I attached a Lascar EL-USB-3 Voltage Data Logger to my Sep 2019 TM3. Over a two week period, with average temperatures around 75F, voltage was logged at one minute intervals with the car in regular use. Minimum voltage seen was 12.50 volts, and maximum was 14.50 Volts, though those appear to be transients. Typically the minimum voltage was 12.75V before a 14.40 Volt top up charge cycle was initiated. Most of this time the vehicle was either in use or plugged into a wall charger. If this is truly a deep cycle battery, and I can't imagine that it isn't, these cycles don't appear to be something that places a great deal of stress on the battery, and I would expect to see a minimum of several years life unless the battery was defective or damaged. This based on my experience with battery banks on liveaboard boats.
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Voltage Logger data on TM3 12V battery
- Thread starter electrongeek
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- 12v tm3 battery
RayK
Active Member
Can you provide a zoomed-in view of one (or more) of the 14.4V transients? I'm curious to see if it's an instantaneous switch to the higher charging voltage, or does it ramp smoothly. If you could repeat a couple of these charging cycles at a faster recording interval (like 1 sec) that would be great.
Did the car always live in a happy range (say 40 to 70% SOC)? These batteries should last YEARS, like 200,000+ miles. It’s when you dip below 10% a lot or constantly charge to 100% that you stress it a lot. Extremely fast charging (supercharger) also puts stress on it. The level 2 speeds is completely find day in and day out though.
smatthew
Active Member
Ah, literally the only spot 12V shows up is the post title. I would assume the 12V isn’t that much of a deal, unless it’s stupid hard to replace or something.
smatthew
Active Member
You're right. All those mentions of 12.5Volts 14.5V, 12.75V, 14.4V in the post body couldn't mean anything.
Here's a hint. If your high voltage battery reads 12.5 volts, it's dead jim.
I have no idea if each cell outputs somewhere in that volt range or not.
RayK
Active Member
@electrongeek You may not have to repeat your experiment as I requested. I found a used Omega EL-USB-3 on eBay and it's on the way to my house. I would ask how you connected your logger to the car. Cigarette lighter... errr, sorry - 12V auxiliary power outlet, or directly to the 12V battery.
RayK
Active Member
Each individual 2170 cell of the traction battery pack outputs somewhere around 3.7V (believe the composition is nickel-cobalt-aluminum). I don't know what each battery module outputs but it's probably a couple of orders of magnitude above that.
SageBrush
REJECT Fascism
Nice !
I'm been thinking about my 12v way too much lately so this thread is great.
How long do the charging sessions last ? The timescale of the photo in the OP is too large to eyeball
I'm been thinking about my 12v way too much lately so this thread is great.
How long do the charging sessions last ? The timescale of the photo in the OP is too large to eyeball
SageBrush
REJECT Fascism
Ahh ... so you thought that OP cracked open his pack, stuck his clips on a cell, and drove off into the sunset.
That makes a lot of sense
My logger came with leads ending in alligator clips. I just attached directly to the 12V battery.
Looks like the longest 14 Volt charge session was about 2.5 hours. Here is a zoomed view of part of the previous graph.
RayK
Active Member
SageBrush
REJECT Fascism
Thanks. Can you guesstimate average charging Amps ? I think that the OEM 12v is ~ 40Ah capacity but I don't have a chart handy to translate voltages into SoCs
... On second thought, I should just look up that chart since my interest is in estimating charging overhead
No way I can see to estimate charging amps. There is a rule of thumb to stop an absorption charge on lead-acid batteries when the charging current (at 14.4 V here ) drops to 3% of the amp-hour capacity of the battery, but no idea how Tesla handles all this.
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