What type of switch for isolator - ie rating

[paulandchez]

I want to add more security to my van so I'm looking at a switch on the neg coil wire. I've got an idea but wondered if a 15 amp switch would be ok or not?

Thanks

Paul

[paulandchez]

Anyone??

I'm not electrically minded and I'm not sure what the current draw is through the switch if it's in the neg coil line.

Thanks

[itchyfeet]

neg of the coil will draw same as the pos which if I remember correctly was about 5A at high revs when I measured it ( draws more at high revs because it has to make more sparks)

so 15A switch would be fine

if you decide to mount the switch at the front you will need much thicker wire there and back to prevent excessive voltdrop.

[MidLifeCrisis]

if you decide to mount the switch at the front you will need much thicker wire there and back to prevent excessive voltdrop.

Or use a relay near the coil that is triggered by the switch.

[itchyfeet]

Yes good idea^^^^ but hes not electrically minded so may need a diagram

[1664]

if you decide to mount the switch at the front you will need much thicker wire there and back to prevent excessive voltdrop.

Or use a relay near the coil that is triggered by the switch.

I disagree. A simple switch in a sectet location is easy and effective and there are plenty of locations vehicle wide to choose from. If you introduce a relay into the equation there is more wiring plus the relay will have to be energised 'on' for the engine to operate (after all, being energised 'off' to isolate the coil when it is parked up will drain the battery so that's no use) so should it fail, van go all stoppy. It will also have to be energised during cranking of course and heaven help any future owner who might be unaware of it's existence if/when it goes t!ts up.

My tuppence worth

[bigherb]

You shouldn't connect any switch in the negative side of the coil you can have over 300 volts in that cable , and especially not one that earths the negative side as a immobiliser that's very dangerous it can cause the coil to explode.

[paulandchez]

Thanks for all the info chaps.
Bigherb, I thought putting a switch in the neg line of the coil was a common way to introduce some extra security? Like I said, I'm not exactly an electrical expert hence why I was worried the switch rating maybe too low. Would you honestly not put a switch in there, and if not, where else could it go?
Itchyfeet, any idea on the gauge of wire needed....assuming the above question leaves me still running 2 wires the length of the van

Thanks

Paul

[itchyfeet]

You shouldn't connect any switch in the negative side of the coil you can have over 300 volts in that cable , and especially not one that earths the negative side as a immobiliser that's very dangerous it can cause the coil to explode.

when its permanently open circuit that wont be happening as that will only happen when switched and when its closed circuit the voltage wont be across the switch but across the ecu so i cant see the problem

http://en.m.wikipedia.org/wiki/Ignition_coil" onclick="window.open(this.href);return false;

agreed dont earth the coil directly

[bigherb]

Thanks for all the info chaps.
Bigherb, I thought putting a switch in the neg line of the coil was a common way to introduce some extra security? Like I said, I'm not exactly an electrical expert hence why I was worried the switch rating maybe too low. Would you honestly not put a switch in there, and if not, where else could it go?
Itchyfeet, any idea on the gauge of wire needed....assuming the above question leaves me still running 2 wires the length of the van

Thanks

Paul

It used to be with points ignition but still bad practice, with electronic ignition it is potentially lethal.
I'll pm you on how to do it.

[itchyfeet]

Ahh i see cap is charged so IF somebody tries to start it you would get 400v across the switch
cant see that as lethal but i agree its not ideal.

Iguess switching the 12v to the ecu would render it dead safely

something new learned

[1664]

ahh, I assumed we would be interrupting the positive to the coil

I tend to skim read

[itchyfeet]

I'm still not convinced the t3 primary ignition is 300/400v charged on the negative, I can't find much written up about it
i'm going to poke my voltmeter around. Capacitors ( condensers) don't have a long life so if it's in the ignition module why do they last so long? If its not in the module where is it?
I wonder if this electronic ignition has the cap charging system or not?
Anybody got knoledge on this?
On the other hand i'm thinking if it is 300/400v on the neg that would explain the heavy insulated crimp terminals that i binned when i re crimped the coil terminals as i'm sure many have done

http://en.m.wikipedia.org/wiki/Ignition_coil" onclick="window.open(this.href);return false;
"More modern electronic ignition systems operate on exactly the same principle, but some rely on charging the capacitor to around 400 volts rather than charging the inductance of the coil"

[bigherb]

http://en.m.wikipedia.org/wiki/Ignition_coil" onclick="window.open(this.href);return false;

The answers in there, (think, where does the 400v come from)

[itchyfeet]

Mmm if you really know what you are talking about why the guessing game?