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Old 25th April 2011, 18:33   #16
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Default Re: Can a dead battery damage an alternator?

Hey R2D2, thanks for quoting the relevant section.

Actually, the reason for damage of alternator is not because the battery puts a load on it, but because it requires a very long time to charge.

I'm quoting a section from the section you quoted.
Quote:
When a dead battery needs to be recharged, it is best to use an external battery charger because you could overheat and damage your vehicle's charging system and you will save a lot of gas and wear and tear on your engine.
Also, from the site.
Quote:
With a dead 120 minute RC (60 amp hour) battery, it would take approximately 90 minutes at 80 amps, 4.8 hours at 25 amps, or 120 hours at one amp to fully charge (100% State-of-Charge) it.
Well, running an alternator for 120 hours non stop is not practical, and obviously will overheat and damage it. The damage is NOT because of load on the alternator.
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Old 25th April 2011, 18:56   #17
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Default Re: Can a dead battery damage an alternator?

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Originally Posted by dhanushs View Post
Hey R2D2, thanks for quoting the relevant section.

Actually, the reason for damage of alternator is not because the battery puts a load on it, but because it requires a very long time to charge.

I'm quoting a section from the section you quoted. Also, from the site.
Well, running an alternator for 120 hours non stop is not practical, and obviously will overheat and damage it. The damage is NOT because of load on the alternator.
Absolutely.. I agree it is not because of the load but the combination of high load + duration taken for an alt to charge a flat battery. This is the 3rd factor in charging the battery in my reply below.

All this said, your alt may even charge the battery back to specs over a period of time. But then is it advisable to take a risk with a relatively expensive part? I wouldnt think so unless it is an emergency.

The advice on that site that is mentioned is to do away with the common misconception that running a car can charge a battery to 100% SOC. Yes, in theory it can, but there's a risk of damaging the alternator. It is very similar to a 'push start' being discouraged for modern FI vehicles. You can..but there's a risk of damaging some components in the engine emission system mainly the cat converter.

Cheers!
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Old 25th April 2011, 19:12   #18
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Default Re: Can a dead battery damage an alternator?

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Originally Posted by R2D2 View Post
Charging a flat battery loads the alternator heavily and puts the stator coil and regulator/rectifier at risk.
An alternator is 'loaded' when the strength of the magnetic field within alternator increases. And this occurs when there is a resistance introduced or there is a change in resistance in the circuit.

The internal resistance of the battery is negligible when compared to other equipments.

Assume, an alternator charges a dead battery through a 100 km drive. In that case, the 'load' on the alternator by the battery is identical to the 'load' if the battery was perfect. ie, ~ no load. Just that the alternator might not charge the battery enough.

I rest my case.
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Old 25th April 2011, 19:46   #19
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Default Re: Can a dead battery damage an alternator?

All said and done; wouldn't it be near impossible for the alternator to charge the battery if the battery itself has lost juice?

@mudit : As you mentioned, the battery is a '09; it has come to ~2years. Is it a zero-maintenance battery or a regular one?

You could have the battery charged independently for 1 day at a stretch and then check the parameters. It could just be the battery giving up.
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Old 25th April 2011, 20:08   #20
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Default Re: Can a dead battery damage an alternator?

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Originally Posted by dhanushs View Post
An alternator is 'loaded' when the strength of the magnetic field within alternator increases. And this occurs when there is a resistance introduced or there is a change in resistance in the circuit.

The internal resistance of the battery is negligible when compared to other equipments.

Assume, an alternator charges a dead battery through a 100 km drive. In that case, the 'load' on the alternator by the battery is identical to the 'load' if the battery was perfect. ie, ~ no load. Just that the alternator might not charge the battery enough.

I rest my case.
I assume you are referring to strength of the magnetic field @ the rotor that is governed by the regulator. Field strength is proportional to the input voltage at the rotor which is connected to the regulator and the battery (to energise the coils when the ignition switch is first turned on).

I am afraid I can't go on trying to convince you. There's plenty of reference material on basic electrical theory and the generator/alternator on the net.

So I will stop here.

Cheers!
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Old 25th April 2011, 22:51   #21
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Default Re: Can a dead battery damage an alternator?

