Removing the main battery, does alarm sound?
Discussion
I'm going to change the "big fuse", but would rather disconnect the battery for the job (instead of just insulating the tools and trying not to accidentally groiund anything).
So, when I take the +ve connection off the battery, is the alarm going to go off, and would the plipper stop it?
(btw, I know that the alarm goes off & doors lock when the battery is re-connected).
Can anyone advise?
So, when I take the +ve connection off the battery, is the alarm going to go off, and would the plipper stop it?
(btw, I know that the alarm goes off & doors lock when the battery is re-connected).
Can anyone advise?
Hello,
When I disconnected my battery nothing happened with the alarm and the same when I reconnected it. But when I was reconnecting it was to re-align the alarm with the fob, because the fob would not work. This was cured by holding the alarm button on the key fob, whilst connecting the main car battery. Had to do this a few times to do the re-alignment. I was ready for the alternate entry method though.....
When I disconnected my battery nothing happened with the alarm and the same when I reconnected it. But when I was reconnecting it was to re-align the alarm with the fob, because the fob would not work. This was cured by holding the alarm button on the key fob, whilst connecting the main car battery. Had to do this a few times to do the re-alignment. I was ready for the alternate entry method though.....
Right, I'll take the +ve off, and not expect the alarm to go off.
If it does (and also when I'm refitting it) I'll stick the +ve back on and cancel the alarm in the normal manner. And remember not to leave the fob shut in the car... (and be ready for any "alternate" method as they become neessary
)
Thanks.
If it does (and also when I'm refitting it) I'll stick the +ve back on and cancel the alarm in the normal manner. And remember not to leave the fob shut in the car... (and be ready for any "alternate" method as they become neessary
) Thanks.
The neg terminal is a pain to get to so just take the pos off. It's true that you should take the neg off first but there isn't too much to short the pos to in the process of removing the terminal - benefit of having so much GRP everywhere! As others have said, you shouldn't hear the alarm if you disconnect just the pos. Don't leave you fob in the car and you need to do both fobs (if you have 2) when you reconnect the pos. There is an alternative method of aligning 2 fobs but I've never been able to get it to work. Maybe I have duff info.
And never take chances with the Big Fuse - always disconnect the pos before you do any work.
And never take chances with the Big Fuse - always disconnect the pos before you do any work.
thegreengoblet said:
The neg terminal is a pain to get to so just take the pos off.
That had influenced my initial comment about just removing the +ve ! I'll just make sure it's secure and not going to flap around and ground on anything.
thegreengoblet said:
...and you need to do both fobs (if you have 2) when you reconnect the pos.
This is interesting, as whenever I've had the car in for a job where the battery was being disconnected (or even in the past when the battery has entirely failed) I've only ever supplied 1 fob. Also, the battery in the "other" fob is flat at the moment, so there's little choice
thegreengoblet said:
And never take chances with the Big Fuse - always disconnect the pos before you do any work.
My thoughts exactly. The Big Fuse might be able to carry 100A, but I'm not sure I can!
I've recently done my big fuse and just disconnected the Positive terminal. When reconnection I probably didn't make a sound connection at first and the alarm triggered.
So just in case have your 'blipper' handy.
Oh and have the boot open so you have access to the fuses - just in case
So just in case have your 'blipper' handy.
Oh and have the boot open so you have access to the fuses - just in case
The basic logic of disconnecting the - first is that if your spanner touches the body of the car while you are opening the -, then nothing will happen BUT if you take the + off first and your spanner touches the body of the car while it's touching the + then you short the battery. 
Not as critical with a "plastic" bodied car but it's still good practice to do it the right way.
Not as critical with a "plastic" bodied car but it's still good practice to do it the right way.
ireland said:
The basic logic of disconnecting the - first is that if your spanner touches the body of the car while you are opening the -, then nothing will happen BUT if you take the + off first and your spanner touches the body of the car while it's touching the + then you short the battery.
Point taken. Where can I get a plastic spanner from
whatever said:
ireland said:
The basic logic of disconnecting the - first is that if your spanner touches the body of the car while you are opening the -, then nothing will happen BUT if you take the + off first and your spanner touches the body of the car while it's touching the + then you short the battery.
Point taken. Where can I get a plastic spanner from
whatever said:
My thoughts exactly. The Big Fuse might be able to carry 100A, but I'm not sure I can!
That's not the way amps work. Current is related to (a) the battery voltage, and (b) the resistance in the circuit. Your body's resistance is about 80k ohms so will never draw 100A from the battery. It's just a big (i.e. large capacity) 12V battery, like 8 AAs. You can happily stick your fingers across the terminals. However, drop a spanner across them (resistance only a few ohms) and it will happily supply enough current to melt the spanner. ireland said:
The basic logic of disconnecting the - first is that if your spanner touches the body of the car while you are opening the -, then nothing will happen BUT if you take the + off first and your spanner touches the body of the car while it's touching the + then you short the battery.
Not as critical with a "plastic" bodied car but it's still good practice to do it the right way.
Not as critical with a "plastic" bodied car but it's still good practice to do it the right way.
I think the real reason, from an old old school mechanic (this guy was like 103 when he told me 15 years ago) said that by pulling the negative off first, there is no longer a circuit for the positive to complete and therefor no sparks when pulling the negative. same in reverse, pos on first the neg to reduce the chance of sparks.
What's the big deal about sparks? The chemical reaction in a car battery produces hydrogen, which can produce water very quickly, warmly and violently when in the presence of oxygen and a spark.
12 volts is not enough to pass through a human unless aided by things like salt water or multiple body piercings. If it does happen to pass through you, 500+ amps will do some damage.
When I was fitting a new big fuse and cables I found with the battery out of the car entirely (hence both pos and neg leads disconnected) I got a (vey small) spark from the pos lead when it touched the water rail - very disconcerting - very TVR
Presumably the battery in the alarm? Or is there something with capacitance that would hold a charge?
Whatever it was, I'd advise wrapping the pos lead in something insulating to avoid a spark and/or damage to the alarm battery or whatever caused the spark.
Presumably the battery in the alarm? Or is there something with capacitance that would hold a charge?
Whatever it was, I'd advise wrapping the pos lead in something insulating to avoid a spark and/or damage to the alarm battery or whatever caused the spark.
methodwares said:
12 volts is not enough to pass through a human unless aided by things like salt water or multiple body piercings. If it does happen to pass through you, 500+ amps will do some damage.
Cough - Watch Strap - Cough.
Yup - I've heated my watch strap whilst changing bulbs behind a dash on a car.
methodwares said:
12 volts is not enough to pass through a human unless aided by things like salt water or multiple body piercings. If it does happen to pass through you, 500+ amps will do some damage.
ok, I always take the watch & wedding ring off before delving into the beast's innards and dry my hands first (sounds more like veterinary, this) (
that's it - the long rubber gloves are what I need!) As for the high amps through the body piercings - enough to make your eyes water just thinking about it. Mind you, I expect some people pay good money for that kind of treatment.
methodwares said:
12 volts is not enough to pass through a human unless aided by things like salt water or multiple body piercings. If it does happen to pass through you, 500+ amps will do some damage.
500 mA is enough to disrupt heart function. And remember that there are some very high voltages around when the engine is running i.e don't test for a spark with your tongue.
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