direct replacement 6 Volt rectifier for Monza

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el_guru
Posts: 24
Joined: Thu Jun 23, 2011 12:10 am

direct replacement 6 Volt rectifier for Monza

Postby el_guru » Sat Feb 10, 2018 3:27 pm

Hi Guys........ again.!

A VERY simple straight forward question thanks...

I have literally spent hours reading up on electrical charging threads and have a dead 6 Volt regulator/rectifier on my 1964 Monza 250.
I will when I have time open it up and replace the diodes that are faulty.

However I need a make and model if possible asap for a modern direct replacement that I can use.

Thanks again for any help...


p.s. I don't need any further advice on checking it etc just a part number and supplier...

ducwiz
Posts: 222
Joined: Tue May 22, 2012 12:52 pm
Location: near Frankfurt, Germany

Re: direct replacement 6 Volt rectifier for Monza

Postby ducwiz » Sat Feb 10, 2018 4:51 pm

I'm afraid there is no direct replacement R-R ("black brick") for your bike.
The Ducati factory once issued detailed instructions how to modify the alternator stator and then use the later wide case R-R. I can send this as a pdf on request.

cheers Hans

p.s. http://www.motoscrubs.com/Ducati_6V_Regulator.htm is a repair guide for the old R-R, on motoscrubs.com

el_guru
Posts: 24
Joined: Thu Jun 23, 2011 12:10 am

Re: direct replacement 6 Volt rectifier for Monza

Postby el_guru » Sat Feb 10, 2018 5:23 pm

Thanks Hans,

I appreciate the reply. However the last thing I want to be doing is pulling the thing apart to modify it to a WC system.

Over the years people have made up rectifiers I was hoping to find one that would do the job as its extremely simple and basic system it doesn't even regulate the voltage...!!!

Otherwise I will replace the diodes that have blown.

Does anyone have a part number for them.?

Thanks again.

JimF
Site Admin
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Re: direct replacement 6 Volt rectifier for Monza

Postby JimF » Sat Feb 10, 2018 6:11 pm

My schematic is a little bit wrong. There are a pair of high power diodes and a pair of low power diodes.

I will try to publish an updated schematic tonight.

There is a very high likelihood that if one of the diodes has failed, it will be one of the high power diodes.

Those diodes are out of production as far as I can tell. They are in a package that employs a metal can. The metal can is then pressed into a cavity in a metal heat sink that is an integral part of the black brick. In this way the heat of the diode is transferred into the heat sink and then dissipated to ambient air.

Ventodue
Posts: 434
Joined: Mon Mar 08, 2010 3:23 pm
Location: Montpellier, France

Re: direct replacement 6 Volt rectifier for Monza

Postby Ventodue » Sat Feb 10, 2018 6:34 pm

el_guru wrote: Over the years people have made up rectifiers I was hoping to find one that would do the job <snip>

Jim will tell me if I'm wrong; but I'm pretty sure that pretty much any full wave bridge rectifier will do the job. I fairly confident this is what Phil Hitchcock advises. And also have a look at this article here:
http://mbvmc.org/restore/diode/diode.html

Loads on ebay for $2 or less.

el_guru wrote: ..as its extremely simple and basic system it doesn't even regulate the voltage...!!!

You SURE about that? Not so, according to the article that Hans linked to.

el_guru
Posts: 24
Joined: Thu Jun 23, 2011 12:10 am

Re: direct replacement 6 Volt rectifier for Monza

Postby el_guru » Sat Feb 10, 2018 6:48 pm

It is a very simple system, that doesn't even regulate the voltage.

The original isn't an easy piece of kit to disassemble though.... :oops: I am amazed at how appalling the electrics are and the connectors, blocks fuses etc are so badly made.

