If One Of The Terminals Came Off Your Car Battery While You Were Driving...

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Dawg

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Master Geek
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#240613 30-Jul-2009 15:11

Mine stopped - Cut out - resets Clock and Radio stations - Can short everything too I'm told

Criggie

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Geek

#240752 30-Jul-2009 20:41

Depends on a lot... Your big current draw is at starting time... the starter motor draws an order magnitude more current than anything else.

So assuming your car has the alternator--> battery charge lead connected to the positive terminal by the same clamp as the power connector, the generated power would continue to provide enough to run the coil to spark the plugs. Assumes that its hasn't shorted on any part of the body, block or chassis.

If the charge lead alone fell off, you'd be fine for ~hundreds of km, provided you didn't use lights or anything. (been there done that with a siezed alternator in the holden)

If the negative lead fell off while driving, the battery would stop charging and that's about all. Of course starting would be a non-event.

HOWEVER any newer car will have an engine management computer with sensors which may shut everything down.

This basic electrical stuff is not hard... way easier to fix up than some of the mechanical or pneumatic systems.
New battery clamps are ~$10 at repco and all you need is simple tools like snips, screwdriver and spanner. And some sand paper and petroleum jelly. Garage would charge you an hours labour for this too.

Dratsab

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#240766 30-Jul-2009 21:52

tonyhughes: Best thing for an Allegro I would say. Do you know what the word Allegro actually means? If not, worth googling. :o)

Way, way, way off topic, but Pajero - as in the Mitsubishi - (which you can google too) is even better viewing

Adamal

544 posts

Ultimate Geek

#240786 30-Jul-2009 23:51

Yup, and thats not an urban rumour either! My mum didn't believe me when I told her, and asked a friend of hers who was a Spanish interpreter.

phlegmboy

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#241586 2-Aug-2009 21:34

A car should not cut out if the battery is disconnected while the car is running, unless the draw of the electrical system is greater than the alternator is rated for. Although an alternator needs a power source when it first starts producing power, once it is generating a voltage, as long as there is sufficient current for the alternator's rotor to generate the required magnetic field (alternators use an electrically generated magnetic field rather than a permanent magnetic such as that used in the old generators) the alternator will continue to supply energy.

I'd go on a Vegan diet but the delivery time from Vega is too long.

richms

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#241642 2-Aug-2009 23:06

Headlights, injectors, ABS systems etc all take a fair amount of power - and at idle the alternator is well down on output - one site I read said its at 15% or so at 600 rpm from the nameplate since there is only so much current the field can take.

So the nice 170 amp alternator is down to putting out only 25? amps if thats the case - I think thats a little harsh tho since the voltmeter in the car doesnt go below 13.5 at idle even with 120 watts of laptop on the lighter socket, the stereo going and the headlights (And I think I had foglights at the time I tried it) and thats just the stock skylike R32 alternator and a pretty pathetic "400 watt" amp for the sounds.

Richard rich.ms

Dell

Shop now for Dell laptops and other devices (affiliate link).

paradoxsm

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#241653 3-Aug-2009 00:33

Toyota MR2 1984 AW11 Regulated Alternator.
Runs fine all the way from Auckland to (almost) Wellington without battery connected, won't roll start due to rotor and stator in alternator requiring a residual current to start generating. terminal came off, could not start it after I fuelled up opened "bonnet" and saw why, terminal had broken off, held it on, started it back up and it made it to Wellington without a hitch. This car has a computer and I certainly would not recommend running it batteryless but it survived.

Morris Oxford 1965 Crudely regulated DC Generator.
Runs fine with battery disconnected, has had no battery for ages, I just start it and take it around the block. It won't roll start again due to rotor and stator in alternator requiring a residual current to start generating/polarisation.

Nissan Primera P11, Ran without battery connected and subsequently blew the computer and half the other electrics up with no warnings that battery wasn't even connected. Computer also seemed to always have issues with low voltages under 10V when attempting to start in previous times, battery had a bad cell but this was appalling. Bad car. (and utterly terrible Exide battery)

Honda MB100 Motorbike, runs and starts fine with no battery, it's only a 2-stroke blat machine with a magneto.

Volvo 740, Have not tried it without a battery, this is my latest beast or is that "cube"/"box" (also have the MR2 still)

paradoxsm

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#241655 3-Aug-2009 00:38

I have been told most new cars will still keep running but immediately show a warning light and/or reduce the engine power allowing you to come to a stop slowly. Newer Alternators put out a fair bit more current,

Mechanic also told me there are new batteries that cannot be fitted to older cars as they need to be charged faster, can anyone confirm?

Criggie

24 posts

Geek

#241667 3-Aug-2009 07:21

Morris Oxford 1965 Crudely regulated DC Generator.
Runs fine with battery disconnected, has had no battery for ages, I just start it and take it around the block. It won't roll start again due to rotor and stator in alternator requiring a residual current to start generating/polarisation.

Generators aren't alternators - massive differences internally.

Alternators have multiple windings and generate AC, which is then rectified. Generators only have one set of windings and work the other way around, by spinning the magnet inside wires rather than the alternator way which spins wires inside magnet.

Also, generators mean the vehicle is positive earth, whereas all modern cars are negative earth.

Criggie

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Geek

#241668 3-Aug-2009 07:28

Mechanic also told me there are new batteries that cannot be fitted to older cars as they need to be charged faster, can anyone confirm?

Yes, that's completely true. Again its probably related to the number of Jap cars we've got on NZ roads... Japanese cars tend to have slightly smaller batteries, more for just starting rather than running accessories for hours with the motor off.

Bigger alternators can provide more power while motor is running, so why have a big battery?

Mine's a 750 CCA battery, and I've left the lights on for ~3 hours once. Started without a problem. That's why I have the biggest one that fits my tray.

JohnS

11 posts

Geek

#242533 4-Aug-2009 17:35

Happened to me. Nearly new Nissan X-Trail petrol powered. Drove around, no problem. Stopped to buy something from a shop. Car completely dead when I tried to restart. Opened bonnet. One lead off battery (after a recent service!).

So, vehicle was happily being powered by the alternator only (which of course, works even at idling speed). Lead had not been tightened, and must have popped off after a bump.

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