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Old 07-21-2021, 03:56 PM   #1
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Adding portable solar panel to existing charge controller

Hello, we have had our 2021 Rockwood Roo 21ss for about a month now and the learning curve has been steep! We had previously owned a TT but did not use anything except the interior lights and fans at times. We were told at the dealership that the 190 watt solar panel on the roof would take care of the 10.7 cubic foot DC only fridge. We came home with one 90 amp 12V battery. As most people on here can imagine we ran out of battery about 18 hours into our first trip!! Since have upgraded to 2 x 6V AGM batteries (220 amp total), installed a battery monitor and bought a generator. Just got back from a 10 day trip with no services. Parked in shade so rooftop solar almost useless. Limped through running generator 4 hours per day and no one was allowed to turn a light on! We have solar on the side and would like to run a portable solar panel through our existing charge controller ( Go Power PWM-30-UL ) that is connected to our rooftop panel. Is this possible and has anyone done it? I Would a 100 watt panel be ok with possible expansion in the future? Any other advice would be greatly appreciated
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Old 07-21-2021, 06:43 PM   #2
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Not worth effort of running wires. Just get something like a Renogy suitcase panel with it's own controller and plug it in or clamp direct on battery.
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Old 07-22-2021, 08:44 AM   #3
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Originally Posted by dsteindl View Post
Hello, we have had our 2021 Rockwood Roo 21ss for about a month now and the learning curve has been steep! We had previously owned a TT but did not use anything except the interior lights and fans at times. We were told at the dealership that the 190 watt solar panel on the roof would take care of the 10.7 cubic foot DC only fridge. We came home with one 90 amp 12V battery. As most people on here can imagine we ran out of battery about 18 hours into our first trip!! Since have upgraded to 2 x 6V AGM batteries (220 amp total), installed a battery monitor and bought a generator. Just got back from a 10 day trip with no services. Parked in shade so rooftop solar almost useless. Limped through running generator 4 hours per day and no one was allowed to turn a light on! We have solar on the side and would like to run a portable solar panel through our existing charge controller ( Go Power PWM-30-UL ) that is connected to our rooftop panel. Is this possible and has anyone done it? I Would a 100 watt panel be ok with possible expansion in the future? Any other advice would be greatly appreciated


It is possible, but not the best idea. It would also be a lot of work. It is best to only combine similar solar panels on one controller. Different wattages, or, different amps and volts, default to the lowest output in amps or volts depending on how you set the system up.

Your best option is to get a portable system of 100-200 watts with its own controller, preferably a MPPT controller and not a PWM controller . The controller doesn't have to be attached to the trailer. It can be placed free standing literally anywhere. Just make sure it is protected from the rain if you are not in camp.

All controllers have specs for max input voltage and amperage. Make sure your panel output is within range.

You can get a decent MPPT for less than a 100 dollars the last time I checked. Don't be afraid to buy an off brand of equipment. They are all made in China and rebranded (some residential panels are made in N.A. and Europe).
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Old 07-22-2021, 02:07 PM   #4
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Hi, thanks for your response. We would also like to get a solar panel extension cord for times when we are parked in the shade. It looks like you need both a positive and negative cable to do that but in some things I've read it appears that people are using a single MC4 to MC4 cable. Does one work better than the other? I've also seen a lot of solar panels with the controller mounted on the back of them but other sources say that your controller should be no more than 3 feet from your battery. Wouldn't it be better to mount your controller on the other end of the system near your battery. TIA
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Old 07-22-2021, 08:24 PM   #5
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Originally Posted by dsteindl View Post
Hi, thanks for your response. We would also like to get a solar panel extension cord for times when we are parked in the shade. It looks like you need both a positive and negative cable to do that but in some things I've read it appears that people are using a single MC4 to MC4 cable. Does one work better than the other? I've also seen a lot of solar panels with the controller mounted on the back of them but other sources say that your controller should be no more than 3 feet from your battery. Wouldn't it be better to mount your controller on the other end of the system near your battery. TIA
I prefer to have controller mounted near battery. For extension "cord" one can use a regular heavy duty extension cord with #10 awg wire. Cut ends off and use MC-4 connectors, one male and one female, on one end of cord. This will allow connection to panel MC-4 terminated wires on panel. Other end needs a polarized connector to connect with wiring from controller. Usually a through panel/wall receptacle with matching plug.

