[philipreji]

In one circuit diagram of the alternator I saw, there are four terminals:

1. unregulated output, to charge the battery
2. regulated output, to feed all other loads in the vehicle
3. output to the "charge lamp"
4. Ground

So at least a few alternators available in the market should have a built-in voltage regulator, in addition to the rectifier diodes. Such a configuration makes sense: (a) the battery gets charged from the preferred unregulated output, and (b) there is no need to have regulators built into every other gadget in the vehicle.

Regarding the original question: IMHO, if the mechanical > electrical > mechanical conversion is 0.90 x 0.90 = 0.81 = 81% efficient, then that route can perhaps be more efficient than the direct mechanical coupling route for the cooling fan. Reason: in direct mechanical coupling we need an extra belt (or a serpentine belt) to include the fan. A new belt is fairly tight, so frictional forces will have to be overcome to rotate the fan. On the other hand after ageing there will be belt slippage causing insufficient cooling. Since there are losses in both cases, overall the electrical fan may be a better option in comparison. Possibility of control through a thermostat is just an added advantage. Pl correct me if I am wrong..

[vivekiny2k]

Originally Posted by amitk26

So you say an alternator converts more then 90% of mechanical energy to electrical , very interesting any source or citation for this data ? then why don't they use same technology in larger turbines to give us more efficient power plants.

90% or less, what else do you think they use?

keep in mind that in power plants there are many auxillary functions, cooling, lubrication, pressure management etc.

about cars, I was wrong. car alternators run at about 60%.

Alternator - Wikipedia, the free encyclopedia

otherwise the efficiency of electrical systems is reported between 95-50%. higher for higher power.

I assumed a controlled enviroment like car will be at the higher side of the range. my bad

[headers]

Originally Posted by SS-Traveller

2. Rev for rev, yes, a mechanical fan is more energy efficient than an electrical fan. But the electrical fans switch off when not required, so save energy. So over a period of time electrical fans are more energy efficient.

I seem to remember that some mechanical fans in some cars used to come with an electric clutch to switch it off and let the pulley freewheel without turning the fan. Does such a thing exist still, and any idea of what cars such a system comes in? Members' inputs

Most modern cars have a clutch fan, even if it is electric or mechanical. The reason is to reduce the load on the engine and increase FE.

I will give more detailed explanation later!

Originally Posted by amitk26

As some people are claiming that removing battery will cause something to go bust in alternator so I asked what is that thing and why exactly should it go bust.

As a corollary to above headers mentioned this for petrol and not diesel there is no fundamental design difference in alternators so I asked another question.

Sir, I am not as technically proficient as you are, but have enough years and miles on the odo to justify my claim.

There is no constructional difference between the alternator for diesel and petrol engines, but the basic difference between a SI and a CI engine that made me tell that SI engines will NOT run on alternator output for a long time.

Why cant Mr. theory test it practically for the benefit of others instead of citing a wikipedia link?

[anupmathur]

From the original intent of explaining the basic fact that it is the alternator, and not the battery, that supplies all the electricals in a car, this thread has come a long way!

It seems, to the minds of some, to have become a challenge to run a car without the battery in place! No body is advised to do this.

It is not because 'elements' of the alternator or regulator will or will not get fried. It is simply because that is not a realistic scenario and it is not going to prove anything one way or the other. Most of all, it is not 'Good Practice'!

Originally Posted by amitk26

1. rectifier != Regulator : A regulated power supply is something which gives DC without ripples a 3 Phase rectifier gives output with ripples.

You seem to be looking for a regulated power supply. That is not the meaning of the term 'regulator' as used for an alternator. This regulator controls the field excitation voltage. And this is just full wave rectified AC, with ripple.
All the electronics in a car have their own regulation circuits built in, if such is required by them. That includes means to suppress surges and spikes.

Originally Posted by amitk26

....based on my background and practical experience of driving a car once with out battery I can safely say , Nothing will go wrong.

You have tried it out and it worked.
This ought to be sufficient to convince our doubting Thomas here that it does indeed work and that no mysterious 'elements' get fried to a crisp!

However, there is a little more to this: It is not necessary that a failure of some component will never occur. At times, yes, only at times, this can cause unexpected and expensive failures of one or more of the electrical/electronic systems in a car, particularly while connecting/disconnecting the battery terminals, because of a severe voltage spike that might get produced.

Originally Posted by headers

Most modern cars have a clutch fan, even if it is electric or mechanical. The reason is to reduce the load on the engine and increase FE.

Which modern car has a clutch operated electric fan?
Also, kindly note that both the objectives you mention cannot be applicable. The load on the engine WILL increase when the electric fan runs, but over the longer term, yes, the FE will improve due to the much lower working-time of the electric fan.
However, compared to a clutch or fluid coupling operated belt driven fan, the electric will invariably be at a disadvantage!

Originally Posted by headers

Sir, I am not as technically proficient as you are,

Err.. well.. it has been kinda becoming a trifle obvious!

Originally Posted by headers

There is no constructional difference between the alternator for diesel and petrol engines, but the basic difference between a SI and a CI engine that made me tell that SI engines will NOT run on alternator output for a long time.

Good example to substantiate the above point!

Originally Posted by headers

Why cant Mr. theory test it practically for the benefit of others instead of citing a wikipedia link?

Because Mr. Theory is not the least interested in proving anything about this inane subject to anyone. In fact, if I may presume that I am the reference, may I repeat: Who, of sane mind, plans to make a trip anywhere without a working battery?

