sx50 avatar image
sx50 asked

charge controller goes in to float when batteries are not charge. is this correct?

I have Victrons 100|50 - bluetooth - MPPT charge controller, and - also bluetooth - shunt.
The charge controller goes in to float every day, even though the batteries are not fully charged (as seen in the app). I had expected the charge controller would only go in to float mode when the batteries are fully charged. Was my understanding wrong, or what is going on?
I have three 140Ah batteries connected in parallel if it matters.

Edit: 100| 50 not 150|50.



  • The Charge controller and shunt are linked via bluetooth on a network.
  • Smart shunt:
    • battery capacity is set to 420 Ah
    • charged voltage: 13.2v
    • discharge floor: 50%
  • Charge controller
    • absorption voltage: 14.7v
    • float voltage: 13.8v
    • equalization voltage: 16.2v

MPPT ControllersSmartShunt
2 |3000

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Alexandra avatar image Alexandra ♦ commented ·

Hi @ssssssssssssssssssssssssssssssssssssssssssssssssss

We would need to know a few more things before we can help you. Is it really a 150/50?

How much solar panel wattage do you have installed? What is your battery type it is possible temperature is causing this? What was your DOD?

What are your settings on the MPPT?

Is this a new install? If so the Shunt may be inaccurate as of now.

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sx50 avatar image sx50 Alexandra ♦ commented ·

Thank you @Alexandra. I have updated my question with settings from the app. Let me know if I can provide more or if a settings screenshot is better.
It is more or less a new install yes. I have put it together in the last month.

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seb71 avatar image seb71 sx50 commented ·

Sunny days or cloudy days?

In cloudy days the charger can switch from Absorption to Float before the battery is charged.

Screenshots with the settings are better.

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sx50 avatar image sx50 seb71 commented ·

Both. This past week it's been sunny everyday and I am not getting to 100%. SmartShunt shows 50-70% yet charge controller is in float.
Any ideas?

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1 Answer
tozz avatar image
tozz answered ·

You mention you've set battery capacity to 420 Ah. But the 420 / 3 = 140 Ah is only when running 20 hours at 1/20 of it's power. Basically 84 watts. Because: 7 Ah x 20 hr = 140 Ah.

That's not very realistic if you will be charging it everyday using solar. 360W of solar / 3 batteries = 120W per battery. Roughly 1,5 times more than the 7 Ah limit / 84 watts for 140 Ah. You probably will be draining them faster than 84 x 3 batteries = 240 Watts as well.

The other value on the specsheet is 119 Ah, when running 5 hours at 1/5 of it's power. That's ~270 watts. 23 Ah x 5 hr = 115 Ah (=~119 Ah). That value is probably more realistic in your scenario.

My guess is your configured capacity is too high.

Two values are specified under capacity (Ah) in accordance with EN. The 
left value corresponds to ampere hours (Ah) at 20 hours with 1/20 power 
uptake, and the right value corresponds to 1/5 power uptake for 5 hours
- 140 Ah
- 119 Ah

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sx50 avatar image sx50 commented ·

Thanks for that.
So you recommend I set my battery capacity to 357 (3 x 119) instead of 420 (3 x 140) ?

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