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Author Topic: Separate battery banks feeding one output  (Read 383 times)

Dawie

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Separate battery banks feeding one output
« on: January 08, 2018, 03:38:19 PM »
Hi All

I have a question which I fear might expose my lack of knowledge but would appreciate any advice please.

Attached rough sketch of what I would like to achieve.  In short I basically have two separate charge controller + battery rigs, I plan to feed both from a single solar panel and would also like to have the output from both "combined" to drive the load.

The reason for this configuration is that the one controller + battery is used for camping but when at home I would like to plug it into my "permanent" 12v DC setup so that the camping battery is also cycled to a degree rather than sitting idle for extended periods.
The batteries are 12V but differ in terms of make, capacity, age.  The charge controllers are also different except for their 20A ratings.  Hence I want to treat these as separate controller + battery systems but simply draw load from both.

I am fairly comfortable (perhaps due to my ignorance) to split the PV input to both controllers but suspect that I can not connect the output from the two controllers in parallel as suggested in the sketch.  Please advise?

Regards
Dawie

SeanB

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Re: Separate battery banks feeding one output
« Reply #1 on: January 09, 2018, 07:55:15 AM »
Better to just simply connect the 2 batteries in parallel, and disconnect the one charge controller, so they both have a float charge applied, and are both cycled lightly.


Dawie

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Re: Separate battery banks feeding one output
« Reply #2 on: January 09, 2018, 02:44:34 PM »
Appreciate your response SeanB, thank you.  I'd like to treat the two battery + controller configurations separately as far as possible for a couple of reasons, primarily to avoid complexity, keeping my camping set as portable as possible without having to modify connections each time it is removed or returned.

Are there any risks connecting the load output of the two charge controllers as described in my previous post?

Regards
Dawie

SeanB

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Re: Separate battery banks feeding one output
« Reply #3 on: January 10, 2018, 08:58:56 AM »
Connecting the inputs will lead to the 2 MPPT controllers ( if that is what they are) trying to fight each other, leading to some oscillation in the chargers. Connecting the outputs leaving the input on the one open should do nothing, as the controller is generally expecting voltage on the output.

However the internal mechanisms of the controllers determines what they will do with commoned terminals, it really depends on the particular charger.

Simple non MPPT chargers you can connect in parallel, as the one with the highest float voltage on the bank determines the end of charge by dumping solar panel power, while the lowest battery hogs all the current till they all reach the same charge state with the same float voltage.

 

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