Topic: CB400F Idle/Charging

[rk]

Okay - so the idle issue seems to have been sorted out, thanks to some #42 pilots and a vac sync, I will still likely drop down to a smaller main as well. However it really only holds a good idle while the battery is fully charged. As soon as the battery becomes depleted it starts to affect the idle, when I disconnect the white wire to the generator the idle picks back up as if I reduced the load on the engine. Which would be normal I'd say if the charging system were working properly... which it isn't. I'm getting pretty much zero charging from the system.

It seems as though the regulator is applying power to the field coil all the time (when I disconnect/reconnect the white wire there is always a spark) although the system itself isn't charging the battery.

I'm pretty new to electronics and Too Tired's post on the charging system and help from IronWorker has guided me through some tests. I thought I'd find a defective component but... everything seems to be working properly?! What gives?

Here's some numbers:

I'm getting about 12V at 5000RPM... the voltage fluctuates a bit with engine RPM but never rises about 12V.

Generator:

Resistance between all the yellow wires from the generator are at around .9-1.4 ohms (on the 200 ohm scale).
Resistance between the yellows and ground = ~1.0 ohms (again on the 200 ohm scale)

Rectifier:

I've got 6 high readings (~445 ohms on the 200 ohm scale) and 6 infinity readings... So this means the rectifier is good... right?

Regulator:
Resistance between white and green wires is ~5.4 ohms
Positive terminal to black wire = no voltage loss
Negative terminal to green wire = gave me no voltage reading... which would make sense because it's an incomplete circuit right?

Wires:
From the negative and positive terminals of the wiring harness to the red and green rectifier wires were both around .5 ohms.
I've done my best to make sure every terminal, connector, wire, etc. is clean, in good shape and making a good connection.

I know I'm missing something, I would really appreciate some guidance on where to go from here and how to get there. Much appreciated!

[TwoTired]

The alternator can only make about 1/3 of it's rated output at idle RPM. 1/3 of 150 watts is around 50 watts.  The standard electrical load for a stock bike is 8-10 amps or 100-120 watts.  In order to keep the spark going, the battery must supply the difference between what the bike needs and what the alternator can supply.  Further, the alternator needs to take some power from the bike for its electromagnet, to make power develop in the stator windings.  So, at low RPM, the regulator should be commanding full power to the alternator field windings.

The battery voltage should rise above 12.6V when the alternator is revved above 3000 RPM.  Depending on battery charge state, it may rise very slowly.  A depleted battery will take about 10 hours of 5000 RPM alternator rotation time to restore a lead acid battery to its peak 14.5V charging state.  To check the charging system in the shop, charge it with a wall supply battery charger, and then move the battery to the bike to check the battery voltage at each 1000 RPM increment.  If it still can't get above 12V, you either have more than standard load for the bike's electrics, a bad battery, or a connection issue.  You could try pulling all but the main fuse to lower the electrical load, just to see how the charging system responds.

[rk]

Awesome - I will try that. Makes sense about the power commanded to the field windings.

I'll have it on the trickle charger tonight so the battery should be in good shape. So if the battery is at a full charge (12V) then the system voltage should be up around 14.5 at around 5000RPM... correct?

The load isn't stock - I have the Dyna S ignition system. I also have an LED tail light and rear signal lights... they should draw less watts... right?

Assuming the system remains below 14V with a good battery and next to no load (with all the fuses pulled but the main one) - then I should adjust the voltage regulator to increase the output? Is this correct?

[TwoTired]

The Dyna S charges the coils WAY longer than the stock points do almost double load.  So, it causes more drain on the system. 3 ohm coils cause even more system load. These two common mods alone can suck more power than the alternator can make at idle.  ~90watts if I recall previous calculations correctly.

A lead acid battery fresh off the charger may read 13-14 volts unconnected to any load or charger.  But after 2 hours it should read 12.6-12.8V.  If so, the battery is "probably" good, although a load test is needed to really "prove" the battery.

