Too many panels for sunny weather??

aglicknmex · March 2012

My new 18panel/235w system is working great in sunny weather. Battery back to full charge 2-4pm, even with heavier use during the day. Cloudy weather changes that.

In SW New Mexico, we have a regular summer monsoon season

during July and August it clouds up almost daily and threatens rain. Oddly, even with the long days, these can be the lowest production months!! The rest of the year we have mostly pure sunshine!!

I am maxed out on my charge controller, so I cannot permanently add another string of panels. But, I am thinking about adding another string of 3 panels to keep my battery going in cloudy weather. To avoid damage or shutdown from too many charge amps, I need to come up with an intelligent way to switch these panels in and out. I really dont want to buy an extra charge controller and I already have the panels.

Most logical is to monitor charge amps into the battery and switch the extra panels in and out. I could build something, but would not consider that "safe and dependable".

Is anyone aware of a commercial circuit that would sense from a shunt and offer some kind of output(I can handle the actual switching part) I would welcome any ideas. This should not really be too hard. Thanks up front.

niel · March 2012

Re: Too many panels for sunny weather??

that is too difficult to just watch the voltage and odds are you'll screw up sooner or later and i'm talking from experience here. the alternative is to put a regulation circuit inline which is what a controller actually is. i don't know what kind of a battery bank you have or its voltage, but even a pwm is better than messing up your batteries by trying to guess when to disconnect the pvs.

vtmaps · March 2012

Re: Too many panels for sunny weather??

What charge controller do you have? Some CC can be set to limit output, and there is no problem just adding more panels.
--vtMaps

aglicknmex · March 2012

Re: Too many panels for sunny weather??

Actually i have the new midnite classic 150. It will limit current. I have not been able to find out if it shuts down or just limits. The guy at midnite I talked to wasnt very clear on how it worked, I wasnt sure he really understood it. Maybe I should get on the midnite forum and see if I can get a better answer???

Mean while, I still think using a current sense circuit set at say 80 amps would work. I like this kind of project, so its just kinda fun exercise...........

and Niels you mentioned monitoring voltage----your right that would not work, has to be sensing a high current and removing the extra panels.

westbranch · March 2012

Re: Too many panels for sunny weather??

IMSMC there is a posting on the Midnite board that has an answer for your issue.

BB. · March 2012

Re: Too many panels for sunny weather??

In general, any good quality MPPT charge controller should limit its output to its "rated maximum". Some controllers even allow you to program the limit down too.

Are you worried about too many solar panels driving the Midnite Classic >80 amps? If so--that is not an issue (that I know of).

If you have too many panels in series and can get Voc-array>maximum rated input voltage for any controller (Voc-cold)--Then that is a real problem and you have to design the series/parallel connections of your solar array to avoid over voltageing the controller.

One of the things that is sometimes done is to take a small MPPT controller and use it to step down voltage from a 24 or 48 volt battery bank to 12 volts. The MPPT charge controller does that very efficiently and safely. Battery banks have way more current available than the typical solar array.

The one caveat is to use an input fuse before the MPPT controller input to protect the wiring of the battery bank in case something gets shorted downstream (wiring, controller, etc.).

-Bill

niel · March 2012

Re: Too many panels for sunny weather??

do you have the pvs in series groups of 3 presently? if so then have them form another series string of 3 with a fuse or breaker on it and add it to the rest of the pvs being inputted to the classic and just be sure it will not exceed the classic's rated limit (depends on both the pv system specs and the battery bank voltage). you will find giving more info that many here can be more specific on the answer, but you can put more pvs to the controller. it just won't output more than either its lower setting or max ability. many at midnite do come here too, but it is a fair question that you can duplicate for their forum as well. edit to add---i failed to read properly as it already exists there. my bad.

aglicknmex · March 2012

Re: Too many panels for sunny weather??

Thanks westbranch,Finally found the thread over at midnite. boB is not too worried about the scenario. Says the classic is pretty tough, but would spend quite a bit of time current limiting. I can cut down on heat and driving it hard, by throwing the breaker on one string when we get one of our really long sunny stretches. Appreciate the help

Too many panels for sunny weather??

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