Topic: 79 cb 650 not charging

[Demon67]

Ok you tech guru's I've got a 79 650 thats not charging and I've gone through the tests several times with no brilliant flashes of insight as to why, checked rectifier diodes, Inf one way low ohms other, checked rotor less than 1 ohm between slip rings Clymer says thats ok, checked stator wires nothing to ground, between yellows 2 ohms. Crank the bike up still nothing above 12.5 volts check stator wire .3 volt ac shut it down before I choke to death on fumes. Check continuity to white and black wires ok so brushes touching slip ring confirmed brushes ok and cleaned slip ring, nothing to ground. Run up again tried checking volts at black and white wires 12.5 finally jumped white wire to ground volts at battery started to drop, shut down, now when I say ground I mean neg term on battery and battery is new. Now I know that I'm not seeing something ( to many trees in forest) but because of creeping senility I don't know what, any Ideas?
Bill.

[TwoTired]

If the rotor (The part that makes the magnetic field) is truely 1 ohm, then it will draw 12 amps from the battery, (provided the regulator allows that).  The white and black wires to the alternator s/b 7-8 ohms.

I'm told you can check for a magnetic field by holding a thin feeler gauge near the alternator cover.  The feeler gauge should move when you switch on the ognition.

Cheers,

[750duo]

Demon

Honda Manual calls out 0.2 ohms for each of the stator coils. Should measure about 0.5 ohm across the yellow wires (0.2 + 0.2 + meter error)

Field coil is 7.2 ohms across the white and black wires.

If everything else appears OK, I would go for a regulator malfunction. If the regulator is not providing excitation voltage to the field coil there will be no output (Normal should be near 14v on the  battery terminals.)

Good Hunting, Tom

[Ibsen]

These are the tests you should carry out according to the Honda workshop manual:

Test 1 - Stator

Test 2 - Regulator

Test 3 - Regulator/Rectifier

Have you checked the carbun brushes btw?

Carbon brushes

And this site is offering a very good fault finding chart:

http://www.electrosport.com/electrosport_fault_finding.html

[Demon67]

To Two Tired I get 18 ohms across B & W wires and tried the magnetic test with a washer on a string, Nada,.

To 750duo the .02 ohms across yellows is roughly what I get and in theory I've put 12 volt on field coil by running wire to white wire directly from battery + term, nothing, and if I use - bat term volts at battery start to drop from 12.03 to 11.5- 11.2.

To Ibby I've looked brushes with alt cover off and checked them for continuity, connector to brush etc, as far as rectifier goes I made a truth table to make sure I didn't miss any of the permutations the tests and wrote every thing down, and as I understand it, diodes if they'll pass volts one way and not the other they're OK I haven't done the variable resistor test, no variable resistor.
Test equipment consists a digital multi meter with diode check frequency hold, volts hold autorange, manual, transistor check etc, it doesn't quite wipe afterwords, but close.
Bill.

[TwoTired]

To Two Tired I get 18 ohms across B & W wires and tried the magnetic test with a washer on a string, Nada,.

I think this bears further investigation.  No magnetic field, no charging.  And, your field coil resistance is over twice what it should be.  Measure your field coil resistance across the slip rings with the regulator disconnected.  If it doesn't read 7.2 ohms and you can trust you test technique and your instrument, you have a bad rotor.

If you want to temporarily bypass the regulator, disconnect the white and black wires from the regulator.  Apply +12v on the black field wire, and 12 v return ( battery -) on the white field coil wire.  This should give you full magnetic strength and full ouput when you rev the motor 3-4K.  Output strength is always RPM dependant even when all is well.

You should be checking and measuring your charging system with a fully charged battery.  A weak or depleted battery can give low and misleading voltage readings as the battery absorbs power.

Good luck!

[JSGAuto]

This sounds very similar to a problem I had.  Everything tested ok per the shop manual.  What was happening was the rotor windings were "pulling apart" at high engine speed.  So when it was statically tested the rotor was good, but at speed was dead.  If everything else is checking out I would take another look at that rotor.  THis is a comon problem on the DOHC Honda's which use the identical charging system. 

As for the test for the field, by holding a piece of metal near it, this never really worked for me.  I wouldn't consider it an actual test.


Good Luck,
Jim

[750duo]

Demon   

If you are reading 18 ohms across the field coil then something is amiss with that coil. By doubling the resistance you halve the current through the windings. It could be simple - such as attachment of the wires to the coil.

An alternator's output is controlled by the current flowing in the field coil. This current creates a magnetic field which causes the alternator to put out.

The SOHC4 bikes are not known for a robust charging system when everything is working correctly. When you reduce the field current to less than half of its normal value, you can expect anemic or no output from the alternator.

As Two Tired put it -

  I think this bears further investigation. No magnetic field, no charging.

Good Hunting - Tom

[Pinhead]

I'd say the easiest thing to check is the rotor. Check for ~6 ohms across the slip rings. If it's less (my bad one had less than an ohm) than you'll have to replace the rotor and probably your R/R. When I changed mine, I first replaced the rotor. Still no charging, until I hooked +12v straight to the rotor via the wires to the brushes. Instant charge. So my regulator was bad and needed replacement. When the rotor shorts it pulls more current than the R/R can handle and it fries. So you'll probably have to replace both.