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Old 18th February 2009, 00:03   #61
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Originally Posted by R2D2 View Post
Well, if you believe so, please go ahead and disconnect the battery +ve cable. It's your car.

Please understand battery voltage and alternator voltage are two different things. One is the recipient and accumulator (battery) and the other is the generator/source (alt). The "Battery Light" on your dashboard works on that principle. Also, ECUs dont increase engine RPM to make up for voltage drops.
I do agree with the spike generation when the battery is disconnected. but the spike is generated when there is absolutely no load on the alternator. and in modern automotive systems, you have a spike protection/surge dampers. Please keep in mind that when such systems are developed by someone, they also find a way to protect it from all kinda hazards.
and to test this i dont need a car, i have lab setup at my workplace to do such testing.
And how do you say ECUs dont do battery management??

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Originally Posted by headers View Post
Sir, the battery is necessary to complete the circuit!

Sir, please understand that:

I did agree with your point of electrical load on the engine.

The alternator does charge the battery for free..if it is there in the circuit, it charges the battery until the regulator tells it to cut off. We do understand that the alternator charges the battery via the regulator @14 volts etc. etc.

The Only point I beg to differ is that "A PETROL CAR WILL NOT RUN WITHOUT A BATTERY IN THE CIRCUIT".

A car with a dead battery can be push started and run because the alternator starts charging the dead battery which in turns supplies the energy required by the car.


Yes Sir, agree with this point also.

The only issue i disagree with my friend anup is "whether a battery is required in a petrol vehicle to run the car - OR NOT" A dead battery still completes the circuit.

And as the alternator always charges at a higher rate than the battery discharge, it is obvious that even a car with dead battery, if push started, would run with the electrical loads.

BUT, anup informs us that a battery is NOT required in running of the car and that is blowing my wits out!
Sir, please check the circuit once! according to you a dead battery completes the circuit, what about a battery with no electrolyte? thats again an open circuit here.

And how do you say that the alternator charges the battery for free? please check it out in petrol cars by turning ON the head lights or any system which consumes more current. when you do this, check with the engine sound. you will notice a change in the engine sound.
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Old 18th February 2009, 00:22   #62
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Dont ICE also run for free? its difficult to digest but it is the perception of many here.there is no fuel comsumed when there is a beast of amplifiers in operation with ear shattering noise.
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Old 18th February 2009, 00:34   #63
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Dont ICE also run for free? its difficult to digest but it is the perception of many here.there is no fuel comsumed when there is a beast of amplifiers in operation with ear shattering noise.
Yes, ICE runs on battery and the battery is charged by the alternator for free.
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Old 18th February 2009, 07:47   #64
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Originally Posted by star_aqua View Post

Sir, please check the circuit once! according to you a dead battery completes the circuit, what about a battery with no electrolyte? thats again an open circuit here.
No Star_Aqua: According to me, a car with a dead battery will not run. But in some rare cases if push started may run if run without electrical loads.

But, The thinking amongst some friends is that a car can run without a battery! And I dont know how!
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Old 18th February 2009, 08:30   #65
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Originally Posted by headers View Post
No Star_Aqua: According to me, a car with a dead battery will not run. But in some rare cases if push started may run if run without electrical loads.
Few months back while i was driving to Chennai from Cuddalore, my Ikon conked-off and refused to start when we were at Tindivanam toll gate. We push started the car and drove till chennai and directly went to Amron battery shop, the service guys checked the battery and declared it dead with zero charge. Changed to a new batter and the Car started normally. After that incident i thought the car ran on alternator as the battery was completely dead!
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Old 18th February 2009, 08:53   #66
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Originally Posted by KSM-Vtec View Post
OK guys read this thread an hour ago and thought it would be a good idea to check my alternator by conducting a small experiment, here is what i did - Started my 2000 OHC Vtec and then disconnected the battery, drove around for more than a 2 kms and nothing went wrong. is that good enough??


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Originally Posted by mail4loys View Post
Few months back while i was driving to Chennai from Cuddalore, my Ikon conked-off and refused to start when we were at Tindivanam toll gate. We push started the car and drove till chennai and directly went to Amron battery shop, the service guys checked the battery and declared it dead with zero charge. Changed to a new batter and the Car started normally. After that incident i thought the car ran on alternator as the battery was completely dead!
Quote:
Originally Posted by headers View Post
No Star_Aqua: According to me, a car with a dead battery will not run.

