question

frankqc avatar image
frankqc asked

Put LOAD output of a MPPT 100|20 into the PV input of another MPPT for battery to battery charging?

I have a single 24V solar panel source

I have two sets of batteries, one 24V (two sealed gel 12V in series) and another 12V (LiFePO4) each with their own Victron MPPT charge controller.

The first MPPT is set at 24V and charges the first set of batteries (sealed gel).
I want to charge the 12V LiFePO4 battery too. What are my options? I was thinking either :

(a) Take the 12V from one of the 24V battery array and put it directly has the PV input of the second charge controller.

Or (b) take the LOAD output of the first MPPT and plug it to the PV input of the second 12V system.

Thanks!


MPPT Controllersbattery charging
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3 Answers
kevgermany avatar image
kevgermany answered ·

Load output on this model is restricted to 1A.

Best way is to add an Orion DC:DC charger.

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frankqc avatar image
frankqc answered ·

@kevgermany You mean something like this ?
https://www.amazon.ca/Victron-Orion-Tr-12-5-DC-DC-Converter/dp/B072C57N84/

But what about my solution (a)? That solution would be free. Can we put a battery as a PV input of a MPPT?

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kevgermany avatar image kevgermany ♦♦ commented ·
One of the units from this page, yes https://www.victronenergy.com/dc-dc-converters
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kevgermany avatar image kevgermany ♦♦ commented ·
Solution a. Not sure what you mean. Do you intend to drop the 24V through an MPPT, or take 12V from one of the series batteries wired for 24V. Pointless using an MPPT for this, it might work, but cost is high.

Tapping a 12V from two 12V batteries in series will lead to unequal states of charge and should not be done.


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frankqc avatar image frankqc kevgermany ♦♦ commented ·
Yes solution (a) would imply unequal battery usage since only one of the two would trickle down to the next setup. Thanks for the feedback!

Solution (b) using the load output would "drop the 24V" with the second MPPT. I've measured and the load output voltage matches the battery, so the load output on the first MPPT is 24V ! Moneywise is also a concern and thanks for mentioning it. In my case the second MPPT is already purchased and the one I'm using cost me only 137$US and later will still be useful when I can buy a dedicate solar panel for it. So far I didn't find any negative point in this temporary setup.

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frankqc avatar image
frankqc answered ·

Actually the Load output I get is 219W @ 9A and the other MPPT reports charging at 202W @ 8.4A so it seems to be working pretty well.

@kevgermany I'm not sure if 1A was a typo or outdated information?

This is the output of the first SmartSolar charge controller MPPT 100|20:screenshot-20221113-144654-load.jpg

This is the second BlueSolar charge controller MPPT charging:
screenshot-20221113-144708-charging.jpg


This is the first SmartSolar MPPT 100|20 providing the load:
20221113-142825.jpg



screenshot-20221113-144654-load.jpg (422.4 KiB)
screenshot-20221113-144708-charging.jpg (411.5 KiB)
20221113-142825.jpg (900.8 KiB)
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kevgermany avatar image kevgermany ♦♦ commented ·

I took the 1A from the data sheet, downloaded yesterday cos a friend is looking at the load output. It's possible that there's a different current on load at different voltages. It's also possible the data sheet is wrong. I'll check.

You can download the datasheet/manual from this link

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kevgermany avatar image kevgermany ♦♦ commented ·

I checked. 1A at 48V, 20A at 12 and 24V. Datasheet needs updating.

As you're running at 24V, the 1A does not affect you.



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dram avatar image dram commented ·
How did you set up the load output on the first charger, can you please share the settings? Thanks.
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