Absorbtion Issues, BlueSolar Charger MPPT 150/85 (VE.Can)

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offgridsa asked Nov 12, '19

Absorbtion Issues, BlueSolar Charger MPPT 150/85 (VE.Can)

I have my absorb setpoint Voltage at 55.36v and my absorb time is 20min. (Lithium batterys)

Today is an example of what can happen often with this charger. At 10:15AM with a burst of sun and strong PV output. The battery's reached 55.36v setpoint to trigger absorb.

Then shortly After this A cloud passed over reducing PV output (or some days it could be a large load in the home activates) this reduced the battery voltage to well below the Absorb Voltage setpoint.

This struggle up and down continues over the 20min absorption timer dropping back to Float at 10:35am.

My past experience with other charge controllers is absorb shows up as a Constant voltage stage and a dead flat line on the graph if the PV output is available to do so. If for some reason they can not maintain the voltage setpoint and the voltage reduces. Then the absorb timer stops counting down and restarts when in can. This insures you actually do get the programmed time at the constant voltage setpoint.

As you can see I'm lucky to have spent 30 seconds in total over the 20min absorb actually at the 55.36v setpoint.

battery charging

not-holding-setpoint-voltage.gif (79.8 KiB)

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Answer 1 · 2019-11-12T03:28:19Z

ejrossouw answered · Nov 12, 2019 at 03:28 AM

Hi @OffgridSA You mention lithium so maybe you can elaborate a bit more on your setup. Which battery and why don't you use dvcc and let the battery manage the MPPT?

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offgridsa commented · Nov 12, 2019 at 05:05 AM

Yes DVCC will most likely be the answer in the end. As its apparent the charge algorithm is very average in this controller. Unfortunately it would require purchasing another controller that works with this DVCC feature.

That said the controller I have now shouldn't have such a simplistic absorb stage. As no matter what kind of battery's you are using it's less than ideal for a controller at this price point. As it stands its just a dumb countdown timer. Triggered once absorb setpoint voltage is reached then basically all conditions ignored until the timer runs down.

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Answer 2 · 2019-11-12T03:53:38Z

klim8skeptic answered · Nov 12, 2019 at 03:53 AM

Hi Offgrid,

Some details about the absorption voltage threshold. Read Marks answer.

https://community.victronenergy.com/questions/31815/victron-what-did-you-do-in-mppt-firmware-146.html

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offgridsa commented · Nov 12, 2019 at 04:59 AM

If a drop of more than 200mv is apparently going to trigger the absorption timer to stop that clearly isn't happening in my example.

It's as if the charger registers the absorption voltage for one second then ignores the battery voltage while the absorb timer countdown runs.

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klim8skeptic ♦ offgridsa commented · Nov 12, 2019 at 07:24 AM

Maybe with a 48v system you would be looking at 800mv?

Clouds are a curse. Fridges that cycle in or defrost are another bummer.

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offgridsa klim8skeptic ♦ commented · Nov 12, 2019 at 10:00 PM

It did get as low as 2000mv below the absorb setpoint and spent a good deal of time below 1500mv.

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