Rectifier ground burnt

[Andrew1975XS]

Hello everyone,
My name is Andrew, I am a new poster but longtime reader.
I have a problem with my rectifier wire. The ground that plugs into the rectifier gets so hot it burnt through the wiring harness. Harness is new from mikes, the wire is a smaller gauge.
Anyway the bike won’t charge but I’m getting 14.5 volts from the power wire on the rectifier. Battery is good, holding 12.6 volts, rotor slip rings are at 5.5 ohms, stator tests out, not sure how to test the regulator, but the bike passes the slap test. The rectifier also tests out good. I’m at a loss, and I need some direction. The bike I’m working on is a 75, but I figured I’d show three of a kind just to get some interest.

 

[Jim]

Welcome to the forum. Nice collection you have there.
You're not the first to have problems with a Mikes new harness. About all I can suggest is going through the harness, ohming one wire at a time to find the problem. sounds like a power wire might be partially shorted to that ground wire. Would help to have additional info such as OEM or aftermarket rectifier.... combined reg/rec... stock charging system... ignition? Some good closeups would be helpful too. Here's the 75 wiring diagram out of the Tech Section.

 

[Andrew1975XS]

Thanks so much for your reply. All oem parts for charging system.

 

[Paul Sutton]

If you find no shorts then I suggest opening up the harness and replacing the main ground wire with a heavier gauge. The modern wiring often uses a thinner insulation(thin wall). This means heat loss is greater so they can get away with less copper for higher currents. I would suggest , just to be sure, you count the number of strands in the wire and use a micrometer to measure the thickness of a single strand. This will allow you to calculate the total copper in square millimeters. From this you, or someone on this forum, will be able to make a suggestion of what to upgrade the wire too.

I Iike the photo of your XS triplets.

 

[gggGary]

What rectifier and regulator, still the stock separate units?
A pic of the brush area and maybe the rectifier and regulator would be good.
Have you opened the regulator checked the points?

 

[5twins]

Although the wiring diagram above doesn't show it that way, the rectifier ground usually runs into the main harness and connects to the "communal" ground wire running through it. That ground wire exits the harness in the coil area and usually is attached to one of the coil mounting studs. Make sure that connection is clean and tight .....

But, it might be better for you to do as the above diagram shows and run a separate, independent ground wire to the frame for the rectifier. It will be easier to monitor and if it does burn up again, it won't take any other wires with it.

This all leads up to the question you should be asking yourself - maybe it's time to upgrade these components? It's easily and cheaply done using an automotive regulator and a rectifier from the electronics world. Your charging system will work more efficiently and it will ease the strain on your rotor and stator, the two "big ticket" items in the system. This Windy Nation rectifier works well .....

https://www.windynation.com/Rectifier/35-Amp-3-Phase-Bridge-Rectifier/-/218?p=YzE9MjA=

 

[David Toll]

I am using the Standard VR115 voltage regulator, (around $20), as recommended by all on this Forum and one of these Chinese rectifiers, (50 amp, 3phase, 1000v, 5 connections). Only about 60mm x 35mm x 30mm.

Has the required heat sink attached and cost around $4.00. 35 amp is apparently sufficient but I couldn't find one. 5Twins has posted excellent advice on mounting and installation in my "Headlight Wiring" thread. Unhappily, it's Chinese, (so get a few) and I am still awaiting delivery, (so practice patience).

 

[Andrew1975XS]

Ok everyone thanks again for your help in this matter, just started poking around the bike tonight as I have been doing favors for my girlfriend all day.
Anyway, I can disconnect the regulator and the ground won’t heat up, I can disconnect the stator and it won’t heat up either. I unhooked the rectifier ground from the harness like 5 twins recommended and jumped it, but it still heats up. I have tried two different regulators that I have, two different rectifiers, and two different stators and I still get the same result.
The first pic is the regulator itself, then the burnt wire from the harness, the ground on the rectifier itself is fine. The stator is below that and then another pic of the regulator point gap.

 

[Andrew1975XS]

My brother and my grandmother with two of our bikes. The one on the right is the one I’m having problems with.

 

[Andrew1975XS]

I have also disconnected all but the essential wires in the harness to run the bike.

 

[5twins]

The rectifier is fed AC current from the alternator and converts it to DC current that the bike uses. The reason that the black rectifier wire isn't heating up if you unplug the regulator or the stator is because doing that essentially shuts the alternator off. No AC current will be produced and sent to the rectifier.

I think you may need to inspect and do some testing on that new MikesXS harness. There have been some issues with some of them lately. I would test all the wires connecting to the regulator, rectifier, stator, and brushes. Maybe some are being fed power that aren't supposed to be.

 

[nhsteve]

I replaced the harness on a '74 TX that had the portion of the harness that fed the rectifier burnt up when I got the bike. In a short time of use the new one did essentially the same thing (my symptom was that the bike would kick start ok, no electric start). I replaced that section with new and heavier wire, and at the same time went with a new combined regulator/rectifier unit and have had no issues. What I believe happened was that the regulator failed and allowed excessive current to flow (could be mistaken, it was few years back). I did think the harness had light wire when I replaced that bad section.

 

[Andrew1975XS]

I have discovered a single red and white wire that I have not investigated but once unhooked, the rectifier does not heat up. The bike runs fine without it. I have trouble with the charging voltage though, which is why I installed the new harness to begin with. It only goes up to 12.8 volts at 4K rpm. I haven’t tried to turn the regulator up, but I’m getting 15 volts from the rectifier power wire and nothing is heating up. I need to do more work but I just had surgery so it’s gonna be a week or so before I get back to the garage.

 

[5twins]

If you have 15V on the red power out wire of the rectifier, you should have that at the battery too. That red wire is supposed to run to it and supply it with charging voltage.

 

[Andrew1975XS]

Hey 5twins thanks for your continued responses. So when the red wire is disconnected from the harness then I get 15 volts, when it is connected back into the harness, I only get 12.7 volts.

 

[Andrew1975XS]

Found the problem why the ground was heating up. Red wire was connected to the brake lining indicator light. I dutifully plugged that into the red and white harness. It is actually supposed to be brown.

 

[David Toll]

Wire colours have proven to be repeatedly unreliable. There is rarely a match between existing harness colours and the new stuff available and 5t has pointed out some of the differences in original Yamaha wiring between even consecutive models. It can be considerable. It helps to become expert with a voltage meter though often, the cause for failure, lies in an incorrect connection, (like yours). I mistook an activated brake lamp for a tail lamp because I wasn't applying a brake. It was a maladjusted brake switch causing the lamp to light. Persistence and patience is the key. Well done!