[Sutripta]

Originally Posted by R2D2

It's the battery float charge voltage.

As long as the alternator is charging, once battery terminal voltage has reached ~ 14 V (or nearabouts, as set by the AVR), it should remain there. If everything is OK.

Regards
Sutripta

[R2D2]

Originally Posted by Sutripta

As long as the alternator is charging, once battery terminal voltage has reached ~ 14 V (or nearabouts, as set by the AVR), it should remain there. If everything is OK.

14V is too high and will evaporate the electrolyte faster than expected.

Float voltages @ 100% SOC ranges from 12.8V to 13.6V depending on temperature and battery chemistry.

Normally float voltage is around ~13.6V @ 27 deg Celcius/80 deg F. Should you be interested, more reading on charging algorithms here:

Battery Basics - Batterytender.com

I use a Deltran Batterytender with temperature compensation to maintain the car battery when it's not in use.

My car's alternator hovers at 13.2-13.3V. The alt voltage is not temperature compensated.

[Sutripta]

^^^
An alternator AVR is not a battery tender. (At least not in the cars we are talking about.) It has a single setpoint, and a single mode of operation.

Regards
Sutripta

[R2D2]

Originally Posted by Sutripta

^^^
An alternator AVR is not a battery tender. (At least not in the cars we are talking about.) It has a single setpoint, and a single mode of operation.

Regards
Sutripta

That's what I said too Sutripta albeit not in so many words - to quote from my post:

"I use a Deltran Batterytender with temperature compensation to maintain the car battery when it's not in use.

My car's alternator hovers at 13.2-13.3V. The alt voltage is not temperature compensated"

If I may elaborate further:

The battery tender is microprocessor controlled; with temperature, voltage and charging Amps being inputs to the 'servo circuit' if I may call it that.

The alternator's regulator/rectifier has a single operational algorithm.

[Sutripta]

Originally Posted by R2D2

That's what I said too Sutripta albeit not in so many words - to quote from my post:

"I use a Deltran Batterytender with temperature compensation to maintain the car battery when it's not in use.

My car's alternator hovers at 13.2-13.3V. The alt voltage is not temperature compensated"

If I may elaborate further:

The battery tender is microprocessor controlled; with temperature, voltage and charging Amps being inputs to the 'servo circuit' if I may call it that.

The alternator's regulator/rectifier has a single operational algorithm.

I don't think we are saying the same thing.
The difference of opinion is because you said

Originally Posted by R2D2

Voltage dropping from 14.4V to 12.5 or 12.8V is normal as that's what happens when the battery is fully charged.

and I said

Originally Posted by Sutripta

As long as the alternator is charging, once battery terminal voltage has reached ~ 14 V (or nearabouts, as set by the AVR), it should remain there. If everything is OK.

You are saying that in a car, expected behaviour is battery terminal voltage will hit a peak, and then come down, while the alternator is supposed to be working.
And I'm saying the terminal voltage will remain steady.
Both can't be right!
This is in the context of Shuvc's problem, and reported observation.

The charging regimes used by a battery minder, (or for that matter the exact AVR setpoint value) are not really relevant to present discussion.

Regards
Sutripta

[R2D2]

Originally Posted by Sutripta

You are saying that in a car, expected behaviour is battery terminal voltage will hit a peak, and then come down, while the alternator is supposed to be working. And I'm saying the terminal voltage will remain steady. Both can't be right!

I assure you that I know the diff between an alternator and a charger - even if they perform the same function. An alternator is designed to maintain a battery @ 100% SOC while a charger can charge a flat battery. That is why charging a flat battery is not recommended hy driving a vehicle. You could burn the stator coils and/or the regulator/rectifier.

The reason I pointed you to the Deltran site is for additional information on charging.

The 'fixed voltage' you refer to is what I call the 'float voltage' which is different from the peak voltage that's at around 14.4-15VDC depending on the alternator and regulator/rectifier in question.

Ok, let's start off with a bit of a background - though I am a computer/software engineering professional, shortly after graduation in the late '80s my love for cars and bikes led me to work in a garage as a technician ('mechanic' in those days).....for free. You see, I not only tuned single and multi cylinder carburetted 2/4 stroke car and bike engines, with my background in electronics also repaired the electricals (an 'Electrician' as referred in garages ) among other things.

I am still a keen DIYer.

That's true both cannot be right. Therefore Sutripta, here's another site that you may find interesting. www.batteryfaq.org by Bill Darden. This is one of the best sites you can get for knowledge on batteries. Please read the section on "HOW DO I CHARGE (OR EQUALIZE) MY BATTERY?" Very specifically look at 9.3.1 and the graph entitle vehicle charging voltage. You will note how alt voltages vary according to termperature as well. High end European cars use temp compensated charging. The point I am trying to make here is that alternator voltages are never fixed and vary according to the state of charge and temperature, where temp compensation is a part of the charging circuit.

