Combining solar panels

R1campr · 01-10-2023, 10:22 PM

I have a 25watt x4 (100w) harbor freight mobile system with a regulator/ controller and SAE quick connects. I used to use it on my last camper, kept a SAE connector attached to the battery.
We now have an 1808 fbs that is prewired for solar on the roof. I’m wanting to put a 200w panel up there and have a 40amp mppt controller (I know, overkill for now) to put in the pass through. Does anyone know how I can use both the panel on the roof and my mobile panels at the same time? That way I can point the mobiles at the sun if the one on the roof is shaded. We are in Ohio, so, usually not a lot of direct sunlight. I also take a generator in case I need it. Battery is an SLA 100ahr.
I was thinking I could wire the panels to bus bars then a disconnect then to the mppt. If so, is there a bus bar out there that has a switch, breaker, or disconnect on it? And do I need to be able to disconnect both the positive and negative wires before the mppt? Not just the positive wire, In case I want to unhook the battery

eyecando · 01-20-2023, 11:25 PM

Just parallel the 200 watt solar cell wiring with the portable solar cell wiring.

You only need to disconnect one wire from the output of the controller to disconnect it from the battery. It is advisable to have a fuse on the output positive of the charge controller so you would only need to remove the fuse to disconnect it from the battery. I would also add a fuse to the input to the controller.

Marine359 · 01-21-2023, 03:33 AM

I would not advise connecting two panels of different voltage or amperage. The lower rated panel will determine the output of the array. Also, if vastly different, one panel could feed the other and cause damage. You may want to review this article: https://www.alternative-energy-tutor...-together.html

Best solution is to have two separate charge controllers. One for the roof mount and one for the portable. If you are connecting the portable through a SAE port, then there’s no need for a disconnect, because you just pull the plug. For a roof mount, you should connect the incoming wiring in the pass thru to a manual reset breaker switch, then wire it to the controller. You’ll also need a junction stud to connect the negative wires. When you want to disconnect the PV array just press the button on the breaker.

I like having bus bars. It makes wiring so much easier. I also like my Blue Sea Systems Spade fuse block. It sits between the bus bars and controllers and some loads. I connect both charge controllers to the fuse block, and insert the appropriate size fuse.

For some ideas, take a look at the photos on my Mods and Adds Album: https://www.winnieowners.com/forums/...albums376.html

R1campr · 01-21-2023, 09:27 AM

Thank you Eye and Marine.
I’ve got a breaker for the positive side wire from the solar panel and the mppt. And a block for the negative wire. Still need a fuse for the battery side.
For my portable 100w, I have a controller, I think it is a PWM controller, not sure of the amps. If i connect the two battery positives from the controllers, then to a fuse then on to the battery, would that make the two controllers clash in some way? Or mess up any reading I get from the 40a mppt? As I have a Bluetooth connection with it.
Thanks for your help

R1campr · 01-21-2023, 09:53 AM

Marine, the picture you have of the 12v outlet, where did you tie in to the wires for it? Also did you add a fuse for it or just rely on the fuse at the box for that wire?

Marine359 · 01-21-2023, 10:21 AM

Quote:

Originally Posted by R1campr

Marine, the picture you have of the 12v outlet, where did you tie in to the wires for it? Also did you add a fuse for it or just rely on the fuse at the box for that wire?

I installed two 12v/usb outlets inside at bedside where they are easy to reach. The wiring goes under the cabinet surfaces next to the bed, and then into the pass thru where they are wired into my spade fuse block. The fuse block is wired to my bus bars. Each outlet requires a 15amp fuse. If you don’t use a fuse block, you’ll have to use inline fuses.

Marine359 · 01-21-2023, 10:31 AM

Seconding Bob C post. It doesn’t matter how many charge controllers you have connected to battery simultaneously, as long as you don’t exceed the battery maximum input amperage. That’s pretty unlikely when charging a LiFEPo4 with PV. Your max amperage coming from each controller is the rating of the controller. For example, a 100/30 mppt controller has a maximum input of 100vdc, and a maximum output of 30 amps dc. A portable panel with its own onboard pwm controller is not likely to output more than 5 amps. If you have a portable panel with no onboard controller, you can connect it to a 75/15 mppt and maximum it’s potential charge amperage. At this very moment my 75/15 mppt connected to 11w portable is producing 23watts @ 1.5 amps.

BobC · 01-21-2023, 10:36 AM

Quote:

Originally Posted by Marine359

Seconding Bob C post. It doesn’t matter how many charge controllers you have connected to battery simultaneously, as long as you don’t exceed the battery maximum input amperage. That’s pretty unlikely when charging a LiFEPo4 with PV. Your max amperage coming from each controller is the rating of the controller. For example, a 100/30 mppt controller has a maximum input of 100vdc, and a maximum output of 30 amps dc. A portable panel with its own onboard pwm controller is not likely to output more than 5 amps. If you have a portable panel with no onboard controller, you can connect it to a 75/15 mppt and maximum it’s potential charge amperage. At this very moment my 75/15 mppt connected to 11w portable is producing 23watts @ 1.5 amps.

I accidentally deleted my post but, in a nutshell, I my recommendation is separate fuses on the pos wires from the two controllers, connecting them (downstream of the fuses) at a pos bus bar before going to your battery bank to avoid a proliferation of wires on your battery terminal.

Marine359 · 01-21-2023, 11:06 AM

Yes, agree each controller should have its own fuse between controller and bus bars or battery; unless you have a spade fuse block wherein you can connect all controllers and insert the appropriate size fuse for each of them, obviating the need for inline fuses.

eyecando · 01-21-2023, 08:56 PM

I agree that separate controllers would be best to get maximum output especially with mismatched panels.

As long as the panels are rated for nominal 12 volts, there is no problem with paralleling them as long as the controller is rated for the current and voltage that could be supplied. With the panels paralleled and with full exposure to sun on all the panels, the resultant output may not be what you might expect with mismatched panels, but you won't damage anything.

I suspect that paralleling two slightly voltage mismatched panels will result in a current greater than the one with the highest voltage but I haven't tested this situation.

My Navion came from the factory with two 100 watt panels and a separate input for a portable panel that just parallels the installed panels at the input to the solar controller.

Realize that when the installed panels are partially shaded such that one panel sees full sun and another sees no sun, the panel that is fully exposed is backfeeding the one in the dark. This does not result in any damage.

A great use for a portable panel is that it can be placed in a spot with good exposure when the installed panels are fully or partially shaded.

I have replaced my two factory supplied stick on panels with four 100 watt panels. The output of the four panels has always been under 20 amps, so even with an additional 100 amp panel, I will stay below the 30 amp rating of the PWM controller. One of these days Ill replace the controller with an MPPT unit.

eyecando · 01-22-2023, 08:16 AM

If using an MPPT controller and placing the panels in series or a series parallel setup, it would be important to have matched panels in order to get the expected output.

Also realize that the solar panels are not zero impedance devices. Therefore, paralleling two not identical panels would not mean that any one panel would control the output. Paralleling would definitely not reduce the output. Each solar panel has an open circuit output voltage greater than the battery voltage with significant impediance in series. Each panel would supply current. The exact values would depend on the parameters of each panel, the controller, the batteries and the exposure.

I have a second trailer that with four identical 100 watt panels in a series parallel combination with a Victron MPPT controller. It works well, but I have not compared the output between the RV (PWM controller) and the trailer (MPPT controller) under identical conditions. The RV has 200 watts of LiFePO4 batteries while the trailer has over 200 watts of AGM batteries. This makes comparisions difficult also.