No worries about the "alternator +" lingo. Things get lost in translation on forums (this one and others) all the time.
It's nothing to do with the forum: just the nature of written communication.
As long as the PV (i.e. the terminals on the DCC30/50S) to which a solar panel would normally be connected to "see" power, true, that power source will be primary, and have as its primary mission the task of charging the house battery (middle of page 15 of the manual.)
Yes: the DCC30S will only put out 30 amps max; the DCC50s 50 amps max. This can be provided by one energy source, or split in half if (and by) both energy sources (the terminals for the PV input and starter battery input on the DCC30S) are both energized. And the fact that the PV source comes from my "pedaling a bicycle to produce current" (or your shore charger) and the starter battery input from my "ferret in his exercise wheel" is technically agnostic to the the DCC30/50S.
And yes: amperage is delivered when demanded, provided its present and capable of traveling along the infrastructure (gauge of wires or electronic circuitry of the DCC3050S) of that it travels through.
I can't imagine any advantage to a appliance that demands, say 3, or 10, or 15, or 20 amps, but happens to be connected to a 20 amp circuit, if you catch my inference. As long as nothing bad might happen to the Gopower unit you reference in delivering less than its rated amps: something I suspect it must (be able to) do in the end (of 3) stages of its battery charging, then no harm is likely to occur either.
Noted: the Gopower is a 3 stage charger. Nonetheless I suspect the end stages of charging a battery must curtail power, suggesting the product limits the current in provides at different stages of charge of the battery it charges.
As for the price savings between the Gopower 50 and 35 amp unit, I'd be curious to know if that is also realized in utility bill savings: even is so, likely not much I'd guess.
"And the Gopower has the ability to deliver a fixed output voltage adjustable 13Vdc to 16.5Vdc. So that makes it a dumb charger and to my thinking a good stand in for an alternator."
If you hook the Gopower up to the PV inputs of the DCC30S, when the house battery is fully charged, the power the Gopower provides should be converted by the DCC30S into
trickle charging power for the starter battery. See
Solar Power Input on page 16 of the manual for the conditions and current levels at which this happens.
If you hook the Gopower up to terminals on your
starter battery, the house battery will get charged only if (it needs to be charged and) the voltage on the starter battery exceeds the thresholds under
Alternator Input at the top of page 16 of the manual. Notice that these thresholds are more easily achieved if you run an additional line from the starter battery to the IGN terminals on the DCC30S to make the DCC30S think that you are running a smart alternator--even though you likely don't have one under your hood.
In the case of hooking the Gopower up to the PV inputs of the DCC30S, house and starter battery get charged by the DCC30S' rules, not the Gopower's rules. In the case of hooking the Gopower up to the terminals on your starter battery, we can expect the Gopower's rules to be followed for the starter battery, but charging the house battery will likely be by the DCC30S' rules.
"There is still some trepidation about using the PV+ for the converter. I don't know if there is different circuitry behind that input."
I think the input to the PV terminals of the DCC30/50s is "technically agnostic." As long as your not exceeding any current limits, and providing DC input in the "12V range" (which is usually up to what, 20 volts? for a solar panel) the DCC30S shouldn't care what (relatively clean) power source is energizing those terminals. Personally, and provided it's safe, I'd prefer in your case for the Gopower to input itself into the PV terminals of the DCC30S--more on that below.
"There must be some difference in the circuits from the PV to the ALT if PV trickle charges the chassis battery."
Yes. Plugging your Gopower into the PV terminals of the DCC30S will cause the alt terminals ofthe DCC30S to output only trickle charge levels. While plugging your Gopower on the starter battery terminals will allow up to 30 amps of power to charge the house battery, if the house battery needs charge, and
provided the DCC30S meets the criterion on the top of page 16 of the manual for starter battery voltage. If these conditions aren't met the house battery gets nothing.
It seems to me that hooking your shore power up to the PV terminals of the DCC30S is the best way to go, much as I suggest that you check with Renogy first. Your starter battery should not need more than the trickle charging the DCC30S will provide it after the house battery is charged, provided your starter battery and alternator are in good working order, and you don't tax the starter battery without the engine on, but for engine cranks.
" I'm just trying to think this through and asking a lot of questions to anyone who might have insight to offer. I'm curious to know if you think I'm actually better off with the 35A model. And what you think of my plan to use some sort of transfer switch to disconnect the alternator when I go to shore power."
If you stick with the DCC30S and have no foreseeable greater current usage for the Gopower beyond this discussed scenario then why spend more for the 50amp version? As for your use of a transfer switch to disconnect the alternator when you go to shore power, that idea "loses me" a bit.
Here's what I see happening: If you hook your Gopower up to the starter battery, and you pull into your driveway, I suspect you are going to turn the engine off first. Thereafter you plug in your shore power to energize the Gopower. Why are you worried about your alternator? Worse case you forget to unplug the shore line when you start your engine in anticipation of travel. What bad may happen--pulling the shore line you forget to disconnect notwithstanding--electrically speaking.
And if you hook your Gopower up to the PV terminals on the DCC30S, you are at most trickle charging your starter battery. There's nothing wrong with that (its just superfluous) with the engine on. And with the engine on the starter battery isn't going to charge the house battery unless all the conditions on the top of page of page 16 of the manual are met, AND, the house battery needs the charge.
Suppose you just pulled in your vehicle into your driveway and somehow your house battery is need of charge, and the engine is on, AND shore power is connected....
that is the same as running your vehicle on a sunny day with a solar panel. Two energy sources charge the house, then starter battery, all coordinated by the DCC30S just as designed.