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Old 21st February 2009, 15:36   #196
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Originally Posted by amitk26 View Post
I posted detailed explanation on why battery has no role to play in rectifier going bust. There is a Baleno circuit diagram which does not show any regulator. Can you please look at the alternator of you petrol car first and find if there is anything which can be called regulator ?
Amit, the regulator is built into the alternator. It performs 2 functions 1) regulates the field current in the rotor windings which in turn determines the voltage/current induced in the stator coils. 2) It rectifies the 3 phase AC from the stator windings (3, each placed 120 deg apart), i.e converts AC to DC and supplies it to the battery and the rest of the car's electrical circuits.

P.S. - Modern cars have regulator/rectifier built into 1 unit, this unit is a part of the alt.

Rgds,

R2D2

Last edited by R2D2 : 21st February 2009 at 15:51.
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Old 21st February 2009, 16:25   #197
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Originally Posted by headers View Post
Old School diesel vehicle, can run indefinitely with the battery removed.
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Originally Posted by amitk26 View Post
By the way you belive that alternator in only petrol car would go bust ? What is difference between alternator of petrol and diesel car ?
This is an answer I'd really like to hear!
I currently believe that there is no significant difference in the alternators other than to ensure that the ones for diesels can give full output at lower rpms.
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Old 21st February 2009, 17:18   #198
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Originally Posted by anupmathur View Post
no significant difference in the alternators other than to ensure that the ones for diesels can give full output at lower rpms.
True. Diesel engine alternators are generally more powerful (output Amps) and give off those Amps at lower RPMs when you compare petrol and diesel engines CC for CC.

The reason is diesels, given their much high compression ratios, take 2-4 times more power to start compared to petrol motors. This means a larger drain on the battery which in turn means the requirement of a significantly larger battery which needs its charge restored faster for longer life.

Rgds,
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Old 21st February 2009, 17:29   #199
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Originally Posted by R2D2 View Post
True. Diesel engine alternators are generally more powerful (output Amps) and give off those Amps at lower RPMs when you compare petrol and diesel engines CC for CC.

The reason is diesels, given their much high compression ratios, take 2-4 times more power to start compared to petrol motors. This means a larger drain on the battery which in turn means the requirement of a significantly larger battery which needs its charge restored faster for longer life.
Thanks R2D2.
I think these are marginal differences dictated by the conditions under which the alternator must serve.

I'm more keen to know what prevents 'old school diesel vehicle alternators' from ending up with burnt elements on indefinitely long runs, with the battery disconnected!
In that sense, how are they different from the alternators used in petrol engined cars?

Last edited by anupmathur : 21st February 2009 at 17:40.
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Old 21st February 2009, 17:40   #200
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Originally Posted by anupmathur View Post
Thanks R2D2.
I think these are marginal differences dictated by the conditions under which the alternator must serve.

I'm more keen to know what prevents 'old school diesel vehicle alternators' from ending up with burnt elements on indefinitely long runs!
In that sense, how are they different from the alternators used in petrol engined cars?
Well, to be honest, I've never had an opportunity to drive a vehicle with no battery in it. For one, I am too lazy to push start the thing.
So from practical experience I really dont know.

From what workshop manuals and other reading tell me, driving with no battery is not a good idea. I am not about to experiment and risk my car's electricals, ECU and ICE.

Rgds,
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Old 21st February 2009, 17:42   #201
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Originally Posted by R2D2 View Post
Well, to be honest, I've never had an opportunity to drive a vehicle with no battery in it. For one, I am too lazy to push start the thing.
So from practical experience I really dont know.

From what workshop manuals and other reading tell me, driving with no battery is not a good idea. I am not about to experiment and risk my car's electricals, ECU and ICE.
LOL, ditto here!
As I had posted earlier, I have no intention of making any kind of trip without all stock components of my car being in good order!

We'll just have to wait for headers to tell us about this.

Last edited by anupmathur : 21st February 2009 at 17:44.
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Old 21st February 2009, 17:50   #202
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We'll just have to wait for headers to tell us about this.
HI,

well for one, i dont want to disappoint anybody here by not agreeing to your views.

Its just that, i HAVE run the old diesel Amby without battery [remove battery after startup] as the battery has no role in a compression ignition engine.

Its not the same in a Spark Ignition engine and you guys are not going to agree, so I rest my case!

