Proper Wiring for two controllers to one battery bank

[Cadillac_Jack]

Ok guys here is what I have, and what I want to do.

I have two 120 watt panels running through a 10 year old PWM charge controller to a set of two group 27 deep cycle 12 volt Trojans.

I also have the original 50 watt panel that came with the camper siting unplugged.

I just purchased the Rouge 2024 MPPT controller. I am going to run the 120 watt panels through the Rouge controller to the group 27s.

So now I have the original 50 watt panel along with original PWM controller. I want to wire this up to the same battery bank. My questions are in regards to proper wiring.

Do I run the wires from both controllers straight to the battery?

Or do I run the wires from both controllers through a set of 12 volt circuit breakers then run them separately to the battery?

Or do I run the wires from both controllers through a set of 12 volt breakers then join the wires together then to the battery ?

Maybe I need to fuse the leads and don't need the breakers at all?

Thanks for any thoughts from the experts.

[NinerBikes]

Link of studyConsider a MPPT when you get 24V panels over 200W each, or your whole solar panel setup is over 360 Watts total with 24V panels. Rogue MPPT 2024... $250

Consider a PWM charge controller if your panels are all 36 cell 12V design making 17-18V each at Max load, 22-23V unloaded. Solar 30 Adj Voltage to 15.0V PWM 12v/24v 30 amps max.... $29

No brainer, for me. Save the money on the controller and go buy another 120 watt panel, and still put some change in your pocket.

BFL13 did a comparison on MPPT vs PWM, do a search and read up what his real world findings were... He doesn't have a dog in the hunt for either brands.

Although not a direct comparison, you have to keep temperatures in mind when running MPPT's, they lose their gain when it gets hot, and provide less or no benefit then. If you camp spring, summer and fall, you should take that into account.

Link

[Cadillac_Jack]

atreis wrote:
Wiring them in series lowers the line losses between the panels and the controller (it's amperage - the flow of electrons - that's resisted - and the higher voltage - how hard those electrons are being pushed - helps too). The MPPT controller will take care of outputting the correct voltage to the batteries.

When wiring different panels (or sets of panels) in parallel, the VoC should match as closely as possible. (If producing at all, most panels will produce they're rated voltage, even if they're mostly shaded and producing very low amperage.) If it doesn't, the lower of the two voltages is what will be used, with any difference wasted.

When wiring different panels (or sets of panels) in series, the VoC does't matter much (with an MPPT controller) but the Imp should match as closely as possible. If they don't match the higher-current panel will end up being limited to the same amperage as the lower-current panel with the difference wasted. (If the panels don't have bypass diodes, the same thing will happen if one of the panels is shaded. Some panels, Kyocera for instance, have bypass diodes between groups of cells as well. Some of the super-cheap panels don't have bypass diodes at all.)

There are many references online, some better than others, for the fun of wiring in series vs. parallel, and series-parallel. These are but a few:
Solar Facts
MPPT Solar
Solar Panels Venue

Exactly right. Not sure what the other gentleman is talking about. My batteries are 12 Volt. The camper is set up for 12 volt. Two 6 volt batteries in series are 12 volt. Meaningless for this discussion.

Higher volts push more amps.

I will never be able to match my two 120 watt panels. As I said before, they are no longer made and besides, I don't have the room.

Mismatching panels of different size is a definite no go, so adding a third panel in parallel is a bad idea.

I am well aware of what series wiring does to 12 volt batteries. Why are we talking about it?

My original post was in regards to wiring a second controller. The rest is well known to me.

So running my two large identical panels that suffer no shading in series thru my MPPT controller will net more power to the batteries.

[NinerBikes]

Cadillac Jack wrote:
I am after voltage. Higher voltage will push more amps into the batteries. Thus the MPPT controller.

Lower line loss, and more voltage.

Not sure why it matters that the batteries are in parallel.

Parallel batteries means you are running two 12V batteries parallel, as in your whole electrical system is 12V based. Running parallel combines the Amp hours of the two 12V batteries. Two 110AH batteries at 12 V gives you 220AH at 12V total.

If you were wired in series, your electrical system would then be 110AH, but your voltage would now be 2 x 12V, or a 24V electrical system.


