anyone still running the front headlight on there modified engines?

#1
im just wondering as im having trouble getting a led light bulb for my modified engine, it revs higher and in-turn makes too much voltage for the bulb to handle then it burns out (ive already burned up 3 leds and the OG bulb)
anyone have a solution for this?
(im probably going to run with no light altogether, im pretty sick of it)
 
#2
You need a rectifier/regulator. It will stabilize and limit the voltage. Another option is to use an incandescent bulb. They are not as picky about the electricity they are getting.
 
#3
You have not given us any details to work with. LED are much more tolerant of unregulated voltage but do not like AC. Can you tell us what charging system you have on what engine and what kind of led light bulb you are burning out? I run them on all my lighted motors unregulated and have had zero issues using LED headlamp bulbs and led tailight bulbs.
 
#4
You have not given us any details to work with. LED are much more tolerant of unregulated voltage but do not like AC. Can you tell us what charging system you have on what engine and what kind of led light bulb you are burning out? I run them on all my lighted motors unregulated and have had zero issues using LED headlamp bulbs and led tailight bulbs.
i have 2 coils with magnets on the fly wheel (i cant remember what its called)
but it has + and - its similer to a atv lighing system. it has a h6m base. im burning out the cheap amazon leds
https://www.amazon.com/Headlight-Ya...UTF8&qid=1545167032&sr=8-5&keywords=h6m+bulbs
heres the other one that i burned out
https://www.amazon.com/Motorcycle-H...UTF8&qid=1545167067&sr=8-4&keywords=h6m+bulbs
 
#5
Got it! I have same system on a bike, clone engine with twin charging coils and two wires coming out. First off I have no idea why you are blowing them but my guess is they are not AC tolerant. Couple of solutions. First is the one I use and that is to use a full wave rectifier to convert the AC to DC. here are a couple of pics of the rectifiers and another of the same setup as yours on one of my bikes. The other much simpler way but not having tried it not sure it fixes the issue if it really is a AC issue is just put a 1K resistor in line with the lights. One other thought is that I have had the lights break because of vibration as they are soldered to the metal shell with a solder bridge from shell to circuit board. It may be they are OK but no longer connected between Circuit board holding leds to the metal shell. On the picture of the bike with the full wave rectifier the box after it just has a electrolytic cap in it to smooth the rectified DC so light does not flicker.
 

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cfh

Active Member
#6
LEDs don't care if they get AC. Leds are basically diodes, so they will only work on the positive side of the AC voltage. The negative side will be ignored. you can get "flicker" depending on how many cycles per second the AC voltage measures. If you use a bridge rectifier (or even a 1/2 wave rectification), the LED won't flicker.

The thing that LEDs *do* care about is voltage. Nearly all LEDs run at 1 to 3 volts. To use them at a higher voltages there needs to be a limiting resistor (or a regulation circuit, which is a lot more expensive, hence most don't use it). Hence most LED applications use a 1000 ohm limiting resistor when the input voltage is 12 volts. But if the input voltage goes above 12 volts, all a sudden the 1000 ohm limiting resistor isn't high enough. Then the LED gets above it's desired 1-3 volts, and fails.

if you know ohms law and the LED current draw, and voltage required for the LED, and the input voltage, you can figure out the exact resistor needed....
 
#7
Got it! I have same system on a bike, clone engine with twin charging coils and two wires coming out. First off I have no idea why you are blowing them but my guess is they are not AC tolerant. Couple of solutions. First is the one I use and that is to use a full wave rectifier to convert the AC to DC. here are a couple of pics of the rectifiers and another of the same setup as yours on one of my bikes. The other much simpler way but not having tried it not sure it fixes the issue if it really is a AC issue is just put a 1K resistor in line with the lights. One other thought is that I have had the lights break because of vibration as they are soldered to the metal shell with a solder bridge from shell to circuit board. It may be they are OK but no longer connected between Circuit board holding leds to the metal shell. On the picture of the bike with the full wave rectifier the box after it just has a electrolytic cap in it to smooth the rectified DC so light does not flicker.
Thanks for taking the time to post Ole4.

Since white LED's have no frequency spectrum, "white" headlamps utilize a blue/yellow that appears white. The lamps with the multiple LED's are intended to be used with voltage regulators.

