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

BFL13
Explorer II
Oct 16, 2014
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 amps

Since 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
2oldman
Explorer II
Oct 17, 2014
I'd parallel the panels,use one controller and forget the fuses.
westend
Explorer
Oct 17, 2014
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.
2oldman
Explorer II
Oct 18, 2014
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.
BFL13
Explorer II
Oct 18, 2014
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.
MEXICOWANDERER
Explorer
Oct 18, 2014
I like the idea of placing fuses not breakers between the controller and the battery bank. A controller that somehow finds itself in Armageddon Mode will source battery potential and that can pose a genuine fire hazard.

The controller with the best range of tweaking should play the part of the Alpha of the pair. I would imagine that to be the MPPT controller. The PWM can be the Beta, and be set .2 volt lower for absorbsion limit.
2oldman
Explorer II
Oct 19, 2014
BFL13 wrote:
it has to do with the MPPT trying to find two different MPPs and getting nowhere.
Hard to say unless it's tested. Seems like a lot of messing around for 2-3 amps.
BFL13
Explorer II
Oct 19, 2014
2oldman wrote:
BFL13 wrote:
it has to do with the MPPT trying to find two different MPPs and getting nowhere.
Hard to say unless it's tested. Seems like a lot of messing around for 2-3 amps.

I saw somewhere that during the moment it is hunting, the voltage jumps to Voc and back down then gets "on" MPP and nothing is getting done for that moment (which is every two minutes in the version I saw this about)

So if it is always hunting between two mismatched panels, would it ever get anything done?
JiminDenver
Explorer II
Oct 19, 2014
IF and when I get the bigger controller, I can see what happens with mismatched panels since I already know what each panel is good for on its own. General consensus is that it's not a good idea.

BTW I combine up to tree systems on one bank but they are three identical controllers with matching settings.
NinerBikes
Explorer
Oct 19, 2014
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.

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