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Old 21st February 2009, 20:27   #211
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Exclamation Battery dependency,,we are stumbling over entire "Electricals"

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Originally Posted by SS-Traveller View Post
As far as my understanding of the working of an alternator goes, you CANNOT get current from the alt without initially providing it some excitation current (to the rotor) - after which, it is a closed cycle in which the alt produces current, which feeds the rotor, which produces current etc. So, without a batt in place, push-starting a petrol car won't work at all.

But the old Amby diesel, with no electricals in its rotary pump, WILL push-start without batt in place if you provide enough pre-heat to the cyls by some other means than the glowplugs - like letting the engine "sniff" a flame through the intake manifold, as used to be done by taxi drivers.

But again, both modern petrols and diesels will continue to work for some time if battery-started and then removing the batt - till the electronics behind the alt are nicely toasted to a crisp... following which the rest of the electronics in the car will soon need a decent burial.



Thanks to Many Team-BHPians for shedding light on Battery/Alternator dependency on "running" a car

SS-Traveller kudos to ur Knowledge on such matters inspite of being From MEDICAL background

I had a chance of driving my Bike without Battery for Few days
I also observed that

1. Regulator is not performing well ( Head & Tail lamps get Excessive voltage MOMENTARILY on Revving up engine) instead of smoothing out the Voltage supply to Bulbs

2. Filament of Head lamp which I used more got blackened (due to current surges)

3. The Regulator & Ignition electronics survived in my case


While trying to answer Battery dependency we are stumbling over entire Electrical( read Electronics) aspects which is a Vast in nature. For example Suzuki Zen has electrical Fuel pump, Hyundai i-10 has Electronic Power steering,supply to ABS servos and Ultimately the Programming & Architecture of ECS of ur Car model which Holds the Ultimate "Key" whether u can drive "Your" car after removing Battery for XYZ reason

I will recollect some good advices as suggested by some of You to be kept in mind while driving without battery

1. Don't risk driving without battery. Shud it get discharged call a battery Vendor & first get it Charged if U are staying in a Urban locality

2. Ask Experienced mechanic whether You can (shud) drive ur vehicle without battery & For How many Kms ( or time Duration) you can do so

Last edited by khan_sultan : 22nd February 2009 at 11:00.
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Old 21st February 2009, 20:31   #212
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Originally Posted by anupmathur View Post
Gosh, headers, at least give it a try.
Try what sir?

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Originally Posted by SS-Traveller View Post
As far as my understanding of the working of an alternator goes, you CANNOT get current from the alt without initially providing it some excitation current (to the rotor) - after which, it is a closed cycle in which the alt produces current, which feeds the rotor, which produces current etc. So, without a batt in place, push-starting a petrol car won't work at all.


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Originally Posted by R2D2 View Post
One of the ways to get a modern car run without a batt is to start it using a battery and then disconnect the terminal wires. Once the alt is producing an output, a part of it will be used to keep the field windings energised. I do not believe that this is advisable as you rightly pointed out the alt and its regulator will be toast as will the rest of the electricals in the car.



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I seriously doubt anyone here is planning to try these stunts!
what stunts ?? driving a car without a battery?


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Originally Posted by R2D2 View Post
This one sentence represents the views of almost all members on TBHP. Amen to that!

Rgds,
??
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Old 21st February 2009, 21:47   #213
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what stunts ?? driving a car without a battery?
Exactly! Or are you planning to try?
To let you into a secret, I never did and do not in future intend to drive a car without a battery! ..................... ???
Is my earlier post about the battery swap in the Baleno so difficult to understand? It was approaching midnight, we were far far away from home, and we had no options.

And when it comes to electric fan vs engine driven mechanical fan, I maintain what I said earlier! The electric will not magically 'release' a few more horses in your old Gypsy!
Now, if you were to drive in very cold areas, like ambient temp 12 Celsius or below, yes you'll gain because the electric fan will quite possibly not need to cut in at all, whereas the engine driven one would still consume power!

Cheers!
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Old 22nd February 2009, 00:26   #214
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Originally Posted by Lightning2 View Post
I will recollect some good advices as suggested by some of You to be kept in mind while driving without battery

1. Don't risk driving without battery. Shud it get discharged call a battery Vendor & first get it Charged if U are staying in a Urban locality

2. Ask Experienced mechanic whether You can (shud) drive ur vehicle without battery & For How many Kms ( or time Duration) you can do so
Just wanted to add an important point here - The alternator is designed to maintain a fully charged battery and not charge a dead battery. If you have a dead battery, it's best to take it out of the car and have it charged using a bench charger.

