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Voltage Spikes

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rogerharrop
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Voltage Spikes

Post by rogerharrop »

Hello All,

I inherited a pair of basic squeeky horns on my Dart so I decided to replace them with a pair of twin tones. I fitted them and they worked fine but then the next time I tried only one worked and then none. I went back to the supplier and they kindly replaced them, assuming a fault. I fitted them these week and again they worked prefectly - until I started the engine - then dead as DoDos. I've bench checked them, it's not the relay which is fine but the horns are quite dead.
I'm not brilliant electically but it has been suggested to me that on starting there can be a voltage spike of 15/16 volts and that's the cause.
A question, if I was to fit a voltage suppressor like this https://www.ebay.co.uk/itm/Waterproof-D ... 3555939746
ahead of another pair of new horns should that provide the protection to sort the problem?

Many thanks

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John-B
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Re: Voltage Spikes

Post by John-B »

Are you sure you have connected the horns correctly? Cheap horns can be connected with either terminal to positive but air horns need to be only positive to positive terminal.
They use a lot of juice so need a good earth.
I'm not sure that a voltage spike is relevant unless you happen to be pressing the horn button to create a circuit while using the starter motor.

Sydsmith
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Re: Voltage Spikes

Post by Sydsmith »

Roger, I presume you are using the same wiring and relay? I also presume the new horns you are using are conventional twin tone horns and not air horns? In which case I can't see why the old horns worked OK and the new ones last only five minutes, except perhaps if the supplier has perhaps supplied six volt versions in error or he has a duff batch.

Most horns are straightforward electro magnets with a diaphragm to make the sound, no electronics as such and nothing complicated or electronically tender about them, they are usually very robust and will withstand quite a bit of misuse.

I cannot see why there should be an upward spike when the starter is engaged, on the contrary, because of the load on the battery, the voltage will almost certainly fall not rise.

Unless you have your hand on the horn button and the horns are sounding when you turn the ignition key to start the car, there cannot be a voltage across the horns, in which case in the unlikely event there was a spike it could not destroy the horns.

My guess is the horns are either faulty or they are supplying 6 volt horns in error. Syd

rogerharrop
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Re: Voltage Spikes

Post by rogerharrop »

Many thanks Syd. Yes it's the same wiring but the pold horns didn't have a relay but the new ones do. The new ones are twin tone not air horns.
Based on what you have said I've gone back to them to check the batch and 6/12V labelling

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Re: Voltage Spikes

Post by Vortex O'Plinth »

The SP250 was not originally fitted with a horn relay although either you or a previous owner have (wisely) fitted one. You say the relay is fine so I presume you have checked that it still passes current after the horn failure? Most automotive relays will handle the horn current draw without problem but some with a low current rating may be marginal.

Do the horns work if you connect them directly across a 12V battery?
Nick

"Don't bother with the Air & Space Museum - there's nothing to see.......".

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Brian-H
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Re: Voltage Spikes

Post by Brian-H »

rogerharrop wrote: Fri Sep 18, 2020 7:01 am .... it has been suggested to me that on starting there can be a voltage spike of 15/16 volts and that's the cause.
Presumably the seller suggested this and is clutching at straws because, as has been said already, there's no voltage across the horns unless they're operating.
rogerharrop wrote: Fri Sep 18, 2020 7:01 am A question, if I was to fit a voltage suppressor like this https://www.ebay.co.uk/itm/Waterproof-D ... 3555939746
ahead of another pair of new horns should that provide the protection to sort the problem?
That's not a voltage suppressor, it's a 48V DC to 12V DC converter, which wouldn't do anything (it needs a continuous 48V DC supply to give out 12V DC).

It is possible to get continuous voltage spikes when a spark-ignition engine (with conventional distributor) is running, but again as already said, they don't have the energy to damage a horn, certainly for the brief period of time that a horn operates (and definitely not at all when the horns are not operating). The best way to suppress such voltage spikes to something electronic (e.g. a solid-state windscreen wiper delay mechanism) is to fit an inductor in the supply line to the device, but you won't need such a thing for a car horn.

As has also been suggested, when testing the horn, test it directly across a car battery.

If the horns are from ebay and new and cost under £10 then they're probably made in china.

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Re: Voltage Spikes

Post by Sydsmith »

Did you get to the bottom of this Roger?

If it is the case that Rogers problem is Chinese rubbish, you have to question why these terrible Chinese products are allowed out of the country, it is such a waste of world resources and material. They set up a factory "design" the product put in the tooling and make a load of total trash. All that effort to make a product that is so poor it breaks almost before you use it.

There is so much of it, I check everything I buy now and avoid Chinese like the nasty plague they have perpetrated on the world.

I am sure the only reason they get away with it is because it is so cheap, you can buy a pair of wind tone horns on fleabay for £15 post paid, folks buy ,find it is rubbish then dump it without complaining or asking for a refund.

The mind boggles at the amount of manufacturing going on in China as I write spewing out absolute cr*p which is sent all over the world and used for a fleeting moment then thrown away. Some of the children's toys are so poorly made from such poor material you have to wonder why retailers put them on the shelf.

Not that I am biased of course. Syd

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Re: Voltage Spikes

Post by Vortex O'Plinth »

Sydsmith wrote: Mon Sep 21, 2020 9:59 am Did you get to the bottom of this Roger?.......

.......The mind boggles at the amount of manufacturing going on in China as I write spewing out absolute cr*p which is sent all over the world and used for a fleeting moment then thrown away. Some of the children's toys are so poorly made from such poor material you have to wonder why retailers put them on the shelf.

Not that I am biased of course. Syd
It's what you might call poetic justice Syd. Back in the days of Empire we raided our dominions for their raw materials, using cheap native labour to harvest them. After shipping home, they were processed into crap that was used to pay for more raw materials.

Now that our domestic labour force demands a wage sufficient to support the affluent life style that we see as our right, and our status as a manufacturing nation has declined into obscurity, third world countries have realised it's more profitable to manufacture the crap themselves and sell it back to us.

I've bought several pieces of Chinese 'rubbish' that have functioned just as well as domestic counterparts at three times the price.

Not, of course, that I am biased either.......... ;)
Nick

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Brian-H
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Re: Voltage Spikes

Post by Brian-H »

Blame this bloke for making it all too easy

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Ian Slade
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Re: Voltage Spikes

Post by Ian Slade »

The UK price of Chinese goods depends on whether the vendor has either a return or scrap agreement with the manufacturer, the more expensive uk price where you can actually get a replacement or refund works out on a 3 or 4 failures per unit purchased, check the Alibaba price then the uk vendor price and you get the failure rate. Strangely high end TV and electronics i.e those companies that have their own factory inspectors an QC are normall quite reliable.
Having said that the SP was made before electric spikes were considered a problem, spikes only became a problem with the indroduction of electronics, QED, keep the SP original and the problem doesn't exist :)
Owner since the 70's, Genghis is slightly to my left.

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