Electrical Question to settle an argument

TSC · Jan 30, 2014

Am I correct is saying that the battery is used to start the vehicle and run any electrical systems when the car is not in use, when the vehicle is running it's the alternator that runs the vehicle, meaning the alternator does not just charge the battery.

martynv8 · Jan 30, 2014

Thats as i understand it.

StuckAgainSteve · Jan 30, 2014

TSC said:
Am I correct is saying that the battery is used to start the vehicle and run any electrical systems when the car is not in use, when the vehicle is running it's the alternator that runs the vehicle, meaning the alternator does not just charge the battery.

The battery supplies current when the current draw of the alternator is exceeded by the electrical load, any "spare" will charge the battery.

Datatek · Jan 30, 2014

TSC said:
Am I correct is saying that the battery is used to start the vehicle and run any electrical systems when the car is not in use, when the vehicle is running it's the alternator that runs the vehicle, meaning the alternator does not just charge the battery.

Correct. However, with the engine idling and a lot of load, the battery will make up the difference between alternator output and the load.

gfromleeds · Jan 30, 2014

As he said^
The battery takes up the shortfall when the alternator dosent provide enough

roccotune · Jan 30, 2014

I believe that the battery also acts to stabilise the alternator output

Datatek · Jan 31, 2014

roccotune said:
I believe that the battery also acts to stabilise the alternator output

Yes that is true, alternator output is pretty spikey and not good for modern electronics, the battery smooths it all out. Older cars would happily run once started with the battery removed.

odyssey · Jan 31, 2014

By older cars Datatek, do you mean those with dynamos, I was always told not to disconnect the battery on a running engine with an alternator as it would kill the electronics (don't remember if it was the diode/rectifier) in the alternator.

A

martynv8 · Jan 31, 2014

My battery managed to disconnect it'self whilst driving from Wrexham to Sheffield. It wasn't until i arrived home, switched off & went to lock it that i discovered the battery + terminal had disconnected. Everything fine after a radio code & window re-set

Datatek · Jan 31, 2014

odyssey said:
By older cars Datatek, do you mean those with dynamos, I was always told not to disconnect the battery on a running engine with an alternator as it would kill the electronics (don't remember if it was the diode/rectifier) in the alternator.

A

No not dynamo's that's really really old

Pull the battery off with no other load and you risk killing the alternator, as long as there is some load the alternator will be fine.
I've accidently turned off the master switch when I had my boat isolating the battery and never had a problem but that is more risky.

odyssey · Jan 31, 2014

Thanks Data - useful to know.

Alastair

Datatek · Jan 31, 2014

odyssey said:
Thanks Data - useful to know.

Alastair

If you are a long way from support and the battery fails, if you can start the car with a jump and then turn on the side lights before you disconnect the jump leads, you should then be able to run without the battery. Just a caveat on the P38 as the electronics may not like the electrical noise.

TSC · Jan 31, 2014

Thanks everyone.

Electrical Question to settle an argument

TSC

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martynv8

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StuckAgainSteve

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Datatek

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gfromleeds

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roccotune

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Datatek

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odyssey

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martynv8

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Datatek

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odyssey

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TSC

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