1977 KX 650 b1 HOT rectifier

The reason the rectifiers need heatsinks is because when they are turned on, they dissipate power based on the current multiplied times the voltage drop across them (about 1.5V when turned on). When they are OFF, they don't have much current flow (only a tiny leakage current). That means the power dissipation increases as the charging current required to feed the battery increases.

Locozuna wrote:

Yeah the fins are to dissipate the heat as it bleeds off un-needed voltage.

EDIT TO ADD:
There is a topology of regulator called a shunt regultor which does regulate by "shorting out" one of the phases of the alternator, but the manual on mine shows a standard type configuration with series SCR's not shunt. Hence they get hotter as charging current (or bike electrical system demand) increases. Mine is a single phase and I think it is a series regulator.

However, if the shunt design is used, it does basically short out the excess current to ground.

OK, so alot of real tech talk here and I am really learning alot! If I understand correctly then the stator sends the rectifier AC current and this is changed to DC current and then the system is regulated by the regulator? If there is a problem where the rectifier thinks it needs to keep sending current it will continue until cooked? The battery is fully charged now and still fires up the rectifier like red hot.. How can we best narrow it down?

skydailey wrote:

OK, so alot of real tech talk here and I am really learning alot! If I understand correctly then the stator sends the rectifier AC current and this is changed to DC current and then the system is regulated by the regulator? If there is a problem where the rectifier thinks it needs to keep sending current it will continue until cooked? The battery is fully charged now and still fires up the rectifier like red hot.. How can we best narrow it down?

The rotating permanent magnets on the flywheel spinning inside the stationary stator winding create AC voltage. That is connected to a bridge rectifier set that turns the AC voltage in DC voltage pulses which are applied to the battery, which basically acts like a giant filter capacitor which smooths it into DC with very little AC ripple riding on it.

The regulator design is what I am not 100% clear on: my manual shows a rectifier/reg which is a series type where the switchable diodes (the SCR's) are in series with the battery and turn the voltage from the stator winding on and off.

This is probably atypical or just wrong as many motorcycles use a shunt regulator which means the stator windings connect to a rectifiers which are NOT switched on and off (just standard rectifiers)connecting the generator output to the battery, but there is some kind of shunting SCR wired from each stator winding to ground which basically "shunts to ground" whatever current is more than what the battery and motorcycle need to run at any given time. This means the stator winding is pumping out 100% current all the time and the shunt determines how much is siphoned off to ground.

If the reg/rect module is a shunt regulator, it's kind of hard to guess what kind of failure would make it heat up since the full current output of the alternator stator winding is going somewhere all the time, either through a rectifier to the battery or an SCR to ground.

This is a seriously crappy design method.

Could he use something from this website to make his motorcycle work properly?

oregonmotorcycleparts.com/rectifiers3p.html

Sure looks like it:

oregonmotorcycleparts.com/VRRPM.html

The VRRPM2 is for all permanent magnet alternators equipped bikes that have 2 AC leads from the stator.
This unit is only for bikes with 12v electrical systems.
$89.00
VRRPM2

This unit ships as you see it with about 10" leads and
instructions for you to wire it up. See below for finished
units with connectors.

This unit will is for bikes with 2 AC leads and early Honda singles and twins with a split
charging coil. See article 4 on our FAQ page. Max charging is set at 14.5v. This unit
measures 65 x 95 x 38mm thick. The mounting holes are 80mm center to center and it
may require some custom mounting on your bike.

All Honda singles and twins up through 1978
Kawasaki KZ400, KZ650, KZ750 twin, H2 triple, KH series triples.

So this product takes place of the rectifier and regulator? If so that is great! Will it work on my bike?

skydailey wrote:

So this product takes place of the rectifier and regulator? If so that is great! Will it work on my bike?

That seems to be the claim, I have never used their products myself.

bountyhunter wrote:

skydailey wrote:

So this product takes place of the rectifier and regulator? If so that is great! Will it work on my bike?

That seems to be the claim, I have never used their products myself.

