Use led light for warning signal

[cwah]

Hello there,

I'm looking to use warning signal for my bike, but with a very minimalist set up (less visible is better). So I'm thinking about using these led strip:

HobbyKing R/C Hobby Store : High Density Waterproof LED Flexible Strip - Yellow (1mtr)

Combined with a car signal controller:
Load Resistors LED Indicators Flash Rate Controllers | eBay

These led strip are very bright and I'm sure I'll be noticed on the road. But I'm don't know about the best way to make them blink?

Would the resistor work?

ps: sorry I have very limited knowledge in electronic.

 

[KirstinS]

my electrical skills are up to very little as well. All I can add is that I ran two similar strips of maybe 10 LED each off a 9v battery. They were rated 12v but were still perfectly bright at 9v

I placed them on my backpack for extra visilbilty in winter. I just bought a 9v battery holder with a switch from Maplins and soldered together

But I'd love to know how to make them flash as well

 

[neptune]

@Cwah. I am not sure just what you are trying to do here as you say less visible is better. At one time Tandy/ Radio shack use to stock a flashing LED. I am not sure if it was designed for 12 volts or 3 volts . It was cheap enough to experiment with. A standard LED needs about 3 volts . So if the flashing LED is rated at 3 volts, connect it in series with 3 more standard LEDs , and supply the string with 12 volts. All should flash. Or add another 8 in series and run it on 36 volts. Don`t forget to use a 2 amp fuse if you run it from the bike battery.

 

[rog_london]

@Cwah. I am not sure just what you are trying to do here as you say less visible is better. At one time Tandy/ Radio shack use to stock a flashing LED. I am not sure if it was designed for 12 volts or 3 volts . It was cheap enough to experiment with. A standard LED needs about 3 volts . So if the flashing LED is rated at 3 volts, connect it in series with 3 more standard LEDs , and supply the string with 12 volts. All should flash. Or add another 8 in series and run it on 36 volts. Don`t forget to use a 2 amp fuse if you run it from the bike battery.

Whoa, careful there. A basic standard LED is in essence a constant voltage device rather than a constant current one - so you always need some sort of external current limiting (a suitable resistor is the low-cost low-tech answer). You're not dealing with a string of fairy lights in series with one flashing bulb which interrupts the supply to the others so they all flash together.

If your flashing LED is rated at 3 volts, during its 'off' period it would have to withstand 12 volts as the other LEDs would be dropping nothing.

A standard LED 'needs' around 20-50mA, and will drop around one volt. Series-connecting three of them (for instance) will still need the same current but you'll drop around three volts TOTAL. Increasing or reducing the current will make little difference to the voltage drop over quite a wide range of current, but go much above 50mA and you risk overheating and burn out.

If an LED is rated at 3 volts, it's not a 'standard' LED. It incorporates a driver to regulate the current at that voltage. It's not suitable generally for series-connecting as how the driver will behave becomes unpredictable under those conditions.

If you want to use voltage-rated LEDs, they need to be correct for parallel connection to the actual supply voltage you're using. If the rated voltage is more than three or four volts the driver will certainly be a DC-DC converter to give the LED itself the required current at a much lower voltage with the necessary limiting and also so that power is not wasted as heat.

Suffice it to say it's all quite complicated, and while I've tried to make it clear what the problems are if you're confused I'm not surprised!

Rog.

 

[neptune]

@rog_london. I understand your point , and I see what you are getting at. The problem is that it does not help Cwah with his query. So what I am asking is, can you suggest a simple way to make these LEDs flash without building a dedicated LED flasher circuit based on a 555timer chip. The only other way I can think of is to buy a cheap set of Christmas tree lights using LEDs and running off a plug in 12 volt power supply, and sustitute a battery instead of the power supply.

