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.

You can just put the controllers on the same bank directly if convenient each with its own pos wire fuse sized to the current on each, close to the battery bank. Or if you want, you can do the same thing by running a wire pair from the bank posts to extend them to some convenient point and parallel the controllers onto the end of that pair. You would fuse the pos wire of that with a bigger amp fuse because it will carry the total ampsSince the rule is to disconnect the array before the battery is disconnected from the controller, and to connect the battery to controller before connecting the array to the controller, I like to have a convenient switch on one of the two wires between controller and array. In this case you would have one switch for each set

I'd parallel the panels,use one controller and forget the fuses.

Paralleling different panels with different electrical characteristics to one MPPT controller is not a good idea. That's not the intent here, though. The OP should have no problem connecting the output of the two controllers at the batteries. Both input connections should be fused for the amperage of the wire within a couple of feet of the batteries. If the separate outputs from the controllers are joined at a midpoint, as BFL suggests, then both outputs should be fused before that junction and the battery termination will also have to be fused. When using "fused" in this post, a guy could also use circuit breakers instead of fuses, the main thing is to circuit protect any wiring.

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.

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.AFAIK, it has to do with the MPPT trying to find two different MPPs and getting nowhere.

Proper Wiring for two controllers to one battery bank

38 Replies

JiminDenver
Explorer II
Oct 24, 2014
Over the weekend I'll have all three of my Eco-w's wired up. :)
BFL13
Explorer II
Oct 24, 2014
I ran my two controllers on the same battery bank with no problems at all, so IMO there is a lot of theory going on here and not that much actual real life.

I ran a Solar30 PWM off a 130w panel plus an Eco-Worthy MPPT of a 230w panel where both controllers were set to 14.8v and they added their amps perfectly all the way up from morning to reaching 14.8v.

There are so many old-wives tales on this forum about not paralleling different chargers on the same bank it is hard to believe they won't change their minds when faced with the facts. :(
atreis
Explorer
Oct 23, 2014
I've no idea how to make use of two different types of controllers that can't talk to each other. There are controllers that can be paralleled (MidNite Solar's KID is the one I'm aware of) but that would mean purchasing two expensive controllers just to make use of a 50W panel .. not worth it.

So... If it's not reasonable/practical to make use of two controllers...

A) If you run the 2 120W panels in series, the VoC is too different from that of the 50W panel, so you can't use the 50W panel. Use the 240W available, and be happy.
Upside: Easy, efficient.
Downside: You lose 50W.

B) If the VoC of the 50W and the 120W panels is reasonably close, you can parallel all three. Just combine them as close to the controller as reasonably possible in order to lower the line losses. (In this case, MPPT didn't get you anything - a PWM would have worked fine. Chalk it up as a learning experience. :) ) Enjoy the 290W, and be happy.
Upside: All available wattage is used from existing panels.
Downside: Money spent on the MPPT controller was possibly wasted.

C) Sell all the panels and replace them with new identical panels that fit, wire them in series, make full use of the nice controller, and be happy.
Upside: New panels are more efficient - might be able to get more than 240W in the same amount of real estate.
Downside: Expensive.

Sometimes there is no perfectly optimal solution and one just has to pick.
Almot
Explorer III
Oct 23, 2014
Ninerbikes - yes, I would sell existing 120+120+50 panels and get 2 new 120W. Or, better yet - 3*120W if they fit. Or 2*140. Or 3*100. Any of these choices would be better than existing old-ish 2*120. With existing 2*120W the OP is under-utilizing a very good controller.

I would not rush trading a good MPPT for a PWM. Rogue quality and features are outstanding. With a few identical 12V panels in series it will work fine.

I would not buy Rogue - or any MPPT - with existing 2*120. Small camper, budget considerations (otherwise why keeping old panels?) would lead me to some PWM in this case.
OTH, if the goal is getting maximum energy out of the existing roof real estate, I would get multiple identical panels and then either MPPT or PWM again, depending on the roof layout and on panels voltage.

There is something to old concept of doing it right the first time.
NinerBikes
Explorer
Oct 23, 2014
Cadillac Jack wrote:
NinerBikes wrote:
Cadillac Jack wrote:
UGH! In my first post I said that I just bought a state of the art MPPT charge controller. So now I am supposed to trade it in on a 50 dollar PWM Chinese knockoff? ? ? ? ?

