Stator musings

[Feetup]

Maybe I have too much time to think, but I have one of those linear minds that gets stuck on topics from time to time. 'Least thats what my wife tells me.
Any way, I have spent a lot of time fussing over the OEM charging system in my head wondering where Mother Honda went wrong.
Tell me if this sounds right to you.
The alternator is a permanent magnet type. Unlike a conventional excited field alternator, whenever the magnets spin, alternating current is made. How much current is made depends on the strength of the magnets and the number of turns of wire, and up to a point, how fast the magnets are spun. The frequency of the AC (alternating current) depends on the relationship between the number of magnets in the rotor and the number of poles in the stator (fixed) and of course on the RPM of the rotor. There is no way to vary the current produced to match needs, it simply produces all it can, all the time.
The rectifier is no more or less complex than any, simply a bridge rectifier that flips the negative wave to positive, and the three phases overlap to produce a lumpy direct current. Noisy in electronics but the big lead acid storage battery doesn't care and does a great job of filtering out the lumps which are too numerous and too small to bother any of the electrical components except for radio/intercom and we can filter that out with capacitors.
The trouble is, the alternator is producing somewhere around 350 watts, depending on the RPM of course, but it is producing it all the time. We probably need that much right after cranking up for a brief moment to give the battery a good swift jolt to shed any sulfating of the plates that may have occurred from sitting dormant, and give it back what the starter motor took away, but once the battery is getting close to it's full charge it needs almost nothing, and the other systems on the bike simply cannot use all the rest. And what is more, the alternator will produce something in the neighborhood of 50 volts peak to peak which when passed through the full wave rectifier will still be over 25 volts DC. We can't use anything more than 14.5 volts or we boil the electrolyte in the battery like we were making tea, and destroy the plates and hence the entire battery. We would soon loose all the bulbs and electronics, and most likely become a stew in our own electric clothing. So, what does mother Honda intend to do with the rest. Well she simply wastes it, and turns it into heat. Shunts it to ground through a resistance. 350 watts is a lot of heat! Hold your hand close to a 200 watt light bulb if you don't believe me. What's more she sticks this source of heat in a very warm environment, not too far behind the radiator. Even the 1940's technology of the boys from Milwaukee sticks the heat sink out front in the wind!
This design works O K on smaller bikes with 60 or 100 watt systems and even then it is more of an accountant's choice.
I have heard folks say that sticking the alternator inside the engine, in a very harsh environment is the biggest reason they fail, but I'm not sure I am convinced of that. I'm starting to think that the biggest reason they fail is that they are working as hard as they can, all the time.
The conventional alternator in the poorboy type applications has a field made from an electromagnet, not a permanent magnet, so the amount of current produced is dependent on how much current is applied to this field. If we only need 20 watts, the regulator feeds just enough current to the field to produce 20 watts, keeping it at the voltage the regulator has been set at. There is nothing made that is not needed, and the only heat produced is from inefficiencies that cannot be designed out of the system.
I think Mother Honda could have designed a brushless variable field alternator and stuck it in the same place and it would most likely have lasted forever, but for reasons known only to her and a handful of engineers who aren't talking about it she chose to use basically the same technology that Mr Lucas stuck on my old Norton Atlas, she just didn't use the dreaded zener diode to waste the excess.

OK, you wise and thoughtful ones, your thoughts?

[Guest]

Tim, you're making my brain hurt! I'll contemplate all that this winter when I'm changing my stator.

[Guest]

Huh?

[Guest]

reminds me again the two things I know about electrics

1. I don't know much about them hock:

2. they bite me when I mess with them :lol:

and do you know why the English drink warm beer?

all their refrigerators are made by Lucas :roll:

[jcmaun]

On another site that I frequent that deals with a model which also has a permanent magnet, the recommendation is to add some driving lights to use up some of the excess energy so that less heat is generated. Haven't seen that recommendation on this site though.

[pauln]

Tim, thanks for the excellent explanation. That is the way I understand it as well, but it took me a while to figure it out. Before the wing, I never knew the difference between a stator and and alternator, but I learned. Honda finally got it right starting with the 1500s, but we are still stuck with stators (unless we do a poorboy).

I think that shunting the excess to ground through a resistor is rough on the regulator/rectifier (which explains why a lot of them fail - including mine), but I wonder if doing that or using up the power through other accessories really makes any difference as far as the stator itself is concerned. It simply makes full power that gets used up one way or another (reg/rect or accessories), so I still wonder what Honda did wrong to cause the stators to burn out?

The stators fail because the insulating coating on the wires gives way for one reason or another and then wires physically touch other wires and/or the base they are wound on. The question is why does the coating break down? Simply too much heat in the area and in the wires? Do chemicals in the oil eat it away? Did Honda use a poor coating in the first place? A combination of all of these? It would be interesting to hear the opinion of an electrical engineer who works with these things (stators in general).

Regardless, we are saddled with an unreliable charging system on all of the 1200s. I don't have time to tour on mine at present, but if I did, I would be very hesitant to do so knowing that the charging system could quit at any moment. I am hoping to convert mine to a poorboy this winter to eliminate this headache.

[Dave-85-LTD]

I have concerns about useing every possible led light replacement, as a way to "save" energy, because in this type of system, the stator is generating full design power when ever the magnet is spun at a high enough speed.

If we "save" wattage or power at each light bulb, then we must disapate more power or heat at the regulator.

I am going to leave my bike as stock as possible, as far as regular type light bulbs are concerned, but any additional lights will be LEDs

I had a lot to learn about this type of -- stator---rectifier----regulator, system but fortunately my uncle owns Smith auto electric in PA. so he helped explain a shunt type regulator system

[Ed Z]

Here's an idea for ya... Hows about putting a thermostat switch on the regulator that will turn on a set of driving lights (or something like that) when it reaches a preset temp... This should reduce the heat that is generated by the dumping of excess current to ground (as it normally does)... Really all it would do is move the heat (light bulb heat) to a different area on the bike... But, in any case it should reduce the heat in the stator wiring and regulator as well... Just a thought I had passing through the wind tunnel between my ears...

[Guest]

GRRRRRRRRRRR :x