Fan temperature sensor

[MarekH]

This is a classic case of a solution not doing what you think it claims to. It doesn't actually increase the cooling capacity of the system - it simply half turns the fans on when the original system still has some untapped cooling capacity of its own. The penny drops when, in the video, Tom explains that the fans go to full speed when the original Otter switch kicks in.

The basic system is already designed such that the radiator has more cooling capacity than the engine has to produce heat and there is already a feedback mechanism to discard the excess cooling capacity. When the designers judge that to fall short (i.e. when above the Otter temperature switching point), they call in the cavalry and apply fans 100%. This controller simply adds some cooling via fan when there is still an excess to be had by the original system. In principle, there is nothing wrong with that, but it doesn't add any cooling.

You can't actually tell or even control what the "correct" engine temperature is closer than plus/minus 3'c because of the way the thermostat works. This is a graph of an engine idling on the driveway. RPM is constant, so total waterflow is constant. The car is stationary, so airflow is zero. Cooling capacity is constant. The car engine rpm is constant, so heat generation is constant. The temperature still yo-yo's between ~82'c and ~88'c. This can only be because the thermostat is moving - nothing else is changing! It is quite clearly only letting the radiator have the minimum amount of water it can and thanks to the way the wax melts and resolidifies, there is a delay and hysteresis naturally present that you cannot design away. If you have thermostats in your car, you are stuck with this as a limitation. This is how the feedback loop works.



See http://forum.etypeuk.com/viewtopic.php? ... ph#p132484 for explanation.

So if the thermostats are not yet fully open, all the new controller can achieve is make the E to F slope slightly steeper and more quickly push the temperature down towards the designed operating temperature. That's no bad thing, but the system has not yet lost control, so it isn't actually needed. If the thermostats are fully open, why are we messing about with PWM? For God's sake, turn the fans on 100% NOW! That's my point.

The thermostat and PWM aspect are somewhat duplicating each other. The further above the minimum engine operating temperature the water is, the higher the duty cycle is for water sent for cooling (the thermostat is just a water splitter). The PWM switch is also set up for a higher duty cycle based on radiator exit temperature. If it succeeds, then the thermostat acts against it and if the radiator succeeds with what the thermostat gave it, then the fan PWM duty cycle drops. You don't need two PWM type control mechanisms competing for feedback control prior to the thermostat being fully open. This will be a great system if it is tweaked for what is not covered by the original, rather than adding a layer of complication* that duplicates the original.

What is actually needed are two things:- 1/ if the radiator exit temperature is too high as judged by the new programmable Otter switch (which, as a concept, I have no problem with), just go to 100% fan - the thermostat will tell you when the job is done - going via PWM simply means the temperature takes longer to stabilise at the minimum operating temperature than need be. So let's just have a user settable Otter switch and be done. 2/ Instead of duplicating the enabling of cooling capacity, programme in the safe operating area of the engine and force the fans 100% on when you are heading out of that region. Put bluntly, stop playing with PWM percentages and instead place a Hall effect sensor in the tacho and speedos - when below 20mph AND below 1500rpm AND rpm>0, force the fans ON 100%. We already know an average radiator is good when there is airflow and waterflow, but overheating occurs when waterflow and airflow are at their minima - so use the programmable nature to pre-empt that. You either need these fans or you don't - you never half need them, or 70% need them.

annotated Image5.jpg (43.35 KiB) Viewed 3622 times

This acts as a speed sensor for the fuel injection system I built.

So, in summary, the custom controller looks nice, but it may not actually be doing much.

kind regards
Marek


*There is a design hazard here - I don't know what chip is doing the switching here, but if it is a transistor, then there will be heat dissipated in there and looks to be a surface mount (rather than through hole) item. For an average 6amps drawn, it'll see 6x0.67=4watts of heat to lose. That's why, with my lack of education ten years ago, I used a TO220 package mounted in free air, not a surface mount item. Tom's controller also it has to not fail at ~95'c operating temperature if it is sitting on a radiator. Also, people do mount bigger aftermarket fans in there and they draw utterly HUGE currents. Obviously, they ought to disclose that to Tom before they go for this "upgrade", so I hope it uses a nice cool running MOSFET or is happy switching a good 30amps at 11kHz. If not, they will blame Tom rather than themselves for any potential overheating episode.