The voltage at the battery must go above 12.6V to put energy back into the battery.  Below that voltage (good battery), and the battery is expending energy into the bike's system.

[rk]

Also - are the numbers I provided helpful/comprehensive... or should I be testing other things as well?

[rk]

Okay - so if the Dyna S system sucks so much power... how do people get around this? I have 5 Ohm coils, is there anything that can be done to bump up the output or do I need to put the points and condensers back on?

Seems like a huge waste of $$?

[TwoTired]

Also - are the numbers I provided helpful/comprehensive... or should I be testing other things as well?

The resistance reading you posted are reasonable, as well as the rectifier tests.  However, "about 12v" leaves too much wiggle room for accuracy.  As I said, anytime a lead acid battery reads less than 12.6V while running, indicates it is draining.

5Ω coils should be tolerable, as long as you don't spend much time operating below 2-3000 RPM. Or, switch the lighting off.

Be aware, you could still have something dodgy in the charging circuit connectivity ot bike switches and connectors, but it appears the charging component measurements apart from the Vreg seem to test good.

Something else to look for is a voltage loss between the battery post and the regulator, or regulator voltage lost between vreg and alt. field coil.  If you power that coil with less than full battery voltage the alt. can't make full output at any RPM.

[Bodi]

I suggest checking the bullet connectors under the sprocket/oil pump cover in the alternator wires (all five). I find these a problem on almost every 350 or 400 I look at. A bit of water/dirt can get in there since the back is somewhat open where the chain goes through, and they get heat cycled every ride since they are right against the engine block. Any extra resistance - especially in the field wires - reduces alternator output considerably. Clean both ends of each and squeeze the female ends gently to tighten the springiness a bit if they look fairly clean and clear. If they look like they have overheated - blackened plastic sleeve or corroded metal parts - I would cut them off, then solder the wires together with heat shrink over the connections. Since the wires don't really need to come apart - if you absolutely need to remove the alternator and take it far away you only have to disconnect the neutral switch wire and engine connector - this isn't a crippling modification.

[rk]

I'm still not 100% convinced my vreg is working properly... what's the best way to be completely sure I can rule it out as the culprit?

My alternator connectors are black and greasy, I cleaned them up and 'tightened' them but it hasn't really made the difference yet. I think I'll cut them and solder them together. That would hopefully lower the resistance of the yellow wires from the stator to the rectifier, rights? Which raises another question... does it matter which yellow wire goes where? Obviously I will make sure they get connected to their respective counterpart but does it matter which goes where to the rectifier?

When I say ~12V I mean it barely touches 12 when the bike is running at 5000 RPM and the battery is fresh... so I'm pretty certain the battery is doing nothing but draining.

You guys are really helping me out here, I truly appreciate the expertise and time.

[TwoTired]

Do specify the Voltage reading of your "fresh" battery.  This is important.  If  an assumed good battery is used for testing system voltage, and the battery ISN'T good, you will have a difficult time locating any other issues in the charging system.

If you are using the stock vreg, it should internally connect the black wire terminal (E) to the White wire terminal (F).  With the vreg unconnected to anything, you should measure zero ohms between those terminals. Using a voltmeter and the vreg connected in circuit, at idle the same voltage should appear at both the Black wire E terminal and the White wire F terminal.

You should be able to bypass a suspect vreg to verify the rest of the charging components.  Disconnect the white wire at the vreg and connect the white wire via external jumper directly to the battery POS terminal.
Run the engine and measure the battery voltage at 1000, 2000, 3000, 4000, and 5000 RPM.  A good fully charged battery should rise to at least 14.5 V and may go higher if all is healthy.  Don't apply more than 15V to the battery for more than 30 seconds or so, as you have taken on the function of the Vreg to limit how high the voltage can rise.

If you can't get the voltage this high, try again without the headlight fuse installed (or switch lighting off).  Unloading the alternator will make it easier reach the voltage peaks.

