[TR] TR4A Horn Question

[Dave Connitt]

Hi Jerry,
The horn button controls a specific “horn” relay in this harness but it’s recommended current limit is 15 amps. The horns I have pull 17.25 amps. The horns I have are new and I bet the original ones needed less current. I am going to call Scott Harper tomorrow and see if he has some old ones. 
I thought about increasing the wire size of the horn circuit.
Dave Connitt 

Sent from my iPhone

> On Jan 27, 2021, at 5:12 PM, Jerry Van Vlack <jerryvv at roadrunner.com> wrote:
> 
> Dave are you going thru a relay? If yes then which fuse is blowing? You could always increase the wire sizing from the relay to the horn and fuse it accordingly. But why am I even giving advice to an EE?
> JVV
> 
> -----Original Message----- From: Dave Connitt
> Sent: Wednesday, January 27, 2021 4:46 PM
> To: Paul Tegler
> Cc: triumphs at autox.team.net
> Subject: Re: [TR] TR4A Horn Question
> 
> I read through my Advanced AutoWire manual just now and it specifies a horn circuit max. current of 15 amps so I will need to find some horns that have a coil resistance of about 1 ohm if I don’t change anything else. I know the relay is rated at 30 amps.
> Sigh..
> Dave Connitt
> 
> Sent from my iPhone
> 
>> On Jan 27, 2021, at 4:35 PM, Paul Tegler <ptegler at verizon.net> wrote:
>> 
>> ...not sure of the coil spec...but just for a reference....
>> a normal buss style fuse marked 'rating' is the spec holding current. (should not blow) It can take 10+ minutes to blow at 25% over the spec
>> The 'voltage' rating is the guaranteed 'disconnect blocking' voltage after the fuse blows.
>> 
>> So your horns must be spiking higher than the fuse rating to blow it quickly
>> 
>> ptegler
>> 
>> 
>>>> On 1/27/2021 3:50 PM, Dave Connitt wrote:
>>> Hi All,
>>> One of my winter projects is to determine why the horn fuse in my TR4A keeps blowing.
>>> I had installed a Advanced AutoWire harness during the restoration. The harness contains a 20 amp fuse for the horn. The horns are new as of the restoration. I went through the wiring harness and could not find a issue there so now I am looking at the horns themselves and that is where I need your help. I measured the horn coil resistance and it is 0.8 ohms in both of them. If I use 13.8 VDC as my battery voltage, I get 17.25 amps at the fuse which is too close to the 20 amp fuse rating in my opinion. If the resistance was even 0.9 ohms, the fuse current would be a little over 15 amps which would make more sense. Does anyone know what I should see as a horn coil resistance on a good horn?
>>> Thanks in advance,
>>> Dave Connitt
>>> 
>>> Sent from my iPhone
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>> 
>> -- 
>> Paul Tegler
>> ptegler at verizon.net  www.teglerizer.com
>> 
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