[anupmathur]

Originally Posted by SirAlec

Probably your idle rpm were set too high than normal.

We're talking alternators, not dynamos! The idle rpm can be left where the maker set it. An alternator will even charge the battery at idle!

[amitk26]

Guys peace you have digressed the discussion in to weather a car will run with battery disconnected or not etc but lets get back to original point of discussion from which this thread started ( spliced from original)

The point was about load on a engine put by a mechanical fan running by a belt from engine vs load on engine due to an electrical fan of same power consumption. Anup Mathur rightly pointed out that there is no reason to belive that an electrical fan will not load the engine.
Law of conservation of energy holds true everywhere isn't it ?

ideally if there are no energy losses in the system then both of them should load the engine equally because alternator is ultimately drawing then energy from engine.

In case of a mechanical fan losses are due to fan belt slippage where as in in case of electrical fan the loss is due to efficiency of conversion of mechanical energy to electrical by alternator. Which of them is greater ?

I would say if the belt and pulley is new the loss will be less in case of mechanical fan but we all know it is no longer preferred the reason(s) are

1. Electrical fan can keep on running after engine is switched off to cool the engine down , This happens in most modern Diesel and Petrol Engine.
Car manual tells you not to worry about fan running for some time once you switch off these days.

2. Over a period of time due to wear and tear the loss tends to increase in case of mechanical fan where as in case of electrical fan this is almost constant through out life of the fan / alternator

[anupmathur]

Originally Posted by amitk26

The point was about load on a engine put by a mechanical fan running by a belt from engine vs load on engine due to an electrical fan of same power consumption. Anup Mathur rightly pointed out that there is no reason to belive that an electrical fan will not load the engine.
Law of conservation of energy holds true everywhere isn't it ?

Thanks, Amit! A wee bit of support at last!
It's not only about conservation of energy; there is more to it.

There seems to be an overwhelming consensus amongst the lay public that anything electrical in the car is fed by the battery and hence 1) does not represent a load on the engine, and 2) the alternator charges the poor depleted battery and does it for free since the engine is spinning anyway!

Most here find it impossible to accept that ALL electrics in a car are fed from the alternator while the engine is running and that the voltage prevailing in the circuits is close to 14 volts at such times, if not a tad higher!
If the battery were to feed the same loads, with engine off, the voltage would be 12 or lower!

The higher voltage source will feed all loads. This is not easy for many to digest!

If an alternator is malfunctioning or its capacity has been exceeded, the output voltage from it will drop. That is when the battery will start feeding the circuits, but will do so for a very limited time before it runs out of juice!

[Samir Taheer]

I think we all need to agree that you need the battery in place to complete the circuit - But i don't agree with the theory that the electricals draw power from the battery when the car is running. To put it simply - If you jump start a car (and you would only do that if the battery is dead), once the car has started you can use all the electronics/electricals. The batter does NOT charge instantly, it takes a few hours. So where does this juice come from? I would think the alternator.

I dont deny that the battery has absolutely no role in providing juice to the car - but i would argue that most of the work (when the car is running) is done by the alternator. Or else you wouldnt be able to run your car or, anything in it, after you've jump started it.

[SirAlec]

Originally Posted by anupmathur

We're talking alternators, not dynamos! The idle rpm can be left where the maker set it. An alternator will even charge the battery at idle!

then why do we have the need to jump charge it from mains charger, when the battery is low.

and did I say i am talking about dynamos/generators.

[star_aqua]

Originally Posted by anupmathur

Most here find it impossible to accept that ALL electrics in a car are fed from the alternator while the engine is running and that the voltage prevailing in the circuits is close to 14 volts at such times, if not a tad higher!
If the battery were to feed the same loads, with engine off, the voltage would be 12 or lower!

The higher voltage source will feed all loads. This is not easy for many to digest!

If an alternator is malfunctioning or its capacity has been exceeded, the output voltage from it will drop. That is when the battery will start feeding the circuits, but will do so for a very limited time before it runs out of juice!

Well said Anup you have summerized each and every point in simple words. Hope now atleast many will try to digest!

