question

thomassolar avatar image
thomassolar asked

Victron, what did you do to the absorption timer in MPPT firmware 1.46?

EDIT:

I had misunderstood the changelog. Mark explained in his answer. So then it's ok :-)


For more than one year we fighted to get Victron to change the firmware in the MPPT regulators to be more suitable for us using lithium ion batteries. The problem was that the regulator changed to absorption and started the "absorption time counting" BEFORE actually reaching the set absorption voltage. This caused the batteries to never Reach the set voltage, because With a large lithium pack it can take hours to rise the voltage the last 200mV.


In Version 1.42 this was fixed :-)

Now the MPPT blue Solar charges all the way up to the set absorption voltage before switching from bulk to absorption and before starting the "absorption time Count Down".


But what have you done in the Version 1.46?? Have you reversed this very welcome change from 1.42? This is what I found in the changelog:

Absorption time counter start to be incremented now when the battery voltage (or charger voltage when external sensor is not applied - i.e. BMV or Smart Battery Sense) is 200mV (for 12V, scalable to 24V/36V/48V systems) below the absorption setpoint. That threshold was 50mV on the previous version. This was changed to avoid extending too much the absorption stage.


Can someone in Victron please answer? Have i misunderstood something? Or have you now destroyed the change in v1.42 that actually made Victron useful in Our systems??


EDIT: I MAY HAVE MISUNDERSTOOD?? MAYBE THIS DOESN'T MEAN THAT THE TIME COUNT DOWN STARTS 200Mv BELOW SET ABSORPTION... MAYBE THIS CHANGE IS ABOUT INCREASING THE ABSORPTION TIME WHEN THE REGULATOR IS NOT ABLE TO KEEP THE ABSORPTION VOLTAGE DURING THE FIXED OR ADAPTED ABSORPTION TIME (FOR EXAMPLE BECAUSE OF A CLOUD)? AND THAT IN V1.46 IT DOESN'T START INCREASING BEFORE IT MEASURES A DROP OG 200Mv? IF SO, MY CONCERN IS NOT THAT CRITICAL.

ANYODY KNOWS?

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1 Answer
Mark avatar image
Mark answered ·

The switch from bulk to absorption occurs when the exact the absorption voltage is achieved and not before (after a short delay to provide confirmation).

The 200mV threshold applies only to the absorption phase count-down timer.

This change was made as extensive field testing indicated that in reality many systems on many days (when there is not an abundance of solar available) could/did not maintain the EXACT absorption voltage continuously - so at times the charge voltage would drop slightly (by say 50 to 200mV) and stay in this range for an extended period, then bounce back up to the exact absorption setpoint voltage when the solar conditions had improved.

As a result a 1h FIXED absorption time (as programmed) could turn into 2 or 3h in reality, with the battery receiving a charge voltage that is 'almost' the specified absorption voltage for much of this time - this scenario is undesirable and can lead to overcharging.

This change intends to find the ideal balance/logic to cover real usage with varying solar conditions and many users with inadequately sized solar arrays.

At the same time the absorption phase timer will not keep counting if the charge voltage drops excessively due to insufficient solar power - so batteries will receive the correct charge time at (or extremely close to) the set absorption voltage.

2 comments
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thomassolar avatar image thomassolar commented ·

Thank you for responding so quickly. I am very happy that I had MISUNDERSTOOD the change you made in 1.46. Thank you for clearifying :-)

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Mark avatar image Mark ♦♦ thomassolar commented ·

No problem, I'm glad that its now been clarified and that your happy with the revised logic.

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