How well do you trust the meter you are using for accuracy?  Have you got another battery (car?) to measure while running?  It is frustrating to use test tools that lie to you.

[crazypj]

Resistance between all the yellow wires from the generator are at around .9-1.4 ohms (on the 200 ohm scale).
Resistance between the yellows and ground = ~1.0 ohms (again on the 200 ohm scale)

I know I'm missing something, I would really appreciate some guidance on where to go from here and how to get there. Much appreciated!

That's not good, the yellow wires shouldn't be grounding at all.
You did have them disconnected from harness when you checked?

You could try 'full fielding' the field coil (supply battery voltage directly)
 At idle you should get around 14~16 volts.
DON'T rev it, unregulated voltage can get real high real quick

[rk]

So I charged up the battery (around 13.3 V right off the charger, dropped to around 12.5V after sitting overnight) and installed an inline switch to the headlight. I also cut and soldered the yellow wires are the connecters were in less than great shape.

Took a reading off the battery before I took off today, it was right at 12.5 - rode for about and hour around town and the voltage was 12.5 when I got home. So I think that's progress... right?

The idle STILL hangs at 3000RPM unless I back off the idle screw and then it won't hold an idle. I'm still trying to find a place to find a smaller main jet... I have some #75s that came with the carb rebuild kit and there's #90s on the bike... With the pipe, pods, porting, and boring I feel like #75s would be too small... thoughts?

[iron_worker]

12.5V is a little low. Check this out:

http://www.energymatters.com.au/renewable-energy/batteries/battery-voltage-discharge.php

Your battery may not be in good condition from it being fully discharged a lot while you had your charging problem.

IW

[TwoTired]

Took a reading off the battery before I took off today, it was right at 12.5 - rode for about and hour around town and the voltage was 12.5 when I got home. So I think that's progress... right?

It's not awful.  But, if the bike was charging as well as the wall charger, I'd expect 13.5 or so immediately after the ride.

A lot depends on what RPM average you did on the ride and how long you waited when coming back to measure the battery voltage.

Why do you resist the charging /RPM test?  Don't you want to know when the bike can charge the battery?  You can do this test in about 3-5 minutes right in your parking place.

[rk]

Are you talking about just measuring system voltage at 1000RPM increments?

I did that and it fluctuated from about 11.5-11.9V from idle to 5000RPM...

[TwoTired]

Are you talking about just measuring system voltage at 1000RPM increments?

I did that and it fluctuated from about 11.5-11.9V from idle to 5000RPM...

Probably broke, then.  But, test conditions matter.

Did you rev long enough to watch any voltage trend upwards?  It takes time to build up voltage in a depleted battery.  The battery can dump 200-500 Amps in a very short time.  But, with a 1-2 amp charge rate, it will take 10 hours plus to recharge fully.  The battery voltage varies with the state of charge.

[rk]

My multi-meter's broken? That's possible... it's new but it wasn't the most expensive tool I've ever purchased.

I had the charger on it again... 13V when I pulled it off. Ran the bike and it maintained over 12V...

At Idle + 2000RPM it read 12.1V
3000 RPM was around 12.2V
4000 RPM was around 12.3-12.4
5000 RPM was 12.5V
6000 RPM and it stayed at 12.5V

I tried jumping the white wire to the battery... the numbers were exactly the same.

However, I noticed when I had the white wire un-powered, I expected the voltage to drop to something 12 or less regardless of RPM... but it fluctuated with engine RPM from around 11.9-12.1V... does that make sense? I was under the impression there was no output from the generator with the field coil de-energized.

[TwoTired]

A lead-acid battery must receive more than 12.5 V on the bike to charge it up to full.  Your wall charger does this.  Your bike does not appear to.  If the battery is good, your bike's charger is not.

Charge the battery on the wall charger.  Remove it from the wall charger and let it sit for two hours.  Then measure the battery voltage.

I was under the impression there was no output from the generator with the field coil de-energized.

There isn't in a properly wired bike.  No magnet=no alternator.