Can You Jump Start A Hybrid?

SH20 · November 19, 2018

Has anyone actually ever jump started a hybrid, if so what is the procedure to do it safely. Is the hybrid Battery isolated from the Battery that turns the engine over?.

Cheers

AmbroseJohn · November 19, 2018

The engine is actually started by the traction Battery. The 12v Battery only fires up the computers that control the system.

If the 12v Battery is flat, you can jump it, just the same as a normal car. If the traction Battery is flat, good luck.

Britprius · November 19, 2018

43 minutes ago, SH20 said:

Has anyone actually ever jump started a hybrid, if so what is the procedure to do it safely. Is the hybrid battery isolated from the battery that turns the engine over?.

Cheers

The hybrid Battery is the Battery that turns over the engine. The 12 volt Battery boots the computers and runs things such as the hydraulic brake booster motor, and all the ancillaries as in a normal car.
The 12 volt Battery can be "jumped" as in a normal car, but great care needs to be exercised not to reverse polarity the connections, and the engine on the car being jumped from should not be running.
The 12 volt Battery is isolated from the hybrid Battery, but is charged from it by a DC to DC converter.

John.

Shahpor · November 19, 2018

10 hours ago, Britprius said:

The 12 volt battery can be "jumped" as in a normal car, but great care needs to be exercised not to reverse polarity the connections, and the engine on the car being jumped from should not be running.

I hate to contradict you John, but the manual for my GS says otherwise:

As you can see, it says to start and keep the engine of the car being used to charge from running during the jump start.

Herbie · November 20, 2018

2 hours ago, Shahpor said:

I hate to contradict you John, but the manual for my GS says otherwise:

As you can see, it says to start and keep the engine of the car being used to charge from running during the jump start.

I'm not sure how this came about - perhaps someone failed to remove the relevant passage from the manual or something but I can tell you quite categorically that the engine of the 'donor' or second car does not need to be running when you start the car with the flat Battery.

With a 'normal' non-hybrid car the starter motor draws a current of at least 300A to crank the engine so it's desirable to have the engine of the second car running to ensure its own Battery doesn't suffer and lose charge itself.

Because a hybrid car doesn't have a traditional starter motor, the 12V Battery in a hybrid car only has to power up the entry/exit system and also power up the computers necessary to get the hybrid system up and running and bring the car to the READY state. As you'll see below, my clamp meter is showing that these systems are drawing a current of just 15.32A from the Battery of my RX450h to bring the car to the READY state, which is a hell of a lot less than the 300A or more needed for a normal starter motor, and is low enough that any 12V Battery should be able to supply it easily and without the engine of the second car running.

Shahpor · November 20, 2018

That is very interesting Herbie, and actually what I thought it should be since, like you say, the 12v Battery doesn't start the engine.

Since I have been in the fortunate position to never have to try it myself, I can only go by what I have read.

Incidentally, this is from a brand new manual that Lexus Sidcup gave me a couple of weeks ago since they lost the original one when they sold me the car.

It would be nice if there was a way to check that this is correct or not with Lexus, but I doubt they would claim any different from what the manual states.

Britprius · November 20, 2018

16 hours ago, Shahpor said:

I hate to contradict you John, but the manual for my GS says otherwise:

As you can see, it says to start and keep the engine of the car being used to charge from running during the jump start.

On checking with the handbook you are correct, but as a retired electronics engineer it would go against everything I have learned over many years.
To start and have, and have the engine of the downer car running is going to put lots of voltage spikes onto the hybrid ECU supply lines something I would avoid where ever possible. I think these instructions are left overs from the standard car manual.
As member "Shahpor" above points out it is not as if hybrids require a lot of current to get to ready mode, and why on earth would you need to run with the jump leads connected for 5 minutes when once the hybrid goes to ready it's 12 volt Battery is being charged from the traction Battery even if the hybrid engine has not started, and no external help is then required or even desirable . In fact heavy jump cables are not required to "jump" a hybrid 1.5 mm flex will work perfectly well as long as the leads are kept to a reasonable length.

John.

Shahpor · November 20, 2018

I bow to your wisdom John and would certainly not have the second car's engine running were I in need of a jump start

royoftherovers · November 20, 2018

1 hour ago, Shahpor said:

I bow to your wisdom John and would certainly not have the second car's engine running were I in need of a jump start

This thread has been of significance to me as at the beginning of September and for the first time, due to what can only be described as a senior moment, I left home and drove here to Andalucia having left my GS unattached to my solar charger.

I leave here on Friday and am due to arrive back on the Wirral on Monday where I expect to find my GS 12 volt Battery as flat as a pancake!

