Where to connect solar panels with batteries?

[wheresthelove83]

Good afternoon!


I've got an '82 22 ft Winnebago Brave and I'm trying to run solar power to meet as many energy needs as are feasible. I've got a 12v 105w panel and a 12v 160w panel which will be wired in parallel for 265 watts, and a battery bank consisting of four 6v, 208AH golf cart batteries wired in series-parallel for a 12v, 416AH house bank; as well as a 12v starting battery (some marine starting/deep cycle that came with the rig, looks newer and still has some life in it). Currently, they're separated by an isolator, which allows the generator to charge both but prevents them from contacting each other, i.e. keeps the old battery from ruining my shiny new golf cart batteries.

Is there any reason it would be a bad idea to run my charge controller to just upstream of the isolator, provided the isolator is sufficiently dioded to keep generator current from travelling back toward the solar panels? Or would it be better to simply run the charge controller to the house battery side of the isolator and leave the charging duties of the starting battery to the generator/alternator?

Thanks in advance!

[DaveVA78Chieftain]

Some of the biggest problems people run into with solar design are:
1) To small a cable size such that there is to much resistance in the cable creating loss.
2) To many connections.  Each connection results in voltage loss.  Direct from solar controller to battery bank post is correct method.
3) Wiring run to long such that it results in excessive voltage loss.   That's either panel to controller or controller to battery.

Cable size and length should be selected such that there is no greater than 2% voltgae drop.  http://www.affordable-solar.com/Learning-Center/Solar-Tools/wire-sizing

Currently, they're separated by an isolator

Used for:
1) Engine start if chassis battery is depleted by cross connecting chassis and house battery systems
2) Allows engine alternator to charge house battery bank while driving
3) Stock isolator system does not cross connect battery banks so generator can charge chassis bank unless it has been modified with something like a BIRD controller.

Diodes on Solar Controller leg to battery will prevent back voltage to solar controller.



Dave

[ClydesdaleKevin]

I'm using Blue Sea 80 amp circuit breakers on both sides of the charge controller to isolate, or more specifically, turn on and off, the solar system when I'm plugged into shore power, or the engine is running.  I made a whole post on the setup with lots of pictures.

Kev

[moonlitcoyote]

I love that picture Dave, simple pictures like that make things easier to understand.

[wheresthelove83]

Is a junction box still necessary with weatherproof MC4 connectors, or is it just good practice to keep all conections in a junction box?
Kevin, what's the reasoning behind a circuit breaker on either side of the charge controller?
Also, I'm replacing the factory inverter with an inverter/charger that has inputs for A/C to charge my batteries from the generator/shore power as well as converting the DC from my batteries into AC for my wall outlets. Unless it would be better to leave the current inverter to do its job and run just shore power to the new one...

Also, where should the output of the new inverter meet the AC lines to the rest of the RV?

[DaveVA78Chieftain]

Is a junction box still necessary with weatherproof MC4 connectors, or is it just good practice to keep all connections in a junction box?

There are different ways to skin the cat. As long as you are using MC4 Y connectors you should be ok. 

Kevin, what's the reasoning behind a circuit breaker on either side of the charge controller?

Key is protection whether you use a fuse or CB's.  CB's were used for convenience.

Also, I'm replacing the factory inverter with an inverter/charger that has inputs for A/C to charge my batteries from the generator/shore power as well as converting the DC from my batteries into AC for my wall outlets. Unless it would be better to leave the current inverter to do its job and run just shore power to the new one...

Original charging device is called converter, not inverter.  Original 1982 converter unit typically was an older design which was known for boiling batteries dry.  Today's inverter/chargers are typically 3 stage units.  The float mode in today's modern units is set to take a lot of the worry out of boiling the batteries dry. 

Also, where should the output of the new inverter meet the AC lines to the rest of the RV?

This will depend directly on size of inverter/charger.  Note: Your inverter/charger will not operate the AC.  Takes a huge battery bank to do that.  Even though you have a 416ah battery bank, to prevent battery damage, you do not want to draw it down lower than 50% State of Charge (208ah)

Dave

[wheresthelove83]

Are the air conditioner circuit and wall outlet circuits mutually exclusive? Can I tie the inverter output in anywhere I can find wires going to a wall outlet without it going to the air conditioner?

Where could I find a wiring diagram for the A/C systems, as most of the service manuals only go as far as chassis wiring?

Thanks so much for taking the time to answer my questions!

[DaveVA78Chieftain]

Like a stick and brick house, input power (shore or generator) is feed to the main AC circuit breaker panel.  Just like a house, all AC power branches out to the different areas from that panel.   Determine what each CB breaker feeds and you will have your answer.

Dave