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florin8080 avatar image
florin8080 asked

Mppt 100/20 absorption and float not respect settings

Hello

I have the following system:

- Victron mppt controller 100/20

- 1 regular flooded lead acid battery 95Ah

- 1 solar panel 370W, 34.09V, 10.86A


My problem is that the values for absorption and float voltages seems to be fixed, 14.3V and 13.4 V.

The controller doesn't take into consideration my settings, for absorption 14.4-14.6V and for float 13.5-13.6V.

The absorption time is 4h, adaptive mode and tail current 3A.

In a sunny day, the controller stays many hours in float mode, at 13.4V, and my battery seems to be not fully charged.

Is something wrong with my settings or what?

Thank you in advance.


MPPT SmartSolar
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9 Answers
florin8080 avatar image
florin8080 answered ·

Rebulk offset is 0.1. Regarding the temperature compensation, it is default. Temperature it is normal.

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florin8080 answered ·

Does someone know why the voltage drops. The interval is exactly at 10 minutes. It is too precise to be random from the sun. These drops are also on the PV Power. This is happening on bulk stage.

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pwfarnell avatar image pwfarnell commented ·

This is answered so many times here, every 10 minutes the controller sweeps the panels entire voltage range to find the maximum power point as this may change with shading during the day.

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florin8080 avatar image florin8080 pwfarnell commented ·

Ok. Thanks. I didn't know and didn't search . I thought it was from my system.

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Alexandra avatar image
Alexandra answered ·

@florin8080

Temperature compensation might have something to do with it.

Or it is not re bulking. So check the rebulk offset.

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JohnC avatar image
JohnC answered ·

@florin8080

Your set 4 hour Absorb time is quite short for Adaptive mode, so it may be getting way less. The 3A Tail is a fair level, but it may never be achieved if Absorb is too short. For floodeds I'd increase Float to 13.6V, it won't hurt them over a solar day. It'll help top them off.

Temp Comp is actually quite important. What is "normal" for you may not be for the mppt algorithm at daybreak.

Best grab a copy of the manual from the Victron website, it will explain a lot of this stuff.

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jetlag avatar image
jetlag answered ·

The temperature is measured in the MPPT and if this is located far away from the battery, this might cause such a problem. A friend of mine hat such a situation in his caravan. The MPPT charger was next to the roof and and the battery was in a cupboard at the floor. The MPPT was way more hot than the battery was and the voltages were not reached.

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florin8080 avatar image
florin8080 answered ·

According to the battery capacity, absorb time should be around 4 h. The temperature is 30grC. I tried to increase float voltage to 13.6 V, but maximum achieved is 13.4V. For example, today is 13.27V. For the moment i am not in the location to change parameters.

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florin8080 avatar image
florin8080 answered ·

In the weekend i've made some test. I charged the battery with a charger and when the battery was full, i 've connected the solar controller. In few minutes the voltage rise to 14.5V (absorption) and then went to 13.6V (float ).

When i charged the battery with the solar controller, the absorption voltage stopped at 14.2V

Why this difference?

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pwfarnell avatar image pwfarnell commented ·
As mentioned above, is the MPPT in a location that is hotter than the 30grC because the MPPT uses its temperature to set the charge voltage. The higher the MPPT temperature, the lower the voltage. Read the manual on temperature compensation. If the battery location and temperature is different to the MPPT and it is a Smart Solar with Bluetooth you can add a Smart Battery Sense to monitor the battery temperature and send this to the MPPT if they are in Bluetooth range.
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florin8080 avatar image florin8080 pwfarnell commented ·

Thanks for the reply. Ok , i understand the lower voltage is from the temperature compensation, but for 0.3V, the temperature of the mppt should be more then 41grC (18mV/grC), and for sure the battery temperature it is not that hot. In this way the battery will not charge enough. Why victron didn't use a small sensor, like Easun for example. If Victron use the internal temperature from the chip, the temperature it is more then 30grC only if it is in standby. This is not correct for temperature compensation, in my opinion. Previously i had a Easun controller, and because i want to monitor charging parameters, i switch to Victron.

The MPPT it is near the battery.

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pwfarnell avatar image pwfarnell florin8080 commented ·

If the controller is a SmartSolar with Bluetooth buy a Smart Battery Sense and it will work properly using the battery voltage and temperature.

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florin8080 avatar image florin8080 pwfarnell commented ·
Ok. I 've placed an order for it.
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jetlag avatar image jetlag florin8080 commented ·
I assume, that Victron does not use a external temp sensor, because it is anyway a good point to mount/locate the MPPT next to the battery. The PV voltage is higher then the battery voltage, so the current is lower and the losses are also lower then when you reduce the cable length on the battery side.

That's why it is always better to place the MPPT next to the battery, so it also will have the same ambient conditions like the battery. Then the temperature compansation will work fine.

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JohnC avatar image JohnC ♦ jetlag commented ·
A standalone Victron mppt only sets it's Temp Comp once a day, when it starts up in the morning. After that it's internal sensor is subject to internally generated heat. Similar with Adaptive mode Absorb time, V changes when production begins, so those decisions are made on startup only.

In a more comprehensive system with a GX device, T, V and even A (for the Tail function) can be passed across to the mppt (via DVCC) for real-time corrections. And managed batteries can even take over total control. So doesn't really matter then where it's mounted.

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jetlag avatar image jetlag JohnC ♦ commented ·
Ok, was not aware of that. Thanks for the info.

But with this explanation, some of the behavioor I observed does not make sense any more... Have to re-evaluate it. ;-)

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florin8080 avatar image
florin8080 answered ·

Update: I installed a smart battery sense and now the voltages are ok, according to the temperature compensation. Abs and float voltages are 0.05V less.

The voltage difference between Smart Controller and Smart Battery Sense is 0.04V. Shouldn't be the same? The cable length between solar charger and battery is 1 m.

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jetlag avatar image
jetlag answered ·

If there is no current flowing between the charge controller and the battery, the voltage should be the same.

But of course a difference of 40mV is no problem and always depends on the accuracy of every component. So there might be always a small shift between the values. If it is not too big, then there is no problem.

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