 

[rog_london]

If I were looking for a cheap(ish) and easy(ish) way to do it, I'd first look for a flashing LED with my required voltage range - which for the purpose of this idea would be from around 5 volts to around 14 or 15 volts. (for safety on a nominal 12 volt supply). It would need to have a compatible current rating to match the standard LEDs I wish to series connect - I did mention 20-50mA, but that's ball-park and of course you can get LEDs which require a higher or lower current than that - I'd guess as brightness is the main idea, 'high brightness' red LEDs would be what you'd go for. So, when you connect your flashing LED in series with the others, if the LED is turned off it would 'see' 12 volts, which would be within its rating. However, when turned on, it would drop whatever voltage was needed to achieve its desired running current, which you know would be compatible with the remaining 'dumb' LEDs (20-50mA or whatever they are rated for). Each of these would drop about a volt - so in theory you could comfortably have, say, five of them plus the flasher. This would leave 7 volts for the flashing LED when turned on, which ought to be enough.

Obviously you'd tweak things a bit - if your flashing LED had a range of 8 to 15 volts, you'd only be able to run three 'dumb' LEDs in series. You could add a parallel resistor to the dumb LEDs to pass a bit more current if the flasher turned out to need more than the 'dumb' LEDs were rated for, though this would be wasteful as well as being a further complication and best avoided.

I hope that's reasonably clear. To sum up: you absolutely need a flashing LED which accepts a range of voltages as the input, it needs to suit your power supply (which dictates its high voltage rating) and you need to know that the current it draws when it's on is within the rating of the 'dumb' LEDs.

Your basic idea was a sound one! It just needed to be buttoned down a bit. Cwah is just a bit too gung-ho and would do exactly what you say without seeing a problem lurking.

Rog.

 

[neptune]

@Rog . Thanks for posting that detailed information, and at least it gives him some idea of what to do. The thing about LEDs is that they are fairly cheap, so you do not risk a great deal by a suck-it-and-see approach, as long as you remember to use a low amp fuse.

 

[oigoi]

Cwah I would use the led strip that you have suggested (as it is 12v) and power it using a flasher unit like this one to make it flash:

Indicator Flasher Relay Unit 12v 3 Pin use with bulbs up to 23 watt inc's LED | eBay

 

[rog_london]

Hello there,

I'm looking to use warning signal for my bike, but with a very minimalist set up (less visible is better). So I'm thinking about using these led strip:



Combined with a car signal controller:


These led strip are very bright and I'm sure I'll be noticed on the road. But I'm don't know about the best way to make them blink?

Would the resistor work?

ps: sorry I have very limited knowledge in electronic.

Hi Cwah!

I've looked at your pics and the two websites. A couple of points:

(1) The standard unit comprises 60 LEDs, which would be 20 sets of 3 in series with an appropriate resistor for each set of 3. The current rating for this is almost half an amp at 12 volts, so would present a serious load on your system assuming you used a full metre. Getting that to flash would require some custom circuitry.

By the way, a pop up appeared on that page inviting me to click on something to go direct to the checkout for a discount - I'd advise you not to do that as likely you're being phished and your credit card might get hit pretty hard after you've given your details to a bogus web page.

(2) The second item is not connected with your requirements at all. It's a resistor designed to draw roughly the same current as a direction indicator lamp (or possibly two) would do on a car - from memory 21 watts time two, or almost four amps. This is because, if you replace your turn indicator lamps with LED based ones, you reduce the current draw to a fraction of normal, and the flasher relay will complain - usually by operating much faster than usual. This is deliberate and designed to give the driver a warning that there's an indicator bulb blown!

It's no use to you - and you don't want to use a car flasher relay - trust me.

Rog.

PS - just seen Oigoi's post - that flasher unit might be suitable as it's rated for LEDs and therefore would not be current-sensitive. Just don't forget to disconnect the 12 volt feed to it when you're not using the LEDs as, like your converter, it WILL draw current when it's idle. It might also 'tick' and be damned irritating - you take your chance with that.

 

[cwah]

Thanks Rog for this detailled explanation.

I just purchased the led from Hobby King as they may be appropriate. Which resistor should I buy in order to get it work?

Also, you mentionned that the flasher unit froml Oigoi may work. So if I get this unit, could I directly make my hobby king led work without resistors?

I'm so a beginner in electronic lol. Thanks for this

 

[rog_london]

Thanks Rog for this detailled explanation.

I just purchased the led from Hobby King as they may be appropriate. Which resistor should I buy in order to get it work?

Also, you mentionned that the flasher unit froml Oigoi may work. So if I get this unit, could I directly make my hobby king led work without resistors?

