[dashoin]

@ Vina -
Speed control for series motors - neither do I remember any other method. Last time I saw a series motor was in a starter application for some heavy earth moving equipment about 10 years back. BTW, I am not too sure about the voltage part of it - at least these HEM had the same voltage rating. Logically, the voltage of the DC bus and the starter motor should be the same. In case I go with a motor of lower voltage rating, then for the same power output, it would have to draw more current.
Regarding the heat generated, ceiling fans do not have enclosures which would protect them from water. They do generate heat - try touching one after continuous operation. reason why they dont fail is that the class of insulation is usually A or B which is far higher than the temperature of the fan. Additionally, the ambient temperature is on the lower side. So even with a 50 deg ambient and a temperature rise of 25 deg - total temperature comes to 75 degC which is OK.
Regarding conversion efficiencies, 95 % is valid for 3 phase motors/ alternators with significantly higher ratings. These alternators would have an effciency of about 75~80%. It can operate at full load without any problem continuously - as long as we keep the temperature in control. The thumb rule for is that the life of a motor/alternator reduces by 30%(or 50%?) every time you exceed the design temperature limits. I have seen motors reach a temperature of 110 degrees within 30 minutes of their operation at 85% load ( these were rated for 2000KW with and efficiency of 94%). The insulation limit was 120 deg C with a design of 150 deg C. Our alternators normally have 105 deg C insulation limits or in rare cases 120 deg C. The electronics at the aother end are rated for 140 deg C.

@ deralte

Well, I had given the basis of sizing the alternator with all OEM loads PLUS the float charging. You had said that a duty cycle would be considered for OEM loads. Now applying electrical engineering approach to this, intermittent loads would be considered in the sizing with a fractional multiplier or not at all. Now, when these loads would come on line, only thing which has to give way is charging. So, if I assume that the duty cycle would not be considered for the loads i.e., we are considering all the loads, the alternator would be fit for extended operation at 100% load.

Regarding the approach taken for car component engineering, I cannot comment on that. Basic machine design data required for the vendor to design the alternator would be the ambient it is expected to work in, expected output and the duty cycle. This forms the base on which a machine designer does all the work you have pointed out. The basic design data has to be given by the manufacturer as he is designing the complete package. Database engineering is not design engineering, it is selection engineering.

@Sutripta.

Regarding charging regimes, you are welcome to your opinion. I would not discuss charging regimes in an automotive forum - there are other forums where it would be more appropriate.

In case the specific gravity of your battery shows a decline, it means either your battery is going or your alternator does not have the capacity to charge it due to overloading etc. Best option would be to remive the battery and get it charged from the battery vendor/FNG. Recording battery terminal voltage and specific gravity is a standad PM practice recommended by battery manufacturers for industrial applications. Same can be easily followed here.

@Aroy

The utility generators are not sized for duty cycles and neither are they subject to continuous overloads. Additionally, their cooling regimes are much more complex and efficient (hydrogen cooling etc). Cool you car alternator properly and you would be able to extract more out of it.

[Aroy]

Originally Posted by dashoin

@Aroy

The utility generators are not sized for duty cycles and neither are they subject to continuous overloads. Additionally, their cooling regimes are much more complex and efficient (hydrogen cooling etc). Cool you car alternator properly and you would be able to extract more out of it.

Theoretically yes you are right. In practice, especially in third world environments, the power generators run at and beyond 100% rated capacity for extended period.

Yes all power motors/alternators require cooling, as even 1% loss at say 10MW is 10KW of heat that has to be evacuated, unless we want the machine to melt!

And then we have Diesel/Gas Generators in the 1-10MW capacity, used for short term/captive power, which are literally larger brothers of the neighborhood gen sets, which require extensive cooling of both the engine and the alternator.

[DerAlte]

Originally Posted by Sutripta

... Sometime back, there was a proposal for '42 V' automotive electrical systems. Where did the value 42 come from? ...

It starts with the cell voltage of the battery, which is dependent on the battery technology. 12V is 6 cells of 2V nominal (2.3V open circuit) in series in a Lead-acid one. The real open-circuit value is 13.8V (2.3V per cell x 6), colloquially referred to as 14V - and that is the min. voltage required to charge a healthy battery. 42V - coined by BMW and Daimler - was 14Vx3 required for charging. Had it become universal (switching to it would have been a royal pain for all manufacturers and vendors, incl. semiconductor vendors), it would have gone in the direction you wanted: 14V bus.