I now know not to have the engine running when ,I or the Lexus RECOVERY TEAM attempt to power up the 12 volt Battery (my handbook reads as Shahpors), but what on earth happens if the computer does not start the engine running ? Will my Hybrid Battery have died a death?

Watch this space !!

Britprius · November 20, 2018

4 hours ago, royoftherovers said:

This thread has been of significance to me as at the beginning of September and for the first time, due to what can only be described as a senior moment, I left home and drove here to Andalucia having left my GS unattached to my solar charger.

I leave here on Friday and am due to arrive back on the Wirral on Monday where I expect to find my GS 12 volt battery as flat as a pancake!

I now know not to have the engine running when ,I or the Lexus RECOVERY TEAM attempt to power up the 12 volt battery (my handbook reads as Shahpors), but what on earth happens if the computer does not start the engine running ? Will my Hybrid Battery have died a death?

Watch this space !!

The hybrid Battery will be fine. There have been many reports of hybrid batteries standing for years without loosing charge. Until the car goes into ready mode the hybrid Battery is completely isolated from the rest of the car. I would be amazed if the 12 volt Battery has any charge though.

The most critical thing when jumping a hybrid is correct polarity connection of the jump leads. Just touching the leads the wrong way can, and will at minimum give some very expensive, and difficult to get at fuse replacement.

John.

royoftherovers · November 20, 2018

Much appreciated John. Many thanks.

SH20 · November 20, 2018

Just been reading the threads after I asked if a hybrid can be jump started. Plenty of opinion I see and good to know that the 12 v Battery is for lesser functions. I did note that on the inside edge of my boot lid there is an official Lexus sticker attached stating quite clearly to ring an 0800 tel number number if you intend to use jump leads. I guess it's to make sure you don't get things wrong and everything goes sideways on you.

Thanks for all the info from people with greater knowledge on such things.

cruisermark · November 21, 2018

Mmm maybe someone should ring that number and see what they have to say - would be interesting 🤔

Herbie · November 21, 2018

17 minutes ago, cruisermark said:

Mmm maybe someone should ring that number and see what they have to say - would be interesting 🤔

Maybe folks should just stop overthinking things 😉

It's quite simple - one 12V source is below par and you're replacing it with another 12V source.

As an experiment, someone could just try it - nothing bad will happen, it'll either work or it won't - and I'm 100% confident that it will work without the donor car's engine running.

After all, what do you think happens when someone uses a Battery pack jump-starter like I linked to above - they don't have an engine but they still start hybrid cars, and normal ones too.

Rutlandlex · November 21, 2018

I think I would rather put some juice into the Battery before starting the car because if you just connect the leads, start the car then disconnect the leads then the voltage will drop back low again which could affect the running of computer which manages the hybrid system maybe even causing it to cut out again depending on how bad it is.

At least if you put some charge in from the donor car then when the leads are disconnected it should have enough voltage to carry on running as normal with no ill effects.

Herbie · November 21, 2018

30 minutes ago, Rutlandlex said:

I think I would rather put some juice into the battery before starting the car because if you just connect the leads, start the car then disconnect the leads then the voltage will drop back low again

No it won't, that can't happen unless there's something wrong with the traction Battery and then you have major problems anyway and the 12V Battery problem will pale into insignificance.

In a normal car the Battery is just used to start the engine. Once the engine is running and the alternator is spinning, the alternator runs all the car electrics and if there's enough surplus it will also charge the Battery.

In a hybrid, the 12V Battery is used to get the hybrid system running and once it is, all starter motor and alternator duties are taken over by the traction Battery. So, 12V source (say Battery pack like above) gets the hybrid system up and running, which then uses a DC/DC converter to drop the 288V traction Battery voltage to about 14V to start charging the 12V Battery.

Sherra · November 21, 2018

I have used a pals connected 12v Battery to put mine into READY mode when I didn't think and sat listening to the radio in the local health centre once, using jump leads and simply waiting a couple of minutes when connected with no engines running before trying with no problems at all. Also used a spare Battery recently when following a short holiday then an emergency admission to hospital left the Battery too low to get it into READY mode again with no problems

Britprius · November 22, 2018

The strange thing about all this is that Lexus say in the handbook to disconnect the 12 volt Battery before charging it. The great majority of home mains chargers have a very clean "electrically" low current output "usually about 4 amps" that would do no damage to the hybrid systems.
However Lexus seem happy to say you can charge your Battery still connected from another car that will have a very dirty supply "electrically", and with an output of circa 100 amps typical of modern alternators. This into a Battery clearly labeled "if OEM" maximum charge rate 4.5 amps.

