Dim lights at idle/low RPM

[xwhatsit]

Hihi,

The joys of my wiring continue -- just before WoF is due, of course. It did this 6 months ago, what a coincidence!

Just this morning (well probably last night too), the lights have become very dim. Main headlight does just OK, especially when the RPM is up, but indicators, tail light, brake light, horn etc won't go at the same time. If I switch off the headlight, then there is enough juice to flash the indicators, honk the horn, do whatever I like.

When I was at my girlfriend's place an hour ago, I borrowed the father's multimeter and measured voltage across the battery (capacitor) terminals. With headlight on, voltage is about 5V at idle and reaches up to 10V when revved (just enough to light the indicators). With headlight off, it gets between 12 and 15V.

So my amateur guess is that there's just not enough output to run everything. What should I be looking for? Just about to go down and hunt out how to test the alternator. Anybody got any other tips? Reg/rec?

[Ixion]

Rectifier out on on side will reduce output to 50% .

Alternatively, the alternator could be out on one (or more) phases (not sure if the CB250RS has a multiphase alternator).

Could be regulator, though less likely if you are getting decent voltage with lights off. (ie its a current drain/voltage drop problem, not a low voltage one).

David Reid is the man to PM.

EDIT: Given the amount of bits you have , swapsies is probably the quickest fix

[xwhatsit]

Cheers Ix. Yes, I've noticed Mr Reid normally seems to know actually what he's talking about, unlike the rest of us drivelers.

Three-phase alternator. Would it die all of a sudden like that though?

Well I'll go and swap the regufier, see if I get my blinkenlights back.

Girly's father is an electrician, although he doesn't know much about automotive stuff. His English and my Cantonese are rubbish, but I think he was saying it's very unlikely that a fault in the headlight circuit (like a short, what else would cause a sudden increase in current draw?) would cause the results I'm getting -- I'd have no headlight whatsoever and a faint burning smell.

EDIT: Given the amount of bits you have , swapsies is probably the quickest fix

Yeah man -- just with the places I get my bits, who knows what sort of condition they're in either

Fettling is only fun after you've fixed the problem and had a few beers to celebrate your own genius.

[Ixion]

Three phase means the alternator has three sets of wires. Like having three little alternators in one. If one set of wires dies (cause a wire breaks or cause it burns out) you loose one third (or one half ? I always get confused with multiphase, I think you actually lose half the out , which sounds illogical). Ditto if a diode goes in the recifier.

Very unlikely to be a short. COULD be a high resistance through a dodgy earth connection. Easiest way if you have a multimeter with a high amps option is just to measure how much the headlight is drawing. Should be headlight watts divided by 12, roughly.

Have you got a spare good recreg? If so it's a quick swap. I think I may have one, though GK why.

[xwhatsit]

Alright, swapped the regufier, still no go. Interestingly though, the manual gives specs for `5 - 40ohms between the green wire and each of the three yellow wires'. I'm getting around 500ohms on both regufiers. I gave away my other one so don't have a third to reference it to.

So I went on to the alternator. Manual says should check for continuity between all of the three yellow wires coming off the alternator. I'm getting continuity between all three pins, so that's OK. What I am getting, which the manual says is bad, is also continuity between the yellow wires and an earth point on the bike (engine fins).

The manual seems to be looking for maybe one of the yellow pins having continuity to earth as being bad, but I'm getting all three. Does this mean I should be looking further before swapping the alternator (want to avoid this as it means taking off the side case and draining all the oil, pain in the arse).

[xwhatsit]

The manual seems to be looking for maybe one of the yellow pins having continuity to earth as being bad, but I'm getting all three. Does this mean I should be looking further before swapping the alternator (want to avoid this as it means taking off the side case and draining all the oil, pain in the arse).

Pffft, what am I saying? If the three wires have continuity to each other, then all it takes is one coil to earth out then all three will have continuity to earth.

Anyway, one of my spare stators isn't looking very good -- could be all the bits of piston and bore stuck to it. The other stator, still in an intact engine (missing cylinder head etc.) has good continuity between coils; as far as I can tell, no continuity to earth. But where should I find earth on an engine disassembled like that? There's no wires attached to it anywhere. If I pull the stator off, where should earth be?