Originally Posted by Sutripta

... what happens and why, when we connect these two in parallel. ... 'What is the output if one shorts the output of two gates, one at 0, the other at 1. In the digital case, algebra and logic have no concept (operator) for 'shorting'. But of course we can do it in the physical world. ...

Good old Circuit Theory, working out the impedances to find out what will be the ultimate voltage and how much current will flow where.

Originally Posted by vina

From what I have heard in analog design forums it is usually called the 14V bus. Reason is obvious - it is at 14V (+/- tolerance) almost all the time. ...

If the tolerance is +/-20%, it would be 11.2-16.8V. Have you measured 16.8V in a car at any time? Even accounting for ripple, you won't get that if the battery is in circuit. OTOH, 9.6V or less is quite common in a car.

Originally Posted by vina

... some smart guys in their ivory towers decided things and then that became the standard ...

You have serious problems with authority. Go out and smell the coffee, buddy (OK, OK, just joking)

Originally Posted by Sutripta

... Regarding alternator sizing: Some questions
If one had to write one or two sentences explaining the requirements of an alternator for any particular vehicle, what would it be?
I would think it is more a matter of philosophy, ...

What goes out initialy is "We want an alternator, here are the model numbers of the electrical loads".

Originally Posted by dashoin

... Now applying electrical engineering approach to this, intermittent loads would be considered in the sizing with a fractional multiplier or not at all. Now, when these loads would come on line, only thing which has to give way is charging. ...

How laissez-faire! What kind of electrical engineering approach is that? That sounds more like a caterer saying "no more rice left to feed the marriage party"!

Originally Posted by dashoin

... Regarding the approach taken for car component engineering, I cannot comment on that. .. The basic design data has to be given by the manufacturer as he is designing the complete package. ...

Car manufacturers design cars: the chassis and the drivetrain. They also manufacture those, and make the body from scratch. For design and manufacture of everything else they rely on vendors: body and exterior embellishments (most manufacturers), interiors (minus plastics whose design is done in-house), components (anything from hinges & nuts & bolts to radiators, alternators, etc.), and sub-systems (like cable harness, AC, ICE, ...). Car manufacturers integrate, which means they only need to specify the interfaces, such as mounting hole geometry, mating gear config, belt size, ... For everything else, the vendor figures out the specs and design. The process is participative, i.e. the car manufacturer participates in a process that the vendor conducts. Influences sometimes from prior field experience, but does not specify. They only specify the cost range for each BoM component.

It is a different story when an existing car is to be manufactured in another country - like VW Polo in India. Then, either the existing vendors supply the parts, or for parts that need to be procured locally (indigenous content!) a ready design drawing is given to a competent new local vendor to manufacture it.

Originally Posted by dashoin

... Database engineering is not design engineering, it is selection engineering ...

Why the scorn? Do you design from first principles always? Good show! That is hardly productive.

[Sutripta]

Originally Posted by DerAlte

It starts with the cell voltage of the battery,
......
Good old Circuit Theory, working out the impedances to find out what will be the ultimate voltage and how much current will flow where.
Statute of limitations now applies to comments.

......

What goes out initialy is "We want an alternator, here are the model numbers of the electrical loads".
No, don't mean a RFP or RFQ.
If you were writing the definitive treatise on automotive electrical systems, and had to say what alternators are, what they are supposed to do, and why, in a couple of sentences, what would those sentences be. Something which you write below the headline, but before you dive into the subject.
And hard data please.

Originally Posted by dashoin

@Sutripta.

Regarding charging regimes, you are welcome to your opinion. I would not discuss charging regimes in an automotive forum - there are other forums where it would be more appropriate.

I would think battery charging regimes are more appropriate for this forum than aspects of power station engineering (eg. temp rise of boiler feed water pump motors, cooling systems of turbogenerators)

In any case here's my understanding.
Trickle Charge: Current oriented charging method to keep a fully charged battery at 100% SoC. Normally not suitable for charging batteries from low SoC. (Until one has lots and lots of time)
Float Charge: Voltage oriented charging method to keep battery at 100% SoC. Can also be used for charging batteries (with a few qualifiers) from low SoC.
Equalising Charge: Voltage oriented controlled overcharging method. Used under special circumstances.

