Mix 12v battery bank and 24 volt solar panel

[Johnxhc]

I am designing a 6 100ahr battle born battery bank and 800w-1200w solar panel system for my 2017 35' motorhome.

I understand that high voltage system is better as it requires smaller size cable and more efficient, smaller size charge controller, but I also would like the motor home alternator charge my batteries when I am driving (no a deal breaker but it is nice to have it) , Also the wires between the batteries ,bus bar & fuses are very close, so I do not see that much benefit on 24v battery bank system on my motorhome . Please let me know if I missed anything here.

I am thinking about wire the solor panel at 24v and leave the battery bank at 12v use this MPPT charge controller:
VICTRON ENERGY 30A SMARTSOLAR MPPT 100/30 CHARGE CONTROLLER W/ BLUETOOTH
Maximum PV Open Circuit Voltage: 100V
Battery Voltage: 12V/24V Auto Select

It looks like I will be able to take the 24v or even 48v from solor panel and charge the 12v battery bank and take advantage of both 24v and 12v system, could anyone confirm that ?has anyone done this before?

Also Battle born also sell the battery isolation manager, have anyone had any experience on this?
Please advise.
Thanks in advance.

[Daveh]

Yes, that will work.  You run the voltage from the panels to the mppt charge controller and then 12 volt out to the 12 volts system of the motorhome and to charge the batteries. I assume you also have an inverter that runs off 12 volt. The size if the charge controller will not be maxed out because the rating is based on the output amps which for 12 volt will be twice has high as if it was running a 24 volt.   If you switched to a 24 volt battery though that would require you to also have a 24 volt inverter and a downconverter to change the 24 volt to 12 volts to run your 12 volt system.

You could also run two or more of you solar panels in series to get a higher voltage down to the controller. For instance 2 24 volt panels in series would be the same as one 48 volt panel. You would then run other pairs of 24 volt panels in parallel to get a 48 volt system. Although higher voltage achieved by running panels in series makes the wire run to the charge controller more efficient it has the downside that if one panel in a series of panels gets shade it will take down the output of all panels in that series. For that reason I think your proposal of running 24 volt panels wired in parallel down to the charge controller is a good idea. The Victron is a good choice as long as battleborn tells you it is appropriate for their recommended charge settings. Do you know what inverter charger is running in your motorhome and whether battleborn is good with that charger. 

I do not know about Victron's isolator but I would imagine your motorhome already isolates the starter battery from the others. I own only a fifht home so I will defer to others on that topic.

I think the best resource for you right now would be Jack Mayer's website on RV Solar. He still stops by here now and then. Reading through that a few times makes all of this terminology less mysterious. 

I used to be unsure of Battleborns since they were new to the market and  I had built my own lithium pack. However numerous reviews plus Will Prowse cutting one open on You Tube has made me a believer.    http://www.jackdanmayer.com/rv_electrical_and_solar.htm

 

 

 

 

[oldjohnt]

John, I'm NOT any Solar expert but will go ahead and offer my thoughts until the more experienced gents can offer their views, here goes:

1) Sure a 24 Volt battery bank has advantages HOWEVER

     a) I don't think Battleborn (unklike some other brands) are suitable for series connections so you're stuck with 12 iffffffff thats true??

     b) If your Batteries and Inverter (or Inverter/Charger) and other components are relatively close and you use big enough wires (no big deal on initial installation) running at 12 volts is fine      PLUS you avoid the expense of a 24 to 12 Converter to power the RV 12 volt devices

2) USING ALTERNATOR TO CHARGE

      a) If you go with a 12 volt battery bank, a 12 Volt DC to DC Charger is fairly typical and readily available, and of course, get one suitable for those Lithium batteries. I have seen a few 12 Volt to 24 Volt DC to DC chargers but many are for Lead Acid or AGM and small systems, Im unsure if they make a big enough 12 to 24 DC to DC charger suitable for Lithium  ???????? 

3) SOLAR PANELS I would consider (SUBJECT TO any potential SHADING in series connections) configuring the panels (if possible and feasible) at even 48 volts (Vmp higher) versus 24.  That can reduce wire size and line voltage drop (subject to current and wire size and length) and most MPPT Solar Charge Controllers accept up to 100 Volts PV Input. THIS DEPENDS ON YOUR ROOF of course 24 or 48 would do fine, your roof your choice.  I run my four 24 Volt panel 1080 Watt system in series parallel 48 Volts and may see 70+ volts down to my MPPT...... 

 You didn't ask but a hybrid pass through 3000 Watt Inverter/Charger with blue tooth and that matches your charge controller would make a nice package to go with 600 AH of Lithium and 1200 solar watts   GEE ITS FUN TO SPEND YOUR MONEY LOL

 Do as the experts and vendors and professionals advise nottttttttt me

John T

[Daveh]

Yes. I agree with John on all of the above. I came out on the other side of whether to increase solar panel to 48 v but I could be very easily convinced to go that direction depending on my roof layout and if I frequented parts of the country were partial shading was more of an issue. (I bypassed the factory prewire and ran 2 awg wire from my roof to controller or I am sure I would be in a 48 volt configuration  I asked about your inverter/charger because I consider that an extremely i,important component. Maybe more important than the batteries. To really see the benefit, power and flexibility of that battery bank you should be looking at the Magnum Hybrid series or the Victron Multiplus hybrid line.

[oldjohnt]

Dave, I've read about using by pass diodes to reduce shading effects, but based on my roof space and where the AC and vents were I didn't worry all that much.  I have two side by side panels in series up front in parallel with two in back, works for me even if NOT ideal or perfect. If I were much younger and knew Id still be camping in the same RV for 7 or more years Id love to design a whole new Victron and Lithium based system with blue tooth and smart phone monitor and control wooooooooo hooooooooooooo I can run ALL BUT AC with what I have (not latest or all the bells n whistles) and I get by...

John T    

[jcussen]

All the panels I have installed  in the last 10 years have bypass diodes built in. If you take the cover off the junction box on the back of the panel, you will see them. I am running two strings of panels in series, one at 120 volts down, and one at 60 volts. Lot easier and cheaper running 10 gauge wire than 4 gauge.My solar controllers will accept up to 150 volts and output 12 volts, so no problems. Have tried running series and parallel in the same shaded situation and have not seen much difference in output. I do use Victron inverters, battery monitor, and solar controllers. Like them because they are bluetooth on my phone, getting too old to run wires from bays to interior anymore.