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Old 6th July 2007, 09:21   #16
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Originally Posted by low_bass_makker View Post
also because of the large load of the starterthis causes the voltage drop which will be bad for some stuff thats why they are switched off by the key switch
Perfect. True engineer speaking!

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but then, i feel its bad for the power antenna.. because i see its become really slow and noisy now.. what say guru's?
Slow and noisy? The antenna needs a good wipe, that's all - must have accumulated grime. No, the antenna motor is not affected by the switching - they are tested for 10000 cycles at least at design time, equivalent of 20 years normal usage. Grime accumulated on the antenna increases friction, which increases the load on the motor, which affects speed and noise produced.

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Scorpio - nothing turns off.. still continues to work.. is it bad??
IMHO no, it is not bad.

Scorpio is 'different' - it is a "vendor-designed" vehicle, since M&M doesn't have a conventional "design center" like other auto manufacturers (no, HM and Premier don't count).

Each sub-system vendor decided what is good or not good for their product. In this case they must have defied convention and decided "vehicle start conditions don't affect our product/sub-system". Well, Scorpio has not been around long-enough for that wisdom to be tested, but they are doing good, and deserve plaudits.
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Old 6th July 2007, 09:46   #17
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Originally Posted by navin View Post
well that maybe for 2 reasons.

1. the number of on board gadgets has gone up dramatically
2. lethargy.
True.

In the 60's there was only 1 ECU (in the "car radio"), only 2 motors (starter and wiper) and limited electrical load (ignition, lamps, indicators, horn). In rare cases there were power windows, electrical heating (H in HVAC) and a few other odds and ends. And no 'global warming'.

Today there are more than 50 ECUs (at least 20 in the Indian cars; well, not all the ECUs are recognizable since they don't look like the engine ECU, i.e. a square alu box with large hidh-density connectors), and other than the wheels everything else is electrically driven. In hybrids even the wheels are driven electrically.

Lethargy? In a way, yes. The excuse is "convention", and most designers don't defy it - for the risk of failure. Of course, it needs a lot of hard work to "defy" convention (passion, research, prototyping, testing, field proving).
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Old 6th July 2007, 11:16   #18
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But many ECU's including the semiconductors in The ICE system do not react favourably to rapid voltage drops.
While this may not be apparent in the case of, say, a brand new Bosch battery (since we're discussing new generation batteries with deeper cycles and a more regulated closer-to-12V always tech), it could happen when the battery is 3 years old.
I believe the manufacturer has to make provision for this.\

Allow me to elaborate specifically with reference to 2 loads - A HU(Negligible load) and a starter (Massive load).

I know for a fact that certain over-engineered HU's do not take kindly to the voltage dropping below 10V and while most of the time, this will not lead to immediate failure, it greatly increases the possibility of a on board failure.
While a new battery may not drop to that level during a cold start (owing to it's high current delivery), the same battery towards the end of it's life-cycle, will suffer in it's current delivery, logically causing a drop in voltage (during the cold crank). The voltage will automatically translate as a sharp drop in the +Vcc of the (already) running HU.

Once the car starts, the alternator will raise the voltage, by self-generation, bringing it to a more acceptable >13V. The HU and the entire ICE will thrive on the >13V.
So assuming the battery is towards the end of LC, why subject the HU to a drop below 10V for a few seconds and then a sharp rise (once the car has fired up). Far easier to shut down the Vacc for those few seconds, get the car fired and restore Vacc.

Also makes sure the multiple minor loads (Lights, ICE blah blah) are all deprived of any current drain.

The true exception to this rule is the Power antenna. It has 3 connections, earth, +V and Vcontrol (like the bloue Pconnect of the amplifier). When Vcontrol is cut off, the antenna is designed to retract, thereby needing current flow from the battery for the operation.
So if the HU is on, the power antenna raises itself (load during the raise). Now you crank. The HU Vacc is cut off so the HU has no load.
BUT the Vconnect to the antenna is cut off, causing the power antenna to retract, by design. This retraction is also a load. So even in a modern car, the start load would be the Power Antenna retraction and the starter.
Of course the load of the retract action is miniscule in comparison, but since we're discussing all load, I thought I'[d discuss this one.
Only way to avoid this is to make sure the HU is in "power off" mode, before the starter is cranked.

