<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Michael,<div class=""><br class=""></div><div class="">Thanks for the explanation. That makes good sense.</div><div class=""><br class=""></div><div class="">Given that at least three vehicles support SOC MIN and MAX, I’ve gone ahead and made standard metrics for those. I haven’t modified all the vehicle modules to store them, but think that can be done for at least Roadster, Kia Soul and Twizy (and maybe Nissan Leaf). Can the maintainers of those modules set appropriately? Should be very simple.</div><div class=""><br class=""></div><div class="">I’ve also created a generic textual v.b.health metric that can be used to record a textual indication of vehicle health (perhaps the calculations behind v.b.soh). Very vehicle specific.</div><div class=""><br class=""></div><div class="">I’ve then modified the Tesla Roadster module to store v.b.soc.min and v.b.soc.max, and to calculate v.b.soh (based on %cac remaining x %soc inbalance). Maybe tune it later, but I think it should give a pretty good rough indication of health. That is all in an edge release ready to go out tonight.</div><div class=""><br class=""></div><div class="">Regards, Mark.<br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On 24 May 2018, at 12:12 AM, Michael Balzer <<a href="mailto:dexter@expeedo.de" class="">dexter@expeedo.de</a>> wrote:</div><br class="Apple-interchange-newline"><div class="">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" class="">
<div text="#000000" bgcolor="#FFFFFF" class="">
Mark,<br class="">
<br class="">
I introduced this originally, it's meant to be (1), the overall
indication of battery health.<br class="">
<br class="">
As the wikipedia article says, there is no general industry
definition on how to calculate this.<br class="">
<br class="">
On the Twizy, the SOH is given by the BMS, while the CAC is
calculated by the OVMS by monitoring the charge process and counting
coulombs. The BMS SOH is the (normally invisible) limit for the
usable capacity, as the Twizy always shows a range of 0-100% SOC
regardless of the SOH. It's also the base for any warranty
replacement of the battery (if it's rented you'll get a new one when
SOH is below 75%).<br class="">
<br class="">
The BMS is proprietary and without any available documentation, it's
a complete mystery how it calculates the SOH.<br class="">
<br class="">
While the capacity would normally be the major factor in a SOH, the
Twizy BMS (LG Chem) has actually other ideas on this. For example
it's been at 100% for the first three years, then at 99% for another
two years, while my CAC value showed the actual degradation (long
term linear with cycles). It's then begun to drop rapidly over a
short period of time and is now close to my CAC level. My cells are
still pretty good balanced under load as well as open circuit, the
balance also degraded more or less linearly. There are also no
obvious temperature indications that could explain the SOH curve.<br class="">
<br class="">
<br class="">
Generally I recommend to use this for the value the car provides, if
any.<br class="">
<br class="">
If the car doesn't provide an SOH, any calculation that fits…<br class="">
<br class="">
<blockquote type="cite" class="">
<ol class="MailOutline">
<li class="">An overall indication of battery health? 100% being
perfect, and 0% a brick?</li>
</ol>
</blockquote>
<br class="">
…will do.<br class="">
<br class="">
<br class="">
<blockquote type="cite" class="">
<div class="">Kia Soul seems to be closest to the implementation I
was thinking of. Find out the difference between SOC LIM MIN and
LIM MAX, and use that as an indication of imbalance in the pack.
But Nissan Leaf seems to be more like (CAC/160)*100 (where 160
is the CAC for a brand new vehicle).</div>
<div class=""><br class="">
</div>
<div class="">Or should we just add SOC_MIN and SOC_MAX if these
are used in many cars? Or an imbalance percentage?</div>
<div class=""><br class="">
</div>
<div class="">Or should we combine the both (so CAC/160*100 gives
us percentage capacity loss, and SOCMAX-SOCMIN/SOCMAX*100 gives
us imbalance of the pack, then we perhaps multiply the two
together to give an overall indication of health)?</div>
</blockquote>
<br class="">
If breaking down SOC into the peak min and max cell values I suggest
also adding the average and peak standard deviation, plus either the
average cell SOC or the number of cells to derive that.<br class="">
<br class="">
Interior resistance of cells would be another option for standard
metrics of cell health, but seems to be rarely available (and needs
a reference).<br class="">
<br class="">
I've got the cell module voltages and temperatures on the Twizy. I
record their peak values and deviations under load and calculate the
standard deviation. This monitoring shows only a minor difference
against the values I recorded five years ago. I'm pretty sure if I
also had the internal resistance, that would give a much clearer
image.<br class="">
<br class="">
Regards,<br class="">
Michael<br class="">
<br class="">
<br class="">
<div class="moz-cite-prefix">Am 23.05.2018 um 16:42 schrieb Mark
Webb-Johnson:<br class="">
</div>
<blockquote type="cite" cite="mid:AB7F1501-2FBD-4944-82FC-65C086F87A5B@webb-johnson.net" class="">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" class="">
<div class=""><br class="">
</div>
What is MS_V_BAT_SOH used for?