Rgds,
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Old 22nd February 2009, 07:28   #215
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Originally Posted by anupmathur View Post
To let you into a secret, I never did and do not in future intend to drive a car without a battery! ..................... ???

And when it comes to electric fan vs engine driven mechanical fan, I maintain what I said earlier! The electric will not magically 'release' a few more horses in your old Gypsy!
Now, if you were to drive in very cold areas, like ambient temp 12 Celsius or below, yes you'll gain because the electric fan will quite possibly not need to cut in at all, whereas the engine driven one would still consume power!
Thanks for your advice sir! I guess we are at different levels altogether!
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Old 22nd February 2009, 08:30   #216
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Thanks for your advice sir! I guess we are at different levels altogether!
You're welcome, headers!
Different levels, LOL! I like that.

Unfortunately, one of us has to be wrong about this electric-fan vs engine-driven fan thing!
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Old 22nd February 2009, 15:32   #217
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The alternator is designed to maintain a fully charged battery and not charge a dead battery. If you have a dead battery, it's best to take it out of the car and have it charged using a bench charger.
True to an extent. A good battery which has just been drained by using it, can be restored to full charge once or twice by using an alt. A bad batt with a dead cell, for example, is best removed and replaced before the alt actually manages to explode it.

The reason for that is: When a good batt is discharged, the alt will charge it at the max rate it can - let's say, a 70A alt will deliver practically 70A when driving in the daytime to a 55Ah batt. Doing it for a few minutes builds up the voltage in the batt, and the alt reduces the current thereafter. But a bad batt with one cell damaged doesn't build up the voltage, so gets a constant 70A dosage delivered to it - the alt does not cut out. Result: Boiling electrolyte, warped plates, and high risk of exploding batt.

If you suspect your batt went dead because of a dead cell, it's safer to bench-charge it. If you just bought a new batt and it was only slightly charged at the dealers', let your alt do the rest and bring it to full charge.

Quote:
Originally Posted by anupmathur View Post
You're welcome, headers!
Different levels, LOL! I like that.

Unfortunately, one of us has to be wrong about this electric-fan vs engine-driven fan thing!
The root of the argument was that: electric fan vs. mechanical pulley-driven fan. For an alt to generate 5A to run an electric fan, there's less load on the engine (but not a free lunch), than a mechanical fan with its pulley, belt and air drag. That was, is, and always will be, TRUE, whether anyone accepts it or not. Reason: Electric fans are more ENERGY EFFICIENT than mechanical fans.

And finally, as to running cars without batteries in place, my take on that is: since the time I'd converted my old Amby to alt from dynamo in 1984, I would personally brain any mechanic/electrician who so much as loosened the wires from the batt terminals when the engine's running, on any of my cars. Forget running them for "a few minutes".

Your cars? I don't care. Good for you if you've still got a dynamo...

Last edited by SS-Traveller : 22nd February 2009 at 15:36.
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Old 22nd February 2009, 17:04   #218
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Originally Posted by SS-Traveller View Post
The root of the argument was that: electric fan vs. mechanical pulley-driven fan. For an alt to generate 5A to run an electric fan, there's less load on the engine (but not a free lunch), than a mechanical fan with its pulley, belt and air drag. That was, is, and always will be, TRUE, whether anyone accepts it or not. Reason: Electric fans are more ENERGY EFFICIENT than mechanical fans.
And this is what I believe:
Electric fans are nowhere near as efficient as mechanical fans at moving the same amount of air since you have to convert mechanical to electrical then back to mechanical energy, and that has losses.

The gain with electric fans is only when they are OFF! And they might well be off for significant durations, depending on the driving conditions and ambient temperature.
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Old 22nd February 2009, 17:23   #219
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The gain with electric fans is only when they are OFF! And they might well be off for significant durations, depending on the driving conditions and ambient temperature.
Agreed. Therefore, on a long drive in pleasant weather, the ram effect of the air flowing through the radiator means the electric fan does not switch on for hours on end - so it's a whole lot more energy efficient. So all car manufacturers chucked belt-driven mechanical fans for the electric fan.

Last edited by SS-Traveller : 22nd February 2009 at 17:24.
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Old 22nd February 2009, 17:49   #220
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.... the electric fan does not switch on for hours on end - so it's a whole lot more energy efficient. So all car manufacturers chucked belt-driven mechanical fans for the electric fan.
Again I would beg to differ!

