Relay issues when motorcycle idling

[CarlosT]

I have a relay which in theory switches when my motorcycle headlight is on and powers my led strip lights. The problem is when idling the headlights dont put out enough current apparently and the relay switches on and off constantly. Can anyone suggest a solution baring in mind I know very little about electronics.

 

[MikeMl]

What is your nominal headlamp voltage and wattage (or current?)
What is the relay coil voltage and resistance?

 

[CarlosT]

I am not at the workshop but I believe it is a 5 / 10amp 12v relay with 5 pins of which we only use 4. The headlight i am not sure but I am guessing 35 watts? Sorry if thats not accurate enough. We had previously a 30 / 40 amp relay and that didnt switch until we were fully accelerating.

 

[MikeMl]

Why do you need to use a relay? Why not just wire your LED strip lights in parallel with the headlight? Are you worried that the headlight switch will not carry the additional current?

How much current do the LED strip lights require?

Is there a battery in this system?

 

[Joe G]

also, knowing the type of motorcycle may help others give answers, some of the single and v-twin bikes give "surging " while idling. My yamaha doesn't give a smooth voltage output until a bit after idle...I happened to notice it when checking my output to compare with a coworkers motorcycle alternator...And as Mike stated about the relay, there may be better ones for your application.

 

[CarlosT]

Thanks for all the replies, this is a very active forum! Allow me to explain... we are an advertising service in Cambodia that provides illuminated signs on tuktuks. A tuktuk is a carriage that holds 4 people behind typically a 125 scooter like Dailim and Honda dream. These bikes are mostly very old and many of them don't even have a battery until we put one in. Running the LEDs in parallel with the headlights causes them to flicker like crazy unless the bike is at half to full acceleration. So our current solution is to hook them straight to the battery and give the driver a switch but for one reason or another they forget to flick the switch when they are driving a customer. With a small relay between the headlights and battery we almost have the perfect solution I am just wondering if we can add a capacitor or something that will boost or smooth the current from the headlight at idle. These headlights go very dull at idle and basically illuminate in conjunction with the accelerator.

 

[CarlosT]

I guess one solution would be to complete the circuit with the battery using the headlight switch but it would require getting right into the head of the bike which would be complicated for our techies. Is that a possible solution?

 

[MikeMl]

Are you up to a simple hand-wired solution that might use a transistor, a resistor, capacitor and a rectifier?

What electronic parts can you obtain easily locally (transistors, relays, rectifiers)?

How much current do your LED signs draw?

Is the battery you add just for the add-on sign (in other words, you don't care about the flickering headlight at idle)?

 

[picbits]

I'd personally use a rechargeable battery which trickle charges via a simple boost/buck converter than provides the "extra" power for when you need to sit there with the bike on idle. You may even find there is enough current at idle to power the unit anyway if you use a half decent boost converter.

 

[alec_t]

Personally I'd ditch the relay and use an NFET as a low-side switch for the sign.

 

[kinarfi]

what bike do you have, model, year, engine size, etc. I can probably get a schematic of it off the net and all the details we need.

 

[Diver300]

With no battery the headlight will be probably be directly lit from AC from the alternator.

You could try adding a bridge rectifier so that the relay is fed from DC instead.

 

[alec_t]

I think the OP's gone off on his tuktuk . Not seen since Wednesday.

 

[CarlosT]

Hi everyone, sorry I went missing on my tuktuk I like the sounds of a bridge rectifier i was actually thinking the ac feed from the headlamp on these old bikes may be the issue. Could anyone advise me which of these to buy (preferably the cheapest) would any of these ones do the trick? Or do I have to get the 10 times more expensive **broken link removed**ones? I also like the sounds of replacing the relay with an NFET but can't seem to find anywhere that sells it does it go by another name?

 

[CarlosT]

It seems that the common name for an NFET is a mosfet as far as I can see. Could i use one of these to replace the relay totally? Would the ac current be enough to trigger it?

 

[alec_t]

That N-MOSFET will be fine. You would need to rectify the AC to trigger it, but the bridge rectifier wouldn't be needed for that; a single low-power diode (e.g. 1N002) would do. I'll sketch up a circuit.

Edit:
Here you are. Component values aren't particularly critical.

 

[Diver300]

You could use the cheaper bridge rectifier, or even one with a much lower power rating that would be even less money to buy, if all you want to feed is a single relay coil.

The cheaper one you posted a link to is rated at 50 A. You only need about 0.1 A for a relay coil, so a 1 A rectifier would be fine. The more expensive one also contains a regulator, which basically throws away excess power as heat to stop the battery from being overcharged.

If you are connecting that relay coil (via a rectifier) to a headlight bulb that works at the moment, you do not need a regulator. The voltage will not vary too much to cause you any problems.

 

[MikeMl]

Carlos,

You never answered the question about the battery?

 

[CarlosT]

Mike - the bikes typically have a 12v 6ah battery for the electric starter button but the headlights seem to run directly off the alternator power, they do not flickr when idling they just go extremely dim particularly on the older bikes. Most of the bikes are either Dailims or old Honda Dreams.

Alec - thanks for taking the time to draw up a detailed diagram! It is a bit confusing to me because I am a web designer by trade but one of my colleagues is an electrician so he will understand.

Although I like the N-MOSFET solution I already bought 200 relays so I am wondering if this simple diode would be enough to make the relay work or if I would need a bridge rectifier. This diode is insanely cheap, would it work?

The relays i bought are rated at 30A and they do work when the bikes hit a certain amount of acceleration, but flicker at low revs and are off at idle. Another 5a relay i found flickers on or just above idle. Seeing as I already have 200 of the 30A relays I am hoping the diode will be our saviour. Or a cheap bridge rectifier.

 

[CarlosT]

**broken link removed**. From the description "
Heavy Duty 12V Automotive Relay with Wiring Harness and Socket. These come in a complete set with a 30/40 amp 12 volt relay & 5 wire relay socket wiring harness.
These can be used in a variety of ways but are popular for high amperage applications such as Fuel Pumps, HID Headlights, Strobes, Fog Lights, Stereos, Air Ride Suspensions, Fans, Air Horns, Car Alarms, Remote Starts and so much more. They can be used in conjunction with a switch or using any 12V + or - trigger. A trigger can be anything from the accessory or ignition circuit to a switch which provides a positive or negative trigger. They can even be used with your aux output from your alarm!"

I read this as pretty much anything can trigger the relay and assumed the 30/40 amp was like the ceiling of current it could handle.