how do I Use flash LED on direct 6VDC motorbikes

[mamun2a]

Hi every one I;m new here.
I want to use flash LED light with motorbikes engine current (6 V, amp is unknown but guess its over1.5 amp to 5). can any one tell me how do I down the high current flow to save the LED's from burning??

 

[fingaz]

You will need to include a resistor in series with the led(s).

LED's use a specific voltage (dependant on the colour, type)

So what you need to do is use the formula below to work out what resistor you need.

Series resistor = supply voltage - led voltage / led current

In your case supply voltage = 6v

led voltage = You can get this information from the supplier of the led's though generally it's Blue led = 3.5v, white led = 3.5v, red led = 2.3v, orange led = 3.8v, green led = 3.4v (these are for hi brightness led's)

led current = usually 20mA for most hi-brightness led's (this = 0.02A)

So for a blue led on 6v, you'd do this:

Rs=6v-3.5v/0.02=125hm: closest higher value is 150hm: so you'd need a 150hm: resistor

but you need to check what the voltage drop of your particular led's is. If you want more than one, it's best to wire a separate resistor for each led. see the diagram attatched

 

[mamun2a]

thanks for quick reply.
yes i use bright white LED.
dear do u tell me, Why I found 15-17+ volt with my general (chinese) multimeter when engine starts, what volt actually comes out?

 

[Hero999]

It sounds like the power isn't regulated and can range from 6V to 17V. I don't even know if a flshing LED can stand the higher voltage. You need a constant current source like the LM317, the circuit is on the datasheet which can be found from Google.

 

[The Mad Professor]

Some sort of semiconductor regulator is going to be a must have item if you are adding any form of electronics, motorcycle voltage regulators can often be very simple devices consisting of little more than a crude relay and shunt resistor. Six volt systems are found on small Japanese mopeds and to a greater extent on eastern european machines built prior to circa 1995.
Almost forgot the Enfield, is still big in India and many of the early models feature six volt electrics as well.

 

[fingaz]

Generally the 6 Volt system on motorbikes is CRAP (and I speak from experience). The regulator/rectifier units I have come across are really unreliable.

To be honest, I'd use a regulator to supply the power to the LED circuit. You can either use a LM317 (as Hero999 suggested) which is a varaible voltage regulator capable of supplying up to 1.5A, or something like a 7806 (AN7806, BA17806T, H7806A etc) which is a fixed 6V regulator. this will be capable of supplying up to 1A. Either should be sufficient to power quite a number of led's, but the fixed regulator needs no other components.
for information on either of these regulators, you can go to www.datasheetcatalog.net (and just type in LM317 or AN7806)

I recommend you check regulator/rectifier on the bike, or get it checked because if it's not working correctly, it will damage your battery. You should be able to get information from the manufacturer on the correct charging voltage, or from a good service manual for your model. (17V to power a 6V system does seem a bit excessive)

 

[HarveyH42]

There is a thread dealing with the LM317 in constant current mode (did this about a month ago). Only need one small resistor to set it up.

R = 1.25 / (required current in amps)
R = 1.25 / .02 = 62.5 ohms for 20mA

The resistor is connected between Vout and ADJ. Your LED is connected between ADJ and negetive (ground). This is correct, don't use Vout as the output (learned this the long way...).

I've had a 2.2v 70mA superflux Pirahna style LED running off a 6V 100 ma wallwart like this for at least a month now, (well since I last posted in that LM317 thread, when I got it running). Nothing is getting even warm to the touch.

 

[Nigel Goodwin]

Generally the 6 Volt system on motorbikes is CRAP (and I speak from experience). The regulator/rectifier units I have come across are really unreliable.

Generally there is no regulator at all, the battery will be charged directly from the alternator via a rectifier, and the headlight is fed directly from a seperate winding (this winding automatically limits, due to it's construction, but gives poor headlight at low speed, and somewhat better at higher speeds).

I recommend you check regulator/rectifier on the bike, or get it checked because if it's not working correctly, it will damage your battery. You should be able to get information from the manufacturer on the correct charging voltage, or from a good service manual for your model. (17V to power a 6V system does seem a bit excessive)

Obviously it can't read 17V if it's connected to the battery, that will clamp it at a bit above 6V or so (depending on the charging current) - I wonder if he's reading from the headlamp winding, without the headlamp as a load?.

