Opinions on basic truck/van charging system (All in one DC/DC/MPPT?) that will use both alternator and solar for house Lifepo4 battery

Drewgold

New Member
Joined
Oct 11, 2021
Messages
4
Long time lurker first time poster. I know this sort of question gets asked a lot but I have been unable to find an answer to my main question which is this:

Is there some benefit to the dual input DC/DC and MPPT charge controllers (such as the offerings from Renogy) other than the saved space and somewhat simplified wiring?

I'm reluctant to go with a dual input controller for the sake of redundancy. If the dual controller were to fail, it could take the entire charging capability with it. In my mind, having a separate MPPT and DC/DC controllers adds a certain redundancy to the system should one component fail. It's also unclear whether the alternator charging can be manually switched off with the dual controller? I'd like the option to turn off alternator charging if desired. On top of this, there seems to be little or no cost savings for the dual unit vs two separate chargers. Am I missing other benefits to a dual controller other than a potentially cleaner install?

My planned power system for a small camper will use a single 100ah Lifepo4 house battery, 80w solar panel, then either a 20A Renogy MPPT solar controller with a separate 20A DC/DC charger powered by the vehicle (with 70A alternator) OR the Dual 30A DC/DC charger with MPPT.

Open to any feedback anyone may have!

And big thanks to everyone who contributes to this forum, it is an amazing resource.
 

pollenface

Solar Addict
Joined
Nov 14, 2020
Messages
495
Location
Perth, Australia
Most decent dc-dc chargers have an MPPT input. Some will prioritize the solar power (while driving) to save alternator draw when charging your deep cycles. If you want to use a separate solar controller for redundancy that's your choice.
 

Zwy

Solar Addict
Joined
Jan 3, 2021
Messages
1,049
70 amp alternator, you could just run a long wire with a toggle switch back to the LFP battery. 10ga or smaller. You don't have much amperage to play with so charging from the alternator will be limited. There is no way you could run 20A or 30A DC/DC at full output without eventual failure of the alternator.

The idea of using the long wire is to create resistance in the circuit to limit charge current. You won't get full charging but if you want cheap and effective, it will work.
 

hodgo1981

New Member
Joined
Feb 6, 2020
Messages
6
Long time lurker first time poster. I know this sort of question gets asked a lot but I have been unable to find an answer to my main question which is this:

Is there some benefit to the dual input DC/DC and MPPT charge controllers (such as the offerings from Renogy) other than the saved space and somewhat simplified wiring?

I'm reluctant to go with a dual input controller for the sake of redundancy. If the dual controller were to fail, it could take the entire charging capability with it. In my mind, having a separate MPPT and DC/DC controllers adds a certain redundancy to the system should one component fail. It's also unclear whether the alternator charging can be manually switched off with the dual controller? I'd like the option to turn off alternator charging if desired. On top of this, there seems to be little or no cost savings for the dual unit vs two separate chargers. Am I missing other benefits to a dual controller other than a potentially cleaner install?

My planned power system for a small camper will use a single 100ah Lifepo4 house battery, 80w solar panel, then either a 20A Renogy MPPT solar controller with a separate 20A DC/DC charger powered by the vehicle (with 70A alternator) OR the Dual 30A DC/DC charger with MPPT.

Open to any feedback anyone may have!

And big thanks to everyone who contributes to this forum, it is an amazing resource.
I'm in a similar situation with planning my new build and conversion to LFP batteries. In my old setup, I've just used a very simple voltage sensing relay for charging from the alternator then a very cheap 10A MPPT for charging an AGM battery.
I too am considering the 30A DC-DC/Mppt renogy charger, or maybe going to Victron for individual units tailored to amperage I expect to use.
After my recent research, I am leaning towards Victron, even though its likely to cost about 30% more.
This is primarily because one element I would like is whole of system monitoring. Whilst Renogy has bluetooth communication, its seems they run 2 seperate BT comms protocols and not all their devices have comms, you cant have a didgital dsiplay monitor adn BT monitoring at the same time and its hard to get information about it. Where as the Victron communication system seems leaps and bounds ahead, they have a huge range of devices that communicate, it can simultaneously communicate via BT or via a monitoring panel.
 

Drewgold

New Member
Joined
Oct 11, 2021
Messages
4
70 amp alternator, you could just run a long wire with a toggle switch back to the LFP battery. 10ga or smaller. You don't have much amperage to play with so charging from the alternator will be limited. There is no way you could run 20A or 30A DC/DC at full output without eventual failure of the alternator.

The idea of using the long wire is to create resistance in the circuit to limit charge current. You won't get full charging but if you want cheap and effective, it will work.
So you feel that even a 20A DC/DC charger would be too hard on the Alternator? The Renogy units actually allow for an accessory wire to be run, when powered it will reduce the charger output to 10A.
My truck is an older Toyota diesel so uses pretty limited power once started. I believe they came with an option for 55A alternators or an 'upgraded' 70A alternator which I have. It's an imported truck and the alternators are hard to get so I don't really want to risk cooking it. Maybe I'll have to stick at 10A to be safe.
 

Zwy

Solar Addict
Joined
Jan 3, 2021
Messages
1,049
So you feel that even a 20A DC/DC charger would be too hard on the Alternator? The Renogy units actually allow for an accessory wire to be run, when powered it will reduce the charger output to 10A.
My truck is an older Toyota diesel so uses pretty limited power once started. I believe they came with an option for 55A alternators or an 'upgraded' 70A alternator which I have. It's an imported truck and the alternators are hard to get so I don't really want to risk cooking it. Maybe I'll have to stick at 10A to be safe.
70a isn't much when you consider a blower motor can draw 25a on high speed. Add in lights and a few accessories and you're at 40a or more quickly.

10a is ideal for an alternator that size. Running a wire straight back can net you 10a at less cost but you won't get a full charge into the bank. It would depend on how much you want to push to the bank and your usage. Any solar?
 
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