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Old 29th November 2011, 17:28   #1
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Default Power / Energy required by the Starter motor

On the dos/don'ts of long term parking thread there has been some discussion on whether or not battery will be charged up in a reasonably short time.

I do know a few things about batteries, but not much about cars' electrical systems so here are a few questions:
  1. What is the average current draw of the starter motor if, for example, it is cranked for 5 seconds.
    1. I'm assuming in the first few hundred microseconds it will draw a lot more current than later, also I'm assuming that in "normal conditions" we don't have to crank 5 seconds to start the car.
  2. What is the typical cranking time on most cars - is there any car on which this exceeds 5 seconds when the car doesn't have a fault?
  3. How much o/p voltage must the alternator develop before battery can start charging again (i.e. charging circuits are on). I'm assuming this will be higher than the voltage at which alternator takes over vehicle's power supply from the battery (roughly battery terminal voltage + diode drop)
  4. Is there any limit on the charging current to be provided by battery charging regulator? How much is it?
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Old 29th November 2011, 18:09   #2
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Default Re: Power/Energy required by starter motor

Vina,
I am here again. . Here are some info that I have. They may not answer all your questions though.
Starter motor current depends on the vehicle we consider. For a 4 cylinder petrol engine of about 1200 cc, at a typical Indian ambient weather one can expect about 800 milli-seconds to reach 2/3 or idle rpm. 5 seconds is also practically possible on a Diesel engine that is not warm enough.
Yes, there is a limit on the charging current. A battery supplier recommends the same to the automotive OEM or the agency who is responsible for the development of charging system. "How much" depends again on the Ah rating of the battery. As a thumb rule 1.5C or 2C will be the maximum. One can find a DIN 44 battery being charged by a 60 or 70A alternator. One can open the hood and find Ah rating of the battery and the current rating of the alternator.
This in turn limits the maximum current output of the alternator. Alternators have a system called "Load controlled regulator". The function is to control the voltage as a function of current. At max current operation the alternator is controlled at minimum voltage. And at min current (most of the alternators) reach 14.4V. The pulley ratio for the alternator & crank pulleys is decided such that even at idle, the alternator cuts-in and charges the battery. The ratio is also limited by the max speed the alternator can be operated. For instance the Greaves Engines that drive the diesel powered 3 wheelers have a huge ratio, as these engines are low speed engines, still the battery has to be charged.
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Old 29th November 2011, 19:32   #3
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Default Re: Power/Energy required by starter motor

Quote:
Originally Posted by vina View Post
On the dos/don'ts of long term parking thread there has been some discussion on whether or not battery will be charged up in a reasonably short time.

I do know a few things about batteries, but not much about cars' electrical systems so here are a few questions:
  1. What is the average current draw of the starter motor if, for example, it is cranked for 5 seconds.
    1. I'm assuming in the first few hundred microseconds it will draw a lot more current than later, also I'm assuming that in "normal conditions" we don't have to crank 5 seconds to start the car.
  2. What is the typical cranking time on most cars - is there any car on which this exceeds 5 seconds when the car doesn't have a fault?
  3. How much o/p voltage must the alternator develop before battery can start charging again (i.e. charging circuits are on). I'm assuming this will be higher than the voltage at which alternator takes over vehicle's power supply from the battery (roughly battery terminal voltage + diode drop)
  4. Is there any limit on the charging current to be provided by battery charging regulator? How much is it?
1.
For Toyota Landcruiser the motor is 2.5kW "NEW" TOYOTA LANDCRUISER STARTER MOTOR HZJ80 HZJ75 90- | eBay
For Ford Fiesta it is 0.8kW "BRAND NEW" STARTER MOTOR FORD FESTIVA 91-97, 1.3LTR, 3 BOLT, | eBay
So it can be assumed that the motor will vary from 0.8kW (Alto?) to 3kW+ for heavier diesels (check in the Denso Catalog in the links given further). So the current drawn will be between 70A and 250A. (That is why we need that thick cable for the starter, and similarly for the Jump Start Cable)
2.
- Small petrols in normal weather : 1 sec
- Small petrols in cold weather : 5-10 sec
- Diesels in warn weather 2-5 sec
- Diesels in cold weather - 10+ sec
- Maximum experienced - 2 min on a cold day
3.
- The battery will start charging when ever the alternator voltage is more than its voltage, though the charging current is dependent on the battery design.
- Most manufacturers give the charts for charging voltage and currents for each battery
- So do voltage regulators http://www.sfindustrial4u.com/upload..._SQ300-450.pdf.
- Similarly alternators have data chart which state the voltage and current characteristics at various RPM.
L9911 datasheet(2/15 Pages) STMICROELECTRONICS | CAR ALTERNATOR MULTIFUNCTION SMART VOLTAGE REGULATOR

Denso Catalog : Types, download Starters and Alternators catalog. This has both the starters and the Alternators.
4.
- Limit of charging current for battery is there in the battery specifications
- Limit for Alternator is specified on the Alternator
- Alternator regulator chips and diodes are matched to the alternator, hence if it is a 100A alternator the limit will be 100A + some reserve.

