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TR2/3/3A Windtone WT618 horn current

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71TR6

71TR6

Jedi Hopeful
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Hello All,
I'm refurbishing my TR3A's WT618 windtone horns and ran into a slight issue. I was able to get a copy of the Lucas Windtone Horn article " Hints from Austin's Morris Garage" and noticed that the current draw should be 2.5-3A. After pulling the pin out, polishing it, lubricating it and then reassembling and adjusting, the best current draw I can get is 8.6A. This is better than the original 11.1A it was drawing before cleaning but still more than double what it is supposed to be drawing.

Anyone have any thoughts on why these horns are still drawing so much current or is this normal for a 60 year old horn? I really, really, really don't want to fry my wiring harness or toast the horn switch after I reinstall these horns.

Thanks,
Ron W
59 TR3A in pieces but going back together
71 TR6
 
If I remember my high school electronics teacher correctly, the amp draw had to do with the winding of the device and other variables, wire size and I forgot the rest. Anyways if the deice draws more amps, and again I am kinda guessing, the connections and resistance will cause a higher amp draw. If I had a new horn or a very clean one, I would try to check that one. Might be the gauge is out of calibration.

I guess I would see this as a blast of power because horns are not honked for long. I would put my hand on the wires just out of the fuse box and reach over and honk the horn for a few seconds. If the wires got hot, I would look for bad connections creating resistance. Especially, if it is an early car with the screw down connectors. If it did not, drive on.

steve
 
Is the horn sounding when you make the test?

In my experience, most of these old-car horns draw about 10 amps, peak. But the current goes on and off rapidly--that's how they make their sound--so the AVERAGE current is much lower, usually a few amps. If you are preventing the horn from sounding (reasonable for all of us who like keeping their eardrums intact) you will see the higher current.

Also, if you measure the current with a digital meter, all bets are off. Digital meters are not happy with a voltage or current that is not constant; it makes them go nuts. An analog meter will indicate an average current accurately.
 
Tuning has a large impact on current draw too. I used an ammeter and tuned to get a reliable beep at the lowest current. The key is to get the tune in resonance with the spring in the diaphram, so the solenoid is not fighting the resonance.
 
I played with it and got it down to 6.5 A but that’s the lowest that it will go. I’m going to button it up and put a relay in the circuit just for insurance.

Thanks for everyone’s response.

Ron
 
They should be powered from one of the 2 fuses on the firewall, so a relay is redundant. I guess you could up the value of the fuse and use a resettable relay to keep from replacing fuses...but I think 6.5 amps times 2 is still well under the fuse rating anyway. The horns are such high draw that they chose to give them their own fused circuit...and 1 of only 2 fuses on the car. I think the draw will always be much higher than the 2.5 amps you were shooting for. The fuse is rated at 35 amps, so I think 10 amps is closer to normal draw.
 
That 2.5-3 amp expectation seems low to me. Not sure if yours are the same as the Windtones in my TR6, but they each drew over 5 amps after rebuild.

Ed
 
Thanks for all the comments. Great point Steve on the digital meter- so given the sinusoidal oscillation, I agree that I'm probably averaging considerably less than the 6.5A showing on my digital meter. If I can ever find my old Radio Shack analog meter I'll check it out.

As far as a fuse, a fuse alone will still allow the full current to go through the horn contacts and beat them up pretty good. With my horns not working properly, there was considerably more current going through the horn button contacts than I believe they were rated for. As a result, the contacts and the horn button plate had a serious amount of erosion (aka: EDM'd for those tool and die makers out there :smile:).
Hornbutton.jpgHornContact.jpg

My thought is, running the horn current through a 30A relay contact and using the horn button to energize the low current coil should extend the life of the button considerably and ensure I never have to touch it again. I figure since I'll be running the headlights with a couple of relays, I might as well do the horn too and have all the relays in a nice cluster under the dash.

Thanks again for everyone's comments! Very helpful as always.

Ron
 
Running the horns with a relay is a pretty commom practice--I'm a little surprised to hear that the TR3s didn't do it that way.

Ed
 
Relay still won't help the contacts any more than a fuse.

Just read your other post...you're talking about the trafficator contact. I thought your were worried about the horn contacts. If you get the oil and dirt off the trafficator I don't think you will have trouble with further pitting.
 
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