Resistors?

cbertozz

cbertozz

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Location
Australia
I see resistors on all the wiring diagrams I have, and although I have resisted caps I'm not aware of any inline as per the diagram. Should there be some? (No idea why the pic of diagram isn't appearing)

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If you mean resistors I assume you're referring to the ballast resistors in the ignition coil circuit?  They are unnecessary and certainly can be junked if you have an aftermarket ignition.  (I'm assuming you're not misreading diodes as resistors in the pilot/headlamp circuitry)
 
Rob said:
If you mean resistors I assume you're referring to the ballast resistors in the ignition coil circuit?  They are unnecessary and certainly can be junked if you have an aftermarket ignition.  (I'm assuming you're not misreading diodes as resistors in the pilot/headlamp circuitry)
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Yes the coil ones are what Im referring to. Just given I'm.chasing this odd signal or interference which shuts stuff down randomly it was the one thing in the wiring diagram that was different.

The Smart Turn System would work fine with bike off but would stop working some time after bike was running, the recent LED flashwrs that double as running lights would suddenly flash randomly when bike was running even though fine when ignition on but engine off, and now I have this random stalling which seems to reset the ignition but only when the LED spots are on.

All good now I know that they are not needed.

 
cbertozz said:
The Smart Turn System would work fine with bike off but would stop working some time after bike was running, the recent LED flashwrs that double as running lights would suddenly flash randomly when bike was running even though fine when ignition on but engine off, and now I have this random stalling which seems to reset the ignition but only when the LED spots are on.
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The battery alone gives a smooth power supply. But when you run the engine there's all sorts of electrical noise flying around the wiring harness. It comes from the alternator and ignition systems and can be messy enough to upset some electronic doohickies. You'd think something designed to be fitted to a vehicle would have filtering circuitry to protect it against electrical noise, but I've come across many that will bench test OK but fail in service.  As an example, the tacho needle on my track bike would bounce all around the dial when powered from the bike's electrical system, so I supplied it with a 9V battery and it works fine.

The LEDs interfering with the ignition is a bit more of a puzzle. LEDs are pretty benign things. They normally have a series resistor to reduce the voltage across them when powered from a 12V system. Nothing to produce system noise.

But resistors are inefficient. All they do is soak up energy and produce heat. That's not a problem with wee little panel lamps that draw bugger-all current. However, your LED headlights would draw a much higher current than panel lamps, so resistors wouldn't be a sensible way to reduce voltage.  This is pure speculation, but I'm wondering whether the LED headlights have some kind circuitry like an inverter/transformer/rectifier to reduce the voltage supplied to the actual LEDs. Something of that nature could feed some uncontrolled frequency back into the bike's wiring system that's upsetting the ignition's electronic brain.
 
PS: I just checked, and yes, LED headlights have an electronically controlled low voltage, constant current power supply. Such device are known for producing electrical noise. The noise can be transmitted to other devices in two ways. RF (radio frequency) interference or line interference.

RF is transmitted via electromagnetic radiation, with cables to the device acting as antennas.
Line interference is carried as electrical signals along the wires.

You can suppress RF interference with the use of ferrite beads on the wiring to the headlight's power supply.
You can reduce line interference with the use of smoothing capacitors. You'll need someone with more electronics smarts than me to work out capacitor type, size and location.
 
Wow! nearly as good as the 'Earthing' thread. 

The primary function of a resistor in the primary ignition coil circuit is to limit current flow, thus extinguish the spark.  Modern ignition coils don't need external resistors because the coil circuit and materials are designed to saturate instantly when the spark (current flow) is generated. 



 
When fitting modern ignition systems there is often guidance to locate the black box away from the engine.
Maybe your LED relay system is too close to your ignition box(es)?
 
I seem to remember the first generation FI on the Superbike Ducatis didnt like the radar signal being emitted at some UK race circuit that was also an airport.
 
sweetas said:
The primary function of a resistor in the primary ignition coil circuit is to limit current flow, thus extinguish the spark.
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It's not quite that simple Tony.

Coil resistors aren't there to extinguish the spark. In fact, they have little effect on the spark because they're in series with the primary winding of the coil. Whereas the current that makes the spark happens in the secondary winding. 

The coils are designed to run on a lower voltage than the nominal 12V system. The reason for that is that when cranking the engine to start, the starter motor pulls the system voltage down to maybe 8V. If you have a coil that needs 12V to make a spark, the engine won't start.

But once the engine has started, the system voltage typically rises to around 14V because the charging system kicks in. That's likely to overheat an 8V coil, so it needs a series resistor to prevent the poor thing from being cooked.