But, The thinking amongst some friends is that a car can run without a battery! And I dont know how!
Is there lack of accounts to show that cars can indeed run without the battery?

Further, some people think that a few of the car's systems are fed by the battery and a few from the alternator, at the same time! This is not the case. The source with the higher voltage feeds everything!
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Old 18th February 2009, 10:34   #67
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Here is some info from wikipedia:

“A car battery is a type of rechargeable battery that supplies electric energy to an automobile. Usually this refers to an SLI battery (starting, lighting, ignition) to power the starter motor, the lights, and the ignition system of a vehicle’s engine”

“The starting (cranking) or shallow cycle type is designed to deliver large bursts of energy, usually to start an engine. The SLI batteries usually have a greater plate count in order to have a larger surface area that provides high electric current for short period of time. Once the engine is started, they are recharged by the engine driven charging system”

“In normal automotive service the vehicle's engine-driven alternator powers the vehicle's electrical systems and restores charge used from the battery during engine cranking”

“The deep cycle (or motive) type is designed to continuously provide power for long periods of time (for example in a trolling motor for a small boat, auxiliary power for a recreational vehicle, or traction power for a golf cart or other battery electric vehicle). They can also be used to store energy from a photo voltaic array or a small wind turbine. They usually have thicker plates in order to have a greater capacity and survive a higher number of charge/discharge cycles”

In a nutshell, the prime use of the battery is only to start the car, and provide a few initial sparks (in a petrol engine) to get the engine going. The starter motor draws a huge current (about 400 Amperes if I am not mistaken). A normal 40-60 AH car battery will get substantially discharged in this effort. Once the engine is running the alternator will take over, providing power for the sparks as well as the other gadgets. In addition, it will also charge the battery.
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Old 18th February 2009, 12:08   #68
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A car will run with a completely dead battery as long as the battery has some sort of capacitance left. When the engine is on - the battery is a "power cleaner" more than a battery.

Example: My batter is was dead - suphated beyond the point of no return. I was able to jump start the car and reach my destination. After a 30 minute drive I turned the car off - and when I switched to the ignition ON position - NOTHING. The battery had no power, and held no power the entire time. The alternator powered the car the entire time.

I did notice that the voltage was slightly off - headlights would flicker and the RPM wasnt perfectly constant. this was probably because of the horrible condition the battery was in.
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Old 18th February 2009, 12:32   #69
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why are people with half knowledge confusing others here.
All cars can run without battery once started.
Its alternator who is powering everything in a car.
You can remove the battery and car will keep running. it is not needed to complete any circuit.
battery cannot power the car if alternator is producing 13v and above.
battery comes in parallel in overload situation weather momentary or continious.
you can push start without battery as long as alternator rotates to develop a voltage sufficient to run the ecu and ignition circuit.

Any other theories, please put in with proof, let me correct myself also.

Last edited by gigy : 18th February 2009 at 12:34.
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Old 18th February 2009, 13:26   #70
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Attaboy gigy.

All true except the last line. When you push start the car, it will be very hard to get the alternator to rotate fast enough to overcome the drain from all the static loads. A dead battery is again a huge current drain . Yes you heard that right, you are better off with a disconnected battery than a dead battery sitting and drawing current from the alternator.

Vijay
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Old 18th February 2009, 13:28   #71
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All this depends on the alternator rating?
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Old 18th February 2009, 13:33   #72
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If you disconnect battery after starting the car, it will keep running, thats what I observed in Indica and the Safari.
However if your alternator is not working, and you remove the battery terminal, engine dies in the indica. So you need someone generating power, either it has to come from battery or it has to come from alternator.
Once on a long trip, my alternator died, and the battery drained. Car stalled. with new battery it would run.
After alternator replacmenet, the mechanic started car, and then disconnected battery to see if engine dies. since it did not die, it was a crude way of checking that new alternator is okay. Later I used to multimeter to properly verify this.
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Old 18th February 2009, 13:50   #73
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why are people with half knowledge confusing others here.

All cars can run without a battery once started - I wouldnt go as far as ALL Cars. I tried taking out the +ve lead on my Suabru and it died.

