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Old 01-23-2013, 10:01 PM   #21 (permalink)
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Here's another weird behavior I saw today. As I might have mentioned, I usually get a background charge of about 5-10 amps just under 65% SoC. And I have a positive recal threshold/checkpoint at 72%, which I believe is fairly typical. Now, if I drop below 65%, I'll get the background charge and it will take SoC up to 70.2% and stop. Today, I dropped below 65%, background charge kicked in, and it took it up to 70.2% - BUT it also positively recal-ed up to 75%. Like yesterday's musing, this I've never seen before, ever. Over my travels today I lost precisely 2% capacity (yesterday I lost 5%)... And, the really weird thing is my pack voltage was quite lower than it normally is when it does a positive recal; it was only about 164, rather than the usual 168-169V...

True, I get the 'forced charge' after a negative recal and the pack seems to positively recal not at 72%, but at 60% and/or at a particular number of net amp-hours (it seems to put back in exactly enough to get the pack up to 6500 mAh, from the point at which it negatively recals. For example, if you negatively recal at 50% SoC, the car assumes or calculates that you have 3250 mAh in the pack and then puts back in another 3250). But, negative recal and forced charge is a different routine than just a typical background charge...

So... I don't know, grid charging does seem to do something to the pack beyond what the car can do alone; grid charging produces some seemingly anomalous battery management behavior. I just can't really see what the car is thinking when it decides the pack is at a particular SoC, when it decides the pack is at 75% SoC. Maybe it's the 164V mark: if the battery sits at at least 164 volts for a period of time the car believes the battery is at 75% SoC. Usually I'll get a pos recal at 72% when the car takes the voltage up to 168-169, yet it usually quickly drops to about 164-165... And yet, there doesn't seem to be much difference in pack voltage whether the battery is fully charged 100% or what the car believes to be 75%. So there's a little more to it... Pretty sure it's gotta be the rate of change in voltage under various loads, and/or something similar... Rate of change in temperature at the 4 thermistors might play a role... Just not something that can be easily spotted when all I have is pack temperature...
Does anyone know exactly how the car's "SoC" gauge reading (bars) is computed and set by the car?

What is SoC? (as long as I've been reading this forum I should know this, but I don't right at this moment)

Is your SoC in your post from the OBDIIC&C gauge? I have read that the car's SoC meter is not accurate and the OBDIIC&C gauge provides a much more accurate value. How does the OBDIIC&C gauge compute SoC?
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Old 01-23-2013, 10:55 PM   #22 (permalink)
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Soc..State of Charge.
Hang around maybe Peter or one of the other EG's will respond.

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Old 01-24-2013, 12:01 AM   #23 (permalink)
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Nobody really knows intimately. What we do know is that the SoC meter on the dash is controlled by the MCM, while the actual SoC reading available from the OBDII port is from the BCM. There is definitely a fudge factor between the two.

The dash SoC is arbitrary and based on the condition of your battery. The BCM SoC is actual.

With a deteriorated battery, you'll see BCM SoC in the 40-50% range while the dash SoC is in the 60-100% range.
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Old 01-24-2013, 08:37 AM   #24 (permalink)
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Soc..State of Charge.
Hang around maybe Peter or one of the other EG's will respond.

Willie
Thanks Willie....I did not state my question very well. The word "Charge" could have various meanings and was looking for some explanation in terms of measurements (battery or otherwise), e.g, volts, amps, mAh, etc. I'll try to pursue in Eli's post.
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Old 01-24-2013, 09:47 AM   #25 (permalink)
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Nobody really knows intimately. What we do know is that the SoC meter on the dash is controlled by the MCM, while the actual SoC reading available from the OBDII port is from the BCM. There is definitely a fudge factor between the two.

The dash SoC is arbitrary and based on the condition of your battery. The BCM SoC is actual.

With a deteriorated battery, you'll see BCM SoC in the 40-50% range while the dash SoC is in the 60-100% range.
For a given car, is the fudge factor between a two (MCM/car gauge and the BCM/OBDII gauge) a constant? Or does it vary over time as the system parameters vary? Has anyone compared?

Is the car gauge driven by a straight analog signal from the MCM or is there a MCM signal (bin/Hex) output accessible that something else uses to drive the car SoC gauge?

When you say XX-YY% range, range of what? new battery (6500) mAh, something else? Once I know that then maybe I will understand what the different percent ranges you quote for a deteriorated battery represent.

