Energy Usage of electric cars

[Fantomas]

I recently looked at the fuel economy results of FS Uk of the electric cars and noticed a difference.
Looking at the FS UK numbers (divided by 0.65, because of the conversion factor given in the rules), it seems like any single car used more energy than it had sitting around in their accumulator compared to the given numbers for accumulator capacity in the FSG Program Magazine.
Furthermore three of them, Zurich, Eindhoven and Zwickau, used more energy than allowed by the FS UK Class1A rules for the maximum accumulator capacity. Why were they not disqualified?
As far as I know you can never use all the energy from a battery without destroying it.
Anyone knows what happened? Or are the numbers given by the teams in the FSG Program Magazine just nuts and cannot be trusted?

Fantomas

[Fantomas]

I recently looked at the fuel economy results of FS Uk of the electric cars and noticed a difference.
Looking at the FS UK numbers (divided by 0.65, because of the conversion factor given in the rules), it seems like any single car used more energy than it had sitting around in their accumulator compared to the given numbers for accumulator capacity in the FSG Program Magazine.
Furthermore three of them, Zurich, Eindhoven and Zwickau, used more energy than allowed by the FS UK Class1A rules for the maximum accumulator capacity. Why were they not disqualified?
As far as I know you can never use all the energy from a battery without destroying it.
Anyone knows what happened? Or are the numbers given by the teams in the FSG Program Magazine just nuts and cannot be trusted?

Fantomas

[TommKG]

As far as I know, the data in the result sheet is the actual kWh each team used.

E.g. Delft used 4,1 kWh, Zurich 5,5. etc.

So you don't have to divide it by 0,65.

Furthermore the data from UK seems a little bit high, I know that some guys from Zurich calculated their needed energy with roughly 4,5kWh, so the energy meter wasn't that accurate... As far as I know, all numbers on the FSG Magazine about energy storage were correct.

[Fantomas]

But in the Class1A rules and in the published scoring/result sheet it says that it is calculated by the amount of CO2 generated in kg e.g. Minimum Volume (kg) 4,119

Confusing...
Can anyone of the participating teams comment on that?

Fantomas

[JasperC]

I heard from someone on our team that the listed data are indeed the usage in kWh, even though the score sheet itself indicates otherwise.

Cheers,
Jasper
DUT Racing Team 2008-2010
Delft University of Technology

[Yannick]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Anyone knows what happened? </div></BLOCKQUOTE>

The number are, as far as we know, the kWh of energy used. We think that our "fuel" consumption was measured wrong. Our own measurements matched those of FSA and FSE at the respective competition, so we think we had it also right in Silverstone.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> Or are the numbers given by the teams in the FSG Program Magazine just nuts and cannot be trusted?
</div></BLOCKQUOTE>

The amount of energy stored in the accumulator given in the FSG program is the nominal amount (nominal voltage times nominal capacity). It's not a random number in our case. I don't know for other teams, but I'd say they also put the real value. However, the nominal ammount of energy is not a very helpful number, think of it.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">As far as I know you can never use all the energy from a battery without destroying it. </div></BLOCKQUOTE>

Yes, in the case of LiPo cells, I think you should not discharge them lower than 2.8 V or you will damage them (some unwanted chemical reactions will start). But look at a Voltage/Capacity chart, and you will see that there is not much energy stored after this voltage anyways.

I'm not an accu guy and if I told some BS please bear with me

Bye

[Fantomas]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">The number are, as far as we know, the kWh of energy used. We think that our "fuel" consumption was measured wrong. Our own measurements matched those of FSA and FSE at the respective competition, so we think we had it also right in Silverstone. </div></BLOCKQUOTE>

Did you hand in a protest?
I had a quick look at the specifications of the EnergyMeters of both competitions. FS UK uses a current transducer and transmits the signal over an analogue connection, which should be prone to pick up a lot of noise. The shunt used at FSG and FSA seems to be better suited for this application.

Have you had the chance to have a look at the data recorded during Endurance to see, if noise was the problem?

Fantomas

[Yannick]

I am not sure if a protest was handed in. It would not have altered the result anyway (we still would have used more than Delft, and they were way ahead of us). Keep in mind that in Silverstone it is a fuel economy competition, not efficiency like in FSA or FSE.

I was at the parc fermé when the data was read out from the energy meter. Noise was not an issue, but their voltage measurement on (our) device had an offset. They said that the measured average voltage was around 160 V. Fully charged our voltage will be 152 V, so this is not possible.

Yannick

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Fantomas:
I had a quick look at the specifications of the EnergyMeters of both competitions. FS UK uses a current transducer and transmits the signal over an analogue connection, which should be prone to pick up a lot of noise. The shunt used at FSG and FSA seems to be better suited for this application. </div></BLOCKQUOTE>
A shunt would also use an analogue signal, in fact I know of no way of measuring current 'digitally' without some form of analogue to digital conversion. Presumably the FSG shunt has to be wired into the high-voltage cables and actively cooled? If I understand correctly the FSUK sensor is just looped over the wires in a non-contact way?

Regards, Ian

[Fantomas]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">A shunt would also use an analogue signal, in fact I know of no way of measuring current 'digitally' without some form of analogue to digital conversion. Presumably the FSG shunt has to be wired into the high-voltage cables and actively cooled? If I understand correctly the FSUK sensor is just looped over the wires in a non-contact way? </div></BLOCKQUOTE>

The shunt used by FSG is directly bonded to a PCB which carries an ASIC to digitize the measured current. This leads to an analogue signal wire which is only some millimeters long instead of being routed through the whole car.

