Are the batteries really isolated during ESS stops?

[Flanders]

@jebiruph Thank you for the response. @ShadowsPapa more or less said what I was going to, perhaps more. Let me just ask this: Do you know whether the PCR remains open for the duration of an ESS stop?

Taking a step back: It is widely claimed on the JL and JT forums that for the duration of an ESS stop,

1. The PCR remains open.
2. The AUX battery powers the vehicle.
3. The main battery is largely unloaded.

At this point I am confident that 2 and 3 are false. Of course if 1 is false then 2 and 3 are also. I think that is likely.

I only started looking at this when my JT wouldn't charge the battery when driven immediately after a moderate discharge. It didn't just fail to charge, it steadfastly refused to charge, holding 12.8V even while engine braking downhill where it usually pulls it up over 14V. When I got home and plugged in a charger, it took 3Ah charge in about 10 minutes - which the vehicle could have easily done on the drive and for some reason chose not to.

Inspired by @ShadowsPapa, I connected a DMM to the main battery terminals and drove it around. I was concerned that it might actually be discharging when the dash showed 12.8V since it usually reads over 12.80V on the terminals 24 hours after a charge. I found the dash was reading about 150mV lower than the multimeter, alleviating that concern. I also noticed that during ESS stops the meter and the dash voltage reading were falling at about the same rate with that 150mV offset. That surprised me somewhat, having read a great many forum posts on batteries. Hence this thread.

It also occurs to me that there is some risk in this type of experiment. The leads to the multimeter in the cabin are connected directly to the battery positives - there are no fuses in the current path. If one of the banana plugs were to get pulled from the multimeter and contact the metal surfaces inside the truck...

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[sharpsicle]

@jebiruph Thank you for the response. @ShadowsPapa more or less said what I was going to, perhaps more. Let me just ask this: Do you know whether the PCR remains open for the duration of an ESS stop?

Taking a step back: It is widely claimed on the JL and JT forums that for the duration of an ESS stop,

1. The PCR remains open.
2. The AUX battery powers the vehicle.
3. The main battery is largely unloaded.

At this point I am confident that 2 and 3 are false. Of course if 1 is false then 2 and 3 are also. I think that is likely.

I only started looking at this when my JT wouldn't charge the battery when driven immediately after a moderate discharge. It didn't just fail to charge, it steadfastly refused to charge, holding 12.8V even while engine braking downhill where it usually pulls it up over 14V. When I got home and plugged in a charger, it took 3Ah charge in about 10 minutes - which the vehicle could have easily done on the drive and for some reason chose not to.

Inspired by @ShadowsPapa, I connected a DMM to the main battery terminals and drove it around. I was concerned that it might actually be discharging when the dash showed 12.8V since it usually reads over 12.80V on the terminals 24 hours after a charge. I found the dash was reading about 150mV lower than the multimeter, alleviating that concern. I also noticed that during ESS stops the meter and the dash voltage reading were falling at about the same rate with that 150mV offset. That surprised me somewhat, having read a great many forum posts on batteries. Hence this thread.

It also occurs to me that there is some risk in this type of experiment. The leads to the multimeter in the cabin are connected directly to the battery positives - there are no fuses in the current path. If one of the banana plugs were to get pulled from the multimeter and contact the metal surfaces inside the truck...

Yes, I’ve always been under the impression that #1 is incorrect. That would effectively defeat the purpose of the system.

 

[Mr._Bill]

The intent of the Aux Battery is to protect the computers from low voltage situations that would lead to reboots. It would make sense that the battery separation only occurs when these situations are most likely, and that is when the starter is activated. Keeping the batteries paralleled until the end of the ESS event, when the engine restarts, would prevent the rapid drain of the Aux Battery and explains why a larger capacity was not used.

 

[ShadowsPapa]

it really didn't matter in the first test where I had the Fluke connected - N1 or across the crank battery.
I later used two meters (sorry, forgot to take pictures other than mental) and it was the same.
The voltage across the aux battery and the main battery followed each other.
I don't see how that's possible if they are disconnected while the engine is off for the ESS stop - it would take a load absolutely perfectly balanced.
Naw, no way, they can't predict if the HVAC is on low or high, the lights are on or off, and so on.