Last edited by Aroy : 29th November 2011 at 19:34.
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Old 30th November 2011, 01:01   #4
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Default Re: Power/Energy required by starter motor

Quote:
Originally Posted by ilangop View Post
Vina,
I am here again. . Here are some info that I have. They may not answer all your questions though....
Quote:
Originally Posted by Aroy View Post
Thanks to both of you. Lots of hard to find information and also lots of easy to find information that can make one slog on the internet (while wife is shouting and daughter is trying to break the laptop). I'm extremely grateful to both of you.

Please do see http://www.team-bhp.com/forum/techni...ml#post2594022 (Long-term Parking : Do's and Don'ts) this is the reason I asked for the information in the first place.

@ilangop - can you explain the "load control regulator" a bit more. I didn't understand why would you have smaller current for smaller voltage. Or is it the excitation current of the armature (to get higher voltage o/p when the load is higher)?
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Old 30th November 2011, 10:02   #5
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Default Re: Power/Energy required by starter motor

Quote:
Originally Posted by vina View Post
@ilangop - can you explain the "load control regulator" a bit more. I didn't understand why would you have smaller current for smaller voltage. Or is it the excitation current of the armature (to get higher voltage o/p when the load is higher)?
Yes the field is controlled to regulate the output voltage. Hope you get some idea on going through this data sheet.
http://www.st.com/internet/com/TECHN...CD00003201.pdf
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Old 30th November 2011, 13:36   #6
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Default Re: Power/Energy required by starter motor

Haven't gone through the thread. Are you accounting for variable dynamic compression for different cars? We have observed that beyond a certain amount of dynamic compression, a healthy OE starter and a healthy battery with healthy wiring is unable to crank the engine due to too much compression lol.
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Old 30th November 2011, 20:12   #7
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Default Re: Power/Energy required by starter motor

Quote:
Originally Posted by ilangop View Post
This in turn limits the maximum current output of the alternator. Alternators have a system called "Load controlled regulator". The function is to control the voltage as a function of current. At max current operation the alternator is controlled at minimum voltage. And at min current (most of the alternators) reach 14.4V.

Quote:
Originally Posted by ilangop View Post
Yes the field is controlled to regulate the output voltage. Hope you get some idea on going through this data sheet.
http://www.st.com/internet/com/TECHN...CD00003201.pdf
Hi,
Really not understanding this 'Load Controlled Regulator'
Could you please explain
A) what exactly it is supposed to do
B) And why.

Also, how is the current measured?

Regards
Sutripta
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Old 30th November 2011, 20:33   #8
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Default Re: Power/Energy required by starter motor

Quote:
Originally Posted by vina View Post
Is there any limit on the charging current to be provided by battery charging regulator? How much is it?
Definitely yes, there is a limit. Of course, the exact figures will depend on the battery rating / capacity. Each battery will have "recommended" charging current (jn amperes) at which the battery is to be charged. Any faster, and the battery will either heat up or result in "surface charging" (or probably, there is a better word for it) and both will lead to ultimate failure of the battery.

Problem with running a car for short durations only is that such use will cause "surface charging" only. I am speaking of vehicles with long duration parking - 1 week or more.

Quote:
Originally Posted by pranavt View Post
Haven't gone through the thread. .
Aw. C'mon. Not even a full page.

Quote:
Are you accounting for variable dynamic compression for different cars? We have observed that beyond a certain amount of dynamic compression, a healthy OE starter and a healthy battery with healthy wiring is unable to crank the engine due to too much compression lol.
Are you (a) accusing the manufacturers' R&D of incompetence in the electrical department?

or

(b) saying that these guys are not smart enough to keep the "dynamic compression" of an engine low enough while being cranked up?
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Old 30th November 2011, 20:55   #9
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Default Re: Power/Energy required by starter motor

Quote:
Originally Posted by BaCkSeAtDrIVeR View Post
Aw. C'mon. Not even a full page.