 

[fingaz]

Obviously it can't read 17V if it's connected to the battery, that will clamp it at a bit above 6V or so (depending on the charging current) - I wonder if he's reading from the headlamp winding, without the headlamp as a load?.

Unless there is a broken wire, and the voltage he's reading is not being 'clamped' by the battery (because it's not connected) or there's no electrolyte in the battery from constant over-charging.

I never thought that he may be reading the voltage for the headlamp though, this is quite probable. I never actually tested the voltage across the headlamp supply before, never had cause to. I would imagine it can get quite high (17v?) at higher revs with no load.

Still, I think the solution is to use a voltage reg. and power the led's through that.

 

[mamun2a]

ya ya lot of reply.
nigel is right there is no regulator, the battery charged via rectifier. the bike is made 1984/5, by yamaha, 80 cc. its manual is now history ( lost). Its 5 wire come out from engine. I dont know all the come out wires keep the the same volt or not. among them only one wire is rectified and charged the batteries, rest of all are direct to headlight and other bulbs. I also want to know the bikes current supply and wiring system.

but dear all i want simple solution, like may b a high watt resistor or use the LED in series or something like that. is it possible???

 

[fingaz]

Ok, Like both Hero999 and I (and others) have already said. . . You will need a VOLTAGE REGULATOR to run the LED's. It would be no good just using a large resistor because the voltage fluctuates. If you did this, the led's would get brighter and dimmer as the voltage alters. You need something like a LM317 or AN7806, this will output a constant voltage to supply the LED's.

If you want the LED's to only come on with the engine running, you could take the 6V feed from the headlamp, Rectify it and use it to supply the regulator. I wouldn't advise using the feed to the battery unless you have a switch in line with the LED's because they would be on all the time. (until your battery went dead)

 

[Thunderchild]

are you sure there is a battery ? I have a moped that has no battery and it all runs on 6 volts straight from the alternator even the hooter only works because it is ac making the diaphram flick back and forth because of the reversing of polarity and it's pitch varies with the speed of the moped :lol. if you put a DC meter on a and AC 6 volts that is 12 volts peak to peak plus a sinusoidal waveform that has an RMS of 12 volts (or 6 if measured corectly) will be 1.4 times peak voltage and that can easily turn out 17 volts. either there is a problem with the bike or your measuring in the wrong place the power to the lamps might come straight from the alternator so that if there is a battery it is used only to start the bike.

your best bet is to take from the battery and use a constant current source that you can make with any transistor (BDX53/54 is a good general purpose)
and a zener diode as a constant voltage reference in tis way you replave the limiting resistor totaly and can use any voltage rating led you like

 

[Hero999]

I was talking about a curent regulator not a voltage regulator, although the latter can be used with a current limiting resistor in series with the LED.

There's really no need for an LM317, I'd use a JFET with the gate connected to the source which will limit the current to about 10mA.

 

[Thunderchild]

I too was saying curent regulator perhaps my referent to the zener diode confused you this is needed because the constand current is set with a base resistor(s) so needs a constand voltage to set the current

 

[The Mad Professor]

I thought I would post this link here rather than on the new thread that
has been started as it kind of makes more sense.

Mamun2a , you have told us the moped is a Yamaha 80cc (1985),
but not the model name , some variations do exist in the wiring
however this link should give everyone a better idea of what you
are dealing with.

**broken link removed**

 

[mamun2a]

mad prof. many thanks to u, 4 the links, actually i dont know the models. nyway thanks again.

Hero999 pls explain me JFET (I'm sorry if its a silly q.)

thunderchild many thanks to u, i want to talk u in PM if u agree.

mamun2a

 

[Thunderchild]

sure you can pm me or email me if you can't find my email on here then go to my site linked in my sig there is an email link on every page

 

[Hero999]

Look at the attachment in my previous post, simply connect it in series with the LED.

 

[mamun2a]

hero please JFET means what?
what thing I connet in series with LED.
forgive me if i bother u.

mamun2a

 

[fingaz]

JFET is Junction FET (Field Effect Transistor) Look it up on google www.google.com