Horn 6V to 12V

I recently converted from a 6V system to 12V. The horn still works be doesn't sound as cool now. It is higher pitched and louder. Recently it started to kinda drag....sounded ill. So I took her apart last night and cleaned her up (pix is pre-cleaning) then put some WD-40 on it and put it back together. When I honked the horn it was incredibly loud! It is still too high pitched and doesn't sounds good. I read that the jam on on the back can be loosened and then the tone can be adjusted so I will play with that tonight. Is there any harm using the moter on 12 volts?

Probably wont hurt it a bit. You could install a resistor like maybe a ballast resistor to lower the voltage.

What size resistor should I get?

The horn is just one complication. What are you doing for a 12 volt generator?

'26DBJeff' has just posted a request for a 6 volt generator perhaps you could do a trade?

You do realise that your car is known as a 6 volt 2 unit model? It just makes things more complicated when ordering parts in my view but then I like to keep things just as DB intended.:cool:

Ray.

The horn is just one complication. What are you doing for a 12 volt generator?

'26DBJeff' has just posted a request for a 6 volt generator perhaps you could do a trade?

You do realise that your car is known as a 6 volt 2 unit model? It just makes things more complicated when ordering parts in my view but then I like to keep things just as DB intended.:cool:

Ray.

it starts so much easier on the 12v. I have the generated disconnected. The only electrical load on the battery is starting, the horn and the coil....since I don't drive at night. I drove it a long time Saturday and honked the horn 3 dozen times I still had plenty of starting power. So for now, I will just recharge the battery in my shop.

oh, I also added a 12v fuel pump as the vac tank was giving me issues. I think I have the tank fixed but I've not plumber it back in yet. So the elec fuel pump is another elec load.

I may have the gen rebuilt.....and converted to a 12 v.....or I might go back to the 6v system. I'm still on the fence. For right now I am enjoying the heck out of driving it and just doing small improvements.

Probably wont hurt it a bit. You could install a resistor like maybe a ballast resistor to lower the voltage.

So I bought a 1.25 ohm resistor....but it measures 1.5 ohms. I put it in series with the horn.....and the horn did not work. I measured the resistance of the horn and got 1.0 ohms. So 1 ohm plus 1.5 ohms is 2.5 ohms. At 12 volts, this is 4.8 amps.....so the horn saw only 4.8 volts.....which evidently was not enough to turn the motor. Otoh, the motor impedance is an inductive load so a dimple voltage divider may not work. I will try with a 1 ohm resistor or less.

Mike, there is a possibility that your 6 volt generator will produce enough to charge the 12 volt battery if you move the adjustable third brush - but I think it depends on whether there are resistors built in or not as there are no external resistors on the car so far as I know. (I know the 6 volt dynamos we use on Austin Sevens can kick out 20 volts and they need a resistor). If you wanted a reduced charge setting for the summer months so as not to over charge the battery (and not have to drive with the side lights on to compensate) you could fit that 1.5 ohm resistor into the charging system with a separate switch.

Whether the cut out will need replacing I am not sure. I found you can't use a 12 volt cut out with a 6 volt system but whether you can do it the other way round I am not sure.

Another thought; if a good earth does not cure the starting issue and you have heavy duty battery cables, it could be that the starter itself is not running true Does it get hot? This was the trouble with mine. Also the armature may have been replaced with a 12 volt one which is made of smaller gauge wire.

Btw, you will have to replace all your light bulbs with the 12 v system but you probably already thought of that.

Ray.

I used a 1 ohm, 1 watt resistor I got at Radio Shack. My horn is a 6V Klaxon (not original but looks period correct).

What size resistor should I get?

I am not up on the values of these resistors and such. If it were me I would try a ballast resistor. But it would appear that there is more knowledgeable advice here.

You must be on the right track if you now know that it wont run on 4.8 volts.

I used a 1 ohm, 1 watt resistor I got at Radio Shack. My horn is a 6V Klaxon (not original but looks period correct).

That sounds about right. I measured the resistance thru the horn and got ~1 ohm. So adding a 1 ohm resistor would drop 6 volts across the resistor and 6 volts across the motor (horn).

I found a 0.8 ohm resister....here is my math:

1 ohm thru motor coils + 0.8 resister = 1.8 ohms</SPAN></SPAN></SPAN>

V = 12 V</SPAN></SPAN></SPAN>

I= 12 / 1.8 = 6.7 amps</SPAN></SPAN></SPAN>

So 6.7 Volts across motor and 5.3 Volts across resister.</SPAN>

</SPAN>

You will need about a 25 watt resistor. The 1 watt aint gonna do it. 4 amps X 6 volts drop is 24 watts.

:confused: confused

I understand the power calculation assuming 4 amp draw. My horn does seem to work fine with the 1 ohm, 1 watt resistor. Is this because duty cycle is very short (a short blast or two of horn)?

I understand the power calculation assuming 4 amp draw. My horn does seem to work fine with the 1 ohm, 1 watt resistor. Is this because duty cycle is very short (a short blast or two of horn)?

Yes. The power rating is instantaneous power. But energy is power x time. So is you only draw 4 amps for a short period of time you do not produce enough heat to burn out the resister (or start a fire). I would suggest you find a higer rated rated resister.

This is the one I ordered from Autozone on-line. It hasn't come in yet so I can't vouch for it working......but based on my calculations, it 'should' work.

https://m.facebook.com/story.php?story_fbid=10153260393794115&id=641824114

This is the horn after the 0.8 ohm resistor added dropping the voltage.

If you can't see the video, LMK. I am uploading to utube but it is slow going.

Sorry, don't have a facebook account so can't see the video.

I watched it.......the horn sounds PERFECT!.......

http://youtu.be/u-D95AsqZMM

Finally got it uploaded to utube

I haven't done this before and I am not sure what it is all about. It says I have to sign in. Presumably I need to open an account with 'Google One account' Exactly what am I signing up to please?

Ray.

Hmmm, IDK. I thought you could just click that link to utube.

You tube states that it is a private video.

You tube states that it is a private video.

My bad. I think I fixed it and made it publix. LMK

OH YES! That is a great sound.

Sounds like the dive horn on a Submarine

Sounds just like it should.