Remove Stock 40w Panel Before adding?

TriBeard wrote:
I checked all three panels with a multimeter today with full (but not directly overhead) sun. The two 100w panels were about 20.5v at their individual leads, and the 40w panel was between 21.5 and 22.4V at it's lead. I guess I've just never run the batteries low enough to see any higher amps coming in. We're preparing for an 11 day trip where we'll only have power 2-3 of those days, so it should be a better test of the system than the last couple short outings have been.

Be sure to let us know how it goes. Don't leave us hanging! :B

I checked all three panels with a multimeter today with full (but not directly overhead) sun. The two 100w panels were about 20.5v at their individual leads, and the 40w panel was between 21.5 and 22.4V at it's lead. I guess I've just never run the batteries low enough to see any higher amps coming in. We're preparing for an 11 day trip where we'll only have power 2-3 of those days, so it should be a better test of the system than the last couple short outings have been.

MrWizard wrote:
When camping
The most power will occur at solar moon IF the batteries are low enough to accept it,
Example: rain yesterday, rain this morning
It's almost noon and the sky has cleared up

Exactly!! Amperage will be greatly reduced when battery is nearing full capacity, and far greater when battery is needing a charge...

When camping
The most power will occur at solar moon IF the batteries are low enough to accept it,
Example: rain yesterday, rain this morning
It's almost noon and the sky has cleared up

Agreed, but if theres and shadowing over a panel, its harvest will be drastically reduced...Make sure your in full sun...For a bit of troubleshooting and a good place to start, you can disconnect each panel (say one panel at a time) to confirm a possible output reduction at the controller - no reduction in amps means that that panel(s) or wiring is not functional...

Good Luck,

3 tons

I did wind up just going ahead and adding the two additional panels to the OEM connector with a splitter, and everything seems to be working normally. It is hard to tell how much power the panels are pulling because I think the charge controller I have only shows me the current amps that are going into the battery, not the amps the panels are producing/capable of producing. I've never had the batteries run low yet, but the highest I've seen (I've actually had these installed for about a week but started second guessing my install) is about 6-7amps. I know I won't get 240w in reality, but on a sunny day I figured I'd get 180ish or so, which would be more like 12-15A right?

It’s important to avoid conflating 12 and 24 voltage terms...

Your existing panel is a ‘12v panel’, as are the 100w panels you are considering...

What ‘12v panel’ refers to is merely a shorthand jargon for ‘nominal’ battery voltage (not actual), nor does it refer to ‘actual’ panel output...

The typical 12v ‘any-brand’ panel has 36 cells, each cell output is at approx 0.5v - 0.6v x 36 = approx 18’ish volts which is an ideal amount to overcome inherent wire run, connector and controller-heat loses and still provide the battery the 14 + (or so) volts needed to overcome internal chemical resistance (chem soup sluggishness)...

https://en.wikipedia.org/wiki/Solar_cell

As a ‘practical matter’ the efficiency advantages of mono vs poly have more to do with per sq inch roof-top footprint...(a photon yield thingy).

No real need to overthink matters - I would simply utilize the extra OEM connecter (by adding a duplex splitter), parallel connect the additional two panels, then call it a day...JMO

3 tons

I agree. Same voltage, keep it. Different voltage, remove or disabled and save.

TriBeard wrote:

naturist wrote:
Assuming all panels are the same voltage, a 30 amp controller should be able to handle all 240 watts of panels. Put them all in parallel, and it should be fine. 240 watts at 12 volts is 20 amps, well within the controller’s capacity.

Of course, upgrades are always possible. But the simplest is just adding the 200 watts.

Judging by the spec sheets I was able to find, the voltages are within a volt or two of each other, but they're not identical.

Volt or two isn’t important. Raw voltage from a 12 volt panel is going to range from about 8 volts to about 19 volts depending on sun. What matters is spec voltage, thus a 12 volt panel can’t be parallel with a 24 volt panel, which will put out between 16 and 38 volts. The panels will adjust their own output to cover a volt or two.

Same thing happens if one panel is in sun, other in shade. Two panels of same nominal voltage will be fine, the shaded one just won’t contribute.

naturist wrote:
Assuming all panels are the same voltage, a 30 amp controller should be able to handle all 240 watts of panels. Put them all in parallel, and it should be fine. 240 watts at 12 volts is 20 amps, well within the controller’s capacity.

Of course, upgrades are always possible. But the simplest is just adding the 200 watts.

Judging by the spec sheets I was able to find, the voltages are within a volt or two of each other, but they're not identical.