I have also mentioned numerous times that I cannot match my two 120 watt panels for multiple reasons!

A prior poster questioned why I would run my panels in series when My batteries are in parallel. DOUBLE UGH!

Of course my batteries are in parallel, I said so in my first post when I said I was running dual group 27 Trojans! Triple UGH!

Completely obvious and totally irrelevant.

Its a camper for crying out loud not a cabin.

So you bought a top of the line MPPT charge controller for $250, for a camper, when you have two mismatched 120W panels no longer made, and a 50W panel. A PWM would have handled all of that, no problem, with no ill effects... run them all the panels parallel, tie them in whereever,either at the input side of the controller, or at another junction box. 10 ga wire panels to controller will handle all the amps.

You sir quite obviously cannot read. Which is of course why you should not post replies to threads that YOU DO NOT READ! ! ! ! !

MY TWO 120 WATT PANELS ARE PERFECTLY MATCHED! What don't you understand about that? I then said on numerous occasions that I cannot put up another matching 120 watt panel because

A they are 72 cells and no longer made &

B I don't have the room

READ AND COMPREHEND!

You are the one that brought in the pablum of why I would run two panels in series while my batteries are in parallel. WTH ? ? ? ?

You brought a completely irrelevant argument to the table and then try to make me look stupid ???

If you had read the very first post in the thread, then you wouldn't be saying silly******about how my batteries are wired or why I don't buy a 50 dollar Chinese piece of crap!

For the love of God!

First you post that you have two 120 watt panels hooked up to an old PWM controller. Hooked up to 12v electrical system. That's telling me that you have 36 cell panels putting out 18V. Not 72 cell panels putting out 36V. You can't put 36V into a PWM charge controller and get 14.4V or a bit more going to your batteries.

Then you post you can't match them.

Then you post they are perfectly matched.

A few years back, folks were posting that adding watts with solar panels at a dollar a watt was making adding panels more cost effective than adding MPPT to small systems under 30 amps for 12V panels.

MPPT now only makes economic sense where large 225 to 250 watt panels at higher voltages can be bought for $.70 to .80 a watt, with multiple large panels, 3, 4, 5 or a bit more.

Google and Search function are your friend... it's already all in here. Posting conflicting nonsense will not make you popular around here.
NinerBikes
Explorer
Oct 23, 2014
Cadillac Jack wrote:
NinerBikes wrote:
Cadillac Jack wrote:
UGH! In my first post I said that I just bought a state of the art MPPT charge controller. So now I am supposed to trade it in on a 50 dollar PWM Chinese knockoff? ? ? ? ?

I have also mentioned numerous times that I cannot match my two 120 watt panels for multiple reasons!

A prior poster questioned why I would run my panels in series when My batteries are in parallel. DOUBLE UGH!

Of course my batteries are in parallel, I said so in my first post when I said I was running dual group 27 Trojans! Triple UGH!

Completely obvious and totally irrelevant.

Its a camper for crying out loud not a cabin.

So you bought a top of the line MPPT charge controller for $250, for a camper, when you have two mismatched 120W panels no longer made, and a 50W panel. A PWM would have handled all of that, no problem, with no ill effects... run them all the panels parallel, tie them in whereever,either at the input side of the controller, or at another junction box. 10 ga wire panels to controller will handle all the amps.

You sir quite obviously cannot read. Which is of course why you should not post replies to threads that YOU DO NOT READ! ! ! ! !

MY TWO 120 WATT PANELS ARE PERFECTLY MATCHED! What don't you understand about that? I then said on numerous occasions that I cannot put up another matching 120 watt panel because

A they are 72 cells and no longer made &

B I don't have the room

READ AND COMPREHEND!

You are the one that brought in the pablum of why I would run two panels in series while my batteries are in parallel. WTH ? ? ? ?

You brought a completely irrelevant argument to the table and then try to make me look stupid ???

If you had read the very first post in the thread, then you wouldn't be saying silly******about how my batteries are wired or why I don't buy a 50 dollar Chinese piece of crap!

For the love of God!

Title of thread "How to wire 2 controllers to my battery supply?" And now you have a MPPT. and $250 plus shipping missing from your account. And 72 cells for 120 w panels, but 36 cells and 18V for the 50 w panel

I'd sell the 72 cell panels, and for anything under 360 watts, I'd go to all 36 cell solar panels at 18V.

