Resistors to stop blowing bulbs?

Long story...

my italjet conquistador with a 90cc Minarelli keeps blowing bulbs.

Three wire like a V1, EEB (External ground, External coil, Brake,) system. Unlike the V1, if you bypass and ground the brake it starts, but won't stay running. If you leave the brake wire open, bike runs fine.

Only needs coil wire to run, can leave power and brake open.

All new wires, all fresh grounds, no shorts, working coil and CEV stator (I have two identical stators and coils, both tested, checked, and same outputs to eliminate a coil or stator problem.

New points, condenser (also checked and working fine.)

Tried wired to handlebar switch, and wired direct eliminating switch, same results. New brake switch, works same as old brake switch, both function properly.

Basically, the wiring is fine. Everything that could go wrong has been checked, replaced, rewired, regrounded, etc.

Used standard 6v and 12v bulbs, both blow. Tried led bulbs, melted.

One bulb blows, then overloads the other and blows. (Taillight blows, headlight blows next, and vice versa.)

Tried two bulb taillight, one for brake, one for light, taillight blows.

So I'm thinking inline resistors to overcome whatever surge is killing the lights, but I have no idea what type to use, and looking for electric gurus to help me out.

Re: Resistors to stop blowing bulbs?

Hepatitis J [OFMC] /

You just need a regulator

Re: Resistors to stop blowing bulbs?

So it's not just the voltage or the current that blows bulbs, but power. Power is current times voltage, so if you're getting the voltage you want (I assume this is a 6v system?) you need to reduce the current.

Inline resistor will reduce the voltage but not the current. You would want to run a small resistor in parallel with the taillight/brakelight, like some mopeds have to mitigate the bike dying when the brake light burns out. Unless you're getting like double the expected voltage, where you'd want an inline resistor.

It's all like really easy math, so if you have a 6v 3W light bulb you rearrange the P = I * V equation to find the current you want; I = P/V yields 0.5 amps. Anything over half an amp is likely to fry that 6v 3W bulb. Measure the current going through the bulb with a multimeter. Measure in series, not parallel like measuring voltage or resistance or you'll break your multimeter; unplug the wire providing power and hold the positive lead of your multimeter to it, touch the negative lead to where the wire plugs in. Bulb will light up and you can measure the current.

As for determining how big of a resistor you want, let's do that math. Arbitrarily we can say you measure, you're getting 1.2 amps max, that's too high. So measure the resistance of the bulb you're going to be using (quick guesstimation math puts a 6v 3W bulb at 12 ohms thanks to V=IR). You want 0.5 amps max, so we need to get 68% (0.5/1.2 is 32%) of the current to go somewhere else (through our new parallel resistor).

So getting the resistor's value that we want: V=IR and I(resistor)=0.68*I(bulb), use these two equations to solve for the necessary Resistance = 6v/(.68*1.2) =7.4 ohms.

Sorry for the long post but if that doesn't make sense let me know and I can try to explain it better.

Edit: I spent like half an hour writing this and double checking my circuit theory, like Hep J says you can just put a regulator in the circuit that's causing issues and it'll probably work. Soldering a resistor in parallel is way cheaper though. (edited)

Re: Resistors to stop blowing bulbs?

A regulator is a far better solution than using a resistor in parallel OR in series (both will reduce the power consumed by the bulb if sized correctly, but it's dumb and wasteful).

Especially if you use a good switching regulator instead of an LDO one. (edited)

Re: Resistors to stop blowing bulbs?

EVEN STILL, an LDO regulator will do the same job as a resistor, but better in every way.

Re: Resistors to stop blowing bulbs?

> Brian F Wrote:

> -------------------------------------------------------

> EVEN STILL, an LDO regulator will do the same job as a resistor, but

> better in every way.

For sure, I've seen plenty of bikes that rednecks wired up with a resistor on a circuit that just gets hot as shit. I've never put a resistor on any automotive circuit; it's just the wrong way to go about it compared to putting a regulator on

Re: Resistors to stop blowing bulbs?

Probably Fred /

Try opening up the flywheel to coil air gap to the big end of the specifications

Re: Resistors to stop blowing bulbs?

Cool, thanks guys! Guess I'll be ordering a regulator...

Re: Resistors to stop blowing bulbs?

Blaine- The artist formerly known as Plumber Crack "(OFMC)" /

> Nick MBC Wrote:

> -------------------------------------------------------

> So it's not just the voltage or the current that blows bulbs, but power.

> Power is current times voltage, so if you're getting the voltage you

> want (I assume this is a 6v system?) you need to reduce the current.

>

> Inline resistor will reduce the voltage but not the current. You would

> want to run a small resistor in parallel with the taillight/brakelight,

> like some mopeds have to mitigate the bike dying when the brake light

> burns out. Unless you're getting like double the expected voltage,

> where you'd want an inline resistor.

>

> It's all like really easy math, so if you have a 6v 3W light bulb you

> rearrange the P = I * V equation to find the current you want; I = P/V

> yields 0.5 amps. Anything over half an amp is likely to fry that 6v 3W

> bulb. Measure the current going through the bulb with a multimeter.

> Measure in series, not parallel like measuring voltage or resistance or

> you'll break your multimeter; unplug the wire providing power and hold

> the positive lead of your multimeter to it, touch the negative lead to

> where the wire plugs in. Bulb will light up and you can measure the

> current.

>

> As for determining how big of a resistor you want, let's do that math.

> Arbitrarily we can say you measure, you're getting 1.2 amps max, that's

> too high. So measure the resistance of the bulb you're going to be using

> (quick guesstimation math puts a 6v 3W bulb at 12 ohms thanks to V=IR).

