question

lawrence-craig avatar image
lawrence-craig asked

DVCC Charge Mode

bbee471d-da59-49dd-a50d-6a5fa7c28b21.pngHi there. I have 3 x MPPTs connected to VenusOS on a Pi. DVCC is enabled.

Not a massive issue but today, I had an issue where my smallest panel (Portable Array, 100W) was on Float but my other 2 sets were on Absorption (Aft and Coachroof 275W total). All were unshaded. This meant that the portable wasn’t providing any power output to help Absorption phase. Any idea what’s going on?


Thanks


DVCCmppt state
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lawrence-craig avatar image lawrence-craig commented ·

Pic shows watts portable array as zero.

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4 Answers
klim8skeptic avatar image
klim8skeptic answered ·

If the portable panel was set up after the 2 other mppts have started producung power, the portable mppt could have registered a higher battery day start voltage.

This can affect the adaptive absorption time duration, resulting in the portable mppt going to float early.

Just a thought.

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lawrence-craig avatar image lawrence-craig commented ·
Ah yes, I know what you mean. I am not sure this is the case as it would have started at the same time as the others but definitely worth a look. Thanks
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lawrence-craig avatar image lawrence-craig lawrence-craig commented ·
Can confirm this was the case. The portable was shaded for a while so went to “off” state and then when it restarted/unshaded went straight to Abs then Float. At the time the voltage was 13V+. Thanks for the help!
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johanndo avatar image
johanndo answered ·

If they are controlled by DVCC they wouldn't show Bulk, Absorption or Float, they charge as slaves / remote control and are regulated by constant current / constant voltage settings and turned off when charging finishes.


Maybe your BMS doesn't tick the right boxes for DVCC, check the documentation.

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lawrence-craig avatar image lawrence-craig commented ·
I'm not sure that's correct. As I have Lead Acid batteries and as I understand it, DVCC just limits charging current and voltages, and the MPPTs run their own algorithm (which are all matching). The DVCC function definitely works as it controls the MPPTs when I change the max charging current.
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Alexandra avatar image
Alexandra answered ·

@Lawrence Craig

DVCC and synchronised charging are not the same.

With DVCC each mppt with be told to either produce or not produce . You will see each mppt will be shown as under external control.

In the absorption stage not much amperage is needed as the battery is just being kept at a constant voltage to balance off.

So really it means at this point you had more solar than was needed for this stage of charge and the mppt was floating or doing nothing.

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JohnC avatar image
JohnC answered ·

Hi @Lawrence Craig

DVCC alone shouldn't put the mppts into External Control. The SVS and STS (if you have a temp sensor) components give the mppts the same data to work from, but doesn't control them. SCS can limit their output, but that's not the same as controlling Charge State.

What you could try is using the Tail settings in the mppt to terminate Abs at the set Amps. (Leave the existing Fixed/Adaptive settings there, but maybe make them a little longer so they don't interfere). With DVCC this isn't their own Amps, but the Amps passed across from the shunt. This works great for accurately optimising Abs time with a single mppt, but I haven't heard how it works with multiple mppts. For my own fla batts I chose a Tail Current equivalent to ~3% of battery capacity. Suits me, but your choice. Try it..



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