Go Back   Team-BHP > Under the Hood > Technical Stuff


Reply
 
LinkBack Thread Tools Search this Thread
Old 18th February 2009, 17:39   #106
Senior - BHPian
 
esteem_lover's Avatar
 
Join Date: Jul 2006
Location: Madras/Py
Posts: 7,550
Thanked: 405 Times
Default

Quote:
Originally Posted by gigy View Post
everyone has posted about failed battery, i have experienced failed alternator. the headlights were going dim, then no horn, display lights went dim, switched of ac and headlights managed to reach a safe place as it was night. let the alternator cool down. after a hour with minumum electrical load reached home. next day the electrician told me its a failed rectifier unit. car was started and less than a minute the alternator was boiling hot.
To generalize it if battery failed you can continue, don't shut engine, keep only stock load on,switching of AC is recommended.
If alternator failed stop as soon as possible in a safe place else the car is going to stop till the battery gives way.
If its a exotic and luxury one which can sense the ripple disturbance in DC line and sense dead battery, you anyway don't have a option, it will decide to shut down.
My alternator failed 2 months back. The first indication was the battery light in the instrument panel, but the battery was not losing charge in a hurry, so kept using the car for a few days & then checked with the electrician who said that the alternator has gone kaput and now the battery is also weak. Mind you I never had to push start the car (thanks to ding dong). But after a few days, the horn & headlights started to fade, but the battery still had enough juice to start. Before everything came to a standstill, I replaced the alternator.
esteem_lover is offline   Reply With Quote

Old 18th February 2009, 17:41   #107
Senior - BHPian
 
Join Date: Jul 2008
Location: Bangalore
Posts: 1,902
Thanked: 294 Times
Infractions: 0/1 (5)
Default

Quote:
Originally Posted by Samir Taheer View Post
Thanks Amit, I understand what your saying - The Argument on here earlier is that the Battery plays no role in powering Electricals/Electronics and its all provided by the alternator - hence why do we need 2 batteries or bigger capacity batteries and not just allow the alternator to play its role?
Samir I responded for the same question agin in concise words

You need 2 batteries or a single bigger battery to provide more peak current for a short time when the total load is high enough to cause voltage drop below 14 Volts ( or whatever is alternator rating).

One Example of this peak load is activating a lift kit in your example high end SUV which can cause big load for few seconds and alternator voltage may drop to 12 V for those seconds and current will be drawn from battries.
When this lift kit is not activated the batteries will keep on charging from 14 V across the alternator.
Another instance can be a Spike from amplifier in Zen example the RMS current from amplifier is low but peak currents are high which necessitates a bigger battery or 2 battery in parallel

Let me repeat again as long as Battery ( 1,2 or whatever number) and alternator are connected in parallel current will always be drawn from higher voltage source this is basic law of physics.
amitk26 is online now   Reply With Quote
Old 18th February 2009, 17:47   #108
Senior - BHPian
 
Join Date: Jul 2008
Location: Bangalore
Posts: 1,902
Thanked: 294 Times
Infractions: 0/1 (5)
Default

Quote:
Originally Posted by gigy View Post
If you look at the specification of engine in those SVU with two batteries you will see most of them are powerful than our local trucks. diesel engine is based on compression ignition, so the starter has to be real powerful. to reduce heavy current the voltage is doubled.
A more normal method to achieve higher compression is better gearing ratio then a starter moter drawing double the current.

Can the owners of these 2 stock battery Luxury SUV or Merc. please open up hood of their car and post rating of their alternators or measure the voltage using a multimeter and post it here to clear confusion ?

You can then pick up the relevant possibility from my post below for a logical explanation, I am kinda discounting 24 Volt system theory as it looks like a bad system design to me for reasons i posted below.

Last edited by amitk26 : 18th February 2009 at 17:50.
amitk26 is online now   Reply With Quote
Old 18th February 2009, 17:48   #109
Senior - BHPian
 
Join Date: Sep 2007
Location: New Delhi
Posts: 2,984
Thanked: 95 Times
Default

Guys, I'm finding it amusing that there is talk of making this generic thread vehicle specific!

It started out by simply clearing some 'fundas' for people, to let them know that it is only the starting that is done by the battery. After that, just about everything that needs electric power is fed by the alternator.

To bring in all kinds of retrofit equipment and ICE into the equation to complicate the issue, to talk about how many kms or hours a car will run without a battery!!

Who, of sane mind, plans to do a trip anywhere without a working battery, may I ask?

I think the thread has served its purpose and we should stick to genuine doubts or practical questions, rather than levitating this to a new level of mockery.
anupmathur is offline   Reply With Quote
Old 18th February 2009, 18:19   #110
Distinguished - BHPian
 
supremeBaleno's Avatar
 
Join Date: Dec 2005
Location: Weekdays@Chennai, Weekends@Kerala
Posts: 4,871
Thanked: 1,031 Times
Default

Am I glad I chanced upon this thread - completely overturned what I assumed were facts.

