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Just a heads up. When using multiple charging sources or controllers, the source or controller putting out the highest voltage will shut down the output of the source putting out the lower voltage. Thus as long as output voltage is equal or near equal they will work together, but once one voltage becomes higher, the other controller or source will read that as meaning the batteries are topped off.
Xantrex sent out a white paper to RV techs (yes I was one) a good while back advising them of this.
Steve
Steve and Andra
2012 F350 6.2 gasser SRW LB
Fab Fours front and rear in case we run into a rhino
2019 Northstar Laredo SCExactly. In some cases you might get lucky and have controllers that use the same charging algorithms, but I don’t think you can depend on it. A single large controller and a combiner box is the best solution in my opinion.
Steve and Andra
2012 F350 6.2 gasser SRW LB
Fab Fours front and rear in case we run into a rhino
2019 Northstar Laredo SCWhen I designed and installed my solar system (two 100 watt roof panels and a 60 watt portable folding panel), I saw that given the narrow voltage range within each of the bulk, absorption and float charging cycles, that two competeing controllers would not work. The first thing I did with my portable is drill out the rivets attaching the PWM controller and remove it.
AM Solar, who sold me my two roof panels, were nice enough to review the voltage of my portable and confirm that it could be wired in parallel to the roof panels and all controlled by my single MPPT controller.
Remember the obvious: that when wiring panels in parallel, the amperages combine (are additive) but the voltage of the combined system will be that of the panel that produces the lowest voltage. So if combining roof panels and a portable, you do not want a portable that produces significantly less voltage than your roof panels or you drag the power produced of your entire system down (volts x amps = watts).
Since most panels generally produce similar voltages, one other important aspect of having a portable, is to minimize the voltage drop from the panel to your common controller. Your portable may be rated for a similar voltage as your roof panels, but if you have 20, 30 or more feet of #10 or worse, #12 wire between your portable and your controller, the voltage drop in the cable will make the combined voltage of all panels that much lower and you’ll have less power (watts) from the entire system.
I use marine duplex #8 cable to get from my portable to my system. Due to the finer stands and higher quality of the insulation, the marine #8 is super flexible and voltage drop is minimized. Being duplex, the red and black cables are in a common white sheath to keep things tidy. I use Anderson connectors for an easy, safe, and foolproof method of connecting the cables. The portable can be just 15 feet from my rig or if in a grove of trees, I have a 25 foot extension I can insert to get it even further out of the shade into the sun.
For a combiner, I used mini battery switches with a 1, 2, BOTH or OFF function. So I can use either the roof panels (1) or the portable (2); or combine them BOTH; or turn OFF all sources to the controller. Makes it safe to work on any part of the system and assure myself that the controller is drawing on exactly the panel(s) I want it to.
My setup is two systems operating in parallel with 2-6v GC’s as follows:
300w MPPT multi-stage controller
140w PWM single-stage controller (add-on supplemental system)
I first tried a multi-stage controller on the 140w system, but found it would often shut down or be in conflict with the MPPT controller, rendering the system inoperable…
When I swapped out this supplemental multi-stage controller with a simple ASC brand ‘ON-OFF’ type PWM controller, system performance was greatly improved, plus the supplemental 140w adds a bit of appreciated overall redundancy…From my experience, two ‘multi-stage’ controllers in parallel is a poor Duo…
The simple ASC ‘OFF-ON’ controller (from Mrsolar.com) terminates charging at 14.3v, and resumes again at 13.5v, which compliments the larger MPPT System very well and has proved in this configuration to be the optimum arrangement…
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