question

cdstaley avatar image
cdstaley asked

Parallel dc sources

Can the output of a mppt be put in parallel with the output of a dc~dc converter charger.. why? Because you need power added to lithium bank while plugged into shore power. Let’s say you sleep late and the solar starts pumping power. Who’s going to win. Will they fight each other?

MPPT ControllersOrion DC-DC Converters not smart
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shaneyake avatar image
shaneyake answered ·

They will work together. The current from MPPT + Current from charger = Current to battery. So just make sure that battery can handle the current from both.

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Is that based on an analysis of the circuits of both systems, or observationally. I'm pretty sure that they will work, but I don't know for how long. That formula is for kirchoff's law is what you stated. Kirchoff's voltage law, or the conservation of energy law zero's out voltages in a loop. Since resistances are different in the MPPT, the DCDC, and the internal battery and I think those devices are voltage devices, the current will adjust to get a loop voltage of zero. This means the current's will vary potentially putting excessive current through one or more the the items in the loop. I was sort of hoping that Victron staff monitored this site and an engineer could confirm the succeptability or lack of, of over current issues. Not worried about the battery as the combined current couldn't exceed what the lithium can sink, but thanks for you answer. If you are an engineer at Victron please confirm to validate your claim of compatibility. Thanks again!

cds


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You are overthinking this.

These aren't fixed power sources but are rather actively controlled.

Both the DC-DCs and MPPTs outputs are basically constant current/constant voltage supplies. When charging a battery they will both output as much current as they can until the battery/voltage setpoint is reached. They will limit their current to both achieve MPP on the MPPTs side and also not exceed ratings.

I am not sure what you mean by loop because MPPT and DCDC are not in the same current loop. I am an engineer but not for Victron. Victron staff don't typically respond.

Here is some basics of how parallel supplies work. You don't have to worry about the current being evenly split in your use case.
https://www.asme.org/topics-resources/content/how-to-connect-power-supplies-in-parallel-or-series-for-increased-output-power

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