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Just wondering how the 12v battery to run the in car systems and lights etc is charged

Is it the same basic principle as an ICE or something else ?
 

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The Chevy Volt has a DC/DC converter which keeps the 12V battery charged from the main battery when the vehicle is switched on.
 

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Just wondering how the 12v battery to run the in car systems and lights etc is charged

Is it the same basic principle as an ICE or something else ?
I have seen some electric cars that did have an alternator installed but, it is much better to use a DC to DC converter. An alternator will load down the drive motor mechanically and reduce the performance of the car. The converter is a better, and more direct way to produce 13.4 volts to charge the 12v accessory battery.
 

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An alternator will load down the drive motor mechanically and reduce the performance of the car.
... Now there's a thought .... if you did tie a 12V DC motor to the traction crank then it could either power the 12V circuit/recharge battery, or it could be driven from the 12V battery under max loads!

This is exactly what these 'mild hybrids' already do, they run a 5kW alternator with a big belt that actually becomes the starter motor for 'soft' dynamic starts from stationary.

But, yes, answer to question at the moment is a DC-DC converter.
 

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... Now there's a thought .... if you did tie a 12V DC motor to the traction crank then it could either power the 12V circuit/recharge battery, or it could be driven from the 12V battery under max loads!

This is exactly what these 'mild hybrids' already do, they run a 5kW alternator with a big belt that actually becomes the starter motor for 'soft' dynamic starts from stationary.

But, yes, answer to question at the moment is a DC-DC converter.
Interesting thought. I was once tempted to replace the AC compressor in my old car with a DC permanent magnet motor to assist the ICE. Now that the car is pure electric, I wonder if there is any advantage to adding a second 12v motor that could assist the primary AC motor or act like an alternator as desired. Now you got me thinking about all the possibilities.
 

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Even the Golf GTE doesn't have an alternator..... It doesn't have a starter motor either!

It uses the EV motor to effectively "jump start" the petrol engine, and then once started, the electric motor is used as a generator to charge the EV battery

As mentioned above, the 12v battery is then charged by a DC-DC converter
 

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Wish they did then the flat 12v issue might not occur so frequently, eh @donald ?

There's already a fan belt in the Leaf but not sure what powers this, and obviously only intended for the cooling system, but where there's a will....
 

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Wish they did then the flat 12v issue might not occur so frequently, eh @donald ?

There's already a fan belt in the Leaf but not sure what powers this, and obviously only intended for the cooling system, but where there's a will....
There are not any belts on a leaf. Not sure what you mean?

There are two fans on the back of the radiator but these are driven by their own motors built into the fan.
 

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There are not any belts on a leaf. Not sure what you mean?

There are two fans on the back of the radiator but these are driven by their own motors built into the fan.
I'm sure I've seen a belt in there as I wondered why it was there. Maybe I dreamt it/going mad.

EDIT: Checked today and can confirm without doubt that I must have imagined it. No belts found.
 

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I'm sure I've seen a belt in there as I wondered why it was there. Maybe I dreamt it/going mad.
Was that after a service?..... Sounds like we might find a Nissan workshop tech with loose trousers?.....
 

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. Now there's a thought .... if you did tie a 12V DC motor to the traction crank then it could either power the 12V circuit/recharge battery, or it could be driven from the 12V battery under max loads!
Realistically, the power available from the 12V battery would hardly be worth the effort. More to the point would be powering down the DC-DC converter when the traction battery is down to its last few % to enable you to squeeze a final extra mile of range.
 

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Realistically, the power available from the 12V battery would hardly be worth the effort. More to the point would be powering down the DC-DC converter when the traction battery is down to its last few % to enable you to squeeze a final extra mile of range.
But it already is used like this in some cars. like I say, using a short burst of 12V traction power is the 'micro-hybrid' principle. Cranking batteries are in the 700A range, so that's around 5kW. An extra 5kW on top of 40kW (say, when you have been up a hill and limiting is kicking in). Might be what you need for an important manoeuvre.
 

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Wish they did then the flat 12v issue might not occur so frequently, eh @donald ?
Donald's busy replying to others, so I'll chip in! ;). I'm not sure exactly what you want them to do to improve the flat 12V issue, maybe it was simply create 12V from the 400V battery using dc-dc down converter; but whatever - I think you pretty much have to have a conventional 12V battery around;
a) you need something to power-up the high-voltage contactor when you switch the car on. For safety reasons the mfrs like to isolate the 400V completely when the car's off - who knows what tecchie might prod a 400V wire under the bonnet by accident, and
b) you need something to power the hazard lights if you get a catastrophic high-voltage breakdown which blows that stuff to bits. Donald can probably think up more things needing 12V, like the computer - but as these should only need 3.3 or 5V, I am a bit mystified why 10V on a failing 12V battery stops the computer working properly in some cars ...
 

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Most auto electronics is designed to work to around 9V or so, less usually, unusual for computers and the like to suffer such problems, I agree. However, it might also be current-based. The Ampera happily draws 250W the moment I plug it in (before it does a timed charge) for a few minutes, so if that is representative of computers on the car, that's a 20A draw. If you have a cold battery in poor condition, your 10V battery will dip to precariously low voltages under that instant 20A load as all the computers try to fire up.

You just don't get this in an ICE. If the battery is that bad, then the engine doesn't start up. That usually gets the user's attention enough to replace it!!

It's not a problem looking for a fix. There are plenty of EVs driving around that have no problem at all with a DC-DC converter and a lead acid battery ... and then there are Nissan Leafs.....
 
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