It literally was quicker for me to reassemble the entire cylinder head than to remove, resolder one connection and refit the connector block in the headlamp shell.... :cry: (and I am an ex avionics engineer :oops: )

Thanks for the link.... I have also found a part on Guzzino if anyone has any experience of that part I would appreciate it.

ducwiz
Posts: 222
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Location: near Frankfurt, Germany

Re: direct replacement 6 Volt rectifier for Monza

Postby ducwiz » Sat Feb 10, 2018 7:00 pm

Jim, you are right. I also guess those diodes have disapperaed from the market. Their case # is TO-203, 1/2" press-fit with knurled outer dia. ebay shows a lot of versions made for different purposes https://www.google.de/search?q=einpressdiode&client=firefox-b&dcr=0&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwicts6_g5zZAhWKchQKHVMZDP0QsAQISg&biw=1280&bih=854. They might be found in the (used) 3phase-rectifier boards of the BMW /5, /6, /7 flat twin models (~1970 to 1995?) with BOSCH alternators; most of the Guzzi V-twins also were equipped with this alternator and r-board. The boards are offered on ebay quite frequently https://www.ebay.com/itm/1971-BMW-R75-5-R75-R90S-R90-R80-SM286B-Engine-diode-board-rectifier/292105269165?hash=item4402d4afad:g:yDQAAOSwmCVY~lUR&vxp=mtr, at least here in Germany, for 15-30€, in used condition. From older car alternators (i.e. VW models from '70 to '00) you can also extract them. They all have a more than sufficient power rating for the Monza's weak 60 Watt alternator. But beware: they were manufactured in two different variants or "polarities" (anode or cathode to case), so one must take care to fit the correct type during repair.

We still have some shops here in Germany, which do repair and maintenance on alternators, starters and the like. They often have those diodes in stock as spare parts, and might sell them for a few € each. I personalIy still keep a small stock of them, because I used them many years ago for a conversion of the w/c R-R from 6 to 12 Volts. I suppose there are similar shops in the US, too.

Hans

EDIT: search for "press fit diodes" on ebay. I just cked it, a lot of them are offered there

el_guru
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Re: direct replacement 6 Volt rectifier for Monza

Postby el_guru » Sat Feb 10, 2018 7:15 pm

Hans, veilen danke....

I was actually supposed to be in Germany at the moment.... I have a number of prewar/post war BMW,s now their regulators are complex...!!!

Blimey..... there are a number as you say "press fit diodes" on ebay very reasonably priced, its just a matter of knowing which ones....

ducwiz
Posts: 222
Joined: Tue May 22, 2012 12:52 pm
Location: near Frankfurt, Germany

Re: direct replacement 6 Volt rectifier for Monza

Postby ducwiz » Sat Feb 10, 2018 8:48 pm

You need diodes with 100V blocking voltage minimum and at least 10-20 A continuous load current, so you might order for instance the following "cathode to case" diodes:

https://www.ebay.com/itm/1N3663-DIODE-DO-208AA-400V-30A-FWD-P-F-PRESS-FIT-new-MFR-BSC/130842390578?hash=item1e76d07032:g:~XoAAOxy~ilSS2GJ
https://www.ebay.com/itm/1N3663-DIODE-DO-208AA-400V-30A-FWD-P-F-PRESS-FIT-new-MFR-BSC/132212346318?hash=item1ec8784dce:g:YcMAAOSwK6RZMGle
https://www.ebay.com/itm/1N3661-MOTOROLA-DIODE-NOS-New-Old-Stock-1PC-C496U1F160915/151818904757?hash=item23591ca4b5:g:IKwAAOSwZjJU8Ped

But take care not to order diodes with the "r" suffix. They have reverse polarity/anode to case, will not work at all but make a short cicuit for your battery.

http://mbvmc.org/restore/ducati/ducati%20regulator.html describes the working principle and some tests of the "black brick".

I recommend to start work by localizing the actual fault in the regulator, i. e. checking all diodes, the ballast resistor etc. Also check the alternator stator windings for their resistance and connection to ground, and measure the AC output without any load. Afair FimF stores some test guide sheets on the motoscrubs "tech" page.

Hans

EDIT: https://www.lima-shop.de/en/index.php/cat/c106_Alternator-Diodes.html a german repair/parts shop

Jordan
Posts: 751
Joined: Fri Dec 24, 2010 11:29 am

Re: direct replacement 6 Volt rectifier for Monza

Postby Jordan » Sat Feb 10, 2018 9:16 pm

A friend used to own a 250 Monza that had a non-functioning regulator.
He said it worked well enough without it. That is, the battery did not suffer over-charging symptoms.
I guess the rectifier part of it still worked, or maybe he fitted some other one.


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