I'm using a similar cord with MC-4 connectors at panel, SAE connector at solar connector on side of trailer, and controller mounted in battery compartment between receptacle and batteries.
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Old 07-23-2021, 02:11 PM   #6
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Portable solar

Disagree with most of the comments so far. Very easy to add a 50' (or your preferred length) extension cord. Just hook one end directly to solar input with correct connector on the other end. Then just plug into your panels. Been doing this for years and it's definitely not a problem. Biggest mistake is running to small a cord. My 50' cord is directly wired to input and just rolled up and stored under propane cover.
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Old 07-23-2021, 04:43 PM   #7
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Originally Posted by dsteindl View Post
Hello, we have had our 2021 Rockwood Roo 21ss for about a month now and the learning curve has been steep! We had previously owned a TT but did not use anything except the interior lights and fans at times. We were told at the dealership that the 190 watt solar panel on the roof would take care of the 10.7 cubic foot DC only fridge. We came home with one 90 amp 12V battery. As most people on here can imagine we ran out of battery about 18 hours into our first trip!! Since have upgraded to 2 x 6V AGM batteries (220 amp total), installed a battery monitor and bought a generator. Just got back from a 10 day trip with no services. Parked in shade so rooftop solar almost useless. Limped through running generator 4 hours per day and no one was allowed to turn a light on! We have solar on the side and would like to run a portable solar panel through our existing charge controller ( Go Power PWM-30-UL ) that is connected to our rooftop panel. Is this possible and has anyone done it? I Would a 100 watt panel be ok with possible expansion in the future? Any other advice would be greatly appreciated
Well if that's the same one that came on our 2017, it's a 30 amp pulse wave modulated charge controller. I thought it worked pretty well. We expanded our 200 Watts on the roof and simply spliced the additional panel in parallel at the mc4 connectors on the roof. No problem.

We spliced a line in to add an external panel parallel also and that wouldn't have been a problem we just never got around to doing it. That charge controller should handle about 500 watts of panels and if you wiring everything parallel so it's all going in at the theoretical 12 volt level which is actually between 18 and 20 volts normally there shouldn't be any conflict because the roof panel is putting out a different yield than the ground Mount panel that you might be focusing directly at the Sun.

My rving partner and I have installed or help people install well over a dozen systems and it doesn't sound like you'll be creating any problem at all with yours. Just be careful of the polarity when you're hooking things up so you don't reverse polarity and create conflict. That's a simple matter of having a voltmeter handy before you make every connection.
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Old 07-24-2021, 12:36 PM   #8
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Solar input

My idea was to not use the Zamp input with their puny wires.. I wired a 7-pin connector to match what my truck outlet uses to feed 12vdc battery power through the larger wires. I put it on the output end of my 200W suitcase panel using 12 ga. wires.

When the sun angles change, panels are now easily moved from one side to the other, as the trailer connection is always at the front ..Shorter leads with less voltage loss are nice to have since I don't have to cross wires under the rig.
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Old 07-24-2021, 01:45 PM   #9
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Originally Posted by Bunker View Post
My idea was to not use the Zamp input with their puny wires.. I wired a 7-pin connector to match what my truck outlet uses to feed 12vdc battery power through the larger wires. I put it on the output end of my 200W suitcase panel using 12 ga. wires.

When the sun angles change, panels are now easily moved from one side to the other, as the trailer connection is always at the front ..Shorter leads with less voltage loss are nice to have since I don't have to cross wires under the rig.
Don't forget, resistance of the wire is a factor of wire gauge and length. You can get away with a short run of 'puny' wire in this application. There are only a couple of feet of wire between my side inlet and the battery box. The longer the wire run to the battery box from the panel, the heavier gauge you want to minimize line loss, especially if the controller is at the panel, where voltage has already been reduced.
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Old 07-25-2021, 04:18 PM   #10
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Voltage drop

The equation for calculating % of voltage drop also requires a known current value along with the resistance from the total two-way length and size of wire. I often see that people overlook those when they try to figure how much loss they may incur without really knowing what their battery charge current may be.
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