Like some others here, before seeing this thread, my understanding was :
1) If a car is started and battery is disconnected, engine would die. Because my assumption was that not only does battery provide juice for initial start, but also provides juice for keeping it running. Guess am proved wrong.

2) In case of a car with a dead battery, my assumption was the battery needed to be present & connected, even though fully dead, for the car to start via push-starting. Sounds like it is not really a necessary.

3) My assumption was that the alternator's sole purpose in life was charging the battery and all the power requirements of the car were taken care of by the battery, in which process it would lose its charge, which the alternator would replenish. Again proved wrong.

Stand corrected on quite some battery stuff. Ofcourse I don't really plan to run the engine and disconnect the battery and check if engine still runs. Neither do I plan to remove battery and try a push-start. But guess its good to know these things.

Last edited by supremeBaleno : 18th February 2009 at 18:21.
supremeBaleno is offline   Reply With Quote
Old 18th February 2009, 19:54   #111
Senior - BHPian
 
Join Date: Sep 2007
Location: New Delhi
Posts: 2,984
Thanked: 95 Times
Default

Quote:
Originally Posted by supremeBaleno View Post
Am I glad I chanced upon this thread - completely overturned what I assumed were facts.
Ofcourse I don't really plan to run the engine and disconnect the battery and check if engine still runs. Neither do I plan to remove battery and try a push-start. But guess its good to know these things.
SupremeBaleno, my example earlier in the thread is a Baleno which ran without the battery in place!
Ran, as in the engine did not die on the battery being removed altogether, for about five minutes.

You never know when such knowledge might come in handy. While you are not really being encouraged to try any of this upon a fine day in your daily life, perchance, upon that one unusual night far away from home, shop and city, when things don't work out right, this information could prove very useful!
anupmathur is offline   Reply With Quote
Old 18th February 2009, 20:11   #112
Senior - BHPian
 
headers's Avatar
 
Join Date: May 2006
Location: Greater Chennai
Posts: 4,524
Thanked: 405 Times
Default

Quote:
Originally Posted by anupmathur View Post
SupremeBaleno, my example earlier in the thread is a Baleno which ran without the battery in place!
Ran, as in the engine did not die on the battery being removed altogether, for about five minutes.
Sir, 5 minutes is easy. Can the baleno run without battery for say 20 kms or so? Then I could appreciate and thank you for educating me!
headers is offline   Reply With Quote
Old 18th February 2009, 20:19   #113
Distinguished - BHPian
 
supremeBaleno's Avatar
 
Join Date: Dec 2005
Location: Weekdays@Chennai, Weekends@Kerala
Posts: 4,871
Thanked: 1,031 Times
Default

Hey Vikram, I am not sure I understood the difference between engine running 5mins or 20kms. My thinking was the moment you remove the battery, engine dies. But that does not seem to be the case. So, if engine runs for 5mins even after removing battery, why do you feel that it won't run for more duration ?

BTW, is there any damage to the car, if we unplug battery while engine is running and run car like that for say a few kms ? Or is it that we need to take care only while reconnecting the battery ie. we need to switch off the engine and ONLY then do the reconnection ? I am getting tempted to try this.

Last edited by supremeBaleno : 18th February 2009 at 20:20.
supremeBaleno is offline   Reply With Quote
Old 18th February 2009, 20:38   #114
Senior - BHPian
 
DirtyDan's Avatar
 
Join Date: Jul 2007
Location: Dharamsala
Posts: 1,680
Thanked: 562 Times
Default

I am coming in in the middle of this thread and I do not have time to read the whole thing so excuse me if I ness up.

Diesels often have 2 batteries OEM for easier starts particularly in cold weather on larger motors such as the merc. One battery may be enough to turn the motor over slowly but not fast enough to start the "heat cycle" that is the ignition system of a diesel. I found this out the hard way a couple times when one of my 2 batteries died. The single remaining battery would not crank the motor fast eough to catch. Also both of my batteries died once. A single battery jump attempt from another vehicle also failed to crank the motor hard enough to catch.

The only reason I can think of on a petrol is that there was not enough room for one big battery but enough room for 2 smaller ones. Its a guess.
DirtyDan is online now   Reply With Quote
Old 18th February 2009, 21:29   #115
Senior - BHPian
 
Join Date: Sep 2007
Location: New Delhi
Posts: 2,984
Thanked: 95 Times
Default

Quote:
Originally Posted by supremeBaleno View Post
BTW, is there any damage to the car, if we unplug battery while engine is running and run car like that for say a few kms ? Or is it that we need to take care only while reconnecting the battery ie. we need to switch off the engine and ONLY then do the reconnection ? I am getting tempted to try this.
You've got it all correct! I see no reason why your car will not run for as long as you want, without the battery.
However, is there a thrill in doing this 'experiment'? After the Baleno incident, I somehow did not feel tempted to see how long the car would run without the battery. It is purely academic and of no practical use unless you find yourself in a situation where you have to do it!
If you need to, by all means, go ahead. The car will run as long as you want it to.

