question

lfarmer avatar image
lfarmer asked

BMV702 Solar / Alternator Setup advice

I have a Kisae DMT1230 installed with a solar panel and two 110 Ah batteries wired in parallel. I'm wondering what settings I should be using for the battery monitor to actually monitor by batteries, as currently it shows 100% all the time.

Battery charger settings:

Bulk and absorption - 14.6v

Float - 13.6v

The currently (default) settings for the battery monitor is set to 13.2v (charge voltage) with a tail charge of 4% and detection time of 3 minutes. I understand this is incorrect for my set up as any charge into the batteries will sync the monitor to 100%.

What should I set my charge voltage, tail charge and detection time to? In the manual its says a couple of points below absorption voltage, however my charger uses the same voltage for bulk and absorption .

Cheers in advance

battery chargingBMV Battery MonitorSolar Panel
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4 Answers
trevor-bird avatar image
trevor-bird answered ·

Hello @lfarmer , Set charged voltage to 14.2 volts, leave tail current to 4% and detection time as 3 minutes. When the voltage increases during the absorption phase, and the current reduces because the battery is charged, the battery monitor will sync to 100%. If you are testing this feature allow the SOC to go below 90% for it to go through that cycle.

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JohnC avatar image
JohnC answered ·

Hi @lfarmer

Try increasing the Charged Voltage to just below the Charger's set Float. 13.5V should do it, but if the charger temp-compensates or reads a slightly different V to the BMV, then make allowances for that.

The 4% Tail is too high. I use 0.6% for fla batts, 0.7% in winter's short days. You can experiment with this. And you haven't mentioned batt type.

The detection time I raised to 5 min. This is to avoid the effect of passing cloud, when Current can drop, but the V can be sluggish following it and can cause false syncs. Even when early in the charge cycle. You can see this in the Trends graphs on a suitable day, so keep in mind.

And some people will say to set Charged V to just below the Absorb V. The difficulty there is that if the charger drops to Float before it syncs, then it won't sync at all. The Tail then would have to be set a bit higher too, as most batts will accept more current at the higher Abs V.

In Victron-speak, 'Bulk' is just a transition stage on the way to Absorb.


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lfarmer avatar image
lfarmer answered ·

Thanks both.

@JohnC I notice the float sits around 13.4 V on the battery monitor so I'll use that value. My batteries are AGM, do that have an impact on what tail I should be using?

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@lfarme0r

The type of batts can indeed impinge. What you really need to do is watch the actual current to see where it 'tails' (levels off) to. Solar comes with a finite length of day, so choose a value that is regularly achievable. And the Amps may actually wander a little, so all of the wandering readings must be under the setpoint you choose for the set time, for it to register a sync. My own true Tail is like 0.4%, but practicalities rule, so I choose a little higher.

The same issue may arise with that 13.4V. Going lower is getting down into mushy territory, and you may need to raise the charger's Float setpoint a little. That won't hurt if it doesn't match the BMV's V, and you could check which one is actually correct (if they differ).

This won't affect you, but Victron mppts have their own Tail setting, to drop from Abs to Float, and can be networked to use the BMV's Current to do that. Mine's set to ~3%, and that usually happens at close to 99.0% SOC. So sort of a double-check. I could sync the monitor at just before that at Abs V, but I'd be 1% out. Many people could live with that.

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trevor-bird avatar image
trevor-bird answered ·

Just watch this video and you will know how to set it up. https://youtu.be/mEN15Z_S4kE

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