zennor diodes

[stinkwheel]

My wee Russian bike has a universal Chinese charging system fitted. It works amazingly well but I've had a couple of regulator failures which cooked the stator. It's loosely based on the old C90 split coil charging systems. So the small rectangular 4-pin reg/recs.

Thing is I have a choice of either a cheap Chinese reg/rec or an old Honda reg/rec. Currently have a Honda one as two of the Chinese ones have failed and the latest one never worked in the first place but it's probably 30 years old.

It occurrs to me that there is probably no reason I shouldn't fit a zennor diode in paralell to it, then if the regulator fails, the zennor can catch it before the smoke gets out. Seem sensible?

I have no experience of zennors other than being aware they need good heat-sinking. Mainly don't know if they have any resting power leakage. It would be convenient to hook it directly to the battery positive like the reg/rec but should I be fitting it to the switched side?

TL;DR
Can I fit a zennor diode in paralell to a standard reg/rec?
If I do, can it be directly hooked to the battery or does it need to be on the switched side?
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Easy-X]

FYI for those who might not already know...

A standard diode allows current to flow in one direction but not in reverse. At some point though a diode in reverse will fail although at a relatively high voltage compared to the expected application.

A Zener diode on the other hand is made to intentionally fail at a lower and much more specific voltage. As a "save my shit" measure one would place a Zener diode (in reverse) between positive and negative to shunt away voltage spikes. For Mr. Stinkwheel's application I would suggest considering two things:

1) What is it you want to save? Placing the new electronics on the switched side will avoid the problem of any potential leakage current but can the switch handle transient power events?

2) High current Zener diodes aren't really a thing people use these days (translation: probably expensive) but they can be used to control a high current transistor:

https://sound-au.com/appnotes/an007.htm
____________________
Royal Enfield Continental GT 535, Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[stinkwheel]

I was meaning one like this which you bolt to something big and metal. Can usually handle up to 50W: https://www.ebay.co.uk/itm/175559413562

So if the voltage regulator fails, the zenner stops it cooking the electrics.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Easy-X]

If the Zener is this is doing the job of keeping the voltage under 15 volts how will you know if the regulator has failed?
____________________
Royal Enfield Continental GT 535, Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[stinkwheel]

[WD Forte]

I don't know what you have exactly but not sure why you'd need a RR and a Zener diode.
If you do want to use a Zener, select one which has a current capacity or wattage rating greater than the output of the stator or it may over heat and fail.
The old ones were finned to handle/burn off any excess powah.

The D0-5 types like the BZY91C12 are 100W but still need to be bolted to something to help them dissipate the heat and the more surface area the better

Edit:

Musing over the first post, RRs usually fail cos they cant handle the heat
This reminded me how I bolted the scooty one which isn't in much of an airflow
to an ally plate with lashings and lashings of heat transfer compound.
So far so good I haven't had any issues with this setup.
https://www.bikechatforums.com/viewtopic.php?t=333262

https://imgur.com/oQrO7EE.jpg
____________________
bikers smell of wee

[lingeringstin...]

I've been running a zener alongside the standard charging system on my bike for like 30 years and it's always worked fine. In fact it actually saved me a lot of arseache when the normal charging system packed in far from home. Got me home from a rally on the zener without any fuss. If I were building another bike today I'd fit a zener in parallel with the normal charging system as a safety measure anyway. They just work.

[Robby]

I don't understand what you're trying to achieve, I need pictures to understand electronics.

However, I do have some experience with reg/rec failures. All of my experience has been with 80s and 90s Japanese bikes using a 3 phase shunt-type reg/rec. They have always failed "closed" for me, meaning they just become an inert brick. I am aware they can fail "open" on the regulator side - so you still have DC coming out of it, but it's DC over 15v.

My preference for any reg/rec problems is to fit a MOSFET one. More efficient so they run cooler. Last time I bought one (several years ago now) cheap clones didn't exist, only decent ones. That may have changed by now. I would still avoid the cheap ones.

If you want to make it complicated then I assume you're using the zener diode a bit like a fuse, but triggered by high voltage rather than high current. In that case I would put it between the reg/rec output and the rest of the bike.

[stinkwheel]

A zenner diode is pretty much what most non mosfet reg/recs use to regulate their voltage output, but it's small and mounted internally.

Back when bikes had magnetos which output DC, they just had a big zenner in a heatsink mounted somewhere on the chassis connected to a live. It dumps anything over the voltage rating to earth. That was the sum total of the voltage regulation.

I was planning on using one as a backup but wasn't sure if it would potentially leach current to ground. Trick would be to put it on the switched side I think.

This bike has already killed one mosfet and the way it's currently configured, wouldn't really be suitable for one. It uses a cheap and freely available reg/rec but I've had one fail and one bad out of the box. Hopefully the genuine Honda one will hold up though.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[lingeringstin...]

Yeah I used to worry about it being permanently "on" but at the time I was in a hurry and thought I could change it later to be on the switched side, but in my experience it never made any difference being permanently connected to the battery hot wire. I suppose in theory if the diode goes bad it could short out and dump the battery to ground but I've never had that happen so to this day my "temporary" rigging is still in place right off the battery hot terminal. Also I used a 15v negative ground diode and the normal charging system shouldn't get up to that voltage unless something's gone wrong, so the diode isn't even in play. It's a "just in case" measure.