Packard Forum Index » Pre-War (1899-1942)

Recheck those horns with an actual car battery. I have a 7amp 12v bench power supply, and using this I thought my horns were totally bad as I had no sound at all, and it tripped the fault on the power supply. Then I tried them with a car battery and a 20 amp inline fuse, and they worked great. Just had to adjust the tone because of the difference between the original 6v application, and the 12v I am running in the car.

I think you will find they pull significantly more than 1.5amps, hence the reason most horns use a relay.

Kev,

Just came up from the garage and saw your post. I decided to try it on the 6V battery and found out it works. I'm am puzzled though why one draws only 1.5A and the other one is in excess of 3A.

Anyway the garage is too cold right now so I'll look at it more tomorrow.

HH56: I plan to take it apart one more time and clean off all the corrosion I can find.

Though usually only momentary, horns require A LOT of current to function properly - probably in the range of 20 -30 amps. To bench-test them you should use a fully charged car battery.

Tbirdman,

If you have or can borrow a digital voltmeter you may want to check the resistance of the coils. Set the meter to a low resistance scale and measure the resistance of the coils. A good coil is going to measure around 4 ohms.

The difference in current draw could be due to a shorted winding in the one of the coils, or it could be because the points are not functioning properly.

If you apply current to the good horn the center core is going to pull down and open the points up. When the points open the core will spring back, closing the points. This rapid movement of the center core and diaphragm makes the sound.

The rapid turn on / turn off of a good horn will show a different current draw on your power supply compared to a bad horn where the center core doesn't move, and the coil is energized 100% of the time.

Regards,

Dave

THis statement:
" I'm using an adjustable 3A power supply. The good horn draws 1.5A. The bad horn is maxing out the 3A current from the supply."

explains this qusetion:

"I'm am puzzled though why one draws only 1.5A and the other one is in excess of 3A."

That's because your power supply is ONLY rated at 3 amps.

As Owen has indicated, a horn requires alot of power which means a lot of AMPS!! Much more than just 3 amps. So any maximum power that the 3 amp power supply could ever produce just simply passed thru the horn circuit with little or no effect. Just not enuf amperage available.

One thing to remember here, Ohms law V=IR

V=voltage
I=current
R=Resistance

If the voltage from the supply is constant at 6V, and a different current is measured then there is a resistance difference between the good and bad horn.

Correct that and you'll have a good horn.

Measured the current draw for two Sparton Model L-A Trumpet Horns of a '32.

Continuous current draw was 7A from the battery, measured using a digital meter. Battery charged to 6.6V, with 800 cold cranking amps capacity.

Correction to my previous post of 4 ohms resistance - The resistance would be 0.94 ohms for the pair.

Well both horns work on the car battery. I didn't test the current when hooked up to the battery as I'm assuming they are OK. What threw me off was the one horn working at 1.5A and the other one was over 3A as indcited by the limitations of the PS. My primary goal was to try to make them sound better and I had them off the car for the radiator recore. Anyway I adjusted them as good as I can.

It appears that the major adjustment for the armature indicated for the 37/38s horns wouldn't apply to these.

I officially end this project. I did learn how to take one apart and how they work so that was fun. Funny thing is I took the one apart because I assume it wasn't working thinking I have nothing to loose. Turns out it probably was working. I hate to take apart things that are working. Now for the Xmas lights.

Thanks for all your help.