Solar mysteries

Crows Nest

Senior Member
RV LIFE Pro
Joined
Jul 3, 2023
Messages
270
Location
Los Osos
A few questions regarding the dark arts of solar panels, lead acid batteries and lithium power stations.

I have an external port to attach a 220w portable solar panel. When I connect this panel directly to my Anker power station it charges with 170 watts. When I connect the panel to the port I get around 65 or 70 watts. My rooftop panel charges at 65 to 85 watts.

The portable panel was oriented towards the sun while the rooftop is of course flat but as noted above the portable panel performs no better than the rooftop one. Also, if I attach the portable panel am I getting charge from both panels? When I plug it in the wattage would jump to around 140 but instantly drop back to 60 or 65.
 
My first suspicion is the wires running to and from the solar controller. In our 21NE the wires from the panels to the controller are 8awg, which might be ok. The wires from the solar port to the controller and from the controller to the battery were ridiculously small, maybe 16 awg. Not sure exactly how you can tell if that’s the reason but it probably involves current testing with a multimeter. Maybe start by checking the size of your wires to see if they’re like ours.
 
If both panels are sharing the same controller, parallel configuration, both panels will be limited by the output of the weaker panel. In this case the roof panel due to sun angle, is limiting the output of the portable. This is why I have a separate controller for my Zamp port. The Anker's controller is only dealing with one panel so it's capable of full panel output.
 
If both panels are sharing the same controller, parallel configuration, both panels will be limited by the output of the weaker panel.

I thought that shading was a worse issue when using series wiring, not parallel.

But I like the thinking that one panel is limiting the other. In parallel the power is limited by the lowest output voltage of either panel (roof or portable). If they are in series, the power would be limited by the lowest output amperage of either panel.

Can you disconnect the roof top panels from the controller and see what power you get from the portable panel alone connected thru the port? That could help clarify if it’s wiring or limits from mis matched panels
 
This is why I have a separate controller for my Zamp port. The Anker's controller is only dealing with one panel so it's capable of full panel output.
Does the wiring from the two controllers get spliced together?
 
I don't have a zamp port for my portable panel (to which I've wired a waterproof controller), and I feel no motivation to install one. It's easy enough to attach it to the battery with alligator clips; that way it feeds the battery directly and doesn't have to pass through a bunch of other wiring & devices.
 
Does the wiring from the two controllers get spliced together?
Not knowing how your trailer is set up, here's mine. The first image shows my solar controller and Wago wiring as it came from ETI. Note, it wasn't wired correctly and the Zamp port and battery were wired together. Essentially that's what you would do with a second controller between the Wago connectors and the Zamp port. The sencond image shows my solar system with two controller; one dedicated to the roof panel and the other to the Zamp port. I've also added a solar disconnect switch for the roof panel and a battery disconnect switch for each solar controller.
 

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If your controller is attached to the portable panel it's running 14.6v at best. Your wire is probably 12 awg and will have more line loss than a panel that has the controller in the camper with either a 6-8 awg wires going to the batteries from the controller.

Two dissimilar panels going to the same controller will also have a loss, unless the panels are matched perfectly.

When we purchased our 5.0 it came with a 170 watt panel and a GoPower PWM controller. Adding a 100 watt portable panel into the GoPower controller gave us not much more wattage. I then purchased a Victron 100/20 for the portable (leaving the 170 watt panels hooked to the batteries) and we found we got as much as 118 watts from the portable PLUS whatever the 170 watt panels was outputting.

Best practice is to have the portable on one controller and the rooftop panels on another controller in the camper, not one with the controller on the panel itself. Both controllers can be separately wired to the batteries.

The output of a 12v panel is usually around 20 volts (I've seen as low as 17.6 and as high as 22v), but the output of the panel mounted controller is around 14.6 volts at best. The higher the voltage the less line loss, allowing you to have longer wires to the solar port (we have three 15' wires, or a max of 45' from the port).

In the end, we had a Victron 100/30 for our three 100 watt panels and one 170 watt panels that luckily had the same VMP. We got as much as 445 watts from the potential 470 watts of panels on the roof. The roof of a 5.0 is not flat, so the front panel was tilted to the front and the other three tilted to the rear, plus one panel could be shaded early/late in the day. The portable's solar port was hooked to a Victron 100/20. Both were wired separately to the battery bank.

Once we had 470 watts on the roof, and had 260 ah's of batteries, we didn't ever need the portable, but it was there just in case.

If you have a GoPower PWM controller, ditch it for a Victron MPPT controller (much more efficient) for your rooftop panel. Also run a separate MPPT controller for the portable. We had a Victron 100/30 for the rooftop and a Victron 100/20 for the portable.

Food for thought,

Perry

Written from Palo Duro State Park where the highs for the next three days are expected to be 30F, 28F, 27F, with the lows 14F, 9F and 22F. We then go to Caprock Canyon SP for 5 more nights where it will be similar temps.
 
My Zamp port is also wired into the same controller as rooftop panel. Easy to change with new controller. According to Perry I want separate wire from each controller to the batteries (two 6v). I line the cut off switches. Thanks.
 
One step you might consider before buying another controller is to check the differences in max volts and max amps for each of the panels (Vmp and Imp). Assuming they are wired in parallel, you can add the max amps together and multiply that by the lower of the two max voltages. This will give you your max power in Watts. You can then compare this to the sum of the rated watts for the two panels to see how much power you are actually losing by having the panels on the same controller. If it’s not that big a loss, some bigger gauge wiring may solve your problem (assuming your wires are undersized, as ours were).
 
What did you use for the disconnect switches?
There are numerous options people use but its my understanding that both wires from the panel should be disconnected (isolated). I watched some videos on Explorist.life and that website also sells products for that purpose. I purchased a low voltage DC breaker and circuit breaker distribution box from Amazon. That specific box is currently unavailable but there are others brands that are nearly identical. Explorist.life has one that is smaller and they have a rotary switch version. They are shown under solar isolator. The photo below also shows the Blue Sea battery disconnect switch I installed for the Controller. Typically, when I disconnect the solar, I then disconnect the battery connection to the controller. When I reconnect solar I do the sequence in reverse; reconnect the battery to the controller, then reconnect the solar. Your Zamp port doesn't need a solar isolator since all you have to do is unplug it. I did however install a battery disconnect on the Zamp port controller.



 

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Disconnects the batteries from the 12VDC side of the power center. This affects lights, frig, MaxxFan, heater etc. It does not disconnect batteries from solar controllers and anything directly connected to the batteries including the break away braking system.
 
It occurred to me that if I don’t need to use both panels at the same time (the portable was meant for use if rooftop was in shade) I could just use a solar shutoff switch for the roof panel which would allow the portable to work alone.

This would eliminate the need for a second charge controller.
 

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