Victron solar controller high charge voltage

[mikedefieslife]

I recently swapped out an old PWM controller and installed a victron MPPT 100/20 controller.

This is connected to four 100w panels (parallel at the moment), whilst another Victron 75/15 is connected to two 110w panels (series).

I also have the Victron battery temp and voltage sensor connected to the network.

I'm running 4 Trojan T105, and am often down 20-30ah by the time I wake up in the morning.

When I check the charging history of my Victron controllers, I'm alarmed to see that battery voltage is often well above what I've set in the chargers.

The settings are 14.82 absorption, and 13.5 float on boat controllers. Temp compensaion is at -20mv

Yet today I see (according to Victron connect) that the battery voltage reached 14.94. Yesterday it reached 15.03 and the day before 15.02.

I have no other charging sources connected or running. What gives?

[john61ct]

Is ambient temperature quite cold at startup?

[mikedefieslife]

In the morning it's probably around 10c and gets up to 18c in the afternoon.

The thing is I often check using the Victron app on my phone, or using my battery monitor, and I've not actually seen over 15v, so it must happen sometime in the afternoon when I'm not looking.

[john61ct]

Odd. check the temp compensation settings, and that the sensors are placed properly.

Try running a few cycles without them

[billknny]

So lets see....

* the batteries are at 10C...
* set voltage for 20C is 14.82V
* temperature compensation is -20mV/deg

So [(10C-20C)*-0.020V/C] + 14.82 = 15.02V

What, exactly, do you think the problem is???

[john61ct]

Yes hitting that V is not the odd part

A. the sensors should vary the compensation with the temp change throughout the day, not just based on startup

B. the live display should match the log

[mikedefieslife]

Originally Posted by billknny

So lets see....

* the batteries are at 10C...
* set voltage for 20C is 14.82V
* temperature compensation is -20mV/deg

So [(10C-20C)*-0.020V/C] + 14.82 = 15.02V

What, exactly, do you think the problem is???

Well that's not what's happening. In the morning when it is 10c outside, the controller is putting out around 13.6v or similar probably due to the low sun. It is the middle of winter here. 15v doesn't seem to show up in the min/max display on the app until late afternoon. By then the temperature is closer to 18c.

Oh well anyway, I need to keep them below 15v anyhow so does that mean going against the temp comp ratings issued by Trojan?

[coull]

You should be able to go into settings and set a limit ie 13.7 high and 11.7 low
I've found these controllers good on my boats and just 12 euros here in Spain on Amazon

[noelex 77]

Originally Posted by mikedefieslife

By then the temperature is closer to 18c.

Is that air temperature, or battery temperature?

Batteries have a great deal of thermal inertia and are often located close to the waterline where sea temperature has an influence.

The standard Victon controller only measures temperature at start up. If you have some of the accessory options the temperature should be constantantly adjusted, but it will not be air temperature.

[CarlF]

I've found that all my Victron equipment can "overshoot" the settings by .1v or so - independent of temperature compensation. I don't know if this is by design or just a "feature" in their software.

In any case, I'd just set the absorption voltage down to 14.6 and see if that does better. I don't believe that this slightly lower setting will have any noticeable impact on your battery's charging time or health.

[FlyingScot]

I have my Victron 100/30's turned down by 0.1-0.2v to ensure that they don't overshoot the max voltage. Easy to do. Took me two days to get it almost exactly right.

As others have mentioned, temp compensation is taken from the controller's internal temperature before they start charging. Remote battery sense or BMV-712 with optional temp sensor will allow it to update based upon battery voltage and temperature all day long.

[john61ct]

Originally Posted by coull

You should be able to go into settings and set a limit ie 13.7 high and 11.7 low
I've found these controllers good on my boats and just 12 euros here in Spain on Amazon

Wut? way too low! And please link to Victron MPPT of any size for 12€ I'll buy a container load.

[john61ct]

Originally Posted by noelex 77

Is that air temperature, or battery temperature?



Batteries have a great deal of thermal inertia and are often located close to the waterline where sea temperature has an influence.



The standard Victon controller only measures temperature at start up. If you have some of the accessory options the temperature should be constantantly adjusted, but it will not be air temperature.

Originally Posted by FlyingScot

temp compensation is taken from the controller's internal temperature before they start charging. Remote battery sense or BMV-712 with optional temp sensor will allow it to update based upon battery voltage and temperature all day long.

OP stated using the remote temp accessory, which is why this is odd.

Either installed / configured wrong or faulty.

Or, just adjust down until it's working the way you want, certainly fine as a temporary workaround

[mikedefieslife]

The battery sense module is stuck to side of one of the batteries in the middle of the bank. Then the wires attached to the positive and negative of the connected pairs i.e in the middle one the cables that make the parallel.

Think I'll just dial the setting back a bit for now, as there really isn't a lot that can be done.

[noelex 77]

If the battery temerature is 18°C and the regulator is set to an absorption voltage of 14.82 @ 25 °C, the adjusted Victron absorption voltage should be 14.93v.

The maximium recored voltage will slightly overshoot this value so your readings of 14.94, 15.03 and 15.02 do not represent a problem.

Trojan actually specify a temperature compensation of 30mV per degree C, based on an absorption voltage of 14.7 V. So at 18° C Trojan would recomend an absorption voltage of 14.91 V (if my memory is correct).

The maximum voltages the system is recording seem OK to me. The typical absorption voltage will be close to ideal.