charge controller question

[wine_guy_3]

I have 6 100 watt panels charging 4 batteries (12 volt system).
Panels are wired in parallel, just because that is the way it happened.

What happens if I wire the panels in sets of 2 in series (3 sets of 2).
Voc would be about 42 volts
Vmp would be about 34 volts.

I'm using a Ghurd controller.
Will there be a problem with the voltage difference between the panels and the batteries.
I was thinking about getting some 250 watt panels to replace the 100 watt panels.
Would this make things worse?

Thanks for the inputs.

 

[DamonHD]

If I've understood correctly, with a simple dump charger, the higher voltage of panels in series won't do any good (you'll be throwing most of it away while voltage is clamped to battery voltage) and you may fry something if the clamping goes wrong.

Rgds

Damon

[mab]

You'd get about half as much charge into your battery with them in series pairs a you do with them 6 in parallel. Unless you connect them to the battery using a good MPPT controller as these will convert high-volts low-amps from the panels to lower-volts higher-amps for the battery.

I'm guessing you're asking as the 250w panels are more usually in the 30-45v Vmpp  range? If you can look into the connection box of the 250w panels you might be able to re-wire them as 2 halves in parallel which would make them suitable for 12v charging - but it does depend on if the panels have the internal 'midpoint' connections accessible in the box.

Or you could consider converting to a 24v system? It has a lot to recommend it if you're moving to higher power.

[Scruff]

If you put another back box on the opposite end of the panel you can intercept the solar tab wire and make for instance 72 cell series into 2 x 36cell parallel with a bittov ingenuity. The backing material is very easy to cut through.
Any time I've thought of doing it though, a cheap used MPPT controller popped up and saved the day.

[wine_guy_3]

Thanks for the replies.
so.....
with a dump controller (not MPPT) it really doesn't matter what the panel voltage is, it will get clamped to the battery voltage?
so...
as long as I keep the system at 12 volts, the combination of panels does not matter.
I can mix and match 100 watt and 250 watt panels, but will be wasting the capability of the larger panels.
The only way around this is to get an MPPT controller.

I'm actually running four controllers on the same panels;
   One for Main battery bank charging
   three separate controllers for the ATV, mower, and tractor.

This setup is in a remote cabin. I only get up there once per month, and I want the batteries charged when I get there.

[DamonHD]

Yes to most of what you say, but in general I would NOT put multiple controllers on any one set of panels.

Multiple controllers feeding into one battery bank is generally fine (I'm doing it right now: main MPPT and small cheap PWM for a separate small cheap set of panels that catch morning sun mainly).

Rgds

Dmaon

[richhagen]

For a simple dumb controller - as opposed to one that boosts or bucks the voltage to be just above that needed to push the current into the battery (MPPT)- you want the maximum power point voltage of your solar panel setup to be at or just a bit above that needed to shove all of that current they produce through your wiring into your battery.  The controler you have is an excellent controller for its cost and what it does and that is why Mr. Hurd is at least a dozenair from selling them.  There is no point of connecting your panels in series on your system with that controller though because you would reduce the current and add voltage you do not need. 

On a side note, I have a couple of MPPT controllers in use and they are different animals.  They make better use of the power of my panels, but they also have a lot more parts and relays and such and are a huge amount more expensive.  I also have a bunch of non MPPT controllers in use, such as Trace C40's, some home brew that just open the circuit when the voltage gets too high and such.  While the MPPT controllers get a very noticeable amount more power out of the panels, I suspect that the simpler controllers will outlast them by a long shot.  I have wondered, but never actually calculated, given the life expectancy of panels, wiring, batteries and such, if it is economically worth the extra money for mppt versus using the difference to add more panels.  Currently, my belief is for me that it is worth it in my case, but this is largely because I am in an urban area where space is limited and so getting extra power out of that space has an added value.   Rich

[wine_guy_3]

Option #47
Leave the six panels in parallel with the PWM controller.
Add more (bigger) panels with a MPPT controller.
Run them in parallel to the batteries.

I could also use two MPPT controllers, one for each set of panels.

At 600 watts of panels I (theoretically) have up to 50 amps from the panels.
I either need to go up to 24 volts (new inverter) or go to two MPPT controllers to keep the amperage low.

I have two sets of #4 wire from the collection box at the pole to the controller in the garage.
Sound curious?
Any feedback would be appreciated (no pun intended)

[Scruff]

4mm² solar cable is 32A rated. Careful how you parallel them.