Help from you math and electronic gurus (non XS related)

[2XSive]

It's been a minute since I've been active on this site, but I have continued to lurk as time permits. Truly enjoy all the posts, and I hope to make it to at least one rally next year. That aside, I have been having fun restoring my very first bike I had...a 1976 Kawasaki KE175. Rotary side valve. I have it running great, but the last step is the charging system. One thing is certain, the voltage regulator is fried and NLA, unless you want to pay like $200 for used. So I unpotted the original, first Pic. It uses just 4 diodes which I cannot identify. The service manual shows how the regulator operates, pics also attached. The last Pic is me at 16 with that bike. My question....how should I calculate the value of the diodes used? The symbols in the service manual indicate they are PN Junction Diodes, so I am assuming these would be zener diodes? Any thoughts? Thanks in advance for any help....I know there are experts on this forum, or at least people a lot more knowledgeable than me.

 

[2XSive]

Blue and white wire attached to the regulator comes from the magneto charging circuit. Black is ground. By regulating the AC charging winding in the magneto, it also regulates the AC coil used to power the 6v AC headlamp. The charging coil is wound with the headlamp coil within the same winding. There is a small rectifier used downstream to change the 9v regulated AC output to DC to charge the 6v battery.

 

[Jim]

The symbols in the service manual indicate they are PN Junction Diodes, so I am assuming these would be zener diodes? Any thoughts?

What you put up of your manual says the diodes are the "opposite" of zener diodes. That's above my knowledge level. Curious to see what you find out...

 

[2XSive]

I read that as well, Jim. However, the diode symbols in the diagram use that of PN Junction Diodes, aka zener diodes. By looking at each of the three diagrams as to when voltage flows, the positive and negative symbols switch. Could it be that the negative wire rigged to the anode side of the diode creates the opposite effect of a traditional zener config? I'm a bit stumped.

 

[2XSive]

I was.able to determine that the wires are soldered to the anode parts of the diodes, for both the magneto output wire as well as the ground wire. I tested two of the diodes still work, at least they show some resistance on the ohm meter with positive lead on the same side the wires are soldered to. That is, I am assuming it must be the anode side.

 

[Jim]

I read that as well, Jim. However, the diode symbols in the diagram use that of PN Junction Diodes, aka zener diodes.

I'm stumped Larry. Here's a zener diode symbol. They say it's not a zener diode... and their symbology back that up.

 

[jpdevol]

I'm easily confused by all those theoretical transistor properties and such, but I'm not sure Zener diodes existed in 1976 (were known as such). The described circuit could have certainly worked as described regardless.

 

[2XSive]

Hmmm...thanks, Jim. I stand corrected. When I looked up the symbol online it showed a straight line for the Zener, but after searching further, the diagram just reflects a general or junction diode. I sent a PM to Kawasaki out of hope they'd be willing to dig into their engineering archives, but doubt I'll hear anything. There must be a way to calculate the diode sizing and type, based on the voltage and current that it passes. Over my head...but fun trying to figure it out.

 

[Jim]

Without looking it up, zener diodes were used all the way back to at least the 60's, JP. At the least they were around when this text was written, 'cause they say their diode is biased opposite of what a zener would be. Quiet the dilemma... at least for me.

 

[2XSive]

Gotta love 70s tech. This bike uses a cdi ignition, too, when Yamaha and others I think waited until a few years later. Kawasaki was a bit of an early adapter.

 

[Jim]

My BSA Victor uses a zener diode for voltage regulation. It works by cutting off voltage above a certain level.... which was common back in the day and I completely understand.
Kawasaki however, is using a diode that only conducts above a certain level near as I can tell, that current is sent back to the coil to cut it's voltage when it rises above the set value..... basically using inductive reactance to cancel itself out. I know, crazy, right?!?
Never ran across such a system before. I'm completely baffled.

 

[2XSive]

A tunnel diode does what the manual describes, based on my research. Fairly rare from what I can tell.

 

[GLJ]

As far as I remember from my electronic classes a Zenner passes current when the voltage gets above it's threshold voltage. Why it was used as voltage regulation on Brit bikes. Dumped the excess energy. Not real cheap but very simple.

 

[Jim]

A tunnel diode does what the manual describes

Just off the top of my head, that's what I was thinking too. not really versed on tunnel diodes though. I really wish some 'lectrics genius would pop in and educate us.

 

[GLJ]

Kinda like a "avalanche" diode but different. Been too long to remember things I haven't used in too many years.

 

[GLJ]

Like everything in electronics there is a opposite. Just can't remember what it's called. May come to me while I'm sleeping. Or not!

 

[Jim]

As far as I remember from my electronic classes a Zenner passes current when the voltage gets above it's threshold voltage.

I think we're saying the same thing, Greg. The alternator coil charges the battery. The zener diode is paralleled into the coil output and ground. When the voltage rises above the set point, the zener diode starts conducting, directing any voltage above the set point back to ground.
So yes, it conducts when the voltage gets too high, dumping the excess.

I said "cutting off." I should have said "dumping the excess."

 

[2XSive]

Just guessing which is never good when it comes to electronics, but what about a Schottky diode? "In a Schottky diode, the current flows forward when sufficient forward voltage is applied."

 

[2XSive]

Interestingly enough, I figured that factory regulator is configured like a rectifier. I plugged the one AC leg from the magneto that goes to the factory regulator, into one AC leg of this KBPC5010 rectifier, with negative leg to ground, and low and behold I'm getting proper regulated AC voltage to the headlamp, and the DC leg of that rectifier puts out proper regulated voltage for charging the 6v battery. With a little rewiring, it should work. Just don't know whether it will eventually fry the magneto winding and/or whether this rectifier can handle the AC voltage spikes at higher rpms.

 

[2XSive]

After more digging, I did find these automotive diodes that are the exact same dimensions of the factory regulator. Ordered them just to test and see.