Would like to know more.

In case the specific gravity of your battery shows a decline, it means either your battery is going or your alternator does not have the capacity to charge it due to overloading etc. Best option would be to remive the battery and get it charged from the battery vendor/FNG. Recording battery terminal voltage and specific gravity is a standad PM practice recommended by battery manufacturers for industrial applications. Same can be easily followed here.

Goal is to know about the electrical system/ battery, and have enough information to predict what is going to happen next, while driving.

Regards
Sutripta

[vina]

Originally Posted by Sutripta

...

Trickle Charge: Current oriented charging method to keep a fully charged battery at 100% SoC. Normally not suitable for charging batteries from low SoC. (Until one has lots and lots of time)
...

I know only in the context on Li-ion and NiMH batteries.

Trickle charge: Very slow charging regime when the battery has gone into a deep discharge state. Followed till the terminal voltage crosses a (pre-set) threshold - for Li batteries usually 3.2V to 3.4V. Once the pre-set is reached normal CC-CV (For Li batteries used for cellphones - constant current into the battery till terminal voltage under charger reaches 4.2V, or some other pre-set, constant 4.2V thereafter) regime proceeds.

The trickle charging is done to (1) increase the life of the battery (2) in case of Li batteries prevent catastrophic damage (read-> explosion)



What you guys are calling float charge is also sometimes called trickle charge, but that is known to be wrong usage in context of Li/NiMH batteries. AFAIK there is no name for that regime - the phone/PC etc. basically runs on the charger (rather than on the battery - battery does act like a massive capacitor) and once the battery charging current falls below a pre-set threshold you see a message "battery full" on the screen.

More complicated circuits may shut off the charger once another threshold is breached subsequent to the "battery full threshold" - but that is usually not done.

All the pre-sets above are provided by the battery manufacturer.

For CE applications batteries are never overcharged as far as I know, especially Li batteries.

[dashoin]

@ Sutripta -

You made my day!. All three are meant to keep the batteries in charged condition. This is where your float charger steps in and monitors the voltage of the battery. Trickle, float and equalizing basically keep the voltage at the desired level. (Note that I am concentrating only on the lead-acid batteries over here. Ni-cad and other types would be different. And if you mean Tap cell equalizing charge, then its a form of boost charging for battery banks). The DC voltage applied across the terminals is not significantly higher than the rated voltage. The changeover happens when the current drawn by the battery goes higher than a limit - this happens when the battery has been discharged. This is when boost charging is required. This gives voltage at a higher level than the float charging thereby "forcing" current into the battery.

I just checked out a couple of wiring diagrams I had for the battery indicator - it seems it would come ON in case of a malfunction in the alternator. Now if you are trying to avoid this, I would still suggest monitoring the battery regularly. In case of a drop in the specific gravity, you could have a look at the alternator. I would have suggested getting the alternator brushes checked but loss of integrity of the enclosure during inspections ( i.e., no cracked packings etc) would lead to more problems. If you get the indicator while driving, it would be time to cut out except the most essential load and try to conserve the battery as long as possible. Some of the old threads do mention problems in alternators post the 70K mark. This might be one of the factors you can consider for preventive maintenance.
OT, it seems we are in the same line of business.

@Aroy,

OT, to run an alternator at overload, you need to have an engine rated for that. Present standards allow 10% overload once in 12 hours for diesel engines. The alternator with its cooling systems would be able to sustain, but the prime mover would not. See, the point of overloading comes into picture when the duty cycle is considered. Now, as all have agreed that the alternator is rated based on sum of all loads, we can leave that out of the picture and consider efficiency of charging. If you read Sutriptas latest post regarding trickle charging, my contention would be clear.

@ deralte

Regarding loads, you are providing input data in form of "model numbers of electrical loads".

The rice statement is appropriate - if you provide a fixed amount of rice to the caterer and more guests turn up, the rice is bound to run out till you get more rice. Same is the case with the alternator. Once you have sized it on the basis of your earliest posts (duty cycle), you would end up in a situation like the caterer!.

Regarding the vendors, you have now given the input data to proceed for design - refer above.

