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RE: RE: STREP FP6 proposal

Title: Message
In the early 1980s I used to work for Motorola. We took a  Lancia Delta and stripped out all the wiring (approx 1500m) and replaced it with a power bus (10m) and a fibre optic connection (30m) for signals. Each light cluster (for example) had an MCU controller. In total, we had about 30 (compare this to around 80 MCUs in a modern high end car). However, in the early 1980s, the MCUs were all NMOS and had a current drain of a few mA. If the car was parked at the airport for a week, you had to disconnect the battery in order to ensure that it would start when you came back.
(By the way of digression on car alarms - every time Concorde used to take off from Heathrow, there was a wave of car alarms followed it down the car park at the side of the runway as the ultrasonic detectors were triggered - this didn't do much for everyones batteries. Alas, Concorde is no more)
In most automotive systems, many of the circuits are powered continually in a standby mode. Car batteries should not be discharged too far if they are going to cold crank a car - so although you may have a 60AH battery, you will not want to discharge it much below 40AH. Take into account the self discharge (which increases as the battery gets older - sediment starts to cause greater leakage across the plates) and you can see that you probably don't want to use more than 10AH in a period of (say) 3 months - a best guess at the length of time a car may be in a showroom without being started up and run. This gives a maximum current drain of around 5mA. Also, don't forget that automotive electronics have to be specified down to -40 Centigrade; at this, the cold cranking capacity of the battery is greatly reduced (when I met my wife, she had a Voshkod 2 - this was a Russian motorbike which did not have a battery - batteries freeze in Siberian winters - instead it had a permanent magnet alternator with four separate windings with the most terrible peaky waveforms - I know because I built an electronic flasher unit for it).
The idea that you can use a PIC to do the power management defeats the object of most of the electronics - you simply cannot get all the wiring into the car - this is why electronics and smart signalling are used.
I am not actively involved in automotive electronics today, but I wouldn't mind betting that 5mA is considered on the high side for total "off" current drain.

Tony Gore

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-----Original Message-----
From: owner-occam-com@xxxxxxxxxx [mailto:owner-occam-com@xxxxxxxxxx] On Behalf Of Ruth Ivimey-Cook
Sent: 12 May 2005 11:18
To: sjmaudsley@xxxxxxxxxxxxxxxxxxxxxx; 'Ruth Ivimey-Cook'; eric.verhulst@xxxxxxxxxxxxxxxxxxxxxx; occam-com@xxxxxxxxxx
Subject: RE: RE: STREP FP6 proposal

The Evo case seems more to be a case of the absence of proper power management. There should have been a controller whose job it is to manage the power budget and ensure that essential services (itself, traction control, injection control, etc) are given priority over non-essential services (hifi, aircon, electric windows). Even a basic PIC could do that job! 
And one might be able improve the parked case: why have half a dozen systems powered up so that the keylock and alarm can function? ... or does an alarm system take a good deal more than a few tens of milliamps to operate by itself. ....fx: search google... that said, in a 15 minute search I didn't find any car alarm specs that even mentioned a power budget. I guess that speaks for itself.

From: Stephen Maudsley [mailto:sjmaudsley@xxxxxxxxxxxxxxxxxxxxxx]
Sent: Thursday, May 12, 2005 10:07 AM
To: Ruth Ivimey-Cook; eric.verhulst@xxxxxxxxxxxxxxxxxxxxxx; Ruth.Ivimey-Cook@xxxxxxxxxx; occam-com@xxxxxxxxxx
Subject: Re: RE: STREP FP6 proposal

> supplies to automotive and in this market high reliability,
> low cost and low power are severe boundary conditions ).

I can readily understand low cost and high reliability, but why is low power,
when you've large numbers of amps being generated in the next compartment?


Whilst that is true, when you run out of amps the effects can be catastrophic. I recall the case of the Evo where the driver turned on the hifi, the voltage rails dropped, the traction control failed and it wrapped around a lamp post on the next bend. That may have been a case of successfull Darwinism but with 30+ computers then there is more of an effect to take into account.

I suspect that as we attempt to use the technology for lower power cars (look at the price of fuel...) that the power budget is more of an issue.