Since you have a 12V system, your batteries are in parallel to run everything at 12V.

You need 14.8 to 15.0V to charge your 12V system. That's plenty high voltage. A Solar 30 PWM charge controller is one of those controllers that is Voltage adjustable up to 15.0V. It does 12V and 24V system charging.

Solar 30 PWM adjustable charge controller

You can find this exact same PWM charge controller rebranded and sold in the USA for $55-80, all day long on Ebay. You can buy this one, it's sold from Los Angeles, and it will be at your door in 3 working days, if you order first thing in the morning. I know this is true, I just bought one. It does indeed deliver 14.8, or 14.9 or 15.0V. Connect it to one positive terminal on one battery, and one negative terminal on the other battery since you are running your batteries parallel.

Adding another panel to this 30 amp charge controller, regardless of size, on the input side of the solar panel, is fine... with a PWM charge controller, it is all about the AMPS of input, the charge controller takes care of the output voltage and makes it all the same, it does not have problems like a MPPT does with mismatched panels. It's about the amps on a PWM charge controller.

You are making this more complex and difficult than it needs to be, when you are working with 12V solar panels in small sizes. MPPT's are for huge 200 watt plus high voltage 29V panels, to get them down to 12V usage and charging a 12V system. If you have more questions, ask BFL13 about the differences, and small charging 12v panels vs large 24V panels, where MPPT controllers become a factor.

With a PWM and 12v panels, the line run is such that you can afford to lose up to 2 to 3V and not have an effect on pre voltage on the input side of the controller having an effect on the OUTPUT voltage of the charge controller. You worry about big V losses only between the output of the charge controller run to the battery terminals. You over come that loss by mounting the controller as close to the battery as possible without getting gassed by the battery, and short fat wires, to limit the loss on that wire run only.

[atreis]

Wiring them in series lowers the line losses between the panels and the controller (it's amperage - the flow of electrons - that's resisted - and the higher voltage - how hard those electrons are being pushed - helps too). The MPPT controller will take care of outputting the correct voltage to the batteries.

When wiring different panels (or sets of panels) in parallel, the VoC should match as closely as possible. (If producing at all, most panels will produce they're rated voltage, even if they're mostly shaded and producing very low amperage.) If it doesn't, the lower of the two voltages is what will be used, with any difference wasted.

When wiring different panels (or sets of panels) in series, the VoC does't matter much (with an MPPT controller) but the Imp should match as closely as possible. If they don't match the higher-current panel will end up being limited to the same amperage as the lower-current panel with the difference wasted. (If the panels don't have bypass diodes, the same thing will happen if one of the panels is shaded. Some panels, Kyocera for instance, have bypass diodes between groups of cells as well. Some of the super-cheap panels don't have bypass diodes at all.)

There are many references online, some better than others, for the fun of wiring in series vs. parallel, and series-parallel. These are but a few:
Solar Facts
MPPT Solar
Solar Panels Venue

[Cadillac_Jack]

I am after voltage. Higher voltage will push more amps into the batteries. Thus the MPPT controller.

Lower line loss, and more voltage.

Not sure why it matters that the batteries are in parallel.

[NinerBikes]

Why would you run the panels in series, when you only have 2 12v batteries to charge, and they are wired in parallel?

Take both panels, in parallel and route them into a 12v PWM charge controller rated at 30 amps, in case you add one more panel. One short run of heavy thick wire from the charge controller to the paralleled 12v batteries, and you are complete.

[Cadillac_Jack]

NinerBikes wrote:
If you have two matching 120W panels, those are each close to 7 amps each charge rate. Why even bother screwing with the 50 watt solar panel and it's measly 2.5 addtional amps, when you already have 14 amps? Get another matching 120W panel if you can, and sell the 50 watt panel.

120W panels for 89 AH group 27's AGM's is plenty, for most applications.

Next time when your replace the Group 27's Trojans, consider 6V T105's instead. Much, much, much easier to keep charged, they don't have the crappy acid to lead ratios that car type sized batteries do, so that the damn battery can fit under the hood without shorting out at the terminals.

Trojan should make a T-105 AGM Side terminal batteries for cars already, for no shorts.

When you match batteries, you should match panels also... seems to me just to be common sense.

