Classic SOC Q & A

[Resthome]

I would like to understand the Classic SOC a little more so I have created this Classic SOC thread so we can have a discussion with the forum experts and Midnite on this functionality as it currently stands and any future enhancements or changes.

I have a lot of questions and assumption in regards to the Classic new SOC measurement. So here is my list of assumptions and questions:

• It is clear that the declared battery capacity is used to calculate amp hours remaining as well as SOC %
  
• 
  I can see how the Percent of Capacity change per degree C of battery temperature applies to the AH Remaining reading.
  
• 
  I think I understand the battery charge efficiency factor (CEF) %. For example a battery with a charge efficiency factor of 90% would require 10.0 amp hours to store 9.0 Ah to the battery.
  
• 
  The CEF is used to determine the rate the SOC % counts back up.  But is it counting back up to the declared Battery Capacity or the temperature compensated Battery Capacity?
  
• 
  What is the Classic using to count down the SOC % ?
  
• 
  Does the SOC function require 100% of Amp hours removed be returned ?
  
• 
  I'm assuming the rate of discharge has no bearing on the Classic SOC % calculation. Is this correct ? 
  

Maybe boB can give some perspective on how the Classic SOC % is calculated.

[vtmaps]

3.  I think I understand the battery charge efficiency factor (CEF) %. For example a battery with a charge efficiency factor of 90% would require 10.0 amp hours to store 9.0 Ah to the battery.

7.  I'm assuming the rate of discharge has no bearing on the Classic SOC % calculation. Is this correct ? 

Regarding the charge efficiency, it would be very cool if it could vary depending on SOC and/or voltage.  I think the CEF is much higher during bulk charging than during absorb.

Hopefully there will be  way to program in a Peukert factor... some battery monitors do have a Peukert setting and the rate of discharge does affect the SOC calculation.

--vtMaps

[boB]

• 
  The CEF is used to determine the rate the SOC % counts back up.  But is it counting back up to the declared Battery Capacity or the temperature compensated Battery Capacity?
  

It is counting up to whatever the present temperature compensated capacity is.  If you were
to take a 100K Ohm pot and plug it into the Batt temp sense jack (the sensor is 10K at 25C),
and at that time, the SOC% was at, say, 90%, and you adjust the temperature, the AH remaining
would stay still and the percentage SOC would change to show the remaining amp-hour's percentage
of that capacity as you turned the pot..

• 
  What is the Classic using to count down the SOC % ?
  

Counting down does not use any special treatment.  It just counts down AH from where it was.

• 
  Does the SOC function require 100% of Amp hours removed be returned ?
  

Well, if I understand the question correctly, it would require 100% plus the inefficiency
to be returned to get back to 100% SOC.  Your previous assumptions are all correct.

• 
  I'm assuming the rate of discharge has no bearing on the Classic SOC % calculation. Is this correct ? 
  

Hopefully there will be  way to program in a Peukert factor... some battery monitors do have a Peukert setting and the rate of discharge does affect the SOC calculation.

Resthome, you are correct.  No special treatment or Peukert factor at the moment for discharge.
It would not be all that difficult to add that to the discharge though.  Would probably want to
be able to adjust the Peukert exponent I would think.

Regarding the charge efficiency, it would be very cool if it could vary depending on SOC and/or voltage.  I think the CEF is much higher during bulk charging than during absorb.

"Amp-Hour" efficiency is pretty much constant AFAIK.  It is the "Energy" efficiency that changes
with charge state because there are more kW-Hours used up for the SOC% increase you get
in the constant voltage Absorb stage than are used for the Bulk charge stage.

I would think there is at least some amp-hour efficiency change in different charge stages but
I don't think that it is all that significant.  Please let me know if you find otherwise though.

boB

[boB]

Something that came to mind from a previous Resthome thread was that another "number" that could be displayed is time left at present rate of discharge.  Down to some depth of discharge.  0% or 50% default I suppose.

[cybermaus]

Does the SOC function require 100% of Amp hours removed be returned ?

Well, if I understand the question correctly, it would require 100% plus the inefficiency
to be returned to get back to 100% SOC.  Your previous assumptions are all correct.

But it also re-sets to 100% if the charging logic detects a full battery. I have seen where it slowly counted up to 89%, and then jumpted to 100%. Presumably due to the fact I had set CEF to from default 94 down to 92% for 'safety' reasons.

Hopefully there will be  way to program in a Peukert factor... some battery monitors do have a Peukert setting and the rate of discharge does affect the SOC calculation.

Resthome, you are correct.  No special treatment or Peukert factor at the moment for discharge.

Aha, that is the reason why my 20 year old monitor discharges a few % faster. Its default Peukert factor is 1.27.
And the reason it when up slower is because it had a default CEF of 90% (changed that to 92% also)

---

A small question remains (not sure if this is the correct thread): When the WBjr re-sets to 100% due to full-battery detection, the other monitor does not also re-set (and this, over time it walks way off)

According to its manual, it should detect 'other' charge equipment (like dynamo) and re-set to 100% if two conditions are met:
- It sees a float voltage of at least 27.2V ( setting called FLOAT LEVEL)
- At this voltage, it sees the charge current drop to below 2% of the nominal capacity (460Ah bank so 9.6A, setting called "RETURN AMPS")

Does this make sense? I had the impression this would match the classic, but the Mastervolt does not re-set.
Is there some way to tick the other monitor by presenting these values?
Or advice how to tweak these settings to match the Classic?

[vtmaps]

If you were to take a 100K Ohm pot and plug it into the Batt temp sense jack (the sensor is 10K at 25C), and at that time, the SOC% was at, say, 90%, and you adjust the temperature, the AH remaining would stay still and the percentage SOC would change to show the remaining amp-hour's percentage of that capacity as you turned the pot..

That doesn't sound right... Let's say my batteries are resting at 90% SOC at room temperature.  I have a certain number of AH remaining.   If the batteries get cold, should there be fewer AH remaining?

--vtMaps

[boB]

If you were to take a 100K Ohm pot and plug it into the Batt temp sense jack (the sensor is 10K at 25C), and at that time, the SOC% was at, say, 90%, and you adjust the temperature, the AH remaining would stay still and the percentage SOC would change to show the remaining amp-hour's percentage of that capacity as you turned the pot..

That doesn't sound right... Let's say my batteries are resting at 90% SOC at room temperature.  I have a certain number of AH remaining.   If the batteries get cold, should there be fewer AH remaining?

--vtMaps

Oh, I don't know....   The capacity (max) went down with temperature and that would be the maximum amp-hours it can hold and so now the amp-hours has to climb up to that newer (lower than before) value.

The battery temperature shouldn't really be changing this fast I wouldn't think so it shouldn't really be an issue...

Keep thinking on it...   Right now, it seems to work pretty well so we won't touch it yet.

It is definitely food for thought though !  At least things like this help me get to sleep faster.

boB