question

Christian Lindermann avatar image
Christian Lindermann asked

Impossible? How can I achieve my charging goal in a Camper Van?

Good Morning community.

Apparently my requirement is very exotic, at least I can't find a solution for it.

But first my equipment:

  • Campervan with DIY Lithium battery (Winston LiFeYPo4 cells), ECS-BMS, separate charging and discharging branch, each with Victron Battery-Protect for UVP on OVP protection
  • BMV-712 Smart as battery monitor with temperature sensor attached to the Battery
  • SmartSolar MPPT 100/20 Charger
  • Cerbo-GX connected to the BMV and MPPT via VE-Direct cable
  • DVCC function is active

So what is my goal? quite simple: charge the battery and then use available solar power for the current power consumption.

Unfortunately I can't get any further here. The charging process goes well with my settings up to about 90% SOC, but then the MPPT goes into the float phase and the battery is discharged again. Due to the property of lithium battery, the rebulk voltage will not be reached...

How can I configure the system so that the MPPT delivers the current power consumption and keeps the battery on the SOC until there is no longer enough solar energy available?
I hope someone can help, thanks in advance.

Christian

MPPT ControllersBMV Battery MonitorLithium BatterySOCDVCC
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3 Answers
JohnC avatar image
JohnC answered ·

Hi @Christian Lindermann

Try increasing the mppt Float V a little. What you're looking for there is the point where the mppt takes priority over the standing battery V. So then the mppt will supply the loads. Only when the solar tapers off and it can't hold that float V will the batts discharge.

You also need to work on why the SOC shows 90% when Absorb terminates. Most likely it's just the BMV has drifted, and if the batts won't accept charge then SOC should be ~100%.

You mention a temp sensor. Temp comp should be off with Li batts.

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klim8skeptic avatar image
klim8skeptic answered ·

Unfortunately I can't get any further here. The charging process goes well with my settings up to about 90% SOC, but then the MPPT goes into the float phase and the battery is discharged again. Due to the property of lithium battery, the rebulk voltage will not be reached...

You might want to expand on this a bit..

I charge my cells/battery up to 3.5/14v and let them have 20-30 mins of absorbption/balancing.

I use 3.35/13.4v as a float. Yes the battery will loose a couple% SOC before the mppts start supporting the set battery float voltage.

This works well for me. My battery and BMV get fully charged, and synced to 100% every second day. (historical average)

Cough up some details / figures.

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Christian Lindermann avatar image
Christian Lindermann answered ·

Thanks for your answers, but sorry, please don´t get attached to the 90% SOC, as this is one of my presets which didn´t charge my battery to full SOC. It´s a kind of "daily-programm" to not stress the battery unnecessarily...in the normal charging preset 100% SOC will achieved of course (incl. time for balancing the cells).

Oh and the temperature sensor is just to prevent charging below 5 degrees


So ok, increasing the Float Voltage would be a possibility but is this really the right way? Holding the battery on a high voltage isn't ideal, is it?

My hope was by adding the Cerbo-GX to the system, I get it more intelligent!?

The Cerbo knows and shows the current flow an the DC-side, so why isn´t it possible to tell the MPPT give that actual needed current?

Thought DVCC were designed for that?

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JohnC avatar image JohnC ♦ commented ·

@Christian Lindermann

It seems you're looking for an 'exotic' solution. DVCC has some features for current limiting, but it's not really that dynamic. See the Cerbo manual.

Try the Float V thing. I'm not talking a big V difference here. Like I use 0.1V over 48V to prioritize charge sources. Maybe you have 12V batts, so try 0.02V. That's not much, hopefully more than any background noise on the V. And would need to be synced via DVCC with the battery V.

The 'right way' is the one that works best. Or when there's no other option. Victron systems can deal with complex stuff, but usually with a Multiplus/Quattro and fully compatible BMS. You don't have all that, so the mppt is pretty much standalone.


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Christian Lindermann avatar image Christian Lindermann JohnC ♦ commented ·
Ok, thank you John. I´m on 13.28V float voltage right now.

Let´s see...


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JohnC avatar image JohnC ♦ Christian Lindermann commented ·
@Christian Lindermann

Just to be clear, the mppt Float setting should be slightly higher than the standing battery V at your chosen 90% SOC.

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Christian Lindermann avatar image Christian Lindermann JohnC ♦ commented ·
Jep, understood. I monitored the standing Voltage over the last night, and it was at 13.27V. So first try is 0.01V higher float voltage...
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