Motobecane Zener Diode

Does anyone know of a modern replacement for the 6 volt systems zener diode? We have tried a 6.8 volt 50 watt zener but it doesnt seem to keep the lights bright enough. Also if anyone has one for sale let me know.

backwards

Re: Motobecane Zener Diode

What makes you think it is the diode?

I think you could try to bypass it briefly to confirm if it is the problem

Have you tried that?

I can probably get you a used one if you need it

Re: Motobecane Zener Diode

You don't bypass the zener to test it.. you disconnect it. If the lights suddenly get much brighter (do NOT rev the engine high!) then the diode is likely at fault.

I'm still trying to solve the mystery of the 'zener' on the motobecane. I don't think it's a standard zener part, but actually two zener diodes in opposing series. On other mopeds with a zener system, the part is referred to as the 'double zener diode'.

This makes sense for an AC system, as a single zener diode would completely clip one half of the AC waveform, reducing the power output by half, and heating up the exciter coil in the magneto.

I'm still surprised that some old pro hasn't chimed in and set this matter straight.

Re: Motobecane Zener Diode

A double zener diode would explain why it tests both ways at 8.3 volts. Im curous to see if a normal zener diode would work if it grounded out the lights and not the spark. so anode to frame and cathode to head light fixture. so the spark would get 6 volts and the lights would get the zener voltage. (its really late so i hope this makes sence)

dan if you have a diode i could use, let me know.

Re: Motobecane Zener Diode

OK. I might find out about a couple of junkers today

Re: Motobecane Zener Diode

Does anyone have the spec for the zener diode, or one they can read the numbers off of please?

Thanks~M

Re: Motobecane Zener Diode

Well, I stopped by Vetco and they have zener diodes in this format in 10W or 50W. I'm thinking about trying the 7.5v 50W, but at $25 I wanted to do some more research first.

According to this calculator, and another, 50W should be just about right. I'm basing this on a 6v 45W (7500ma) max load, as listed at mopedjunkyard 18W headlight and 21/5W tail are the max numbers I found, though some 6v moby diagrams show as low as 6W/4W/4W lol, and 12V to 18V max input voltage (12v as tested, but i've read it can put out up to 18v).

I think I will go back and try one of those out, got a guy coming to look at the moby tomorrw. The only thing that worries me is this calc and this calc come up with much different numbers, but they require a minimum voltage higher than the output, which is certainly not happening on the moby.

peace,

~M (edited)

Re: Motobecane Zener Diode

***Kim Jong illest*** /

Murder Legendre Wrote:

-------------------------------------------------------

> I'm still trying to solve the mystery of the

> 'zener' on the motobecane. I don't think it's a

> standard zener part, but actually two zener diodes

> in opposing series. On other mopeds with a zener

> system, the part is referred to as the 'double

> zener diode'.

do you mean a waveform clipper?

Re: Motobecane Zener Diode

Talked to the OP about this and he confirmed it's a double zener (he also had a nos one for me, Thanks Nick!). I guess the mystery/search for a suitable generic replacement component continues.

peace,

~M

Re: Motobecane Zener Diode

Well, apparently it was just a bad connection! I re-installed the diode today just to be able to putt the bike around during the day, and all is well XD.

I re-soldered the lead coming off of it (i had already cut it off in anticipation of soldering it on to the new zener), and used some copper anti-seize on the threads. I also put some bulb grease on the connectors, but I had checked those and the ground connection previously, so I think it was either the threads in the aluminium heat sink were oxidized, or the solder joint went bad.

Anyway, hope this can help some people; before you get a new zener, clean the threads and re-solder the connection, even if it looks ok.

peace,

~M

Re: Motobecane Zener Diode

Got a nos unit today (thanks Nick Con!) and the numbers read as follows:

PZ-500OT7719

The third 'o' is wider than the first two, which leads me to believe it's a letter, not a number.

Peace,

~M

Re: Motobecane Zener Diode

Glad it was an easy fix! Yay Motobecane.

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