Quote:
Originally Posted by DirtyDan View Post
The only reason I can think of on a petrol is that there was not enough room for one big battery but enough room for 2 smaller ones. Its a guess.
The most likely and logical reason!
anupmathur is offline   Reply With Quote
Old 18th February 2009, 22:40   #116
Senior - BHPian
 
R2D2's Avatar
 
Join Date: Oct 2008
Location: Punya Nagari
Posts: 1,167
Thanked: 230 Times
Default

Quote:
Originally Posted by star_aqua View Post
I do agree with the spike generation when the battery is disconnected. but the spike is generated when there is absolutely no load on the alternator. and in modern automotive systems, you have a spike protection/surge dampers. Please keep in mind that when such systems are developed by someone, they also find a way to protect it from all kinda hazards.
and to test this i dont need a car, i have lab setup at my workplace to do such testing.
And how do you say ECUs dont do battery management??
ECUs are protected, yes, from static discharges and voltage surges, but NOT from ill advised actions.

Star_aqua, trying this on a test rig the way you do at your workplace and on a car belonging to someone are two very different things. If the test rig goes bust your company wont mind because it is after all a test rig in a test lab. But a car's electronics getting fried due to a voltage surge is different thing as the owner will need to shell out the money for what can turn out to be some very expensive repairs or replacements. The exception is of course if the car is owned by you, your company and they have authorised you to experiment as you wish OR ofcourse a friend/relative who doesnt mind.

How do I know the the ECU doesnt manage the battery? Coz I have my car's workshop manual and wiring diagram. It may be different for other cars. Temperature compensated charging & the voltage regulator are built into modern alts.

Rgds,

R2D2

Last edited by R2D2 : 18th February 2009 at 22:44.
R2D2 is offline   Reply With Quote
Old 18th February 2009, 23:35   #117
Distinguished - BHPian
 
SS-Traveller's Avatar
 
Join Date: Jan 2009
Location: New Delhi
Posts: 5,739
Thanked: 5,862 Times
Default

Quote:
Originally Posted by R2D2 View Post
Temperature compensated charging & the voltage regulator are built into modern alts.
Interesting thread with equally interesting arguments. The one point that finally came up by R2D2 was the fact about the electronic charge control unit built into modern alts (in lieu of the "cut-outs" - the black box which controlled the charge from a dynamo 20 years ago). Cars can run without batteries - that's a given in most cases. But can the alt run without a batt? Prolonged running of an alt without a connected batt will fry the voltage/ current controlling electronics of the alt, because there is no "back voltage" from the batt - the regulator cannot sense a battery, so regulates voltage as far as possible at the cost of generating heat. Upto a point, the voltage will hold at 14.4~14.5V - then, once the controller fries due to the heat and voltage rises, say good-bye to the rest of the electronics - ECU first, ICE, anything else.

BTW, if you were to carry out electric welding on your car chassis, please disconnect the plug from the back of the alt. The regulator has a good chance of cooking if left connected while electrowelding is carried on for a long enough time.
SS-Traveller is offline   Reply With Quote
Old 19th February 2009, 01:40   #118
BHPian
 
star_aqua's Avatar
 
Join Date: Aug 2008
Location: BLR
Posts: 612
Thanked: 86 Times
Default

Quote:
Originally Posted by R2D2 View Post
ECUs are protected, yes, from static discharges and voltage surges, but NOT from ill advised actions.

Star_aqua, trying this on a test rig the way you do at your workplace and on a car belonging to someone are two very different things. If the test rig goes bust your company wont mind because it is after all a test rig in a test lab. But a car's electronics getting fried due to a voltage surge is different thing as the owner will need to shell out the money for what can turn out to be some very expensive repairs or replacements. The exception is of course if the car is owned by you, your company and they have authorised you to experiment as you wish OR ofcourse a friend/relative who doesnt mind.

How do I know the the ECU doesnt manage the battery? Coz I have my car's workshop manual and wiring diagram. It may be different for other cars. Temperature compensated charging & the voltage regulator are built into modern alts.

