Dim lights at idle/low RPM

[xwhatsit]

Cheers guys!

I remember you writing, Dave, that a battery resists going over-voltage and holds the voltage in the circuit at around 70% of the peak output I'm getting. A capacitor doesn't care and I get almost the full amount. But the alternator doesn't care, does it? All of this is just extra voltage in the lighting, the alternator is upstream of that.

Good-o. I'm looking up how to rewire stators in case it happens again -- don't have a spare now Looks like a pain in the arse!

Well the bike ran OK to work and back, although being paranoid I lugged the engine everywhere. It starts easier now too. Lights were blinding coming home in the dark, to the point where the speedo backlight is distracting me. I think the stator was a little shitty anyway before it completely gave up the ghost.

[CookMySock]

No battery -- replaced that with a capacitor a few ten-thousand miles ago.

Thats a good trick. Never heard of that before. What size/voltage capacitor ?

running around everywhere with a full battery means the heat has to be chucked away somehow. Just through the reg/rec (which stays reasonably cool, big thing with fins) -- or through the stator as well? [.....] Coincidentally, this has happened just as I've put a standard front sprocket on, meaning that at 100kph the revs are a lot higher. I wonder if that was the straw that broke the camel's back?

I was thinking the same thing.

Hows your electrical theory ?

When you fling a magnet past a wire you induce a VOLTAGE in it (not a current) so rotating magnetic field machine acts a Linear RPM to VOLTAGE converter. Of course this makes no sense does it ? The voltage is normally a constant 11 to 13V. Try disconnecting the coils and testing them with the volt meter, you will see the voltage swing widely and linearly with RPM.

The short explanation is, the extra voltage is dissapated as heat in the internal resistance of the windings and other resistive devices in the circuit. So with extra high rpm and sustained open road riding, those coils will overheat for sure. There is no wasted or lost voltage. It is all burned as heat, in this case, the coils.

Refer Kirchoffs ; "The directed sum of the electrical potential differences around any closed circuit must be zero."

Reading material for this ;

http://en.wikipedia.org/wiki/Kirchhoff's_circuit_laws See Kirchhoff's Voltage Law

Or should I just put it down to old age (this engine's had an awful belting in its life) and not worry too much?

That too.

I'm looking up how to rewire stators in case it happens again -- don't have a spare now Looks like a pain in the arse!

Thats a good skill to have. You really just to know what wire size, and how many turns, and how it was wired up.

Steve

[davereid]

...a battery resists going over-voltage and holds the voltage in the circuit at around 70% of the peak output...

Yep, your battery is being charged by rectified AC.. it starts at zero volts, rises to a peak voltage and then drops back to zero, before starting the cycle again.

A battery will tend to hold the voltage at about 70% of the peak applied voltage.

Your capacitor will charge to almost the peak of the applied voltage, limited only by the internal resistance of the power source, and its capacitance.

In the real world, it doesnt matter much. Your bike will be drawing electrons, (current), so there will be a voltage drop in the stator windings, that will help to lower terminal voltage, by creating heat in the stator.

Lots of the electrical parts on your bike don't really care if they are fed AC, DC or rectified AC. Your headlight, tail light and brake light don't care, and indicators only care because the relay that makes them flash may care.

DB makes the point that as rpm increases, the open circuit voltage of the stator increases.

In very extreme circumstances, this open circuit voltage may become high enough to threaten the insulation on the windings. There will be no heat though, no until you connect the system to a load.

In the real - world, you won't be running your stator open circuit, so as rpm increase, if the load remains the same, current flow will increase. This of course will cause heat to be generated in the stator.

And if the voltage gets too high, you will start to blow bulbs etc, as they can't cope with the extra heat either.

So your voltage regulator will kick in, drawing current from the stator, and heating itself, and the stator up in the process.

By drawing extra current from the stator, the terminal voltage drops, as the stator has a finite internal resistance.

Seems amazing it all works really!

