I read the OP's post thoroughly.
Because of the layout out his text, the inclusion in plan of a 4 hour windup (infinite resolution) timer and other intrinsic factors particular to his post...
I feel the poster knows exactly what he is doing and why he is doing it :)
This is all too obviously a charge augmentation in support of meaning auxiliary to an existing onboard charger.
Now to answering his questions:
350 watt power supplies have a circuit board ten ampere fuse. I have not dissected the 1500 model but there must be a circuit board fuse or the power supply cannot meet either UL or CSA safety specifications. This is a Taiwan unit from one of the largest power supply manufacturers in the world. The inclusion of a circuit board 20 - 30 amp soldered cartridge fuse therefore must be considered a "given" not a guess.
If that soldered fuse should go open circuit, there is a problem with the circuit inside the cabinet. Replacement of the fuse is minor compared to repairing the cause of fuse failure. OK? These fuses are vastly over capacity of the unit in question.
Therefore it must be concluded that any safety device used in the circuit would be from the batteries to the unit -because- of failure or fault in battery to power supply input compromising. A short - a connection pulled loose.
Aside from this perspective must be maintained. Are there circuit breakers protecting the circuit from the battery to the onboard converter and distribution DC fuse panel? Arguing for the power supply circuit to be fused must automatically include argument that the OEM battery to converter supply be similarly protected -both circuits- at the battery end. It would be irrational to argue for one and not the other.
I measured a spurious .001 ampere draw between battery and unpowered power supply. This may or may not have an origin of bleed in the unit's capacitors. The effect if not worth chasing down IMO. The 100 volt PIV rating of the schottky rectifiers precludes current reversal.
Racer 4, presents a clear indication he knows what he wants and he is pursuing a path in which he feels comfortable.
The timer proves he acknowledges the minutes or hours to be assigned is to be considered. it is obvious he realizes voltage values as presented by the manufacturer. If he chooses 14.8 volts then by trial he can discover the time parameter versus starting battery voltage how much to wind the Intermatic. I fail to acknowledge that someone with the intent of assembling such a system cannot comprehend time calculations versus observed starting battery voltage. For a vast majority of RV'ers time spent at Vmax becomes almost laughably easy intuitive.
Check when the battery cells start to bubble then terminate the charge. Note the time spent charging versus the starting voltage. Is this overwhelmingly complex? if yes, then the use of a 3-stage converter is mandated. Some folks are crippled in some areas of mechanical aptitude.
It is the crucial time spent at IDEAL Vmax that conventional converters have no way to deal with. They compensate by demanding inappropriately long term charging spent at lower voltages. Inappropriate because it is similar to watching a draft horse pack a lunch box. Generators and generator run time are both expensive and for many including me - I don't want to endure unneeded and excessive noise and fumes. Then there is the matter of the grinning cashier at the gasoline station.
Occasional top charging can be increased in amounts per kWh drawn by letting the electrolyte bubble slightly longer every tenth charge. If two hours seems to be ideal for regular charging starting at a certain voltage then top charge by adding 15 minutes to the two hours.
Proponents of totally automatic charging are fully entitled to have the right to charge the way they wish. But they do not have the right to declare operator controlled sophisticated"custom" charging as being deleterious, hazardous, or invalid. The louder they yell the more they discredit themselves.
I have spent far too much time with batteries to have the wool pulled over my eyes.
BUT BUT CAVEAT BUT BUT READ THIS...
Batteries can not be equalized by cranking up voltage to 16.0 volts. AMPERAGE LIMITATION and THROTTLING is an absolute must or batteries will be damaged. Use paralleled 12 volt 50 or 100 watt light bulbs to throttle amperage to 5% of rated ampere hour capacity. This does mean the direct disconnection of the main charge lead line from power supply to batteries during the equalization event. And the disconnection of batteries to hotel loads for overvoltage protection.
I feel I must address the situation where a bi-directional charge relay will allow inappropriate flow of high voltage to the chassis battery. I am familiar with the Blue Seas and the Sure Power charge dividers. Both units, have a terminal to chassis negative that must be in-circuit for the device to work. The chassis negative circuit employs an 80 milliamp flow to enable the device. A small switch can be used to interrupt the charge divider operation during equalization.
And finally, a fully recharged battery is a longest lived device. undercharging a flooded battery is electro-chemical arteriosclerosis. People who total 5% of the kWh transactions of a serious off grid boondocker are poor choices to hear opinions about battery lifespan versus charge protocols. Hydrometer and total kWh transaction accumulations are the sole valid points to consider.
I wish Racer4 good fortune and will dispose myself to his questions.
Charger augmentation is not for everyone. It may or may not be appropriate for even 7% of RV users. But if it is warranted, then nothing else but charge augmentation on the face of the earth can do it's job and the penalties at least to me are unbearable. Forcing myself to be stupid is not one of my strong points.
