KERS store must between driver & engine....

[scarbs]

Does anyone know if the MGU system is DC or three phase AC? From my time with an electrical contractor, a 3 phase system would be more efficient, and require a higher gague (smaller) wire to transport the electricity between the MGU and storage system. If it is a high amperage DC system, the wires would become enormous for any distance longer than 3 feet.

Scarbs, do you happen to know anything about this?

Thanks!

The systems are DC, the distance in between the component sis minimal. For most less than a foot (30cm), for McLaren certainly less than 2 feet (60cm). I was told by bob Bell, that the cables are thick (like jump leads he said!), but I have yet to confirm their size from pictures.

[xpensive]

Never thought of that one really, a 60 kW DC-lead, what Voltage?

[ackzsel]

Don't they use a fairly high voltage? That wouldn't require very thick conductors (insulation should be thicker, though, but that weighs less.)

[Professor]

On the road hybrids are at about 300vdc. So,60,000w/300v = 200 amps. The wire size would be #2/0 if it had a 90c insulation. If the voltage is higher, the amps are lower. A cable with a high temp insulation could be a smaller gage.

[xpensive]

Interesting, Aluminium wire for minimum weight perhaps?

[Professor]

Sure, but aluminum must be a larger size than copper for the same ampacity. But, it is half the weight.

[xpensive]

Copper has indeed only 60% of Al's resistivity, but is more than three times heavier.
Any other negatives with Al for such a purpose, overheating perhaps?

[Professor]

The conductor, whether aluminum or copper, is capable of a much higher ampacity than the insulation. Insulation is the limiting factor. Factors are: the load in watts, the voltage, the ambient temp, the number of current carrying conductors in the raceway and the temp limits of the connectors.

Aluminum is difficult because the connections get loose and cause an increase in resistance, they get hot, and you have "cold flow", meaning that they change shape when not under load and cool off. So more looseness, etc, etc.

Bare conductors in free air have an ampacity twice as high (approx.)as the same insulated conductor. Raise the ambient temp, ampacity drops. Put several current carrying conductors in a raceway, ampacity drops. It is a heat proble.

[Conceptual]

The conductor, whether aluminum or copper, is capable of a much higher ampacity than the insulation. Insulation is the limiting factor. Factors are: the load in watts, the voltage, the ambient temp, the number of current carrying conductors in the raceway and the temp limits of the connectors.

Aluminum is difficult because the connections get loose and cause an increase in resistance, they get hot, and you have "cold flow", meaning that they change shape when not under load and cool off. So more looseness, etc, etc.

Bare conductors in free air have an ampacity twice as high (approx.)as the same insulated conductor. Raise the ambient temp, ampacity drops. Put several current carrying conductors in a raceway, ampacity drops. It is a heat proble.

I thought it all came down to surface area? I was taught that electricity only flows on the outer surface of any wire, so stranded wire gives you more surface area.

And aluminum should be a larger wire than copper due to the stated resistance issues. Although, if the MGU/Flybrid is DC, I would have to seriously ask why when the efficiency is so low, as well as starting torque in comparison TO 3-phase AC.

Any more info would be great!

[Professor]

The cross sectional area of a conductor is the most important factor in calculating ampacity. The NEC (National Electric Code) used in the USA includes table 8 in chapter 9. This table lists resistance values, diameters. and cross sectional area of a cable. A cable of a particular gage, say #10, has the same CSA whether stranded or solid. But, the stranded cable has a larger diameter due to the wasted space in the twisted construction.

I haven't looked at the flybrid system for a while, not since Williams went their own route. So, I'll need to think about that one. I have the cable stuff on the tip of my tounge because I just taught the code this semester at the college so my head was deep into the subject for the past few months.

[alexbarwell]

Conceptual, the notion of conductance being in the surface only relates to extreme frequencies, referred to as the skin effect - at DC the entire CSA of cable is used (or things like jumpleads would have a plastic core for instance)but at upper VHF, UHF and beyond the effective, theorised micro-elements that constitute the wire generate a back-emf in adjacent elements causing high resistance to passage of signal in all surrounding elements. Only the elements at the surface have no elements for half their circumference, so less (half) induced field/reactance/resistance/impedance, so the signal flow effectively migrates to the outer surface - go from UHF on co-axial cabling to microwave on wave guides (looks more like plumbing!) and the signal actually flows in the contained airspace, not the 'pipe'. At DC inductors (chokes) present minimal impedance, whilst capacitors present infinite impedance (I know this isn't quite right), at extreme frequency the capacitor (air gap) tends to a short circuit and the inductor goes to infinite impedance...

[Conceptual]

Conceptual, the notion of conductance being in the surface only relates to extreme frequencies, referred to as the skin effect - at DC the entire CSA of cable is used (or things like jumpleads would have a plastic core for instance)but at upper VHF, UHF and beyond the effective, theorised micro-elements that constitute the wire generate a back-emf in adjacent elements causing high resistance to passage of signal in all surrounding elements. Only the elements at the surface have no elements for half their circumference, so less (half) induced field/reactance/resistance/impedance, so the signal flow effectively migrates to the outer surface - go from UHF on co-axial cabling to microwave on wave guides (looks more like plumbing!) and the signal actually flows in the contained airspace, not the 'pipe'. At DC inductors (chokes) present minimal impedance, whilst capacitors present infinite impedance (I know this isn't quite right), at extreme frequency the capacitor (air gap) tends to a short circuit and the inductor goes to infinite impedance...

I understand the language, but miss the point.

Are you saying that AC frequency flows on the outside of the wire, where DC uses the entire cross sectional area?

[Professor]

The skin effect is an AC problem due to frequency. The "depth" of the skin is dependant on the frequency of the source. As the frequency increases, so does the resistance. The depth of the skin decreases with increased frequency.

AC power distribution is at low frequency and the depth of the skin is = to the radius. So, the entire CSA is used as the conductor.