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madarles avatar image
madarles asked

What voltage is on the load of the MPPT when it is in float stage?

Hello,

I'm a bit lost, maybe someone can help me. I have VE Smartsolar MPPT 100/20 and VE Gel battery at a remote place.
My question is: What voltage is expected on the load of the MPPT when it is in float stage?

Backgound story:
I have a relay module, which is powered by this MPPT and I can access it through internet. I have a graph of the input voltage values of this module. On this graph, I can see the bulk stage and later the absorption (14,4V). But absorption never ends. Today was a fully sunny day, the absorption voltage started lowering after 6 hours, when the sun was starting to go down.

This MPPT is new, before this I had a VE PWM charge controller. With this controller the float stage (13,8V) was visible on this graph.

So I'm a bit scared, that it will kill the battery. The other explantion could be that it is normal with this MPPT to have absorption voltage on the load while in float stage.

Can somebody confirm this?

The full system is:
- 3 pieces of VE 115W poly panels in series with ideal orientation
- VE Smartsolar MPPT 100/20
- VE 110Ah Gel 12V battery
- full consume is about constant 12W (Relay modul, 2 IP cameras, 4G router)

Thank you very much.

Balázs



MPPT SmartSolar
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3 Answers
pwfarnell avatar image
pwfarnell answered ·

The battery terminal and the load terminal have the same voltage. This means that your new MPPT is not going into float. Some PWM controllers could go into float earlier than ideal and the MPPT types are better in this regard.

You have a lot of panels for a singe 100Ah battery so it pays to be cautious which means if you have a fixed absorption period set then you may overcharge. Can you send some screenshots of your MPPT settings and details of current and voltage supplied by the MPPT to the battery while still in good sun after it has been charging.

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madarles avatar image madarles commented ·

Thank you for your fast respond.
I can create screenshots of the settings on friday when i can drive to this place.

Here is the voltage graph for yesterday on the relay module input: https://madarles.hu/sites/default/files/ve01.png

The values are not completely accurate, but the trend is clearly visible. There is a battery sense module for temp componsation, that is why absorption is not fully constant.

I will post the MPPT settings on friday
Thank you!

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pwfarnell avatar image pwfarnell madarles commented ·
Any information on what the current was during the 6 hours of absorption, especially towards the end.
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madarles avatar image madarles pwfarnell commented ·
No info about current :( On friday i'll try to get currents from it with the app.
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madarles avatar image madarles pwfarnell commented ·

I've just realised, that maybe there was very sort time of float stage today and even yesterday, which can be seen on this graph: https://madarles.hu/sites/default/files/2d.png

Maybe the contoreller does a fix 6 hours absorption, and there is no time for float, because sun goes down. 6 hours is too much i guess, right?



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pwfarnell avatar image pwfarnell madarles commented ·
@madarles

I think I know what is happening now you have pointed out that it did go to float after 6 hours. The default maximum absorption time is 6 hours. The default charging algorithm is adaptive absorption. See page 20 of the manual for details. If the battery voltage when the sun starts to shine is less than 11.9V then it uses the max 6 hours. If the voltage is higher then it uses a shorter time. Your battery does not seem to be holding the voltage up very high, at the end of charge it is dropping quickly to 12.2V and then overnight below 12.0V.

You may be able to get by with a shorter absorption time or end absorption on tail current if the current is going below 2A, that is 1A tail current for the battery and 1A load for your devices. These settings are under the expert user setting.

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madarles avatar image madarles pwfarnell commented ·

Thanks, that makes sense. The battery may no longer be in good condition. But i also have to check the real voltages on the controller with the app when i'll be at the location. I noticed it recently, that the relay module may show about 0.2-0.3V lower voltage on its input then the controller shows, especially when there is no charge. That is why i wrote earlier, that values on the graph are not completely accurate.

Thanks again for helping me figuring this out :)

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regman54 avatar image
regman54 answered ·

For your question about the float stage voltage check your battery and charge controller owners manual. Most batteries can be kept indefinitely on a float charge. My own non-Victron deep cycle AGM for example has a recommended indefinite float charge of 13.6v.

