The other battery

  The lovely big LiPo battery is nothing without all the support electronics around it, and all of those run on the standard 12-volt "auxiliary" system based around a traditional lead-acid car battery.  This is an investigation into the 12V system characteristics in the Kona.
 
12V rail run very high by DC/DC converter It's worth knowing what the DC/DC down-converter for the 12V system produces, and when.  I was surprised to see that it usually runs rather high in the Kona on full power-up, where in the Prius it stays down around 13.8 or 14.  14.7 volts really is too high to hold a lead-acid battery long-term, even an AGM, and it wasn't like it had been dead and needed a high-rate charge or anything.  At random times I saw it dip back down to a more reasonable 13.8, particularly while actually driving, but most of the time it seemed to stay up around 14.5 - 14.7.  I asked a couple of dealer service guys about this; they had no idea if it was normal or not.  I suggested to them that they might eventually see a lot of these cars come back with 12V batteries cooked dry by the low-voltage converter.
On a bit of further study, the circumstances around auxiliary voltage fluctuation get even weirder.  I posted a more complete set of observations in a running thread over at InsideEVs, and still had no solid explanation why the level is all over the place until certain loads are turned on.  The other folks who chimed in earlier seemed to think that 14.7 or higher was okay, so in this case maybe it's not worth worrying about too much.

Three amp draw from 'powered off' electronics I also did some quiescent-current measurements, because questions about that always seem to come up.  A great example is seen in this forum thread, where there seems to be a lot of misunderstanding about the system and the dubious "battery care" feature.  I posted some of my early discoveries into that thread, but here's the more in-depth dump on what I could observe.  To simulate a fully everything-closed condition, I had to click the hood latch closed so I could leave the physical hood open and still have direct access to the battery.

After powering the car down, various systems stay alive to do internal housekeeping and wait for any short-term events.  This draws over 3 amps from the 12V battery for a while, which of course is now no longer being fed by the DC/DC.

In a couple of minutes, that level drops to somewhere between 150 and 300 milliamps, which is still too much for a car just sitting parked.  This is somewhat variable, trending generally downward.  During this time, one can occasionally hear more relays turning off around the car as their related control units finally decide to go to sleep.

After something like *20 minutes*, the current finally dropped to where the clamp-on couldn't accurately measure it anymore.  A quick test with lifting the negative terminal off its post while bypassing the connection with a milliammeter showed the fully quiescent current down to 16 milliamps.  That's acceptable, and a 40 or so amp-hour battery should be able to hold that up just fine for many days -- as long as you do *nothing* with the car.  As soon as anything changes, like clicking the RKE or opening a door, all those standby systems power up again and the whole slow 3-amps-to-trickle dance happens over again.

One thing to note is a distinct possibility that "final" sleep current may occasionally be a bit more in other Konas due to the cellular modem still exchanging data to the BlueLink network.  This may drain a battery faster, as noted later in that same forum thread, from someone who put his own BlueLink setup in a confused state.  In *my* car the possibility for that has been permanently eliminated, by the means described in the "going dark" section.  My reading was also taken without the "battery care" user option being enabled, which supposedly brings on the traction battery and DC/DC automatically once in a while to push a little maintenance charge into the 12V.  But that's more electronics needing to stay working to keep track of the 12V voltage, time, or whatever its criteria are, which may be more of the idle overhead it supposedly works against!  I didn't test this further [yet]; understanding the steady-state characteristics of my rock-bottom quiescent drain gave confidence that I could disable the "care" option and not worry about it too much.


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