When you say the dash SoC is arbitrary and depend on the condition of the battery, are you referring to it still goes from zero bars to 20 bars but the battery only has maybe 10% "capacity" of a new battery? So, 20 bars really only represents the equivalent of 10% of a new battery which isn't much (10% of 6500 mAh?).
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Old 01-24-2013, 01:40 PM   #26 (permalink)
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.....When you say the dash SoC is arbitrary and depend on the condition of the battery, are you referring to it still goes from zero bars to 20 bars but the battery only has maybe 10% "capacity" of a new battery? So, 20 bars really only represents the equivalent of 10% of a new battery which isn't much (10% of 6500 mAh?).
I can help answer at least part of your question.

My battery pack is currently on the weaker side at only 1/2 the normal capacity, so call it 3700 mAH.

If I were to trickle charge the battery all the way up, and then immediately drive the car, the SOC would start out at let's say 19 bars.

I have MIMA, so let's say I'm using quite a bit of Assist and the battery voltage is now getting close to 144 or so, on my car the SOC will still show about 50%. As the voltage drops lower, and some of the weaker cells start to drop out, the SOC will drop slowly at first, but within a short period will very quickly just before the battery runs flat, and cuts of Assist.

It's like the SOC does not really know the true state of capacity of my deteriorated battery, but somehow assumes full capacity until it determines that cells are dropping, and THEN adjusts to SOC to suit.

Maybe this helps, Jim.
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Old 01-24-2013, 08:47 PM   #27 (permalink)
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I can help answer at least part of your question.

My battery pack is currently on the weaker side at only 1/2 the normal capacity, so call it 3700 mAH.

If I were to trickle charge the battery all the way up, and then immediately drive the car, the SOC would start out at let's say 19 bars.

I have MIMA, so let's say I'm using quite a bit of Assist and the battery voltage is now getting close to 144 or so, on my car the SOC will still show about 50%. As the voltage drops lower, and some of the weaker cells start to drop out, the SOC will drop slowly at first, but within a short period will very quickly just before the battery runs flat, and cuts of Assist.

It's like the SOC does not really know the true state of capacity of my deteriorated battery, but somehow assumes full capacity until it determines that cells are dropping, and THEN adjusts to SOC to suit.

Maybe this helps, Jim.
Thanks.

So, let me take this one step at a time and try to show understanding (at the same time probably revealing my electronic ignorance!)

Doing the trickle charge will level off at somewhere around 3700 mAh for your battery (it only has a capacity due to deterioration of about 50% of a new 6500-8000 mAh battery). It will read a voltage somewhere say between 170 and 200 V at this point. (if the car had charged it the max would be 192V per Eli post).

The car will set the car SoC gauge to "full/19 bars" and probably assume the battery has the full 6500 mAh in it.

You use MIMA (prevent any type of charging by the car?) while assisting thus taking mAh out of the battery. The voltage reading from the battery will drop to say 144V (as computed by the 6 voltage taps on the battery or maybe even a direct reading across the battery? or a readout on the OBDII gauge?) and the MCM or something will have changed the dash SoC gauge to 50% (maybe 8-10 bars or half lit up in green). The car will have somehow measured the amount of mAh (?) that had been used in assist in order to set the car SoC gauge to 50% (3250 mAh used in assist).

As the voltage drops below 144V (the sum of the 6 voltage taps is less than 144V?), the car SoC gauge is at first adjusted slowly down based on ? , but then quickly downward and the assist is blocked out (perhaps as the voltage reading on the battery reaches the lower allowed battery voltage (120V or so?)

Comments?

I still don't think I know exactly what SoC is (how it is computed to set the car gauge or how the BCM computes it to send out the data used by the OBDII gauge.)
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Old 01-25-2013, 12:39 AM   #28 (permalink)
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Let me take a 'quick' stab at this...

First, there's really three things we're talking about when we talk about state of charge in the Insight: what the in-dash gauge shows you, what the car thinks the state of charge is, and what the 'true' state of charge is - three different things.

The in-dash gauge reflects what the car thinks the state of charge is, but the implementation is so whacky that it does this very badly. The bars correspond to percentage capacity ranges and amp-hour counting - yet each bar doesn't represent the same amount, it's not linear. For example, the top bar in my car equals >76% (generally 76.1% to 81%, though if you charge with a grid charger it goes higher). Bar 19 equals 68.1% to 76%. Bar 18 equals 60.1% to 68%. These top three bars alone represent 5%+8%+8%=21% of the battery capacity - and yet there's 20 bars! The next few bars to about 50% SOC equal only 2% each.

Though the in-dash gauge corresponds to real state of charge numbers in percentages and/or amp-hour counting, each bar doesn't represent the same amount, which makes interpreting the in-dash gauge less than ideal.

Each percentage-point of state of charge corresponds to a real number - 65 mAh; use 65 mAh and you drop the state of charge by 1%. Charge 65 mAh and you raise it by 1%, at least, that's what the car does, that's mainly how the car keeps track of state of charge. In general, the car has a set figure in mind - 6500mAh - and keeps track of what goes in and out of the battery, and then it's just simple math to calculate the state of charge.

