Zener dioide connectivity?

aries · May 23, 2011

Hi
I have a single phase RM 23 alternator stator with 3 wires. Apparently these require two zenor diodes be used. Can anyone guide me how the second diode needs to be connected up please. Thanks

L.A.B. · May 23, 2011

On the 850 Mk3, the second Zener is fitted to the D/S Z-plate.
Note that the 850 Mk3 RM23 also uses a half-wave 49181 (2DV 406) bridge rectifier, and that each Zener connects to a stator output wire on the AC side of the rectifier.

L.A.B. · May 23, 2011

I just noticed, if it's a 3 wire stator then it can't be an RM23 ?

Josh Cox · May 23, 2011

Could you post more information, photo ?, the instruction on the unit ?.

Generally speaking you can hook two Zeners in parallel to share to load ( or use a higher capacity heat sinked unit ).

L.A.B. · May 23, 2011

Josh Cox said:
Generally speaking you can hook two Zeners in parallel to share to load

You can, but the two Zeners are then supposed to be a matched pair-if they are fitted in parallel on the DC side.

Josh Cox · May 23, 2011

True, beta matching is often important, but we are not working on the space shuttle here.

L.A.B. · May 23, 2011

Josh Cox said:
but we are not working on the space shuttle here.

Nevertheless, the high output alternator (RM24) kits were normally supplied with a matched pair of Zeners.

http://www.oldbritts.com/17_333131.html

Because of the higher current being produced, a matched pair of Zener Diodes are employed to conduct the surplus current to earth under low load conditions.

It was also recommended that the Zener wires should be approximately equal in length.

Run the 2 brown wires to the Zener Diodes via a route where they can be taped to the existing loom. Ensure that these wires will be equal in length within 100 mm (4") before cutting.

aries · May 23, 2011

Hi All
Yep, I got cofused about the RM 23. This is a single phase 3 wire, numbered 47174, fitted some years ago to my 1972 commando. Concerned that overcharging will cause problems elsewhere. I cannot remember which diode of the rectifier the second matched zener connected to. Cant get my head around electrics and may be easier to buy a power box!!.

L.A.B. · May 23, 2011

aries said:
This is a single phase 3 wire, numbered 47174, fitted some years ago to my 1972 commando.

So I'm guessing two of the three stator output wires (Green/Yellow/ and Green/Black?) are connected together, and then connect to one of the AC terminals on the rectifier, and the third stator wire is White/Green(?) which is connected to the other rectifier AC terminal (the AC terminals are the outer spades on the Lucas single-phase rectifier and the DC ouput is the centre spade terminal)

If so and you have a matched pair of Zeners and a full wave pre-850 Mk3 Lucas rectifier then the Zeners can both be connected to the DC output wire-which is usually Brown/Blue on a '72 model.

aries · May 23, 2011

Thanks for all your input. Try to retain some originality, but have decided to go with a power box. Now gotta figure where to stick it on the bike!
Cheers.

Jeandr · May 24, 2011

aries said:
Thanks for all your input. Try to retain some originality, but have decided to go with a power box. Now gotta figure where to stick it on the bike!
Cheers.

Wise decision :wink:

Jean

Zener dioide connectivity?

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