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12 volt accessories?

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There are a number of tesla patents w.r.t ESS balancing. One of them describes how the car is constantly monitoring the battery balance.
Do you have a patent number? I tried going to pat2pdf.org the other day and the site was down :frown:

Not exactly. Each brick has it's own voltage. 69 cell make a brick. You cannot measure the voltage of an indivdual cell.
Thanks for clarifying the term. I knew about the 11 sheets (9 series within each) but had lost the 'brick' definition in my notes. So, I guess that means there are 11 sheets and 99 bricks in the ESS, with exactly 9 bricks per sheet.

The only way to measure the voltage of an individual cell would be to have an electronic switch that could disconnect the parallel brick to isolate one or more cells, but I recall seeing that those connections are all soldered permanently. So, of course you're right that individual cell voltages cannot be determined.

That said, within a brick there will be passive balancing. A voltage is applied during a charge, but each cell reacts slightly differently such that when charging stops the voltage of each cell can be slightly different. As soon as the external voltage is removed, current will flow between the 69 cells in a brick until they all settle to the same voltage. I suppose some of this will occur during charging, too, so I'm not sure how much passive settling remains to be done after charging is complete, but there is surely some non-zero amount of hysteresis and the hysteresis will not be identical for every cell in the brick. But whatever degree exists, it's probably more pronounced with a range charge than a standard one.

The vehicle logs record the Average brick voltage, the min voltage, and the brick number of the min voltage. AFAIK, they don't record the max.
Thanks for bringing this up. It is, of course, undocumented, but some folks have been referring to those as max and min rather than average and min. There is, supposedly, a pair of brick numbers, which implies that it is actually max and min, since there cannot be an average brick number. If this reverse-engineering is correct, then the brick number is a byte, not a full word, and the upper byte represents the brick number for the max. I have not graphed the brick numbers to confirm whether this interpretation makes any sense with the data I have.

None of the above is intended to imply that Tesla Motors are not balancing between bricks and/or sheets, I'm merely pointing out that some settling occurs passively within a brick.

EDIT: I seem to have gotten my wires crossed between two separate threads. This one is more about whether Tesla Motors ever pulled power from an individual sheet for 12 V purposes, and another thread has been discussing balancing and settling in terms of final ideal range after a charge has completed. My point here is merely that they could make it work if they wanted to, and the story I heard was that they tried it at first and then decided to take a different approach - if only we had a Service Manual with a high-level wiring diagram!
 
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Do you have a patent number?
Doh. TEG beat me to it... :) But when all others fail United States Patent and Trademark Office While you are there, take a read on some of the other Tesla Motors patents.

...The only way to measure the voltage of an individual cell would be to have an electronic switch that could disconnect the parallel brick to isolate one or more cells, but I recall seeing that those connections are all soldered permanently.
Spot welded, I believe. Read the patents.

That said, within a brick there will be passive balancing. A voltage is applied during a charge, but each cell reacts slightly differently such that when charging stops the voltage of each cell can be slightly different. As soon as the external voltage is removed, current will flow between the 69 cells in a brick until they all settle to the same voltage.
Yes. But the balancing that is measured and managed is the balance between the 99 bricks. It is not possible to read the indvidual cells in a brick. Acording to the patents, a cell can be removed if it shorts.

Thanks for bringing this up. It is, of course, undocumented, but some folks have been referring to those as max and min rather than average and min. There is, supposedly, a pair of brick numbers, which implies that it is actually max and min, since there cannot be an average brick number.
It depends on the record. For brick temp there is a min, max, and average. so there are a pair of bricks for that. For voltages, it is min and avg. For Ahr capacity its minBrick and average. I believe the code I sent you documents the brick numbers correctly. I believe my code is correct. The data in the log correlates well with CAN bus data I collected at the same time. But if you have a specific record element that you're not sure about, let me know and I can confirm the data.

My point here is merely that they could make it[pulling the 12V off of only one or two sheets] work if they wanted to, and the story I heard was that they tried it at first and then decided to take a different approach
I think you need to recheck your source, you might be confusing it with another battery tradoff. Pulling extra current out of only one (or two) sheets (or bricks ), of the traction battery, to run other loads (e.g head lights) is simply not done on an EV. It's a well known bad idea. The Tesla guys are smarter than that. Checkout the EV JB built while at stanford.
http://www.jstraubel.com/944EV/EVproject.htm JB, CTO and one of the founders of Tesla Motors, handled 12V loads correctly in his EV.
 