Understood. Oddly enough I have already come to the same conclusion. I am going to concentrate on the two 120 watt panels. I am wiring them in series and running 8 gauge MC4 wire to the Rouge through a plumbing vent. This will decrease my wire run to well less than 10 feet.

From the charger to the batteries I only have a 24 inch run, and it will be 6 gauge fused before and after the charger.

Later on I will take down the 50 watt panel, and replace it with a 100 watt unit and use the same wire route to the second charger thus I will be gaining an additional 6 amps plus absolutely no combiner boxes or holes in my roof.

Unfortunately, I can no longer find the Evergreen 72 cell 120 watt panels, so I will have to build a second array.

As to the T 105s, already been down that road. They will not fit in my battery box. The Trojan 27 TMX was really the best I could do, and still have a fair amount of room to work on and water the batteries.

The Trojan group 27s that I have are 105 AH each. I should be sized pretty well with the two 120 watt panels in series. I bought a relatively cheap watering system from Amazon, and it works flawlessly.


I also have the remote meter for the Rouge. Very exited about this setup.

Thanks for all the replies.

[NinerBikes]

westend wrote:

2oldman wrote:

westend wrote:
Paralleling different panels with different electrical characteristics to one MPPT controller is not a good idea.

Not sure why that would be always true. It's pretty simple to try it and see the amperage reading at the controller.

It is because the "knee" of the IV curve is different in the two different panels. That "knee" is where the MPPT controller observes the characteristics of the panel's output and determines how to sort voltage, amperage and resistance.

Think of it this way: The MPPT controller is lecherous. It likes to rub knees. If it has Charlise Theron in on one chair and Rosie O'donnell in another chair, it will get confused and start examining just Rosie's leg rather than Charlise's appendages. The result will not be pretty.

I can't erase that from my mind... I am feeling gravely ill after visualizing that nasty scenario.

[2oldman]

westend wrote:
.. it will get confused and start examining just Rosie's leg rather than Charlise's appendages. The result will not be pretty.

ARG!

[westend]

2oldman wrote:

westend wrote:
Paralleling different panels with different electrical characteristics to one MPPT controller is not a good idea.

Not sure why that would be always true. It's pretty simple to try it and see the amperage reading at the controller.

It is because the "knee" of the IV curve is different in the two different panels. That "knee" is where the MPPT controller observes the characteristics of the panel's output and determines how to sort voltage, amperage and resistance.

Think of it this way: The MPPT controller is lecherous. It likes to rub knees. If it has Charlise Theron in on one chair and Rosie O'donnell in another chair, it will get confused and start examining just Rosie's leg rather than Charlise's appendages. The result will not be pretty.

[BFL13]

Here is where I saw that about the 2 minute hunting, part way down in DSchmidt's post here. ( Too bad he isn't here to help with the gizmo's etc)

http://forums.motorhomemagazine.com/index.cfm/fuseaction/thread/tid/26464298/gotomsg/26953604.cfm

[2oldman]

JiminDenver wrote:
Wouldn't the Rogue just handle all three panels in series? There would be nothing to confuse it then.

No, series would be worse. The amperage in the circuit would be that of the 50w panel.

[2oldman]

And we don't know if these two controllers will work together anyway. If one is slightly higher voltage, won't that tell the other controller the bank is charged?

[JiminDenver]

Wouldn't the Rogue just handle all three panels in series? There would be nothing to confuse it then. My mismatched panels are 24v and different types.

[NinerBikes]

If you have two matching 120W panels, those are each close to 7 amps each charge rate. Why even bother screwing with the 50 watt solar panel and it's measly 2.5 addtional amps, when you already have 14 amps? Get another matching 120W panel if you can, and sell the 50 watt panel.

120W panels for 89 AH group 27's AGM's is plenty, for most applications.

Next time when your replace the Group 27's Trojans, consider 6V T105's instead. Much, much, much easier to keep charged, they don't have the crappy acid to lead ratios that car type sized batteries do, so that the damn battery can fit under the hood without shorting out at the terminals.

Trojan should make a T-105 AGM Side terminal batteries for cars already, for no shorts.

When you match batteries, you should match panels also... seems to me just to be common sense.