A DIY 12 volt battery monitor - Page 2 - 2017+ Chrysler Pacifica Minivan Forums
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post #11 of 33 (permalink) Old 05-07-2019, 08:22 PM Thread Starter
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@m0ebius604 Here is a chart that shows what happens when you turn off the van and don't plug it in right away. At 13:45 I turned on the van just long enough to move it from outside the garage to inside. It had been parked outside because we were fixing a broken garage door spring. At 14:00 I set out on a brief expedition, parked for 5 or 10 minutes, then drove home. At 14:33 I was back in the garage again. You can see a short discharge spike at that time because the automatic headlights come on as I enter the garage and stay on for a minute or so after I shut the van down. The van doesn't go completely idle until 15:10, 37 minutes later. For the last five minutes before going idle there is a brief flurry of activity that pushes the discharge current from around 1.0 amps to 1.2 amps. I'm not really sure what that might be.
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post #12 of 33 (permalink) Old 05-07-2019, 08:28 PM Thread Starter
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If I could make a suggestion; With the single calibration data point I would say your calibrated for the 6.5amp range as tested .. but still unknown for fine current measurement. Its best to confirm high, medium and lowest values to consider the tool accurate for the range of use if you want to draw conclusions from your data and should definitely be done for a home built tool. Much like I require calibrating my DVOM yearly for work. It still reads numbers, likely accurately enough for “checks” but isn't considered appropriate for diagnosis.

The calibration might not be linear.
I did also check it with a load of around 1 amp and that was OK. I'll try it with a resistor that produces a load of 20 or 30 milliamps and see if it can get that right.
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post #13 of 33 (permalink) Old 05-07-2019, 10:32 PM
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Great work @ AZBean!

Have you considered adding a CAN module to read data from the sensor? @m0ebius604 posted a link to the datasheet some time ago.

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post #14 of 33 (permalink) Old 05-07-2019, 10:59 PM Thread Starter
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Great work @ AZBean!

Have you considered adding a CAN module to read data from the sensor? @m0ebius604 posted a link to the datasheet some time ago.
Thank you. No I didn't consider trying to read the CAN bus. I don't know much about it. Can there be two masters on the same bus? In any case I really didn't want to open myself up to warranty denial claims because I modified the wiring.

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post #15 of 33 (permalink) Old 05-07-2019, 11:44 PM
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I also don't know much about CAN. I guess the data is there and can be passively read by inserting thin wires into the back of the sensor connector. They can be removed in seconds without a trace.
I recently bought some load resistors and better quality test leads. Was planning to measure the shunt, but I fractured my wrists and can hardly type in the cast, let alone work with my hands.

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post #16 of 33 (permalink) Old 05-08-2019, 08:39 AM
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I also don't know much about CAN. I guess the data is there and can be passively read by inserting thin wires into the back of the sensor connector. They can be removed in seconds without a trace.
I recently bought some load resistors and better quality test leads. Was planning to measure the shunt, but I fractured my wrists and can hardly type in the cast, let alone work with my hands.
" I fractured my wrists and can hardly type in the cast,...",
Sorry to hear about your medical problem. Does this have anything to do with your avatar?
Don't want to derail this great thread. I am very thankful for the members that are invetigating the electrical systems/problems of the Pacificas.

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post #17 of 33 (permalink) Old 05-08-2019, 04:45 PM Thread Starter
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@m0ebius604 , I did check the low current accuracy of the battery monitor this morning by connecting a 620 ohm resistor between the jump start posts under the hood. Using a multimeter I found this resistor was drawing 21 milliamps. I then compared the uploaded data on my computer before and after attaching the resistor. Sure enough it did detect a difference. Before adding the resistor the average idle current over a fifteen minute period was 22.5 ma. After attaching the resistor it was 37.5 ma. Bear in mind that there is a quantizing effect in these readings that results in an uncertainty of plus or minus 8 ma. This is because the shunt resistance is so low and the chip I am using reads the shunt voltage in increments of 2.5 microvolts. To get any better accuracy I would have to add my own shunt to the battery with a higher resistance, perhaps 1.5 milliohms instead of 0.15 milliohms. Anyway I am pretty confident that the idle current of my Pacifica is somewhere between 14 ma and 30 ma. I suppose I could attach my multimeter in series with the battery but that would risk blowing the fuse in the multimeter if the car should suddenly wake up and decide to draw current in the amps range instead of milliamps.
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File Type: jpg Idle with resistor.JPG (97.2 KB, 6 views)
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post #18 of 33 (permalink) Old 05-08-2019, 09:23 PM
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" I fractured my wrists and can hardly type in the cast,...",
Sorry to hear about your medical problem. Does this have anything to do with your avatar?
Don't want to derail this great thread. I am very thankful for the members that are invetigating the electrical systems/problems of the Pacificas.
Funny, almost everyone asks that! I have an electric scooter, similar to the rental ones available in many cities. Was riding it slowly with my son, and the tiny front wheel couldn't make it over a large pothole. Fell on my hands...
I've been careful and lucky riding the bike so far. Well, mostly lucky.
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post #19 of 33 (permalink) Old 05-08-2019, 10:23 PM
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@m0ebius604 , I did check the low current accuracy of the battery monitor this morning by connecting a 620 ohm resistor between the jump start posts under the hood. Using a multimeter I found this resistor was drawing 21 milliamps. I then compared the uploaded data on my computer before and after attaching the resistor. Sure enough it did detect a difference. Before adding the resistor the average idle current over a fifteen minute period was 22.5 ma. After attaching the resistor it was 37.5 ma. Bear in mind that there is a quantizing effect in these readings that results in an uncertainty of plus or minus 8 ma. This is because the shunt resistance is so low and the chip I am using reads the shunt voltage in increments of 2.5 microvolts. To get any better accuracy I would have to add my own shunt to the battery with a higher resistance, perhaps 1.5 milliohms instead of 0.15 milliohms. Anyway I am pretty confident that the idle current of my Pacifica is somewhere between 14 ma and 30 ma. I suppose I could attach my multimeter in series with the battery but that would risk blowing the fuse in the multimeter if the car should suddenly wake up and decide to draw current in the amps range instead of milliamps.
Thank you for your trouble! This accuracy is totally fine.

Great job!

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post #20 of 33 (permalink) Old 05-08-2019, 10:34 PM Thread Starter
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I also don't know much about CAN. I guess the data is there and can be passively read by inserting thin wires into the back of the sensor connector. They can be removed in seconds without a trace.
I recently bought some load resistors and better quality test leads. Was planning to measure the shunt, but I fractured my wrists and can hardly type in the cast, let alone work with my hands.
I did a little research on what the IBS might be transmitting. I came to the conclusion that it is probably using the LIN bus protocol instead of the CAN bus because it is slower, cheaper and more suited to this particular function. In any case I could only find one sensor that had any public documentation on the data it sends: https://www.vishay.com/docs/21037/wb...0a00010001.pdf. It transmits voltage, current and temperature. This one is more complicated and contains a microprocessor which needs to be programmed and the data transmitted will vary depending on the software that is loaded: https://www.nxp.com/docs/en/data-sheet/MM9Z1_638D1.pdf. In any case none of them physically look like the PacHy's sensor and for that matter, LIN bus or CAN bus, nothing could be read unless the car is powered on, whereas my gadget can collect data while the car is off.

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