Solarman:
secondly, I DID give you an example of typical losses, but you either missed it or choose to ignore it ?
Seems I got off on the wrong foot here, so I apologize. I neither missed nor ignored it. I thought rather that I had failed to communicate my thoughts accurately to you, and that would of course, skew your answer. Please excuse any impression of criticism that I may have given. I am here to learn.
the "converter" you talk about that is in virtually every RV as you describe IS a buck converter it down converts a higher voltage to a lower one.
This may have been my failure. I was under the impression that a buck converter is a DC to DC device that, according to Wikipedia, uses electronics to switch a DC source on and off rapidly into a single-coil choke (or capacitor, or both), effectively dropping the voltage seen by the load and smoothing out the square wave generated by the high speed switching. Is not a typical RV converter an AC to DC device, using a two-coil step down transformer to reduce the voltage, and then rectifying that? From my days (now many years ago) in high school electronics, I was under the impression that an AC transformer can be very efficient, perhaps better than a buck converter? That is why I felt I may have thrown a wrench into your calculations.
thirdly, the cost was mentioned, it is implied in the inverter/battery and panel increase.
Again, my lack of deep knowledge here may have gotten in the way. In my simple little brain, I didn't see a need to change a panel, but rather to just use what is already there. I already do that on our unit, simply plugging the trailer into the inverter (after unplugging the converter), and making sure the fridge and hot water tank are on propane-only operation.
As to batteries, I was trying to grasp and apply what you had already told me in another thread regarding the inadvisability of paralleling batteries to gain capacity. IIUC, 4 x 12v batteries in series is preferable to 4 x 12v in parallel. Again, I use this only as an example, not suggesting that 4 x 12v is a good choice of RV battery bank. Just trying to grasp some principles here.
I do see the need for a higher voltage input inverter, and a possible increase in price there.
fourthly: you will STILL need a means of charging your high voltage battery pack on those occasions when solar fails due to inclement weather.
Point conceded.
and lastly, battery size is defined by your expected watt/hour usage over a 24 hour period AND the number of days spare capacity to cover cloudy days
Agreed. As noted above, I was just trying to come up with a simple example, and was not suggesting a formula that should be followed.
The whole reason I started this thread is because I was reading elsewhere about how people have put in hybrid 12v / 48v systems, and to power the 12v lights and 12v propane appliances, they used small buck converters for each device, or string of devices. That looked unnecessarily complicated to me. The wiring in the RV is already there, and sized for the appliances and lights to run at 12v. Why run that wiring at 48v, only to step it down for each device?
In the final analysis, it may well be that 12v is just plain and simply the best overall solution for an RV. This thread had more to do with any theoretic advantages. 12v has wiring and resistance limitations as we all know. I was just exploring a possible alternative that also avoided the multiple small buck converter issues of running trailer wiring at more than 12v.
So, again, my apologies if I gave the impression of ignoring you. That was NOT the case. I just thought that I had misinformed you.
Frank.
