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Old 15th February 2009, 10:33   #1
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Question Alternator Dependency: Will a vehicle run with the battery disconnected?

NOTE from Team-BHP Support: Discussion here is an offshoot from this thread : http://www.team-bhp.com/forum/technical-stuff/43232-airconditioning-gypsy-3.html


Quote:
Originally Posted by headers View Post
Have replaced the stock fanbelt driven fan to an electric fan to save on engine power as well as improve efficiency.
Headers, the only time you'll be saving engine power is with the electric fan OFF!
The belt driven fan loads the engine to an extent determined by the rpm you are at.
The electric fan will come on full blast regardless of engine rpm. This can load the engine more than the stock fan, at lower engine rpms. After all, the alternator has to feed this electric fan in real time and this represents a load on the engine!



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Originally Posted by khan_sultan View Post
  • What is that in the area that I have marked as Yellow. I think it is there in the other pic that you have put as well.
That is the AC compressor.

Last edited by khan_sultan : 17th February 2009 at 16:06.
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Old 16th February 2009, 07:13   #2
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Originally Posted by anupmathur View Post
The electric fan will come on full blast regardless of engine rpm. This can load the engine more than the stock fan, at lower engine rpms. After all, the alternator has to feed this electric fan in real time and this represents a load on the engine!
HI, while I agree to your first point that the engine improves in efficiency while the fan is OFF, I disagree on you point above!

You want your engine to be more responsive to your inputs, then get all auxillary load OFF the engine. If your electrical system is great, then the loads on the alternator and battery can be managed easily!


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Old 16th February 2009, 09:07   #3
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Originally Posted by headers View Post
.....I disagree on you point above!
You want your engine to be more responsive to your inputs, then get all auxillary load OFF the engine. If your electrical system is great, then the loads on the alternator and battery can be managed easily!
Headers, you are right: "Get all the auxiliary load off the engine".

The alternator too is an auxiliary load.

Look at it this way: Suppose the engine driven fan draws a maximum of 100 watts worth of power from the engine. This gets supplied directly by the engine in mechanical form via the drive belt.

Now, consider an electric fan rated for 100 watts. It is the alternator that will supply this 100 watts. From where? Certainly not from the battery!
The alternator will produce this 100 watts by taking that amount of power from the engine, again in mechanical form via the drive belt, and supplying it in electrical form at its output terminals!

Hope the above is clear enough.
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Old 16th February 2009, 11:56   #4
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Originally Posted by anupmathur View Post
Now, consider an electric fan rated for 100 watts. It is the alternator that will supply this 100 watts. From where? Certainly not from the battery!

@anupmathur: Now I'm a little foxed at the above Sir!

Any electrical load is supplied from the Battery right?
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Old 16th February 2009, 12:05   #5
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Originally Posted by headers View Post
Any electrical load is supplied from the Battery right?
Not so.
The battery will supply only when the engine is off.
With engine running, the alternator takes over and supplies the electrical requirements AND charges the battery.
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Old 16th February 2009, 12:07   #6
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I was actually thinking the same thing.
Isn'tall the electrical load on the Battery and its the alternator that charges the battery in turn.
This is why even with the engine off, the electric appliances keep function (which means that the battery is being drained) and then when we fire the engine the alternator starts to charge the battery.
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Old 16th February 2009, 12:13   #7
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Originally Posted by anupmathur View Post
Not so.
The battery will supply only when the engine is off.
With engine running, the alternator takes over and supplies the electrical requirements AND charges the battery.
Sir, the Alternator IMO does NOT directly supply current to any appliance in the vehicle.

Please try removing the battery after starting the vehicle and running it, especially a petrol car. It will NOT run!