[CookMySock]

Seems amazing it all works really!

naw its quite simple. Stator is basically a constant current output. Rectifier converts current to DC. Shunt regulator clamps it at 13.2V If any current is flowing into the battery or electrical bits, the shunt regulator shares this current making sure it doesn't move off 13.2V Um, thats it. Much simpler than a car system.

Steve

[avgas]

ummm sorry to state the obvious a bit here but have you check the electric demand.......all it takes is 1 dodgey earth (eg water in you head lamp) and your whole system gets drained due to most current going through the lowest parrallel resistance (the short). This really only comes into play if you have replaced the fuses with the a higher rating (or in my case a piece of wire).

However in saying that i would normally assume that your alt. is at fault. Or your batt has a dead cell (kinda like trying to push current through a brick wall). Sadly gatorade electrolites will not fix this.

[avgas]

naw its quite simple. Stator is basically a constant current output.

Lol i certainly hope not - unless your refering to RMS.

[CookMySock]

Lol i certainly hope not - unless your refering to RMS.

for a constant RPM, and considering its comparatively high internal resistance, it is effectively a constant current output device. We can get the paper and pencil and calculator out, and argue the technical side of it if you like, but I'll beat you, and I can't really be effed anyway, and it doesn't matter a shit in the end, the bike powers itself and charges its battery, woohah!

Sorry. Raining. Bored.

Steve

[davereid]

for a constant RPM, and considering its comparatively high internal resistance, it is effectively a constant current output device. We can get the paper and pencil and calculator out, and argue the technical side of it if you like, but I'll beat you, and I can't really be effed anyway, and it doesn't matter a shit in the end, the bike powers itself and charges its battery, woohah!

Sorry. Raining. Bored.

Steve

Its not even close to a constant current source, unless you count zero rpm, when its a constant source of zero amps !

The amount of current an alternator (or any power supply) will deliver depends on its own internal resistance, and the resistance of the load.

So..

At (say) 3000 rpm, with no load, your alternator will deliver no current.
At (say) 3000 rpm, with a zero ohm load, the alternator will deliver its maximum current.

[xwhatsit]

I'm not even going to pretend to understand half of that. All I know is -- give the FPGA 5V, wire up the crystal oscillator just right, and DON'T TOUCH ANYTHING! I like software for a reason

My current concern about all this is more earthly anyway -- I reused a gasket (from the engine I pinched the stator from), which looks perfect. Loctite Blue silicone as well. Unfortunately it's leaking oil anyway after getting hot.

I'll get another gasket for my next oil change in a couple of weeks. Perhaps more to do with using the alternator cover from the other engine too (couldn't be bothered taking the stator out of the inside of the cover first -- plus, the new alternator case looks nicer, and the gearshift seal is in better nick). Gasket surfaces not perfectly machined for each other or something.

[pete376403]

Make sure you keep the engine oil at the correct level. If the Honda is anything like GS Suzukis, the engine oil assists alternator cooling.

[xwhatsit]

Make sure you keep the engine oil at the correct level. If the Honda is anything like GS Suzukis, the engine oil assists alternator cooling.

I check it before every ride anyway -- it has a habit of suddenly disappearing on long hot runs with so little in the sump (1.7 litres).

Wondered about fitting an oil cooler for a long time, #1 for more cooling, and also so I could then fit an oil filter (250RS has none). Not so keen on the idea because of the weight and bulk, but it seems more and more wise.

[Ixion]

Cheers guys!


Good-o. I'm looking up how to rewire stators in case it happens again -- don't have a spare now Looks like a pain in the arse!

I done a few. Easy enough, but damn tedious. You can make a little winding jig, or use a lathe in backgear. But it's still tedious.

Easiest way to figure the turns is to weight a few metres of the wire of the old coil (as much a s you can be bothered unwinding ). Then hack all the old cardboard , and as much of the hard lumpy shellac stuff as you can off the old coil, and weigh the coil. Simple arithmetic will then give you the length of wire in the coil. Meaure the diameter of the coil at around the half way mark, more arithmetic and you have the number of turns.