BUT, this is only like the first cut, the running totals, the car uses to keep track of state of charge. It also knows what I'd call 'performance targets': the battery should perform in such and such a way if it's really at such and such state of charge... This is where it gets tricky.

There's a couple, if not a few, things that prevent a straight forward accounting-like procedure like this from working. One is self-discharge. Another is inefficiency. Park the car over night and you lose state of charge. Since the battery isn't a perfect storage medium, especially the older ones, what current is sent to the battery doesn't necessarily stay there. Additionally, what current you can pull out of the battery isn't everything that's stored in it... Suffice it to say that having a set capacity figure of 6500 mAh and keeping track of amps in and amps out can fairly quickly cease to reflect the true state of charge. So the car has additional 'routines' that it does, plus perhaps some performance thresholds, to estimate the true state of charge...

A couple of the performance thresholds might be the top and bottom voltage thresholds, whether for the pack as a whole or for each of the ten voltage taps, I don't know. It looks to be something like 180V at the top and 120V at the bottom. The car throttles current to stay within this range, or perhaps it changes voltage to within this range to throttle the current. It seems as though, when it has trouble doing this, it spazzes-out, more so at the bottom - negative recal at the bottom, perhaps positive recal at the top.

One routine, having to do with charging and positive recals, seems to rely on low current charges and discharges in succession, plus perhaps time, to find the 75% state of charge level. From what I can tell, NiMH batteries reveal their state of charge when subjected to loads.

For instance, if the battery's at 165 volts at time 1, you charge it at 1 amp for a few seconds and it goes up to 167 volts at time 2, and then you subject it to a discharge current of 1 amp and voltage drops to 164 volts at time 3, and so on, in multiple successions, this perhaps reveals the state of charge... It's not so much the voltage that's important; it's how the voltage responds to set charge and discharge loads over time. I don't know if there's a target voltage or what, but one idea is that whatever voltage the car has in mind, it's trying to see how stable it is. You can throw a bunch of amps, a bunch of regen, at your HV battery when the voltage is say 155V, and it will shoot up to say 184V and then quickly throttle down to 180V. When you let off the regen, depending on how many amp-hours you dumped into the pack (and other things), the voltage will drop. Is the pack full, is it at 75% SoC now? The car will run it's routine to see how stable the voltage is. I'm mainly thinking about the 72% positive recal threshold at this point; the state of charge as the car knows it will hang at 72% while it runs this routine. As you continue to drive and regen and assist, the car keeps track of the amps-in and amps-out as usual, but it's doing so according to this fishing expedition, which looks to me like seeking a particular voltage threshold, or maybe a couple thresholds, and figuring out when it's stable enough to call it "75%"...

Insight state of charge is a serious melo-drama.
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Old 01-25-2013, 12:59 AM   #29 (permalink)
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Lots of stuff.
The OBDIIC&C does not compute SOC itself, it displays the reading from the BCM.
The OBDIIC&C can calculate Ah/Wh in/out of the battery which can be quite revealing if used correctly.

The BCM calculates SOC using a sophisticated algorithim we don't know everything about.
However we do know.

1) It counts current in/out of the battery very accurately.
2) It measures the overall battery voltage and also monitors the ten voltage taps.
3) It measures the battery pack temperature.
4) It responds to overall battery high/low critical voltages and voltage tap high/low critical voltage taps and discrepancies.
5) It tries to keep the Battery Soc between 80-20%

It's using this info in it's program to caculate an SOC and protect/manage the battery. As the battery is made up of 120 cells in series and they are not perfectly matched they go out balance which we all know and dread. The BCM responds to this by doing neg recals when any cells reach empty.

Your last post is getting the idea of what is happening.

The OEM Soc gauge is driven by a serial data signal from the MCM, which is based on the info recd by the MCM from the BCM. The Soc part of the gauge is a very slow refresh/update rate compared to the assist/regen sections so it cannot change quickly even when the SOC changes in an instant due to say a neg recal.

Although we have done a lot of work on this we don't fully understand the data stream between the BCM and the MCM, there could easily be a battery Soh (State of health) parameter or flag in there which causes a scaling change on the Soc display so it's range is reduced/expanded whatever etc etc.
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Old 01-25-2013, 01:19 AM   #30 (permalink)
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...The BCM calculates SOC using a sophisticated alogorithim we know little about....
I'm pretty sure it calculates state of charge most of time just as I explained it: a fixed capacity of 6500mAh and keeping track of amps-in and amps-out. I would describe it as having additional routines or algorithms to deal with the times that the straight forward calculations don't 'add up'...
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