I have a 180 watt solar panel on my trailer's roof, connected to a PWM charge controller. My controller is rated to handle an additional 100 watt panel. I would like to add this as a portable panel so I can charge when parked in the shade, or have both panels going when parked in the sun, if necessary. I have two 6v Trojan GC batteries, so the extra 100 watt panel will be put to good use. The question is, should I spend the extra $50 (at Renogy) for a portable suitcase with a charge controller when I already have one in my trailer? I could buy a suitcase without a controller, but is there an advantage to having the full suitcase with controller? Maybe versatility down the road?
Portable Solar panels- DIY vs Solar Suitcase
- Thread starter Mfitz
- Start date
ConcordCarlos
Member
While using the portable with its own controller, is there any “interference” if the built in panel/controller is also feeding to the battery? Even if the built in is partially shaded and at less than full output? In my mind you are simultaneously charging the battery from two sources.
LivinDaDream
Member
No problem at all, I do it fairly frequently with two MPPT controllers in the same way you're planning. Just be sure that you have both set for similar charging parameters. The only PWM controller I've ever used only allowed you to set a PV cutoff voltage when charging and I typically had it set to 14.4V. Might want to check your manuals to see if you have that sort of setup or a more sophisticated model that has actual battery type profiles.
To answer the rest of your question, power does not flow back into one of your solar controllers if it's not able to supply power at a voltage higher than that of the battery or the battery and power flowing in from another source, vis a vis your other controller feeding power from the panels in the sun. If both controllers can supply power at a voltage above that of the battery, then power will flow from both and charge your battery faster.
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ConcordCarlos
Member
Good to know . I would think that with both controllers my monitoring the battery status , they would protect the battery from over charging ? My built in Victron shows reduced wattage when the battery is nearing full charge , transitioning to float. At first I thought there was an issue with the panel when the app was showing 2 - 5 watts in full sun.
LivinDaDream
Member
Whether or not you can rely on your controllers to prevent overcharging will depend on how your controllers are set up and how sophisticated they are. I'd dig into the manuals and learn exactly how each works. From what you describe it seems like you are transitioning to float mode, but without knowing what voltage that's happening at and what your specific batteries require, it's all just guessing. Do you have a good multimeter you can use to read the voltage at the batteries? Also good to see if you can go to your battery mfr site and find what they recommend for charging profile voltages.
rruff
Explorer
Input voltage will be "controlled" by your battery, and each circuit will deliver charge as it is capable.
One thing to consider for your portable is running it at 24V with an MPPT controller to cut down on wiring size/losses. May not be worth it though, depending on how long your cable is.
ConcordCarlos
Member
I have the Victron 75/15 currently . I have it set for AGM as I am running Odyssey (s). I was thinking about carrying two panels so I could set them out and leave them to track during the day without me having to move by one panel constantly.
ConcordCarlos
Member
I don’t think I have more control than the pre-sets. Will dig into the manual .
LivinDaDream
Member
I don't own any of the Victron units, but I've looked at them and they all have user adjustable settings in addition to the presets for your AGM batteries. The Victron AGM preset should be fine. Shouldn't cause any issues with your PWM trailer system as long as it's also set for AGM batteries.
ConcordCarlos
Member
The trailer question came from the OP, but good to know .
Ok, so it looks like I should be fine running a 100 watt Renogy solar suitcase with a 20a PWM controller at the same time as my roof mounted panels also charge the batteries. I think this is the way I will go since it lets the Solar suitcase work as a stand alone system should I want it to down the road.
ConcordCarlos
Member
current settings via the pre set . Need to review Odyssey’s set points before I mess with it .
67cj5
Man On a Mission
To Charge AGM's properly you need to set the Charge Voltage and the Float Voltage depending on what the Abient temperature is IE the Battery Temp, You can't just use someone elses set of figures and apply them to your setup unless they live next door to you, Your setting Rates need to match the Abient Temp at the Hottest part of the day and as winter comes on you need to adjust the settings to match, It soulds daunting but it is really easy using one of Victrons MPPT Smart Controllers.
Using a higher Voltage in 30*c /90*f temperatures will shorten the battery life, and the hotter the Temperature the lower the Voltage settings must be.
Using a higher Voltage in 30*c /90*f temperatures will shorten the battery life, and the hotter the Temperature the lower the Voltage settings must be.
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