I'm so a beginner in electronic lol. Thanks for this

That LED string won't need any external resistors - as I mentioned the LEDs appear to be grouped in sets of three with each three having the approriate resistor already built-in. So, in effect, in the one metre string you'll have 20 parallel-connected sets, each comprising 3 standard LEDs with an appropriate series resistor. It should run happily from your 12 volt converter. Try it without the flasher to make sure everything works as planned (and don't forget to use an appropriate fuse) and then insert the flasher in the circuit between your DC-DC converter and the lamps. The flasher has three connections - input positive (which will go to the 12V positive output of your converter), output positive (which will go to the red lead on your LEDs) and common negative/ground which connects to the black wire on your LEDs as well as your common ground on the converter.

Which terminal is which will hopefully be labelled - either on the body of the flasher or supplied on a piece of paper! The only assumption you can probably make is that the middle terminal will very likely be ground.

Rog.

 

[cwah]

Thanks rog for this very clear explanation.

I purchased the flasher and the led strip. Just wait for the parcel to arrive now

Will keep everyone in touch

 

[cwah]

I received the flasher.

It has 3 prong marked L, P and X.

There was no instruction at all but I've read online that X was for the battery, P for the ground and L for the signal.

I did that:
- Connected the X to the red wire of the battery
- P to the black wire of the battery and the black wire of the led strip.
- L to the red wire of the led light.

It was 12V continuous voltage.

It worked... during 20second. Led was blinking that was nice..


But then it stopped. The flasher was very hot, the 18AWG wire were also hot. Not sure what happened, but it looks like it's using too much power and stopped?

Now the led do not blink anymore, but if I leave the battery connected to the flasher, it still getting hot.


Not sure what I can do now?

 

[rog_london]

Nothing helpful - sounds as though your info was wrong, as you obviously had some sort of overload in the flasher, and I'd guess that you might have got the input and output crossed over.

I'd expect it to get warm - not hot - and I definitely would not expect the 18SWG wire to get hot.

Buy another flasher and try again, but you really need to know which terminal is which. Three cryptic letters don't help much, though I'd have guessed that 'L' might be 'live' and the battery connection, and 'X' might be the output. It's also possible that 'P' might be 'positive' which means a common-positive connection. Some old vehicles had/have positive earth, though AFAIK they're all negative earth these days.

Remember what I said before - a small fuse (not too much more than the expected load) can save you a lot of grief!

Rog.

 

[rog_london]

I have a little more info - it turns out that X and L you got right - but P is NOT a common negative - it's a low-power feed for a pilot bulb which flashes in time with the lights you're controlling - so you should have left P unconnected, with the flasher in series with your load.

Rog.

 

[vhfman]

I am not sure if this will help.
X=B on this diagram.

Chris

 

[cwah]

Thanks guys.

I'm at work now so I can't try anything. Will see if I can do something tonight at home.

Thanks again, really appreciated.

 

[cwah]

Guys, I connected the light in series with the flasher as pictured.

- X for the 12V red.
- L in series with the light and the ground.

The light are now on.

But they do not blink. Did I do something wrong or the flasher is not working because of the problem yesterday?

 

[rog_london]

Well, yes, almost certainly the heater part of the flasher will have got so hot it's melted part of the internal structure so that the bimetal strip which opens and closes the contact(s) can't do that.

You probably need a replacement. It might be worth seeing if you can get into the unit you now have (as you won't make it any worse!) and see if it looks as though you can free it.

Vhfman's little drawing gives you an idea of how it works - the top 'bar' with the two contacts is a bimetallic strip - two metals (usually brass and steel) are brazed together so that as it heats up the dissimilar expansion rates cause the strip to bend, opening the contact - then it cools, remaking the contact, and the whole thing repeats.

Rog.

 

[cwah]

Thanks Rog. You're always helpful

I haven't found any screw to open the flasher, and as the seller propose me a refund for it, I'm simply going to send it back to him.


I've found 2 other flashers that I may use:
- This really cheap one: Electronic LED Blinker Flasher Relay Fix 3 Pin 12V NEW | eBay

- And this one seems smaller but not sure if it would work: Electronic LED Blinker Flasher Relay Fix 3 Pin 12V NEW | eBay

I'm probably going to get the first one, as it's really cheap.