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Old 05-21-2022, 01:25 PM   #1
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dual solar controllers question

So I see lots of threads about using more than one controller, but I have yet to find an answer to this question of mine.

I currently have 300 watts roof mounted. So I know when I am on shore power, the controller "behaves" differently, moaning it does not push as much power to the batteries since the convertor is working, especially when it is in boost.

So, how do multiple controllers work together if one see the higher voltage of the other, does it not step down? They are not communicating so can only register the current voltage, and if one is putting out 13.8 volts, the other would shut down right?

Or is it that one set, say the roof mounted, is not producing enough so the other senses the lower voltage and produces to its potential?
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Old 05-21-2022, 02:01 PM   #2
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Different charging sources, chargers, alternators and solar controllers have slightly different charging parameters, but they will all adjust to one common voltage at the battery. Then each will supply current based on that voltage, some reduced, some not and all will coexist fine.

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Old 05-21-2022, 02:31 PM   #3
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ok, so you will not actually increase the charging capacity by adding one source to the other, but one may produce more in the absence of the other, and therefore working together to charge
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Old 05-21-2022, 03:04 PM   #4
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Typically multiple charge controllers are combined at a bus bar or power distributor (eg Victron Lynx) and then connected to the battery bank.

All power sources are fused accordingly prior to this distribution block.
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Old 05-21-2022, 05:16 PM   #5
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I have two solar charge controllers rated 50A each. I have seen each one pushing 35A to the batteries. That's about the best my solar panels can do. If I had more panels, they might push more amps. They just see voltage. When one turns on and starts charging, it tries to put out 14.6V but if the battery needs charging, the actual voltage at the battery might be 13.4V. The other charge controller sees that and also starts pushing amps. If the battery is really hungry, then the voltage will still sit around 13.4V. Once the voltage starts rising as the battery charges, both controllers will see that and throttle their charge per the charge profile. Mine is set to absorb @ 14.4 and float @ 13.4. Once the battery hits 14.4V, the controllers will switch to float. Once the BMS says "enough", it will cut off the charge and the controllers will show 0 amps.

If I have the inverter/charger running, it works the same way. They all seem to contribute something until the voltage hits 14.4V and then all go to float until the BMS has had enough.

The key is to make sure all your charging sources are set to the same voltages. I also have a DC-DC smart charger connected to the truck. That is also set to 14.4V and 13.4V. If I set any of them to different voltages, they would contribute differently.

I hope that makes sense.
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Old 05-22-2022, 09:38 AM   #6
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Over thinking

It is complicated, but you do not need to over think it.

Multiple controllers connected to a battery bank will usually work fine together. Some may contribute more than others for electrical reasons. Overall, the battery bank will be the primary control on current.

Controllers are usually in voltage regulation mode. Deeply discharged batteries will take more current than nearly fully charged batteries.

The only time you will get full current from a controller is when the batteries will take more than the controllers can deliver. If a controller is idling it is because the battery bank is not absorbing more.
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