Just my 50 paise.
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Old 6th July 2007, 11:23   #19
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vow sambaba your 50 paise looks like a big big baloon

anyways thanx for the detailed explaination sir
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Old 6th July 2007, 11:49   #20
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It happens all the time in my WR and 800. Never considered it as a big issue.
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Old 6th July 2007, 14:30   #21
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There used to be a time when I was the one giving the long technical sermons.
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Old 6th July 2007, 16:26   #22
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There used to be a time when I was the one giving the long technical sermons.
we all are waiting to return of that time.

"The Return of Navin Ji"
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Old 6th July 2007, 16:56   #23
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Interesting topic. And some nice long detailed explanations too.
Had been experiencing this in most of our cars and never thought to be abnormal.
Merc also shuts down the blower of the Aircon etc.. and after a very short pause, everything comes back to normal.
Prado also behaves in the similar way.
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Old 6th July 2007, 17:52   #24
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Well said, Sam - your reasoning is correct. Of course, there is a slight difference between 'perceived' and actual power-down.

* What we see on the HU is the perceived power-down because we see the display going off and coming back on again. Actually the HU resets itself without interrupting the BAT line (if it did, the settings will be lost, including the time setting). When the ignition key is in OFF position, the HU goes to sleep, but is still powered (that's how the red LED can flash after the front panel is removed). Reset is just a short 'sleep'.

* In the headlamp circuit, the relay is turned off for the duration the key is in the 'Start engine' position. The headlamp circuit has an ECU today. In older cars they wouldn't go off, one could see the headlamps dimming when the car was started (voltage drop, as you correctly explained)

* Power antenna is sub-system of HU, like HU is sub-system of the vehicle. So everytime HU resets, PA goes down and then up again.

The difference is "unit told not to draw power" v/s "power is cut off at source". Auto electrics follow the first one as a convention. But, since this is a "convention", designers can actually flout it (as observed in the Scorpio)!

Last edited by DerAlte : 6th July 2007 at 17:54.
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Old 6th July 2007, 18:37   #25
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head lamps dont go off in all the cars, newer ones included. Again depends on if the ecu is programed to do so as Deralte mentioned and this is funny coz headlamps are major power hoggers.

i know CRV it doesnt and in iKON it does switch off as soon as the engine stops turning.
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Old 6th July 2007, 18:58   #26
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Originally Posted by DerAlte View Post
Well said, Sam - your reasoning is correct. Of course, there is a slight difference between 'perceived' and actual power-down.

* What we see on the HU is the perceived power-down because we see the display going off and coming back on again. Actually the HU resets itself without interrupting the BAT line (if it did, the settings will be lost, including the time setting). When the ignition key is in OFF position, the HU goes to sleep, but is still powered (that's how the red LED can flash after the front panel is removed). Reset is just a short 'sleep'.

* In the headlamp circuit, the relay is turned off for the duration the key is in the 'Start engine' position. The headlamp circuit has an ECU today. In older cars they wouldn't go off, one could see the headlamps dimming when the car was started (voltage drop, as you correctly explained)

* Power antenna is sub-system of HU, like HU is sub-system of the vehicle. So everytime HU resets, PA goes down and then up again.