What a mix and match mess. Time for a complete overhaul. Same as needing a new 200 amp main panel at home. Remodel time.

I bought a brand new 150w 18V panel for $120, just the other day, I may pick up another... 300 watts, $240, out the door, brand new solar panels. 30 amp charge controller... $29, brand new. $269 for 300 watts. What am I missing here in the math? I am certain that at mid day, I'm good for 16.4 Amps at 15.0V with that set up.

As has been said before, the price per watt for 36 cell solar panels now is so low that it makes MPPT controllers no longer economically viable for much under 30 amps input at 17 or 18V on a 12V system.
NinerBikes
Explorer
Oct 23, 2014
Almot wrote:
Cadillac Jack wrote:

MY TWO 120 WATT PANELS ARE PERFECTLY MATCHED! What don't you understand about that?

Calm down. Some people might have difficulties with reading, and some - with counting. This is what I read in your previous post:
Cadillac Jack wrote:
I have also mentioned numerous times that I cannot match my two 120 watt panels for multiple reasons!
. What you really meant - I guess - was that you can't match the 3rd 120W panel with existing 2*120W.

One more thing - for those reading, if anybody still is :) - I noticed people saying "... this 30A controller". The OP's is 20A, not 30. It's a scaled down version of 30A Rogue. 320W max panel wattage.

Funny, the opening of this whole thread asks about wiring 2 controllers, to one battery bank, does it not? So where did the fancy bank breaking MPPT enter the thread? Far cheaper to buy any other 120W panel for $150 and a $30 30 amp PWM charge controller. More amps, every single time, from adding another 6.6 amps from another 120W panel, than any mppt could make up with only 2 panels. False economy.

And a triple face palm.
NinerBikes
Explorer
Oct 23, 2014
Cadillac Jack wrote:
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.

This is a false statement, if all panels are connected in parallel, even with the 50w panel added in for the extra 2.5 amps, it will work with the other two 120w panels, with a proper PWM controller.

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.
Almot
Explorer III
Oct 23, 2014
Cadillac Jack wrote:

MY TWO 120 WATT PANELS ARE PERFECTLY MATCHED! What don't you understand about that?

Calm down. Some people might have difficulties with reading, and some - with counting. This is what I read in your previous post:
Cadillac Jack wrote:
I have also mentioned numerous times that I cannot match my two 120 watt panels for multiple reasons!
. What you really meant - I guess - was that you can't match the 3rd 120W panel with existing 2*120W.

One more thing - for those reading, if anybody still is :) - I noticed people saying "... this 30A controller". The OP's is 20A, not 30. It's a scaled down version of 30A Rogue. 320W max panel wattage.
Cadillac_Jack
Explorer
Oct 23, 2014
NinerBikes wrote:
Cadillac Jack wrote:
UGH! In my first post I said that I just bought a state of the art MPPT charge controller. So now I am supposed to trade it in on a 50 dollar PWM Chinese knockoff? ? ? ? ?

I have also mentioned numerous times that I cannot match my two 120 watt panels for multiple reasons!

A prior poster questioned why I would run my panels in series when My batteries are in parallel. DOUBLE UGH!

Of course my batteries are in parallel, I said so in my first post when I said I was running dual group 27 Trojans! Triple UGH!

Completely obvious and totally irrelevant.

Its a camper for crying out loud not a cabin.

So you bought a top of the line MPPT charge controller for $250, for a camper, when you have two mismatched 120W panels no longer made, and a 50W panel. A PWM would have handled all of that, no problem, with no ill effects... run them all the panels parallel, tie them in whereever,either at the input side of the controller, or at another junction box. 10 ga wire panels to controller will handle all the amps.

You sir quite obviously cannot read. Which is of course why you should not post replies to threads that YOU DO NOT READ! ! ! ! !

MY TWO 120 WATT PANELS ARE PERFECTLY MATCHED! What don't you understand about that? I then said on numerous occasions that I cannot put up another matching 120 watt panel because

A they are 72 cells and no longer made &

B I don't have the room

READ AND COMPREHEND!

You are the one that brought in the pablum of why I would run two panels in series while my batteries are in parallel. WTH ? ? ? ?

You brought a completely irrelevant argument to the table and then try to make me look stupid ???

If you had read the very first post in the thread, then you wouldn't be saying silly******about how my batteries are wired or why I don't buy a 50 dollar Chinese piece of crap!

For the love of God!