Quote:
Originally Posted by mudittandon View Post
...after half an hour of keeping the car running (idling), the battery is still not charged.
...is it possible for a drained / draining battery to damage the alternator!?
@mudittandon: You are not very likely to damage your alternator with half an hour of charging - however, if you had a dead battery and decide to drive non-stop to Jaipur with it, yes, you can damage the alternator as R2D2 mentioned...
Quote:
Originally Posted by R2D2 View Post
Vehicle charging systems are not designed to recharge fully discharged batteries and doing so may damage the stator windings or the diodes (from overheating)."
The other issue is one of permanently damaging your battery, because the plates are likely to warp and crack with the high current (around 60-80 amps for an usual car alternator) that goes into it when charged on the vehicle. Bench charging with a low current charger (2-5 amps) makes the battery recover its charge without damage to plates.
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Old 26th April 2011, 00:07   #22
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Default Re: Can a dead battery damage an alternator?

Trying to charge a dead battery yourself can cause the battery to go toast - deep discharged batteries must always be charged to some minimum state of charge (depends on the battery) with a small current. Large current on a deep discharged battery can cause permanent damage to plates and even short circuits.

Normally the regulator circuit in a battery charger monitors the battery and adjusts the current. Since in a vehicle the regulator is built into the alternator - if the regulator was not designed for this kind of a deep discharge condition then it may end up damaging the battery and itself.

By the way, running alternator long will not damage with alternator by heat - if heat is the culprit it will kill the alternator in a few minutes - more likely the voltage limiter circuit in the alternator is the one to get damaged.
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Old 26th April 2011, 14:56   #23
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Default Re: Can a dead battery damage an alternator?

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Originally Posted by dhanushs View Post
Well, running an alternator for 120 hours non stop is not practical, and obviously will overheat and damage it.
Not obvious to me. Don't think anything detrimental will happen to the alternator running 120 hrs @1 amp.

Quote:
Originally Posted by R2D2 View Post
...
But then is it advisable to take a risk with a relatively expensive part? I wouldnt think so unless it is an emergency.

The advice on that site that is mentioned is to do away with the common misconception that running a car can charge a battery to 100% SOC. Yes, in theory it can, but there's a risk of damaging the alternator.
Depends on quality of engineering. And cost cutting, which goes by the name of 'value engineering' nowadays.
Continuous high currents is more likely to damage the wiring loom. Which is also 'value engineered'. Maruti owners with a melted alternator connector know that.
If with an alternator with properly functioning AVR, you can continuously send a high current through the battery for any length of time, the battery most probably has a cell dead. Toast -> Burnt Toast.

To be operational in a car, does the battery have to be at 100% SoC? How should a car charging circuit determine EoC?

Regards
Sutripta

Regards
Sutripta
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Old 26th April 2011, 16:31   #24
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Default Re: Can a dead battery damage an alternator?

10.5V is considered cutoff for most ECUs, so no, 100% charge is not required.

Lead-Acid batteries reduce current demand (trickle) as they approach capacity. That is why they do not need a charging circuit, just overload protection when charging from low of dead state.

In older cars this was referred to as a cutout. Nowadays it's usually inline fuse that does the job, and anyway you should not be starting a car with a dead or close to dead battery.

Lack of this will cause one or all cells (usually the one with lowest impedance) to self-destruct, or the alternator windings to burn up, or some other failure in the charging system.

Ambassadors and Fiats of old came with an ammeter which was a manual backup for the often malfunctioning cutout, if it went over 20 (amps) you were supposed to slow down.
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Old 26th April 2011, 20:38   #25
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Default Re: Can a dead battery damage an alternator?

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Originally Posted by Sutripta View Post
Not obvious to me. Don't think anything detrimental will happen to the alternator running 120 hrs @1 amp.
Sorry for phrasing it completely wrong.

What I meant is, if at all any damage would occur, then that will be only because of prolonged and continuous use, and NOT due to load on the alternator.
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Old 26th April 2011, 20:49   #26
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Default Re: Can a dead battery damage an alternator?

^^^
Hi,
You and I differ (to a greater or lesser degree) on practically every point. But what exactly are you referring to by 'this' in
Quote:
Originally Posted by cranky View Post

Lack of this will cause one or all cells (usually the one with lowest impedance) to self-destruct, or the alternator windings to burn up, or some other failure in the charging system.
Regards
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Old 26th April 2011, 22:15   #27
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Default Re: Can a dead battery damage an alternator?

Protection.

Please enlighten with your points of view.
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Old 27th April 2011, 01:44   #28
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Default Re: Can a dead battery damage an alternator?

