for me.
Caveat: I will have to keep an eye on the TV battery and make sure it does not get overcharged when I use the system. I’d expect in a longer run of the system, the Alternator voltage would begin to drop. I will test that on the way to Daytona. We will see if the Alternator will regulate to a float charge with both the TV and CTC SOC at near 100%.
Summary/Details: I will provide some data below by way of screen shots on Victron Monitor; however, note that I started with a State of Charge (SOC) at 84%. I shut everything off for the test, but prior, to get to 84% SOC, I was running everything in my CTC (All lights, fans, radio, inverter, Television, etc.. ) except the microwave and Air Conditioner. The CTC would only draw 22.3A. It would have taken a very long time to get the SOC lower at that rate and I figured this would be a good test in any case. Today, the AC compressor would not run since the temp was in the mid 60’s , so I'd run the microwave intermittently for 2 to 3 minutes at a time and get -118A draw on the batteries. Needed to do something to draw down the SOC! The bank of 4 Duracell 6V Golf Car Batteries seems robust.
Initial charging startup current was 34A. I realize that if the SOC was lower, the circuit would draw more current, but from what I saw with a 1.6 VDC drop @ 34A (54.4 Watts dissipated) from the truck to the CTC, the total line resistance (6GA wire @ ~25ft total plus common ground return, Connector contacts x3, Bus Bar Connections, etc.) will self-limit the current from the TV alternator based on CTC battery voltage and total series resistance.
I will try some day with a lower SOC like near 50%, but I suspect, I will never exceed the 50A I set as a max continuous current based on the gage wire I selected. For completeness and just to be sure, I also switched in the Solar Panels for a few minutes while I had the TV charging to see how the system balanced outputs. It did about what I expected.
Each system equally contributed (very close to equal) and I was getting a 46.3A charge. The sun was good here today and I would easily get 24A from the panels even though they are dirty.
Note, the fact that the battery took 46.3 A with the Solar and the TV charging , it reinforces or adds credibility to the assumption that the TV Alternator and line resistance is limiting the charge to the 34A and that a lower SOC would not result in significantly higher current. The alternator has the capacity to provide much more and would if it was not being limited/regulated. So here are the screenshots from my Smartphone and Victron App with two phone camera pics at the end:
CTC Battery Bank initially drew 34.0A from the TV when turned on with 12.8VDC on CTC batteries and 14.4VDC on TV battery.
15 minutes latter the CTC Batteries built up to 13.28VDC and current went down to 23.9A and TV voltage remained at 14.4VDC.
After 30 minutes… charging away … decided to end the test as it would just be an hour or two at that rate and the Batteries would recover to >90%. The last 10% could take a while. I was most concerned with the max current as I noted in previous post.
I also wanted to see that I would get a decent rate of charge. A Sterling 1230 or CTEK 250S DC to DC charger would only give a max current of 30A, so neither would charge faster in this case. So absolutely no benefit there.
Here is a pic of the TV and CTC plugged in together and the photoshopped Tag for anonymity. It is time for a new tag. It is getting worn out.. I think maybe next year.
Here is the relay bottom right in pic with TV battery and 75A Blues Seas fuse on terminal in view on top left of pic. I did note that the terminal fuse was ambient temp to touch and the connectors in rear were the same. No discernable heat from either.
I did take some temp readings with my infrared thermometer and the Alternator never got above 166F which is close to what it normally runs and relatively cool from what I understand. The continuous duty relay maxed out at 104F. TV Battery 97F (warm under hood) and CTC Batteries never got above 76F the whole time.
The fact that the entire circuit only dropped 54W at peak current of 34A with the battery absorbing 438W, the system charged @ 89% efficiency. Not too bad especially since the alternator has plenty to spare. I do expect the efficiency will go down if I start with lower SOC because the line resistance is fixed, but it also gets better as the SOC increases and charge current decreases. It was at about 93% when I ended the test.
Not a worse case test, but is representative of "typical use", so for now,
I am going to call it good! More later on the TV Battery and potential for overcharge. I will figure that out next and also let you know how it goes whenever I get a lower SOC and have opportunity to test further. In any case, this is first hand data for me and I am absolutely convinced this is adequate for the intended purpose. I am sure there will be some theoretical arguments against a perfect standard, but this works good enough for me with the exception that the jury is still out on the TV battery SOC over a longer use. I can see nowhere else where there is risk of harm and the performance is there.
by Lanval » Mon Feb 11, 2019 7:40 pm 
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