John.

royoftherovers · November 27, 2018

On 11/20/2018 at 4:54 PM, royoftherovers said:

This thread has been of significance to me as at the beginning of September and for the first time, due to what can only be described as a senior moment, I left home and drove here to Andalucia having left my GS unattached to my solar charger.

I leave here on Friday and am due to arrive back on the Wirral on Monday where I expect to find my GS 12 volt battery as flat as a pancake!

I now know not to have the engine running when ,I or the Lexus RECOVERY TEAM attempt to power up the 12 volt battery (my handbook reads as Shahpors), but what on earth happens if the computer does not start the engine running ? Will my Hybrid Battery have died a death?

Watch this space !!

Went to GS this morning and the 12v Battery was as flat as a fluke!

Opened the car with the key and tried to open the Boot with the switch below and to the right of the steering wheel. No joy, so opened the Boot with the key .

AA man arrived and started the car with his Battery Pack. He said that the voltage was low and did not look like rising and that a new Battery was probably required.

The original had lasted 5 and a bit years, so I asked him to quote for a replacement with a 5 year warranty. While he was checking on his PC I called Lexus Chester who quoted £343 with a 3 year warranty. Ouch !

AA man could not obtain necessary Battery.

Car was kept running while AA man inflated all tyres to necessary pressures and is still running to put some charge into the 12v Battery.

I will take the car out for a good run after lunch and see if that rejuvinates the 12 v Battery.

What have others replaced their GS 450h 12v Battery with at what cost please?

And all because in a very senior moment I was unable to connect the Solar Charger in early September !!

Britprius · November 27, 2018

1 hour ago, royoftherovers said:

Went to GS this morning and the 12v Battery was as flat as a fluke!

Opened the car with the key and tried to open the Boot with the switch below and to the right of the steering wheel. No joy, so opened the Boot with the key .

AA man arrived and started the car with his Battery Pack. He said that the voltage was low and did not look like rising and that a new Battery was probably required.

The original had lasted 5 and a bit years, so I asked him to quote for a replacement with a 5 year warranty. While he was checking on his PC I called Lexus Chester who quoted £343 with a 3 year warranty. Ouch !

AA man could not obtain necessary Battery.

Car was kept running while AA man inflated all tyres to necessary pressures and is still running to put some charge into the 12v Battery.

I will take the car out for a good run after lunch and see if that rejuvinates the 12 v Battery.

What have others replaced their GS 450h 12v Battery with at what cost please?

And all because in a very senior moment I was unable to connect the Solar Charger in early September !!

See my thread on fitting a larger 12 volt Battery to the GS450H in the GS section. Cost £80 for a Battery with 40% more capacity.
There is no reason to pay such a large sum for a Battery. You can buy batteries with a 4 year guarantee for circa £70. There is a temperature sensor on the OEM Battery, but this can gently be prized off, and taped, glued, or even blue tacked to the top of the new Battery. This senses Battery temperature, and adjusts the charging voltage accordingly.

John.

royoftherovers · November 27, 2018

1 hour ago, Britprius said:

See my thread on fitting a larger 12 volt battery to the GS450H in the GS section. Cost £80 for a battery with 40% more capacity.
There is no reason to pay such a large sum for a battery. You can buy batteries with a 4 year guarantee for circa £70. There is a temperature sensor on the OEM battery, but this can gently be prized off, and taped, glued, or even blue tacked to the top of the new battery. This senses battery temperature, and adjusts the charging voltage accordingly.

John.

Many thanks John.

Had car ticking over for a couple or three hours and just been out for a run.Will see if it will start under own steam tomorrow.

Farqui · November 27, 2018

3 hours ago, Britprius said:

See my thread on fitting a larger 12 volt battery to the GS450H in the GS section. Cost £80 for a battery with 40% more capacity.
There is no reason to pay such a large sum for a battery. You can buy batteries with a 4 year guarantee for circa £70. There is a temperature sensor on the OEM battery, but this can gently be prized off, and taped, glued, or even blue tacked to the top of the new battery. This senses battery temperature, and adjusts the charging voltage accordingly.

John.

royoftherovers · November 28, 2018

On 11/27/2018 at 5:35 PM, Farqui said:

Many thanks for the reference.

royoftherovers · November 29, 2018

On 11/27/2018 at 2:58 PM, royoftherovers said:

Many thanks John.

Had car ticking over for a couple or three hours and just been out for a run.Will see if it will start under own steam tomorrow.

Did not use the car yesterday due to inclement weather. I had left in unlocked however so as not to drain the Battery.

Went to it today and it fired up immediately.Took it for a run up the M53 and back,some 25 miles AND 6 BARS ARE SHOWING on the Hybrid Battery Indicator.

It seems that all is well again.