The difference is "unit told not to draw power" v/s "power is cut off at source". Auto electrics follow the first one as a convention. But, since this is a "convention", designers can actually flout it (as observed in the Scorpio)!
i like to add my 1 paise here.


the HU and the power antenna have two things common that is

the ground wire
the battery wire
and the remote turn on.

when the starter is switched on the power from the remote turn on is switched off which causes the HU to turn off and not to reset thats why the the time and other functions are preserved . and same the case with power antenna the movement the remote wire current is off the antenna starts moving back and when the key is left . the current return the antenna start opening again.
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Old 6th July 2007, 23:40   #27
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Quote:
Originally Posted by DerAlte View Post
* What we see on the HU is the perceived power-down because we see the display going off and coming back on again. Actually the HU resets itself without interrupting the BAT line (if it did, the settings will be lost, including the time setting). When the ignition key is in OFF position, the HU goes to sleep, but is still powered (that's how the red LED can flash after the front panel is removed). Reset is just a short 'sleep'.


* In the headlamp circuit, the relay is turned off for the duration the key is in the 'Start engine' position. The headlamp circuit has an ECU today. In older cars they wouldn't go off, one could see the headlamps dimming when the car was started (voltage drop, as you correctly explained)
Actually, the logic for the headlamp and the HU is similar. Let me explain.

It is a common misconception that the (Yellow) always on wire is used to maintain memory (settings, clock, FM stations etc) and the HU physically runs off the (red) ignition on 12V, ignition off 0V wire.

In effect the red accessory supply merely triggers the HU to operate or not. Except for the circuits that need power always on to keep the memory, every other circuit shuts down using the accessory on and off. But the true load of the HU remains on the (yellow) always on wire. A simple testament to this fact is that the yellow wire is always of a better gauge than the red wire.

And that is the same logic(not method ofcourse) by which a headlamp relay/solenoid works. While the switch controls the headlamp state, the actual load of the lamp is transferred directly to the battery.
and that's what I was saying earlier

Quote:
Originally Posted by Sam Kapasi View Post
The voltage will automatically translate as a sharp drop in the +Vcc of the (already) running HU.....

.....Far easier to shut down the Vacc for those few seconds, get the car fired and restore Vacc.
Where Vcc is the battery voltage(yellow) and Vacc is the accessory wire (red)

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Originally Posted by DerAlte View Post
* Power antenna is sub-system of HU, like HU is sub-system of the vehicle. So everytime HU resets, PA goes down and then up again.
A power antenna funtions perfectly well without a HU. It is a simple circuit, similar to the 3 wire logic of a headlamp solenoid and a HU and an amplifier and many other devices in the automobile.
Earth, Always on and trigger.

The power antenna can be opened simply by providing 12V (low current) to the trigger terminal. You don't actually need an HU for this. The minute the 12V is 0V, the antenna retracts. When the HU is on, the blue wire (often the same one that switches power amps on and off) triggers the antenna.

My point was, in a working HU, if the Vacc is switched off, the load is immediately gone. (The 12V running the memory circuit is less than a trickle) At the same time, since the trigger wire is now 0V, all power amps (if any) immediately go off, and their load is immediately gone too. In an "on" headlamp, if the Vacc is switched off, the relay/solenoid clicks back into the Normally_Open state and the load is immediately gone.

However...
A completely open power antenna has no load on the battery, but if the Vacc is switched off, the load increases for a few seconds while the antenna retracts itself. Instead of the load reducing (like the other gadgets) the power antenna actually draws current (to retract itself) while you are cranking.

AND I'd like to add that the power antenna actually draws more current during the opening and retraction motion than a standard HU does.

Last edited by Sam Kapasi : 6th July 2007 at 23:43.
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Old 7th July 2007, 01:06   #28
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Sam Bhai what are we discussing here????
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Old 7th July 2007, 10:19   #29
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LBM, Der Alte and I have having a conversation (I would not call it a debate, as we do not disagree) in and around load factors on the battery during the ignition click on-off.

That is related to the title of the thread, is it not?
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Old 7th July 2007, 10:25   #30
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Originally Posted by Sam Kapasi View Post
LBM, Der Alte and I have having a conversation (I would not call it a debate, as we do not disagree) in and around load factors on the battery during the ignition click on-off.

That is related to the title of the thread, is it not?
Yes Sam Bhai but I think we all are giving the same answer in a different language...and we are going round and round here.
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