Weber wonders whether weather induces incorrect...

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coulomb
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Weber wonders whether weather induces incorrect...

Post by coulomb » Sun, 26 Jul 2015, 16:45

Weber wonders whether weather induces incorrect indicator intensity

Project day finished up a little early last night, and Weber had to leave the benches bare for today's building of a batch of CMU boards. So we thought we'd take Mexy the electric MX-5 for a drive -- just for the pleasure of it. We dropped in unannounced at a friend's place, but he wasn't home. So we continued driving, trying to find somewhere to buy a coffee.

Near the start of the drive, I mentioned to Weber that although he had charged the battery pack to full, the fuel gauge only read about 7/8ths. He said that he had a theory about that; we thought that the colder weather causes the bimetallic strip in the fuel gauge to not move as far as it would in summer, where we set the PWM ratio to achieve a full indication. (Hence the title of this post.) He thought that this was hidden in a typical ICE car by the fact that the fuel gauge usually indicates well over 100% at full, but a bit less over 100% when cold. Oh well, I thought, we have no range anxiety today.

However, by the time we found our coffee place, the needle was down to about 45%. Could it be that we really would have trouble getting back? Well, we'll be spending a bit of time having coffee, so why not plug in somewhere?

Well, we don't have Newton's nose (Jeff Owen's) for finding power points. Driving around the parking lot, we didn't find any; on foot we found just two. One was a double power point supplying a DVD vending machine, but the power point was located about 3 metres above the ground. The other one was at a delivery bay, with two industrial bins, some shopping trolleys, and at no extra charge, rotting fruit and some waste vegetable (?) oil. Our noses had directed us to an exquisite smell:

Image

These bins are quite large; you can see Weber's head just poking above the left one, and he's pointing to the power point.

Image     Image

Image     Image

The charge was uneventful, and the coffee and chocolate just barely hot enough. So was the charge needed? The 3/4 hour that we charged didn't make much difference to the SOC reading; perhaps 3%. Ten amps really is pathetic charging for an EV; it's just over 2 kWh per hour. So I drove somewhat carefully on the way back, just in case.

In the end, we ended up with 25% SOC indicated on the meter, so there really was no need to panic, and the charge was not needed at all. But I think it validates Weber's theory that the gauge reads lower in winter. I suppose summer will tell us for sure. They really are rather crude indicators, probably highly non-linear as well. But I suppose it's all that is really needed.

At least it turned an ordinary drive into a bit of an adventure.
Last edited by coulomb on Sun, 26 Jul 2015, 14:25, edited 1 time in total.
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Weber wonders whether weather induces incorrect...

Post by coulomb » Sun, 26 Jul 2015, 22:59

I realise now that the theory doesn't really explain the 25% SOC remaining at the end of the drive. I forgot to mention that, not having driven Mexy for a while, shifted to *fifth* gear for a lot of the highway driving on the way out, instead of third (perhaps fourth) gear as is more appropriate. I guess I'm used to highway driving in fifth gear, and just didn't think about it. So the motor would have been running at rather higher current than normal. This must also have impacted pack drain on the way out, so that it may well have used about half the pack's energy over the moderate distance we would have driven.
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Weber wonders whether weather induces incorrect...

Post by Richo » Tue, 28 Jul 2015, 20:24

Leave the windows down so the gauges get nice and cold.
Check the SOC.
Then put a heater in and blast it full of hot air for a few hours.
Check the SOC.

That'll prove if your theory is correct.

So the short answer is NO but the long answer is YES.
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Weber wonders whether weather induces incorrect...

Post by offgridQLD » Sun, 02 Aug 2015, 03:23

Nice find with the outlet.

I would have thought accurate (or close as you can get) SOC readings. Would be one of the most critical bits of instrumentation in a Ev. A SOC gauge that misrepresents the true SOC can get you in all kinds of trouble ....adventures Image

I understand the the aim was to keep the interior looking stock and I think it's good how the factory gauges are put to use. For the most part like you say it's good enough. Though what about some kind of digital gauge hidden in the glove compartment or Bluetooth to your phone.

All that cooking oil yuck. That reminds me I noticed oil grease smell near my Imiev in the garage last week. On closer inspection I discovered a spray of grease in the rear wheel arch. It had me going for a while looking for broken CV boots - wheel bearing but nothing. Turns out the day before I parked next to a bunch of earth moving equipment that was restoring the shopping center car park surface. I guess I had ran over a big dollop of grease from the grader or excavator. My nice clean EV tainted with a spray of dinosaur juice Image

Kurt
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Weber wonders whether weather induces incorrect...