 

[jebiruph]

Here's a post from the owner of Genesis Offroad where he confirms that the system separates the batteries during an ESS stop and if it detects that the batteries are not separated for 6 consecutive events, an error is assumed and ESS is disabled.

https://www.jlwranglerforums.com/fo...e-limit-anyone-with-issues.45582/post-1007151

" The ESS system, like a lot of other systems in the new JL, does some diagnostics in the background. When you stop at a red light, the ESS system looks for a voltage difference between the 2 batteries to make sure the dual battery control relay has separated the batteries. With our system, we eliminate the small aux battery and replace it with a second full sized battery. The positive wire from the small battery comes up top and gets connected to the cranking battery. That means the ESS system will no longer see a voltage difference, so it will think the dual battery control relay is stuck in the closed position, and will then log an entry into the OBDII system. After the 6th stop/start cycle, it will display a message on the ESS screen on the dash saying Service Stop/Start System, Stop/Start Disabled, and the engine will not turn off at the next stop. This counter is reset when you manually cycle the ignition. "

 

[ShadowsPapa]

Here's a post from the owner of Genesis Offroad where he confirms that the system separates the batteries during an ESS stop and if it detects that the batteries are not separated for 6 consecutive events, an error is assumed and ESS is disabled.

https://www.jlwranglerforums.com/fo...e-limit-anyone-with-issues.45582/post-1007151

" The ESS system, like a lot of other systems in the new JL, does some diagnostics in the background. When you stop at a red light, the ESS system looks for a voltage difference between the 2 batteries to make sure the dual battery control relay has separated the batteries. With our system, we eliminate the small aux battery and replace it with a second full sized battery. The positive wire from the small battery comes up top and gets connected to the cranking battery. That means the ESS system will no longer see a voltage difference, so it will think the dual battery control relay is stuck in the closed position, and will then log an entry into the OBDII system. After the 6th stop/start cycle, it will display a message on the ESS screen on the dash saying Service Stop/Start System, Stop/Start Disabled, and the engine will not turn off at the next stop. This counter is reset when you manually cycle the ignition. "

The same thing can be accomplished by leaving them connected and disconnecting them at the time of the ESS restart, like the FCA documents state, including all IBS and ESS troubleshooting docs and the TSM itself.
They may be assuming it is open the entire time, when it could be closed and open only during the startup itself. That's when the documents state it's checked.

It wouldn't be the first time a 3rd party vendor was incorrect about something.

If it's connected during the stop, like my voltage tests have shown, and disconnected at the moment of the restart, it can do that voltage test right then and there, and come to the same conclusion.
Sorry, I don't take their document as conclusive since it can still be tested at the moment of the start cycle when FCA says the PCR opens.

Otherwise, someone has to show me how both batteries drop by the same amount of voltage over the time/duration of an ESS stop lasting a minute or more - if they are indeed separated.
I find no other explanation, other than what FCA says.

I'm going with the FCA documents, which lay out in every case, it's closed except at the onset of a startup.

Genesis' explanation works perfect if the PCR is closed during the stop and opens only during restart. It would still detect the aux voltage fine.

The battery voltages follow each other almost perfectly - no way if they are apart with systems running for over a minute. Also no way the aux battery can handle the entire drain by itself during a long ESS stop.
I've checked the voltages of both batteries at the same time during a stop, they follow each other almost perfectly. only being connected can explain that.

 

[ShadowsPapa]

@jebiruph Thank you for the response. @ShadowsPapa more or less said what I was going to, perhaps more. Let me just ask this: Do you know whether the PCR remains open for the duration of an ESS stop?

Taking a step back: It is widely claimed on the JL and JT forums that for the duration of an ESS stop,

1. The PCR remains open.
2. The AUX battery powers the vehicle.
3. The main battery is largely unloaded.

At this point I am confident that 2 and 3 are false. Of course if 1 is false then 2 and 3 are also. I think that is likely.

I only started looking at this when my JT wouldn't charge the battery when driven immediately after a moderate discharge. It didn't just fail to charge, it steadfastly refused to charge, holding 12.8V even while engine braking downhill where it usually pulls it up over 14V. When I got home and plugged in a charger, it took 3Ah charge in about 10 minutes - which the vehicle could have easily done on the drive and for some reason chose not to.

Inspired by @ShadowsPapa, I connected a DMM to the main battery terminals and drove it around. I was concerned that it might actually be discharging when the dash showed 12.8V since it usually reads over 12.80V on the terminals 24 hours after a charge. I found the dash was reading about 150mV lower than the multimeter, alleviating that concern. I also noticed that during ESS stops the meter and the dash voltage reading were falling at about the same rate with that 150mV offset. That surprised me somewhat, having read a great many forum posts on batteries. Hence this thread.

It also occurs to me that there is some risk in this type of experiment. The leads to the multimeter in the cabin are connected directly to the battery positives - there are no fuses in the current path. If one of the banana plugs were to get pulled from the multimeter and contact the metal surfaces inside the truck...

Here's more - every single document I find says they are connected except during a cranking event -

This document, like all of the other documents, states they are always connected, except during initial starter engagement. It takes only a small fraction of a second to get the information it needs.