Regarding the compliments given, no comments. My approach to electrical engineering has been the same way for many years.
I do guess you are getting a wee bit personal in your writings - cool down, we are all entitled to our opinions AND our ways of working.
Just a request - please go through you earlier posts in a logical manner - you haave first disagreed and and later on agreed to the concepts. Guess we got you convinced on our approach!


@ Vina

Wait for me Buddy, I need that coffee

[vina]

Originally Posted by dashoin

@ Sutripta -
...
OT, it seems we are in the same line of business.

@Aroy,

OT, to run an alternator at overload, you need to have an engine rated for that. Present standards allow 10% overload once in 12 hours for diesel engines. The alternator with its cooling systems would be able to sustain, but the prime mover would not. See, the point of overloading comes into picture when the duty cycle is considered. Now, as all have agreed that the alternator is rated based on sum of all loads, we can leave that out of the picture and consider efficiency of charging. If you read Sutriptas latest post regarding trickle charging, my contention would be clear.


...


@ Vina

Wait for me Buddy, I need that coffee

Waiting. Meanwhile:

The first time I interacted with Sutripta dada, I thought the same, later I found everyone interacting with him would think the same


On Alternator running overload- if you are talking about generators I understand. For cars, why can't alternator be overloaded? Engine generates much much more than alternator's capacity.


On an earlier comment you made on efficiency - I don't know much about specifics of cars, but I did measure motor-alternator coupling's overall efficiency (power in power out) in college, over a decade ago. That was more than 90% if I remember correctly - at least one of them was clearly above 95% efficient and even the other one had to be at least 90%. I remember because I went into the lab thinking I would be lucky to get 50% (i.e. 70% each)

I don't remember the power but I think it was less than 5HP on each rated. We ran it from less than 50% rated to slightly above rated for our experiment.

If you have direct experience, I'll go by your numbers. I mean DC-DC converters easily top 95% peak efficiency and 90% in a wide band of power o/p, however I have seen designs done deliberately for 70% peak efficiency, because other considerations (cost etc.) were more important and 70% did the job pretty well.

[DerAlte]

Originally Posted by Sutripta

... No, don't mean a RFP or RFQ. ...

Originally Posted by Sutripta

... If one had to write one or two sentences explaining the requirements of an alternator for any particular vehicle, what would it be? ...

Isn't that the same (with a few words missing or implicit)? The RFP/RFQ is/has to be more precise than any other document, since there is a tangible end-result involved. The essential words related to 'precision of expression of need' may be in the document (explicit expression), have pointers to them (implicit expression) or the whole thing has to be a part of a process that governs discovery of the same.

Originally Posted by Sutripta

... If you were writing the definitive treatise on automotive electrical systems,...

Thankfully, fortunately or unfortunately, I am not in the business or profession of writing treatises!

Originally Posted by Sutripta

... but before you dive into the subject. And hard data please.

IP area - tread with care. As one would say in Hindi: 'Marwaoge kya?'

Originally Posted by dashoin

... The rice statement is appropriate - if you provide a fixed amount of rice to the caterer and more guests turn up, the rice is bound to run out till you get more rice. Same is the case with the alternator. Once you have sized it on the basis of your earliest posts (duty cycle), you would end up in a situation like the caterer!. ...

No, it isn't the same case. And no, inferring from Duty Cycle has nothing to do with it, since
a. one has a considerable power margin available from the engine for usage (same as 'enough rice was available')
b. current will be drawn depending on - analyze by circuit theory - impedances of the components in a circuit. Current 'supplied' will never be throttled to 0 - there is nothing called 'there will be nothing left'
c. there is considerable stretch available - till material failure in the alternator - that higher demand can be met. 'Temperature derating' is the gradually diminishing safety margin till burn-out. *Not* that higher cannot be drawn at higher temperatures - as long as cooling is effective
d. there is considerable interplay between current drawn and voltage, till voltage goes to 0; current drawn will 0 *only* when voltage = 0

Originally Posted by dashoin

... Regarding the compliments given, no comments. My approach to electrical engineering has been the same way for many years.
I do guess you are getting a wee bit personal in your writings - cool down, we are all entitled to our opinions AND our ways of working.
Just a request - please go through you earlier posts in a logical manner - you haave first disagreed and and later on agreed to the concepts. Guess we got you convinced on our approach! ...