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Originally Posted by harjeev View Post
I was actually thinking the same thing.
Isn'tall the electrical load on the Battery and its the alternator that charges the battery in turn.
This is why even with the engine off, the electric appliances keep function (which means that the battery is being drained) and then when we fire the engine the alternator starts to charge the battery.
Yes sir, I guess we are right

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Originally Posted by esteem_lover View Post
@anupmathur... the alternator will not load the engine as heavily as the alternator plus the mechanical fan.
Yes Sir, thank you
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Old 16th February 2009, 12:27   #8
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Quote:
Originally Posted by esteem_lover View Post
@anupmathur... the alternator will not load the engine as heavily as the alternator plus the mechanical fan.
Quote:
Originally Posted by headers View Post
Yes sir, I guess we are right

Guys, you need to seriously brush up on the electrical components of the car!

This will help: Just what is an Alternator??

Last edited by anupmathur : 16th February 2009 at 12:29.
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Old 16th February 2009, 12:32   #9
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Quote:
Originally Posted by anupmathur View Post
Guys, you need to seriously brush up on the electrical components of the car!

This will help: Just what is an Alternator??
Sir, rather than reading on the net, why not practically check whether your car runs after removing the battery!

IFF your theory of alternator supplying juice for the car AND charging the battery is true, then the car should run without a battery, else i guess you are mistaken!

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Old 16th February 2009, 12:59   #10
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Quote:
Originally Posted by headers View Post
Sir, rather than reading on the net, why not practically check whether your car runs after removing the battery!
Headers, the only occasion I had to TEST this out was when a friend's Baleno battery got fully discharged due to using the stereo and the blower too long in the parked car.
With no jump start cables, I had to take the battery out from a Zen and plonk it in the Baleno.
The Baleno was started and then the battery was disconnected and put back in the Zen. Did the Baleno engine stop while this was done? No, Sir!

And you do not have to believe my theories. There are many other sources that will tell you the correct answers. One such source I have posted above, but you have obviously not read the article.
With a car running, yes it is the alternator that supplies the electricals.
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Old 16th February 2009, 13:11   #11
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Quote:
Originally Posted by anupmathur View Post
And you do not have to believe my theories. There are many other sources that will tell you the correct answers. One such source I have posted above, but you have obviously not read the article.
With a car running, yes it is the alternator that supplies the electricals.
anupmathur, this could be true of the later cars, but we are discussing the old Gypsy here which will not run if you take out your battery. The battery completes the circuit. Will check this though.
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Old 16th February 2009, 13:15   #12
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Quote:
Originally Posted by esteem_lover View Post
anupmathur, this could be true of the later cars, but we are discussing the old Gypsy here which will not run if you take out your battery. The battery completes the circuit. Will check this though.
The old Gypsy will keep running with the battery disconnected.
Disconnected means you unplug the positive terminal.
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Old 16th February 2009, 14:58   #13
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Quote:
Originally Posted by anupmathur View Post
The old Gypsy will keep running with the battery disconnected.
Disconnected means you unplug the positive terminal.
Well Sir, None of my cars run with the battery positive terminal disconnected!

Thanks for the education though!

Cheers
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Old 16th February 2009, 16:58   #14
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Quote:
Originally Posted by headers View Post
Well Sir, None of my cars run with the battery positive terminal disconnected!
Headers, could you please tell which car/s you have tried this out on?
Is the car fitted with a security system? etc..

May I point out that learning never stops. I would like to keep myself updated.

One thing I can say with confidence: Our normal mid bracket cars keep running with the battery disconnected. ie, positive terminal unplugged.

With some of the more expensive cars there could be elaborate monitoring systems which will not allow operation if any monitored parameter is incorrect. Such cars will go off on the battery terminal being disconnected.

Another point of caution is that, sometimes, in rare cases, the regulator might conk off (due to a voltage surge) upon reconnecting the positive terminal on a running engine! Good practice would be to turn off the engine and then reconnect the terminal.
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Old 16th February 2009, 18:06   #15
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The reason why your car can operate normally even though the battery light is on is because your car can run off the energy stored in the battery. Your car will run fine until the battery goes dead. At that point, nothing in your car will work. When the battery light is on, you can still drive your car to the garage -- you will not damage anything. But you want to get to the garage before the battery fails and your car dies.
@ Anupmathur: Sir, this is from the link you provided. Guess I'm still sure about cars not being able to run with battery positive terminals disconnected!
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