[myJagV12]

Hello Marek,

I used a BTS50500-1TAD automotive high side power switch and on the backside of the PCB mounted a small cooling. Imo this gives better heat dissipation than with a TO220 housing and also to the terminal lead.
At 85°C the switch has a nominal load current of 33Amps and the switch signals over-temperature to the MCU ( which also measures the temperature at the FET).
Of course the only chance when the MOSFET is no longer happy is to stop PWM switching and permanently turn on the switch (not implemented yet but I think 100% PWM does just the same). The on resistance will than likely be lower than that of a Lucas Relay (I am more concerned about the temperature of the MCU which is the -6 85° version and not the -3 125° version in the moment).

"It is specially designed to drive high current loads up to 80 A, for applications like switched battery couplings, power distribution switches, heaters, glow plugs, in the harsh automotive environment."



I wrote before that I still have to test the device on the road and I will add bluetooth to report the measured values (up to 4 external temperature sensors). Even if the device will not help improve the cooling it costs way less than an original fan relay and I like smooth starting ;-)

BR, Tom

btw: the connection to the otter switch was made primarily because of AC - the temperature is measured +/- 0.5°C anyways but I could detect if the IN-Signal was triggered at lower temperature which is than likely the AC being on (and run the fans at a lower speed than )

edit: there is also a design hazard with failing fan relays

[myJagV12]

Hi Marek,
Regarding your graph showing the opening and closing of the thermostats.
You could also interpret this as a cooler cooling too strong :D
The better the cooler the faster the thermostats act and with an "ideal cooler" cooling just as much as necessary they should/would remain half open or at least act less often - no ?

That said would mean an opening thermostat does not require 100% (of an "overdimensioned" cooling system) necessarily but eg. 90% air flow might be ideal to stabilize the temperature and protect overheating.

BR, Tom

[MarekH]

Dear Tom,
these sorts of FETs simply weren't available 15 years ago when I was designing and prototyping these sorts of things. The options available to us now far exceed our wildest dreams and the main concern these days is that the technology moves on so fast that these chips get removed from the market before WE consider them obsolete. (The photo I posted is well over ten years old.)

Do a forum search for my posts on "thermostat" both here and on jag-lovers.com (and Mike Frank has written about them extensively on his Coolcat website) for an in-depth discussion of what actually goes on. There is a lot of misunderstanding of the topic.

The analogy/example Philip quotes is sensible, but it is describing a system that works, i.e. one which has excess cooling capacity and that means his thermostat always denies him access to the pool of cold water he builds up at the bottom of the radiator, so augmenting a well maintained system isn't massively helpful. That means he gets a one-time thirty seconds worth of cold water to play with in a crisis. (You can't get the temperature down lower than the thermostat temperature.)

Here'#s a link to demonstrate what a radiator full of cold water does for you - the example is how to remove heatsoak from the heads post shutdown. Running the engine longer than 45 seconds or so is counter-productive as we have used up our pool of cold water and are back to normal running again.

https://forums.jag-lovers.com/t/solving ... ple/377151

The only time something a controller this comes into its own is when the cooling capacity is barely exceeding heat generation. Helpful though it may be, what is really needed is to repair the radiator at this point and simply running the fan at 100% does everything you designed it to do but does it more and quicker, so the PWM aspect is only of value if you can get much the same airflow for less electricity. What your switch does is really just make the radiator slightly more powerful, but what is needed from an active device like this can deliver is to address the low rpm (low waterflow) and low road speed (low airflow) scenarios, e.g. stuck in stop-go traffic or crawling up an Alpine pass. Those situations are when d(heat generation)/dt exceed d(heat dissipation)/dt and the temperature creeps upward. (Heat generation may be low, but when heat dissipation is close to zero, you are in trouble.)

kind regards
Marek

[myJagV12]

these sorts of FETs simply weren't available 15 years ago ...

..., but what is needed from an active device like this can deliver is to address the low rpm (low waterflow) and low road speed (low airflow) scenarios, e.g. stuck in stop-go traffic or crawling up an Alpine pass.
Marek

Well we can think of a device that is running the fans @ higher than 100%.
Of course this could be done but that does stop making sense.

