Duplicating duff battery effect - vehicle security

[CompoSimmonite]

My car hasn't been used much for over a month and when I went to it yesterday it wouldn't start. Engine only turned over very slowly a couple of times without firing, radio went out when engine turning over and I suspect lights would have dimmed if they were switch on.
Today I've been thinking that this would be an excellent security measure for the opportunist thief. No way will a joy rider then get out the jump leads and even somebody after a "getaway" car will walk away.
So can anyone think of a way to duplicate the duff battery effect ? I'm thinking of a device that would fit between the battery and vehicle earth could be best way.

 

[jerrytug]

How about one of those newfangled "switch" thingies to cut off the battery?

 

[rtbcomp]

Headlight bulb in series with the battery, it may not have enough resistance to stop the radio & ECU working and the dashboard lights would come on with the ignition, but it wouldn't turn the engine.

 

[bigegg]

You'd want a way of reducing the voltage to about 8 or 9 volts.
So a couple of resistors of 3:1 ratio and ratings of about 5kw each.
The battery would also drain VERY quickly.

Alternatively, howzabout a 6v motorbike battery which is swapped for the normal battery - again you'd need a relay that would carry 400a @ 18v - the switching ampage could be lower tho, because you'd never switch whilst cranking.

 

[skotl]

You'd want a way of reducing the voltage to about 8 or 9 volts.
So a couple of resistors of 3:1 ratio and ratings of about 5kw each.
The battery would also drain VERY quickly.

Alternatively, howzabout a 6v motorbike battery which is swapped for the normal battery - again you'd need a relay that would carry 400a @ 18v - the switching ampage could be lower tho, because you'd never switch whilst cranking.

And a 200A fuse

I'm with jerrytug - just fit an isolator switch in a secret place

 

[rtbcomp]

^^ the type with a by-pass fuse would be best to keep the electronics & parking lights powered up, but it would blow as soon as the start button was pushed.

This doesn't exactly replicate the duff battery though, because nothing would work after the fuse has blown, whereas using the headlight-bulb method the low-current circuits would come back on when the key was released, just like with a low battery

 

[Parm]

If the car is modern it will almost have a memory in the emu that will require a battery feed

Why not just fit an alarm and immobiliser

Edit beaten to it by pdg and rbtcomp

 

[MoreWellie]

combine the suggestions

1. fit an isolator switch in a discreet location
2. wire a headlight bulb across the isolator switch

that way the radio and clock will retain their settings and when you try and start the car the dash lights will go out

you need to make sure the headlight bulb is somewhere that it won't be obvious even at night

EDIT: don't do this on something like a modern bmw that needs an ecu reset by the dealer if you change the battery

EDIT 2: don't put the isolator somewhere the passenger can kick it off as alternator diodes don't like charging a suddenly missing battery. Found this out by needing a new alternator...

 

[Shedendman]

In the old days you pulled a spark lead off or removed the rotor arm,loads of battery but your not going anywhere

 

[wristpin]

Battery isolator

 

[WorkshopChris]

These have been around for years:-
http://www.halfords.com/motoring/ca...lcA6S7KyNnbN7YcVWIUd4-XAcqmdwQdhoCX7sQAvD_BwE

 

[RonA]

Many years ago a contributor to practical electronics came up with a circuit which cut the feed to the coil randomly. Theory was the car would start as normal but keep cutting out/resetting randomly giving the thief the feeling the car was faulty. He was confident that even if the car was stolen, it would be abandoned within half a mile. Probably quite difficult to achieve with modern electronics but the thinking was sound.
RonA

 

[Hood]

I once fitted a switch under the dash of a pickup, it just broke the power lead to the coil. The engine could spin and spin but would never start. Probably not so easy on modern stuff though.

 

[CompoSimmonite]

I should add I'm thinking of this for an older vehicles with no electronics. I have three vehicle which fall into this catagory. I think a battery change over switch and a 6v motorcycle battery will work.

 

[optima21]

the trouble is that once they have broken into your car, the damage is already done. have a visible deterrant like a disklok and they leave your car and look for another easier target

 

[Shedendman]

the trouble is that once they have broken into your car, the damage is already done. have a visible deterrant like a disklok and they leave your car and look for another easier target

I'd rather have my motor damaged than to find it wrapped around a tree or in the local canal

 

[CompoSimmonite]

the trouble is that once they have broken into your car, the damage is already done. have a visible deterrant like a disklok and they leave your car and look for another easier target

One of my vehicles is an open roadster (Marlin) and others 4x4's (UMM & Mahindra) with locks you can open with virtually any key !

 

[colnerov]

Hi, There are other ways to disable an engine from being started than that suggested by Hood which is easily bypassed because it's a fairly common trick, but I won't put them on an open forum for security reasons. Another problem is if they can't get it started they could come back another time and just tow it away. The best way is to have a number of visible measures as a deterrent so they try elsewhere. To answer the original question, if you alter the timing of the dist it can sound like a flat battery but it will involve going under the bonnet every time you leave it or want to use it. As said it can lead to them towing it away.

Colin

 

[Robotstar5]

At one time you could get a key operated one way valve that fitted in the brake line, remove key and dab the brakes keeps the brakes on, just put the key in to release the pressure when YOU want to drive it.

 

[Shox Dr]

At one time you could get a key operated one way valve that fitted in the brake line, remove key and dab the brakes keeps the brakes on, just put the key in to release the pressure when YOU want to drive it.

I don’t believe you can have devices that lock the braking circuit; either open or closed