Immobiliser Drains Battery - useful advice

I had an alarm system fitted to my 1987 GLS last year, seemed sensible as I have to park on street and I'd had the car re-sprayed, so it looks more nickable than it used to.

The alarm is an Autowatch 346 RLI BB. It works fine but causes a major problem: I only drive the car once a week or so, and in between times, the immobiliser/alarm drains the battery. I tried not turning it on, and it still drains the battery. And of course as the battery has got older, the problem has got worse.

AutoWatch called me back and were INCREDIBLY helpful. Essentially, they get lots of phone calls every week from people with the same problem, especially camper van owners, who don't drive the vehicle that often, and because they street park, can't use a trickle charger.

There are only two solutions: one is to disconnect the battery when parked (this doesn't de-activate the immobiliser, only the alarm). AutoWatch suggested buying new style battery which doesn't needs spanner, just has taper fit, with a clip that pulls and pushes on and off with a lever.

Or possibly to fit an isolater, which switches off when battery hits around 12.1 V  - as I'm no mechanic, I need to look into the costs on this.

Anyone tried the immobiliser solution?
Cheers, spudlet.

The problem is probably someone has wired up the imobiliser incorrectly (well in a BASIC way) they'll be a relay somewhere thats getting +12v all the time what you need is a simple 2 relay circuit.

You need to find the wire from the imobiliser (which will be going to the +12v side of a relay) and connect another relay from the ignition, so that the contact from the ignition will turn the 2nd relay on, which will only turn on when the Imobilser is OFF and connected, and the Ignition key is turned.

What you have at the moment, is an Imobiliser that will work (IE Imobilise the vehicle) when the imobiliser is disconnected (breaking the circuit), or the imobilser is turned ON (ie in reverse, breaking the circuit) this works, but has significant drain on the battery.

Same thing as what happened on Pedders Car, I believe.

Its hard to explain with words though, hope you understand

why dont you get a solar trickle charger that people with boats use,im sure even thought there low AH rating they will account for a immobiliser/alarm flashing

there around £30 and about the 30cmx15cm just leave it on the parcel shelf,might look a bit naff but better than leaving the alarm off

The problem really needs looking into, an alarm should not flatten a good battery in a week

Thanks for replies, madferret I think I get you, and I think you are suggesting what my breakdown guy was getting at - I'll pass your thoughts on to my mechanic man.

Also, good thought re solar charger - I did get one when I first had the car (pre immobiliser) but as I street park in Hackney, it was nicked within the week…might try again though.

Just drove through Suffolk in the sun, after a battery re-charge and a silver valet wash, and it did make it all worth while - never saw another Mark 1 though, a little lonely…

cheers, spudlet

I did have a circuit diagram somewhere. I'll dig it out, all you need is 2 relays (although you could do it with a handful of resistors, transistors & relay etc.. if you have the ability)

circuit diagram might well be useful, if you can dig it out no trouble…not something I would tackle, but my mechanic man could!

Thanks, spudlet

Its actually easier than you think, all you need is IGN feed, Alarm +12 through feed/immobliser off, and to break the circuit (usually the starter feed) could also be CIS/Fuel cut off solenoid/Fuel Pump etc..

Anyway its floating about somewhere shouldn't be too much trouble to find, I'll have it done this evening/tomorrow depending on when I finish work

My car has an immobiliser and a decent battery, I'm able to leave it a week or more and the battery doesn't flatten. When not running, the immobiliser and the clock's pretty much the only electrical items running. So it should last for ages. No need for double relays, etc. Sounds like a dodgy immobiliser.

I agree paul! I too have an imobliser for my car and can leave it for more than a week before the battery drains.

Paul its the method of immobilsation not the mobiliser itself.. Yours will probably do it via electrical means and a built in relay as stated above..

i dont understand what you are saying how can the immobiliser be wired so as to flatten the battery? all there is inside an immobiliser is two relays when power is cut (ign off) the relays drop out, and will not reset till right code is put in (ie key or transponder) i would suggest that if the alarm is flattening a healthy battery in a week its faulty, if its been doing it for a year get the installer to sort it out.or get autowatch to look into it.
 i fit autowatch alarms and immobilisers and have never had this problem i leave one of my cars for over a month and it still starts.

Hi racer, I can assure you that it IS this immobiliser, it does not cut out when the engine is off, which is why it would need an isolator to make that happen. The guy at Autowatch gets many calls from people with the same problem and explains it very patiently and in great detail, poor bloke.

I know lots of people don't have this problem, it's just down to which model immobiliser you get.

Dont worry its normal to doubt me

What a lot of people do is wire a relay so that it is permantly on, so that when the immobiliser is disconnected the circuit breaks and you have an immobilsed car, what people dont realise is that relays suck current like mad, the best way to do it is a two stage break in the circuit, as will show when I remember where I put the circuit diagram last time I was asked this question.  :wink:

The diagram (oversimplified possibly)



Left is the power sucking version, right is the 'improved' version.

Pic doesn't show up and uses a file format from the 19th century - any chance of converting it to JPG so we can see it?

Not really, your a smart guy I'm sure you can figure it out

Well, I get a "page cannot be displayed" message on that URL you gave. Can you host them on photobucket instead?