Rgds,

R2D2
R2D2, please understand that nobody here is asking you to test it on your vehicle. There are certain things which cannot be tested on vehicle and hence needs a test bench. do you know how the automotive systems are tested? please do know what a test bench is and why is it used for and then you try to differentiate between a test bench and a real car.

and please note that a workshop manual or the wiring diagram will not tell you what features an ECU has and ECU has a seperate manual which will not be given to you and it is only meant for the OEM and it can be used by only calibration engineers.
star_aqua is offline   Reply With Quote
Old 19th February 2009, 07:35   #119
Senior - BHPian
 
Join Date: Sep 2007
Location: New Delhi
Posts: 2,984
Thanked: 95 Times
Default

Quote:
Originally Posted by SS-Traveller View Post
Cars can run without batteries - that's a given in most cases. But can the alt run without a batt? Prolonged running of an alt without a connected batt will fry the voltage/ current controlling electronics of the alt, because there is no "back voltage" from the batt - the regulator cannot sense a battery, so regulates voltage as far as possible at the cost of generating heat. Upto a point, the voltage will hold at 14.4~14.5V - then, once the controller fries due to the heat and voltage rises, say good-bye to the rest of the electronics - ECU first, ICE, anything else.
SS, that's an interesting point you have raised: Can an alternator function without a battery connected (as a load)?
Earlier you have mentioned that a car can run without a battery, that's a given.
There seems to be a slight contradiction here.

IMO, no 'back voltage' is required from the battery for the alternator to perform it's functions. The battery 'back voltage' is used simply to determine at what point the charging of the battery should be stopped. Otherwise the battery will get seriously over-charged and get 'fried'! The battery back voltage is not used to 'clamp' the voltage produced by the alternator.

Since the alternator and the battery are simply two sources connected in parallel, the one with higher voltage will feed the car's electrical requirements.
Without a connected battery, the alternator will still be having the load of the car's electricals, no matter that the load might be well short of the rated capability of the alternator.

Now, my queries are:

1) How/Why would this result in frying the voltage regulator? That's like saying that a very small load can fry the regulator!

2) Is it possible that the regulator will fry if running (hypothetically) with ZERO connected load?

3) Would not a manufacturer have built in a small permanent load to prevent the above from happening, if the danger of getting fried is so clearly a possibility?


BTW, I agree about the arc welding caution you have mentioned. That can very easily fry certain components on an unlucky day!
anupmathur is offline   Reply With Quote
Old 19th February 2009, 08:15   #120
Senior - BHPian
 
headers's Avatar
 
Join Date: May 2006
Location: Greater Chennai
Posts: 4,524
Thanked: 405 Times
Default

Quote:
Originally Posted by supremeBaleno View Post
Hey Vikram, I am not sure I understood the difference between engine running 5mins or 20kms.
Biju, why not TRY it? But dont blame me for the consequences!

Quote:
Originally Posted by anupmathur View Post
I somehow did not feel tempted to see how long the car would run without the battery.
Why not Sir, the baleno told you that he needs a battery badly!

Going by your logic, my next question would be "Why do cars need battery at all ?"


Quote:
Originally Posted by SS-Traveller View Post
Prolonged running of an alt without a connected batt will fry the voltage/ current controlling electronics of the alt,
Correct, but a slight correction if I may. The regulator / diode is a current limiter from the alternator. It will charge the battery at a max rating voltage specified between various alternators, battery types and sizes.

The Alternator is a pure charging device, It cannot take the dynamic loads of the cars electrical system and will surely bust the regulator. Temporary running for few minutes is one thing whereas prolonged running for 30 minutes or so is another.

Friends, feel free to try this in your own petrol car. The price to pay would range from the alternator regulator failure to higher expensive electronics.

And thats why facts remain - A battery is needed in a car!

Quote:
Originally Posted by anupmathur View Post
Now, my queries are:

1) How/Why would this result in frying the voltage regulator? That's like saying that a very small load can fry the regulator!

2) Is it possible that the regulator will fry if running (hypothetically) with ZERO connected load?

3) Would not a manufacturer have built in a small permanent load to prevent the above from happening, if the danger of getting fried is so clearly a possibility?

Sir, please remove your battery physically from your car [wagon R] I'd presume, run it for a day maybe without battery. You'd get all your answers..or read my post above:
headers is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Battery / Alternator / Voltage Regulator problem? babe_on_wheels Technical Stuff 83 29th July 2014 13:11
Car Battery / Alternator Capacity Query jinu_joseph Technical Stuff 41 29th January 2013 13:37
Battery Not charging light on - Alternator giving 14+ !! What is it ? karizma_devil Technical Stuff 90 30th August 2012 21:00
Can a dead battery damage an alternator? mudittandon Technical Stuff 35 28th April 2011 21:05
Battery / Alternator problem in Ambassador Diesel adrian Technical Stuff 5 11th December 2009 14:25


All times are GMT +5.5. The time now is 13:55.

Copyright 2000 - 2014, Team-BHP.com
Proudly powered by E2E Networks