MLucas said:
In our case, the 12V battery is recharged when the traction battery is being recharged (pg. 1-17) or from the DC/DC convertor when the 12V is depleted.
Not really - The 12 volt battery never gets 'depleted' because when the car is running, it's not doing anything. From your link:
"The DC/DC converter is used to charge the 12-volt auxiliary battery and power the electrical equipment of the car (radio, wipers, lights...)." Yes, if the auxilliary battery was somehow depleted, the Converter would indeed charge it, but because it (the converter) "power(s) the electrical equipment of the car (radio, wipers, lights..." the 12 volt battery is basically not in use, so it never needs recharging . . . . unless the car sits for a month or so between uses and the radio clock runs it down
When the vehicle is in operation, the DC to DC converter is always running, so the 12 volt battery isn't actually powering anything - When you put a 5 amp load on that 12 volt battery, the DC to DC converter outputs 5 more amps, so the battery never really sees that load . . . . all 12 volt loads are actually running directly off the traction battery via the converter
all of the time, so the 12 volt battery never runs down and there's never any need to 'charge' it. It's only real function is to power everything at startup . . . . without it, you can't start the car, but once it's started, the car would operate just fine if you removed the auxiliary battery. All 12 volt loads actually run directly off the converter all the time . . . . the power comes from the traction pack through the converter, not from the 12 volt battery itself
You are correct that it works very similar to an ICE car with an alternator. Nothing 'runs' off the 12 volt battery there either - When you turn on the headlights and present the battery with a 10 amp load, the voltage regulator outputs 10 extra amps from the alternator toward the battery, so the headlights are really running directly off the alternator, so the battery never runs down. The same thing is happening continuously with an i car - Whatever 12 volt loads you present to the battery, the DC to DC converter outputs that amount of current so that the battery is never allowed run down, much the same as with an ICE car - When you pull into the garage after either a long or short drive with either car, the SOC of the 12 volt battery is the same as it was when you left - Fully charged because you never actually ran anything off the battery in either car during your drive
You're probably too young to remember, but Chrysler introduced the first mass produced car using an alternator in 1960. Prior to that time, cars all had DC generators and they could not output enough current at an idle to run the engine electrical system, much less the lights and accessories, so everytime you came to a stop, the headlights would dim, because they were running off the battery. Chrysler's big advertising blitz included a demonstration where they started the car and then removed the battery and drove it around.
"This was the year of the "alternator test" - when Chrysler introduced the first alternator, it dramatized the event by driving a Fury from Detroit to Chicago, without any battery!" You could not do this in an ordinary car, because the engine would die when the RPM's came down low enough that the DC generator could not keep up . . . . but you could with an alternator because nothing (except the starter motor) actually ran off the battery
We could do the same - Start the car, remove the battery and then drive around using only the DC to DC converter, because our battery is also only needed at startup
Don
