RX 450H - Jump Starting Another Car

[BlackCat]

Quick question. I thought I had read somewhere - in the Owner's Manual - that you should not use a Hybrid Lexus to jump start another car. I have searched the Manual inside out (and this site) and I cannot find any reference to it. (I wonder was this in the 400h manual?).

Of course the Manual gives instructions on how to use another car to jump-start the 450H.

So does it follow - is it safe to use the Hybrid Lexus to jump start another car that has a discharged Battery???

[olliesgrandad]

I seem to remember the answer is no, but I welcome being corrected on this 

[NemesisUK]

I was also under the impression that one shouldn't use the hybrid to jump start another car.

I thought it was to do with the fact hybrids don't have the traditional alternator charging system of non hybrids and their 12v batteries were not of the same charge capacity as they aren't used to start the engine of a hybrid car as they only power the entry system and start-up computers?

[Herbie]

Never use a hybrid to start another car unless it's another hybrid.

In a normal car the Battery is only used to crank the engine. Once it fires and the alternator is spinning then its the alternator that supplies all the car's electrical demands and if there's enough 'spare' capacity it will also keep the Battery charged.

A starter motor in a conventional car will draw upwards of 300A when cranking the engine, which is why when jump starting a car you always get the engine of the donor car running first before attempting to start the recipient car; firstly to stop the donor Battery from going flat and secondly, if the donor Battery isn't quite up to the job, the recipient car will draw power from the donor alternator, not the Battery.

Hybrids don't have alternators; they charge the 12V Battery from the 288V traction Battery via a DC/DC converter that steps the high voltage down to around 14V. The DC/DC converters cannot supply anywhere near as much current as an alternator and if the recipient car tried to pull such current from it, there would probably be a big bang and all the magic smoke inside the converter that makes it work would escape and it would be a very expensive job to have some more magic smoke installed

[NemesisUK]

Thanks Herbs, I was sort of right then but you explain it perfectly 

[Britprius]

The problem is with the magic smoke it is a dealer only smoke there is no aftermarket equivalent. This makes it extremely expensive. The other item that is likely to expire is the 150 amp fuse built into the Battery terminal. This will blow if subjected to starter motor currents.

John.

[BlackCat]

Many thanks for all the replies, I am certainly glad I asked the question!

I had always thought that this was the case, but could find no written proof. It is surprising that the 450H Owners Manual does not refer to it.

Thanks again.

[PaulK.US]

I had the same question — this is very, very good to know. Read on if you’d like to hear a story why I’m grateful to have read this:

Like many, I’ve helped others jump start their car over the years, and been so grateful for the help myself.  

For that reason I always have a pair of good jumper cables in my car, and since we have 7 cars for the two of us & five kids (youngest in college) I make sure there are cables in every car.

Until now, when I bought my 2012 450H (absolutely love it) November last year. Never thought to get cables because it’s a hybrid and I learned the big Battery starts the engine.

Couple days ago I was old Cadillac SUV suddenly couldn’t start her car. The couple next to us had cables and because of the panels in the back of the Lexus over the Battery I thought to ask the guy leaving the store if he’d mind doing the jump start. 

All’s well that ends well, because I didn’t wind up with a very expensive repair bill trying to be a Good Samaritan!

[brendangeorge]

On 3/22/2020 at 12:26 PM, Herbie said:

Never use a hybrid to start another car unless it's another hybrid.

In a normal car the battery is only used to crank the engine. Once it fires and the alternator is spinning then its the alternator that supplies all the car's electrical demands and if there's enough 'spare' capacity it will also keep the battery charged.

A starter motor in a conventional car will draw upwards of 300A when cranking the engine, which is why when jump starting a car you always get the engine of the donor car running first before attempting to start the recipient car; firstly to stop the donor battery from going flat and secondly, if the donor battery isn't quite up to the job, the recipient car will draw power from the donor alternator, not the battery.

Hybrids don't have alternators; they charge the 12V battery from the 288V traction battery via a DC/DC converter that steps the high voltage down to around 14V. The DC/DC converters cannot supply anywhere near as much current as an alternator and if the recipient car tried to pull such current from it, there would probably be a big bang and all the magic smoke inside the converter that makes it work would escape and it would be a very expensive job to have some more magic smoke installed

You should not try and jump start another hybrid either.
 

[Herbie]

37 minutes ago, brendangeorge said:

You should not try and jump start another hybrid either.
 

Why would you say that?

Of course you can, no problem whatsoever.

[stepheneric]

On 3/22/2020 at 12:26 PM, Herbie said:

Never use a hybrid to start another car unless it's another hybrid

 

5 hours ago, brendangeorge said:

You should not try and jump start another hybrid either.

 

4 hours ago, Herbie said:

Why would you say that?

Of course you can, no problem whatsoever.

I for see a "domestic" developing. "My money is on Herbie coming out on to.p