Poundy

No Alternator or Starter Motor

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When we last visited Lexus for a new auxiliary Battery fit, the service tech informed me that the CT200h was neither fitted with an alternator or a starter motor. We were a bit pushed for time so I didn't get him to elaborate on it. I am okay with the way the hybrid Battery system gets it's charge from, but I am wondering if that is the case, where does the Auxiliary Battery gets it's charge from and what starts the petrol motor when required? Still feeling my way around the hybrid lol! so any knowledge on the matter would be appreciated.

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The 12V Battery powers the entry/exit system and also boots up the computers to bring the hybrid system into the READY state. Once READY, the 288V traction Battery provides the power to charge the 12V Battery via a DC/DC inverter/converter.

As you rightly say, there is no alternator because they are belt-driven from the engine and in a hybrid, the petrol engine doesn't run all the time. This is also why the power steering is electric rather than a belt-driven hydraulic steering pump and why the aircon is also electric rather than a belt-driven compressor.

I'm not sure but I think MG1 (Motor Generator No.1) runs the petrol engine up to a certain speed when needed and then the ignition circuits are energised, eliminating the need for a starter motor.

I'm sure you'll find a few videos on YouTube and/or better explanations via Google but I think I'm 'in the ballpark' with those explanations as far as I understand the system.

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Thanks Herbie that's great information, I am a glutton for car Knowledge and will start to research the CT more and try to get a bit more up to speed on it. Perhaps that was why the Lexus tech thought the old Aux Battery still had some useful life in it and I had jumped the gun getting it replaced when it was reading low 12s. It has a very small part to play in the great scheme of things. Still all done now and good for a few more years hopefully.

 

Thanks to you too John I have copied it to my Lexus info folder😊

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14 hours ago, Poundy said:

Perhaps that was why the Lexus tech thought the old Aux Battery still had some useful life in it and I had jumped the gun getting it replaced when it was reading low 12s

Quite possibly. In a standard car the starter motor can draw upwards of 300A to crank the engine but because there's no starter motor in a hybrid, the Battery doesn't have to be so big and beefy. You'll see in the photo below that my RX450h only draws 15.32A from the 12V Battery to get the car into the READY state (and there's a handy reference voltage chart too).

 

clamp.thumb.jpg.369dcc5441f39b7cb0cf36ebc8a89672.jpg

 

bvolts.png.62716b0d260afaac33fd61fc961355e6.png

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It should be noted that although lead acid batteries are not considered fully discharged until the voltage falls to 10.6 volts. They are considered to be deep discharged at the 50% level of around 12 volts "depends on temperature". Going below this level is destructive to the Battery, and the damage is not reversible.

John.

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On ‎1‎/‎12‎/‎2019 at 11:30 AM, Herbie said:

Quite possibly. In a standard car the starter motor can draw upwards of 300A to crank the engine but because there's no starter motor in a hybrid, the Battery doesn't have to be so big and beefy. You'll see in the photo below that my RX450h only draws 15.32A from the 12V Battery to get the car into the READY state (and there's a handy reference voltage chart too).

 

clamp.thumb.jpg.369dcc5441f39b7cb0cf36ebc8a89672.jpg

 

bvolts.png.62716b0d260afaac33fd61fc961355e6.png

So if the 12v Battery is charged off the hybrid I/C is it still subject to the car being run for a specific amount of time to make this happen. Or will it always have power available as long as the hybrid Battery is charged? i.e if the car is stood for a long period and the hybrid Battery has charge could the 12v still go flat.

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8 minutes ago, Poundy said:

So if the 12v Battery is charged off the hybrid I/C is it still subject to the car being run for a specific amount of time to make this happen. Or will it always have power available as long as the hybrid Battery is charged? i.e if the car is stood for a long period and the hybrid Battery has charge could the 12v still go flat.

Vehicle has to be in 'Ready' for it to charge the 12v aux Battery. It will go flat if the vehicle is left for a long period, and that period is typically shorter than for a normal car as that 12v Battery has a smaller capacity. Two to three weeks isn't an issue if the Battery itself is in good condition.

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9 minutes ago, Poundy said:

i.e if the car is stood for a long period and the hybrid Battery has charge could the 12v still go flat.

Yes indeed it can. The traction Battery will only charge the 12V Battery when the car is in the READY state.

The 12V batteries in these cars aren't very big because they don't have to do much. You know how big the RX450h is, but the Battery is only 51Ah, with CCA being about 300A if I remember correctly and, given that they are 'small' and that there is always a drain on them (for the alarm, radio memory etc) then the charge doesn't last long. It's not unusual for a hybrid car to have sat at the airport for about three weeks and need a jump start before it'll move.

That's why I always carry one of these in the boot. They work brilliantly well, hold their charge superbly and, although I've not had to use mine (yet) there are plenty of videos on YouTube showing them in action. They are well worth every penny in peace of mind alone - highly recommended.

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37 minutes ago, Herbie said:

Yes indeed it can. The traction Battery will only charge the 12V Battery when the car is in the READY state.

The 12V batteries in these cars aren't very big because they don't have to do much. You know how big the RX450h is, but the Battery is only 51Ah, with CCA being about 300A if I remember correctly and, given that they are 'small' and that there is always a drain on them (for the alarm, radio memory etc) then the charge doesn't last long. It's not unusual for a hybrid car to have sat at the airport for about three weeks and need a jump start before it'll move.

That's why I always carry one of these in the boot. They work brilliantly well, hold their charge superbly and, although I've not had to use mine (yet) there are plenty of videos on YouTube showing them in action. They are well worth every penny in peace of mind alone - highly recommended.

Thanks Guys,

Herbie I got a Tacklife T8 MAX for xmas, nice bit of kit, lol! it is in the jag so am well prepared, I also have CTek smart charger so I might wire the comfort lead up to make it easier to get to. The car only does 3-4k a year local stuff.

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Something else to consider regarding Battery capacity, and run times.

Generally batteries have a designated capacity given in AH "amp hours", but what is not often understood is that this figure is calculated at a given rate of discharge "most often at a 20 hour rate". This means a 40 AH Battery will have the ability to run a 2 amp load for 20 hours. However this does not mean if you load it at 4 amps it will last for 10 hours or loaded at 10 amps it will last for 4 hours. As in Members Herbie's picture the radio, and display screen runs at over 15 amps.

In fact as the discharge rate rises the apparent Battery capacity falls quite dramatically.

Batteries at 3 years old can easily have lost 50% of there new capacity without showing outward signs of this apart from when electrical accessories are used while standing.

Many batteries on Ebay "if you read the small print" are rated at a discharge rate of only 1 amp. This has the effect of increasing the apparent AH capacity to make the Battery look on paper better than it is.

John

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