Couple of questions about DC-Dc charging

MEXICOWANDERER wrote:
There is an easy way to do this but it's going to make the people who have never done it howl in anguish.

The feeder circuit from the alternator to the house batteries must be restricted. Restricted means resistance. The circuit must be made correctly. Professionally designed.
A charge division must be incorporated and the only one I have found to be reliable is a White Rogers 200-ampere capacity solenoid that actuated automatically. A smart solenoid that prefers chassis battery first then house battery. This system needs no switches. Both the Blue Seas and Sure Power solenoids are good brands. The bi directional allows automatic charging in the opposite direction as well. Preferable.

Amperes limiting is done via a fifteen foot length of FUSIBLE LINK wire. 10 AWG and ten to twelve feet in length. Fusible Link wire is tin coated but it's secret is in the insulation. Cross-linked polyethylene which can tolerate extremely high temperature.

USA auto manufacturers have utilized restrictive alternator output wire size for decades and of course they have utilized fusible link wire for gross amperage violations for the same amount of time. Decades.

For many years, GM used a 13 gauge alternator charge wire on their 10DN, 10SI, 12, 15, and 17SI alternators. Ford and MoPar did the same.

The issuse you face with a Ford 3, 4, or 6G, is the alternator has twin internal rans driven by the rotor. And underhood temperatures can read 240 degrees which is punitive for an alternator cooling inlet temp.

Fifteen feet of restricted gauge wire will limit ultimate amperage passage to around 60-70 amps. The preferential charge protocol of the "smart solenoid" inherently limits total amperage delivery.
The fusible wire must not be bundled or wrapped.

For over a decade General Motors avoided using a separate block resistor on their ignition system by using a STEEL CORE coil ignition wire. There was an override for starting booster voltage originating at the R terminal on the starter motor solenoid. Ford used this design as well.

Just make sure your wire is cross link type and is fifteen feet in length.

It would be light years more reliable than any electronic circuit.

you could do this if all you are worried about is the amp output, but the purpose of a DC to DC charger is the selectable charge profiles as well as the maximum amp output, its like putting a 3 stage charger under the hood of your truck. so instead of just outputting a voltage and current in a profile for a starting battery you can now pick a proper profile for deep cycle, agm, Li etc. for yyears I have been disabling the charge line going back to my trailer,fithwheel and now camper to increase the life of my batteries. yes the altanator on my 2014 f350 is ECM controled and it does stuff that is not condusive to charging so the best way to combat this is using a dc to dc charger in the trailer or camper that conects to a new set of cables wited directly from the battery to a new heavy plug. I also plan on taking advantage of the upfitter switches in the fords so I can select when it is able to charge and when it isn't. if its sunny, let the solar charge it, if its night or dark, maybe the dc-dc can help out....

Steve