 

[Flanders]

@jebiruph cites Shane Smith, owner of Genesis Offroad. I have no idea what the whole disabling ESS after 6 stops has to do with anything. Nobody is claiming that the batteries are never isolated, just that they aren't isolated for very long. The statements I find relevant are these:

With the stock 'dual batteries', when you turn the engine on, it cranks from both the large battery and the small battery together.

This is what I observed. The service manual says the batteries should be isolated during inital starter inrush but the scope trace above shows they aren't. Or weren't in that one cold start.

When you stop at a red light and the engine stops, the batteries are separated from each other, and the small battery supplies power to the vehicle (lights, radio, fans, etc).

This is the question in the subject line. I consider it doubtful, for several reasons discussed above. The fact that a relatively small load pulls the small battery below 12V in seconds is IMO enough to settle it in the negative.

When you lift your foot from the brake and the engine restarts, it cranks from the large battery, then the batteries are reconnected to recharge the small one.

I hope it is true. If the whole point of the AUX battery is to protect the PCM from low voltage during cranking, and it's not doing so on cold start (as Mr Smith claims and I confirmed), that only leaves ESS restarts for the AUX to serve any purpose whatsoever.

The service manual states the batteries should be isolated for the first 20-40 milliseconds of cranking and that you'd need a scope to check whether this actually works. I suppose the next step is to drive about triggering ESS stops with oscilloscope probes attached under the hood and the leads fed through the window.

 

[ShadowsPapa]

@jebiruph cites Shane Smith, owner of Genesis Offroad. I have no idea what the whole disabling ESS after 6 stops has to do with anything. Nobody is claiming that the batteries are never isolated, just that they aren't isolated for very long. The statements I find relevant are these:



This is what I observed. The service manual says the batteries should be isolated during inital starter inrush but the scope trace above shows they aren't. Or weren't in that one cold start.



This is the question in the subject line. I consider it doubtful, for several reasons discussed above. The fact that a relatively small load pulls the small battery below 12V in seconds is IMO enough to settle it in the negative.



I hope it is true. If the whole point of the AUX battery is to protect the PCM from low voltage during cranking, and it's not doing so on cold start (as Mr Smith claims and I confirmed), that only leaves ESS restarts for the AUX to serve any purpose whatsoever.

The service manual states the batteries should be isolated for the first 20-40 milliseconds of cranking and that you'd need a scope to check whether this actually works. I suppose the next step is to drive about triggering ESS stops with oscilloscope probes attached under the hood and the leads fed through the window.

I made a nice set of leads using silicone wires - VERY flexible, don't get stiff in the cold, and I ran them between the right cowl and fender area and into the cabin from there.

In my voltage checks:
I clipped to the stud at the top of the IBS because that's what really matters for powering the systems - and to the positive clamp where there's a bit of a strap sticking up to clamp onto.
For the aux battery, I went directly to N1 and to the negative lead coming from the aux battery at the top of the IBS.

I also ran tests using the cluster voltage reading, readings from the 12v outlet using an adapter I made that could connect to a volt meter, etc.
I was trying to find any connection area that would show voltage differences when stopped.
No matter how I connected things, the voltages always matched +/- a tenth of a volt or less. (drop in wiring, differences in volt meters can account for tenths or hundredths of a volt)
My readings indicate that during an ESS stop - things are connected.

I would love to see anyone try to explain why the MAIN/crank battery voltage drops in almost lockstep with the aux battery during an ESS stop, especially when that stop lasts for a minute or more. How can they drop in almost exactly the same amounts over that long a time, unless they are still connected together.

Still waiting to see someone explain how aux battery voltage and main battery voltage drop almost exactly together during a whole ESS stop.
I can only see one explanation - for that 30 seconds to OVER one minute, the batteries are still connected.

Here's another take - if they were disconnected, and the aux battery alone was handling the HVAC fan, lighting, and everything else going on, the aux battery voltage could easily drop a full volt below the main battery. Once reconnected, there'd be a pretty good jolt as unequal voltage batteries were suddenly connected.

It seems to check the delta.

I've found other information showing exactly how low the aux battery is allowed to go before ESS is disabled, and/or a code is set and so on.

 

[Flanders]

I made a nice set of leads using silicone wires - VERY flexible, don't get stiff in the cold, and I ran them between the right cowl and fender area and into the cabin from there.

In my voltage checks:
I clipped to the stud at the top of the IBS because that's what really matters for powering the systems - and to the positive clamp where there's a bit of a strap sticking up to clamp onto.
For the aux battery, I went directly to N1 and to the negative lead coming from the aux battery at the top of the IBS.

For the voltmeter, I used a pair of 2m silicone test leads with 4mm banana plugs on both ends. These are 2.5mm2, a little over 13AWG, and 2 meters is (just) long enough to reach from the HCFA to the passenger seat. I have a bunch of different crocodile clips and grabbers that take a 4mm banana plug. The best ones have screws so that the banana plug can't be pulled out. I clamped on the N1 and N2 studs, not the ideal contact, but it shouldn't matter as long as the clips aren't moving around. The input impedance of the DMM is 10MOhms.

