Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board Rectifier and zener diode

In process of restoring 67 Lightning. Would like some feedback on the merits of keeping the original rectifier and zener diode. Is there a way to test the units I have to see if they are functioning properly? Or should I buy new? If buying new, which ones are the best? Also, what is a tympanium electric voltage regulator? Is that a replacement option? Thanks.

This is IMO....

The rectifier & Zener diode are ancient technology. If you are doing a restoration for a garage queen...then by all means, fit a rectifier and diode. There is actually information in the BSA shop Manual on how to test them. The Zener will allow limit voltage once it reaches a certain threshold and is harder to test.

If you are going to ride this bike, then go modern. The modern charge controls (my personal preference is Podtronics), have much more stable output and work quite well.

Hi,
If they work, you won't have to spend on replacements.

Connect the electrics. Connect the rectifier and Zener last. Connect the rectifier before the Zener.

When connecting the rectifier, connect the Brown/White(?) wire to the centre plate last; if the fuse blows, replace both rectifier and Zener with a combined regulator/rectifier (see below).

When connecting the Zener, connect the Brown/White(?) wire to the male spade terminal last; if the fuse blows, replace both rectifier and Zener with a combined regulator/rectifier.

When you can run the engine, connect a Voltmeter (or multimeter set to Volts) across the battery; good fully-charged battery, meter should display 12.6V.

Start the engine and raise the engine rpm slowly while watching the meter, it should display Volts increasing with rpm until about 3,500~4,000 rpm, when the meter should display between 13.8V and 15.3V. Continue to increase the engine rpm until you are sure the meter displays the same Volts despite the increased engine rpm. The meter should not display reducing Volts until the engine rpm is allowed to fall below the aforementioned 3,500~4,000 rpm.

Ime, no. Apart from the expense (~$30 each?), some new Zeners are unreliable - allowing DC Volts well in excess of 15V (19V? ). Regrettably, you can't tell if a Zener is faulty 'til you connect it and test it as above, but then some vendors refuse to exchange or refund.

Tympanium is one make of a number of different combined electronic regulator/rectifiers; even Wassell Lucas offer them.

If you buy a reg./rec., I advise one of only two:-

. either https://www.ebay.com/itm/5Pin-Regul...r-HONDA-CB-CBR-600-900-1100/154013786708 plus https://www.ebay.com/itm/5-Pin-Regulator-Rectifier-Male-Plug-Connector-For-Honda-CBR600-CBR600RR-CBR250R/254700995204;

. or Podtronics 3-phase;

... Podtronics is about three times the price of the Ebay one, but has US-based backup if you need it ...

. the Pod definitely doesn't require spark plugs, caps or HT leads to be changed for resistive; the Ebay reg./rec. only might; some other reg,/rec. definitely do.

Reasons I advise only 3-phase reg./rec. are:-

. You can connect your bike's existing single-phase stator wires to two of of the reg./rec.'s three Yellow wires, either detaching the unused third Honda Yellow wire from the plug or insulating the end of the Pod's unused third Yellow wire.

. If you wish/have to change your bike's stator, new ones are all about the same price irrespective of output, which makes the high-output 3-phase stator the most obvious choice(?); 3-phase reg./rec. already fitted, new 3-phase or single-phase stator can be connected; only single-phase reg./rec. fitted (e.g. Tympanium), either you're limited to single-phase stators or you have to replace the reg./rec. too.

If you have/decide to replace the rectifier and Zener with a reg./rec.:-connect the reg./rec. DC wires directly to the corresponding battery terminals, not in place of the old rectifier or Zener connections. I put an automotive blade fuse/holder in one of the wires between battery and reg./rec., to preclude any possibility of a fault in the reg./rec. causing a short-circuit.
. connect the reg./rec. DC+ Red wire to the battery +ve terminal;

. connect the reg./rec. DC- wire (Ebay Honda reg./rec. Green wire, Podtronics Black wire) to the Brown/White wire originally connected to the rectifier's centre plate, the bike's Ammeter will continue to show both charge into and discharge from the battery.

Hth.

Regards,

One more concern, though this isn't likely to be the reason you're asking: if you wish to switch to negative earth you'll need to replaced reg/rec and zd.

I did a quick video on how I test zener diodes (on the bike)

One way to check!

15 volts + will shorten the life of your battery.
As that is a digital meter, it may be a little misleading too.
Better to test with a decent analogue type meter.

