Wbjr temperature compensation

[Muskoka]

Per my questions in the Classic forums, I'm trying to find an optimal EA value to terminate absorb, while dealing with the jitter. Thanks to the help of others, and Bob, he might have something up his sleeve to help with that.

I have another question in regards to the EA value, that deals more I think with the Wbjr, so I'll ask here.

I've thought about this question for a while, and whether to even ask it, but I think my logic is correct. I searched around but couldn't find an answer.

Is the value we manually plug in for EA absorb termination temperature compensated? I don't believe it "compensates" for temperature in any way?

My batteries, depending on the time of year, have roughly a 40-50 degree Celsius swing in temperature. In the winter, when temps can easily reach -30c my batteries might get down to 0c, and in the summer when temps reach +30c, my batteries can reach mid to high 40's c, while charging.

This variance in temperature has a huge impact on the amperage value going in and out of my system, as well as my bank capacity.

If that EA value we manually plug in is not temperature compensated, I'm going to have to manually change it multiple times throughout the year. Is my assumption correct?

I know the charge voltage values we plug in are compensated, provided you use the sensor, but what about the EA absorb termination value, it's not compensated for, is it?

Plugging in for example a EA value of 5a for winter absorb termination, certainly is not going to work for summer, when that amp value is going to be considerably higher. My voltages are compensating correctly, anywhere from 14.4/5/6/7v in summer, to low/mid 15v's in the winter, but the EA absorb termination value will always remain the same, whatever value I manually plug in.

I don't know if there's even a way to work around / deal with, what I'm asking? Or perhaps my logic is "out the window", and that EA value doesn't need to be compensated for at all.

[Vic]

Muskoka,

IMO,  the temperature compensation value that is set (particularly for LA batteries),  is to compensate for the required charge voltage change,   that results from changes in battery temperature.

If the correct compensation value is used,  one would expect that this attempts to keep the effect of battery charge voltage fairly constant vs changes in battery temperature.

Within reason,  the compensation value attempts to keep the battery charge current equal to the that would exist when the battery temperature is at the Reference temperature (usually 25 - 27-ish C).

Hope that the above makes some sense.     FWIW,   Vic

[Muskoka]

Hi Vic, I get that.

But it has nothing to do with the setting of a EA value. As the bank cools the voltage goes up, amperage down, and vise versa as the temp increases.

So the temperature compensation is working fine for changes in system charge voltages, but that does nothing, has no affect at all, on the amperage setting for EA.

The absorb cycle is not terminating based on voltage, it's terminating based on a "fixed" EA value, but my EA value moves greatly depending on the bank temperature. Not what I plug in, but what it should actually be set to, based on temperature.

In my mind that "fixed EA" value only works if the battery bank temperature remains constant, or very close. Mine swings upwards of 50c, so how can  a "fixed" amperage value work. EA needs to adjust based on the temperature of the battery, and I don't think it currently does that.

To state again, my winter end amps is around 5 amps, let say. And in the summer it's 10, maybe 11 amps. How can a fixed EA value work properly?

I'm not trying to be thick, I just don't see how EA can work properly on a system like mine with such wide swings in bank temperature. A fixed EA etting of 5 amps in the winter is nowhere close to what the value needs to be set to for summer.  My system would never get close to that 5 amp EA setting in the summer, not even close, but can get there in the winter, due to the system temp.

[Vic]

OK,  the thing is,  at a constant battery temperature,  if the  Absorb voltage (let's say as an example),   is increased,  the battery charge current (WbJr current)  increases,   and the converse is also true).

As the battery temperature changes,  these setpoint voltages must change (be  compensated),  in order to maintain the intended charge voltage values.   A charge voltage change results in a WbJr current change.   If the charge voltage change results from a battery temperature change,  the WbJr current should remain constant,  if the proper compensation value has been entered into the Classic.

There needs to only be one compensation for changes in battery temperature.   The compensated voltage will retain the effect  of the EA setting with changing battery temperatures.

The ideal compensation values provided by battery manufacturers,  could possibly need to be a bit more precise than our ability to set them.   BUT,  like so many things with FLA batteries,  there are SO many variables that affect battery charging,  and its termination,  that getting fairly close  is usually all that we need to shoot for.

On our system,  we have a relatively high string Vmp vs battery voltage  (106 V,  vs 48 V battery).   And,  near the end of Absorb,   the Vin to the Classic is often in the 115 - 122 V range (due to light loading on PVs).   These relatively high PV string voltages cause more Jitter than would somewhat lower Vins.

As noted,  before,  loads on the inverter,  will affect the voltage drop in the cable and breaker that is on the output of the Classic,  that connects to the battery.

Heavy loads on the inverter during Absorb also usually increases the Ripple voltage on the battery terminals.  Ripple voltages and CC voltage dithering are a primary cause of WbJr current Jitter.   Near the end of Absorb,  the battery impedance is relatively high,  so,  the battery is not particularly good at damping this ripple.

Again,  just my opinion,   and perhaps too much inability to try to explain what we are thinking.

FWIW,   Vic