It seems you don't like anything but Lucas relays and your TO220 FET's. Your opinion !

I will add a Gyro in the new design so the device detects idling without hall sensors at the speedometer but still in your opinion you would run the fans 100% when starting the engine .....

BR, Tom

edit:
As a conclusion running fans at lower than 100% is ridiculous and those Mazda engineers must all go for training right ?

[MarekH]

Tom,
what Mazda chose to do with a twin fan setup for a car with a totally different engine and a much smaller volume of coolant is up to them and has no bearing on what is needed for 5.3litre engine mounted in a confined space and with 19 litres of coolant circulating. To add to that, their fans shift a different amount of air to that which the Lucas fans do and their radiator size is different. It looks like their thermostats are unlikely to be 74'c ones Philip has fitted or even the 82'c ones Jaguar specified. If you want to follow the example you quote from your Mazda table, you'll not be turning on your fans below 105'c. Good luck with that.

Mazda obviously feel that even at 105'c, their fans will shift so much air that they will not need to be run fully. You cannot conclude anything useful about our Jaguars from this.

Also, the Jaguar fan relay 12v comes from a green wire which is fused from the ignition switch's white/pink accessory terminal, so during cranking, the fans cannot run anyway. From my previous advice, let "rpm>0" read "rpm>160" to stop yourself feeling obliged to run a fan during cranking if you have inadvertently rewired your car incorrectly.

kind regards
Marek

[myJagV12]

Marek why should I wire my car incorrectly and no I won't use the Mazda RX7 cooling params.

It was just a sample that other cars using thermostats are still controlling fan speed which in your opinion seems to be counterproductive in itself.
I won't have cooling issues with a new powerful radiator in place, a rebuilt engine, new coolant, thermostats ... Anyways I will install my device and record temperature changes picked up (also at the front and rear of the engine) and play with the thought to install two CWA-400 (similar to the D.G. design) - that's when this all makes more sense of course.
Thank you for your input !
BR, Tom

[MarekH]

Tom,

There is nothing wrong in incorporating new technology into our cars. I can easily imagine that fitting a massive Coolcat fan onto a new radiator will mean it won't be necessary to run the larger more powerful fans as much, or that such a car can be safely run hotter because it can drop the temperature more quickly once the fan is deployed. Just because it is done on a different (Mazda) car doesn't mean it'll have the same effect on ours. Empirical evidence shows our cars have most of their problems at low revs and low/zero road speed.

"Counterproductive" is when you actually make something worse than before.

No one is saying PWM is counterproductive in itself. No one is even saying your switch is a bad idea. To have a worthwhile design, you need to decide what was wrong with the original first, what the new design goal is going to be and then work towards that, then test it and finally deliver a result.

Other designers (e.g. from Mazda) are working to a different brief, using different parameters because they have different objectives, e.g. 88'c thermostats for emissions purposes, the desire for a smooth idle, perhaps running different levels of ignition advance and air:fuel ratios. This has no bearing on our fifty year old cars. If you learn anything from this, it is probably that their (e.g. Mazda's) cooling systems is so overspecified that it can idle all day, with aircon on, at low revs with no ambient airflow and still not overheat - so it is not a surprise that Mazda don't need to run their fans at 100% duty cycle once up at road speeds - but this says nothing about our cooling systems.

What is slightly worrying is that now you are telling us you will fit a new radiator. That's great, but it'll be harder to determine whether it is the switch that is effecting the improvement. For people with an averagely maintained stock system, this whole thread is just a confusing bun-fight of claims on your part versus me working out what the actual effect might be and whether the credit for this is attributed to the right component. That's not a criticism of what you are trying to do, but making sure the perspective is correctly put into context.

kind regards
Marek

[myJagV12]

Hi Marek,
I did not claim a lot just told that I'm switching the fans with a FET device instead of an old almost rotten Lucas relay with the advantage of smoothly starting the fan (at least) and maybe hook in before the not so precise OTTER switch might become active. I would never dare to say that this will help anyone having cooling issues to solve them - you might have misunderstood me.
One would be better off cleaning his radiator, use more efficient fans or low temperature thermostats but you can tell them the right measurements for sure.
So to the name of the thread: I use a digital temperature sensor.
Best Regards,
Tom