[Squiggles]

If ya run outta bits, i've got a 250rs reg/rect and a couple of other honda/universal ones

[xwhatsit]

If ya run outta bits, i've got a 250rs reg/rect and a couple of other honda/universal ones

Cheers mate! Don't think it's the regufier though. These particular types are very reliable, people are always buying ancient CX500/CB250RS regufiers and hooking them up to modern Honda sportsbikes when their ones die.

Can anybody help me with this bit? I want to check a stator that's out of the engine to see if it's earthing out. Where should I take earth from on a stator? Obviously I can't take the engine fins or negative battery terminal.

[Motu]

The coils are wound around an iron core.....that's the basics of the electrical magic stuff.And the stator is bolted to the engine.....which is connected to the frame.....which is covered in so much crap we call it the earth....

[xwhatsit]

Cheers Motu. So one would be in trouble if there was continuity between the iron base of the thing and the wee yellow wires that come out the plug.

Oh well, picked up some oil, let's start whipping off bits!

[xwhatsit]

F$$$##ng stuck bolt on alternator cover

If I ever find the gorilla who spannered on this engine before me I'll hit him over the head with a chair... then run very fast if he feels it.

My other spare stator looks mint.

[homer]

stupid question ....but i guess youve tested the battery and its actually fine .
just before you start pulling bits off.

[xwhatsit]

stupid question ....but i guess youve tested the battery and its actually fine .
just before you start pulling bits off.

No battery -- replaced that with a capacitor a few ten-thousand miles ago. It still checked out OK, holding enough charge for a few seconds to light the lights after the engine was stopped.

Anyway, all done now. Previous owner of the engine had seen fit to A) do without a gasket, instead using copious amounts of orange goop, and B) use Loctite on all the bolts holding the alternator cover on. Fucker! In the end, had to drill one bolt off after it rounded off. Application of hairdryer seemed to loosen the hold the remaining shaft had on itself, and vicegrips worked after an hour of fiddling thank god. Skinned my knuckles getting another bolt off; she always extracts a blood sacrifice! Hopefully that'll keep her (and Mr Haynes, who was soaked through two chapters) happy for a while

New stator works beautifully. Bike appears to start much more easily too, I wonder if the stator phase relating to ignition has been a bit sad for a while. Can use the horn at lowest idle with headlights on now (still a bit quiet with no battery of course), which I could never do since I pulled the battery off.

The first stator in the pics is the farked one I pulled off. Can't really see it in the photos, but the transparent epoxy insulation goop is cracked in a few places.

Anyway, what I want to know now is, how do I prevent this happening again? I presume having a capacitor in place of a battery puts the stator and reg/rec under higher load -- the `battery' is charged in a few seconds, and 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? One thing that was mentioned when I blew a bulb or two was to put a 24V truck lightbulb somewhere in the circuit to eat up a bit of power.

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?

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?

[Ixion]

Doubt the capacitor thing makes much difference. This type of system has a shunt regulator, which just pipes anything over 16 volt odd to earth. So the alternator is constantly putting out whatever it puts out, which is either fed into the battery, or to earth. No battery would mean more laod on the regulator, since its shunting mor eoften. But not much difference to the stator. They deteriorate with age the insulation cracks and windings short out. Just an old age thing.

[davereid]

Well done that man !

A battery, being a chemical device, is always treated with suspicion by electrical folk, which is as it should be, as you can't trust em.

But, a battery does have a couple of nice features, much nicer than a capacitor.

Firstly, a battery doesn't like going over-voltage. It will get warm, and gas (hydrogen) in a fight to keep them volts where they should be.

A battery will try and hold system voltage to the average of the applied rectified AC.

A capacitor onna other hand, will cheerfully charge to the peak of the applied (rectified) AC voltage.

Then when you toot yer tooter, it will rapidly discharge to the bottom of the cycle.. thus no tooter.

So, running a bike without a battery ? Is it OK ? Did it damage the stator ?

My guess is that the stator would have died anyway.

Good job sorting it out.