Its the alternator which is powering everything in a car - The Alternator powers almost everything. Why do SUV's have 2 batteries? Possibly to relieve some of the load from the alternator? They still start with one battery. So why put the second one in?

You can remove the battery and the car will keep running. It is not needed to complete any circuit - Read point 1

Battery cannot power the car if alternator is producing 13v and above - Read point 2 + What if the alternator is generating more than 13V but the load is higher? I think you are contradicting you're next point here.

Battery comes in parallel in overload situation weather momentary or continious - Agree

you can push start without battery as long as alternator rotates to develop a voltage sufficient to run the ecu and ignition circuit - Maybe in older cars. Thats why you had hand cranks. Maybe some newer cars with older tech in them. But not with most modern cars.

Any other theories, please put in with proof, let me correct myself also - You were going to correct yourself?

I would'nt say people have half knowledge (even though there is no such thing as 1/2 knowledge), its in fact people's opinions. So lets not go about slagging off the other person, but instead listen and learn.
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Old 18th February 2009, 14:03   #74
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Quote:
Originally Posted by Samir Taheer View Post
why are people with half knowledge confusing others here.

All cars can run without a battery once started - I wouldnt go as far as ALL Cars. I tried taking out the +ve lead on my Suabru and it died.

Its the alternator which is powering everything in a car - The Alternator powers almost everything. Why do SUV's have 2 batteries? Possibly to relieve some of the load from the alternator? They still start with one battery. So why put the second one in?

You can remove the battery and the car will keep running. It is not needed to complete any circuit - Read point 1

Battery cannot power the car if alternator is producing 13v and above - Read point 2 + What if the alternator is generating more than 13V but the load is higher? I think you are contradicting you're next point here.

Battery comes in parallel in overload situation weather momentary or continious - Agree

you can push start without battery as long as alternator rotates to develop a voltage sufficient to run the ecu and ignition circuit - Maybe in older cars. Thats why you had hand cranks. Maybe some newer cars with older tech in them. But not with most modern cars.

Any other theories, please put in with proof, let me correct myself also - You were going to correct yourself?

I would'nt say people have half knowledge (even though there is no such thing as 1/2 knowledge), its in fact people's opinions. So lets not go about slagging off the other person, but instead listen and learn.
Half knowledge is indeed dangerous. So do not generalize.
Such statements are generalization
1. SUVs have 2 batteries. Well some may do, whatever SUV I have seen in India has just one battery
2. Maybe in older cars statement : Well I have observed engine running with battery disconnected in a pretty new car with a Delphi common rail.

Regarding. Alternator voltage : If your alternator is not generating 12.9-13V+ at idle with full load on there is a problem. In most cars with healthy alternators, even with headlights and AC switched on the voltage is atleast around 13V. For example when I just start the indica, and connect a multimeter, switch on lights and radio etc(no AC yet),. I can see voltage going down to 12.5V or so at idle. After that there is an audible click, and engine note slightly changes, and the voltage goes up. So there is a mechanism in even a very basic devoid of ECU car like the 2002 indica to maintain around 13V atleast at idle.

So if you have such equipment in a car that you are draining battery even when car is running, eventually you will drain the battery.

Finally coming to the statement about whether cars can run with battery disconnected, it depends on idle voltage. If alternator is not generating enough voltage at idle(happens with old alternators with weak coils) the engine will die when battery is disconnected. Roadside mechanics often use this trick to take a rough idea about the health of the alternator.
They start car, switch on lights, radio and AC on idle, and then disconnect battery terminals. If car keeps on running apparently alternator is okay. So in your subaru, connect a multimeter and see whats the idle voltage.
If its below 12.9V or so, rev the engine till the voltage is at steady 13V+. Then with engine still at slightly higher revs than idle, disconnect the battery and see if the engine dies.
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Old 18th February 2009, 14:09   #75
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Quote:
Originally Posted by gigy View Post
why are people with half knowledge confusing others here.
Quote:
Originally Posted by Samir Taheer View Post
why are people with half knowledge confusing others here.
Hey!! What's wrong with you guys?!

Nobody here is DELIBERATELY trying to confuse anybody!
You seem amazingly cocksure about your own knowledgr levels! Dangerous sign!

We're all here to share and learn. So let us not make this a slanging match!
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