DC horn relay with AC trigger circuit?

[sime66]

I’m thinking about using my existing horn button for a better DC horn, fed from my new battery.

Will my AC horn circuit work as the trigger for a DC horn relay?

If this would work I just need to run the old AC horn wiring through to the relay, will that work?

I'd run the DC horn wiring from battery, through the relay, and I realise it would only work with the engine running.

[sime66]

Something like this, not sure if I need the rectifier or not, or where wire from 85 should go, maybe as shown, but earthed?

[sime66]

I've been reading up and asking around, and this is what I'm going to do.
The little Bridge rectifier is plugged into the horn AC wiring and will sit behind the horn cover. The relay is already on the little board in my toolbox.
Hope it doesn't go bang!
If it works I'll let you know.................

[sbwnik]

I don't think it'll work. I can't put my finger on 'why', but something looks wrong.

I'll have another stare later, but why not just use a Vespa five pole reg/rec, run a DC feed wire up the frame to the battery (It'll charge it too), change the switch for a DC one, connect the AC feed to the lights and the feed from the battery to the horn, change the horn for a DC one... Job done.

I think.

[sime66]

I posted the wiring and little toolbox fuseboard I did from my new battery before, this is phase 2.

I've done the reg/rec, battery, etc. and it's all already got fuses and relays in my toolbox - job done, so putting a DC switch in would be easy.

I'm trying to use the normal AC horn switch because I think it would be neat to have a good DC blast off the old switch.

This little rectifier is just to make that existing (horn) switched AC circuit work as a trigger for the DC relay on the DC horn circuit.

[fraggleexport]

Hi Sime66,
I'd be interested to see if this works. Any luck? Cant quite get my head around whats wrong but Im sure that your system wont be happy sharing the same chassis ground. I hope Im wrong!
Kevin

[sime66]

I know what you mean about sharing the same ground, but that works anyway with an AC scooter with a battery. My new DC already works alongside the existing AC system, sharing a negative earth. I have the 12v DC fuses, relays etc. in my toolbox up and running. I can't see why it won't work, but I think maybe the blue and yellow off the AC horn onto the rectifier might be a bit of trial and error. Here's my logic:
. If there is 12v(ish)AC where the horn was, then swapping the horn for a rectifier will give me 12V(ish)DC. I can use this DC as the trigger circuit for my DC horn relay. When you press the AC horn button, there will be an AC circuit, the rectifier gives a DC signal, which triggers the Relay to connect the circuit of my 12V battery to my new DC horns.
I have a little gif animation of the rectifier; whichever way the AC comes, it still has negative earth, which is the same for the DC:

(I know it's only half-wave, and I don't know if that applies or if it will be a problem)
I hope to do it tomorrow evening, my horns came today, but the rectifier didn't. The recifier is £3 and the size of your thumb, so it literally just plugs in, and one DC (+) wire pokes into the glovebox to the relay, and one (-) goes to Ground
Here's the horns, They are high/low Fiamm AM80S (£9.00 second-hand on Ebay). Very loud, but not a Mod accesory; they'll be going under the floor I think. (I want the noise, not the show).

The battery arrangement and panel in my toolbox can be seen at the bottom of this thread:
vespa.proboards.com/thread/3476/motobatt-any-good
Anyway, the time for theory is over, suck it and see tomorrow, I'll let you know how I get on..........
(if it doesn't work I'll just put a DC foot horn button LHS on floor; all the rest of it will be the same anyway).

[fraggleexport]

absolutely...suck it n see. Bear in mind the current required to actually activate the relay coil, although you should have enough there if its previously working a horn. If its not a smooth enough output from the rectifier then a couple of capacitors soldered on should do the trick. Fingers crossed:-)

[sbwnik]

Bingo.. You've answered where the flaw may be.
The half wave 'may' cause the same tone fluctuation that you get with the stock horn.

All you can do is try!

[sbwnik]

Bingo.. You've answered where the flaw may be.
The half wave 'may' cause the same tone fluctuation that you get with the stock horn.

All you can do is try!

[sime66]

It works!!

I'm trying to put some film and photos up to demonstrate, but I'm having a bit of aggro with Proboards, which I will sort out in good time, but,

Subject to a bit of tidying up of wiring, and checking over. My new DC horns do give a good blast off the AC switch, just by using a £3 bridge rectifier to the relay.
It might be that the DC can be cleaned up with a tweak (capacitor?); I'm not sure, it is very wet outside (and under my horncover and in my toolbox), so for now I'm just happy to know it works.

You can have photos, but film will have to follow:









These are the film locations (I'll post them properly when I've sussed it again):

s1290.photobucket.com/user/sime6954/media/P1110478_zpsb4d3a366.mp4.html

s1290.photobucket.com/user/sime6954/media/P1110479_zps4768d1e4.mp4.html

s1290.photobucket.com/user/sime6954/media/P1080664_zps86dc5a03.mp4.html
(I left the camera runnig, so ignore the black)

[sime66]

Film

[fraggleexport]

Good stuff! nice work....it does still sound a little unhappy, but not as pathetic as the AC ones. I think that may only be because the coil is only receiving half wave rectification and not a nice smooth DC. As long as the relay can handle that long term then bobs your uncle!

