Is my buddy smarter than I?

[XJINTX]

I was camping with some friends this past weekend in the rain. Various setups and I was the only FWC onsite. Looking at the other setups I mentioned the Hawk had an additional SOLAR plug at the back so I could plug a second backup solar when needed. It was a rainy weekend and batteries were getting low. I mentioned I might plug another guys portable Solar panel in for some extra charge. My "knowledgeable" buddy said that the panel had to be a same power as my 160W on top???? Does anyone know if this is true? I always assumed I was fine as long as polarity matched. Do they need to have the same power rating?

 

[Optimistic Paranoid]

An interesting question. First of all "power" is watts. They absolutely don't have to be the same watts.

Volts are electrical pressure, so if one set of panels is putting out a higher voltage than the other, and it raises the BATTERY voltage higher than the voltage provided by the second panel, I suppose that would keep any current from the second panel from flowing to the battery. Theoretically. In the real world, I'm not sure that would actually happen.

Why don't you just borrow the other guy's portable panel, plug it in, and see what happens?

And do let us know how the experiment goes.

 

[XJINTX]

Why don't you just borrow the other guy's portable panel, plug it in, and see what happens?

And do let us know how the experiment goes.

I actually have a 100W Renology panel here at home. Guess I may plug it in and try... if it will not hurt anything.

 

[patrkbukly]

Interesting question;
I was just at the Overland Expo West and spent some time with the Overland Solar folks who are now the solar provider for FWC.

The very knowledgable guy there explained to us that in the situation you describe, it actually will send less to the battery because the controller will seek the lowest coming in. He explained it in great electronic engineering speak which I can't repeat like him but in summary thats what he told us.

This came after my buddy with me was going to buy one of their portable 100 watt mobil panels to use when he is parked in shade.

 

[CarlG]

This is why I wired up an A / B / A+B selector switch for roof solar / rear solar when I re-wired for lithium, so that if my roof was shaded it didn't draw down the voltage of the rear portable panel.

 

[rando]

Ideally your roof and portable panels should be close in Vmp if they are to be paralleled, but realistically it doesn't really matter (assuming they are either both '12v' or both '24v' nominal panels).

The MPPT controller will find the maximum power point for the combination of the panels, which will probably be closer to the Vmp of the lower voltage panels but their currents will still add. Shading one of panels won't draw down the voltage of the other as the shading primarily has an impact on current, not voltage. This is happening anytime you have two panels in parallel, I had two panels in parallel in my roof, and shading one panel would not bring down the output of the other.

 

[So Cal Adventurer]

Another thing to consider is polarity of the plug to your buddies panel.

Unless its a ZAMP brand panel, chances are 90% it will have its polarity backwards for how the FWC is wired.

 

[Norsman]

Another thing to consider is polarity of the plug to your buddies panel.

Unless its a ZAMP brand panel, chances are 90% it will have its polarity backwards for how the FWC is wired.

I thought Zamp SAE plugs are reversed from normal polarity for SAE, as in they cover the positive terminal for safety.

Here is my FWC plug polarity on the back wall, the unprotected terminal is positive and shows current from the panel on the roof.

https://norsman.smugmug.com/Camping/FWC-Misc/n-72Mqkn/i-2c34DvN

The image will most likely not work, I have never had more difficulty in sharing links and photos than this forum.

 

[Old Crow]

HI, Norsman-

Take a look at this explanation and see if it helps. I've got to run so I only had time for a quick look for info but that one has a photo of Zamp solar port wiring and also the wiring off the typical Zamp panel.

I could see the photo, by the way.

.