Voltage spike possible?

R

Rutabaga

Active Member
1976 CT 90I bought several months ago, really great shape, runs great and I’ve put about 500 miles on it in the last ninety days, approx 100 of that on mountain dirt trails. Twice it has blown a fuse under the same circumstances when the bike is stationary but I am trying to start off from a dead stop with the wheels either in sand or mud and the engine starts to pull as I add throttle but stalls. A few days ago it was a rather extreme situation where the mud/rock mix was so thick inside the wheel wells of the fenders the bike would not move in Low Range headed down probably an 8% grade in mud off the mountain. I tried to make it move without destroying the clutch but it stalled and blew the fuse. The mud was solidified like concrete and it took about an hour with a screw drive to remove enough so I could at least move the wheels by hand while on the kickstand. Got them to rotate by hand, replaced the fuse and away we went albeit very slowly and slippery. I am wondering if there is a voltage spike occurring when it stalls under load and the field current collapses causing a spike and resulting in the fuse blowing? I have thought about facing the front wheel into a wall and making it bog down under power to see if I can repeat this occurrence. I have no other electrical issues, everything works fine. I am not an electrician nor will I be offended by questions or suggestions.
Yes, the milk crate is grounded properly.
 

Attachments

  • IMG_4843.jpeg
    IMG_4843.jpeg
    3.2 MB · Views: 43
  • IMG_4842.jpeg
    IMG_4842.jpeg
    2.9 MB · Views: 39
  • IMG_4841.jpeg
    IMG_4841.jpeg
    3.2 MB · Views: 36
  • IMG_4840.jpeg
    IMG_4840.jpeg
    3.2 MB · Views: 40
Sweet bike! and those trails look amazing! where were you riding if you don't mind me asking?

As for your problem, my first thought is maybe your battery is low on acid? my CT90 exhibited some similar funky behavior when the battery was getting low. The battery on these bikes is the voltage regulator for the charging system.

Second, do both your headlight and taillight work? in 75 they made them always on, and adjusted the charging system to create more output all the time to account for that; if one of them is out it can create a fuse-blowing imbalance.

I can't think of specific reasons for why it would only happen in high load, low rpm situations. Other than maybe a intermediate short to ground from one of the connectors or cables that only happens at that specific engine vibration? That might be a little far fetched though.

Last note(well, more of a tips), I hold my milk crete on with worm-drive style hose clamps, makes for a little bit cleaner of an install, very sturdy too! for extra comfort a lumbar pillow is another great addition :LOL:

Hope this helps, -Kyle
 
My 90 popped a fuse last summer. It was the 2nd time in about 20 yrs. But like a dodo, I didn’t bother to check it and just pushed it home the 1 1/2 miles. Let me tell you, pushin makes ya thirsty.

The battery wiring was bulky and cramped, so I took the time to redo it and clean it up a bit. We will see how that does.

Wow, 500 mi in 3 months. You a badass rider. I did 500 in 10 yrs.
 
One of my favorite local spots to ride is Mount Mingus and its trail systems. This is along Forest Road 132, I start at about 5000’ and climb to 7000’ on a 15 mile jaunt up the mountain side then 15 miles back down. The general area is just North of Prescott Valley, Az.
After talking to a number of people I am leaning towards the problem being an intermittent short that is going to require some old fashioned wire inspection time. To answer your question, all lights work all the time, no bulbs burning out, battery is new and acid levels are good, it holds a charge. The general consensus is I have a direct short to ground in order to have a fifteen amp fuse blow. I am committed to pulling panels, the gas tank, battery, headlight rat’s nest, ignition switch, etc in order to solve this little mystery. I most always enjoy the process and frequently get a good grin from the results.
Thanks for the input. Happy trails.
 
Looks like one hell of a trail system! Makes me wish I was on the trails right now. Good luck on the wire hunt. My CB350F pops a fuse every 150 miles or so, I haven't had the gumption to tear into it yet,

Let us know what you find, -Kyle
 
After many conversations and looking here I started pulling things apart in search of an electrical anomaly and something probably pretty common. I think I may have found a potential candidate; the rectifier. I think it may be the original because the wires are riveted to the terminals, something you would have the luxury of doing when building a wiring harness on a pre-production wiring jig. I need guidance from the muses about drilling out rivets from those connectors and ending up with a valid connector for the new rectifier to replace it. My goal is to pull it and test it but replace it regardless. The terminals show significant signs of age and swapping it out now is convenient and preventive maintenance. Still looking for any gross wiring shorts on the remainder of the harness. IMG_4853.jpegIMG_4851.jpegIMG_4854.jpegIMG_4852.jpegIMG_4849.jpeg
 
Pulled the rectifier out today for testing and had to drill out the riveted connectors. I think this is the original unit. That’s 50 years old and according to my tests( CT90Restoration.Blogspot) style it is good but here are the numbers for independent assessment:
G-Y .545
G-P. .541
Y-R .540
P-R .542
R-Y No reading. (OL)
R-P “ “
Y-G “ “
P-G. “ “

Going to put a new one in and continue the hunt for the fuse blower.
 
