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How Is 12 Volt Battery Charged


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Could someone explain how the 12 volt Battery is charged in the RX 450 h?

Is it being charged all the time the car is moving? Or does it only get charged while the high voltage Battery is being charged?

I've read there are three electric motors -- two that drive the front and rear wheels and the third that starts the engine and acts as a 'generator'. But I'm not clear whether the generator is continuously charging the 12 v Battery.

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The petrol engine according to the diagram for a 2011 model has a conventional alternator fitted so it would appear the auxillary Battery is charged by this when the petrol engine kicks in. This system would probably explain why if you sit in the car without the engine running listening to your stereo for an hour or so the Battery flattens just like a conventional car.

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the aux Battery should be charged anytime the vehicle is in 'Ready' state. The inverter is providing a 12v feed from the HV batteries.

There is no conventional starter, alternator or engine powered PS or AC on a hybrid engined vehicle. The aux drive belt is completely eliminated.

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Thanks for your reply Colin. Glad to hear there's no alternator or fanbelt to bother about.

Do you know what the 12v Battery discharge rate is on the 2013 RX 450h when it's double locked? I think I read somewhere that the current is 177 milliamps. If that's so then the 50 Amp hour Battery will discharge in about 12 days if the car is left, which matches the account in one of the posts I have read. I am surprised Lexus isn't more upfront about this in the manual.

One of the posts reports a flat 12 v Battery after parking and running the stereo for 90 minutes. That I find surprising also. Is that what you would expect?

I am delighted with my car. I've had it just over a month and its a worthy successor to my GS300. I keep an eye on the 12v Battery voltage and so far it's been in the range 12.6 -12.8 volts. V. satis.

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the aux battery should be charged anytime the vehicle is in 'Ready' state. The inverter is providing a 12v feed from the HV batteries.

There is no conventional starter, alternator or engine powered PS or AC on a hybrid engined vehicle. The aux drive belt is completely eliminated.

How are the HV batteries charged? there must be some kind of charging device driven by the petrol engine.

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the aux battery should be charged anytime the vehicle is in 'Ready' state. The inverter is providing a 12v feed from the HV batteries.

There is no conventional starter, alternator or engine powered PS or AC on a hybrid engined vehicle. The aux drive belt is completely eliminated.

How are the HV batteries charged? there must be some kind of charging device driven by the petrol engine.

the hybrid Battery is charged by the petrol engine, via the generator motor, or regeneration from braking via the electric motors.

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Do you know what the 12v battery discharge rate is on the 2013 RX 450h when it's double locked? I think I read somewhere that the current is 177 milliamps. If that's so then the 50 Amp hour battery will discharge in about 12 days if the car is left, which matches the account in one of the posts I have read. I am surprised Lexus isn't more upfront about this in the manual.

Toyota's standard recommendation is anything over 50mA is potentially a problem. I've not seen anything specific to hybrid models to indication it should be more and I've also read about Prius owners who have measured < 25mA so I feel 177mA is just not correct.

I believe the owners manual gives recommendations to disconnect the Battery if leaving the vehicle for 30 days so they must feel in ideal conditions it should last that long otherwise they would recommend a shorter time. If a Battery did only last 12 days by design then many would be swapped out under warranty because too many people would end up deep-cycling their Battery when going on holidays and destroying them.

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Thank you once again Colin for the information and the perspectives. I guess the unfortunate experiences I've read about are exceptions rather than the rule.

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