What do isolated and non isolated mean with respect to DC/DC chargers?

[Freep]

I'm preparing to swap out my AGMs for LifePo4s and Updating all the sources for charging my batteries. I've upgraded my panels and added a Victron MPPT that supports LifePo4. I'm upgrading the Progressive Dynamics 4045 Might Mini so it will support LifePo4. Then I started wondering about how the batteries charge from the alternator.

Right now the battery is charged from a Blue Sea Systems BatteryLink Automatic Charging Relay. It seems that this just dumps power from the alternator to the DC system and doesn't really do much else. So I think I'll have to buy a DC/DC charger and I keep seeing isolated and non isolated DC/DC chargers.

What's the difference? How do I determine which one I should use?

 

[Freep]

Here is a basic diagram of the current setup.

 

[gnubie]

The output terminals of an isolated converter are not DC connected to the input terminals. If you put an ohm meter across the + terminals there will not be continuity, and the same with the - terminals. It can be useful when you have mixed grounding systems, ie + grounded chassis, - grounded equipment. If you need this sort of isolation you should check with the seller to confirm that - is not pass-through as there are converters that only have + isolated.

The power losses in an isolated converter are typically a bit higher than a non-isolated unit, assuming similar quality points. Fully/partially isolated units use a high frequency transformer internally, while non-isolated designs use an inductor.

Images shamelessly pulled from Wikipedia.

Non isolated buck / boost


Isolated

 

[Freep]

I'm trying to determine what size DC-DC charger I should get. I'm driving a 2014 Ram 3500 turbo diesel dually. I'm pretty sure the alternator is not going to be stressed by any DC-DC charger I will put on it. With the 271ah 12v LFP battery I'm building should I be happy with a 30 AMP DC-DC charger or should I go higher? The MPPT I currently have is a Victron SmartSolar 100/30. I've almost pulled the trigger on a Victron Orion-TR Smart 12/12-30 but I keep wondering if I should go for more amperage.

The cells have a max charging of 1C and standard charging of .2C

Typically we will drive 4-8 hours to get to the next campsite.

One thing I keep thinking about is the Onan generator we have but barely use. If I know I can start the engine and charge the batteries quickly, I might dump the generator and put more batteries in. I'd love to get rid of that generator.

 

[redhatengineer]

I'm trying to determine what size DC-DC charger I should get. I'm driving a 2014 Ram 3500 turbo diesel dually. I'm pretty sure the alternator is not going to be stressed by any DC-DC charger I will put on it. With the 271ah 12v LFP battery I'm building should I be happy with a 30 AMP DC-DC charger or should I go higher? The MPPT I currently have is a Victron SmartSolar 100/30. I've almost pulled the trigger on a Victron Orion-TR Smart 12/12-30 but I keep wondering if I should go for more amperage.

The cells have a max charging of 1C and standard charging of .2C

Typically we will drive 4-8 hours to get to the next campsite.

One thing I keep thinking about is the Onan generator we have but barely use. If I know I can start the engine and charge the batteries quickly, I might dump the generator and put more batteries in. I'd love to get rid of that generator.

You've probably already done whatever you're going to do but for anyone else looking into this, the Orion can be run in parallel to increase charging capability.

 

[TrevorDavis]

You've probably already done whatever you're going to do but for anyone else looking into this, the Orion can be run in parallel to increase charging capability.

Helpful advice!