Also listed at Z1E. Click here > Combo Unit

Good Luck!

The first rectifier posted by MFolks from Oregon motorcycle parts is what you need for your bike skydailey:

Could he use something from this website to make his motorcycle work properly?

oregonmotorcycleparts.com/rectifiers3p.html

If you have 3 yellow wires coming from the stator (or alternator) and have a separate rectifier and regulator (

No brown wire.. This system is a seperate rectifier and regulator.

), and your bike is a '77, this is what you need to go with. The second one posted by bountyhunter(

Sure looks like it:

oregonmotorcycleparts.com/VRRPM.html

The VRRPM2 is for all permanent magnet alternators equipped bikes that have 2 AC leads from the stator.

) is for a '78 model with a 2 yellow wire stator permanent magnet type system that uses a combination rectifier/regulator and will not work for your bike. I know because I bought a '77 KZ650 C1 that has a '78 C2 motor that uses the combination rectifier/regulator and I went through a bit of confusion when I had to replace the reg/rec. Thought I could use the '77 rectifier, but had to buy the combo rec/reg. It wasn't until I checked the motor serial# that I realized I had a '78 motor that uses the previously mentioned 2 yellow wire stator permanent magnet type system.

I have a good (I tested it to be sure) rectifier for a '77 KZ650 if you need it. Also have three voltage regulators for the same bike as well if you need 'em. As I posted before, I'd test your rectifier and regulator to see if they're good, then replace as necessary. I repeat, don't buy the combo rec/reg unit from Oregon Motorcycle Parts ...it won't work for your bike. Now the one from Z1 should work, as the ad claims it will replace the separate reg and rec, and is for the '77 C1/B1.
Here is what your rectifier and regulator should look like:

The top pic and to the right is the rectifier. Bottom pic is the regulator.

"If you have 3 yellow wires coming from the stator (or alternator) and have a separate rectifier and regulator"

I have 3 yellow wires a green wire and a red wire coming from the stator. My rect. and Reg. seem to be in good shape "just bought them from oreg. MC parts".. Thank you for the offer! Just spoke to the guy at Oregon MC and he says that as long as the rect. isn't bubbling the paint off it is fine and should get very hot naturally.. Does that sound right?

I have 3 yellow wires a green wire and a red wire coming from the stator.

That part sounds right, which means you have a separate rectifier and regulator setup on your bike. Not sure I follow your meaning when you wrote:

My rect. and Reg. seem to be in good shape "just bought them from oreg. MC parts"

Does that you mean you bought a new separate rectifier and regulator from Oregon MC Parts? Or you bought a combo unit to replace your separate rectifier and regulator? A little confused here...I'm no electrical guru, but I do know that if you're overcharging or undercharging the battery that typically means you could have a problem with the rectifier, regulator, combination rectifier/regulator, or the alternator/stator, as the case may be, regardless how hot the rectifier is (although a smoking hot rectifier is usually not a good sign). Test components and replace as necessary.
A good way to test the rectifier (it worked for me twice, anyway) can be found on Oregon MC Parts website: "3. How do I to test a rectifier?

Start with one lead of the meter (or test light) to the positive lead on the rectifier. Touch the other test lead one at a time to each of the
AC terminals of the rectifier. At this point you will either have continuity or not but it should be the same with all the AC terminals on
the rectifier.

Swap the test leads (still working with the positive terminal of the rectifier) and repeat the test. This test should have the opposite
result as the previous test. Again the result should be the same for each of the AC leads.

Move on to the negative lead off the rectifier and repeat the 2 previous tests. This is test is easier with a test light than with an
electrical meter. The point is to check that power flows one way but not the other and the exact numbers isn’t as important. If your
meter has a buzzer for continuity, this works very well too.

This will catch a bad rectifier 95% of the time. The rest of the time they only fail under load and will usually get pretty hot."

The owner/operator of Oregon MC has a great reputation, and he seems extremely knowledgeable...I'm sure whatever advice he gave you is good. Hope you fix your problem.