Also look at section 5 - HOW DO I KNOW IF MY VEHICLE'S CHARGING SYSTEM IS OK OR LARGE ENOUGH

Want even more reading? Here's www.batteryuniversity.com and CAR BATTERIES ARE NOT 12 VOLTS

Here's a small experiment that you can try with your own car(s). The battery is assumed to be in good condition and fully charged.

a) Switch on the headlamps and lights for about 10-15 minutes to remove the surface charge from the battery and reduce the SOC

b) Connect a good DVM like a Fluke meter, preferably one with Min/Max/Avg hold readings, to the the +ve and -ve terminals

c) Start the car and hold the revs at 2000-2200 RPM

d) Please note the readings on the DVM. It will rise to 14.4v (+/- a few 100 mV) and then gradually drop and settle anywhere between 12.8-13.8V as the battery picks up charge. Use the Min/Max/Avg reading function of the DVM to ascertain voltages.

Originally Posted by Sutripta

The charging regimes used by a battery minder, (or for that matter the exact AVR setpoint value) are not really relevant to present discussion.

Can't agree with this statement. I find they are relevant. If you are proposing another theory about battery charging please elaborate

[Sutripta]

^^^
That is an impressive list of URLs!
(Incidentally I have followed Buchmann's thoughts on the web ever since I saw his equipment detecting, accurately, SoL for mobile phone batteries.)

Once again the question is not one of what is ideal for a battery, but of what happens in a simple alternator / battery system (as in the Baleno).

Nowadays you are getting ECU controlled AVRs, but the older simpler ones are not that. Those are set to one fixed voltage. When the alternator is charging but not current limited, it is the AVR which controls the terminal voltage, not the battery. So though it would (greatly) extend battery life if the float voltage were brought down once equalising charge was over, and corrected for temperature, in a simple setup (ie alternator with a simple AVR), it is not.

In one of the graphs referred by you, the float voltage is depressed after equalising charge is over. It is a desirable feature of the charger, not a Pb-acid battery characteristic (unlike say NiCds under constant current charge). And being relatively simple to implement, was done for donkey's years in three stage bench chargers.
In the other table (source from Bosch) it shows desirable terminal voltage with temperature. Which has to be maintained by the external circuit.

My observation over the years has been that in a simple system, the float voltage remains constant.
And this is consistent with what (little) I know of the technical side of things.

Since we can't meet and conduct a joint experiment (or can we?), maybe you can educate us on the technical side as to why the terminal voltage will (not should) drop in a simple system.
Always willing to learn.

Regards
Sutripta

[R2D2]

^^^^^^

Sutripta,

Unfortunately I am based in Pune and you in Kolkata. Otherwise we could could surely have conducted a joint experiment. I am truly not sure how a Maruti Baleno's alternator performs. Guess it must be a Nippon Denso or a Lucas-TVS unit. I had an Esteem in the early 2000s and frankly didn't check the voltages, but I did notice that water top ups were required frequently compared to my current car. It is possible the Marutis of yore used constant voltage charging.

But I hasten to add, the battery was also a normal Lead antimony battery - not low maintenance. Hence this is one of the factors for the frequent top ups. I had the same experience with my Father's 1995 Esteem. All this changed with the appearance of low maintenance batteries in the early 2000s.

One of the key things for any alternator assembly designer (I am not a component designer, just a person with a technical bent of mind who has repaired simple auto & non-auto electronic and electrical circuits in the past) is to fix output capacity, and balance output voltages and amps with long battery life. Most alternators are tailored to the expected electrical load plus the type of battery that the car will eventually use. For e.g. it is not recommended to use use a AGM/VRLA battery in a car that comes factory fitted with a wet battery. OEM parts have their designs drawn up by car mfrs and as such detailed specs for OEM parts are never available.

As mentioned before constant voltage charging burns off water faster than dynamic (or variable voltage and amp) charging would. Balancing these factors i.e. retaining battery water, quick charging and affording low maintenance are critical factors in auto charging systems. Add to that is the heat in a tropical country like India which has a major impact on battery life. So IMO dynamic charging voltages preferably temp compensated are the need of the hour here. It isn't very difficult to implement. Other than alternator design, battery chemistry and construction goes a long way in achieving these objectives.

I think you will find answers to nearly all your queries about charging voltages, amperage, battery types, maintenance and many more in sites referred to in that impressive list of URLs.

Cheers!

[Sutripta]

Originally Posted by R2D2

One of the key things for any alternator assembly designer (I am not a component designer, just a person with a technical bent of mind who has repaired simple auto & non-auto electronic and electrical circuits in the past) is to fix output capacity, and balance output voltages and amps with long battery life.

There are reasons why a car AVR setpoint is set to what, in other applications would be considered on the high side. This is true even of the modern breed of VRLA batteries, which are extremely sensitive to damage to even slight prolonged overvoltage. One of the (main) reasons for the push towards more intelligent AVRs now. (eg. Hyundai Eon. Though as of now, not aware of its exact strategy). Am sure the answers will be there in great detail somewhere in that impressive url list you have quoted.