And what makes you so skeptical about Wikipedia? For a man who, of his own admission, is not very proficient in this area, it is amusing that he be questioning the veracity of such a source. While I grant that Wiki is not the most authoritative source, it generally presents a wealth of knowledge most of us do not possess. Further verification/validation can be done through other sources, if in doubt.

[SS-Traveller]

Originally Posted by DerAlte

Your neighborhood battery-wallah has achieved what possibly no one else has achieved. All the best, your battery is in good hands.

Naah, my batterywallah didn't do it - someone not reading this thread did. But my battery certainly is in good hands - my own. As I mentioned in an earlier post, I'll personally brain someone fiddling with my car's electrics improperly...

[anupmathur]

Originally Posted by SS-Traveller

As I mentioned in an earlier post, I'll personally brain someone fiddling with my car's electrics improperly...

SS, I too have a thing about the electricals of my car!
I have NEVER left my car out of sight when any work is being done on the electricals! Heck, even otherwise!
I even had my security system and stereo etc.. fitted at home under full supervision!

Often, I supply hardware and dress from my stock - things like wire tap-offs, splicers and joiners, lugs and eyes etc... if required. I do not let normal Bohr's electrical insulation tape to be used. I supply rubber self-bonding tape.

[headers]

Originally Posted by anupmathur

I have NEVER left my car out of sight when any work is being done on the electricals! Heck, even otherwise!
I even had my security system and stereo etc.. fitted at home under full supervision!

Its shows sir, from your posts that you are THE MAN for all things electric! - Thank you for making me respond.

It aint gonna work henceforth!

[isldhn]

@Anup Mathur.
Sir,
My Santro has been giving me starting problems since last 6 months now. I have already changed to a new battery(amaron) and have also got the self motor serviced. The alternator works fine as I have jumpstarted my car and then removed the battery terminal and have checked with the headlight's on. Today a mechanic took out my battery and said that it needed full charging as it has not been charged fully(1200 amp or what). Actually me car just goes from home to my Dad's office which is just around 9-10 Km's and back. So the mechanic said that your battery has never been charged fully. But there is no low battery light coming on in the dash. Is the mechanic telling me the truth about the battery low charge or is there any other problem. Could you please throw some light on the above matter. Thank you in advance.

[anupmathur]

Originally Posted by headers

Thank you for making me respond.

It aint gonna work henceforth!

My dear friend, I responded only because I had been prodded to do so!
You might have noted that I am not terribly 'active' here anymore!
As I said, I am not quite the one for slanging matches!
Yours Truly, Mr. Theory. !!?





@:isldhn, your mechanic could be right!
An alternator can be at an impaired level of functioning. It might still be able to manage the loads like headlights etc.. but that does not mean it is working as designed/intended.

Assuming that your car's battery is new and that the connection cables and connectors are in optimal condition and that belts are not slipping, a simple voltage check can reveal whether the alternator is working fine.

With the engine at the designed idle rpm, measure the voltage at the battery terminals. It should be definitely higher than 13.4 volts and should not be higher than 14.5 volts.
No other loads should be on at this time.

Then, as a second step, turn on your headlamps and stereo etc.. and ask someone to rev the engine to about 2500 rpm. The voltage should again show between 13.4 and 14.5.
If it has dropped to lower than 13 volts, you can be sure the alternator is not working fine.

By the way, the voltage measurements at the battery terminals and at the alternator output terminals should show the same readings, plus or minus 0.2 volts.

[isldhn]

@Anup Mathur.
Thank you sir for such a prompt reply. Repeating my question again, will the lights on the dash go on if the battery is not fully charged,coz mine does not. And further this problem occurs occasionally. Whenever it does I have to call a mechanic with a spare battery and get the car jumpstarted. Most of the times the car starts fine. Can this be due to a faulty start (or self) motor. Will definitely check the voltage of the alternator as you said.

[anupmathur]

Originally Posted by isldhn

Repeating my question again, will the lights on the dash go on if the battery is not fully charged,coz mine does not.

I suppose you mean the ignition light on the dash does not go on after the car is started?
It need not go on. That ignition light works on the voltage differential across it. If the alternator develops 12.2 volts and the battery voltage is 12 volts, the ignition light will stay off, even though both the voltages are lower than they should be.

[scooby05]

Originally Posted by star_aqua

SL500 is a 24v system.

SL500 is NOT a 24 volt sytem. Its a standard 12 volt.

[dustom_99]

although the engine running has nothing to do with alternator or battery,it just needs some current at high voltages for the spark and some other tits bits like fuel pump etc,mordern cars with ecu just wont let the vehicle start until they have a stable (12.2v) in them,old cars can start and run without battery provided alternator field is energised with its own output+initial 12v current to get up and excite itself+ open circuit or no load voltage should not be lower then 12.2 volts.

usually when battery is disconected and the altornator has no load condition,it produces very minimal current that too AC,which gets spiked out and filtered.
which further reduces both voltage and current ,this low voltage current is just not good enough to keep the feild in excited state hence altornator's output is further reduced,finally leading to engine shutdown.

and for belt driven fans.they were jst not good in condition when vehicle was on heavy load on low rpm.like hill climb in tall gear.(drivers are ignorant to let there vehicle perform in taller gear even when rpm gets nearly till idle,subjecting there vehicle to wide open throttle periods,just because there vehicle can produce just enough torque,however not realising that belt driven fan will let the cooling system down,which would have needed max efficiency ijn wide open throttle conditions.


hence the electrical system,thermocouple-sense the temp-work on full balast to cool the engine coolant-go back to sleep until further orders. not load or rpm dependent