Cheers
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Old 21st February 2009, 17:50   #203
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Originally Posted by R2D2 View Post
True. Diesel engine alternators are generally more powerful (output Amps) {TRUE} and give off those Amps at lower RPMs when you compare petrol and diesel engines CC for CC.
The Amp rating of an alt fitted to a diesel vehicle may be higher, but giving off those amps at lower RPM? when compared cc for cc? I'm not sure what you mean - the same alt that comes on a diesel, if installed on a petrol will have less amp output for a given rpm?


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Originally Posted by anupmathur View Post
what prevents 'old school diesel vehicle alternators' from ending up with burnt elements ... how are they different from the alternators used in petrol engined cars?
+1 there.

Never heard of any difference between alts installed in diesel or petrol vehicles. Ok, diesel vehicle alts have a higher amp rating (say 80A) as well as a higher batt rating (say 70Ah) than the same vehicle with a petrol engine (say, 60A alt and 55Ah batt). But the alts are not constructionally any different so as to produce higher amps at lower rpm...
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Old 21st February 2009, 18:00   #204
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Originally Posted by SS-Traveller View Post
But the alts are not constructionally any different so as to produce higher amps at lower rpm...
At what rpm will an alternator be able to deliver rated output?
If it is something as low as 2000 rpm, it really would not matter. Can it?


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Originally Posted by headers View Post
Its not the same in a Spark Ignition engine and you guys are not going to agree, so I rest my case!
Gosh, headers, at least give it a try.
How are the alternators different?

Last edited by anupmathur : 21st February 2009 at 18:02.
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Old 21st February 2009, 18:11   #205
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Originally Posted by R2D2 View Post
Well, to be honest, I've never had an opportunity to drive a vehicle with no battery in it. For one, I am too lazy to push start the thing.
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Originally Posted by anupmathur View Post
...no intention of making any kind of trip without all stock components of my car being in good order!
Quote:
Originally Posted by headers View Post
i HAVE run the old diesel Amby without battery [remove battery after startup] as the battery has no role in a compression ignition engine.

Its not the same in a Spark Ignition engine and you guys are not going to agree, so I rest my case!
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.

EDIT: And finally to answer Anup's question, yes, ALL alts can give 90%, if not 99%, of their rated output at @3000 rpm (i.e. rpm of the alt pulley). A lower rpm engine will have a smaller alt pulley to increase the rpm of the alt, vs. a higher rpm engine. So the same alt can produce the same current in a 500rpm engine too, so long as the pulley ratio (engine main to alt) allows the alt to spin at 3000 rpm or more.

Last edited by SS-Traveller : 21st February 2009 at 18:15.
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Old 21st February 2009, 18:23   #206
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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.
Absolutely. With no current in the field windings, there's no output at the stator. But then this does not apply to a car with a dynamo. So if at all someone drives a car without a battery (engine off condition)it would probably have to be one of the premier padmini, Standard Herald, Amby generation cars.

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. But then there are some owners who are adventurous and will be willing to try.
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Old 21st February 2009, 18:35   #207
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[quote=SS-Traveller;1182312]The Amp rating of an alt fitted to a diesel vehicle may be higher, but giving off those amps at lower RPM? when compared cc for cc? I'm not sure what you mean - the same alt that comes on a diesel, if installed on a petrol will have less amp output for a given rpm? [quote]

What I meant when compared with a 2L petrol, a 2L diesel will have a more powerful alternator (max output Amps) and produce a significant portion of that at lower rpms. This is ofcourse a rule of the thumb there may be variations but this is what I have noticed.

For example, a Corolla with a 1.8L engine has a 35A battery, the Corolla Altis 1.8L has a 45A battery and a 1.9L diesel Octavia has a 70A/74A (DIN74)battery. The alts are sized accordingly

Rgds,


Rgds

Last edited by R2D2 : 21st February 2009 at 18:38.
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Old 21st February 2009, 19:07   #208
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But then there are some owners who are adventurous and will be willing to try.
I seriously doubt anyone here is planning to try these stunts!
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Who, of sane mind, plans to do a trip anywhere without a working battery, may I ask?
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Old 21st February 2009, 19:44   #209
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Originally Posted by anupmathur View Post
Who, of sane mind, plans to do a trip anywhere without a working battery, may I ask?
This one sentence represents the views of almost all members on TBHP. Amen to that!

Rgds,
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Old 21st February 2009, 20:27   #210
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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!
So let's call it a day!

But one thing that I'd like to clarify to headers:

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Originally Posted by headers View Post
Its just that, i HAVE run the old diesel Amby without battery [remove battery after startup] as the battery has no role in a compression ignition engine.
That old Amby's alternator survived because it was not an alternator at all! It was a dynamo! Right?

Last edited by anupmathur : 21st February 2009 at 20:28.
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