LOL Cool down? Personal? Where?
* You seem to be finding it difficult to differentiate between persons and ideas - hence the feeling of affront. Especially if beliefs are questioned
* You are most welcome to 'your' approach. Never had the luxury of coarse approximation myself
* My emotions are reserved for the few people in this world I love, or love to hate. You are not one of them!

As far as "disagreeing & then agreeing" is concerned, your reading seems to be more interpreting rather than reading as it is. You are most welcome to interpret it in any manner if it gives you happiness, as long as you don't express in public anything other than on the technical subject at hand.

[vina]

Originally Posted by vina

...
If you have direct experience, I'll go by your numbers. I mean DC-DC converters easily top 95% peak efficiency and 90% in a wide band of power o/p, however I have seen designs done deliberately for 70% peak efficiency, because other considerations (cost etc.) were more important and 70% did the job pretty well.

I did a quick google search. Most alternators seem to be doing between 60-70% efficiency, though this is total efficiency (including losses in diodes/regulator etc. etc.). The other numbers you quoted are also in the ballpark for Bosch alternators - as I wrote earlier I defer to you on this.



Coming to batteries, my inverter's manual (and sources on the internet) had this to say (summary of all):

Bulk charging - initial charging of a significantly discharged battery with a constant current. Usually this is specified by battery manufacturers and is of the order of C/5 (C=AH capacity). Faster charge than manufacturers' recommendation leads to surface charging, but not much of a long term consequence otherwise. Battery terminal voltage usually remains less than 14.4V during this mode (for a typical 12V lead-acid battery). Higher than 14.4V leads to gassing so is usually avoided in regular charges (equalisation, below, is different)

Constant Voltage (CV) charging - Happens once the charging terminal voltage reaches 14.4V. The charger doesn't increase the voltage beyond this point, charging current starts to reduce.

Float charging - some do not differentiate between this and constant-voltage. Others say that once the CV charging current drops below a battery-specific threshold, the charger reduce the voltage to something like 13.5V - enough to keep battery charged, but less than the CV voltage.

Equalisation charging - NOT done except in specialised chargers. Once the CV current becomes too small (about 2% of the 20hr current), the charger becomes a constant-current charger again, and charges till voltage stops rising OR rises to 15.5V (roughly, don't remember the numbers, but I guess they have to be supplied by battery manufacturer).


Trickle charging - similar to Bulk charging above, except it is done with very small currents. Takes a lot of time to charge the battery, but there is no risk of surface charging. Most uncomplicated chargers do this.



Most important sources for above:

SuKam inverter manual
Wikipedia articles (http://en.wikipedia.org/wiki/Lead%E2%80%93acid_battery and others)
http://www.evdl.org/pages/hartcharge.html

a few others which essentially said the same things (terminology used was slightly different sometimes)

[Sutripta]

Originally Posted by vina

I know only in the context on Li-ion and NiMH batteries.

Talking only of the lead acid cell so far.

Originally Posted by dashoin

@ Sutripta -

You made my day!.
Happy to help!

OT, it seems we are in the same line of business.
Possible, but unlikely!

Originally Posted by vina

Waiting. Meanwhile:

The first time I interacted with Sutripta dada, I thought the same, later I found everyone interacting with him would think the same

Everyone?

Originally Posted by DerAlte

Isn't that the same (with a few words missing or implicit)? The RFP/RFQ is/has to be more precise than any other document, since there is a tangible end-result involved. The essential words related to 'precision of expression of need' may be in the document (explicit expression), have pointers to them (implicit expression) or the whole thing has to be a part of a process that governs discovery of the same.
By its very nature, RFP/ RFQ has to be for a specific case. I was wanting a more general statement.

Thankfully, fortunately or unfortunately, I am not in the business or profession of writing treatises!
Given your command over words and languages, that's a shame. And a waste.

IP area - tread with care. As one would say in Hindi: 'Marwaoge kya?'
How about hard data from historical cases? Case studies.

