Immobiliser / Starter circuit
Discussion
A long, long time ago, my immobiliser failed. So I had an overide button fitted for the starter motor.
A couple of years later, the alarm siren failed, so Carl Baker fitted a new alarm and immobiliser, and all was good again.
Fast forward a few months, the immobiliser failed again, so I reverted to the overide button.
Back to the current day, and I finally stumbled across my starter relay at the weekend. The coil has a permanent ground. I tested the switched positive from the immobiliser, and was surprised to see it was there when the original starter button was pressed. As the relay wasn’t clicking, I presumed a faulty relay, and replaced it. Alas, the new relay wouldn’t fire either.
I had to leave the car at that point. I could have an open pin at the relay holder, but I suspect the 12v+ I’m seeing, is a ‘ghost’ voltage, where it can’t carry any load. I’ll get a 12v test lamp and prove that theory.
The thing that I found strange though..... They’ve used a 3mm cable just to fire the coil on the relay. The load side doesn’t look any bigger, so effectively, the relay’s doing nothing
Certainly not saving weight or cost.
The 5 litre cars at work, have a 0.35mm cable to fire the coil on their starter relays.
So it’s got me wondering why TVR used such a huge cable to fire the relay, and why my immobilisers are dying.....
I remember when I first started selling alarms and door access, and learning about fitting a diode when wiring up magnetic locks, electronic locks etc... Basically, anything with a coil, to prevent back EMF burning the control modules out. I always fitted an IN4004 diode.
I’m puzzled as to why TVR have used that big a cable. Unless nobody at the factory thought of fitting a diode, and putting a bigger cable in, was the only answer they could come up with ?
A couple of years later, the alarm siren failed, so Carl Baker fitted a new alarm and immobiliser, and all was good again.
Fast forward a few months, the immobiliser failed again, so I reverted to the overide button.
Back to the current day, and I finally stumbled across my starter relay at the weekend. The coil has a permanent ground. I tested the switched positive from the immobiliser, and was surprised to see it was there when the original starter button was pressed. As the relay wasn’t clicking, I presumed a faulty relay, and replaced it. Alas, the new relay wouldn’t fire either.
I had to leave the car at that point. I could have an open pin at the relay holder, but I suspect the 12v+ I’m seeing, is a ‘ghost’ voltage, where it can’t carry any load. I’ll get a 12v test lamp and prove that theory.
The thing that I found strange though..... They’ve used a 3mm cable just to fire the coil on the relay. The load side doesn’t look any bigger, so effectively, the relay’s doing nothing
Certainly not saving weight or cost.The 5 litre cars at work, have a 0.35mm cable to fire the coil on their starter relays.
So it’s got me wondering why TVR used such a huge cable to fire the relay, and why my immobilisers are dying.....
I remember when I first started selling alarms and door access, and learning about fitting a diode when wiring up magnetic locks, electronic locks etc... Basically, anything with a coil, to prevent back EMF burning the control modules out. I always fitted an IN4004 diode.
I’m puzzled as to why TVR have used that big a cable. Unless nobody at the factory thought of fitting a diode, and putting a bigger cable in, was the only answer they could come up with ?
Just noticed this......
https://www.abacuscaralarms.co.uk/re-coding-meta-a...
Other models may be wired like that, but we know that looking at the Cerbera diagrams, the starter relay is a factory fit. And the immobiliser still fries, long before the wiring, the relay, or the 40A fuse that’s fitted on the relay
I’m convinced it’s EMF, not load that’s killing them.
In fact, I know my starter motor has killed my immobiliser . So next time I work on it, I’ll see what the current draw of that coil is. I expect it to be negligible.
https://www.abacuscaralarms.co.uk/re-coding-meta-a...
Abacus said:
Problems arise because TVR have wired the immobiliser circuits the wrong way around. The M36 has two immobiliser circuits, circuit 1 can handle currents of up to 10 Amps & should be wired to the fuel pump or ignition circuit, circuit 2 is rated at 25 Amps & is designed to be connected to the starter motor circuit. TVR have wired these circuits the wrong way round, the starter goes through the 10 amp while the fuel/ignition goes through the 25 amp circuit. All being well there are no problems even though the two relays are wired the wrong way around. Problems arise when the starter solenoid begins to wear, in so doing it demands more & more power to function, when the current flow to the starter gets passed the 10 Amp limit of circuit 1 problems start. This situation gets worse when when the engine is hot which in turn makes the starter solenoid hot causing it to demand more power. This is known as the hot start problem, eventually the starter circuit will burn out causing total failure of the starter. Adding an extra 'hot start' relay to this circuit is not a permanent fix as the starter will still demand more power which could eventually burn out the ignition switch or associated wiring leading to the failure of the starter itself. Before this happens we recommend to have the starter inspected & have it repaired or replaced if found faulty.
To me that reads that they think there’s a wire going directly from immobiliser to starter motor. And they suggest that adding a starter relay will burn out wiring etc...Other models may be wired like that, but we know that looking at the Cerbera diagrams, the starter relay is a factory fit. And the immobiliser still fries, long before the wiring, the relay, or the 40A fuse that’s fitted on the relay
I’m convinced it’s EMF, not load that’s killing them.
In fact, I know my starter motor has killed my immobiliser . So next time I work on it, I’ll see what the current draw of that coil is. I expect it to be negligible.
Edited by RUSSELLM on Monday 10th August 21:56
RUSSELLM said:
Just noticed this......
https://www.abacuscaralarms.co.uk/re-coding-meta-a...
That's about as bad as it gets, all that type and it doesn't explain the problem (+ bad grammar)https://www.abacuscaralarms.co.uk/re-coding-meta-a...
Abacus said:
Problems arise because TVR have wired the immobiliser circuits the wrong way around. The M36 has two immobiliser circuits, circuit 1 can handle currents of up to 10 Amps & should be wired to the fuel pump or ignition circuit, circuit 2 is rated at 25 Amps & is designed to be connected to the starter motor circuit. TVR have wired these circuits the wrong way round, the starter goes through the 10 amp while the fuel/ignition goes through the 25 amp circuit. All being well there are no problems even though the two relays are wired the wrong way around. Problems arise when the starter solenoid begins to wear, in so doing it demands more & more power to function, when the current flow to the starter gets passed the 10 Amp limit of circuit 1 problems start. This situation gets worse when when the engine is hot which in turn makes the starter solenoid hot causing it to demand more power. This is known as the hot start problem, eventually the starter circuit will burn out causing total failure of the starter. Adding an extra 'hot start' relay to this circuit is not a permanent fix as the starter will still demand more power which could eventually burn out the ignition switch or associated wiring leading to the failure of the starter itself. Before this happens we recommend to have the starter inspected & have it repaired or replaced if found faulty.
Starter solenoid pull-in current is higher than its hold-in current
Once the grease in the solenoid core has started drying out, it takes longer for the plunger to travel through the core and sometimes the plunger will stick rather than travel
Starter solenoids when hot can sometimes cause the plunger to travel slower through the core
The longer the plunger takes to travel, the longer the pull-in current is being drawn through a relay or ignition switch
Less than 10 Amps pull-in current? Don't think so, been a while since measuring one and Bosch wouldn't supply requested information
Will be good to know what current your solenoid draws for pull-in and hold-in
Very interesting
Back EMF
You're on the case. Yes, modules won't be wanting too much of it, relay contacts seem to handle it well
Prefer relays with resistors for Back EMF protection, got fed up with people blowing relay diodes
Edited by Penelope Stopit on Tuesday 11th August 09:33
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