Energy efficiency is defined as the ratio between the energy at output to the energy consumed at input.
This ratio is worse for electric fans compared to belt driven fans, for the same amount of air to be moved at the same velocity.
The power taken from the engine to move an equal mass of air at same velocity is larger for an electric fan, due to conversion losses and the fact that alternators themselves do not work at 100% efficiency. I would not call that more energy efficient!

Over extended durations, the total energy consumed by a belt driven fan is larger because it is always running, whether required or not! That is probably why makers have shifted to electric fans.
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Old 22nd February 2009, 17:55   #221
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@ Anup: You missed the smiley!...
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Old 22nd February 2009, 18:22   #222
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Originally Posted by SS-Traveller View Post
... it's a whole lot more energy efficient. So all car manufacturers chucked belt-driven mechanical fans for the electric fan.
Could it be possible that the reason is something totally different? Like: how does one 'belt-drive' - with a transversely mounted engine - a fan whose axis is 90deg to the engine?
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Originally Posted by SS-Traveller View Post
... A bad batt with a dead cell, for example, is best removed and replaced...
Very true - that cell will never hold charge again.
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Originally Posted by SS-Traveller View Post
before the alt actually manages to explode it.
How?
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Originally Posted by SS-Traveller View Post
... a 70A alt will deliver practically 70A when driving in the daytime to a 55Ah batt. ...
An alternator current capacity is the maximum current that is recommended it is loaded for. It will deliver ONLY what the load is drawing. It CAN deliver more, however in conditions where the heat generated in its coils far exceeds the heat taken away - the insulation goes up in a puff of smoke.

And 55Ah is a discharge rating, not a 'current drawn' rating of a battery
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Originally Posted by SS-Traveller View Post
... so gets a constant 70A dosage delivered to it - the alt does not cut out. Result: Boiling electrolyte, warped plates, and high risk of exploding batt. ...
The constant '70A' is a myth: as and when the voltage of the battery increases, the current drawn by it reduces (please draw an electrical schematic and do the maths).

However, the real problem is heat produced (the chemical reaction due to charging is exothermic). If the charging is not controlled, the plate coating tends to fall off at higher temperatures. Ergo - cell failure. And no, the chemical reaction neither converts Lead Sulphate into an explosive, nor does it take the electrolyte to boiling point.
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... If you suspect your batt went dead because of a dead cell, it's safer to bench-charge it.
You can charge it till the cows come home, but a dead cell does not hold charge any more - the damage is irreverseable
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Originally Posted by SS-Traveller View Post
... For an alt to generate 5A to run an electric fan, there's less load on the engine (but not a free lunch), than a mechanical fan with its pulley, belt and air drag. That was, is, and always will be, TRUE, whether anyone accepts it or not. Reason: Electric fans are more ENERGY EFFICIENT than mechanical fans. ...
Simple maths: the energy needed to move air has to be supplied by the engine in either case. As Mathur-sab explained, it is when you are converting energy mech -> electrical -> mech that some energy is lost to heat, hence using electrical fans is a compromise solution where you are actually losing energy.
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Originally Posted by SS-Traveller View Post
... my old Amby to alt from dynamo in 1984 ...
Errr... what is the difference between dynamo and alternator (as far as the loads are concerned)?

Last edited by DerAlte : 22nd February 2009 at 19:02.
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Old 22nd February 2009, 19:33   #223
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@ Anup: You missed the smiley!...
LOL, I don't think I missed it! I second guessed it!
I suspect it was put there as an 'escape hatch'!

@DerAlte: Thanks for your lucid and logical comments.
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Old 22nd February 2009, 19:57   #224
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Originally Posted by SS-Traveller View Post
If you suspect your batt went dead because of a dead cell, it's safer to bench-charge it. If you just bought a new batt and it was only slightly charged at the dealers', let your alt do the rest and bring it to full charge.
If the battery state is at a more than a 80% Depth of Discharge (i.e. <20% State of Charge) I'd prefer using a bench charger. Alts are designed primarily to maintain a battery in optimal state of charge given normal loads on a battery which includes starting the motor. Heavily discharged batteries put an unnecessary load on the alt and in turn your engine. Also, it is easier to monitor battery status including sp. gr. when its attached to a bench charger.

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I would personally brain any mechanic/electrician who so much as loosened the wires from the batt terminals when the engine's running, on any of my cars. Forget running them for "a few minutes".
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Old 22nd February 2009, 19:59   #225
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Could it be possible that the reason is something totally different? Like: how does one 'belt-drive' - with a transversely mounted engine - a fan whose axis is 90deg to the engine?
Absolutely. Touche!
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