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Old 05-28-2015, 07:24 PM   #1
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2 Portable Solar Panels

I want to get 2-100 watt portable solar panels with controllers for each. I'm hearing conflicting answers from manufactures. Can I connect 2 portable solar panels with controllers to my single battery bank of 2-6 volt batteries. I want to do this way so at any time I can use 1 panel or 2 and also would be able for each panel to be used any where. I also have the option for non controllers with the panels and I provide my own controller. Hope I'm making sense. Any help would be greatly appreciated.
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Old 05-28-2015, 07:48 PM   #2
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Here is how I did portable panels.

I have six 100w panels on the roof, and two 100w panels portable that I can set out as needed. One controller for all.

The roof panels go to a combiner box on the roof with a single cable down to the controller. Another wire in parallel from the controller goes to the two portable panels. The portable panels connect in parallel via a Y harness, so I can connect either one or both panels.
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Old 05-28-2015, 08:43 PM   #3
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I assume your portable panels do not have controllers. You have 1 central controller for all the panels. I trying to connect 2-100 watt panels with each a controller to 2-6 volt batteries, not sure if possible. If I have to i will get a controller and mount near the batteries and get 2-100 portable solar panels without controllers.
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Old 05-28-2015, 09:52 PM   #4
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JWLSC: If I understand, you want to do what is called "stacking" controllers. And "yes," you can use two controllers to charge the same battery bank. It is best if they are both similar types of controllers, however. The better controllers will feature diode protection to prevent the output charge current of one controller from passing through the other "stacked" controller. \ken
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Old 05-28-2015, 10:21 PM   #5
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So I can connect each positive from the controllers to the battery and each negative to the battery. I would have 2 quick connects off the battery bank. Each would connect to the out put from each controller. Would it work in this fashion. Or do I have to use y connectors from the controllers to have just 1 positive and 1 negative connected to the batteries. They will be same controllers and panels.
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Old 05-28-2015, 10:29 PM   #6
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Yes, your first option would work. Mine are connected to opposing posts in the battery bank. That is to say that the positive and negative connections from one controller go to opposite corners of the battery bank (call them east and west, where east is positive and west is negative). And the the positive and negative connections from the second charge controller go to the remaining two corner posts of the battery bank (call them north and south, where north is positive and south is negative).

It shouldn't make a difference where you connect, however (positive is positive and negative is negative, regardless where you connect to the battery bank). I'm a believer that it spreads out the charge and load more evenly. And the posts tend to get pretty crowded, so it makes it easier to connect the new set of cables if you use all four corners of the battery bank.

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Old 05-28-2015, 10:39 PM   #7
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JWLSC: I just re-read your original post and it sounds like you may have just two 6-volt batteries. I misunderstood ... thinking that you had 2 sets of two 6-volt batteries. In a two 6v battery configuration you will not have four corners to connect to -- just two. Your connections from both controllers will need to go on the same battery posts.

You might want to consider using just one pair of connections to the batteries that terminates in a quick-disconnect. The "Y" connectors you mention could be used at the quick-disconnect to split off to the two panels, or not (will depend on how you want to set up your portable panels - my guess is that you will always want to use both portable panels, and prolly on just one controller).

When it comes to battery connections, I would opt for fewer connections, rather than more. Be sure to use the right size wire between the controller and battery bank (Bigger is better; distance matters).

Sorry for the confusion in my previous post.

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Old 05-30-2015, 06:12 AM   #8
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Hi John and Ken,

I'm certainly no expert so am mostly just rambling here.... That said, I'm not sure that will work very well (two panels and two controllers to one battery bank).

I think it depends on the controllers capability. With two controllers, I think they will be fighting each other to provide optimal voltage and you will never get the full 200 watt output (minus losses). That is, one controller will see the battery voltage low and pass current thru which will cause the other controller to see high voltage and will cutout/reduce output - maybe they will cycle back and forth. I'm not sure.

Now, if the controllers provide an interconnect (like the Morningstar's do) then they can talk to each and work together. It would be better to have a single controller for the entire array - especially for such a low power setup.
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Old 05-30-2015, 07:32 AM   #9
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Your 2 controllers, won't see high voltage until the battery is near full charge. When that happens, a single controller will cut back also.
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Old 05-31-2015, 08:12 AM   #10
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I agree, one [properly-sized] controller is certainly the preferred and more common option. But the OP was asking about a two-controller system:

Quote:
I want to get 2-100 watt portable solar panels with controllers for each ... Can I connect 2 portable solar panels with controllers to my single battery bank of 2-6 volt batteries. I want to do this way so at any time I can use 1 panel or 2 and also would be able for each panel to be used any where.
It's not unusual to have an on-board solar/charge controller supplemented by a portable system with a separate charge controller (we do). In his question, it sounds like he wants a system that is [essentially] two portable systems. As long as the two controllers are both similarly "smart" and either PWM or MPPT, I don't think he would have any problems.

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Old 05-31-2015, 02:21 PM   #11
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Suppliers reply

I ask this because Zampsolar says only 1 controller per battery bank. But Renogy says "For our units you can have a max of two systems on the same bank". So I guess it depends on the controllers being used. I want portable as I camp in the shade a lot and I don't think roof mounted panels would work that well for me. What are some of the better Portable solar solutions.
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Old 05-31-2015, 04:33 PM   #12
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You could mount the controller permanently near your batteries, fused of course, then using a quick connect as both the combiner and the connector to the controller, fused of course.
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Old 05-31-2015, 05:20 PM   #13
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As a current producing device, a solar panel only need a fuse, to protect it from other panels backfeeding to it, if It shorts and overloads the wire.

In a 200 watt setup, there will not be enough current to overload either wire, so a fuse is not necessary.

The fuse would have to be rated higher then the panels output, and would never blow. If It was less, it would blow, every sunny day.

If you add enough panels to overload 1 panels wires, you then need fuses in the combiner box, rated to protect each panels wiring, in the event one shorts out.

Since the output of a controller is hooked to a battery, capable of discharging hundreds of amps, in a short, It needs to be fused to protect the wires from burning. Not from the solar output. This is why the fuse needs to be near the battery.

Again, the fuse will be higher then the solar output, so it don't blow, in use.
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Old 05-31-2015, 06:02 PM   #14
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If I have portable panels with out controllers and use the morning star t45 controller. Would I use a fuse between the controller and the battery. If so what size fuse would be appropriate. Also what about the fuse between the panel and controller, which size fuse.

Would this work
Controller to battery 60 A
Panel to controller 30A
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