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I think you need to recheck your source, you might be confusing it with another battery tradoff. Pulling extra current out of only one (or two) sheets (or bricks ), of the traction battery, to run other loads (e.g head lights) is simply not done on an EV. It's a well known bad idea. The Tesla guys are smarter than that.

Yes, BUT.

When my Ranger did the recall fix for the wires leading to the backup battery, he said that the very early ESS units did indeed have a 12V output. It was only intended as an emergency backup to keep the headlights on, etc., in case of an ESS failure, but it still caused problems and was phased out and replaced with the lead-acid backup battery.
 
I too had heard that "12V from a dedicated sheet" rumor long ago.
Maybe they built a prototype pack that way or something.
But, best I can tell they didn't do that in production.
 
Yes, BUT.

When my Ranger did the recall fix for the wires leading to the backup battery, he said that the very early ESS units did indeed have a 12V output. It was only intended as an emergency backup to keep the headlights on, etc., in case of an ESS failure, but it still caused problems and was phased out and replaced with the lead-acid backup battery.
Yes But.

All 12V power does come from the ESS (the lead acid is for failure of the ESS). It just comes from a DC/DC converter that converts 375V to 13.5V & 12.5V. Here's the data sheet I found on line: Martek-Power PS2450. I found it a year+ ago from some partial picture someone posted/gave me/flickered. I could only make out the Martek-Power logo, but it matches the 12.5V and 13.5V supplies used in the roadster and has the same water cooling inlets as the sheets. I got to see a closed up ESS during my HQ tour. You can see that the diagonal slope on the side of the ESS matches the PS2450 and the connection of the cooling tubes too. TEG, got any pics of the ESS cooling tubes? Notice 11 water connections on the bottom and one on the side (for the PS2450).
 
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I too had heard that "12V from a dedicated sheet" rumor long ago.
Maybe they built a prototype pack that way or something.
But, best I can tell they didn't do that in production.

Doh! I open my mouth to find my foot. :smile: It must have been, as Doug said, for emergency use only, not for everyday 12V loads. I.e. Worst case emergency when everything else fails and you don't care about battery balancing.
 
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Here's the data sheet I found on line: Martek-Power PS2450. I found it a year+ ago from some partial picture someone posted/gave me/flickered. I could only make out the Martek-Power logo, but it matches the 12.5V and 13.5V supplies used in the roadster and has the same water cooling inlets as the sheets. I got to see a closed up ESS during my HQ tour. You can see that the diagonal slope on the side of the ESS matches the PS2450 and the connection of the cooling tubes too. TEG, got any pics of the ESS cooling tubes? Notice 11 water connections on the bottom and one on the side (for the PS2450).
Thanks for that data sheet. Very impressive! 120 A on the 13.5 V output, 36.5 A on the 12.5 V, and over 2 kW total, all at 90% efficiency! It looks like the 12.5 V output is very precisely regulated under all supported loads, whereas the 13.5 V output can vary a small amount (probably not a problem for the types of loads connected). I don't think I've seen a power supply with that much capacity, efficiency, and accuracy, but I'm glad to see that it's likely to be the one used in the Roadster.
 
Does anyone has pictures of the DC/DC-Converter? (Btw do I have to look for two different converters? Even in the 2011 version?). Or can somebody tell me where i have to look for it/them?

Thanks, faclristo
 
Hm... Thanks! But no good news for me!

I want to measure the current and voltage at the output of the converter. In addition, I need the battery current and voltage at the input. This is necessary for the performance of the 12V power and the efficiency of the converter.
I have no chance to open the ESS or get the required sizes elsewhere?

Thanks, falcristo
 
Disconnecting the power to measure current and voltage will probably void the warranty, and will most certainly expose you to dangerous voltages that could kill you. I think this qualifies as one of those subjects where: if you have to ask how to do it then you most certainly should not be doing it.
 
Correct! DON'T TRY THIS AT HOME!
I didn't mention that this measurement is in a laboratory and the car doesn't need warranty anymore. It will be save as it can be.
I asked for the exact position of the DC-DC-Converter (in the ESS, right?), couse there is discribed the cooling tubes of the ESS. But the picture above shows the battery-pack with its cooling tubes. I didn't get the difference yet. I am assuming that I must not open the battery to find the DC/DC-Converter, right?
 
Not in the "PEM" (the box above the motor), but rather inside the Battery Pack (sometimes called "The ESS").

http://webarchive.teslamotors.com/display_data/TeslaRoadsterBatterySystem.pdf
Architecturally, the battery pack is comprised of 11 battery modules (otherwise referred to as “Sheets”), a main control and logic PCB (printed circuit board), and a 12V DC-DC power supply.

battery-01.jpg

battery-02.jpg