Hello Tony. Haven't seen you here for a while Sir. Good to have you back onboard.
Some lovely looking 'lectrickery there. You make it all sound so simple -
when I look at wiring diagrams & looms, all I see is a mass of confusing spaghetti.So- bearing in mind I'm putting this bike together on the cheap, using as many original, (cheap), parts as I can, & want it to be reliable enough for a Summer get-to-work bike if needed, just what components from my pile of bits do I need to squish into the box?
I'm happy to stay with the standard battery set-up & have already made a container for said Batt'. Is the twin lead coil I photographed O.K? Seperate rectifier & regulator, or is the finned jobbie a later combined unit?
To help with laying components out, which unit connects to which? -ignition unit. fusebox, finned thingy, rectifier if needed, coil etc. Wiring can be confusing, and I'm not great at it, but the best thing is to get your head around each separate 'bit' and what it does, then kinda join the dots of all the separate 'bits'.
So what are the main the bits: Power/battery, Ignition, lighting, charging, etc
Apologies to anyone (incl Sir Manky) if I make this very basic
, but we may have some newbies reading this, so here goes......
Power/batteryThe bike runs on 12v DC (hence the battery) and the bike would run/function quite happily for a while (so long as the battery had enough oomph) even if the alternator/rectifier/regulator system wasn't on the bike. In fact many competition bikes run this way.
The battery supplies the power for all the ignition, lighting etc to function
Electronic ignition systemThe bikes needs sparks from the plugs to run the engine, and these have to be at the correct time with respect to the engine internals etc.
The ignition pack (Boyer/Lucas/Yamaha) is a little box-of-tricks that is powered by the 12v battery. At the same time, the ignition pack also feeds the coil(s) with 12v.
This ignition pack is connected to a sensor on the end of the cam, so when the cam is in the correct position (ie with respect to degrees away from Top Dead Centre of the piston) it sends a signal back to the ignition pack.
The ignition pack takes this signal and says 'its time to drop the 12v I'm constantly sending to the coil', which it does, this then allows the HT (high tension) from the coil to reach the plug, which jumps the plug-gap (old machines had a gap of around 25 thousands of an inch, about the thickness of a thumbnail), and hey presto, the engine fires.(in an ideal world)
The sensitive electronics of the ignition pack are best kept away from the HT cables. In fact, on the XS650, I've heard it said (I think by Lucas??) that the metal cover over the sensor/pick-up is replaced with a plastic unit.
A slight side topic - Coils have different ratings depending on their performance (a coil firing a single cylinder 4-stroke engine doing 4000rpm will be firing 1000 times a minute. If a single coil is on a twin-cylinder 4 stroke at the same revs it will be firing 2000 times a minute)
High performance coils take more power (partially dependant on the resistance of the primary coil, and hence the current supplied by the battery), and as such, all coils generate some heat, so they need to be suitably mounted to allow the heat to dissipate.
Its not uncommon for coils to degrade with age. When they get hot (from use and/or engine heat) they can give up the ghost.
So that's kinda one self-contained system.
Lighting/fuses/relays etcAgain this all runs on 12v DC, so there's a feed from the battery which then distributes itself to things like switches (for horn, headlights, indicators, brake lights, relays etc)
Depending on the bikes age depends on the sophistication of the fuse system. Older XS650s (say from early 1970s) have just one fuse, more modern XS650s (1980s) have a fuse box with fuses for specific functions.
The fuse, fed from the positive feed of the battery (one negative earth machines), is located before the component its protecting, and is designed to blow if too much current tries to flow in the circuit its protecting, thus preventing damage to specific components (and maybe even the wiring). There are different ratings (3A, 5A, 20A etc) so its no use protecting a circuit that will be damaged by 5 amps with a 10 amp fuse. Carrying some spares can be useful !
In general, all the above (and the ignition system) use relativity low current (measured in amps) and therefore do not require relays to be used. A 55 watt headlight uses 55W/12V amps = less than 5 Amps, that's why most of a loom is made up of a certain size of wire (ie one that can take the required current without burning out)
If there's a requirement for more power, such as a starter motor which can be up to around 300 Amps, the use of a relay is required. The relay uses the standard size wiring to make a switch in a heavy-duty/high-current circuit, which runs using thicker cabling. Its still all 12v DC.
In order to power things like the starter motor, which take a lot of current, a suitably sized battery and related wiring is required.
Charging systemFrom the above, it can be seen that the 12 v DC battery has a fair bit to do, but it only has a finite capacity, which is where the ability to have a charging system comes in pretty handy (saves carrying loads of 12v DC batteries around!).
If we go back in time, pedal bikes and early motorbikes had a dynamo (remember them?) to produce electricity, and it just happened to be DC as well. To prevent over-voltage from the dynamo feeding the system and frying things like the battery (cos you pedalled really really quickly!), a voltage regulator was fitted, early ones being the famous 'Zener diode'. The regulator generated heat, so was mounted on a heat-sink, often out on the breeze to aid cooling.
One of the down sides of the dynamo was the efficiency, and the dynamo was superseded by the alternator.
Although hugely more efficient, the alternator made that confounded AC (alternating current) sort of electricity, so a rectifier (a converter of AC to DC, good band by the way!) had to be included as well as the regulator.
Early systems had one of each, newer system combined them into a single unit, so depending on the machine, you get what you're given. But the regulator always produces heat, hence its cooling fins, and therefore has to mounted such that the heat can dissipate.
Its not uncommon on modern machines for the alternator to have an in-built rectifier/regulator, so no separate boxes to wire into the loom, sweeter still – until something goes AWOL.
There are no real restrictions for how far away the battery is from alternator etc (Jag XJS has its battery in the boot).
So bottom line of the charging system is that it generates AC, which in converted to DC, limited (regulated) so it doesn't fry things, and its output then goes to the battery which keeps it topped up, thus keeps everything supplied – or so the theory goes................
Breakdowns/failuresOne of the biggest cause of breakdowns is 'electrical', and one of the most frequent reasons is the condition of the wires/connectors, whether the factory fitted snap-together sort just getting old and corroded, home made crimped-on connectors, or switch-gear contacts. (how many of us have pulled a connector apart by holding the wires??)
Modified bikes/cars tend to have the wiring following routes that are new, so tight bends and chaffing should be addressed.
HT leads/caps age and can breakdown.
Water/condensation had the knack of getting where you don't want it, so stuff like WD40 comes into its own.
Old style batteries are lead/acid and need to be maintained.
Newer batteries are 'maintenance free' (phew!)
With luck, that should have either completely confused anyone who read it, or maybe just made it a wee bit more understandable..................
A book worth considering in by a guy called Tony Tranter called Motorcycle Electrics, search Amazon or ebay, but he also did the current (pun!) version of the current Haynes shown in the pic
