Are the batteries really isolated during ESS stops?

[RudeJeepin]

Please define "settled".

Proven...is that better.

Maybe I ventured outside of this forum and found the answers.

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[Flanders]

What scope is it? For $80 I'd seriously consider getting one.

Zoyi ZT-703s. The price is probably higher with tariffs. The best deals are direct from China via Ali Express.

I wouldn't recommend it for general use. The multimeter function is good and I use it a lot. The scope is buggy and imprecise. Sometimes it's exactly the right tool though. You can float the ground, which you can't do with a bench scope (there can be only one ground). I think there are better portables in the <$100 range if you don't need the multimeter function.

On the other hand, you can spend $500 on a portable and still get a buggy imprecise scope that can't do much than the Zoyi. I have a $500 Hantek tablet scope; it's an absolute piece of shit.

 

[Flanders]

@RudeJeepin Bad joke, I apologize.

 

[RudeJeepin]

@RudeJeepin Bad joke, I apologize.

No problem, I just woke from a nap, so probably miss read the room.

But your right. It will never be "settled" for some.

 

[ShadowsPapa]

 

[jebiruph]

I'll give it one more shot. Tell me what you think I've got wrong here, in the fewest words you can.

1. The voltage across the PCR is the difference between the voltages at N1 and N2, shown in the traces.

2. The relationship between current, resistance and voltage across the PCR is given by Ohm's law, V = IR.

3. The voltage across the PCR for the ESS restart is at least 10x 4x that of the cold start.

If the PCR is closed in both cases:

4. The current through the PCR on the restart is at least 10x 4x that of the cold start. This is current flowing from the AUX side towards the MAIN and starter.

5. Hundreds of amps must be flowing through the PCR on the restart. Most of that does not come from the AUX - its voltage remains significantly higher on the restart than on the cold start.

Therefore, either

A. The vehicle electronics have the capacity (i.e., capacitance) to supply hundreds of amps towards the cranking effort; or

B. Everything after 3 is irrelevant because the PCR is open during the restart.

EDIT: Change 10x to 4x. The first rule of Dunning-Kruger club is you don't know you're a member of Dunning-Kruger club.

It's 1. If there is a residual charge in the system electronics, then the voltage you are reading for the aux battery could be wrong.

For example, when I'm driving, my system voltage is frequently in the mid 14 volt range. When an ESS event is triggered, the voltage starts around 14v and drops from there. The aux battery is not 14v, so the residual charge in the system electronics is holding the voltage high until the residual charge is dissipated, then battery voltage takes over.

Since you are reading the aux battery voltage from a point in-between the aux battery and system electronics, the residual charge in the system electrons could affect your reading.


I think I may have an answer my question that lead to this particular discussion, that is if the batteries are disconnected, why does the aux battery voltage follow the pattern of the main battery when the starter is cranked.

Here's the problem, again. Powering the electronics is a constant load and should result in a flat voltage. When the batteries are separated and the starter is cranked, the aux battery voltage should drop and then maintain a constant voltage as I've drawn with the red line. But instead it follows the (attenuated) pattern of the main battery which is cranking the starter.

It occurred to me that because the two batteries share a common ground wire, any voltage drop across this ground wire caused by the main battery could also affect the aux battery, even though the positive wires are disconnected. One way to test this would be to ground the aux battery directly to the body instead of the main battery negative terminal and see what it's voltage looks like on a restart.

 

[ShadowsPapa]

Here's the problem, again. Powering the electronics is a constant load and should result in a flat voltage.

But when the PCR opens, the load is very suddenly shifted to only one battery, a small battery with a smaller amp hour capacity, not a pair where one is a much larger battery.

 

[Flanders]

It's 1.

Strong start, followed by over 200 words that didn't address 1 at all. Can we focus on that?

1. The voltage across the PCR is the difference between the voltages at N1 and N2, shown in the traces.

Let's consider the PCR to include the wires connecting it to N1 and N3, also the inch of busbar connecting N2 and N3. The same current flows through the wires and the relay itself.

With this redefinition, the PCR connections are at N1 and N2, exactly where the scope probes were attached. Can you now accept 1?

1. The voltage across the PCR (including wires connecting it to N1 and N2) is the difference between the voltages at N1 and N2, shown in the traces.

It's Kirchhoff's Voltage Law.

 

[Flanders]

It occurred to me that because the two batteries share a common ground wire, any voltage drop across this ground wire caused by the main battery could also affect the aux battery, even though the positive wires are disconnected.

Bingo.

The probes were at N1 and N2, and the ground clips were on the chassis. When both batteries are discharging,

Chassis potential > MAIN negative potential > AUX negative potential.

