E Golf and a LeadAcid
Discussion
The industry is very much geared up to having all the electrics running on 12v at the moment. That might change in the future once ICE is no more(!), but not for the foreseeable I think. Simply no good reason not to stick with a 12v supply for all the bits common to your ICE products. They could have put in a 12v regulator running off the HV I suppose, in some ways a bit odd that they didn’t considering there must be a battery charger running off the HV.
It's built on the same line as a regular Golf so it's not like they have to put a special one in for it. All the stuff they share with regular Golfs that runs on 12v gets powered by that battery - central locking, alarm, lights, etc. Then just have a small converter off the charging circuit to keep the 12v battery topped up.
Also means that when the car is "off" the big battery can be totally switched off / isolated for safety - the 12v can do the job of switching it back on when you turn the key (or press the button if keyless).
Also means that when the car is "off" the big battery can be totally switched off / isolated for safety - the 12v can do the job of switching it back on when you turn the key (or press the button if keyless).
The Hyundai Ioniq EV has the 12v battery as a partition of the main battery pack https://blog.caranddriver.com/how-the-hyundai-ioni...
The simple answer is because, at the moment, it's cheaper to fit a big, high capacity (power and energy) lead acid Low voltage battery, than it is to fit a Step down DC/DC converter from the HV battery that is suitably sized to deal with the peak LV loads.
Because of the low voltage (12v nominal) even relatively low power consumers draw a lot of current, and current costs money for a DC/DC (because it must be sized to transfer that current). So take a heated rear window, although 'only' 500 watts (around 2/3 of a horsepower) that needs a massive 42 amps! And today, no one is risking using the HV supply for items that can conceivably be touched or damaged (crash damage or wear and tear) so heated seats, head lights, fans, etc all those things still run of the LV system and will for a while yet.
A big LV battery acts as a load leveller, meaning the DC/DC just has to supply the average load as a worst case.
Because of the low voltage (12v nominal) even relatively low power consumers draw a lot of current, and current costs money for a DC/DC (because it must be sized to transfer that current). So take a heated rear window, although 'only' 500 watts (around 2/3 of a horsepower) that needs a massive 42 amps! And today, no one is risking using the HV supply for items that can conceivably be touched or damaged (crash damage or wear and tear) so heated seats, head lights, fans, etc all those things still run of the LV system and will for a while yet.
A big LV battery acts as a load leveller, meaning the DC/DC just has to supply the average load as a worst case.
amstrange1 said:
The legislative requirements for running hazard warning lights and such often provide a boundary condition which dictates the capacity of 12V battery required - or they used to 'til more efficient LED lighting was more prevalent!
Especially in modern cars where switching on the hazards keeps prevent the car from going to sleep, so it sits there with all it's computers running using 10s of amps...... ;-)(my first car, an 1963 series Landrover had such a shonky wiring loom that turning on the hazards mean't you couldn't turn off the engine because somehow the hazard switch was back powering the ignition coil, meaning turning off the key had no effect...... #qualitybritishwiring )
Max_Torque said:
Especially in modern cars where switching on the hazards keeps prevent the car from going to sleep, so it sits there with all it's computers running using 10s of amps...... ;-)
This exact issue was a cause for recall of Toyota Auris some years back if I recall correctly. Funnily enough, Toyota use tiny 12V batteries in their Hybrid cars.Gassing Station | EV and Alternative Fuels | Top of Page | What's New | My Stuff