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colinivancooper avatar image
colinivancooper asked

When does BlueSolar detect voltage to adjust Absorbtion time

On my boat I have a BlueSolar MPPT and solar panels - also a Quattro with shore power and genny etc. There is a BMV too.


The BlueSolar MPPT detects battery voltage "in the morning" to adjust the maximum absorption time. Great when I am off the boat as this maintains the house batteries. However what is the situation when I am onboard? When it detects the voltage I might be charging with the Quattro or even drawing a short heavy load from the batteries.

1. Exactly when is "in the morning"?

2. Can the MPPT reassess battery voltage at another time to adjust maximum absorption times?

A typical scenario for me when at anchor is to run the genny in the morning to do bulk charging of the batteries and then to switch over to the solar panels to do the absorption and float stages. For that to work I need to control when the MPPT starts its daily sequence.

I am thinking of adding a Venus GX to the above … would that help control this? Can it take battery state from the BMV?

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2 Answers
JohnC avatar image
JohnC answered ·

Hi Col, and welcome to the 'community'. A great question, and a tick-up from me for asking it. I'll follow up with vagueish answers..

1. I've never seen this specifically stated, but have always assumed it's about the same time as the mppt detects the necessary Voc from the panels to attempt a charge. So it's pretty early. It will then lock in it's Abs time and temp compensation for the day (the temp thing can be doctored with extra kit).

2. I don't believe so. It's really designed for an 'interference-free' day. And like you say, it's great doing that.

I think a lot of this stuff is under redevelopment for other reasons too, so I expect improvements, whatever they may turn out to be.

And anyone this deep into such intricacies needs a GX box. Highly recommended, and those VRM graphs will assist (err stun) you with their usefulness (whether you're aboard or not).

Hope your question gets some more answers..


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colinivancooper avatar image colinivancooper commented ·

Thanks JohnC. Just getting to realise the scope of Victron kit. It can do a lot. Would be very interested to hear from other living-on-board boat owners about typical setups. It would seem there to be many ways to achieve modern electric power management.

From my use case I am thinking that I can do two things:-

1. Let the PV array wake up and tell the MPPT how long run absorbtion. Then start the genny and run it to the end of bulk. The genny going off will restart the MPPT counting down the absorption time it assessed earlier. So I am just using the genny to get through the high load part quickly.

2. Alternately, to disconnect the PV array until after I have run the genny. As that is usually at least an hour, when I reconnect the PV after genny shutdown it will start a new charging day.

I am thinking 1 is better as it will be a better measurement of how long an absorbtion is needed. And some days I will not need the genny boost and can let the solar do its stuff automatically.

And yes I will get a GX box. Thinking that the Venus is best. I run a lot of my boat from my iPad and so a browser interface is fine. I already have a boat router and wifi.

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colinivancooper avatar image colinivancooper commented ·

PS with 1. I also have to remember not to boil the kettle as it is getting light. Have to time that first cuppa pretty well :-)

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JohnC avatar image JohnC ♦ colinivancooper commented ·

Yeh, I live aboard. A 48/5000 EasySolar was my choice to replace a bunch of other inadequate kit. No shore power. FLA batts.

Generator needed only in winter and not every day either. The short winter days and low sun tests me, and cloud kills me.

My philosophy is to let the solar do what it can over the day, then top off with the genny when almost dark. This is where the VRM graphs come in very handy. On many occasions I may never quite reach Absorb over the day (for me 57.6V +/-), but may actually have hovered in Bulk for much of the day at around 54-56V. Still accepting a lot of charge, but never actually satisfies that theoretical 'time in Absorb'. What I'm saying there is that a high-V Bulk time is almost as good as Abs. Many people will read gospel into their phone apps, but it's more involved than that.

This 'method' of mine means I can't even auto-start the genny without somehow coding-in my sense of batt status - which changes, depending on the day..

This may not make sense to many, and it may not suit most, but I can have my batts often topped up adequately with the genny for just an hour in Abs after sundown. Doesn't meet the accepted 'rulez', but works for me.

Without VRM I couldn't do it properly. That portal is my savior..

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Mark avatar image
Mark answered ·

Based on the new/current MPPT firmware v1.42.

The MPPT determines the adaptive absorption time based on the battery voltage when it 'wakes up' in the morning - which is when the PV voltage is 5v higher than battery voltage.

The MPPT will only determine this once per 'day' and requires the PV voltage to be below battery voltage for >1h in order to trigger a new day.

If you have another charge source active, it's possible for the MPPT to end absorption phase early based on the 'tail current threshold'.

If the MPPT starts a new charge cycle later in the same day, triggered by the battery voltage falling below the re-bulk voltage, then the absorption phase will continue counting down if the original absorption time calculated did not already expire (if there is still time on the clock).

In the scenario that an earlier charge cycle in the same day lasted for the entire absorption phase duration, then a 2nd charge cycle in the same day will skip absorption and go directly from bulk to float once the absorption voltage has been achieved.

At moment the BMV charge current is not provided to the MPPT, but this is in the works. So when available the 'tail current' could be configured as the primary trigger to end absorption phase and should work well - even with your complex/abnormal usage profile.

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colinivancooper avatar image colinivancooper commented ·

Thanks for this. That info helps a lot. So to summarize (to check my understanding):-

a. "night" is any period >1hr with "PV voltage below battery voltage" or, presumably, solar panels disconnected.

b. a "morning" is the PV array giving > battery voltage + 7V or, the panels being reconnected and providing power.

If you are redoing this bit of software it would be very helpful to trigger that sequence from a button, app or event - that is a "reset charge cycle" function that triggers the start of a new "day" or at least reassesses the state of the batteries and sets an absorption period.

I'm not so sure my use case is that unusual? Unless there is a better way to add some solar to a pretty standard marine Quattro installation. Using the genny through a whole absorption phase is very wasteful and without it the batteries are left partially charged.


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Mark avatar image Mark ♦♦ colinivancooper commented ·

No worries...

a. Yes

b. Yes but +5v (not +7v)

Regarding the addition of a 'Manual Re-bulk' [Start Now] button - I agree/support and have actually already asked for this, but I'm not sure if it will eventuate... I will include your request as a +1 and see what happens.

In terms of using a generator/Quattro and solar/MPPT for charging together, I agree that its not that unusual and I do it too. The 'more complex' part to accommodate with your usage profile is that it sounds like your generator is already running and increasing the battery voltage BEFORE the MPPT wakes up in the morning. That means that the adaptive absorption time that your MPPT calculates will not be correct according to the 'real' depth of discharge overnight (this is a problem).

If you can wait until AFTER the MPPT is active then you can get them to work quite well together, particularly with the new Multiplus/Quattro v460 firmware that includes configurable temperature compensation. If BOTH devices use the same battery temperature data (more or less) and use the same temperature compensation coefficient for charge voltage, then you can just set the absorption voltage on your Quattro about 0.1 - 0.2v UNDER the absorption voltage on the MPPT to 'prioritize' the charging.

That will enable the Quattro to do all the initial 'hard work' and get the battery voltage up to the absorption voltage (more or less) and then switch to absorption. However, as the battery voltage is just UNDER the MPPT absorption voltage - the MPPT will still remain in bulk phase and is left to 'finish off' by raising the battery voltage by the last 0.1 to 0.2v (to the MPPT absorption voltage set-point) and completing the FULL absorption phase.

It also provides a clear indication for when to turn the generator off (providing that there is enough solar power at the time to finish off).

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