Topic: Homemade rectifier for my CB750-K4

[jerrybb]

After finally figuring out the no-charge problem, I pinned it down to corroded connections on the main connector from the alternator, the one hidden next to the battery which is no fun to disconnect. Also found that the rectifier was not good, so after checking the prices of new and aftermarket I decided to try to make one per the instructions listed elsewhere on the forum (just search rectifier) and follow the diagrams. I used two Radio Shack #276-1185 and bent up an aluminum box as shown. The wires all connect to the original harness connector, make sure all grounds go to the chassis with nice clean connections. Note, one terminal is not used per the instructions. I left the side of the box open for now for better cooling but may close it up later after I see how hot it gets. The rectifiers are bolted to the alum with brass screws/nuts for the best heat conduction. Maybe I should have use some heat transfer grease behind it, but worse case, I'll have to replace the things. Total cost about $8.  Also had to show a shot of the whole bike, not a museum piece but nice enough for me!  Jerry

[Terry in Australia]

Good job mate, well done! It looks like you've got some other interesting bikes in your garage too Jerry, what are they? Cheers, Terry. 

[Clutch Cargo]

Jerrybb,

What is the current and voltage rating of the Radio Shack #276-1185 bridge?   I will assume that it is low and that is why you used two. 

I did the same job last year.  I used a single bridge assembly from International Rectifier - rated at 35 amps/ 200 VDC - probably an overkill.  Part number is 36MT20ND  - cost $ 19.00  from Digi-Key.    I used a heatsink from an old Pentium CPU chip to cool it.

Check your voltage output - you may have to tweak the regulator output after this type of modification.

[jerrybb]

The Radio Shack  276-1185's are rated at 25a, 50v and the other postings said two should be required because of the sometimes high output of the 750's. Can't give you more info on reasoning, I was only a plumber, not an electronics engineer. When I hook up the voltmeter to the battery I'm getting from roughly 13-14.5v depending on the revs. I know the manual tells the specific outputs at various rpm's, but I think this will work ok. As you say, I can always adjust the reg a bit for more charge.

BTW, re the question about the other bikes in the stable- a '63 Dream thats causing a mystery right now, '68 CL350 Scrambler, '82 CT110 which may be the most fun of all of them!

[Raul CB750K1]

I don't know this particular schematic, but bridge rectifiers are composed of four diodes, with two leads for the alternating input and another two for the DC output. The way the diodes are connected inside is very similar to the star or triangle connection for tri-phase generators, but there is one diode missing, Even when there are four inside, they are connected internally so you can't use two of them and for that reason you need another unit. They withstand high current, are cheap and ready to be bolted for heat dissipation, so no biggie using two units.

[TwoTired]

You need six diodes to rectify a three phase output.  The rectifier bridges chosen only have 4 diodes each.  So, you need two units, using only two doides of the second unit.
If you only rectify two phases with one bridge, you reduce the alternator charge capabily significantly, at least by one third, making a 210 watt 750 alternator into a 140 watt alternator. 

Leave the Vreg setting alone.  It is set to protect the battery from overcharge and boilout on long cruising stretches.  Screw with it and you screw with the battery life. 

Cheers,

[Clutch Cargo]

Here is the bridge that I used - three phase - six diodes.

[maliveline]

how bout posting a step by step procedure on how to make one of these rectifiers from radio shack parts? as far as cutting the wiring harness and plugging the wires into the radio shack components this post is very uninformative.

[the architect]

how bout posting a step by step procedure on how to make one of these rectifiers from radio shack parts? as far as cutting the wiring harness and plugging the wires into the radio shack components this post is very uninformative.

The Search function of this forum is powerful and will unlock the secrets you seek  . Two 2-phase Radioshack bridge rectifiers or a single 3-phase bridge rectifier willndo the trick. Positive to the (+) side of the battery, negative to ground and each of the three phases of the bridge rectifier to each of the three outputs from the field coil of your alternator. And Bob's yer uncle. Personally, I'd splurge the extra $10 for the 3-phase rectifier from Digi Key (I did) and end up with a more elegant install. Just don't forget to heat sink that bad boy.

If you need more, check my build link in my signature. I rewired my entire bike and the information is there.