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Low cost way to monitor your 12V Battery

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So I had this little gadget on my combustion engine vehicle and , well, with all the talk about the 12V battery error message popping up, I thought to revisit this little doo-dad.



20200822_231342.jpg






its this cat:

https://www.amazon.com/gp/product/B07WCW49YM/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1


it's mostly designed for combustion engine vehicles because it shows you cranking amps and things of that nature.

It uses Bluetooth Low Energy so you have to be in about ~30 feet ish to connect to the little guy. it will show you the state of the the battery and when the HV battery charges it, it will show you "charging" and you will see the graph showing you the charging current, it updates as you are connected to it.

Screenshot_20200823-154343_ANCEL Battery Monitor.jpg


things like "cranking test" will not be applicable since there is no starter motor, but maybe, as I think about this, since the HV contactors need voltage from the 12V to close them, maybe this would show up under that option? I will test this if I remember to do so.

anyway, my point to post this was to offer a low cost solution for those to keep track of their 12v charge directly from your phone without having to use tesla fi or those other apps.

there are a few of these on amazon and some may be cheaper. there also may be other alternatives, but i know this works and have had it on model 3 for a few weeks now. I use the ohmmu battery and it works nicely with it.
 
Just don't know why they don't already use a capacitor for a 12V system.

I read somewhere here that the original Roadsters had no 12V battery and ran into all sorts of issues, thus the standalone 12V battery today. And if you're depending on it because you need it (because not having one wasn't good for the Roadster), it can't be a capacitor as it would be no good for long-term storage.
 
I read somewhere here that the original Roadsters had no 12V battery and ran into all sorts of issues, thus the standalone 12V battery today.

A sample set of 1 so take it as so - when I had the 2008 Roadster it had no separate 12v battery and I was happy to have 1 less thing to worry about. At the time, folks were telling me the newer Roadsters had one ( motorcycle sized ) due to DOT regs for emergency flashers being operable even if main propulsion system was offline. I never had issues with the 12v DC-to-DC system
 
A sample set of 1 so take it as so - when I had the 2008 Roadster it had no separate 12v battery and I was happy to have 1 less thing to worry about. At the time, folks were telling me the newer Roadsters had one ( motorcycle sized ) due to DOT regs for emergency flashers being operable even if main propulsion system was offline. I never had issues with the 12v DC-to-DC system
I had a Hyundai Ioniq hybrid that had no 12v battery. Instead it used a section of the High voltage battery to supply the 12v. If that section got depleted there was a button on the dash to push that shunted power from the high voltage battery to start the car then it would recharge that section. I never had any problem with that system. I guess it can be done.
 
I had a Hyundai Ioniq hybrid that had no 12v battery. Instead it used a section of the High voltage battery to supply the 12v. If that section got depleted there was a button on the dash to push that shunted power from the high voltage battery to start the car then it would recharge that section. I never had any problem with that system. I guess it can be done.

Those Hyundais had a separate 12 V li-ion battery, housed inside the HV pack for safety. It was designed to last the life of the car, but could be serviced separate from the rest of the HV pack, just in case.

GSP
 
I have one in one of my ICE cars that is almost identical from Antigravity:

Lead/Acid Battery Tracker – Antigravity Batteries

They have a separate version for lithium 12V batteries.

It is in a car that I don't drive very often. So it is really nice that the phone app monitors the battery via bluetooth just by walking near the car. It gives alerts when the battery voltage drops enough that I should hook the charger up.
 
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So I had this little gadget on my combustion engine vehicle and , well, with all the talk about the 12V battery error message popping up, I thought to revisit this little doo-dad.



View attachment 579857





its this cat:

https://www.amazon.com/gp/product/B07WCW49YM/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1


it's mostly designed for combustion engine vehicles because it shows you cranking amps and things of that nature.

It uses Bluetooth Low Energy so you have to be in about ~30 feet ish to connect to the little guy. it will show you the state of the the battery and when the HV battery charges it, it will show you "charging" and you will see the graph showing you the charging current, it updates as you are connected to it.

View attachment 579854

things like "cranking test" will not be applicable since there is no starter motor, but maybe, as I think about this, since the HV contactors need voltage from the 12V to close them, maybe this would show up under that option? I will test this if I remember to do so.

anyway, my point to post this was to offer a low cost solution for those to keep track of their 12v charge directly from your phone without having to use tesla fi or those other apps.

there are a few of these on amazon and some may be cheaper. there also may be other alternatives, but i know this works and have had it on model 3 for a few weeks now. I use the ohmmu battery and it works nicely with it.

i installed the same unit a few days ago. got consistent 13.40V today, hopefully this unit helps predict battery death.
 
With the socket splitters that show the voltage, what exactly are we looking for to try to determine the health of the battery? I have one and never paid attention to the display until coming across these reports of the 12V battery suddenly failing on people. The reading is around 14.0V first thing in the morning after charging the car. After parking at work all day, it decreases to around 13.0V, decreasing mostly from powering my Blackvue dashcam all day, I assume.
 
I just recently started monitoring the 12V battery voltage with a Raspberry Pi using a custom circuit.

Here's a graph of 24 hours. In the morning, when the car is woken up, you can see the voltage go up to around 14.7V, to recharge the battery from the sleep. Then it drops the voltage down to a "float voltage" of around 13.5V after a few hours when the battery is "recharged" (note: Sentry Mode is on). Once the car sleeps again (note: Sentry Mode is off), the voltage drops down to 13.2V, and slowly decreases due to remaining loads, until the car is woken up again.


Screenshot_20201022-044404.png
 
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you can see over time with these things a charge pattern occurring, and if you see more frequent charging spikes and/or the resting voltage betwixt charges is lower than previous graphs, that could be s sign.

if you see some random 12V errors popup on model 3 screen, that is also a good sign of a near future battery replacement.
 
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I just recently started monitoring the 12V battery voltage with a Raspberry Pi using a custom circuit.
This looks similar to my monitoring. I see charging at ~ 14.5 volts until 13.1 volts and a threshold for recharging at 12.6volts. When the car is at rest and sentry mode is off, the drop from 13.1 to 12.6v takes as little as 12 hours and as much as 18 hours. Since the new nominal capacity of the OEM battery is 33 Ahr (and I figure that ~ 50% of has been used in the drop to 12.6 volts, the juice being used in sleep is on the order of 16 Ahr * 12.8volts over 16 hours, so around 13 watts*.

* presuming like new capacity

<thoughts>
My car is not used enough during Covid to affect much change in vampire loss, but a more normal routine would let the car charge up the 12v during driving instead of at rest. This would be much more efficient because the car is already wide awake while driving so that fixed consumption of ~ 300 watts is already accounted for. I suspect then that what I really need is a 12v that has enough capacity to last from drive to drive. My 2 year old OEM 33 Ahr battery is not enough. I like the idea of a new 45 Ahr PbA replacement when Covid is over.

One thing that bugs me is the slow recharge -- on the order of 3 hours. If that is 10 - 15 Ahr total then the 12v is recharging at 3 - 5 Amps Net. I wonder if that is a hint that my 12v is decrepit, with a lot of current lost as heat. Comments appreciated.
 
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