Need advice from those who are electrically inclined

1. ## Need advice from those who are electrically inclined

I am running a brake light flasher with my secondary LED brake light unit. I have paralelled the LED to my normal brake light circuit with the flasher controller in series with the LED circuit.

When the bike is not running, the circuit reads 12.5 volts and the LED flasher works as designed (when brake light is activated).
However when the bike IS running, the lead wire to the circuit reads 14.5 volts and the LED doesent flash at all, but rather just comes on and stays on.

According to the manual for the flasher, its is intended to function between 6-12 volts only.

Should I just install a resistor to the lead? and if so, of what resistance value? (anybody know the formula?)

Or do you guys have other suggestions?

2.

3. The formula for this is V=IR. V=Voltage I=Current R=Resistance. You will probaly need a resistor inline with the LED lead. The voltage drop you are looking for is about 2.5V at least. You will have to figure out the amount of current that the LED is going to draw and from there you should be able to figure out the resistor value you will need. But also remember this formula P=IR, this formula is for calculating the power that the resistor will have to dissipate. P=Power(heat) I=Current(Amp) R= Resistance(Ohms). Get the appropriate resistor that can dissipate the the power, if you do not get the appropiate sized resistor, you will let the smoke out of the wires(this is bad - smoke/fire).

4. 14.5 volts seems too high for a bike.
Those electrical gremlins most likely are a faulty (ie blown) rectifier.

Does the voltage go up any higher if you rev the engine?
If it does then the recifier is the problem and you may have done some damage to the flasher.

You may also think about installing a voltage regulator in front of the flasher to make sure it only ever gets 12v.

-Sandworm

5. 14.5 volts sounds right. A car will run at 14.5 volts so why not a bike? They are both 12 volt batteries.

6. 14.5 is higher than I like to see a lead acid battery operating but it seems to be pretty standard for bikes. C'est la vie.

Rather than a resistor I'd recomend a 3.1 volt 2 amp zener diode. That way it's not a big deal about how much current the unit draws. One of the 2 amp zeners should do the trick since you're operating LED taillights.

If you want to go this route then PM me for explicit instructions.

7. Wow, so many different opinions from so many professionals, how interesting......

However, according to the Factory Service Manual for my 2000 Honda VTR, anything <15.5 volts at the battery terminals is considered acceptable.

I have not been burning out fuses/lights/ciruits.
Mind you, my CDI convertor went on me just recently, after I bought the bike (see post re ICM vs. CDI......clarification).

Sandworm, I hadnt even considered the blown rectifier issue.
I was under the impression that a blown recifier equated to a non-functioning bike.
Nonetheless, I will definetly check on that. There is a simple test in the manual involving resistance, conductivity, ground etc...

8. it would be blown regulator if the voltage is too high, although i think the regulator / rectifier are the same piece of equipment on bikes. the rectifier just converts it to dc voltage

9. Originally posted by sigtrap
it would be blown regulator if the voltage is too high, although i think the regulator / rectifier are the same piece of equipment on bikes. the rectifier just converts it to dc voltage
Yep. Spot on.

You can test for a blown regulator function by putting the voltmeter onto the battery terminals and revving the bike. As the revs climb from idle to about 2500 or 3000 the voltage should rise smoothly to about the mid 14 to 15 volt range. Revving beyond that point should show the voltage clamped at no higher than 15 to 15.5 (still too high for my taste but apparently Honda thinks it's OK). A blown regulator will let the voltage rise to 20 or more volts as the revs climb to around 5 to 6 K. It would go even higher at redline but I chickened out at that point as I knew it was toast already.

10. The rectifier can be a different unit than the regulator.

Regulators limit DC voltage to a maximum level.
Rectifiers turn AC current into DC.
Inverters turn DC into AC.
"Shunt" rectifiers (like on most bikes) also dissipate any extra energy from the alternator in the form of heat. This is why they can "blow" if the electrical load on the bike is too LOW, ie you remove the headlights.

The alternator on your bike produces ~110vAC in three phases. This is turned into DC by your rectifier and is regulated to a max of 13.9 (or at least it should be) by the voltage regulator. Often the rectifier and regulator are one and the same unit, but occasionaly they are seperate.

If you have a product like an LED display, or a flasher unit that has a max voltage of less than 13.9 (or 15, or 20) then you can install a second regulator on it to make sure that it is not exposed to more than its limit. A small regulator only costs a couple bucks so it might be worth it to protect your \$\$\$ flasher unit.

-Sandworm

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