That means there must be two power supplies to the coil. One directly from the battery (bypassing the resistors) when the starter motor is energised, and one via the resistor when running.

Oddly enough, the resistor bypass was never wired into Laverda starting circuits, so the resistors are always in the circuit with the coils, even when the starter button is pressed. If you want to give your coils a power boost while starting, you can run a starter-activated power supply to them. It's easy enough to do, just take a feed from the starter relay to the coil positive. But I'll either need a diode in it or be controlled by a relay so as not to back-feed the starter circuit while the engine is running.

sweetas said:
Modern ignition coils don't need external resistors because the coil circuit and materials are designed to saturate instantly when the spark (current flow) is generated.
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You have that arse about. Coils don't saturate when the spark is generated, they de-saturate, or discharge. Anyway, coil saturation time has little to do with need for series resistors.

The saturation process happens when the coil is energised by the ignition system (or points) and current is flowing through the primary winding. It takes a little time for the magnetic field in the coil to come up to its maximum strength. That's what saturation means - the magnetic field is as strong as it's going to get. The time it takes to saturate is the dwell time needed by the coil. When the ignition system cuts the circuit, the coil's magnetic field collapses suddenly, inducing a high current in the secondary winding. Zap!

With a points type ignition, the coil is energised for whatever time the points are closed, which is controlled by the points cam, so is the same number of degrees of engine rotation regardless of engine revs. The actual time duration of the dwell gets shorter as the revs increase. But it has to be sufficient to saturate the coil at maximum revs. So when the engine is running slower than maximum revs, the dwell time is longer than it needs to be, and the coil is energised for longer than necessary, making it hot.

Electronic ignition systems overcome that issue by setting a fixed dwell time rather than a number of degrees of crankshaft rotation. So the coil is energised for the same amount of time at all engine revs. That time being as long as the coil needs to reach saturation and no more. With the coil unloaded for most of the time, it'll run cooler, so it is less reliant on the series resistors for keeping its temperature within limits. In most cases you can chuck the series resistors away.

 
Resistors are added in series with the ignition coil primary to damp the primary ringing when the points open.

Coil inductance with stray circuit capacitance and the condenser makes an LC oscillator circuit.

Resistance rapidly damps the oscillation.

"Resitorless" coils are merely wound with 'resistance wire' to negate the need for an external resistor, but means the coil runs hotter due to the heat generated internally from the primary current.

The frequency is much lower than RF due to the large condenser capacitance which is added to slow the voltage rise when the points open and reduce spark erosion of the points.

Resistance in the plug leads is similarly to damp the oscillation in the secondary circuit, however this is at much higher RF frequencies that can cause cross coupling to other circuits in the bike. This is a combination of spark/arc properties in the plug and the coil/capacitance feeding it.

Sounds like this might be getting back into the electronic ignition.

Personally, I would go to Jaycar and buy a small value quality teflon or ceramic capacitor to put across the power leads of the ignition unit as close to the input as possible with as short a leads as possible. This will be an effective high frequency input filter for cross-coupled RF noise. Tell Jaycar the purpose and they can select.

If the ignition box has an earthing connector, use a heavy flat braided strap as short as possible to the nearest frame ground, or maybe the engine since the spark plug is earthed via the head. Braiding, or at least very fine stranded wire, lowers the resistance at high frequencies.

 
The bike in question uses a Bosch electronic ignition system.
No idea if it has electronics inside the black box to suppress the oscillations or not.
It also seems that the ballast resistors are missing, or are they present?
Would this be related to why the engine plays up when the LED lights are switched on?

The explosion-in-a-spaghetti-factory wiring won't be helping, judging from some of the connections shown.
 
Grant said:
The bike in question uses a Bosch electronic ignition system.
No idea if it has electronics inside the black box to suppress the oscillations or not.
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I very much doubt that the old Bosch boxes have any electronic smarts in them at all. They could barely manage an advance curve!
 
Dellortoman said:
I very much doubt that the old Bosch boxes have any electronic smarts in them at all. They could barely manage an advance curve!
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the bike in question does not use a Bosch ignition module, it has a Redax ignition system installed
but not certain if it has a Sachse box or an Ignitech box as was a few years ago we built that engine

 
redax5 said:
the bike in question does not use a Bosch ignition module, it has a Redax ignition system installed
but not certain if it has a Sachse box or an Ignitech box as was a few years ago we built that engine
Click to expand...

I recall posts where the owner was connecting his laptop to the bike and making up his own curves so possibly Ignitech
 
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