[anupmathur]

Originally Posted by Samir Taheer

I think we all need to agree that you need the battery in place to complete the circuit -
.......
I dont deny that the battery has absolutely no role in providing juice to the car - but i would argue that most of the work (when the car is running) is done by the alternator. Or else you wouldnt be able to run your car or, anything in it, after you've jump started it.

Good explanation, Samir.

However, the battery is not required to 'complete the circuit' as you put it.
Since the alternator is the source, the circuit gets completed with the alternator wiring and earth. In some cars you might have one or more wires directly connecting at the positive terminal of the battery. In such cases, if the battery is disconnected, ALL wires should STAY connected together and the LOT should be unplugged from the battery terminal as a connected bunch. The engine, then, will keep running.
What complicates this whole matter is the possibility that in advanced cars that might have various monitoring systems, the car may not run if any parameter is seen as abnormal.

[R2D2]

Originally Posted by anupmathur

Thanks, Amit! A wee bit of support at last!
It's not only about conservation of energy; there is more to it.

There seems to be an overwhelming consensus amongst the lay public that anything electrical in the car is fed by the battery and hence 1) does not represent a load on the engine, and 2) the alternator charges the poor depleted battery and does it for free since the engine is spinning anyway!

Most here find it impossible to accept that ALL electrics in a car are fed from the alternator while the engine is running and that the voltage prevailing in the circuits is close to 14 volts at such times, if not a tad higher!
If the battery were to feed the same loads, with engine off, the voltage would be 12 or lower!

The higher voltage source will feed all loads. This is not easy for many to digest!

If an alternator is malfunctioning or its capacity has been exceeded, the output voltage from it will drop. That is when the battery will start feeding the circuits, but will do so for a very limited time before it runs out of juice!

Anup, you're absolutely right. You've been hitting the nail on the head all along. I read the topic from the beginning and am quite surprised to see the misconceptions amongst many of our members.

Point # 1 - The alternator IS the primary source of electrical energy in the vehicle. It is the generator.
Point # 2 - The battery is a reservoir, an accumalator of charge. The battery supplies power one or more of three conditions are met; the engine is off, the electrical load exceeds that what the alternator is able to supply given a certain RPM AND if the alt is malfunctioning. The battery makes up for the deficit.

And friends, it is important to know that if you disconnect the alternator from the battery (the +ve terminal) while the engine is running you risk ruining the alternator's regulator AND, due to a voltate surge, frying the car's electronics including the ECU. Please DO NOT test an alternatorby disconnecting the battery. It could be done on older cars but newer autos have very sensitive electronics including your ICE system.

The alt is tested by connecting an DVM in parallel to check the voltage (V) or an ammeter in series for the current(A). If you do not have this equipment please take your car to an auto electrical shop or a battery dealer to have it tested.

I have a Corolla workshop manual that clearly warns against disconnecting the battery when the engine is on.

Cheers!

R2D2

[Samir Taheer]

Anup, didnt think you could do this in newer cars.

I thought you could only do that on older cars, but I've never tried it so ill just take your word for it. Thanks.

Edit:- I guess R2D2 just cleared up my last point.

So a Conclusion would be - A) The alternator is the Primary Source & B) Dont try this at home kids - Esp if you have a new car.

Yes?

[anupmathur]

Originally Posted by R2D2

I read the topic from the beginning and am quite surprised to see the misconceptions amongst many of our members.

Thanks, R2D2. I wish our friends Harjeev, Esteem_lover and Headers would join in now. They really need to understand this correctly!
They were very active towards the beginning of this discussion.

[R2D2]

Originally Posted by Samir Taheer

Anup, didnt think you could do this in newer cars.

I thought you could only do that on older cars, but I've never tried it so ill just take your word for it. Thanks.

Edit:- I guess R2D2 just cleared up my last point.

So a Conclusion would be - A) The alternator is the Primary Source & B) Dont try this at home kids - Esp if you have a new car.

Yes?

Samir, a loud "yes!" to both A) and B).

The last thing you want is a fried ECU which will set you back by 10s of thousands of rupees or possibly even lakhs depending on which car you have.

Rgds,

R2D2

[star_aqua]

Originally Posted by R2D2

Samir, a loud "yes!" to both A) and B).

The last thing you want is a fried ECU which will set you back by 10s of thousands of rupees or possibly even lakhs depending on which car you have.