In normal operation (i.e. a running engine car) alternator provides almost all of the car's electrical requirements. the current drwan is substantial under such circumstances (e.g. fast drive on highway at nights with all the lights and ICE etc. on).

In such cases alternator obviously generates heat - and doesn't burn away after hours of driving. the reason - heat is generated but then dissipated by conduction convection and radiation so the temperature remains under control.

For a dead battery with very small current heat by itself can not harm the alternator - there has to be some other electical fault of some kind. Most likely culprit is regulator malfunction (i.e. if the alternator was damaged in the first place - which I don't think it was)
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Old 27th April 2011, 15:08   #29
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Default Re: Can a dead battery damage an alternator?

Quote:
Originally Posted by cranky View Post
Protection.
I take it that you are referring to the main fuse.
Quote:
In older cars this was referred to as a cutout. Nowadays it's usually inline fuse that does the job, ...
Quote:
Originally Posted by cranky View Post
10.5V is considered cutoff for most ECUs, so no, 100% charge is not required.
You're right that SoC=100% is not required. Terminal voltage can dip below 10.5 during cranking.

Quote:
Lead-Acid batteries reduce current demand (trickle) as they approach capacity. That is why they do not need a charging circuit, just overload protection when charging from low of dead state.
To discuss this would take chapters.
It is very difficult to determine SoC of a LA Cell. And thus to determine EoC. It is because of this that there are so many different charging regimes. What you are describing is taper charging.

You 'trickle' charge a Lead Acid Accumulator to a terminal voltage above its norm, you will shorten its life. With modern batteries, the shortening of life/ damage to battery is considerable even for a very small (~50 mV/ cell) increase.

Quote:
Lack of this will cause one or all cells (usually the one with lowest impedance) to self-destruct, or the alternator windings to burn up, or some other failure in the charging system.
The main fuse does all this?

Quote:
Please enlighten with your points of view.
OK. We'll start of from
Quote:
Ambassadors and Fiats of old came with an ammeter which was a manual backup for the often malfunctioning cutout, if it went over 20 (amps) you were supposed to slow down.
For starters, the Fiats/ Padminis did not come with an ammeter.

What was the purpose of the 'cutout'?
To understand that, lets find out what one of the most common models did:- the Lucas '3 coil cutout'.
Essentially it had 3 contacts, each controlled by a coil.
CutOut:- This isolated the dynamo armature from the battery when the dynamo output voltage was less than the battery voltage. Else the battery would discharge through the dynamo. This is also what controlled the 'IGN' telltale.
Voltage control:- One of the coils would open a contact, disrupting feed to the field if voltage rose above its set value.
Current control:- Similarly, there was another coil/ contact which monitored the current output if the dynamo (not current into battery), and disrupted feed to field if current rose above its set value.

The current control was for protection of the dynamo, not the battery.
The ammeter monitored current to/ from the battery, not dynamo.
You could still fry a battery if you set the wrong voltage.
You could burn your dynamo even if the ammeter showed within limits current.

In an alternator, the work of the cutout is taken care of by the diode bridge, the voltage control by the AVR circuit.

What protects the alternator from overcurrent?

Regards
Sutripta
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Old 27th April 2011, 17:34   #30
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Default Re: Can a dead battery damage an alternator?

There is no way to fry an alternator with a batt.dead or alive. Unless you manually short circuit.
Even then fuse will not allow damage to alt by blowing itself up.
Even if a 12v alt rated at 100amps is running fine, batt in any state cannot consume 100amps to overload alt.
Like a House hold simple bulb(resistance) conusmes its rated apms only ,although several 1000amps may be available in the line.
How much current can pass through is dictated by voltage,resistance offered.
Until alt is making 14odd volts ,batt will only take what it wants, not more.
Only way to pass hi amps through a batt is,either increase applied voltage,or reduce its resistance.
A dead batt offers more resistance not less.
If a dead batt was to offer lower resistance,low enough to allow 100+ amps to pass through,
It would boil its fluids in minutes ,as 1200w of energy would simply be heating it.

As far as your problem goes, I think I know whats wrong.
If alt is not giving any output (zero volts),then alt is just fine, its a simple fix.
You would need a multimeter or a volt mtr to check,i am quite sure it will read 0volts on all rpms.
It will be simple diy stuff,mechanic will probably suggest your alt is busted but its not .
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