Topic: Rectifier Test

[B. Alec]

Hey again! 

So my last real problem(I hope), short of a tune-up is the charging system on my '76 550F.  It gives no extra charge to the battery using the RPMs test, and I just tested the rectifier according to the manual and got the following results:

Green lead connected to negative meter lead:
      Yellow lead #1 = 3.5 ohms
      Yellow lead #2 = 3.5 ohms
      Yellow lead #3 = 4.1 ohms

Green lead to positive meter lead:
      Y1 = infinite
      Y2 = infinite
      Y3 = infinite

Red/White lead to negative:
      Y1 = 0
      Y2 = 0
      Y3 = infinite

Red/White lead to positive:
      Y1 = 0 ohms
      Y2 = 0 ohms
      Y3 = 4 ohms

The discrepancy in the Red/White lead tests lead me to believe the rectifier is shot.  Can anyone confirm this interpretation for me? 

I also have a '75 550F SuperSport and did the same test on its rectifier to see if I could just swap it out.  I got these results:

Green to negative:
      Y1 = 4.5
      Y2 = 4.5
      Y3 = 4.5

Green to positive:
      Y1 = infinite
      Y2 = infinite
      Y3 = infinite

Red/White to negative:
      Y1 = infinite
      Y2 = infinite
      Y3 = infinite

Red/White to positive:
      Y1 = 4.5
      Y2 = 4.5
      Y3 = 4.5

This test leads me to believe the rectifier is good.  Can someone confirm this as well?

Finally, the Honda Parts Code on the '75 SS is 390 and on the '76 F is 374.  Does anyone know if the rectifiers are compatible or where I might be able to find out? 

I hope the two charts are clear. 
Thank you very much! 

B. Alec

[TwoTired]

Assuming you tested the rectifier out of circuit...
The first rectifier test results are suspect.

The second rectifier test looks good.

All the CB550Fs from 75 to 77 were product code 390 and they were all Super Sports.

Product code 374 applies to the K models of the CB550 from 74 to 76.  The big F on the side cover does not signify an F model.  It's just an embelishment of the word "Four".

Source = Honda Motorcycle Identification Guide published by American Honda Motor Company

No matter, the rectifiers are interchangeable, anyway.

[Paul]

I know this is a matter of preference and as you mention you already have a spare from your other bike.
I looked into getting a Honda rectifier but couldn't justify (in Euro's) ...124.00 inc vat & carriage I got mine in my electronics supplier for 16.00 . works fine no issues 1 year later.

[oldbiker]

You are right, the first rectifier is useless. There are six diodes in the rectifier and one of them is burnt out. This reduces output by 66%. I know this sounds strange, but in effect of the three phases of the generator only one will be providing current.

[B. Alec]

Alright, thanks! 

1. Is it likely that a bad voltage regulator caused the burnt-out diode?  I've been trying to figure out the regulator test as well, but am still working on it.  I don't want to replace the rectifier if the regulator is just going to kill it. 

2. I unplugged the rectifier from the harness before testing it.

3. I say 550F because I compared the VIN(CB550-1235296) and the Engine IN(CB550E-1072796) to the list at http://www.honda4fun.com/modelli/cb550.html.  So...is that a typo and I actually have a K?  The product code is the same as the earlier K's.  Your source is much better than my Italian website! 

4. Yeah, I thought about not getting the Honda part.  Somebody recommended oregonmotorcycleparts.com and it looks like his homemade regulators are alright at half the price.  $16 sounds even better, though I always heard you get what you pay for. 

Thanks,

B. Alec

[TwoTired]

1. Is it likely that a bad voltage regulator caused the burnt-out diode?

Probably not.  But, I can't make a guarantee.  Most likely cause of failure is exceeding the current rating of the internal diodes.  This can be done by running the bike without any battery (huge current spikes), a battery with no electrolyte in one of the cells of the battery (large current spikes), or a battery with several cells shorted (over current duration).  Reverse connecting a battery into the system won't do it much good either.

