What Is the Voltage Drop for a DC to DC Converter Compared to a Fet Battery Isolator?

Here is another great question! Fabio asks, "Jeff, thanks for sharing your knowledge! I have always wondered if a DC-to-DC converter has a voltage drop similar to a FET isolator? Do you have any insight on that?"
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[@SailingTalisman]

Hi Jeff. When I installed our 840Ah, 24V LifePo4 battery bank last year, I attempted to install (4x) Victron 24/24-17 DC to DC chargers between our 24V stand-alone alternator and house battery bank (2nd 12V alternator for engine and genset batteries) in an effort to protect the alternator. I did this not realizing that my Sterling Power ProReg DW external voltage regulator was at a minimum at least producing a cleaned up AGM charging curve (and about 50A of 24V current) that was compatible with the new LifePo4 batteries. The point is, these (4) DC to DC chargers were advertised as being able to be run in parallel to quadruple the 17A output, but in fact were creating so much voltage drop that I was seeing 8-9V of drop over that circuit. I Googled the problem and saw post after post of people having the same issue, and Victron claiming it was all due to wiring being too light. As an experiment, I rewired the circuit w/ 2AWG pre-tinned boat cable, both pos and neg sides, well above the 6AWG calced w/ Blue Sea Circuit Wizard, and still saw roughly that level of voltage drop. With these units now attempting to convert 17V to 28.8V, I was getting about 17-20A output, which defeated the whole purpose, and this only by setting the Low Volt cutoff to the minimum of 16V. I therefore removed the Victron units and instead added a Balmar Alternator Protection Device (APD) as protection against potential voltage spikes should the (3x) BMS units on the batteries shut off suddenly during charging. Things worked well over the 8 month Caribbean sailing season after that. Am I on the right track here, or would you recommend additional equipment?

[@Timmygobang]

My question would be.
Which is the best way to charge your leisure and starter banks? Argofet, or a DC-DC charger from your leisure to your starter (assuming your alternator is solely charging your leisure batteries)
Always a pleasure to geek out at the school of Jeff 👍🏻🙂

[@RBZ3]

Thanks Jeff!

[@Electronzap]

Good info.

[@casdeop]

Hello Jeff,
I am looking into a new Lithium house battery bank and would like to be able to charge from my existing equipment Solar, Alternator and battery charger. Would it be a good idea to run all the charging currents threw a single DC to DC converter like the Victron Orion TR 12/12-50 ?
Kind regards,
Carlos

[@KubotaTee]

Hi Jeff - I’m curious about using a VSR to share charging loads between my start battery and my house bank versus a battery isolator or combiner. What are your thoughts about this approach?

[@Tanrestednready]

Good stuff
Volume was low

[@sailingheretic]

Isn’t that what a DC / DC converter is designed to do, drop the system voltage from say 24V to 12V ? That’s certainly a big voltage drop, but it’s a desired drop in voltage, right? What am I missing here?

[@chachi5975]

Wouldn't the DC to DC charger be a better choice for a long distance run, say for the windlass batteries. I think it would handle the voltage drop better and deliver the correct voltage. They are also programmable for bulk, absorption and float.