View Full Version : Dim lights at idle/low RPM
xwhatsit
22nd August 2008, 15:55
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
22nd August 2008, 15:58
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
22nd August 2008, 16:03
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 :laugh:
Fettling is only fun after you've fixed the problem and had a few beers to celebrate your own genius.
Ixion
22nd August 2008, 16:09
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
22nd August 2008, 16:45
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
22nd August 2008, 17:45
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
22nd August 2008, 20:40
If ya run outta bits, i've got a 250rs reg/rect and a couple of other honda/universal ones :)
xwhatsit
22nd August 2008, 21:42
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
22nd August 2008, 21:55
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
22nd August 2008, 22:03
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
23rd August 2008, 11:00
F$$$##ng stuck bolt on alternator cover :angry2:
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
23rd August 2008, 12:03
stupid question ....but i guess youve tested the battery and its actually fine .
just before you start pulling bits off.
xwhatsit
23rd August 2008, 16:12
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 :innocent:
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
23rd August 2008, 16:40
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
23rd August 2008, 16:52
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.
xwhatsit
23rd August 2008, 23:01
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 :D 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
24th August 2008, 09:37
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. :laugh:
I'm looking up how to rewire stators in case it happens again -- don't have a spare now :D 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
24th August 2008, 10:45
...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
24th August 2008, 11:13
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
24th August 2008, 11:31
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
24th August 2008, 11:32
naw its quite simple. Stator is basically a constant current output.
Lol i certainly hope not - unless your refering to RMS.
CookMySock
24th August 2008, 12:31
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! :niceone:
Sorry. Raining. Bored. :yawn:
Steve
davereid
24th August 2008, 14:13
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! :niceone:
Sorry. Raining. Bored. :yawn:
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
24th August 2008, 15:15
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 :D
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
24th August 2008, 16:48
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
24th August 2008, 17:51
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
24th August 2008, 22:24
Cheers guys!
Good-o. I'm looking up how to rewire stators in case it happens again -- don't have a spare now :D 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.
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