"GEN" Light status

[Air4Life]

If my "gen" light goes out while the engine is running, is it safe to assume that I have sufficient charging output, or do I need to dig up a meter and check the output?

[Bob_Roller]

All that indicates is that the charging system is working, now how good it's working, is impossible to say, until you put a meter on the battery and check the voltage at around 4000 rpm .

[Olliepup]

Great Bob, What should the voltage at 4,000 RPM be??
Thanks, Dave

[Bob_Roller]

Should be around 14VDC, but being an old machine, it may not put out that much due to degraded parts, loose corroded connections, older battery, etc..

But you should see a voltage increase from the idle reading when you open the throttle and get to around the 4000 rpm area .

[Air4Life]

Thanks.  I will find a meter.  

One observation of my machine that I don't understand, is that when its cold (first started) and the engine is at idle (~1200) the light may flutter in and out; but soon after, when its been warmed and I return to idle, the light is completely out.  I don't understand what makes a warm charging system produce a greater output than a cold one.  That is, assuming it is a greater output to begin with.  

[nhmaf]

They all do that - as things warm up, they slightly expand, possible improving contact on the brushes (by truly a microscopic degree, but..).   Your idle @cold temps is also possible slightly less than when warm, and the threshold is right around that point.

IF you are getting +13.5V or more at the battery terminals @4000 rpm, and the light is completely out by 2000 RPM, sometimes flickers @idle, and is on bright with the key turned on before you start the engine, then things are basically 'normal' and you've not to worry.

[tvrla]

Another factor is that the battery is drained a bit starting the bike when it's cold and takes a while to replace that charge.

I'd say your idle is too high if the charge light doesn't come on.

[Barry]

don't understand what makes a warm charging system produce a greater output than a cold one.That is, assuming it is a greater output to begin with.  

Besides the fact that the voltage regulator setting is designed to drift with temperature changes I agree that it's probably just the battery recovering from the drain of the starter and while the battery is drawing some current the charge voltage will be lower and so the light will come on. Without getting into a complex explanation of why this should be it's basically down to ohms law and a small voltage drop across the battery due to it's internal resistance.

In fact what you have observed is interesting because it's a very good demonstration of the fact that if you are going to judge the charging circuit by measuring the voltage at 3000 revs the battery must truly be 100 % fully charged to get an accurate assessment.

My own observations of making changes to the voltage regulator setting are that it does change the behaviour of the charge lamp so to some limited degree you can judge the health of the system by the lights behaviour.  For example when I had the voltage regulator set a fair bit too high something like 14.6 volts then the light went out and stayed out even at ridiculously low idle speeds of say 700- 800 RPM.

Lowering the voltage setting to the nominal 14 volts will bring on the charge light at those revs.

I'm currently running with a setting of 14.3 volts which as high as you should safely go with a wet cell battery. My charge light now goes out and stays out at a 1000 RPM idle.

Bear in mind that an electronic ignition bike particularly a US version will not exhibit the same charge light behaviour as mine due to substantially more load from the ignition system and headlight. The extra current draw is not balanced by the charging system until higher revs are reached and so the light stays on at low idle speeds.

For me that says US electronic ignition bikes should have the highest possible safe voltage regulator setting and while plenty of owners seem to spend very large sums on upgrading the alternator the very first thing I would do is fit a "high output" or better still an adjustable voltage regulator.

[Air4Life]

Thanks for all the information.

I ran it over to a Battery Plus store and used their voltmeter to measure a voltage running from 11.24 up to 13.5 at reaching ~3,000 rpm's where it leveled off.  

The battery was tested and proved to be kaput.  I replaced the Yuasa with a  "Werker AGM Battery WKDC12-20NB" I needed to fill in the extra 3/4" space at the top, but otherwise it fit perfectly.

By the way, the light flicker (mentioned previously) was very brief to stay on, and with the slightest of engine warm up, less than a minute at idle that is, it was right out, as normal.    

This is a fun little bike, and I'm glad to have the opportunity to be an owner.

[wa1udg]

I think Barry has it right.  My 2 cents would be that the light glows whenever current is being drawn FROM   the battery because the alternator  cannot supply the entire load of the bike at the rpm is is turning,  and it goes out when the alternator is supplying enough to power the bike and also supply a charge current TO the battery.  The higher the voltage across a lead acid battery terminals, the more charge it will receive.  If it is "empty" it will begin to accept charge at a lower voltage than when it is topped up.  (Think of a tall, thin water tank you are trying to fill from the bottom)  When a battery begins to fail, it requires a higher and higher voltage to force charge back into it, and at the same time more and more of what it recieves turns into heat instead of causing the chemical change which makes a batter "accept" charge.  As I mentioned in another post, an "ampmeter' will tell you a lot more about what is going into and out of a battery than a light.  A voltmeter can stay in the "green" because  a failing battery won't load the alternator enough to drag the system voltage down, but the battery can't hold enough charge to start the bike.  

[Air4Life]

Yes, in theory, I understand this state of charge effect on the light at initial start up, but to how it translates to my actual situation is where it gets a little fuzzy.  

There is no way, in my mind anyway, that the fist 30 seconds of running the bike had the effect of charging the battery enough to make a difference to that idiot light, especially when you consider that its hasn't been turning over 1500 rpm's for the entire period of concern.  I will have to be more aware of it now that I have this new deep cell in there.

I tend to think what was pointed out previously by "nhmaf" as having some legs.  In this situation  the brushes begin to make better contact as it comes to life to where it snuffs out that light.  In addition: In humid environments is corrosion a factor?  Is there a slight oxidation that needs to be polished off after its been sitting?  I am getting to be a little to fanatical now, ain't I...

[Air4Life]

With hindsight, the original conditions stated were probably more related to the fact that the battery was on its last legs.  It gave out shortly after the above report.  Since I have replaced the battery with new, it tends to light more at idle than it did with that half dead battery, which was filling up quicker due to its limited working area; it now extinguishes slightly above cut-in speed like others have said it should.

http://www.batteriesplus.com/product/42359-WKDC12--20NB-Werker-Battery/100085-1/102629-SLA-Sealed-Lead-Acid-Batteries/102645-Werker/12V.aspx

[Barry]

Glad you got it sorted and the charging system is behaving as it should. It demonstrates that the battery has to be fully charged and in good condition in order to make any assessment of the charging system.

Reading back over the thread I realised I missed out something fundamental in my post. You were trying to understand why the charging voltage might rise as the engine warmed up. In fact whatever else might be going on in the charging system the voltage regulator has a built in temperature coefficient which causes the charging voltage to fall slightly with rising temperature. That is done to match the batteries lower internal resistance as it warms up. My voltage regulator drops 0.3 volts from a cold start to normal running temperature.

[Air4Life]

"Glad you got it sorted and the charging system is behaving as it should. It demonstrates that the battery has to be fully charged and in good condition in order to make any assessment of the charging system."

Thanks Barry.  True - Underlined to aid the mind.

[Air4Life]

r65 +1