Are you (a) accusing the manufacturers' R&D of incompetence in the electrical department?

or

(b) saying that these guys are not smart enough to keep the "dynamic compression" of an engine low enough while being cranked up?
Neither.

The fact that different altitudes will result is varying dynamic compression due to thinner or denser air.

Our engines have been ramped up in compression from 9:1 to well over 13:1. Even with a wilder cam that bleeds off air at low RPM, the stock starter just isn't able to overcome the increased compression. These engines are built for racing purposes, so it is not relevant to regular factory configurations; but the principle still stands. Comparing starter motor performance without keeping in mind various climatic factors will just keep you guys going around in circles.
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Old 30th November 2011, 22:42   #10
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Default Re: Power/Energy required by starter motor

ok. Just finished reading Dhabharji's post in samurai's jeep thread. It is mentioned that the starter circuit on a jeep will consume about 400 A of current when initiated (the starter is pushed into the flywheel), and approx 50A as the engine is cranked. Link:-

http://www.team-bhp.com/forum/4x4-ve...ml#post2594441 (Mahindra CJ340 joins Team-BHP family)
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Old 1st December 2011, 01:22   #11
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Default Re: Power/Energy required by starter motor

Quote:
Originally Posted by Sutripta View Post
Hi,
Really not understanding this 'Load Controlled Regulator'
Could you please explain
A) what exactly it is supposed to do
B) And why.

Also, how is the current measured?

Regards
Sutripta

dada, I did some search yesterday, found some article from Mitsubishi (electrical department of the automobile unit) and then some and this is what I pieced together:

Let us say a car is running on a highway at a high enough speed and rpm. Let us say that the driver turns some equipment etc. on that has a high current draw.

Now the current draw is high so power requirement suddenly went high. Voltage Regulators are very fast (in comparison with the alternator rpm frequencies and engine rpm frequencies) in terms of their control system response - so the output voltage will not fall much.

This means all of this extra power will show up as a sudden brake to the engine.

Now at moderate to high rpm - not a problem (just like when I change gears I people can feel the shock ). However at idle the engine is tuned to generate very little power by itself (to save fuel) over what is lost in the engine and this sudden kick can stall the engine.

What the Load Response control does is - at low rpms (slightly higher than idle) if any sudden electrical load presents itself, then the regulator deliberately takes time to react - momentarily the o/p voltage will fall (because current has increased, o/p power either remains same as earlier or may even fall) but input power to regulator doesn't increase suddenly, but rather it increases as the Load Response control circuit slowly increases the power output. This process takes a few seconds (most regulators are programmable - you can have 2 to 10 seconds)- enough time for an idling engine (and its control system) to catch up and start producing enough power without stalling.

This function is not good if we look at electrical specs - however it is excellent for engine idle.


Almost all regulators keep looking at the alternator's output frequency and once a threshold is reached (rpm is high enough) the LRC functionality is turned off and regulator will respond as fast as its bandwidth allows (usually response will be of the order of milliseconds at worst if not faster) - there is no further need for it as the flywheel (and vehicle) can provide the required extra power for the first seconds (plus higher engine rpm means engine can ramp up its power output more quickly).


Quote:
Originally Posted by BaCkSeAtDrIVeR View Post
ok. Just finished reading Dhabharji's post in samurai's jeep thread. It is mentioned that the starter circuit on a jeep will consume about 400 A of current when initiated (the starter is pushed into the flywheel), and approx 50A as the engine is cranked. Link:-

http://www.team-bhp.com/forum/4x4-ve...ml#post2594441 (Mahindra CJ340 joins Team-BHP family)


I read that post now - very interesting, I guess I should send him a PM too. Busy going through that thread now.

Last edited by vina : 1st December 2011 at 01:37.
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Old 1st December 2011, 21:04   #12
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Default Re: Power/Energy required by starter motor

^^^
Hi,
Load Controlled Regulator as you have described it is correct. It is the precursor to the intelligent voltage regulator. The philosophy is that the needs of the engine supersede the needs of other subsystems. So shut off/ reduce alternator load when unfavourable to engine, even if it is unfavourable to the electrical system. Most often seen just after a cold start. It is similar in philosophy to shutting off the AC compressor when you stomp on the accelerator. Bad for the AC subsystem, but your power requirement takes precedence.

However ilangpop's post seemed to suggest that this behaviour was entirely internal to the electrical subsystem. Which I find intriguing. So would like to hear from him.

Anybody have any details of Hyundai Eon's system?

Regards
Sutripta
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