Horn - should it have continuity?

[Huw Powell]

http://en.wikipedia.org/wiki/Vehicle_horn

Sounds like it's an inductive load on top of a several hundred Hz square 
wave.

Mark Rosenkrantz wrote:
> Brett,
> You got me thinking now... is a typical automotive horn an inductive load or
> a resistive load?  Not that it particularly matter for this discussion, but
> who's right (I previously said it was a resistive load)?
> 
> Because there's no frequency involved, I had surmised that it's purely a
> resistive load on the +12V/-12V side.
> 
> What's inside a horn to run the "speaker?"  A DC motor?  I'm not sure... but
> I suppose that would make sense.  (I've never had one apart).
> 
> It's purely academic, but does an automotive horn's resistance vary based on
> it's "state" or "mode?"  I'm no EE, so forgive the terms... by those I mean
> "initial starting," "engaged and running," and "shutting down."  And in the
> "engaged and running" (i.e. on and horn blaring) state, would the load and
> therefore the current vary?
> 
> Just curious.  There's probably a wiki out there on just this topic, but
> maybe you, Larry Leung, or someone else might have a ready answer.
> 
> Either way, they are fairly high current and since air bags were added to
> the steering column.... in my limited experience... they're all relayed and
> the horn contacts carry only a small current (mA) to energize the relay.
> 
> Mark Rosenkrantz
> 
> On Mon, Feb 8, 2010 at 12:18 PM, Brett Dikeman <brett.dikeman at gmail.com>wrote:
> 
>> On Sun, Feb 7, 2010 at 5:53 PM, Radek <radek at istar.ca> wrote:
>>
>>> OK, so to check if the horn is shorted (that's what I'm really after),
>> what should I measure?  It is honking,
>>> BTW and is not on the car.  When I connect it to to a battery, lots of
>> spark is created.
>>> The wire I touch to the battery terminal seems to burn a little hole in
>> the terminal.
>>
>> It's a relatively high-current, inductive load, which is why you get
>> the sparking both on connection and disconnect.  Flyback is what you
>> get when you disconnect an inductive load; it's a big spike of current
>> in the opposite direction.
>>
>> In some cars, the horn is relayed...
>>
>> -B
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-- 
Huw Powell

http://www.humanspeakers.com/audi

http://www.humanthoughts.org/