Author Topic: Any way to charge an empty starter battery from the one in the boot?  (Read 402 times)

Bonobo

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Imagine you are in the middle of a desert, and your hybrid jazz 2012 has an empty starter battery. But you have thick and long enough wires, a knife, spanners, screwdrivers and reasonable electric skills. Is there any way to charge an empty starter battery from the one in the boot?
« Last Edit: November 23, 2021, 09:48:39 PM by Bonobo »

Neil Ives

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Re: Any way to charge an empty starter battery from the one in the boot?
« Reply #1 on: November 23, 2021, 09:45:56 PM »
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Neil Ives

Neil Ives

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Re: Any way to charge an empty starter battery from the one in the boot?
« Reply #2 on: November 24, 2021, 03:28:02 PM »
The drive battery holds a high voltage, something like 180volts.
In theory, to be able to charge the baby 12v battery from the drive battery you would need to produce alternating current from the HV battery using a DC to AC device, pass the AC through a transformer to reduce the voltage then rectify the lower voltage AC to DC at 12v. Then you'd need to regulate the current drawn by the baby battery.
I suggest calling out the AA!
Neil Ives

culzean

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Re: Any way to charge an empty starter battery from the one in the boot?
« Reply #3 on: November 24, 2021, 03:52:23 PM »
Imagine you are in the middle of a desert, and your hybrid jazz 2012 has an empty starter battery. But you have thick and long enough wires, a knife, spanners, screwdrivers and reasonable electric skills. Is there any way to charge an empty starter battery from the one in the boot?

Yeah, but before you try make sure you have long cables,  long enough to place the 12v battery behind a wall, preferably the opposite side of the wall to the side where you will be.  Attach cables to 12volt battery and then to the battery in the boot, you should hear a loud bang, and if the 12volt battery is still in one piece it may start the engine.. The batteries for EV motor power in a car will always be in the 200 to 800 volt range.... Good Luck
« Last Edit: November 24, 2021, 05:22:25 PM by culzean »
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csp

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Re: Any way to charge an empty starter battery from the one in the boot?
« Reply #4 on: November 24, 2021, 04:00:15 PM »
Don't even think about trying to charge the 12V battery from the high voltage battery. This would be very dangerous & likely to cause injury & damage the car!

nowster

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Re: Any way to charge an empty starter battery from the one in the boot?
« Reply #5 on: November 24, 2021, 10:30:54 PM »
The drive battery holds a high voltage, something like 180volts.
In theory, to be able to charge the baby 12v battery from the drive battery you would need to produce alternating current from the HV battery using a DC to AC device, pass the AC through a transformer to reduce the voltage then rectify the lower voltage AC to DC at 12v. Then you'd need to regulate the current drawn by the baby battery.
I suggest calling out the AA!
Or a buck regulator.

https://en.wikipedia.org/wiki/Buck_converter

Jocko

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Re: Any way to charge an empty starter battery from the one in the boot?
« Reply #6 on: November 24, 2021, 11:05:17 PM »
You could use a chain of resistors and tap off your 14 - 15v that way.

culzean

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Re: Any way to charge an empty starter battery from the one in the boot?
« Reply #7 on: November 25, 2021, 08:00:30 AM »
One of those occasions you need one of those jump start packs,  or a tow from a herd of camels... 8)  May be a good thing in the desert to carry a fold-out solar panel...  But looking at it, the desert is not the natural home of the Jazz...
« Last Edit: November 25, 2021, 08:13:57 AM by culzean »
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nowster

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Re: Any way to charge an empty starter battery from the one in the boot?
« Reply #8 on: November 25, 2021, 04:23:47 PM »
You could use a chain of resistors and tap off your 14 - 15v that way.
Not particularly efficient, though, and not very well regulated. You'll need quite beefy resistors as they're going to get blooming hot feeding a lead-acid battery. Buck converters can get up to about 90% efficiency.

You could alternatively use a motor-generator (or motor-alternator) set with the correct voltage ratings.

culzean

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Re: Any way to charge an empty starter battery from the one in the boot?
« Reply #9 on: November 25, 2021, 04:39:12 PM »
You could use a chain of resistors and tap off your 14 - 15v that way.
Not particularly efficient, though, and not very well regulated. You'll need quite beefy resistors as they're going to get blooming hot feeding a lead-acid battery. Buck converters can get up to about 90% efficiency.

You could alternatively use a motor-generator (or motor-alternator) set with the correct voltage ratings.

You are in the desert - unlike in UK solar actually works in desert areas....

Do motor generators cater for 12volt DC ( or 15 volts ),  or do you need a 230 volt AC to 12 ( 15 ) volt battery charger as well ?

Where does the fuel for the motor-generator come from ?
« Last Edit: November 25, 2021, 05:02:41 PM by culzean »
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culzean

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Re: Any way to charge an empty starter battery from the one in the boot?
« Reply #10 on: November 25, 2021, 05:04:44 PM »
Imagine you are in the middle of a desert, and your hybrid jazz 2012 has an empty starter battery. But you have thick and long enough wires, a knife, spanners, screwdrivers and reasonable electric skills. Is there any way to charge an empty starter battery from the one in the boot?

Anyone who had even 'less than reasonable' electrical skills would not attempt to connect a 200 volt battery to a 12 volt one.
Some people will only consider you an expert if they agree with your point of view or advice,  when you give them advice they don't like they consider you an idiot

Kremmen

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Re: Any way to charge an empty starter battery from the one in the boot?
« Reply #11 on: November 25, 2021, 05:24:23 PM »
Don't our Jazz MK4 charge the 12v from the HV job?

Some clever electronics there then.
Let's be careful out there!

culzean

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Re: Any way to charge an empty starter battery from the one in the boot?
« Reply #12 on: November 25, 2021, 06:19:04 PM »
Don't our Jazz MK4 charge the 12v from the HV job?

Some clever electronics there then.

It is easy to do with electronics,  but not in the middle of the Western Desert with a flat battery..

Most mobile devices like phones and laptops contain chips that can change the voltage level of the battery to the voltage needed to power various parts of the device, both up and down. mainly using fast switching FET to make the devices more efficient and prolong battery life.
« Last Edit: November 25, 2021, 06:28:04 PM by culzean »
Some people will only consider you an expert if they agree with your point of view or advice,  when you give them advice they don't like they consider you an idiot

nowster

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Re: Any way to charge an empty starter battery from the one in the boot?
« Reply #13 on: November 25, 2021, 06:21:54 PM »
Don't our Jazz MK4 charge the 12v from the HV job?

Some clever electronics there then.

It'll be a version of the buck converter, as previously said, or maybe a chopper/step down circuit like is found in a switched-mode power supply (SM PSU). They tend to work at about 340V DC (rectified 240V mains) on the primary side.

And the motor could be DC powered (off the battery), driving a generator or alternator on a common shaft. (These used to be very common to provide clean mains supplies to the likes of mainframe computers back in the day.)

Jocko

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Re: Any way to charge an empty starter battery from the one in the boot?
« Reply #14 on: November 25, 2021, 06:22:36 PM »
Where does the fuel for the motor-generator come from ?
The HV battery runs the motor which drives the generator which charges the battery.

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