3-Wire OEM to 2 LED: How To Keep Your Running Light/Blinker Combo

[Scrapdog2grand]

Originally Posted by oconeedan

What is the difference between the 50 p/v and the 200 p/v diodes?

I am planning to run a led strip light to my sissy bar, and wire it as a running/brake light. I would wire as you have, but add a resistor to the running light tap, to make it dimmer.

Dan

Stole this from somewhere, great job ACE!!!

Just understand that the voltage dropped across a current-conducting diode does change with the amount of current going through it, but that this change is fairly small over a wide range of currents. This is why many textbooks simply say the voltage drop across a conducting, semiconductor diode remains constant at 0.7 volts for silicon and 0.3 volts for germanium.
A reverse-biased diode prevents current from going through it, due to the expanded depletion region. In actuality, a very small amount of current can and does go through a reverse-biased diode, called the leakage current, but it can be ignored for most purposes. The ability of a diode to withstand reverse-bias voltages is limited, as it is for any insulator. If the applied reverse-bias voltage becomes too great, the diode will experience a condition known as breakdown (Figure below), which is usually destructive. A diode's maximum reverse-bias voltage rating is known as the Peak Inverse Voltage, or PIV, and may be obtained from the manufacturer. Like forward voltage, the PIV rating of a diode varies with temperature, except that PIV increases with increased temperature and decreases as the diode becomes cooler -- exactly opposite that of forward voltage.

Diode curve: showing knee at 0.7 V forward bias for Si, and reverse breakdown.



Typically, the PIV rating of a generic “rectifier” diode is at least 50 volts at room temperature. Diodes with PIV ratings in the many thousands of volts are available for modest prices.

• REVIEW:
• A diode is an electrical component acting as a one-way valve for current.
• When voltage is applied across a diode in such a way that the diode allows current, the diode is said to be forward-biased.
• When voltage is applied across a diode in such a way that the diode prohibits current, the diode is said to be reverse-biased.
• The voltage dropped across a conducting, forward-biased diode is called the forward voltage. Forward voltage for a diode varies only slightly for changes in forward current and temperature, and is fixed by the chemical composition of the P-N junction.
• Silicon diodes have a forward voltage of approximately 0.7 volts.
• Germanium diodes have a forward voltage of approximately 0.3 volts.
• The maximum reverse-bias voltage that a diode can withstand without “breaking down” is called the Peak Inverse Voltage, or PIV rating.

[Aced It]

Wow, don't think I could've ever put it like that, thanks! Does that help Dan?

Sent from my DROID2 using Motorcycle App t from my DROID2 using Motorcycle App

[oconeedan]

Yes, that helps explain it somewhat. BUT, why would you need to get a 200 piv diode instead of a 50 piv diode, when our charging systems put out less than 15v?

The strip lighting I am adding to rear of bike is brilliant and "brake light bright" at full voltage. Any guess as to what resistor I need to add to cut the intensity down to "running light bright"?
Thanks, Dan

[Aced It]

Originally Posted by oconeedan

Yes, that helps explain it somewhat. BUT, why would you need to get a 200 piv diode instead of a 50 piv diode, when our charging systems put out less than 15v?

The strip lighting I am adding to rear of bike is brilliant and "brake light bright" at full voltage. Any guess as to what resistor I need to add to cut the intensity down to "running light bright"?
Thanks, Dan

Because of the single incandescent bulb still being in place for the turn indicator, the 200PIV diodes do the job of eliminating feedback (current leakage) back to the LEDs. Thus keeping the 12V system flowing. I found a guy that did it this way and it works flawlessly. The diodes are apparently the same used in the Kuryakyn kit; while I don't know for sure, it makes sense. There's also a few online calculators you can find to assist with LEDs ...

Zener Diodes
Hobby Resistors

... just to start.

[mattyo]

Originally Posted by oconeedan

Yes, that helps explain it somewhat. BUT, why would you need to get a 200 piv diode instead of a 50 piv diode, when our charging systems put out less than 15v?

Well I was also confused as to why Aced used diodes instead of resistors and why the incandescent bulb diodes are 200V. After a little research it looks like the diodes are in an OR gate configuration, which makes sense. Putting resistors there would allow current to flow back around and decrease the current to the lights. The 200V breakdown still confuses me. As Aced said, the reverse leakage currents are a little lower for the 200V but we're only talking like 1-2uA lower. I checked a few standard Vishay diodes and both the 50V and 200V are rated for an Ir (reverse current) of 5uA at the rated breakdown voltage. The reverse current is fairly linear with voltage up to the breakdown voltage, so this means at a reverse voltage of 15V, the 50V diode leaks 1.5uA and the 200V diode leaks 0.4uA. I can hardly see that as being the reason for using the 200V diodes. Now I don't know the rest of the circuit being used here and I'm sure there's a good reason for the 200V diodes, just wish I knew what that reason was. I know there can be a lot of high voltage transients on the whole electrical system from the inductive kickback off the ignition coils so maybe it has something to do with suppressing those transients? Just a wild guess. If anyone has some other ideas, I'd be glad to hear them. I'm always curious about these circuits because motorcycles seem to use a lot of non-standard electrical techniques.

Good thread Aced!

[JP50515]

Will this work on an 83 vt500? I believe that my flasher relay is mechanical (not quite sure what that means)

[mattyo]

Originally Posted by JP50515

Will this work on an 83 vt500? I believe that my flasher relay is mechanical (not quite sure what that means)

You have to buy what people call an "electronic" relay (even though the mechanical version is also electronic so to speak) which is to say it's solid state. The "mechanical" relays have a capacitor that charges and discharges. The charging/discharging rate is proportionally to the load it's driving. An incandescent bulb draws around 2-4 amps I'm guessing while the LEDs draw around 400mA per bulb. The mechanical relay doesn't work correctly for the LEDs because they are a smaller load and cause a faster charge/discharge rate ie fast blinking. The solid state relays switch at a constant rate independant of load and is why they are often needed when switching over to a LED system.

[JP50515]

Originally Posted by mattyo

You have to buy what people call an "electronic" relay (even though the mechanical version is also electronic so to speak) which is to say it's solid state. The "mechanical" relays have a capacitor that charges and discharges. The charging/discharging rate is proportionally to the load it's driving. An incandescent bulb draws around 2-4 amps I'm guessing while the LEDs draw around 400mA per bulb. The mechanical relay doesn't work correctly for the LEDs because they are a smaller load and cause a faster charge/discharge rate ie fast blinking. The solid state relays switch at a constant rate independant of load and is why they are often needed when switching over to a LED system.

Any chance you've got a lead on where to pick one of these up?

[jpr1968]

Most auto supply places have them. You'll either have to find one that fits the relay socket on your bike or make jumpers to fit beween the socket and the relay.

[mattyo]

Originally Posted by JP50515

Any chance you've got a lead on where to pick one of these up?

shaabam! Super Bright LEDs - Electronic LED Flashers Specifications

I'd go for this guy LED Flasher Unit LF1-S-PIN Specifications

They show the diodes in the circuit as AcedIt has done. I'm still skeptical because the diode symbol is often used in schematics to represent LEDs because they are fundamentally a diode. I'm curious if whoever AcedIt got his instructions from misread that schematic and inserted diodes and LEDs when the schematic really meant for the diode symbol to represent just the LEDs? I should buy a solid state flasher and just play around with this circuit. I'm still confused why those diodes need to be in the circuit AcedIt used.