[sime66]

Cheers Kevin,
Until it's all dry and bolted down, and I'm testing whilst riding, rather than idling and playing with throttle etc., it won't be clear whether the dirty DC is a problem or not. We've all identified the probable drawback with the fluctuating DC wave, and on the film you can definitely notice a warble as revs drop. But, it was also very wet and my temporary earth was shorting with my indicators, so I just put it away, happy to get something, but ready for a tweak under dryer conditions.
I do not think it is half-wave, but I think you've already identified the tweak required though; take a look at top-right and bottom left on the image below, and notice the different DC wave pattern when you add a capacitor, so I might pick your brains about that next..

[sime66]

Not so pleased with myself this morning.
Went out and tidied it all up and went for a spin – headlight very dim, indicators not working, and DC horn not working.
Came home – removed rectifier (hot, as if it had been working all the time), plugged in AC horn, replaced an indicator bulb that must have blown yesterday whilst testing, and it’s all back to normal again (all AC working as normal)
Not going to draw any conclusions; either there is a flaw in the idea, or I have a short somewhere, and it is again too wet to experiment, not to mention the neighbours. I seem to be draining the AC though, either with the wiring, or with the rectifier. Need to chew it over. Whatever the outcome, it was a worthwhile exercise, and it was working yesterday, so not given up on it.
I have rigged up the horn with just a normal DC switch on the relay to make sure that’s all OK, which it is, so now I’m either going to recheck everything and have another go, or get a waterproof foot button and rig it like that (had managed to do the whole thing without drilling though).
Anyway, here is a quick film of horn comparison, whilst I have them both wired up.

FILM

[sbwnik]

Let's see if we can work this out logically.

The button is a break type that interrupts the light circuit to send power to the horn and then back up again.
You've used that current to throw a relay? This is AC power, meaning it's changing 'direction' (no need to complicate the concept - yes I know there are correct terms!)
This relay is carrying DC power (which obviously doesn't change direction) to power the horns from a battery, across its terminals

Best guess: The relay is a DC relay, and the changing direction of the relay is causing it to fluctuate internally, causing both the heat (mechanical work) and the drop in power to the lights (due to the 'fluttering' breaking the contact and allowing only half the current through?)

Does that make any sense? That's not from any knowledge - I've never tried to do this - but just working through what I would expect to happen.

[sime66]

There’s no AC at the relay. It’s a DC relay, and it works now that I’m using a temporary DC button on the trigger circuit. The rectifier was intended to convert the horn AC to DC, and to use that DC as the trigger only (the DC horn power coming from the battery as you said). It is the rectifier that was getting hot, not the relay.
The flaw in my thinking is around the rectifier or the horn switch:
I did expect the rectifier to get hot in use, which would be rarely, and behind the grille was ideal for the heat, (only when horn button was pressed), the fact that it was getting hot with the engine running seems to mean that the rectifier is working at all times – this would explain the heat and the power loss to lighting.
I have two theories (both may be nonsense):
1) The way I’ve wired up the rectifier is allowing one or other phase of the AC to pass through all the time (to earth), thus making the rectifier work at all times and causing the heat in the rectifier and the power drop in the AC. (My horn is on the circuit from the stator to the reg/rec (unregulated), the lighting is the regulated circuit after the reg/rec – whatever I was doing was starving – I suspect by half – the supply from the stator to the reg/rec).
2) The switch arrangement (which I have only just realised is normally closed) is allowing some AC to rectifier all the time, which is causing the rectifier to work at all times and causing the heat and the power drop. I can’t quite picture exactly how a normally closed switch and the blue and yellow wire(s) go together schematically, but I think one side to the horn must be live and the other is switched.
My conclusion is that the idea of using a rectifier to give the required DC to the relay would work, but only for a normally open switch, so that no current was passing unless the button was pressed.
I’ve toyed with two remedies/fixes, neither of which are particularly good ideas:
1) Isolate the AC wiring from the switch (cut the yellow and blue and splice them together to wire Stator directly to reg/rec) and then use the isolated switch and horn wiring on a DC trigger circuit. (This won’t work because the AC horn switch is normally closed. although I could get a normally open, but that’s expensive)
2) Get an electric start button, fix it in the usual place (under the RHS switches) and use it as a horn button (trigger circuit) instead of as a starter button. – This is a bit tatty though.
I haven’t given up trying to understand the theory and the wiring, just for the challenge, but I don’t think a rectifier will work the way I intended with that normally closed switch. I can’t explain why it did work for a while, but probably I just didn’t notice my lights were dimmed, and I may have now buggered the rectifier? I could wire it up again and go round with a multimeter, but now I just think it is best to keep the AC and DC separate, and find a DC answer, which then just becomes a question of where best to put the DC switch.
I don’t think you should have to take your hands off the handlebars to sound the horn, so it is the ‘start’ button as I said above, or a foot button as I said earlier. I think I’m going with the left foot, which after a few days off it, I’m going to do tomorrow (if post arrives).
Thanks for giving it some thought, but I think you’re initial feeling was right, which may well be a good reason why you never tried it.

[sbwnik]

I forgot about hte rectifier (it's been an intoxicant filled evening!)

I suspect you're closer than me, and I'd not be surprised if yes, you have fried it!