Post by T1 Terry » Sun, 02 Aug 2015, 18:11

With the 5th gear v any other gear choice, wouldn't the repurpose of one of the gauges to show motor load be a logical step? Much like the vacuum gauge in the '70s era cars to educate the driver that the pedal position could be effecting the fuel consumption sometimes and a gentle take off resulted in better economy. Funny that you never saw a vacuum gauge as part of a performance car dash :lol:

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Weber wonders whether weather induces incorrect...

Post by bladecar » Mon, 03 Aug 2015, 02:32

Hi T1,

From memory, only a few cars ever had vacuum gauges on the dash to show how the pressure-compared-to-atmospheric varied in the intake manifold when the the throttle butterfly valve was operated by the throttle pedal and allowed more or less air to pass into the engine thereby varying the restriction of flow.

I think, and it can be wonderful for an oldie to do this exercise :) that the EJ Holden was one of the few that comes to mind with this gauge on the dash as standard.

Yes, people, even today, are buying the last Ford and GM performance cars even though they are guaranteed not to have a vacuum gauge since many buyers, via nostalgia, are guaranteed to have a vacuum gauge of their own   Image

I know they have a status in the same way as a ducati or an mv agusta might occupy a space in the pool room or the bed room but - what with the falling dollar and the way of the world, how long before petrol gets to the level that it's going to get to, and I know you know what I mean??

Oh, and I think an ev does need a gauge similar to the vacuum gauge because "enthusiasts" of evs would see one as central to performance.

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Weber wonders whether weather induces incorrect...

Post by offgridQLD » Mon, 03 Aug 2015, 02:44


Heaps of cars in the late 70's early 80's had vacuum gauges. VB Commodore, A lot of Datsuns of the same vintage had them.

Regarding the 5th gear being less efficient due to loading the motor in a less efficient range. I often wondered where the sweet spot was on a car like the Imiev with a single fixed ratio transmission.

Kurt




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Weber wonders whether weather induces incorrect...

Post by bladecar » Mon, 03 Aug 2015, 03:19

Hi Kurt,

Very interesting to know.

I'd lost track of which Holden was which by then and my era included the EH, sometimes the HR, the GTHO and GT, and there were also the rice burners which we rarely talked about (although there was nothing wrong with them :))

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Weber wonders whether weather induces incorrect...

Post by weber » Mon, 03 Aug 2015, 04:45

T1 Terry wrote: With the 5th gear v any other gear choice, wouldn't the repurpose of one of the gauges to show motor load be a logical step?
T1 Terry

Right. Trouble is, you'd have to actually look at it. Image

That's a bit unfair because Coulomb hadn't driven MeXy on a highway since we got full design power (by installing the 750 V WaveSculptor). So even if he was looking, he wouldn't have know what was normal.

The temperature gauge would have been the biggest giveaway that it wasn't operating efficiently, but by the time we realised that, it had already been cooling down for 45 minutes.

The other one would be the tacho; either the actual RPM, or several other quantities such as battery current, voltage or power, that we can choose to display on the tacho by flipping the key repeatedly to the start position while driving. Crazy user-interface I know, but it meant no new switches as well as no new gauges.

But in all cases, it would have needed me to to lean over from the passenger seat and take a look. Had I been driving I would have known immediately from the small change in acceleration for a large change in accelerator pedal position.

It would be great to have a Wh/km display available on the tacho, but with the speedo still being a cable-driven type, our EVCU doesn't have access to road speed or distance measurement (since it doesn't know what gear the car is in either).
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Weber wonders whether weather induces incorrect...

Post by weber » Mon, 03 Aug 2015, 04:47

Image
Last edited by weber on Sun, 02 Aug 2015, 18:48, edited 1 time in total.
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Post by T1 Terry » Wed, 05 Aug 2015, 03:56

Ah, well that explains it, a lack of experience will catch you every time :lol: remember doing the walk of shame carrying the fuel can after running a HO shaker out of fuel due to a heavy right foot, but the thrill was one of those once in a lifetime events I'll never forget, 44 gals of fuel in Wollongong and never made it to Wagga :lol:

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Weber wonders whether weather induces incorrect...

Post by weber » Wed, 05 Aug 2015, 04:08

Awesome. And I must say, in Coulomb's defence, It really is very easy to go from 2nd to 5th in the MX-5 when trying to go from 2nd to 3rd. I've done it many times myself. You almost have to let go of it in neutral so the rather-gentle-springs center it, then push it forward.
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Post by offgridQLD » Wed, 05 Aug 2015, 12:51

Yes, I noticed the shifter on the MX5 has a very tight shift pattern and compact lever. I can see how it could be tricky until your accustom to it. Not to mention you don't have the wimpy 1.6lt ICE gasping for breath under load as a signal anymore




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