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harrycw avatar image
harrycw asked

Help me understand the stages of the SmartSolar MPPT?

I'm a newbie to the fancy Smart controller that Victron provides, and I wonder if my charger readings and settings make sense. I'm also not real clear as to how the specs that Crown Battery provides correspond to the settings that Victron requires in their VictronConnect app.

From having read others' experience, I believe I have the settings right, but I'd like to understand their actual meaning!

My setup:

2-100W 12V solar panels in series

Victron Smartsolar 75/15 MPPT Bluetooth controller

Victron BVM-712 battery monitor plus temp sensor

2 Crown 220Ah GC2 6V standard FLA batteries in series

temperature 7°C

This is my understanding of the "bulk-absorption-float" cycle, please advise if I have it wrong...

Charging starts in Bulk mode, with max available current (up to 50A per Crown, but in reality current is limited by my panels to @ 13.2A)

The starting ''Voltage" in Bulk mode is determined by battery state of charge - and it gradually climbs to "Charged" level, which is equivalent to Absorption level (14.22V per Crown specs).

Once the SOC climbs to the "Charged" (Absorption) voltage-level, the controller switches to Absorption mode, which then limits the voltage to no more than the Absorption setting, and varies the current, gradually lowering the current, as the battery becomes more charged (as the battery accepts less and less). Question: does the controller actually keep the voltage at the 'Absorption' voltage-level (Crown calls it: 'Constant Voltage') during this Absorption phase?

When the charge current drops as low as 5A (per Crown specs) the controller should switch to Float mode (Crown: 'constant current'), and (should?) holds the current at 5A, until SOC corresponds to (controller setting of) Float Voltage (13.5V)? Question: does the controller actually stop charging at this point? ie: No 'trickle charge'?

Obviously, this last is one of my stumbling points. If Absorption Voltage is constant at 14.22V, then when the charger switches to Float mode, the battery voltage will read 14.22, won't it? In which case, 'Float' voltage will read high at this transition point? Or does the Absorption charging voltage drop as the SOC gets closer to Float?

So my confusion comes from Crown specs being unclear to me, and names of 'phases' and specifications not corresponding between VictronConnect, and Crown, and the Victron controller not having specified a 'constant current' for the Float mode

As I said, I'm new at this, and my Victron controller readings aren't following my understanding of the way it should work. For example, during the controller's Absorption mode (set at 14.22V in the app), the voltage will read 13.55V at 1.7A, which seems more like a Float to me. It's a cloudy day, but it seems it could be charging at 14.22 at 1.6A, per the Absorption app-setting. Or is this possibly the temperature compensation?

Ii appreciate any clarity anyone can give me on this!

Thanks.

battery chargingchargercurrent limitfloat
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3 Answers
Murray van Graan avatar image
Murray van Graan answered ·

Question: does the controller actually keep the voltage at the 'Absorption' voltage-level - Yes it does, but the controller could also vary that voltage because of temperature compensation. Ensure that the temp compensation is set up correctly as per the battery data sheet.

Once the absorption voltage has been reached, the controller will hold that voltage for a time depending on the absorption time setting, also taking into account the battery voltage just before charging started. If your battery voltage didn’t drop too much overnight, the absorbtion time will be a lot less than a day where the battery was deeply discharged. Alternatively, once the tail current has been reached (1A for smaller models) the charger will go to float.

Read this for a detailed explanation: https://www.victronenergy.com/live/victronconnect:mppt-solarchargers

Once in float, the controller lowers the voltage to the float voltage that was programmed into the unit. The battery might have been charged at 14,22V, but it won’t stay at that voltage. Once the controller goes into float, the battery voltage will quickly drop, and the controller will then maintain it at the float voltage which is basically just enough to prevent the battery from self discharge.

Did you read the 13,55 absorption voltage, at the battery terminals or on the controller terminals?

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solgato avatar image
solgato answered ·

I understand your confusion as I have questioned the same things and have seen a number of other posts where people were concerned because they too were expecting to see the voltage value they set for Float being achieved when in float.

Since setting my system up a few weeks ago, I have never achieved the Float value I set of 26.4V per my battery manufacturer, which I thought was odd and chalked up to my batteries being a few years old.

That was until today.

For the last few weeks after a full charge cycle, my bank would usually float at about 25.6 without any load other than my BMV-712 which is almost 1V less than my Float setting.

But last night I installed the optional Temp sensor like you have, and today my bank for the first time is floating at 26.44V.

I wonder if your Temp Compensation settings are correct as Murraynated mentioned since my issues (at this point) seemed to be somehow related to Temp monitoring.

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harrycw avatar image
harrycw answered ·

Thanks for your insights @Solgato. I've wondered too if the temp compensation might be a bit out of whack. I wasn't sure if Crown Battery's specs referred to 'per cell' or not. Will have to dig for that.

You've reassured me, re my understanding of how it's supposed to work, @Murraynated... The 13.55V came from the controller, but the BMV read 13.57V at the same time.

I think, as long as it seems to be working as it should be, I'll have to give it some more time, under some actual use, to give me time to learn more about what it's doing under certain conditions. It looks like it's gonna rain and snow for the next few days, so it looks like I'll be learning 'other things' this weekend... :-/

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