Nope. ECU is not that sensitive as you guys think. You cannot start an enigne without battery, but after start you can remove the battery. The monitoring function allways checks for the battery voltage. now battery voltage is nothing but the alternator voltage after removing the battery. If the battery voltage goes below the threshold voltage, then the ECU will automatically increase the engine rpm. And also depending upon the battery voltage, the no of injections per cycle are decided(in case of crde). If still the battery voltage is not sufficient for energising the injectors, then the final step is to shut off the engine. and this happens only if the alternator is not working as it should supposed to be.

[R2D2]

Originally Posted by star_aqua

Nope. ECU is not that sensitive as you guys think. You cannot start an enigne without battery, but after start you can remove the battery. The monitoring function allways checks for the battery voltage. now battery voltage is nothing but the alternator voltage after removing the battery. If the battery voltage goes below the threshold voltage, then the ECU will automatically increase the engine rpm. And also depending upon the battery voltage, the no of injections per cycle are decided(in case of crde). If still the battery voltage is not sufficient for energising the injectors, then the final step is to shut off the engine. and this happens only if the alternator is not working as it should supposed to be.

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.

Rgds,

R2D2

[headers]

Originally Posted by star_aqua

I have done push start of my M800 when the battery was completely dead which could not even able to glow a small LED. How did it start with no juice from the battery??

Sir, the battery is necessary to complete the circuit!

Originally Posted by star_aqua

Nope. i did not remove the battery. What difference will it make?

Answered above. If what my friend anup says is true, we can start the car and disconnect the battery and keep running. Only your horns, Headlights, Taillamps, indicators etc will not work..does it really matter. The battery should also last more than 10 years then.

Originally Posted by hrag

I agree with headers. I have seen this happen in my Indica. After starting, the battery was disconnected - the engine ran for a few minutes and then died.

Thanks Hrishi, guess you have tried running the car without a battery!

Originally Posted by anupmathur

There seems to be an overwhelming consensus amongst the lay public that anything electrical in the car is fed by the battery and hence 1) does not represent a load on the engine, and 2) the alternator charges the poor depleted battery and does it for free since the engine is spinning anyway!

Most here find it impossible to accept that ALL electrics in a car are fed from the alternator while the engine is running and that the voltage prevailing in the circuits is close to 14 volts at such times, if not a tad higher!
If the battery were to feed the same loads, with engine off, the voltage would be 12 or lower!

The higher voltage source will feed all loads. This is not easy for many to digest!

If an alternator is malfunctioning or its capacity has been exceeded, the output voltage from it will drop. That is when the battery will start feeding the circuits, but will do so for a very limited time before it runs out of juice!

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

Originally Posted by Samir Taheer

I think we all need to agree that you need the battery in place to complete the circuit - But i don't agree with the theory that the electricals draw power from the battery when the car is running. To put it simply - If you jump start a car (and you would only do that if the battery is dead), once the car has started you can use all the electronics/electricals. The batter does NOT charge instantly, it takes a few hours. So where does this juice come from? I would think the alternator.

I dont deny that the battery has absolutely no role in providing juice to the car - but i would argue that most of the work (when the car is running) is done by the alternator. Or else you wouldnt be able to run your car or, anything in it, after you've jump started it.

I do agree with your point, but my friend anup tells me that a car can be run without the battery. Else I have misunderstood the issue completely

Originally Posted by anupmathur

Good explanation, Samir.

However, the battery is not required to 'complete the circuit' as you put it.

Originally Posted by R2D2

And friends, it is important to know that if you disconnect the alternator from the battery (the +ve terminal) while the engine is running you risk ruining the alternator's regulator AND, due to a voltate surge, frying the car's electronics including the ECU. Please DO NOT test an alternatorby disconnecting the battery. It could be done on older cars but newer autos have very sensitive electronics including your ICE system.

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!

[R2D2]

Originally Posted by headers

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

Headers, you have it the other way round. The alternator supplies the electrical energy required to run the electronic devices and THEN uses the remaining capacity to charge the battery.

This is assuming the load on the alternator is less than it's output in amps. Ever wondered why, when running with a flat battery, electricians advise you to switch off the AC and preferably drive during the day when the electrical load is less?

Rgds,