Charging batteries on the run to the ramp

[552Evo]

In very simple terms (it's much more complicated) an alernator puts out plenty of volts, much more than 12, it's current (amps) production is limited by various things by design, heat dissipation is a big one, so is size and weight, it produces AC, alternating current, and this needs to be converted to DC (like the battery) to charge, this is where the diode/s comes in, it's kind of like a one way valve, converting AC to DC, it is not boosting anything. Battery chargers are sold as 4amp, or 10 amp or more, at 12 volts, none are sold as 12.6 volt chargers. Now let's be very clear here, I am not knocking this product, know nothing about it, I just like to know what's what when "gizmos" are advertised or spoken about.

All true but there's different types of diodes, also diodes can be used in different ways.
Diodes used inside an alternator - there's 4 of them, connected in such a way to convert the AC into DC. These diodes act like you say as a one way valve.
I'm going by trade school memory here but: there's another type of diode called a zenner diode, these diodes can be configured to act like a gate that opens one way at a specific voltage, and closes or blocks100% the reversed voltage.
So these booster diodes would work like that, in that they would allow an extra 0.5 volt (thereabouts) output from the alternator.
The booster diode slightly changes the voltage sensing circuit within the alternator.
It's a simple idea and it works fine.
Is it the theoretical best way to charge all types of batteries in all conditions, no.
The extra 0.5 volt is beneficial in 2 ways,
if your second battery is mounted away from your primary the voltage drop is compensated for
and
If the two batteries require different charge rates ( ie one more flat than the other) then the half volt will be adequate to charge both without over charging either.
The dc/dc chargers are the best method for multiple batteries and calcium, lead crystal etc but both ways work fine for regular lead acid batteries. Depending on the setup the diode may be adequate for a second calcium battery as well.
Is it getting too detailed in tech now for the OP question ?



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[Force3]

I run 2 batteries, 1 dedicated start and one house. I have Ctek DC-DC charger connected to the start battery which then charges the house battery while the engine is running. For storage, I connect a 40w solar panel, via an anderson plug, to the solar input of the DC-DC charger and it looks after both batteries. I have Ctek bluetooth battery monitors on the batteries and an app on my phone gives me the state of charge for both batteries. I never have to worry about batteries.

[ranmar850]

I can put my old boat, running a dual battery setup, one house, one start, with a parallelling switch always left in the off position, with a VSR across it, away for 6 weeks or more at a time, without bothering to turn the battery switches off, or connect a charger. Motor is an F115 Yamaha with Command Link gauges, it has a Lowrance GPS combo plus a Sitex GPS, VHF, 27mhz, etc. Batteries are now 2 yrs old, never had an issue. You should not need to keep batteries on charge, unless you are A) storing them unused for a very long time, B) they are stuffed, or C) there is something left on. Every accessory runs via a simple switch panel, make sure they are all off.
I never have to worry about batteries, either.