question

greenarc avatar image
greenarc asked

Does the Victron sense automatically adjust temperature compensation?

Hello,


I purchased the Victron Temperature and Voltage Sensor with the presumption that it will adjust the temperature compensation values, however that doesn’t seem to be the case which is highly confusing, because otherwise what is the point.


My temperature compensation value sits on -16.20mV/C. Never changes, even in very low temperatures the MPPT 100/20 controller I have didn’t even use the internal temperature sensor to adjust the values, which is why I got this temperature sensor.


What’s happening? -can somebody please help with this. I’ve just purchased 2 new and expensive AGM batteries because my last ones pretty much died. Don’t want this happening again.


Note that temperatures at the batteries are ranging between 23 and 28C. So I expected to see some change in temp. Compensation.


Many thanks!

Temperature Sensor
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8 Answers
mrhappy avatar image
mrhappy answered ·

@GreenArc,

The temp compensation value is a fixed value that battery producers usually print in the data pages for their batteries, sometimes directly on the battery. It's not supposed to change. It is the data that you can put in to tell the charger how much your particular battery needs to have it's charge current compensated based on temperature.

Let's say that the value is -30.00mV/°C. Then the charger knows that for every degree the temperature increases, it has to reduce the charging voltage by 30 mV. It all happens automagically. If you change to other batteries that have -16.30mV/°C in their spec, you should change the value to just that so the charger handles the new batteries in the correct way.

With a temperature and voltage sensor directly on the battery, those values will of course be the closest to true measurements that you will get, and thus the best information possible for the charger to use.

These things can be a little confusing, different values in the settings are working in different ways, but that is the simplest way I can describe my (although limited) understanding of it.

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nickdb avatar image
nickdb answered ·

Have you set the correct compensation values on the chargers?

Did you enable DVCC and configure the shared temperature sensor?

There is a lot of helpful stuff in the the setup manuals.


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mrhappy avatar image
mrhappy answered ·

The temp compensation value in the settings don't change if you don't change it. It's the value that the charger use to know how to compensate for your particular battery type. How it actually conpensates is not seen clearly anywhere but by analyzing charging voltage

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nickdb avatar image nickdb ♦ commented ·
It's quite easy to check.

If you know your float/absorbtion voltages, the voltage will increase by the increment for each degree beneath 23C and decrease for each degree above.

In my system it is 96mv (as close to 0.1V for practical purposes) so for 5C below 23C it is a 0.5V difference.

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greenarc avatar image
greenarc answered ·

So what’s the actual point of the sensor? How is it adjusting according to the temperature reading it gets?

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pwfarnell avatar image pwfarnell commented ·

The temperature does not affect the temperature compensation value, it affects the float and absorption voltage values. See Appendix F at the end of the Multiplus manual.

if you have an absorption voltage of 14.4V that is the value for 25degC. If your temperature compensation is -20mV/degC and your batteries are at 35degC, then they are 10degC hotter so the voltage is altered by 10 x -20 = -200mV = -0.2V. Therefore, at 35degC, the absorption voltage will be 14.2V (14.4 - 0.2 = 14.2). If the battery is below 25degC then it increases the voltage. There are limits to the range of compensation, see the manual for more detail.

If you do not do this, then with warm batteries you can overcharge and cold batteries undercharge. This is important for cases like my boat where the battery bank is in the engine room and can be 5degC in winter and 40degC in summer.

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mrhappy avatar image
mrhappy answered ·

The point is for the charger to internally have the information it needs to compensate charging voltage correctly based on battery temperature. The sensor is not adjusting anything, it only "reports" battery temperature to the charger, and the charger is adjusting charging voltage based on its value. And since it also reports the voltage at the poles of the battery, if it is connected correctly, I assume that value is also used to adjust the charging voltage to compensate for voltage drop in cables.

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greenarc avatar image
greenarc answered ·

But if the MPPT controller is using this temperature reading to adjust voltage, then why wouldn’t it adjust the temperature compensation value?

Hate to ask but so far it seemed logical to me that it would work for the temperature compensation value.

Much appreciate the time taken to help me understand all this better, thanks.

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greenarc avatar image
greenarc answered ·

Thank you for that. Appreciated. Now the quest to try find the compensation value of my exide ep1500 batteries.

Cheers!

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rithym1964 avatar image
rithym1964 answered ·

I have been saying in my posts that there should be a display (on vrm, remote console or both) of the 'target voltage' that the controller(s) are trying to reach, next to the actual voltage. This would allow you to instantly see whether the temp compensation is being correctly adjusted by the controller(s). As things are Nov 2021 this information is not viewable or buried in sub menus... considering how important temp compensation is for correct battery charging this info should be displayed to monitor easily

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