atlas questions..again

MikeG · Feb 22, 2020

I know one of these brackets is for the Zener diode heat sink, but I don't know where it goes or what the other bracket is:

Any help greatly appreciated....again. I can't believe how little info is out there for the Atlas compared to a Commando or BSA.

Peavey Jeltz · Feb 22, 2020

The one on the right side is the steering stop. Goes under the headstock attached to the plate on the down tubes. Big end on the up side. No idea where the zener goes. Slick will prolly let you know.

Bernhard · Feb 22, 2020

Zener goes between oil/ battery box .should be bolted towards frame on a clean from paint section. (Needs a good earth)

texasSlick · Feb 22, 2020

Peavey Jeltz said:
The one on the right side is the steering stop. Goes under the headstock attached to the plate on the down tubes. Big end on the up side. No idea where the zener goes. Slick will prolly let you know.

Slick's Atlas pre-dated Zeners, so he dunno where it goes. The rectifier bolted to the under side of the tool box. From the shape of the bracket, it might be that it bolted to the tool box under side, with the rectifier stacked on to it.

Specifically, I am guessing that the wide end of the bracket, snugs against the under side of the tool box, then the stud of the rectifier passes thru the hole and a nut clinches from the top side of the tool box. This arrangement grounds both the Zener and the rectifier, and has the advantage of a short wire run from Zener to rectifier. If this guess is correct, the "Zener/rectifier package" would be more in the valley formed by the front end of the rear mudguard and the frame, rather than between the oil tank and battery box.

Again, this is only a guess ..... I will defer to anyone who has actually witnessed where mounted.

Slick

Peavey Jeltz · Feb 22, 2020

The plot thickens. I thought all Atlas models were alternator equipped and therefor included a zener. My (R)atlas came with only a K2FC mag and I added the alternator and a Podtronics after purchase.

robs ss · Feb 22, 2020

texasSlick said:
Slick's Atlas pre-dated Zeners

So - how was voltage control achieved on yours?
You've got me interested here!

possm · Feb 22, 2020

The Zener bracket [which may be the Item on the left] attaches to the [left I think] front tank mount.

Beach · Feb 23, 2020

robs ss said:
So - how was voltage control achieved on yours?
You've got me interested here!

Voltage control was by zener, mounted on left tank mount in 66 and 67 models. Both my 66 and 67 Atlas are 12v using Podtronics). Neither bracket looks right for 66 or 67 zener mount.
Bikes without zener were controlled by light switch. Crude but effective.

MikeG · Feb 23, 2020

Thanks-Steering stop. OK, I can see where it goes now. I've been able to spot the Zener in a few Atlas photos, and it looks like it's mounted to a round aluminum disc below the left front of the fuel tank as per Possm's description. The wiring harness was in place on this bike when handed to me, and the Zener connection is right there so I guess it's correct then. If so then does the Zener require a ground to chassis? If it does then I can see having to remove a few layers of nice new paint or perhaps just run another wire off the aluminum disc ones I find/fabricate one.

kommando · Feb 23, 2020

The zener needs a good earth route back to the battery or it stops regulating and boils the battery, best if its a wire rather than the frame.

Mike40M · Feb 23, 2020

Yes, the zener diode must have a proper ground. Either a ground cable or via the frame or both (preferable).
If originality is no big issue, replacing the bridge rectifier and the zener with a modern regulator/rectifier is a common update.

Bernhard · Feb 23, 2020

Beach said:
Voltage control was by zener, mounted on left tank mount in 66 and 67 models. Both my 66 and 67 Atlas are 12v using Podtronics). Neither bracket looks right for 66 or 67 zener mount.
Bikes without zener were controlled by light switch. Crude but effective.[/QUOTE

Yes the light switch controls the alternator output.
My 65 Atlas had Zener which had just come onto the market in 1963, with 2x 6 volt batteries, because 12v batteries for motorcycles were not available from Lucas yet.
Most alternators up till about 1963 were 6 volt. Lucas sold 10 000 Zener diode sets, many to private owners untaking their own 6v to 12v conversation. You only have, if you have the old 6v alternators, to change over 2 wires to get 12v. With the Zener of course. The heat sink can be bolted almost anywhere , under the seat was a popular choice, with a separate wire fron the zener to earth ground, it should be exposed to cooling airstream yet well shielded from moisture and dirt. Lucas did a 4 page booklet on how to D.I.Y.

dynodave · Feb 23, 2020

For us with early bikes before zener .... the systems were source/load balanced.
For normal daytime running the alternator was connected with 2 stator coils to the rectifier for horn/ brake light load.
For night time running the headlight switch was turned on = MAGIC= the other 4 stator coils were added on a different sector of the switch to make more power matching the increased headlight and tail light load
So simple a electrical engineer could figure it out.

dynodave · Feb 23, 2020

Yes this certainly was a two step operation going from 6V to 12v which includes the zener.
12V became increasingly important due to the kettering inductive discharge system (points-coil) and thereby shelving the "soon to be discontinued" magneto.

dynodave · Feb 23, 2020

MikeG said:
so then does the Zener require a ground to chassis?

So far only the most obscure circuits have any association with frame/chassis ground.
The zener heat sink assy should have 2 wire pigtail for fat fast-on and a red round lug for + red return

Bernhard · Feb 23, 2020

dynodave said:
So far only the most obscure circuits have any association with frame/chassis ground.
The zener heat sink assy should have 2 wire pigtail for fat fast-on and a red round lug for + red return

Yes the wire from the rectifier goes to the spade connection and the lug to the heat sink to dispose of any excess heat. It was simple but a huge breakthrough at that time, - how technology has moved on.

texasSlick · Feb 23, 2020

robs ss said:
So - how was voltage control achieved on yours?
You've got me interested here!

Same as pre-Atlas Dommies..... with a 3 wire alternator controlled by light switch. Crude, and (sorry Beach), not very effective. I boiled over my battery and took the chrome off left silencer and primary chain case. Then later added a switch to open circuit the alternator ..... OK since in those days, no law to run with lights.

If for any reason the battery became disconnected with the alternator in the circuit, the voltage produced would go very high and burn out every lamp filament on the bike, if that lamp were turned on.

Slick

dynodave · Feb 23, 2020

Bernhard said:
Yes the wire from the rectifier goes to the spade connection and the lug to the heat sink to dispose of any excess heat. It was simple but a huge breakthrough at that time, - how technology has moved on.

The zener heat sink assy should have 2 wire pigtail for fat fast-on and a red round lug for + red return. 1/4" Round red lug is for electrical current return to + ground, the round aluminum discs are for heat dissipation coming from the zener body.

Beach · Feb 23, 2020

MikeG said:
Thanks-Steering stop. OK, I can see where it goes now. I've been able to spot the Zener in a few Atlas photos, and it looks like it's mounted to a round aluminum disc below the left front of the fuel tank as per Possm's description. The wiring harness was in place on this bike when handed to me, and the Zener connection is right there so I guess it's correct then. If so then does the Zener require a ground to chassis? If it does then I can see having to remove a few layers of nice new paint or perhaps just run another wire off the aluminum disc ones I find/fabricate one.

Here is a pic of wires. 2 on spade and 2 red on zener mount stud.

dynodave · Feb 23, 2020

Bill and all did the aluminum plates change shape? Bill's pix show rectangles, but I seem to mostly recall round?
Just pulled the 68 dunstall atlas harness out and mine is round plates and it looks to be stock lucas harness without dunstall modifications. I will add that my harness runner continues past the zener with the horn wires. Horn is mounted right near /above zener assy.

atlas questions..again

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