> You want 0.5 amps max, so we need to get 68% (0.5/1.2 is 32%) of the

> current to go somewhere else (through our new parallel resistor).

>

> So getting the resistor's value that we want: V=IR and

> I(resistor)=0.68*I(bulb), use these two equations to solve for the

> necessary Resistance = 6v/(.68*1.2) =7.4 ohms.

>

> Sorry for the long post but if that doesn't make sense let me know and I

> can try to explain it better.

>

> Edit: I spent like half an hour writing this and double checking my

> circuit theory, like Hep J says you can just put a regulator in the

> circuit that's causing issues and it'll probably work. Soldering a

> resistor in parallel is way cheaper though.

I see a bit of confusion here. The only way you would get a 12ohm load to draw 1.2 amps would be to apply 14.4volts across it.

Re: Resistors to stop blowing bulbs?

> Blaine- The artist formerly known as Plumber Crack "(OFMC)" Wrote:

> -------------------------------------------------------

> I see a bit of confusion here. The only way you would get a 12ohm load

> to draw 1.2 amps would be to apply 14.4volts across it.

You're right, my numbers don't all add up. I just pulled the 1.2 amp number arbitrarily out of thin air without thinking about it. I haven't touched circuit theory since undergrad since I moved into software/FPGA stuff.

Re: Resistors to stop blowing bulbs?

♣Slew Foot♣ /

The ceramic resistor block that lowers your brake voltage to running light cracked inside the Tailight housing or aftermarket tail w.o resistor or the resistor inside the headlight bucket burnt. Usually Triggers the ht safety override could pop bulbs also said wiring block grounding inside bucket.

Re: Resistors to stop blowing bulbs?

I have none of those things. It's a 1966 italjet. The taillight is literally from a trailer. It's a Peterson manufacturing company trailer light, with a dual bulb socket.

(Tip if you have an old minibike or an italjet with a "PMCO" taillight. If you need a lens or a housing, look up Peterson taillight, instead of italjet taillight. The difference is $5 for a Peterson lens, and $30-50 for an NOS italjet taillight lens. And it's the same thing.)

The headlight is a simple CEV headlight with the removable two prong bulb holder. The kind with a orangeish metallic back that flakes off.

No resistors, no ceramics.

IMG_20210409_165338.jpg
IMG_20210409_165407.jpg

Re: Resistors to stop blowing bulbs?

Probably Fred /

> baird co Wrote:

> -------------------------------------------------------

> I have none of those things. It's a 1966 italjet. The taillight is

> literally from a trailer. It's a Peterson manufacturing company trailer

> light, with a dual bulb socket.

>

> (Tip if you have an old minibike or an italjet with a "PMCO" taillight.

> If you need a lens or a housing, look up Peterson taillight, instead of

> italjet taillight. The difference is $5 for a Peterson lens, and $30-50

> for an NOS italjet taillight lens. And it's the same thing.)

>

> The headlight is a simple CEV headlight with the removable two prong

> bulb holder. The kind with a orangeish metallic back that flakes off.

>

> No resistors, no ceramics.

I'm in total agreement just back off the airgap and or use a or bigger voltage or watt bulb maybe.

I have a bike for whatever reason would blow the 5 W 6 V bulb

So I went to Walmart and got a 7.5 watt 6v bulb and hasn't blown for five years

Experiment and have fun that's what these bikes are all about

Re: Resistors to stop blowing bulbs?

Using a higher wattage bulb is certainly a valid solution.

Old school 6V systems are typically much lower power than more modern 12V systems. My powerdynamo CDI unit cranks out 100W, compared to roughly 30W for most 6V systems.

Re: Resistors to stop blowing bulbs?

Tried 12v. Still blew em.

Trail tech regulator is on the way.

Re: Resistors to stop blowing bulbs?

♣Slew Foot♣ /

Does it have a regulator box?.

Tie a a3 or cev puch ECT regulator in.

If it has one the ground out is mounted too close to a lighting ground so when it has a spike the regulator spits it out through that out ground on the reggy box. It will hop to the nearest ground.

Re: Resistors to stop blowing bulbs?

Nope. It's less advanced than a V1 moped.

Single bulb headlight, two pole taillight, horn, and one brake switch for the foot brake.

Cev handlebar switch, two position toggle, horn and kill button.

External CEV coil (the cool aluminum can style.)

Basically the same stator and flywheel as a V1, just a little bigger. Same condenser, and same points.

As simple as it gets. And it's all components I've dealt with before, so that's why I'm baffled.

Re: Resistors to stop blowing bulbs?

The trailtech regulator solved it. So far, anyways.

Running 12v bulbs front and rear, regulator on lowest setting. Headlight is dim, but I never ride it at night anyway.

And now the horn works, too.

Re: Resistors to stop blowing bulbs?

♣Slew Foot♣ /

That low voltage headlight is showing where the fault is.

Re: Resistors to stop blowing bulbs?

No, it's the regulator. It has three settings, and the lowest setting keeps the bulbs dimmer for longer life. Since I don't ride at night, and I need the headlight on by law, I just leave it at the lowest setting.

Another thing I learned is the brake light coil on Minarelli V1s isn't designed to kill the bike if the brake light fails, it's designed to stop the headlight from dimming at low idle, which was a law for bikes imported to the US.

The bike dying when the brake light blows is a side effect.

Re: Resistors to stop blowing bulbs?

Pushrod Fifty /

If you use a resistor watch out for the heat that it will put out.

Re: Resistors to stop blowing bulbs?

It's mounted away from anything that could burn up.

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