That rectifier is likely somewhat toxic and made out of selenium. Use caution and wash your hands. Consider the following and you could go even heftier with a 35 amp rectifier.

Digi-Key bridge rectifier part #GBPC2504DI-ND

Manufactured by Diodes, Inc. as part # GBPC2504


GBPC3510 onsemi | Discrete Semiconductor Products | DigiKey Marketplace

Order today, ships today. GBPC3510 – Bridge Rectifier Single Phase Standard 1 kV QC Terminal GBPC from onsemi. Pricing and Availability on millions of electronic components from Digi-Key Electronics.
www.digikey.com www.digikey.com

Typical 25 Amp Silicon Full-Wave Bridge Rectifier
Body has no electrical connection, all terminals are isolated.
Small bikes put out less than 10 Amps so the 25 Amp rating is overkill.
Such low Amps will barely run it warm. No heatsink needed. Bolt to frame.
This unit passes more Voltage to the battery than the stock rectifier.
This unit will withstand 400 Volts reversed and briefly, a 300 Amp surge.
These cost around 5-6 dollars.

GBPC2504-E4/51GI-ND This is the recommended replacement for the above part
number.

Rick
 
Thanks B52 for the links and heads up on the selenium content. I think the one I removed is a solid state later model.
IMG_4849.jpeg
I will replace it with your recommendation of GBPC2504-E4/51GI-ND.
 
The voltage spikes occur on these bikes when you make a hi / low headlight beam switch at 6000 RPM or so. It's an electrical earthquake, comparatively speaking.

Rick
 
Thanks for the heads up. I know the switch works but the HI beam indicator does not currently have a bulb but I don’t ride at night.
Started pulling pieces off today so I could inspect the wiring harness for obvious damage before trying to do continuity checks on the whole nine yards of 49 year old wiring. I’m currently evaluating two options: spend hours visually checking every millimeter of wiring for damage and then doing continuity checks on the very same 49 year old wiring harness and then possibly have to repair it, or, put a brand new harness in there for about the same amount of work and add some more protection in vulnerable spots. What I found today were several places where there was harness cover damage and multiple connector “boots” or other protective sleeves had shrunk leaving the ends of the metal connectors exposed to possible frame contact.
I need to do some research and get a plan together before choosing an option for the wiring and I need to include other maintenance that might be tied into the same time frame.
 
You might as well plan on replacing every last connector. The harness will look great externally and easily pass a multimeter continuity check but might only have a single strand of copper still intact internally.

Rick
 
Well, not surprised.
IMG_4867.jpegIMG_4866.jpegIMG_4868.jpeg
This is the bundle from the stator just at the connector. Haven’t quite located where that would have been but I think in the vicinity of the carb. It’s bent at a really short radius turn to met the other connector. The wires coming out of the case in the top part of the picture are hardened beyond belief. I think this is going to”Full Monty” quickly. I am going to move the rest of the action over to the 90 forum since it will be less generic and more specific to a particular model etc. Thanks for all the help.
 
PLEASE come back with a link to your new thread ! .

Those wires -do- look crispy but it's the corrosion inside the MPC you're holding in the last picture that causes the voltage spikes .

I simply cut the old MPC off and solder the wires , if you're taking any sort of decent care if it you'll never need to dismount the engine again, lasted 50 YEARS SO FAR........

My son's '79 had a similar problem, after a while he gave up and abandoned the bike in my back yard, I was going crazy(er) trying to find the problem and didn't want to drop the engine
 
Oops ;

I had to leave suddenly .

Anyway, the point is / was : I found the short in the black power wire that fed the stoplight switch ~ oddly Honda left enough slack in it that it drooped down and chafed against the inside of the frame where every so often it'd ground out and blow the fuse and usually the $40 seal beam headlight when the alternator spiked .
 
R

Thread 'Full Monty rehab. Maybe.'

During the last four months and 500 miles I’ve owned this 1976 CT 90 I’ve had three fuses blow. The bike is in great shape but it is 49 years old and the wiring shows that clearly.
IMG_4866.jpeg
I’ve decided to replace what I can purchase and rehab what is not available and at the same time do maintenance on other components that need some attention. None of this is unexpected and I have purposely run it in order to find any thing that needs attention, which is very little so far.
IMG_4872.jpeg
I have removed the engine and rear wheel plus all the wiring to the tail area, unbundled the rats...
  • Love

Sorry about forget to set up a link. Hope this does the job.
 
Back
Top