The FSG EM specification says that the shunt is only 50µOhm, therefore it should not need active cooling.

The FSUK sensor uses a current transducer, but these do not only catch the field of the measured current, but also all other fields and are therefore less accurate in general. Furthermore the analogue signal is not directly digitized at the sensor, but routed through the car to the logger as far as I know.

Fantomas

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Fantomas:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">A shunt would also use an analogue signal, in fact I know of no way of measuring current 'digitally' without some form of analogue to digital conversion. Presumably the FSG shunt has to be wired into the high-voltage cables and actively cooled? If I understand correctly the FSUK sensor is just looped over the wires in a non-contact way? </div></BLOCKQUOTE>

The shunt used by FSG is directly bonded to a PCB which carries an ASIC to digitize the measured current. This leads to an analogue signal wire which is only some millimeters long instead of being routed through the whole car.

The FSG EM specification says that the shunt is only 50µOhm, therefore it should not need active cooling.

The FSUK sensor uses a current transducer, but these do not only catch the field of the measured current, but also all other fields and are therefore less accurate in general. Furthermore the analogue signal is not directly digitized at the sensor, but routed through the car to the logger as far as I know.

Fantomas </div></BLOCKQUOTE>
Either way you do it, there will be an expected accuracy of the system. To be fair on the teams we would hope the accuracy would be of the order of -10A/+0A i.e. the measurement would never over-read and could under-read by up to 10A.

According to the FSUK website the transducer is an LEM HTFS 400 which outputs 0.003125V per Amp. Claimed accuracy is +/-1% full scale (+/-4A or 8A range). So we have 2A to play with in digitisation error which is 0.00625V. This is about 10bit resolution which seems achieveable. It looks to be a 4-wire sensor so wiring noise immunity can be improved not only by screening but by twisted-pair techniques.

A 50µOhm shunt would output 0.00005V per Amp (Ohm's law). So for similar +/-1% full scale it has to be accurate to +/-0.5µOhm which would generate a voltage change at the digitiser of 0.0000005V. According to this online calculator:

http://circuitcalculator.com/w...esistance-calculator (http://circuitcalculator.com/wordpress/2006/01/24/trace-resistance-calculator)

this is a PCB trace 1mm thick by 3.4mm wide by 1cm long at 25degC, which has a temperature sensitivity of 0.5µOhm for about 2.5degC change in ambient. I'm sure this can be compensated for in some way, but it looks challenging to me.

Regards, Ian

[Fantomas]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Either way you do it, there will be an expected accuracy of the system. To be fair on the teams we would hope the accuracy would be of the order of -10A/+0A i.e. the measurement would never over-read and could under-read by up to 10A. </div></BLOCKQUOTE>
Since the teams are able to run different voltages, specifying this by the current is incorrect. For example if you run an 400V system with 75kW maximum power you end up (ideally, because the voltage will decrease) with a current of 187.5A. 10A are then 5.33% of the maximum value.
If you use a 100V system, your maximum current could be 750A and 10A would be 1.3%.
That can make a big difference.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">According to the FSUK website the transducer is an LEM HTFS 400 which outputs 0.003125V per Amp. Claimed accuracy is +/-1% full scale (+/-4A or 8A range). So we have 2A to play with in digitisation error which is 0.00625V. This is about 10bit resolution which seems achieveable. </div></BLOCKQUOTE>
That is only the accuracy excluding non-linearity errors, offsets, temperature drift, output voltage noise, etc.

The sensor is only rated to peak currents of 600A. My calculation above shows that you may easily reach this with a low system voltage. Question is, how does the sensor behave under these circumstances? At least Eindhoven should have been able to overdrive the sensor.

I also doubt that every team is able to fit their power wire through the 22mm hole in the transducer.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">It looks to be a 4-wire sensor so wiring noise immunity can be improved not only by screening but by twisted-pair techniques. </div></BLOCKQUOTE>

You may of course protect the wiring against noise by using twisted pair for example, but you will still loose some mV across the wiring, because the current flowing is not infinitely small, which will cause a voltage drop. Digital signal transmission is the way to go in such an application in my opinion.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">A 50µOhm shunt would output 0.00005V per Amp (Ohm's law). So for similar +/-1% full scale it has to be accurate to +/-0.5µOhm which would generate a voltage change at the digitiser of 0.0000005V. According to this online calculator:

http://circuitcalculator.com/w...esistance-calculator

this is a PCB trace 1mm thick by 3.4mm wide by 1cm long at 25degC, which has a temperature sensitivity of 0.5µOhm for about 2.5degC change in ambient. I'm sure this can be compensated for in some way, but it looks challenging to me. </div></BLOCKQUOTE>

Such shunts are not built as traces on a pcb but by using special alloys like Manganin which specific resistance is completely inured to changes of temperature and other ambient parameters. Furthermore a specific high acurracy resistance value is achieved by lasercutting and calibrating the shunt.
Additionally by directly bonding ASIC and sensor you are able to compensate a lot of errors by programming correction factors in the ASIC during calibration in the factory.
As far as I know FSG uses a shunt similiar to this: http://www.isabellenhuette.de/...lyer/IVTenglisch.pdf (http://www.isabellenhuette.de/fileadmin/pdf/Flyer/IVTenglisch.pdf)

As far as I know usually shunts are used in high-precision applications. Actively-compensated current transducers may also be used, but are pretty bulky and more expensive.

Fantomas