I think you will find answers to nearly all your queries about charging voltages, amperage, battery types, maintenance and many more in sites referred to in that impressive list of URLs.

I don't think I've very many queries. (My needs are simple and limited.) And any I might have are likely to be ably served by my current resources. In which the web plays only a small part!

Regards
Sutripta

[R2D2]

Originally Posted by Sutripta

This is true even of the modern breed of VRLA batteries, which are extremely sensitive to damage to even slight prolonged overvoltage. One of the (main) reasons for the push towards more intelligent AVRs now. (eg. Hyundai Eon. Though as of now, not aware of its exact strategy).

I will be surprised if the likes of Hyundai start using VRLA/AGM batteries in their commuter cars. But this step is long overdue if they get it right. Wet batteries have too many issues whilst in operation but VRLAs are sensitive to voltage and ambient temps. I had to replace 4 VRLA/AGM UPS batteries within a year which, as per the UPS mfr, was due to ambient temps. All this with a UPS what has temp sensitive charging. The OEM supplied Chinese batteries were not designed with such conditions in mind. They have since been replaced with good old Exide.

Model specific OEM information is difficult to get unless you are browsing thru enthusiast sites where some people obtain inside info thru various means. But the sites I referenced will be handy to cross check if nothing else.

And any I might have are likely to be ably served by my current resources. In which the web plays only a small part!

Much of the 'research' I do is based on what I read on the 'net + technical books whenever available. As an IT person my professional life revolves around technology including the web. BTW, are you working in the automobile sector?

[Sutripta]

^^^
Hi, Hyundai Eon was given as an example of a cheap car having an intelligent AVR. They claim it is for fuel efficiency: Charge mainly on the overrun. And I'm sure it will have, at most, a flooded electrolyte 'MF' battery.

The 'next' automotive battery, regardless of its Pb-acid flavour, will have monitoring circuits built in. Much like laptop batteries now.

OT- Re your inverter battery life. Do check out all that is mentioned in the inverter brochure/ manual is actually implemented. You might be shocked!

My take on the web:- It is like a diamond mine. To get one rough diamond, you have to go through tons and tons of muck. And then how do you recognise the rough diamond? But as I said before, Buchmann's sites are great.

Me - a layman.

Regards
Sutripta

[R2D2]

Originally Posted by Sutripta

OT- Re your inverter battery life. Do check out all that is mentioned in the inverter brochure/ manual is actually implemented. You might be shocked!

I know this is entirely off topic for this thread. But can you specify what the inverter brochure would say? I am particular about proper installation to the extent I had an electrician install an earthing wire which was not installed by the inverter supplier 2.5 years ago. Earthing was absolutely essential but the the kit was installed when I was away in office so I could not monitor the job.

Originally Posted by Sutripta

My take on the web:- It is like a diamond mine. To get one rough diamond, you have to go through tons and tons of muck. And then how do you recognise the rough diamond? But as I said before, Buchmann's sites are great.

Me - a layman.

Absolutely true Sutripta. It is like searching for a diamond in tons of mud.

You a layman? I detect some modesty there.

Cheers!

[navin]

Originally Posted by shuvc

The Baleno alternator is acting up. The diagnosis is ... When cold it is charging properly, but as the car is run and the engine heats up, the charging voltage keeps on dropping.

Originally Posted by shuvc

They did say readings were taken both at the battery and alternator terminals. No specific temperatures were recorded but the car was idled, revved, with and without AC and headlights during the test.

With time the charging voltage dropped to below 12. This happened with both batteries.

The other observation mentioned was .. Under no load condition, there was almost no charging, whereas under load it was low.

Getting back to the issue at hand....

Shuvc, I dont know much about alternators

When any motor gets hot it's resistance increases (hot wire has a higher resistance than cold wire); an alternator would hence also be similarly affected.

I suspect the alternator winding is damaged. The alternator is hence getting hotter than it should get and hence producing less current (to charge battery) than it should.

One way to check this is by meauring the cold and hot resistance of the alternator. If the hot resistance is less than 70% of the cold resistance then the alternator is over heating. Can you try this?

[ssingri]

Originally Posted by shuvc

With time the charging voltage dropped to below 12. This happened with both batteries.

After this they stitched off the engine and let it cool. Car was started after 30 of mins and once again initial charge under load was fine.

The other observation mentioned was .. Under no load condition, there was almost no charging, whereas under load it was low.

Please do check if a component that is switched on only when operating temperature is reached like a radiator cooling fan or a coolant circulation valve is shorting out.

[shuvc]

Originally Posted by navin

One way to check this is by meauring the cold and hot resistance of the alternator. If the hot resistance is less than 70% of the cold resistance then the alternator is over heating. Can you try this?

Thanks ! But how do I do this?

Originally Posted by ssingri

Please do check if a component that is switched on only when operating temperature is reached like a radiator cooling fan or a coolant circulation valve is shorting out.

Could this be a factor even when there is a drop in voltage at the alternator terminals?