Master Switch wiring

[ArrY]

Hello,

I already found some threads regarding the wiring daigram, especially concerning the master switch

I'm still not sure which measures to take to conform the rules of FSAE.

all inductances (cooling fan, alternator, electric starter..) shall be safely disabled by the master switch.

is it enough to use a relay for every of those components? The relays would be powered by the master switch ad should fall off if the master switch is turned off. No voltage, inducted by the coils when cutting the amperage, should be able to drive other components..

By searching the internet I found out that often so called "self-induction recuperation diodes" that are wired parallel to the inductance are used to consume the inducted voltage.
Is the use of such diodes necessary?

Thank you for your help in advance

Arry

[Bill Kunst]

Absolutely not. Relays are written in the rules as being not acceptable. You must turn off the main supply to all components. If these are run through the computer, just turn that off. If not, create a main supply to the fuse box and just shut that off. Anyway it goes, it has to be a mechanicl switching of the power, and everything must turn off.
Bill

[ArrY]

our master switch of course is a mechanical one as written in the rules. not the master switch itself is relay controlled but the components that are wired behind the master switch

everything is mechanically turned off the battery when the switch is turned, but my problem are the inductances following the master switch that can power the other components by an inducted voltage when powering them off.

i think this is meant in the rules by

Note: Teams are reminded that any alternator field wire must also be
disabled by this switch to prevent any possible feedback through the
field coil circuit.

if components like the ECU are controlled by relays they cannot get any of the inducted voltage (i hope) and i ask myself if that is correctly wired then!

but i'm not sure if the inducted vltage must somehow be consumed otherwise e.g. by those diodes i mentioned.

[Erich Ohlde]

not really sure what you are getting at. a wiring diagram would be helpful

[LCP_KL]

dun understand why you want to control through relays. relays mean more wires, more connections and more areas which can go wrong.
why not keep it simple and use the master switch as it has traditionally been used? of cause, you have to use the 6-pole type...

[Bill Kunst]

once again, no. Thre is absolutely no reason to do this relay stuff, and if you look at the rules you will see that it is not allowed. If a relay fails, the switch will not disable the car. You should be aware of this.

3.4.9 Master Switches
The vehicle must be equipped with two master switches. Each switch must stop
the engine. The international electrical symbol consisting of a red spark on a
white-edged blue triangle must be affixed in close proximity to each switch with
the "OFF"� position of the switch clearly marked.
3.4.9.1 Primary Master Switch
(A) The primary master switch must be located on the (driver's) right
side of the vehicle, in proximity to the Main Hoop, at shoulder height
and be easily actuated from outside the car.
(B) The primary master switch must disable ALL electrical circuits,
including the battery, alternator, lights, fuel pump, ignition and
electrical controls.
(C) The primary master switch must be of a rotary type and must be
direct acting, i.e. it cannot act through a relay All battery current
must flow through this switch. An example of a typical switch that
meets these requirements is shown in Figure D.
Note: Teams are reminded that any alternator field wire must also be
disabled by this switch to prevent any possible feedback through the
field coil circuit.
Figure D

hope this helps
bill

[ArrY]

I thouhgt of relays because wiring them can bedone with thin wires. Thick wires thorugh the whole carmakes it expensive and is unnecessary. therefore e.g. the secondary master switches and consumers like electric starter should be controlled by relay, otherwise the whole amperage of the electric starter would flow from battery to e-starter push button from there back to the e-starter, relay control minimizes use of thick wires and the button itself will be a different one (much smaller and cheaper)

I added a wiring diagramm. This is NOT our car electric, just meant as an example to show the problem.

There is the master switch, cuttin everything from power. The inductance (alternator, fan e.g.) can create a voltage when switching off. I'm not sure if this voltage would keep the relays active even when they are disconnected from the battery supply.

What is the "trick" of the six poled master switch? how does it secure the whole electrics? is it a normal mechanical switch that can connect 3 separate circuits?

can someone give or send some information about those switches and recommend a model?

http://de.geocities.com/el_marryachi/wd.JPG

[ArrY]

@Bill Kunst

I do know the rules. Relays are forbidden to control the master switch. That is absolutely clear. Surely you can use relays in your car, only NOT for the master switch. I mentioned that the master switch is of mechanical (and rotary) type. The problem is the inductance of coils that can create a voltage when switched off (even if you use a mechanical master switch). The voltage keeps components running even if the mechanical switch is turned OFF.

that has nothing to do with the use of relays or not, the relays could help that the inducted voltage does not reach the consumers, but they could be powered and made active by the voltage itself.

i hope now my problem is clear

[LCP_KL]

think about these:
1. our cars a fairly small, all you running are thick gauge wires from the batt to the master switch and then to the mains. (in our car, its the starter relay, the fuel cut relay and the engine stop relay). so not much weight or electrical losses incurred even if you use very big gauge wires.
2. our brake over-travel switch controls the fuel cut relay. so no big wiring there.
3. our secondary on switch is in series with the brake o.t. switch.
4. our starter switch is a low ampere line, (splined from the o.t. and secondary on switch) that merely controls the starter relay.
5. our philosophy is that simple electrical problems are a career stopper. so we dun risk it and keep to as little relays as we can, namely the 3 above.
6. explanation of a 6 pole master switch can be found here: http://users.tellurian.net/hughes/articles/master.html
in a nutshell, you are using the NO or NC switch to discharge the inductance. use a min 3 ohm and at least 10W rating resistor. the more the better. i remembered we fried the resistor while playing with the master switch. it does heat up appreciably. especially if you are revving at 10k and you test its operation by turning it off. hot...

[Bill Kunst]

Originally posted by ArrY:

...The relays would be powered by the master switch ad should fall off if the master switch is turned off...
Arry

Arry,
Why does this look like the exact opposite of part c:

The primary master switch must be of a rotary type and must be
direct acting, i.e. it cannot act through a relay. All battery current
must flow through this switch.


Okay, Maybe I am dumb, but you have to admit that your original post would lead me to the assumption that you do not understand the rules.
Bill

[ArrY]

Why does this look like the exact opposite of part c:

The primary master switch must be of a rotary type and must be
direct acting, i.e. it cannot act through a relay. All battery current
must flow through this switch.

----
This means that the master switch itself must mechanically "cut" the circuit. When you turn the switch, the metal connecting the poles is turned away.
What you are not allowed to use is a switch that itself is controlled by a relay. that means the switch is a box where the switch between the poles is moved by a relay that is somehow controlled (by a hand-controlled switch or whatever). a relay could fail (as you mentioned) an you would not be able to cut the power even if you hammer on the switch.


thias has nothing to do with the usage of relays somewhere else in your car (e.g. the secondary switches can be directly relay-controlled switches, this is explicitly formulated in the rules)

<pre class="ip-ubbcode-code-pre"> </pre><pre class="ip-ubbcode-code-pre"> </pre>