Yes, a dip at N1 should be expected, not because AUX positive is being pulled down, but because chassis ground is being pulled up relative to AUX negative.

I would have mentioned this earlier but you've been raving like a lunatic and I can't figure out what you're talking about most of the time. I didn't want to further muddy the waters.

----

Let's estimate the magnitude of the dip:

The MAIN negative is connected to chassis ground through maybe 2 feet of 4AWG copper wire. Resistance of 4AWG copper is around 0.25 milliohms per foot. Add maybe 0.1 milliohms for termination and contact resistance at each end. Ballpark, 0.70 milliohms on the chassis to MAIN negative connection.

If inrush current is 1000 amps then we're looking at 0.7V drop from the chassis ground to MAIN negative. The voltage drop from MAIN negative to AUX negative would be smaller, maybe 0.1-0.2V.

This would look appear on the blue trace as a dip of ~0.8V recovering exponentially to a steady state.

 

[ShadowsPapa]

All of this while ignoring documents stating how it works (explaining they are disconnected during initial starter engagement), and voltage tests showing both batteries dropping at the same rate during the ESS stop (showing they are connected during the stop).

Two solid indicators of what's going on. Documents, and evidence through volt meters, all muddied by a scope picture - which will be showing a combination of things happening -
dip due to increased load,
and
dip due to the common ground potential changing after the load of the main is removed

Back to the answer -
No the batteries are NOT isolated during an ESS stop event
Yes, they remain connected until the starter sequence is started
and yes, the PCM can do all of that in proper order.
The batteries are isolated for a quick voltage check of the aux battery during a cold/push button start,
that's it.

 

[sharpsicle]

For example, when I'm driving, my system voltage is frequently in the mid 14 volt range. When an ESS event is triggered, the voltage starts around 14v and drops from there. The aux battery is not 14v, so the residual charge in the system electronics is holding the voltage high until the residual charge is dissipated, then battery voltage takes over.

This made me giggle.

 

[LowOnCash]

Bottom line aside from not needing this goofy stop/start system, the 2nd battery is just as worthless as the idea because there is no way it can supply the needed ampere to start the motor, so why not just use the starting battery to begin with. Also, Why would we even need a 2nd battery to start the engine when the main battery is 95% of the time already charged, since it was being charged up to the point of shut-down. To do the system correct (if that were possible) there would be two starting batteries like the Cumming Dodge uses. Has to be the bright idea of some "pencil-Head" sitting at a desk somewhere who drive an electric car to work.

Mike

 

[sharpsicle]

Bottom line aside from not needing this goofy stop/start system, the 2nd battery is just as worthless as the idea because there is no way it can supply the needed ampere to start the motor, so why not just use the starting battery to begin with. Also, Why would we even need a 2nd battery to start the engine when the main battery is 95% of the time already charged, since it was being charged up to the point of shut-down. To do the system correct (if that were possible) there would be two starting batteries like the Cumming Dodge uses. Has to be the bright idea of some "pencil-Head" sitting at a desk somewhere who drive an electric car to work.

Mike

The aux battery does not start the engine...you're going off on a tangent based on a serious misunderstanding of the system.

 

[ShadowsPapa]

Bottom line aside from not needing this goofy stop/start system, the 2nd battery is just as worthless as the idea because there is no way it can supply the needed ampere to start the motor, so why not just use the starting battery to begin with. Also, Why would we even need a 2nd battery to start the engine when the main battery is 95% of the time already charged, since it was being charged up to the point of shut-down. To do the system correct (if that were possible) there would be two starting batteries like the Cumming Dodge uses. Has to be the bright idea of some "pencil-Head" sitting at a desk somewhere who drive an electric car to work.

Mike

You really did miss the whole point. Totally, not even close. Go back and read the REAL reason that aux battery is there, and it's zip to do with starting. It's about electronics, failures of electronics "at power up" and keeping the power to the electronics consistent. Go chat with some people who are EEs.

Has to be the bright idea of some "pencil-Head" sitting at a desk somewhere who drive an electric car to work.

LOL - yup - knows nothing of electronics at all or even this system and the reasoning. Totally missed the point or slept through all of the other discussions and decided to jump in with hate instead of reason.

 

[ShadowsPapa]

This made me giggle.

Seems to me to be more of a "surface charge" on the battery, and the fact these gauges don't respond all that fast. They seem to have some buffering to them to prevent sharp short rises and falls.
I should use analog meters during my next testing.

Also note that most of these systems, including the lighting, has voltage regulation involved. So the "electronics" don't "see" the full system voltage and won't be keeping the lines charged like that.

I ran into some really interesting effects of swapping cards in the slots in the computer systems I was putting together for Compressor Controls Series IV interfaces.

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