Hybrid World Rally Cars

[OldF]

One thing I almost forgot about is the resistivity. Maybe it has something to do with that it’s almost 40 years since I was studying electrical engineering.

However here have been talks about the resistance of water but water, as any other conductor, water don’t have a specific total resistance but the resistance (or impedance) depend on what kind of water (the resistivity of the conductor) and how much water is in question (the length and area of the conductor). The more water the less resistance.

With a cable it’s more simply because with a cable the electricity come in (usually) from one end and go out from the other end and the resistivity, length and area of the cable is known. With water it’s more complicated because in a case of an accident the circumstance varies a lot i.e. the type of water, the length and area of the water conductor.

The resistance is:

R (ohm) = resistivity of the conductor (ohm meter) * length of conductor (m) / area of conductor (m²)

As you can see in a case of electrical accident in water it can be difficult to assess the length and area of the water conductor and also with the resistivity if the type of water is not known.

Interesting article about bath tube accidents with self-testing (crazy). Nothing to do directly with hybrid cars but however with electricity and water.

http://www.powerlogic.com.au/Attachm...iegelmeier.pdf

As said in the summary the path electric source – human in – human out – water – ground or other terminal is more dangerous than the path electric source – water - human in – human out – water – ground or other terminal.

You have to remember that they are not in fact connected in parallel unless the battery pack is submerged and some idiot breaks into the car, opens the cover, and touches both the poles (plus and minus).

That is extremely unlikely. In a real situation where the battery pack or an MGU connected to the battery pack gets shorted by water (which already is unlikely), the connection is going to be water to human to water in parallel with water only and water to body shell to water (very much preferred by electricity) and water to earth to water... So human is about the last thing the battery pack will go through.

Also the voltage over human won't be 600v or 800v or whatever, as much of the current will pass through the water. ).

The case with my example was mainly to show that how a small fraction of the total current can be lethal to a human if a human body is in parallel with any other low level resistance.

In the picture below the human is in parallel with the load of the electric system. Imaging that the dotted line is water and the minus terminal is in water, the body and the water would be in series and parallel with the load. Now the question is: What is the probability for this kind of accident to happen. Luckily the bird is safe.



http://www.allaboutcircuits.com/text...-current-path/


Btw, idiots always exists. It seems that a very common electrical accident is when some idiots are climbing on the roof of a train.

http://www.tukes.fi/tiedostot/sahko_...nunen_2013.pdf

On page 137
APPENDIX 1. Fatal electrical accidents in the Nordic Countries in 2007-201

The latest one was this New Year eve. Someone had clime on the roof on a train and had burned sot bad that even the gender couldn’t be defined at the first place. It’s said that the safe distance from a train power line (25 kV) is at least 2 meter.

Voltage over human would be too small to even be felt (or probably even measured). If you put a volt meter across two points in water that you have shorted with high voltage you are going to get a very small voltage (if even detectable if you have a larger amount of water) as you can in theory see the water as veeeery many resistors in series and the voltage will distribute across them. If you measure between the terminals you are going to get 800v but across two points in the water, just a few micro volt (if even that). )

I’m far from an expert but after reading http://electronics.stackexchange.com...-as-a-resistor this maybe it’s the wrong way to measure the voltage just to put the small probes of a volt meter in the water. Maybe what you said (voltmeter across two points) was just an expression. As I said I’m not an expert in this case but as I understand to get the true value of the voltage/current (or measuring the resistance) true the water is to have electrodes covering the whole area of the water where current/voltage is applied to the water (+ terminal of a battery or the “hot” wire of a house case) and electrodes covering the whole area of water where the current goes back to the source, i.e. path from terminal to terminal in a battery case or a path from “hot” wire to ground in a house case or vice versa. (- terminal of a battery or the ground in a house case).

(Oh and I knew about the 50mA lethal current... I have studied all of these things... I am not worried about the safety aspects of a hybrid rally car in water... Cost of hybrid rally car and feasibility and many other things yes, but safety aspects no).

I didn’t doubt that you didn’t know about that. I didn’t remember the actual value, only that’s very small. That’s why I had to search for it.

If you ever witness a generator overload test, you can try this if you like. It is done by lowering all three phases into the water and shorting them until the point where the generator overloads and the security systems cut in.

If you have any power plant close to you that is being commissioned, make a study visit with a volt meter and you will see! )

No, we didn’t do such drastic laboratory works. And I won’t try it at home by putting the three phases of our sauna heater in the water.