get power, inside the steering wheel, from horn button?

[settra]

hello forum. i want to pass **broken link removed**, inside my sterring wheel, to do some stuff (in our case, asuming to power some LED's is ok). the problem is, that since my car is prety old, there are only two cables going inside my sterring wheel. the cables that power the horn. so i have to make due, with them.
here is what I THINK the schemantics of my horn look like :


meaning, that , when you press the horn, the +12v rail that goes to the relay, closes, the relay energizes, and allowes current to go to the actual horn.
now , what i want to do is something like this :

.


meaning, i still keep the horn button, only with the addition, that is bypassed, with a rail that poweres some LED's. becouse the voltage drop of the LED's in my case is about 12v, the relay ALWAYS get cureent (not only when the button is pressed), but its about 1v, so it dosent energize.
ALL fine and good and tested up to now, and it works prety good, with one exception.
when i turn on the car, the LED's turn on, and no horn **broken link removed**. BUT when i press the horn button, the horn starts hitting, BUT it dosent stop when i realise the button...
anyone has any idea what i have done wrong??

or if there is a better way to pass power inside the wheel, at all??
thanks i
n advance!!

 

[Nigel Goodwin]

As far as I can remember, the horn is usually only a single wire, which is connected down to chassis by the horn switch.

 

[MikeMl]

Most cars have a horn relay. You have found that it takes a lot more current to pull the relay in (shorting your circuit with the horn button), but much less current (that drawn by your circuit after the horn button is released) to hold the relay in.

A typical 12V relay might have a pull-in current of 200mA, while its holding current may be only 50mA . You need to reduce the parasitic current your circuit draws to allow the relay to drop out.

 

[cowboybob]

Nigel's correct. The horn button switch is simply grounding the horn relay.

In essence, with your added LED circuit, once you press and the release the horn button you're "latching" the horn relay, i.e., there's still adequate current flowing into the relay, by way of the LEDs, to maintain the relay's "on" condition.

Not entirely sure of your plan, but if you want the LED(s) to light when you press the horn button, you'll need to power them from the horn connection of the horn relay or at the horns themselves.

<EDIT> I have GOT to learn how to type faster. While I was typing my response, MikeMI posted his response... Oh well...

 

[settra]

yes. the problem is , the relay needs much less current to stay energized...
some more info: after all, the relay may be , BEFORE the horn button. not after. in that case, a resistor in parallel with the relay coil, would provide some extra current for the LED's , without passing through the relay. correct??? how would i calculate what resistor i need??

 

[cowboybob]

yes. the problem is , the relay needs much less current to stay energized...
some more info: after all, the relay may be , BEFORE the horn button. not after. in that case, a resistor in parallel with the relay coil, would provide some extra current for the LED's , without passing through the relay. correct??? how would i calculate what resistor i need??

Not sure what you're suggesting.

A resistor in parallel with the relay coil will simply be bypassing some current around the coil (effectively reducing its ability to close).

 

[settra]

i am suggesting exactly what you sed if the coil closes harder, then it will also stay closed harder. so it might not latch. if the resistor is too small, all the current will pas through it, and then the coil will not close at all. and if the resistor is big, the coil will close easy(problem will not be solved.) i just have to find the currect value for the resistor ...

 

[ericgibbs]

hi settra,
A resistor in parallel with the relay will have no effect upon the relays operation.
The top of the relay coil goes to the +12V of the battery [ via fuses and ignition switch] so when you press the horn button and ground the lower end of the relay coil [ to chassis, 0V] the same current will flow thru the relay and some additional current will bypass the relay coil via the parallel resistor.

E

 

[cowboybob]

settra,

Assuming that your horn button switch is normally wired, i.e., it provides a ground for your relay/horn circuit, then you cannot provide power to anything from that switch except that which is passing through the relay/horn circuit, once you release the horn button (as discussed above).

Thus, if you can locate the horn relay, there will be a connection there for powering your LEDs, either continuously (the 12VDC to the relay) or switched by way of the relay ouput to the horn(s).

It would be helpful if you could provide exactly the way your horn circuit is wired as well as what sort of power you wish to have for the LED(s).

Unless, of course, I'm missing some obvious.

 

[MikeMl]

...Unless, of course, I'm missing some obvious.

The OP is trying to light LEDs in the steering wheel before the horn button is pushed.

Shunting the horn relay coil with a resistor will make more current available to the LEDs, thereby reducing the likelyhood that the relay will latch...

 

[alec_t]

.... but to shunt the relay coil with a resistor would require access to +12V. Does the OP have such access? I was under the impression they wanted to connect the LEDs only to the wiring in the steering wheel.

 

[MikeMl]

The issue of putting extra stuff in the steering wheel is how many wiping contracts and slip rings are on the steering column. The OP cannot add slip rings; he should be able to access both ends of the horn relay coil.

 

[alec_t]

But in post #1 the OP says

since my car is prety old, there are only two cables going inside my sterring wheel. the cables that power the horn.

 

[MikeMl]

But in post #1 the OP says

The return side of the horn button usually goes through a slip ring to vehicle ground. In newer cars, there may be up to twenty slip rings.

 

[jpanhalt]

The connections I have seen in newer cars are all "clock springs" or similar. That is, the wire is coiled to take up the rotary motion of the steering wheel.

Edit: I guess BMW still used slip rings. Maybe some others. I don't drive a BMW.

John

 

[shokjok]

You'll get ground from the horn wire in newer cars. Power feed would be from the turn switch assembly ( two feeds: hazard button ( HOT) and another switched fused input). The assembly is fixed on the column, the horn ground turns with the wheel and presents a challenge to projects fed this way. Also keep in mind that many locales have distracted driving legislation; try to explain your wheel-fed project to a lawman when you get stopped.