The regulator monitors the state of charge of the battery.  When the battery voltage exceeds about 14.5 V, the "regulator" switches the alternator into low output mode to prevent overheating the battery and loss of electrolyte.  At other times, the alternator is putting out the most it can for the RPM it is spinning.   Battery malfunctions wreak havoc with the charging system, forcing them to do things outside design parameters.  Like blow out, for example.

2. I unplugged the rectifier from the harness before testing it.

Perfect.

3. I say 550F because I compared the VIN(CB550-1235296) and the Engine IN(CB550E-1072796) to the list at http://www.honda4fun.com/modelli/cb550.html. So...is that a typo and I actually have a K? The product code is the same as the earlier K's. Your source is much better than my Italian website!

There are some variations about how Honda sold models in different countries, that I don't fully understand.  I suppose I should have asked where your bike was first sold.  If you are in Italy or some other part of world outside North America, perhaps this doesn't apply to your bike.

In my source book : Honda Motorcycle Identification Guide published by American Honda Motor Company

Your numbers fall into the listed series:
Model Year: 1976    Product code: 374
Frame: CB550-1230001~
Engine: CB550E-1067334~

Differences between the F and K models include; frame, tank, seat, exhaust, and carb setup.  All the F models I have encountered have an "F" in the frame number.

Cheers,

[B. Alec]

So much help!  Thanks!

It's funny, because the bike has a 500 exhaust on it(Product code 323) and 500 side covers, too.  I'm not a purist or anything, so it doesn't bother me, but does make me wonder about carb tuning.  I'm guessing that your Honda book supercedes that website and my bike is a K.  I am in America, so I assume it's an American bike.

So, if my field coils and stator test ok, and my rectifier tests bad, I can assume replacing the rectifier will be ok?  I'd like to test the regulator to be sure.  Is it just a matter of taking it out of the circuit and testing the battery voltage at high RPMs?  I see in the manual that the test involves an ammeter between the regulator and battery and a volt meter on the battery, but I don't have these separate testers. 

Thanks,

B. Alec

[TwoTired]

It's funny, because the bike has a 500 exhaust on it(Product code 323) and 500 side covers, too. 

The pipes were designed and stamped into shape for the CB500 models.  The same pipes were used on the 550's through 1976 model.  Er, at least here in North America.

So, if my field coils and stator test ok, and my rectifier tests bad, I can assume replacing the rectifier will be ok?  I'd like to test the regulator to be sure.  Is it just a matter of taking it out of the circuit and testing the battery voltage at high RPMs?  I see in the manual that the test involves an ammeter between the regulator and battery and a volt meter on the battery, but I don't have these separate testers. 

The alternator only makes power when there is a magnetic field for the stator windings.  This is provided by the field coil. The strength of the magnetic field, determines the output strength of the alternator for any given RPM.  The field coil is energized by the "regulator".  It routes either full battery voltage to the field, for maximum alternator output, or inserts a resistance (10 ohms), lowering the battery voltage provided to the field, and thereby the output of the alternator is reduced.
Simply removing the "regulator" from the circuit will disable any alternator output.
You should be aware that if certain normal conditions exist, full battery, electrical loads balanced with alternator output at certain RPMS, the "regulator" will switch on and off so fast it can't really be monitored with simple test equipment.  That's why the manual shows the test set up the way it does and tests the charging system as a whole.

[B. Alec]

Ok, some more information:

Did a field coil and stator test on both bikes:

'76 550(one with the bad rectifier):
Field coil test with ohmmeter set at Rx10:
      Between white and green wires: infinite resistance with both polarities from the meter
      Between green(ground) and red/blue wire: no resistance.
      Between green and each yellow: infinite
Stator test with ohmmeter at Rx1:
      Between each set of yellow wires; .3x ohms

      This looks like the field coil has a short somewhere/is shot while the stator is good.

'75 550(parts/project bike with good rectifier)
Field coil test:
      White/Green: infinite resistance
      Green:Red/Blue: no resistance
      Green/each Yellow: infinite
Stator test:
      Yellow wires: all .3x ohms.

