DC>DC charger AND isolator? Or instead of isolator?

[HRTKD]

The right DC-DC charger will have a sense wire that detects when the truck battery is at a sufficient level (being charged) to allow the DC-DC charger to draw from the truck battery. Some DC-DC chargers don't even need a sense wire.

A DC-DC charger is a one-way circuit. It will not draw from the LiFePO4 battery to charge the truck battery. In my side-by-side, I have an isolator to keep the secondary battery charged without drawing on it. The isolator has a button to allow the secondary to join the circuit for cases where the primary battery is not enough to start the engine. With a DC-DC charger in the circuit, the isolator would not be able to join the LiFePO4 battery to the truck battery to charge the truck battery. You would need a separate circuit that bypasses the DC-DC charger.

 

[BajaMatt]

Thank you. So installing the DC to DC downstream of the Isolator will not harm anything, correct? I may lose optimum alternator charge, but my big concern/goal is to have my solar charge to 14.4V.

 

[HRTKD]

Thank you. So installing the DC to DC downstream of the Isolator will not harm anything, correct? I may lose optimum alternator charge, but my big concern/goal is to have my solar charge to 14.4V.

The isolator may be redundant if you have the right DC-DC charger. The Isolator may not be happy to have a non-battery component downstream where it expects to find a battery. I would try it without the isolator.

 

[BajaMatt]

That's my issue...I kind of can't remove the isolator. It's complicated/dumb.

 

[HRTKD]

That's my issue...I kind of can't remove the isolator. It's complicated/dumb.

Sometimes you have to work with what's there. Be sure to update us on what happens. I'm curious to see if the components will play well together.

 

[BajaMatt]

Will do!

 

[BlindBadger]

Will do!

It's been some months...did you ever test this plan?

 

[fratermus]

installing the DC to DC downstream of the Isolator will not harm anything, correct?

The 1212-series charger mentioned in the first post is normally off until it gets power from D+ anyhow: "The DC-DC will not power on or operate until the D+ ignition cable is connected." - p11 of the manual. I suppose it is possible that a voltage-sensing DC-DC that is powered by the starter battery (watching for sufficient trigger voltage) might get confused if it couldn't see the starter battery.

A thought from your original post:

Or do I use them both somehow?

Ctek did/does market a DC-DC/isolator "Smartpass" combo. They ran in parallel; the isolator would pass ~100A and the DC-DC would pass 20A. At some point the DC-DC would raise the house bank voltage high enough that the (FET-based) isolator dropped out and the DC-DC carried on alone. DC-DC have gotten much cheaper/larger since then so that combo is no longer the Hawt Bling.

From time to time I've idly thought about how to duplicate the Smartpass setup with less expensive components. Not sure it's worth the effort these days, but fun to ponder.