Shore power converter output as input to MPPT charge controller?

[BobG]

I have a tiny trailer (Aliner) that came with a crappy battery charge controller (2 stages) when on shore power. I've added 12v 100w solar panel and Renogy Rover PG 40a MPPT controller to run off grid with a single 12V deep cycle FLA battery. Works fine. The Rover has 4 charging stages including a monthly Equalization. I would like to use the Rover to maintain the battery when on shore power at home (or occasionally when traveling). Could I remove the crappy controller and run the 12v DC out from the Aliner converter to the solar inputs of the Rover and have it manage the FLA battery?
Thanks for any and all help!

 

[gnubie]

SCCs aren't intended to be used like that.

The manual for that SCC says it will limit the current output but depending on how it's MPPT algo works it could still damage itself by drawing too much current from the Aliner converter.

MPPT controllers work by drawing more and more current from the PV input and doing some simple maths to work out where the optimum power can be obtained. If the supply on the PV input does everything it can to hold the voltage up by supplying as much current as it takes the controller could burn out some of its components if the MPPT algo doesn't take that into account or if there simply is no protection at all.

The Aliner converter would also need to be rated to supply the full current the SCC can draw otherwise it will shut off its output to protect itself (or go bang).

All up, you might be able to do it, but I don't recommend it.

 

[BobG]

Wow! Thanks so much for the quick response! I'm very grateful.
I forgot to mention that the converter's output is listed as 13.6VDC and 35A (476W). The SCC max solar input is listed as 12V@520W (43A). Does that make this sound any less scary? I realize that a little bit of knowledge is a scary thing, but it's what I have to work with. ;-)
Thanks again for your help! Could you point me to anything that might help increase my scary bit of knowledge in this area?
Bob

 

[gnubie]

OK, then it's definitely out. A MPPT controller will want to see the PV voltage go to some point above the battery voltage before charging will commence, and then during charging to not fall below some other point. For a Victron CC this means only start when input voltage is >= 5v above battery and cease if input voltage < 1v above battery. Epever units often need the input to stay 2v above battery voltage.

The SCC you have would also likely trip the Aliner's overload too, even if it could be used considering the point above. All things considered if the Aliner charger/power supply isn't doing the job you'd be better off, IMO, buying a separate mains (110 / 240 VAC depending on your location ) charger.

Is there a problem with the Aliner charger or are you just trying to simplify things? It might be practical to have the Aliner charger and your SCC connected to the battery at the same time, or switch the + line from then using a change-over switch of some type. If using the switch you'd have to take care that the solar panels were disconnected from the SCC as the manufacturer's manual states to never disconnect the battery while/if the panels are supplying power.

 

[BobG]

I'm trying to simplify and better maintain the battery. I currently have both controllers connected independently to the battery, but the Aliner controller only has 2 modes, bulk and float. I don't believe that the Aliner controller is fully charging the battery. I'll be able to better measure that later this week. I was hoping that the SCC was able to control the voltage and amperage in either direction, as needed, as long as it had enough power to work with.
Hopefully I can get a good main controller for not too much $$$ or I will find out the current one is doing a good enough job when I get some better data later this week.
Thanks again for taking the time to help educate the noob!

 

[BobG]

To clarify, I meant:
I was hoping that the SCC was able to control the voltage and amperage in either direction (increase or decrease), as needed, as long as it had enough power to work with

 

[SolarRat]

The MPPT needs to see 18+v input to charge a 12v battery. Your mains charger can't do that.

Just replace your crappy mains charger with a good marine on-board charger. I like the marine chargers because they come in many sizes/configurations, waterproof, are designed to keep your bank in top shape and are usually much better quality than standard chargers. If you only have one 12v LA battery just get a single bank model at about 1/10 the amp rating (10 amp for a 100a battery). Look for 3 stage plus equalization (for FLA's, really 4 stages).

 

[BobG]

Thanks for your help! Sorry that it took me so long to get back to here.