      This is exactly like the other one. It seems unlikely, but of course possible, that both bikes happen to have bad field coils while one has a good rectifier and one has a bad one. 

Questions:
Did I do the test right? 
Would a bad field coil cause the rectifier to go bad?  If so, why would it only be bad on one of the bikes? 

I've switched out the rectifiers and would just fire the '76 up and test the charging system, but I want to make sure I won't fry the rectifier if I have a bad field coil.  If I understand what you're saying, a bad field coil would get no voltage from the battery via the regulator, and would therefore send no voltage back to the rectifier via the regulator.  No current to rectifier equals no current spike to fry the diodes?

Continuing thanks!

B. Alec

[TwoTired]

The yellow wires are each one end of a stator winding.  The other end of the windings are all tied together. It looks like a Y , schematicly.  Between any two of the yellow wires should read .35 ohms (+/- 10%) and polarity isn't important.  This is fairly hard to measure with simple equipment since it is such a low resistance and the test lead resistance makes up a portion of the reading.

The field coil is the green and white wires.  It is supposed to be 4.9 ohms (+/- 10%).  Polarity indifferent.
Resistance readings range from 0 to infinite.  If you have resistance readings of infinite on your field coils they are open and cannot create a magnetic field.
Either your description or your readings aren't making sense, I'm afraid.

The red/blue is your oil pressure sender.

Questions:
Did I do the test right?

I'm thinkin...no.

Would a bad field coil cause the rectifier to go bad? If so, why would it only be bad on one of the bikes?

Hard to imagine such a senario.  I think there's some false assumptions here.
 

I've switched out the rectifiers and would just fire the '76 up and test the charging system, but I want to make sure I won't fry the rectifier if I have a bad field coil. If I understand what you're saying, a bad field coil would get no voltage from the battery via the regulator, and would therefore send no voltage back to the rectifier via the regulator. No current to rectifier equals no current spike to fry the diodes?

The alternator directly connects to the rectifier.  The rectifier output is directly connected to the battery.  The "regulator" only monitors this later connection. 

What manual are you using?

[B. Alec]

Ok, I'm working from a Clymer and the Honda manual. 

I redid the test to be sure and realized that what I thought was the green wire is actually green with a red stripe(neutral indicator?).  Who knew? 

New readings between actual white and green read 0 ohms resistance. 

I got no resistance on the field coils for both bikes.  Again, coincidence?  I should find a new field coil, shouldn't I? Will it fry my rectifier if I run the bike with a bad field coil? I'd like to re-test the entire charging system with the new rectifier before I shell out the cash for a new coil...

You are very patient; thanks!

B. Alec

[Robert]

Would a bad field coil cause the rectifier to go bad?

Actually yes. As I understand it, the regulator part of the regulator/rectifier provides hi current (1.6 A to the field coil when it measures below 14.5 V after the rectifier, and switches to lo current if there's measured more than 14.5 V.

If the field coil is shortened (no resistance, resistance = 0 ohm) it would be imaginable that two things could happen (if my theory is right that is, please  correct if I'm wrong)

1. Since there is no resistance at the field coil, hi current will exceed 1.6 Ampere
2. Since the field coil is kaput it renders the charging system useless, the voltage after the rectifier will never go above 14.5 V so the rectifier constantly delivers hi current till it breaks.

[B. Alec]

Well, I got impatient so I just re-tested the whole system with the new rectifier and old field coil.  The results were that the battery was kicking out about 14.5 Volts starting at about 4000RPMs.  It starts at 12V+ and starts going up as I up the RPMs to a top level of 14.5.   I take it there's no way that the field coil could be bad if the the battery is getting this kind of charge, right? 

Does this mean my problem is solved and I don't have to worry about my field coil test results or could the coil still be bad and just waiting to fry my rectifier?  I could be misunderstanding the whole thing, but wouldn't a shorted field coil render the whole system useless?

[TwoTired]

Ok, I'm working from a Clymer and the Honda manual. 

