putting two charge controllers in series to get two 12v out of a 24v panel

[johnmorin]

Just starting to set up a small solar system off grid at the cottage. The price of a 250w panel is barely more than a 100w panel. Proplem is if you are running a 12v inverter the 250w panel will not give you any more power than the 100w panel. What if you put two charge controllers in series so theoretically each would put out 12v at the maximum amp output then you could connect both outputs to your battery bank and get the full use of the 250 watts. Has anyone tried this or have any experience in it. Just trying to save a few bucks on panels and save some space and mounting hardware

Thanks

[paulcheung]

When you use 200+watts panels you required to use the MPPT charge controller.

[Mike90250]

I don't see how 2 controllers in series, can work electrically

[johnmorin]

I don't see how 2 controllers in series, can work electrically

What I understood is that a 250W 24v panel will put out 250/24 = approx. 10amps. I understood that if you are using a 12v system you can only still get 10amps output from the panel, thuss 10amps x 12v only = approx. 120w. If you put two cc in series, the output from the panels will still only be 10amps but if you can get the 10 amps out twice at 12v you should be getting close to your full 250 watts of power to your battery banks no?

[Silver_Is_Money]

What I understood is that a 250W 24v panel will put out 250/24 = approx. 10amps. I understood that if you are using a 12v system you can only still get 10amps output from the panel, thuss 10amps x 12v only = approx. 120w. If you put two cc in series, the output from the panels will still only be 10amps but if you can get the 10 amps out twice at 12v you should be getting close to your full 250 watts of power to your battery banks no?

With an MPPT charge controller you get PV Watts in = battery charging Watts out. 250 Watts/12.5 volts = 20 amps of battery charging current

[Sunking]

The price of a 250w panel is barely more than a 100w panel. Proplem is if you are running a 12v inverter the 250w panel will not give you any more power than the 100w panel.

Wrong. Use a MPPT Controller. You would be right if you were foolish enough to use a PWM controller with a Grid Tied Panel.

[inetdog]

I don't see how 2 controllers in series, can work electrically

I think the OP is planning to run the panel DC output through two PWM CC inputs in series ( panel+ to CC1+, CC1- to CC2+, CC2- to panel-). That might actually work after a fashion if the two CCs were connected to two separate ungrounded 12V batteries. But the OP then suggests putting the two CC outputs in parallel to one 12V battery.
Since a PWM CC does not isolate the input from the output there is no way in the world that would do anything useful and would probably let the magic smoke out of at least one of the CCs. And worse, probably put a dead short on the battery.

[Sunking]

That might actually work

How?

PWM in any orthodox or unorthodox configuration cannot get around the fact Imp of the panel is what it is. So how does connecting two controllers in series comply with Kirchoff's Law for series connected circuits?

[inetdog]

How?

PWM in any orthodox or unorthodox configuration cannot get around the fact Imp of the panel is what it is. So how does connecting two controllers in series comply with Kirchoff's Law for series connected circuits?

If you could just get the PWM controllers to coordinate their on times, you could use a 36V or so panel to drive Imp through two CCs in series, each charging a 12V battery with no ground reference connected to that CCs terminals. The batteries would have to start out with identical SOC too, of course.
It would be a useless exercise, of course, since the right thing to do would be to put the two batteries in series and use one 24V CC.

[johnmorin]

With an MPPT charge controller you get PV Watts in = battery charging Watts out. 250 Watts/12.5 volts = 20 amps of battery charging current

Hey, Thanks, I guess if I had just paid a little more attention to the tutorials on charge controllers I could of answered myself lol!!!! thanks again

[Sunking]

If you could just get the PWM controllers to coordinate their on times, you could use a 36V or so panel to drive Imp through two CCs in series, each charging a 12V battery with no ground reference connected to that CCs terminals. The batteries would have to start out with identical SOC too, of course.
It would be a useless exercise, of course, since the right thing to do would be to put the two batteries in series and use one 24V CC.

OK Dave you know how PWM works, so I will not labor that. However when a PWM controller is full on or Maximum Smoke the duty cycle is 100% or basically a short-circuit or closed switch which connects the panels directly to the battery. So now you have panel Imp current at battery voltage. Just yanking your chain.