Originally Posted by vina

Equalisation charging - NOT done except in specialised chargers. Once the CV current becomes too small (about 2% of the 20hr current), the charger becomes a constant-current charger again, and charges till voltage stops rising OR rises to 15.5V (roughly, don't remember the numbers, but I guess they have to be supplied by battery manufacturer).
Reasons are different.
Actually, for all charging regimes, (as in most other rational things), the technician should know the 'what', but the scientist/ engineer has to know the 'why'. And question the 'why' too, from time to time.

Most uncomplicated chargers do this.
In a lot of cases, marketing turns deficiencies of a system into a desirable characteristic! Talk of turning a bug into a feature!

Think it is time to move on with the focus of the thread.
So let me ask another question. If other considerations lead to the decision that the driver will be provided with only a telltale which can either be on or off, what exactly would you, the designer, have the two states indicate? (For the time being, forget practical considerations of how to implement that)

Regards
Sutripta

[vina]

Originally Posted by Sutripta

Think it is time to move on with the focus of the thread.
So let me ask another question. If other considerations lead to the decision that the driver will be provided with only a telltale which can either be on or off, what exactly would you, the designer, have the two states indicate? (For the time being, forget practical considerations of how to implement that)

Regards
Sutripta

Dada I didn't write about equalisation charging (that I read on the internet) because (1) that may not be the only reason (2) really not needed right now - in any case I don't think any automotive chargers are doing it.

On the question above - as a designer I have a tough choice. I would really like to tell the user (1) His battery is about to die - as in die from old age (2) His battery has life, but it is about to die - as in die to deep discharge ...

Since you (or rather the manufacturers) are giving only pass/fail - some mix of the above criteria with margins in each case will have to be devised and output. The criteria will also include economics - I think in the two I have listed above (2) will take the cake.

[DerAlte]

Originally Posted by Sutripta

... the driver will be provided with only a telltale which can either be on or off, what exactly would you, the designer, have the two states indicate? ...

Originally Posted by vina

... Since you (or rather the manufacturers) are giving only pass/fail - some mix of the above criteria with margins in each case will have to be devised and output. The criteria will also include economics - I think in the two I have listed above (2) will take the cake.

A telltale could be a semaphore (indicating one of multiple possibilities), rather than a flag (binary - only 2 possibilities). Binary indication will constrain the ability to convey the true state, whereas conveying one of possible multiple states would enable a human brain to take the correct decision regarding course of action: should I change the battery now not taking any risk, should I wait for some more days or should I ignore it?

This is similar to traffic lights and other such semaphores that are understood widely without too much training. Traffic lights indicate one of five states, including flashing yellow (everywhere in the world except in TN, where it is flashing red) for 'proceed with caution'. Common battery testers, which basically measure open-circuit voltage, have a similar semaphore marking in color - green: everything OK; yellow: going going; red: gone case. Works well for the common man who understands the color coding better than the absolute voltage of the battery.

If one expands on @vina's logic, one could have chemical instrumentation in the battery which could be converted into a semaphore suitably. Current display technology is sophisticated and cheap enough to handle semaphore display. For example, use of multicolor LED.

[Sutripta]

^^^
Question was not on how to display/ convey information, but on what to display.

Regards
Sutripta

[DerAlte]

^^^
You constrained it to 1 of 2 possible 'what to display'. I was trying to remove that limitation, so that there can be better inferences drawn by the person looking at the telltale. The main objective is to help the person draw the right inferences.

[Aroy]

Originally Posted by Sutripta

^^^
Question was not on how to display/ convey information, but on what to display.

Regards
Sutripta

Back to the topic. Here is what I would do to get all the information I need

. Ammeter in the battery circuit to monitor the current flowing to and from of the battery.
. Ammeter in the Alternator circuit to know how much it is generating
. Voltmeter across the battery for monitoring voltage
. Temperature meter (I miss the meter) to know how hot the cooling circuit is
. Oil pressure meter to monitor the engine oil pressure

I prefer individual analog meters so that I can check what I want without fiddling with selection knobs, so there goes computerized display.

If I ever get a 4x4 with a low ratio GB, I would add the following (a la Pajero)
. Altimeter
. Tilt meter
. Air temperature meter

At present I have none of these in my Alto K10, and remain blissfully ignorant of what is going on, trusting in God (or MUL) that the car will run perfectly without any divine intervention of any sort, as long as I carry out the maintenance as per the MUL booklet! No meters == Ignorance is Bliss.