Motorcycle Immobilizer Relay Question

Thread Starter

Aleksandr Gonzales

Joined Jan 15, 2016
12
Good day!

I am not an electrical engineer nor an expert in this field, so my apologies. I made a diagram for a motorcycle's immobilizer. This what I believe, the alarm module on 'ARMED' mode, outputs negative current (?) through the grey wire. And when in 'UNARMED' mode, no current flows. I put a SPDT Relay (12V) to do the job. However, I have questions regarding the 'ARMED' state, will this drain the battery fast? So I included a 470 Ohms resistor to the diagram, but doubted if the output current will be enough to trigger the relay. Sorry for the terms, quite confusing on my part. Hehe.

circuit-20200731-0043.png
 

MisterBill2

Joined Jan 23, 2018
6,757
The first requirement is to decide what the system should do. If you just want to inhibit the ignition system that is one thing, but what really discourages anybody is if the horn comes on when they go to switch on the ignition. The circuit shown may disconnect ignition power but if the switch turns off then it will start again. a latching relay that engages when a button is pressed will be harder to defeat. And yes, eventually the battery will run down powering the relay. A good trick will be another switch so that the relay only operates when somebody sits on the seat. As soon as they sit the engine dies. That would be effective and not produce battery drain enough to be a problem.
 

Thread Starter

Aleksandr Gonzales

Joined Jan 15, 2016
12
The first requirement is to decide what the system should do. If you just want to inhibit the ignition system that is one thing, but what really discourages anybody is if the horn comes on when they go to switch on the ignition. The circuit shown may disconnect ignition power but if the switch turns off then it will start again. a latching relay that engages when a button is pressed will be harder to defeat. And yes, eventually the battery will run down powering the relay. A good trick will be another switch so that the relay only operates when somebody sits on the seat. As soon as they sit the engine dies. That would be effective and not produce battery drain enough to be a problem.
Hello sir! Thank you for the reply. I wanted to cut the power to the ignition coil and the instrument panel if the alarm system is armed. I will be researching about latching relay. May mind blown. Hehe.
 

jpanhalt

Joined Jan 18, 2008
10,109
You might consider wiring the relay so it is normally open. The "immobilizer" would then become the "mobilizer." Since the engine would presumably be running, the small additional drain should be much less a worry. That is analogous to what people did years ago in high theft neighborhoods by removing the rotor from the distributor or by switching wires in automotive ignitions.

Of course, you have to consider what happens with a dead battery. Why do you even need a relay, if the immobilizer/mobilizer switch is well hidden?

Finally, assume the drain is 30 mA (12 V/400 Ω = 30 mA). A full day = 0.72 Ah. Probably not a problem. But if it is parked for 1 month, it will be a problem.
 

MisterBill2

Joined Jan 23, 2018
6,757
Disabling the instruments and ignition will not do much to prevent a motorcycle from being stolen. It is simple and easy to tow a motorcycle away very quietly, using another one and a tow rope. I have been towed a few miles on a bike with a blown engine and it was not hard at all. Of course that was when I was much younger, but it would still not be a problem. Motorcycles do not have power steering or power brakes and so they handle about the same with the engine off and the tranny i neutral.
 

Thread Starter

Aleksandr Gonzales

Joined Jan 15, 2016
12
You might consider wiring the relay so it is normally open. The "immobilizer" would then become the "mobilizer." Since the engine would presumably be running, the small additional drain should be much less a worry. That is analogous to what people did years ago in high theft neighborhoods by removing the rotor from the distributor or by switching wires in automotive ignitions.

Of course, you have to consider what happens with a dead battery. Why do you even need a relay, if the immobilizer/mobilizer switch is well hidden?

Finally, assume the drain is 30 mA (12 V/400 Ω = 30 mA). A full day = 0.72 Ah. Probably not a problem. But if it is parked for 1 month, it will be a problem.
Sir, at the assumption of 30 mA drain, is the circuit already using the resistor?
 

jpanhalt

Joined Jan 18, 2008
10,109
Sir, at the assumption of 30 mA drain, is the circuit already using the resistor?
I just used the circuit you posted.
1596437360729.png

I used "400 Ω" as the example rather than 470 Ω as it was easier to calculate. A small yet constant battery drain can be a real pita and battery killer if the vehicle is not driven frequently, as is the case with my F-150 small truck.
 

jpanhalt

Joined Jan 18, 2008
10,109
Another disadvantage with a powered immobilizer is that simply cutting or disconnecting a battery lead may enable the ignition, depending on how it is wired and assuming it is magneto.
 

Thread Starter

Aleksandr Gonzales

Joined Jan 15, 2016
12
Another disadvantage with a powered immobilizer is that simply cutting or disconnecting a battery lead may enable the ignition, depending on how it is wired and assuming it is magneto.
Hello sir! I am building this up to a scooter of mine, no kick start, just electric start sir. But of course, nothing is impossible these days with a well-trained thief. But still, better than nothing. Hehe.
 

MisterBill2

Joined Jan 23, 2018
6,757
An alarm system with it's own battery does not require the installer to connect to the bike electrical system at all. And given some of the wiring work I have seen from some folks that is a big advantage. Some of the very worst hacking jobs by those who clearly had no ideas what they were doing, and no tools to do it right.
 
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