Bottom line- those two lamps linked above will fail without a voltage regulator. As electrathon stated, an incandescent lamp will work fine.
 
#8
Did a little digging, found this on voltage. I am not using a resistor but it appears I should be. I have not however blown any bulbs yet using unregulated DC.
As a more direct answer to the question: there is THEORETICALLY no limit to the voltage you can use to power an LED... you just need to add suitable current limiting, usually in the form of a resistor.
If a given LED has a nominal current of 20mA, and has a forward voltage drop of 4V, then to power it with a 12V supply, using Ohm's law (V=IR, or R=V/I), you'd get R=8/.02, or 400 ohms. You could power it directly with 120VAC by using R=56/.02 (since you're only powering it with half the AC wave; the other half is "reverse" voltage and will be blocked because, well, it's also a diode), giving you 2.8k ohms.
The other consideration is power dissipation: 56V at 20mA is 56*.02=1.12W, so your typical small 1/4W or 1/2W resistor would burn up in short order in that circuit. In that case, you'd need to use some kind of either voltage-limiting or current-limiting power supply.
But yes, with the right circuit design, you could drive an LED with almost any common voltage.
 
#10
Modern LED vehicle lights are not just one LED, they are grouped and already are set up for vehicle voltage (generally modern cars charge at 14.4 volts). The magneto setups are quite basic, the faster you rev the engine the more the voltage will climb. This is not to be looked at like a circuit in a stereo you are adding a LED into (then yes, you would limit the voltage with a resister). It needs to be looked at like a vehicle charging system. When was the last time you heard of needing to add resisters to your car wiring when you replace incandescent bulbs with LEDs? Vehicles use the cars battery and a voltage regulator to hold stable voltage to the components. Without a battery your voltage will be low at idle. Without a regulator your voltage will be high at RPM. Probably about 6 volts or more on the swing up and down. LEDs like stable voltage, but can not handle high voltage. A regulator will limit the high voltage. If you really want it to work proper, add a battery so at idle the light will not go dim (or out).

https://www.amazon.com/TC-Motor-Reg...-18&keywords=small+engine+rectifier/regulator
I have not used this one, but it should do the trick. Also, add a battery too (did I say that already?).
 

cfh

Active Member
#11
That is correct they use a voltage regulator to keep the voltage at about 12 volts in cars. but for a mini bike, i'm not sure that is really needed or wanted. it complicates things. what you do need to do is figure out the maximum voltage supplied, and the LED draw, and use a current limiting resistor. that's how i would do it. adding a voltage regulator sounds like work/money. for a mini bike, probably not justified. Having a resistor is pretty cheap.

I have a good "look" for LED draw. So i use ohm's law and get a general idea of what resistor i should use, but go maybe 30% higher in resistance. with just alligator clips try it and see how it works and looks. then you can back it down or increase the resistance, as needed. LEDs are pretty easy to see when you over voltage them, at least to my eye.
 
#12
For me that would not work. (ohms law) The bulbs I use like the ones in my picture are from china and cost a couple of bucks each. No specs are given but as electrathon said and my pictures show there are a bunch of them in each light. I think I will use a 1K 5W resistor and call it a day if I ever have one go out on me. Did find a bunch of led Current limiting resistor calculators if you do know LED forward voltage and current.
https://www.electricaltechnology.org/2014/02/LED-resistor-calculator.html
 

cfh

Active Member
#13
I think 1k ohms is a good place to start. You probably don't need 5watt resistor, but heck higher wattage resistor never hurt anything.
 
#14
I would be curious what the output voltage on the magneto is at idle and at full throttle. Old motorcycles were notorious for headlight to be very bright at RPM and almost no output from the light when idling. You likely have this situation with the magneto system you have. Add to that a resister to limit the voltage you will have normal intensity when revved up (after you find a proper size resister) and almost nothing at idle (the resister will take the dim light at idle and make it dimmer still). You could use the headlight as a poor mans tachometer.
 

cfh

Active Member
#15
This was my fear too. But the good news is that with an LED, if you underpower it, the LED will still light pretty well. Much better than an incandescent. I notice this effect on my minibikes... at idea the light is pretty dim, and at full power it looks 'normal.' But with LED lights this will be far less of an issue. On the other hand, you need to calculate the current limiting resistor based on 'full power'!
 
