MPPT and DC-DC Charger to Use Solar to Charge House and Starter Battery Question

[SkiWill]

So here's the deal, I've got a Land Rover LR4 which is great, but it has a smart alternator and a not so smart charging algorithm that never really completely charges the starter batter. Also, whenever the door opens, all the computers wake up putting a load on the battery. Now, the BMS will supposedly keep the computers from draining to the point that the battery will no longer start the engine, but suffice it to say I'm not exactly thrilled about this algorithm or relying on the BMS to make sure the starter battery always is healthy enough to start the engine. Especially when camping in a spot for a couple of days, not starting the engine but getting things in and out of the car with computers booting up.

Ideally, I'd like to get some charge controller and/or DC/DC that would accomplish the following:

1. Use solar to charge the house battery.
2. When the house battery is charged, use the solar to charge the start battery whether the vehicle is running or not. Again, due to the "smart" charging algorithm, the alternator reduces load and never really charges the start battery fully to increase efficiency. I'll let you judge the intelligence and effectiveness of reducing a few amps at 12 volts on a 375 hp V8 hauling around nearly 7,000 lbs to increase "efficiency."
3. Facilitate charging of the starter battery from the house battery if needed.
4. Finally, my lowest priority is charging the house battery from the alternator, but it would be nice on the odd cloudy day drive. I could honestly live without this.

My house battery loads will be very low. Maybe 1 45-50ish quart/liter fridge and a few GPS units/phones/tablet. I just want to maximize the charge I get from a 50 or 100 W panel on my roof and it seems like I should be able to use it to charge both batteries. Hopefully that's not too unreasonable or expensive of an ask.

My thinking is to prioritize making the solar also be able to charge the starter battery as well as the house battery because a dead house battery means my beer is warm and the milk goes bad. If the starter battery drains, I'm potentially 100 miles of desert away from the nearest town with my family, which is a much more serious situation. From what I've seen, Renogy looks like they have a single MPPT capable DC to DC charger that will charge both the house battery and starter battery from solar. However, based on previous Renogy experience with customer service, quality, etc. that's not an option.

Redarc has an MPPT ready DC to DC charger but it looks like it will only use the solar to charge the house battery and then isolate from the starter unless I'm missing something https://www.redarcelectronics.com/us/dual-input-25a-in-vehicle-dc-battery-charger

Victron has the Orion DC to DC smart charger, and it looks like I could possibly program the DC-DC charger to work with a separate Victron MPPT charger to facilitate what I'm trying to do, but I'm not exactly sure how I'd set it up. I do have a Victron battery monitor and MPPT charger for my teardrop trailer and I am happy with my Victron equipment and app. However, I'd like to hear from anyone that has done this on what has worked well for them and how they set up their algorithms with the Victron equipment.

Thanks in advance.

 

[Hegear]

I have both the redarc and Renogy systems. Both will charge car batteries once you house is fully charged. Both function almost the same. I have had no problems with either brand. Redarc is more compact, and I’m sure a lot tougher. Renogy is obviously a lot more cost effective.

 

[SkiWill]

I have both the redarc and Renogy systems. Both will charge car batteries once you house is fully charged. Both function almost the same. I have had no problems with either brand. Redarc is more compact, and I’m sure a lot tougher. Renogy is obviously a lot more cost effective.

Thank you. That's helpful. I expected that the Redarc should have that functionality, but I couldn't find it specifically called out in their manual. Its compact size, robust design, and built in fan have advantages in my particular application as well so I may go that way.

 

[jonyjoe101]

On my van I use a 2 amp dc to dc converter to charge from the house battery to the start battery. My agm start battery requires 14.7 volts to fully charge and the alternator only goes up to 14.4 volts, so I have to top off the battery every other day. If I don't top off the battery after about a week I start getting weak cranks where the engine turns over slowly. I usually top off the battery for about 5 minutes before I crank the engine over, thats plenty to get a good crank on the engine. The fullriver 27ah agm battery I'm using I bought in 2012 and still performing good.
This is a picture of the charger I use. Its 2 converters a boost that takes the 13.1 volts of my lifepo4 to 19 volts, then a buck converter that reduces the voltage to 14.7 volts. I had to build my own because you won't find many chargers that have an LED readout. With the readout you know exactly how the battery is charging. And I charge the start battery directly from the dash cigarette plug, no need to run wires all over the place.
I havent had a dead battery ever since I been topping off my start battery, almost 3 years now, before I encountered a dead battery maybe twice a year.
On this picture shows an almost full start battery 14.7 volts and the amps are at about 130 milliamps, when the battery reaches 100 milliamps thats a full charge, When the charger starts it shows about 13 volts and 2 amps and the amps drops slowly as the voltage goes up. Thats the beauty of an LED volt amp meter, you can see it in real time. Most charger blinking lights don't tell you anything.


This is the inside of a boost buck converter which make great chargers for all batteries li-ion, lifepo4 and lead acid. You need both a boost and a buck, its the only way to charge from dc to dc of similar voltages and maintain max amps. They also sell all in one boost buck converter. Maybe 20 dollars for the converters and 5 dollar volt amp meter. I have mine set to 2 amps, but you can adjust up to 5 amps output. But in 3 years all my start battery has needed was the 2 amps, after 10 minutes it reaches over 14.6 volts which is good enough. No need to spend 100's to top off the start battery. I wouldnt spend alot of money on a charger without an LED volt/amp meter.



I also carry a lithium jump starter which have failed me before. And due to that failure I also carry a small 16ah oddesey agm which I can use as a start battery in a worst case scenario.

 

[Tesota Overland]

Thank you. That's helpful. I expected that the Redarc should have that functionality, but I couldn't find it specifically called out in their manual. Its compact size, robust design, and built in fan have advantages in my particular application as well so I may go that way.

The BCDC1225D is a quality piece of gear, if you haven't made a decision yet I'd strongly recommend going in that direction. I currently have a Manager30 and just carry a NOCO Boost, worst case I can just charge it through the USB port and then jump the engine (had to do exactly that actually).

The CTek Smartpass 120 and D250SA might be more of what you're looking for if you want self jump capability. I ran this for a few years and was pretty happy with it. Search for "ctek d250sa bundle"