De Lorean EuroTec

Hi guys,

Anyone here hot (or about A level) on electronics??

Old motorcycle project. Oil drains from tank to sump over time when its not running. Logically, you need a tap in the feed line.

Starting the motor with the tap closed gets expensive quite quickly, so the tap needs an to also operate a microswitch to cut/ allow current to the ignition circuit.

I used a direct action microswitch operated by the tap, but mounting it is not straightforward on a flexible line. It works after a fashion, but cutting sparks mid corner can also get expensive, nay- painful! even quicker than the other version.

So. I am thinking maybe a reed switch, with a magnet on the tap. Turn the tap, magnet gets close to reed switch, current flows. If the tap is off, magnet is too far away, so the switch isan open. Except it pulls too much current and fucks the reed switch. I tired it with a bulb, but I want it to be robust. Not sure about current draw of the ignition circuit.

(Q1. How much current can a reed switch handle?? Most seem like 500mA...)

I then tried a Hall effect sensor, however it came without without instructions, I think I also fucked this. Trying different permutations of the live earth and switch wire means that I think I got it to work, (bulb lit when magnet is close by) now it doesn't.

Q2 Could excess current demand also fuck this??

Q3. Could shorting or similar also fuck it??

Can anyone tell meif I am barking up the wrong tree before I throw another few quid at a hall effect sensor??

Or any insight about how to wire it? 3 wires are Brown Black and Blue. Presumably blue is the switched, but with the magnet present will this supply the 12v fed into the sensor??

Cheers! Any insight appreciated,

Andy

I'm not sure on the wiring for the hall effect sensor, but weather you go for hall effect or reed, why don't you use the sensor to drive a relay so you don't risk damaging the sensor. Then use the relay contacts to control your ignition system.

Uh-huh, that's very sensible, thanks Dan.

Now you do understand I'm going to bug you for a wiring diagram for the relay?!

I think I prefer the hall sensor, if nothing else because its easier to mount than a reed switch:



I am pretty sure that by running a bulb thru it I have fried the one I currently have!!

a

You have too much time on your hands Andy

I just looked up your sensor and the max load is 150mA so make sure your relay doesn't draw any more than that. It is also an NPN sensor which means the negative is switched, so wire as below:

Dan 6511 wrote: make sure your relay doesn't draw any more than that

Dan,

Thanks a million for that, much appreciated.

Now, to measure current draw...

(without an ammeter, cos that function is goosed on my DMM)

12v divided by the resistance of the relay coil ??

(or maybe for a buffer, 13.5v to be safe over coil resistance)

Or do I need to actually measure the draw.

Sorry, physics for dummies here!!

(Maybe I just need a new DMM)

a

andyd wrote:12v divided by the resistance of the relay coil ??

Yes thats it, and as you say work it out at 13 volts for a buffer, you'll probably find you have 13v with the engine running anyway.

This relay for example has a coil resistance of 100 ohms so will draw 135mA at 13.5V:

https://uk.rs-online.com/web/p/non-latching-relays/0329834/

Awesome

Kisses for you next time I see you!!

Or a pint, if you are going to be all prudish on me.

Thanks mate,

a

jerzybondov wrote:You have too much time on your hands Andy

Nope, I have late nights in a shed and not enough sleep. You modern motorcycle riders take it for granted that there are no puddles under your bike if it's left for a week!!

Older is still better!

In fact you can see the tap and mk1 microswitch on the oil line between the oil tank and crankcase in that pic...

No oil leaks tho!