#16
Modern LED vehicle lights are not just one LED, they are grouped and already are set up for vehicle voltage (generally modern cars charge at 14.4 volts). The magneto setups are quite basic, the faster you rev the engine the more the voltage will climb. This is not to be looked at like a circuit in a stereo you are adding a LED into (then yes, you would limit the voltage with a resister). It needs to be looked at like a vehicle charging system. When was the last time you heard of needing to add resisters to your car wiring when you replace incandescent bulbs with LEDs? Vehicles use the cars battery and a voltage regulator to hold stable voltage to the components. Without a battery your voltage will be low at idle. Without a regulator your voltage will be high at RPM. Probably about 6 volts or more on the swing up and down. LEDs like stable voltage, but can not handle high voltage. A regulator will limit the high voltage. If you really want it to work proper, add a battery so at idle the light will not go dim (or out).

https://www.amazon.com/TC-Motor-Regulator-Rectifier-Motorcycle-Motocross/dp/B01CGISXFW/ref=sr_1_18?ie=UTF8&qid=1545242284&sr=8-18&keywords=small+engine+rectifier/regulator
I have not used this one, but it should do the trick. Also, add a battery too (did I say that already?).
Actually, resistors are required with cars/trucks when switching to LED. The turn signals will not work properly without inline resistors. I know from experience. They will blink to fast. I had to buy the resistors. Available at your local auto parts store.
 
#17
I would be curious what the output voltage on the magneto is at idle and at full throttle. Old motorcycles were notorious for headlight to be very bright at RPM and almost no output from the light when idling. You likely have this situation with the magneto system you have. Add to that a resister to limit the voltage you will have normal intensity when revved up (after you find a proper size resister) and almost nothing at idle (the resister will take the dim light at idle and make it dimmer still). You could use the headlight as a poor mans tachometer.
Yep. I still say that $8 VR is the way to go.

The lamp assys in question are rated 12-24 and 12-36 v respectively. I haven't messed with Chinese engines, but if someone is increasing the designed RPM, (Frequency) significantly, they are affecting the reactive capacitance in the circuit and that will affect the voltage drop across the LED which is an inductive load. That may explain why a 24 or 36 volt lamp assembly is failing when the rating of the magneto in question is not rated that high. Just a theory I have to explain the failure. A bad socket (intermittant, loose) could cause spikes.
 
#18
Actually, resistors are required with cars/trucks when switching to LED. The turn signals will not work properly without inline resistors. I know from experience. They will blink to fast. I had to buy the resistors. Available at your local auto parts store.
Well, sort of. The replacement LED tail lights work just fine with regard to function and intensity. The issue is that they use so little energy that the turn signal flasher does not see the draw off of them and thinks that the bulb is burned out, so it flashes faster to alert the driver. The resisters are added to trick the flasher into seeing the proper circuit resistance as if there was an incandescent bulb in place. The resisters are not placed in series as a voltage limit, they are installed in parallel to allow some of the energy to bypass the bulb and be drained to ground to up the amperage draw on the circuit. Very different use than we are talking about above.
 
#19
Well, sort of. The replacement LED tail lights work just fine with regard to function and intensity. The issue is that they use so little energy that the turn signal flasher does not see the draw off of them and thinks that the bulb is burned out, so it flashes faster to alert the driver. The resisters are added to trick the flasher into seeing the proper circuit resistance as if there was an incandescent bulb in place. The resisters are not placed in series as a voltage limit, they are installed in parallel to allow some of the energy to bypass the bulb and be drained to ground to up the amperage draw on the circuit. Very different use than we are talking about above.
You are exactly correct sir. I just thought I would mention it as I replaced all the lights on my Dodge 2500 with LED's and suffered the flasher issue.
 
#20
wow, thanks for all your help guys! This is wayy more than I expected!
my idle voltage is at around 13v ( i need to get anither voltage gauge, this one is not very accurate lol)
and my rpm voltage is around 18v (+ or - 2v)
Also the I test the LEDs with a 12v battery I had, they worked perfectly before I put them on the maginito set up (2 minutes and there 20181213_182133.jpg 20181213_183002.jpg blown, when I retest them with the 12v battery, they dont light up at all)
 

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