Dual-Input (alternator + solar) Dual Output Charge Controllers?

[oguruma]

I'm trying to build a solar system for my truck.

I'm going to go with a LiFePO4 100ah battery and I'd like to be able to charge from the alternator and solar. I have a few questions for people that are knowledgeable abotu Dual-Input Dual Output chargers.

1) Is there a brand/model that you'd recommend?
2) If I add a second house battery, is it as simple as wiring it in parallel to the first one?
3) The Renogy model as a 50 amp maximum, and if you use both solar and alternator, it's split at a maximum of 25/25 amps. Does this mean I'd be limited to 2x 100w panels (24amps)? Or does that simply mean the charger itself will charge at 25/25 while the vehicle is running, and then allow the full 50amps off solar when the truck isn't running?

 

[oguruma]

Fwiw.
Assuming 12V system 200W is closer to 16A max.
Anyway, Probably its better off to use DC to DC converter to handle the alternator part of charging, and your favourite lithium capable Solar Controller to handle the solar.
As far as second battery, its simple as connecting it parallel to the first battery.

So you're saying to use a charge controller and a DC-DC converter as two separate pieces of equipment in the system? Instead of using something like the Dual-Input systems?
Doesn't the dual-input system provide the benefits of 1)only having a single piece of equipment to wire in, and 2) allowing the device to charge both the starting battery and the house battery?

 

[ducktapeguy]

I have the Renogy 30A dual input controller. I posted some of my thoughts in a previous thread somewhere on this forum.

There were a few reasons I went with a dual input controller

1. Space. Originally I purchased a DC/DC charger and solar MPPT. This required extra space under an already crowded engine compartment, and just made the wiring more complicated. The Renogy DCC30 fit pretty easily and simplified all the wiring. If you have plenty of space I can see the advantage of separate chargers.
2. Robustness. The renogy DC/Dc charger used active (fan) cooling, while the DCC30S was sealed with an external heatsink. I didn't think any type of fans would last very long in a dusty engine compartment. If you're installing somewhere on the interior then having cooling fans is probably better.
3. Simplicity. Connect the house battery, the starting battery, and solar panel and you're done. The Renogy dual input controller charges the house battery, then automatically tops off the starting battery. You could probably do the same with independent chargers but again the wiring gets more complicated.

I went with the 30A vs 50A controller because I'm charging a 100Ah LifeP04 and I've never seen more than about 13A from the alternator, no matter what state of charge the battery is in. It's probably due to a bit of resistance in the wiring, but even with heavy jumper cables direct to the LiFeP04 I've never seen close to 30A. I only have 100W of solar, so there's no chance of ever getting more than about 6-7A from that so for me 30A seems like plenty of capacity.

The Renogy is a bit weird in the way it splits power. If there's any power coming from the solar, it actually doesn't charge from alternator, at least not from what I've seen. Only when solar input drops to almost 0, or more specifically the voltage drops below a certain threshold, then the alternator will start charging.