BXProject

[jayw]

Why is it that Shitroen chose to put the ECU's under the seats do you think?

Surely they'd have been better off behind the dash or in the engine bay?

Answers on a postcard please!

Jay

[Way2go]

It's a cleaner environment under the seats away from the oily bits!

Actually, it's cleaner from an electrical point of view. Integrated circuits and similar can be damaged by transients and better to keep them well separated from things like the ignition/spark plugs that can induce potentially harmful high voltage transients.

[Vanny]

because its the industry standard way of doing it, and its been like that for many many years. I would also expect that BOSCH had something to do with it. Even now the vast majority of cars have at least one ECU under the seat, its the best place for them to be honest.

Whats your problem with it Jay? The wires are long enough on a valver to move the ECU to the glove box if your really bothered.

[jayw]

That is exactly what i wanted to do, especially as the glovebox will be non-functioning anyway (the roll cage stops it opening). Just thought i'd check whether there was any real technical reason for it being under the seat.

Cheeeers, Jay.

[Vanny]

Location location location, in this case governed by access required, cooling performance, and cost of installation. Cooling performance will be your real concern. Make sure there is plenty of ventilation, this old school ECU's will start to error if they get to hot, and temperatures under dash can get rather extreme with 'normal' driving!

[Way2go]

old school ECU's will start to error if they get to hot, and temperatures under dash can get rather extreme with 'normal' driving!

Temperature, another good point. Normal commercial IC's are not usually rated for operating above 50degreeC and this is going to be position_ambient+Internal_box_temperature. So on a hot summer day the internal electronics are not going to be far short of this under the seat. So in a hotter, less cooled position it could be problematic.

[Vanny]

Erm, where did you get that value from W2G? The least stable IC in the Motronic box (27c256 EEPROM) is rated at 0 to 70c commercial and -40 to 125c automotive (going by Microchip datasheet). I would expect the IC's to be okay. Its the various oscilators and capacitors i expect to be an issue, the timing to the IC's will go to pot and assuming BOSCH did a good job then it will fail safe and probably just shut off.

I would also expect the various DAC's to start playing up with increased heat.

But yes, 70c under dash is easily achievable (the heater matrix should be good for 80c straight off).

[Philhod]

The heater matrix ( which was the only bit I understood ) should be the same temp as the water in the system. Ok a slight drop with the air going through. Which under 1 bar (approx) should, if I can remember? is it 10 or 20 degrees per bar? = 110 - 120 C.

[Vanny]

But the reality is that it isnt that hot, air passing over it means it is continually loosing heat, so the average temp coming off the heater matrix (for it is the heat released from the core that we are interested in, not the temp of the water inside) will be quite a few degrees cooler. Also it is not common for the water temp to be 120c because by that stage either a hose will burst, a core will burst, the cap will come off, or the water will escape trhough the engine inards. Either way the likely hood of seeing 120c for a prolonged period is slim, while idle water temps of around 90c (allowing for fan on/off cycle) and thus 80c air off temperatur are very likely.

[Way2go]

My temperature gauge on the GTi sits at 90 but not sure how closely calibrated that is to degrees.

[Philhod]

Yes the fan should keep it to a specific temp, usually between 90 and a 100.

Reading back, what I wasn't explaining very well was that, raising the pressure allowed the boiling point to rise to 120 degrees, so even at 100 you are still well short of boiling.

Also putting 1 bar inside gives equilibrium, so shouldn't result in busted hoses etc.

[Vanny]

I thought it only took the boiling point to 110c? Anyways, i was thinking more about the reality of the situation, not the hyperthetical (because we all know what value that has!)

[Philhod]

I said that on my first post. I couldn't remember if 1 bar raised it 10 or 20 degrees.

I think it is 20, because the pressurised water reactors I worked on used to take the boiling point up to 450 degrees and run at 400 degrees. The water in the heat exchanger turned to steam and then superheat in 3 stages, using that temperature, it would mean 200 bar, which sounds about right.

[jayw]

So, it's ok to move it then...

Jesus, ask a simple question...

[Philhod]

Tha getz tale ant tales mother on ere lad.

[Vanny]

hang on, at 450c wont water be super heated? In which case the properties will be rather different anywho. If only i had my enthalpy-entropy diagram to hand.

[Philhod]

Yes. That's how it works. Water in H/exchanger is pressurised to 3000psi (or 200 bar). Then it circulates the reactor and heats to 400+ degree's, but because of the pressure, is still water.
This is then used to heat, but kept separate from (obviously because it's irradiated) the water in the boiler, in 3 stages. Which at that temperature turns it into s/heated steam to drive the turbines/Generator.

Note: the water in the boiler,starts with no pressure. As it becomes superheated steam, it attains a pressure in the region of 3000psi as it enters the pressure vessel.

Thus proving the maxim: You cannot create energy or destroy it...only redirect it

[jayw]

Yes. That's how it works. Water in H/exchanger is pressurised to 3000psi (or 200 bar). Then it circulates the reactor and heats to 400+ degree's, but because of the pressure, is still water.

Is that 200 bar or 201 bar taking into account atmospheric pressure of 1 bar... lol

[docchevron132]

Ahh, but atmospheric pressures not a constant either really....

[Philhod]

Oh, bugger. That means they must have to switch off when we get a high pressure over the country then and work on lower pressure when we get a low.


Ho hum. back to the drawing board (alright screen) then!