Agreed. We are talking about battery voltage here, as it relates to the battery open circuit SoC (state of charge).
Typically, yes, but our cars have some subsystems which ONLY work if the battery SoC is above X%.
ISG (Idle Stop and Go) for example, requires a minimum of 78% SoC for it to operate - so a weak or an uncharged battery will cause this system to stop working, with no fault codes. It is merely a condition of operation.
Kia Stinger: Engine Control / Fuel System / ISG (Idle Stop and Go) (Idle Stop & Go) System - (Search for SoC)
Also - several people are hypothesizing that the ECO coast function may require a min SoC in order to function, though finding any documentation supporting this is proving to be difficult.
100% correct, not disconnected via a clutch, but there is reduced voltage output based on driving conditions + battery state of charge.
When the car knows the battery has a high SoC, the AMS alternator management system, can reduce the voltage/load while cruising, and increase the voltage/load while decelerating.
The no-load resting voltage really is "supposed" to be a reliable method to determine SoC.
Based on my cars build date (Feb 2018) - my battery is at least 2141 days or 70 months or 5.9 years old, so my open circuit resting voltage of 12.1v may be correct/expected for its age.
additional data from my 2018 stinger with OEM 90Ah AGM battery
During cranking, at 2°C (36°f), my voltage dips down to 8.2v - still cranks strong
View attachment 83692
Starting an already hot engine with coolant temp at 93°C (199°f), voltage dipped to 9.2v.
View attachment 83693
2018 stinger with OEM 90Ah AGM battery - Car build date was 02/2018
View attachment 83694
That is a lot of great information.
So provided the voltage output of the alternator remains constant at say 14 volts thereabouts, as the battery reaches this voltage the current starts to back off from the alternator. This happens with all batteries and alternators, so when the battery is fully charged all the alternator is supplying is the load and maintaining a trickle into the battery.
There could be an argument to back the voltage off on the alternator once these conditions are met.
Yep. When a battery does a heavy discharge i.e high current drain for short periods, you can take the end voltage much lower per cell. So typically 1.6 volts per cell or even 1.5 volts per cell (9V). That's because the current only comes off the surface of the plates so you have not "discharged" a significant number of amp hours from the cell and, you can put back a 10 second heavy discharge rather quickly with the alternator over say 10 -15 minutes.
So you can do lots of things with a car battery. You can discharge it over say 10 hours with a light load but you have to finish at a higher end voltage to not damage the battery. That's where you extract the most amp hours, or you can discharge the battery with a high current for a short period to a lower end voltage and that doesn't damage the battery like turning a starter motor for example. You get much lower amp hours out of the battery though under those conditions and It could be rated as little as 20 amphours using it like that even though it says 90 ah, 100Ah. That's a nominal rating..
The State of charge needing to be high for stop start makes sense. Pointless to start using a battery to continually start a car during a journey if its charge is already low.
As an electrical guy and spent a lot of time in the battery/charging/UPS/Rectifier industry......I am dead against Stop Start but have it on a new Mazda which has to constantly be turned off at the start of each journey. The Stingers in Australia do not have Stop/Start. Even the latest My23. Mine don't and if they had I wouldn't have bought them.
Consider the failure mechanism for lead acid batteries. Most go though sudden death. What this means is....From Day 1 the positive plate starts corroding. It does this with charge current. Over those 4 or 5 years of life and remembering the lead plates in car batteries are wafer thin. This is to facilitate getting the current off the plates quickly as in feeding hundreds of amps to the starter motor. But they also corrode and after about 5 years one breaks off.
Usually this happens on the last start. So you start the car. A plate then breaks with that high current flowing through its narrowest point, but you drive away because the alternator is now doing the work. Your next start there is either "nothing" or you might have 5 cells left if the sixth is shorted with a broken plate so, a bit over 10 volts. So you have a low cranking voltage.
Now, if this deterioration happens over 5 years of two starts a day on average (a bit more I know)....you start to go to work. You start to come home. Each time the battery recharges, each time the positive plate corrodes a little more.
Now do this 20 times a day in city traffic. Start, recharge, start, recharge, start, recharge, corrode, corrode, corrode, corrode.
I don't want to be in the car in the outside lane of 80kmh with the engine off waiting for a green light and at the last set of lights that plate broke off. My car does not start and I am dead.
I have been in DC power for decades and along with my Electrical engineer colleagues......we have not bought electric cars or solar panels yet and have worked in battery and charging systems, designing, and implementing them for decades. The cost of replacing a Tesla 3 battery is around $17,000. The cost of replacing your solar and battery system is the same again. We will wait and see what happens with batteries with all of these new applications. It's not so much the capital cost. It's the reliability and replacement.
