Coil relay mod question

[T Legg]

All of the coils burned out before the components were damaged by the voltage spike.

Do you mean relays?

the term coil when referring to relays is specific to the very fine coil of wire that creates the magnetism that operate the contacts.When Mike said all the coils burned out I think he meant that they became the weakest link in the event of a voltage spike.

[Sparky84]

So, how do we stop voltage spikes or protect against them?

I have a fuse between the battery and each relay, wouldn't that protect it?

Fuses protect against over current and are usually installed to protect wiring not components.
Unless you install a individual fuse to protect each component which could would be a lot.
That'd also be very small rated fuses also.

[Sparky84]

All of the coils burned out before the components were damaged by the voltage spike.

Do you mean relays?

the term coil when referring to relays is specific to the very fine coil of wire that creates the magnetism that operate the contacts.When Mike said all the coils burned out I think he meant that they became the weakest link in the event of a voltage spike.

I'd agree with that, so when the coils burnt out they couldn't operate and stopped switching the voltage spike through to whatever was being switched.

[Tuned forks]

Travis can check me on this but I'm not aware that fuses protect against excessive voltage.  I think they only protect against excessive amperage.  Travis made a good point about the coils in the relays as well.  I hadn't thought of that.

Joe

[ribbert]

All of the coils burned out before the components were damaged by the voltage spike.

Do you mean relays?

the term coil when referring to relays is specific to the very fine coil of wire that creates the magnetism that operate the contacts.When Mike said all the coils burned out I think he meant that they became the weakest link in the event of a voltage spike.

I'd agree with that, so when the coils burnt out they couldn't operate and stopped switching the voltage spike through to whatever was being switched.

.....yes, but to refer to a relay as a coil is misleading (in automotive jargon anyway) and in this instance Mike has acknowledged he meant "relay".

Doesn't the frying of a component because of high voltage cause heat which in turn results in a short which then creates resistance/load which would blow a fuse? (all in a hearbeat)

Alan, you ask the question about how we protect our bikes from this, I'm not sure I'd bother, it's a pretty rare event (I've never come across it).  Batteries act like shock absorbers for electrical current and absorb such events, unlike mains power which has no such buffer.
You can get 12 v relays with voltage protection (varistors?) but they are not common and I've never seen one in automotive use.

Alan, you sound like an electrician? (as opposed to an auto elec)

I have some questions for the electrically gifted, which I'm not. How does a voltage spike occur and more to the point, how does it get through the battery and how can a relay burn out without triggering a fuse and was Mike's problem actually a voltage "spike" or some other cause and if it was high voltage, was it in fact for a period of time rather than a spike and why wasn't the relay protected?

Noel

[T Legg]

the generator is capable of generating much more than 14 volts but is controlled by the rectifier/voltage regulator circuit the over voltage occurs when the rectifier fails. i guess the word voltage spike means a short term transient rise in voltage Im no expert on motorcycle charging systems,I dont know whether spikes are common i was referring to a regulator failure leading to steady over voltage problem but the problems caused are the same.  current flow called amperage causes heat,the amount of current flow is determined by the equation I=E/R.I stands for current or amperage,E stands for voltage and R stands for resistance so by the equation if you increase the voltage you also increase the amperage and therefore heat causing the wire to burn.A short circuit is when the wire or path of current is shunted around the resistance of the intended load directly to ground a path with much less resistance.decreasing the resistance has the same effect as increasing the voltage in that it allows more current and therefore heat to flow through the wire than the wire is rated at that point the fuse should melt.The contacts of the relays can handle ( depending on the rating) many amps of current flow the very fine magnetic coil wire of the relay can only handle a fraction of an amp so when the voltage rises high enough the current flow increase causes the coil wire to melt very quickly before  even the fuses heat up enough to melt.the voltage from the generator goes through the rectifier to the positive side of the battery but it doesnt have to flow through the battery to get to the other  components.  

[fj-f3a]

T Legg

Thank's for steeling my thunder.

What you say is exactly right.

The Alternator (not generator) is capable of producing much more than 14 volts. The voltage produced by the alternator is controlled by the excitation of the alternators field winding, which in turn is controlled by the Regulator.

A true voltage Spike / Transient can last for much less than a Milli second, maybe a micro second. In electronics, voltage spikes are controlled with filters, either active (which use Operational Amplifiers), or passive (LC or RC networks).
LC = Inductor / Capacitor, RC = Resistor / Capacitor.

As Alan pointed out, a Fuse is there to protect the Cabling only. The cross sectional area and material (usually copper) determines the Current rating of the cable and the type and thickness of the insulation determines the Voltage rating.
(the size of the pipe determines the amount of water which can flow, (current) and the strength of the pipes wall determines the maximum pressure (voltage))
So, if a cable is rated for a Continuous Current of 20A, it would be wise to protect the cable with , say, a 16A fuse. A good rule of thumb is to use a fuse rating 80% of the current rating of the cable.

As for the relay coils burning out, the would require a rather large, short lived over voltage condition or a smaller and sustained over voltage condition.
A normal 12V relay coil is around 90 ohms resistance so, 12 / 90 = 0.133 amps.
But, our motorcycles generally operate closer to 14V so 14 / 90 = 0.155 amps, not much difference.
However, it gives an idea of the fuse rating which would be required in order to protect the relay coil and a separate fuse would be required for each relay, simply not practical.

I have seen Surge Protectors which use an N-channel MOSFET and limit the maximum voltage to approx 18V. I need to do more investigation.

As for what produces a spike, well, the ignition coils are an excellent example. The primary coil is excited with our 14v then, when the ignition module switches the ignition coil off, the collapsing magnetic field produces a high voltage (upwards of 20,000V) in the secondary winding to fire the Spark Plug. This occurs when the current to any coil, including a relay coil, is interupted. (though the voltage produced will not be this high)
The usual way to circumvent these transient voltages is to place an ultra fast, reversed biased diode, of suitable current and voltage rating, across the coil.

Good maintenance should include a regular (say 20,000Km, 12,000 mile) check of the alternator's brushes and slip rings and there may be good reason for the fitment of a Quality Volt Meter to our motorcycles. IMO

Gavin

[ribbert]

Great responses Trevor and Gavin, thanks.



Noel

[Sparky84]

What they said

Spikes are also generated by things being turned off and not just on, go figure, and the coils go off every time a spark is produced.
Is there a way to fit CDI to the FJ's rather than use coils  could be more efficient with bigger spark.

Cheers
Alan

[fj-f3a]

A CDI ignition generates a spark with a higher voltage but a much shorter duration.
Not so good for our low compression engines.

Gavin

[Sparky84]

So to get this right in my head,
- you only need 1 relay.
- the relay only is powered after starting and just stays ON and gives both coils a positive continuously.
- the ignition module stops the negative to the coils to give spark.

So you could still have low voltage at coils if there is bad connections in ignition module after the mod.

Cheers
Alan

[FJ_Hooligan]

No, the relay is activated by the original ignition switched red/white wire with a ground. 

The relay controls (switches) a NEW wire that comes directly from the battery, or a power distribution panel. 

This wire has minimal connections and is usually a lower (thicker) gauge that maintains a higher voltage to the coils.

Yes, the relay stays on with the ignition and you only need 1 coil.  Split the relay output to both coils.

[Sparky84]

Just have to check Ohms on coils now

Cheers
Alan

[Sparky84]

If I was to get new coils would 4ohm ones be ok?

[FJ_Hooligan]

As I remember it, the early models with TCI ignition used 2 ohm coils ('84 to '87) and later model with the CDI use 4 ohm coils.

Someone please check me on that.