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Old 02-04-2016, 09:50 AM   #1
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Double solar system hookup.

Another off the wall solar question. Is it safe to hook up two independent solar systems to the same battery pack? Ex: a Renogy 100 watt suitcase using a 10 amp controller and another independent 75 amp panel run thru another controller. Just a what if.
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Old 02-04-2016, 09:58 AM   #2
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No, you should wire separate systems to a single controller. I installed connectors to my ZAMP portable system in order to remove the ZAMP controller while connected to the AS pigtail. I kept the ZAMP controller mounted to the suitcase so I could use the portable for other stand alone applications, but it is effectively removed from the system and creates a parallel with my permanent panel through a single Morningstar hard wired AS controller.
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Old 02-04-2016, 09:59 AM   #3
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Parallel connections are typically permissible as long as there is not a gross mismatch from one another!
It's basically like having your converter and solar controller together.
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Old 02-04-2016, 10:03 AM   #4
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Here is a rough drawing of my setup:

Click image for larger version

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Old 02-04-2016, 10:06 AM   #5
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Any mismatch of output voltages will cause reduced efficiency of the system....when in the cycle(s), and how much of a mismatch determines how much inefficiency. Theoretically, there will be times in their respective cycles where there is zero gain from one subsystem or the other.
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Old 02-04-2016, 10:22 AM   #6
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Voltage to the batteries is voltage to the batteries..... despite a differential.
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Old 02-04-2016, 10:26 AM   #7
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Originally Posted by AtomicNo13 View Post
Voltage to the batteries is voltage to the batteries..... despite a differential.
Negative. A voltage differential on a parallel circuit will cause resistance in the lower voltage leg, reducing the amperage from the lower voltage leg.
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Old 02-04-2016, 10:29 AM   #8
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Rich (dznf0g) pretty much explained all it. Friend here has a Renogy suitcase, same one you have with a 300 watt Renogy kit on the roof. He kept finding that the roof controller was still charging but the suitcase kept reading as full. Basically the systems were mismatched.

So I helped him bypass the PWM on the back of the suitcase, and we wired it with a SAE plug into the one controller for the roof solar. Works better that way.

The only good way to run two separate controllers is if they can communicate with each other. Like Bluesky and Victron units do.

For example, I have a the SB2512 and SB3024 - the 2512 is slaved to the 3024 for my ground deploy solar.
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Old 02-04-2016, 11:10 AM   #9
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OK, bad idea. It was just feeble brain storming. I do have another new PWM 30 amp controller I could swap out the 10 amp Renogy unit and add the 75 watt panel. Effectively and guessing again would up my system to 175 watts or would that cause too much of a miss match? At this time wanting to stay away from hard wiring a solar system and keep it simple and cost effective.
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Old 02-04-2016, 11:20 AM   #10
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I would need to know more about the specs of your two panels to comment, but if they are close in specs, you probably can parallel them into that controller.
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Old 02-04-2016, 11:24 AM   #11
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The Renogy panels are two 50 watt mono. The other is a 25 year old Siemans 75 watt that still puts out close to its rated amps. I used it on my boat for 10 years in the Carribean.
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Old 02-04-2016, 11:33 AM   #12
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The Renogy panels are two 50 watt mono. The other is a 25 year old Siemans 75 watt that still puts out close to its rated amps. I used it on my boat for 10 years in the Carribean.
More specs on each please. Open circuit voltage (Voc), etc....as well as your controller specs.
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Old 02-04-2016, 11:55 AM   #13
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Running a Trimetric controller and monitor. All neg wiring goes through a shunt that monitor uses to monitor charging. Just got a 100 watt Renolgy suitcase, hooked it up to negative to shunt and batt positive terminal. Working very well.
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Old 02-04-2016, 02:06 PM   #14
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Voltage to the batteries is voltage to the batteries..... despite a differential.
Except that the lower voltage won't be doing anything! The higher voltage would normally feed back into the lower voltage except that the controller has a diode to prevent back voltage.
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