Zeners and diodes are ancient technology but that is what many regulators use including Tympanium. The stock system uses the zener on the output side of the rectifier bridge. Newer regulators that use SCRs have them before the bridge because they work by shorting the generator output. A zener passes current when the voltage exceeds a certain value, increasing to its limit. If the SCR was on the output side of the bridge it would short out the battery also.
To test a zener you need a variable voltage power supply and a load resistor. The load resistor is to limit the current needed by the power supply to bring the voltage up to the full zener level.
Any regulator needs a heat sink or it will burn out. The regulate by shorting the excess current to ground and that is all converted to heat.
If you buy a "modern" rectifier/regulator be sure it is not from a bike that uses LED lighting. Those were made for lower generator output. 90's to mid 2000's generally are good.
The two major manufacturers of regulator/rectifiers are Kokusan Denki and Shindengen.
https://www.shindengen.com/products/electro/motorcycle/reg/

Most later type regulators use a band gap reference. Zeners drift about too much with temperature.
Even using a tl431 is a vast improvement over a zener, knee current etc.when driving scr's.
People like shindengen make ic's with the reference and driver in the chip.
I'm not splitting hairs but that's the truth of it.

no they dont .
an ac regulator is shunting the excess phase output across itself ... not to ground ... the induction is shunted not shorted .
when you shunt an inductor the voltage across the inductor is a function of its resistance .
the shunt is so conductive that the voltage is dampened ... not boosted
and voltage moves quickly to zero ... for each regulated phase .

this is not to say that the SCRs dont get a workout , they do .
the scrs make heat ... so does a plane out finned rectifier .
but your typical ac regulator are not burning it as excess voltage ... l

Something like this?

The single zener regulator is on the output side of the bridge and routes excess current across the power leads so essentially to ground. Zeners develop a lot of heat because of the voltage drop cross them. SCR regulators have them on the input side of the bridge and short across the generator coils. SCRs are On or Off so there is less voltage across them and less heat is dissipated in the device. They still need a heat sink or they would not put fins on the metal case.

The forward volt drop on the average scr is around 0.7v so that times it's current is the heat.
allow for switching losses etc. As Dave says you do need a heatsink.
Also the 2nd circuit there shunts via two low side diodes so that dissipation is doubled.
Plus as you say the drop across the bridge for normal supply. The scr's can be placed directly
across the windings, that does reduce heat generated.

The series arrangement of the first circuit will get very hot, a heatsink will definitely be needed
on that when charging at higher currents.

Later mosfet types use the fets as 'ideal diodes' and reduce losses considerably. In a simple fashion
they are used on just the low side as using them on the high side as well complicates gate drive a little.

All, thanks for the all the great info. Looks like a combined electronic regulator/rectifier is the way to go. Definitely want to get the bike on the road again. Are these relatively straight forward to install? Making sense of electrical/wiring schematics is not a strongpoint of mine. Does it require any alteration to the frame or can it be mounted where the rectifier is now (under the seat)?

Hi,
No alteration to the frame but possibly cannot be mounted where the rectifier is now - don't have a Podtronics to measure but the Ebay Honda reg./rec. is: 3-1/2 inches long, 3 inches wide over the mounting holes, 7/8 inches thick; if you're bending the wires out of the plug to route them around something else, I advise an extra inch on the length, to avoid bending the wires too sharply.


Hth.

Regards,

Stasch, it's easy to install from an electrical point of view.

You have a small number of wires coming from the alternator - maybe 2 or 3.
It's important to buy the the correct Podtronics (or similar) box to match your alternator.

A three phase hi output stator will have 3 wires coming out of it.
You connect those to the three yellow wires out of your magic box.

Then you have red and black to +ve and -ve. That's it.

The real issue is where to mount it. I plan to attach mine to the underneath of my
battery carrier.

Steve.

A new rectifier regulator can be mounted anywhere
that it will see some air flow ... but it can also be mounted to take advantage of
Original harness wire locations and purposes .

add the new rectifier-regulators
black (neg) wire into the harness ( at the old brown/w rectifier wire )
... not into the battery .
the old harness has brown w/white striped wires at the old finned rectifier
That can be repurposed and
already provide a fused negitive battery connection ( no exta fuse or wire needed )
using what the original harness already provided is the more expedient method .

The new red output wire goes to any suitable ground .
Could be under the old finned rectifier mounting spot , if its cleaned up ,
Could be the battery positive terminal .

Hi,
Agree. Then the bike's Ammeter will continue to show both charge into and discharge from the battery.

Regrettably, reg./rec. DC- wire colours vary - usually Black but, say, the Ebay Honda's DC- wire is Green, older Tympaniums' Brown ...

Apologies for my earlier error, I had forgotten your bike was a '67 with an Ammeter.

Nothing to be gained by not connecting the reg./rec. DC+ wire directly to the battery +ve terminal.

"Ground" is nothing more than steel parts of the bike conducting electricity to a wire connected at its other end to a battery terminal (battery +ve on your bike). If reg./rec. DC+ isn't connected to battery +ve, but is connected somewhere else on the bike, that connection, the eventual wire to the battery +ve terminal and any other connections in between do not serve any useful purpose but do provide unnecessary additional potential failure points.

No:-

Hth.

Regards,

Appreciate all the great input! Looks fairly straight forward. Under the battery holder might be the best way to go. Again, thanks.

Appreciate all the great input! Looks fairly straight forward. Under the battery holder might be the best way to go. Again, thanks.

I'm coming to this thread quite late, but if you want to see some measurements and a discussion of Lucas Zener diodes, several posts starting with this one, hidden in a thread about magnetos, may be of interest.