That said, since you have both a Victron battery and charge controller I wouldn't be surprised if there already exists pre-sets made for your particular battery.

I don't have my system setup right now so I can't check for you. If you don't have equipment manuals they can be downloaded here: https://www.victronenergy.com/support-and-downloads/manuals

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madarles avatar image madarles commented ·

Thank you for your respond! My question was that what voltage is on the load output of the controller when it is in float stage. @pwfarnell answered that. Now I don't know if it is normal to have 6 hours of absorption stage? My previous PWM had much less.

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furyjk98 avatar image
furyjk98 answered ·

Howdy, I use 12v 7Ah SMF x 3 batteries with a 75 | 15 MPPT and a 55W MonoPERC solar panel to drive an off-grid Router and an IP-CAM which consumes around 4W - 5W per hour, and around 110W in 24 Hours, and they usually get charged by 11 AM, absorb at 14V for 2 hours, and go to float mode for rest of the day harvesting 4W-5W per hour in the process.

In a day, I get a yield of 110W when checked in the history.

On cloudy days, it will take a full day to get a yield of 110W, even if it can't, I am pretty sure whatever is charged can make it up to another day.

From your setup, I think a 12V 110AH battery and 115W Panels of three is a overkill for the load that you are running, i.e.: 12x110 / 2 = 660W of safe usage of the battery.

The load is around 12W x 24 hours = 288 Watts.
The panels you are using are 115W x 3 = 345W peak power, and you can easily get a full charge by a couple of hours in the morning.

Since you are not running any other load, you can set the charging voltages as follows:
Float voltage - 13.4V
Absorption voltage - 14.0V for 2 Hours
Equalization Voltage, you don't really need it since you never use up the battery 100%. If you wanna do it, you can just set it to 14.4V or 14.8V every 30 days for 2 hours.

If I want to conclude, I don't think you need a 6H of absorption time, 2 hours will be enough for the amount of power you are using at night.

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madarles avatar image madarles commented ·

Thank you @FuryJK98 for your response!

I use 3 panels only at winter, only 1 panel is in use at other part of the year.

I do not really understand this controller, why does it do this, it shouldn't do max absorption time.

I already set max absorption time to 4 hours, and the controller does 4 hours even if the battery had 12,2V in the morning. Maybe the bulk period is to long? My guess is that this battery has issues it is 2 years old.

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kevgermany avatar image kevgermany ♦♦ madarles commented ·
In winter, solar output is very low. My system stays in absorption all day as a result. But as there's little to no charge going to the batteries, there's nothing to worry about. But in summer, absorption is automatically a lot shorter.

Absorption times vary on battery use. So fixed absorption times are not really helpful. More of a safety limit.

For the MPPT, select the second Victron gel setting.

Equalisation is generally not recommended for gel batteries. Only use it if the maker specifically advised it.



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furyjk98 avatar image furyjk98 madarles commented ·

Hi @madarles, you will need more absorption time to properly complete the chemical reactions inside the battery and be ready at its full capacity based on the amount of DOD you do for that day.

The absorption setting in expert mode can be made adaptive or fixed, the adaptive one is more suited to be used with the Lithium batteries to complete the top balancing, however, since you have a Gel battery, you can try experimenting with a fixed absorption time.

You can enable Expert Mode to change the absorption time of the battery, in the absorption section, set it to Fixed mode, and disable the tail current, then adjust the duration of the absorption time based on the suggestion.

Try lowering it to 2 hours, and check the minimum voltage for that day, if it stays the same or higher, you can try reducing it by 50% of the previous day's Absorption time.

If it goes below, you can increase the absorption time by 50% of the current time.
i.e. 1 hour > Increase it to 1 hour 30 minutes.

Then again check the minimum voltage of the battery for the day, and keep it between those two timings.

Each battery's internal resistance and chemical reaction will be different, so you have to find out the best absorption time based on the DOD/day and the age of the battery.

You can refer to this image for the voltage settings, and for more information you can check out this link :

Voltage Settings

1704371471128.png



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