Here is another important note to go along with the above important note:
If you install a voltage-forcing regulator on a current-limited alternator system (as is found on all Hondas prior to 1979 except the CX500/650), there will be a price to pay for it, in terms of power generation. Either the peak voltage must be lowered to the point where the alternator can run cool-ly enough to survive, or else the alternator's life will be significantly shortened by the heat of being forced to raise the voltage to an arbitary value that someone 'wants', like 14.0 volts, to run a given accessory.
Can you explain why you believe the stock SOHC4 regulator is not a "forcing type"?
Honda's (750) manual notes that this type of regulator is a "voltage limiter" type, designed specifically to prevent boiling the battery dry (they were all wet-cell tech when these bikes appeared). In their regulator adjustment instructions, all references were toward adjusting the spring contact so as to pull the moveable contact off the high-charge (relaxed) contact when the battery reached 13.2 volts, and adjustment of the overall gap between both sets of points so as to prevent the voltage ever reaching more than 13.8 volts. The moving contact had to reach the lower (cutoff) contact before the battery reached over 13.8 volts, stopping the charge altogether.
In a modern "forcing" regulator, it instead maxes out the field coil current until the battery voltage reaches [whatever setpoint it describes] and then it reduces the field current to try to maintain that level. With the old wet-cell battery, this makes them hot, and thirsty!
Honda Shop Manual says to adjust i the Vreg for 14.5V when @ 4000 RPM and above.
Surely the Alternator heating is more a function of current or wattage loads than just voltage per se.
You're exactly right about this: the higher the voltage in the system, the higher the overall current that will be required to keep the voltage at those levels. That's just because the load is more-or-less fixed: raising the voltage with the regulator from, say, 13.2 volts to 14.2 volts with, say, a fixed 12-ohm total load, will cause the alternator to change its output from:
[(13.2 x 13.2) x 12] = 14.5 amps (174 watts)
to: [(14.2 x 14.2) x 12] = 16.8 amps (202 watts)
(The 750's total normal load works out to about about 10-12 ohms (averaged over time) with the headlight on and 'proper' lights in all of its sockets (and OEM coils), depending on which model is involved.)
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Seems to me that if the alternator is rated for 156 or 210 watts continuous (model dependent) , Honda designers would have accounted for the heating at the given rating, including expected heat from the engine.
Are you saying they weren't conservative enough?
Are you expecting the field coil or the stator to fail with heat?
Cheers,
It depends on the construction of the unit as to which will fail first: all else being equal, the part with the lesser-heat-rated insulation will give it up earlier as flaked-off insulation that starts shorting out more and more coils as time goes on.
I think Honda's engineers were just a little 'stuck' at the time for their alternator coils, given Hitachi's offerings per yen (and this later got TEC into the fray, mimicing Hitachi's offerings). There was also a severe hydrocarbon (i.e., oil products) shortage in Japan at the time these bikes were being designed, and it showed up as erratic quality of insulation on their 'enamel coated' types of wires. This wasn't limited to bikes: I was an electronics engineer/tech for SONY and Panasonic as well as having my own shop in the early 1970s, and we experienced many coil wire insulation failures in things like stereos, TVs, and CB Radios from Japan, due to poor insulation on the coated wires. The visible result of this was: in the space that Honda gave Hitachi to design the alternator windings and frame, they had to install (X) number of windings to get the current desired: this meant they either had to make the insulation (Y nanometers) thick for the wire size they needed, or else get better coating that could be made thinner that would take the heat, so as to add more windings and cool things off a little bit. For example, in the CB350 twin, NEC led the way with an expensive epoxy for its excellent alternator, but the costs of these Fours was breaking Honda's back in development: so the electrics lost a little bit of the "pie" of the whole cost of the bike to having to use less-expensive wire in these windings. It met the temperature specs IF the bike ran normally and the loads were correct: trouble really only showed up when bigger loads (halogen headlights, extra lights, stereos, etc.) were introduced. Then the temps rise past the hoped-for design parameters, and the enamel coating on the [early, especially] alternators started flaking off. This slowly causes lost output, more heat, more flaking, etc. until their isn't enough power coming out of the windings for a given magnetic field. The 'limiter' then limits field current a little bit less, up to the point where the alternator just can't keep up as its windings fail. In some cases (like the CB750A field coils with less windings, so as to make more magnetic flux lines with the same 12 volts fed) the field finds itself being fed more and more current, generating more and more heat, until is loses lots of the insulation: these are high-failure coils in the 750 family.
To demonstrate this principle to a friend of mine in 1973, I re-wound my old SuperHawk's Hitachi alternator (really a dynamo). Instead of using the gauge of wire Hitachi did, I used a superior (MIL grade) copper-core, 400 degree F enamel-epoxy wire in a smaller gauge (2 sizes smaller), so I could add 12 more winds per field post. While this cost me MORE than a new Honda alternator would have, I also got 14.2 volts on my SuperHawk afterward (these were usually around 12.2 volts at best) without changing anything else on the bike. It ran for 10 more years before I lost track of the bike, no troubles, and the electric starter actually worked! Pretty rare on the old S'Hawks, with their permanent-magnet 'dynamo' type generators.
To do this with, say, the CB500/750 today, it would entail simply removing the wire from an alternator (counting the turns, please...), determining the size of the wire, find some of the high-temp modern epoxy-namel-coated wire in a smaller size (or two), and then fill in the field poles with 10%-15% more turns than it had with the previous wire. This increases the flux action across these coils, in turn increasing the current, being sliced by the steel rotor from the field coil. This makes more current.
In the last of the CB750 SOHC bikes (starting 1975), Honda spent more $$ on making the rotors 'sharper' on their corners and more accurate in their open slots. This also bumped up the current by more accurately defining the maglines of flux through the alternator's coils. Theoretically (although I don't know how to design the tools for it) you can sharpen the edges and openings of an earlier, more rounded-edge rotor in this bike and increase the current a little bit. I do know from experience that sandblasting a rusty rotor WILL improve the output on a K1 CB750 (circa 1994) about 1 amp, from a bike I once did then.