<div class=""><br class="">
</div>
<div class="">For Tesla Roadster, as well as SOC, we have SOC LIM
MIN and SOC LIM MAX. I want to make those available.</div>
<div class=""><br class="">
</div>
<div class="">
<ul class="MailOutline">
<li class="">Kia Soul seems to use:<br class="">
<br class="">
StdMetrics.ms_v_bat_soh->SetValue( 110 - (
m_b_cell_det_max->AsFloat(0) +
m_b_cell_det_min->AsFloat(0)) / 2 );<br class="">
<br class="">
</li>
<li class="">Nissan Leaf uses:<br class="">
<br class="">
StandardMetrics.ms_v_bat_soh->SetValue(ah / newCarAh *
100);<br class="">
<br class="">
</li>
<li class="">Twizy uses:<br class="">
<br class="">
CAN_BYTE(5) on ID 0x424</li>
</ul>
</div>
<div class=""><br class="">
</div>
<div class="">Which is it?</div>
<div class=""><br class="">
</div>
<div class="">
<ol class="MailOutline">
<li class="">An overall indication of battery health? 100%
being perfect, and 0% a brick?</li>
<li class="">Or battery capacity (100% being a new car, and
50% being one who’s range is only half that of a new car)?</li>
</ol>
</div>
<div class=""><br class="">
</div>
<div class="">The definition here seems to lean towards #2
(capacity related), but seems arguable:</div>
<div class=""><br class="">
</div>
<blockquote style="margin: 0 0 0 40px; border: none; padding:
0px;" class="">
<div class=""><a href="https://en.wikipedia.org/wiki/State_of_health" class="" moz-do-not-send="true">https://en.wikipedia.org/wiki/State_of_health</a></div>
<div class=""><br class="">
</div>
<div class=""><b class="">State of health</b> (SoH) is a figure
of merit of the condition of a battery (or a cell, or
a battery pack), compared to its ideal conditions. The units
of SoH are percent points (100% = the battery's conditions
match the battery's specifications).<br class="">
<br class="">
Typically, a battery's SoH will be 100% at the time of
manufacture and will decrease over time and use. However, a
battery's performance at the time of manufacture may not meet
its specifications, in which case its initial SoH will be
less than 100%.</div>
<div class=""><br class="">
</div>
<div class="">As SoH does not correspond to a particular
physical quality, there is no consensus in the industry on how
SoH should be determined. The designer of a battery management
system may use any of the following parameters (singly or
in combination) to derive an arbitrary value for the SoH.<br class="">
<br class="">
<div class="">
<ul class="MailOutline">
<li class="">Internal resistance / impedance / conductance</li>
<li class="">Capacity</li>
<li class="">Voltage[2]</li>
<li class="">Self-discharge</li>
<li class="">Ability to accept a charge</li>
<li class="">Number of charge–discharge cycles</li>
</ul>
</div>
<div class=""><br class="">
</div>
In addition, the designer of the battery management system
defines an arbitrary weight for each of the parameter's
contribution to the SoH value. The definition of how SoH is
evaluated can be a trade secret.</div>
</blockquote>
<div class=""><br class="">
</div>
<div class="">Kia Soul seems to be closest to the implementation I
was thinking of. Find out the difference between SOC LIM MIN and
LIM MAX, and use that as an indication of imbalance in the pack.
But Nissan Leaf seems to be more like (CAC/160)*100 (where 160
is the CAC for a brand new vehicle).</div>
<div class=""><br class="">
</div>
<div class="">Or should we just add SOC_MIN and SOC_MAX if these
are used in many cars? Or an imbalance percentage?</div>
<div class=""><br class="">
</div>
<div class="">Or should we combine the both (so CAC/160*100 gives
us percentage capacity loss, and SOCMAX-SOCMIN/SOCMAX*100 gives
us imbalance of the pack, then we perhaps multiply the two
together to give an overall indication of health)?</div>
<div class=""><br class="">
</div>
<div class="">Thoughts?</div>
<div class=""><br class="">
</div>
<div class="">Regards, Mark</div>
<div class=""><br class="">
</div>
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<br class="">
<pre class="moz-signature" cols="160">--
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