jrhubott avatar image
jrhubott asked

BMV Synchronizing with Smart Solar MPTT using VE.Smart Networking

Why can't the MPPT publish it's charge mode on the VE.Smart network?

This would make it easy for the BMV to synchronize instead of trying to configure the BMV to detect the transition from absorption to float.

I have not had much luck on getting a configuration that always works.

MPPT ControllersBMV Battery MonitorVE.Smart Network
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2 Answers
Mark avatar image
Mark answered ·

That's not a good idea in my opinion, as the MPPT does not know exactly how much charge is going into the battery (some or all could be going directly to a load) or if the battery is in fact fully charged when the absorption phase is complete (since the absorption period only ends based on a timer (or the 1A/2A default tail current threshold that is typically too low to act as a trigger).

If anything it should be the other way around, as the BMV measures the precise current going into the battery and when it drops below the tail current set, while also maintaining the absorption voltage set-point, then the BMV does know that the battery is truly charged.

I believe that Victron are looking into providing the MPPT with the BMV current measurement to use as the tail current reference to end the absorption phase.

In the meantime, MPPT firmware v1.42 actually has configurable tail current to end absorption phase by Victron Connect has not yet been updated to allow configuration of this feature. When Victron Connect is updated this function could be utilized, as opposed to just a timer. The only issue with this is that it will not work well if you are running a load at the same time, as the MPPT has no way of knowing if the charge current is going to the battery or to powering the load. So the trigger condition may not be satisfied even if the battery is fully charged.

I would also recommend that you review all your configuration settings (MPPT & BMV) as it sounds like there may be some room for optimization.

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jrhubott avatar image jrhubott commented ·

I agree with what you are saying but I cannot get a reliable detection of full battery. The following is my current settings for 2 6V Leoch AGM Battery's. The item's in bold are my current settings. I have not got reliable synchronizations with these settings. Any help would be appreciated.

Battery Leoch AGM DTA 6224
Voltage 6
Series 2
20hr rate (aH) 224
10hr rate (aH) 194
5hr rate (aH) 179
Absorption Charge Low 7.2
Absorption Charge High 7.35
Float Charge Low 6.8
Float Charge High 6.9

Solar Settings
Absorption Charge - Mid Point 14.55
Absorption Charge - High Point 14.7
Float Charge - Mid Point 13.7
Float Charge - High Point 13.8

Battery Monitor
Charged Voltage 14.25
Tail Current % 3%
Tail Current (A) 6.72
Charged Detection Time 3
Charge Efficiency Factor 97
Peukert compensation 1.13
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Mark avatar image Mark ♦♦ jrhubott commented ·

For a solar setup your better off keeping the voltage at a little under the absorption voltage (just like you have it now), as long as the MPPT is getting into the absorption phase and maintaining the absorption voltage than I don't expect the BMV 'charged voltage' to be the factor/issue preventing synchronization.

It's more likely that the battery is simply not being fully charged during the absorption phase - either because the absorption time is too short and/or due to lack of sun/charge power.

3% of 224Ah is 6.7A - so unless you can log data you should take the time to watch/monitor the BMV & MPPT during a charge cycle and see/confirm if the charge current (as measured by the BMV, not the MPPT which could be going to a load) is dropping to below the 3% tail current threshold set (<6.7A) BEFORE the MPPT switches from absorption phase to float phase.

If it doesn't then I would increase the MPPT absorption time as the next step. If its due to lack of PV then only more solar panels/power will cure that.

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JohnC avatar image
JohnC answered ·

Hi J. Your settings may be a little optimistic, and it may never sync automatically with such a high 'Charged Voltage' and low 'Tail Current'. What you're asking it to do there is sync only above 14.25V and below 3% (concurrently). Utopian aim for Pb's. Victron defaults are 13.2V and 4%. By all means vary them at will, but this world isn't perfect..

Again, your CEF and Peukert could cause serious drift in your SOC. Very roughly, 97/1.13 suggests 86% round trip efficiency, too optimistic for my preference. For Pb's I think Victron suggest a start point of 95/1.25 = 76% efficiency. In practice, that's about the max I see (floodeds).

Also, your mppt will vary your Abs/Float settings with temp. If your batts are fine with that then ok.

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jrhubott avatar image jrhubott commented ·

I thought Victron recommended .3 below the absorption charge voltage when using solar.

All of the settings came from a Victron video including the Peukert and charge efficiency for AGM batteries.

Any suggestions would be great. I wish that Victron had something better on solar integration especially with a Victron MPPT.

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JohnC avatar image JohnC ♦ jrhubott commented ·

Yeh, I may well have seen that video, but those settings wouldn't work for me..

Eg. Let's say you're daily-cycling your batts. A 'typical' day might be Absorb target by 11am, stay there for 2-3 hours, then drop to Float for the rest of the day. Still accepting charge, so isn't 100%, so you have to decide to accept a practical level for sync, perhaps ideally as late in the Float cycle as possible. Trouble is, by then your V is much lower, and will never sync with a sync V that high.

In this situation, 0.3V below Vfloat might be fine, and tail% doctored to suit.

On a bad solar day you may not sync at all (nor want to), and if you see your SOC drifting away from reality over subsequent days, then adjustments to CEF and Peukert are where to head.

But we all have different kit, usages and preferences. And subsequently, settings.

For you to determine. And I wish you well finding them..

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