With the scope probes I was able to grab the contacts under the N1 and N2 studs, with a good ground connection to the exposed steel HVAC clamp bolted to the cylinder head near the PDC.

Now I really want to know whether the PCR opens during starter inrush after an ESS stop as the TSM says. The AUX battery is simply pointless if it doesn't. I don't have BNC probes with long enough leads to get into the cab and I'm still evaluating the options.

 

[ShadowsPapa]

For the voltmeter, I used a pair of 2m silicone test leads with 4mm banana plugs on both ends. These are 2.5mm2, a little over 13AWG, and 2 meters is (just) long enough to reach from the HCFA to the passenger seat. I have a bunch of different crocodile clips and grabbers that take a 4mm banana plug. The best ones have screws so that the banana plug can't be pulled out. I clamped on the N1 and N2 studs, not the ideal contact, but it shouldn't matter as long as the clips aren't moving around. The input impedance of the DMM is 10MOhms.

With the scope probes I was able to grab the contacts under the N1 and N2 studs, with a good ground connection to the exposed steel HVAC clamp bolted to the cylinder head near the PDC.

Now I really want to know whether the PCR opens during starter inrush after an ESS stop as the TSM says. The AUX battery is simply pointless if it doesn't. I don't have BNC probes with long enough leads to get into the cab and I'm still evaluating the options.

LOL - i bet we both have a drawer full of all sorts of leads for VOMs, scopes and so on, as well as an assortment of all types of clips. I did make my leads so that if something "comes apart", there's no open banana to hit a ground. My Fluke leads are sort of protected anywhere where they plug into the meter itself. It's an antique by today's standards - dates back probably 20 years, but still a great tool.

Not only does the TSM as you quoted state how things are supposed to work, every document I've found as far as training, troubleshooting and so on, state the exact same thing. The snippets I posted come from at least 3 different documents - 2 of them FCA/STAR publications and I sort of wonder if one I have isn't a section from the service manual - can't recall where I got it...........but it's official, where-ever it came from.
So there's the "TSM", and the 3 docs I have, 2 of them FCA/STAR documents, all saying the same thing. So - that means 4 things from FCA are wrong if they don't operate that way. Hard to believe................ they are the ones that have to diagnose and troubleshoot this stuff, and cover it under warranty.

You might like this bit -

This tells me that they are also connected during the stop - think about it a bit -

If the batteries are disconnected for the full duration of an ESS stop, one battery will have a huge drop compared to the other, the delta will always be high or out of range. I need to find the delta figure again...............
If they remain connected and are only disconnected for a check of the difference or delta, that's going to give a more true picture of the aux battery health.
The system compares what the IBS has for the main battery to what it reads from the aux battery on that quick disconnect. Too much difference, the aux battery has a problem, ESS is disabled.

 

[emiddio]

see this thread - https://www.jeepgladiatorforum.com/forum/threads/ess-dual-battery-system-operation.44028/;

The way I understand it is - when things working correctly - at all times when not in an ESS Stop event - the 2 batteries are connected together in parallel;

During the ESS Stop event - they are separated - the Aux battery powers the vehicle electronics, the main battery is not being used until the Start happens;

That way the Start cannot affect the vehicle electronics;

After start then they are in parallel again;

 

[Terminus33]

I thought I read somewhere on this forum in the past that during a crank that auxiliary battery is the one running the starter and the main battery continues to power the rest of the truck and not the other way around.

Or my brain is acting up again.

 

[ShadowsPapa]

see this thread - https://www.jeepgladiatorforum.com/forum/threads/ess-dual-battery-system-operation.44028/;

The way I understand it is - when things working correctly - at all times when not in an ESS Stop event - the 2 batteries are connected together in parallel;

During the ESS Stop event - they are separated - the Aux battery powers the vehicle electronics, the main battery is not being used until the Start happens;

That way the Start cannot affect the vehicle electronics;

After start then they are in parallel again;

You are missing two elephants in the room:
If they are truly isolated during the entire ESS stop, why does the main battery drop almost exactly the same as the aux battery
and
Look again at the technical service documents, training documents and the service manual.

It still isolates things during the crank, just not the entire time.

 

[sharpsicle]

The goal of the dual battery system isn’t to isolate which battery powers which components, the goal is to maintain a constant voltage during starting events. I don’t see how separating it prior to a start event would help achieve that goal.

People see the term “auxiliary battery” and tend to infer the wrong things frequently. It’s not a separate power source for specific circuits, it acts like more of a bridge over the starter draw during restarts.

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