New readings between actual white and green read 0 ohms resistance. 

I got no resistance on the field coils for both bikes.  Again, coincidence?  I should find a new field coil, shouldn't I? Will it fry my rectifier if I run the bike with a bad field coil? I'd like to re-test the entire charging system with the new rectifier before I shell out the cash for a new coil...

As I said, the "regulator" is how the field coil connects to the battery plus terminal.  The other Green lead connects to the battery minus terminal through the bike's wiring.  If your field coil is indeed 0 Ohms.  There is no resistance to current flow.  Therefore, all the power in the battery will be dumped into it, and any device along the current path.  There is no protection circuit, so either something will melt in the current path (wires, windings, or regulator internals) while they dissipate the energy as heat.  Or, you will run out of stored energy in the battery.  Current is inversely proportional to resistance in a DC circuit, which this is.  The wire in the fileld windings is normally long enough to have enough inherent resistance to keep it from melting by limiting the current flow. This length of wire (in turns) is required to make the magnetic feild strong enough to generate power in the stator.  Shorted windings mean there are little or no wires operating in the field coil to create the magnetic field. Therefore, the stator output and rectifier output is nil and that won't stress them much at all.
Ohms law I = V/ R.  or, 13 V / 5 ohms is 2.6 amps.  13v/.5 ohms is 26 amps.  13v/.1 ohms is 130 amps.

I suspect you still have test methodology problems and aren't getting an acurate reading of field coil resistance.

Some meters have a diode test function and a separate resistance function.  They both output in ohms but they differ in the amount of voltage applied to the circuit you are testing.  Are you using the correct range?  Have you got a 5 or 10 ohm resistor about that you can compare your measurements to as a reference?

If your field coils are indeed zero ohms, they're junk.

Well, I got impatient so I just re-tested the whole system with the new rectifier and old field coil. The results were that the battery was kicking out about 14.5 Volts starting at about 4000RPMs. It starts at 12V+ and starts going up as I up the RPMs to a top level of 14.5. I take it there's no way that the field coil could be bad if the the battery is getting this kind of charge, right?

I'd say it can't be as bad as as 0 ohms for sure.  Whether you can achieve full rated ouput, or not, is why the Amps meter is part of the testing.  Also, you don't say what lighting is turned on.  That takes power, too, and changes the RPM where 14.5 V is attained.

Does this mean my problem is solved and I don't have to worry about my field coil test results or could the coil still be bad and just waiting to fry my rectifier?

I doubt your field coil will fry the rectifier.

I could be misunderstanding the whole thing, but wouldn't a shorted field coil render the whole system useless?

That's my assertion.

[B. Alec]

Yes, I was doubting my testing ability, too!  I have an analog multimeter with two ohms functions: RX1k and RX10k.  For both settings, the needle went from the base of infinity all the way to the right at 0 Ohms for the Green to White field coil tests on both bikes. 

I have taillight and both front and back turn signals on, but headlight off(technically not even installed). 

I'm going to work then on the assumption that everything is ok, that my testing is faulty, and that my charging system now works.  because it makes me feel better! 

Thank you so much for your help!

[oldbiker]

If your low ohms range is R times 1k then it is NOT sensitive enough to indicate 3 or 4 ohms accurately. What you read as 0 ohms is suspect. Since you read voltage of  12+ rising to 14.5 when you revved up I believe your charging system is now working correctly since you fitted the new rectifier.

[qcextreme]

check this out  http://www.denniskirk.com/jsp/product_catalog/MMYSkuDisplay.jsp;jsessionid=TGY5N3LQ44ZWXLA0WTISM4VMDK0NCIV0?leafCatId=41202&catId=412&store=Main&mmyId=3787    I also i'm in need of a new Rectifier they have them in Denniskirk.com which one fits my needs better does the 1st one replace both Rectifier and Regulator??

[bryanj]

Resistance on the field should be 4.9 ohms and on the stator 0.35 ohms on each pair. I have never found yet a ruined field and to have two rather suggests wrong tests