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Discussion Starter #1
Hey guys, picked up a neat cafe style '78 CB550. On my ride home wednesday it shut off. After trying to restart it multiple times it just gave out - made me think it flooded. A guy jumped me which allowed me to make it home. Popped in a new battery and it worked well for a little more than 24hrs but then the same thing after stopping to refuel. The starter tried to fire but it never caught. After a few tries, it either flooded or the battery gave out. Lights kept getting dimmer.

My local cycle shop suggested grabbing a multimeter and checking stuff out. The battery reads >12v DC but ~ 8.5 is getting drained while the bike is just sitting with the ignition off. Some youtubers noted that a little resting draw is normal but it is usually less than 1v.

After pulling out the electrical stuff, here's what's going on... (Pardon the blurry pictures)



Here's the electrical with the multimeter connected through the battery's positive. You can see the reading.





The two connections on the left here all go to the motor/brakes/clutch/tach/etc. When either is unplugged, the draw drops to 0.





What is the grey unit on the right in the above picture? When just one of the connections is unplugged, the multimeter drops to .08-.04. Pictures:

Connected


Disconnected - yellow wire







Could this be the problem? What is it and should it be replaced? Or would you recommend taking the bike to the shop to have a professional look at it?

Any advice would be great, thank you!

Unk
 

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ZAMM Fanatic
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Unk, no offense, here's what I'd do, IN ORDER.

First, download and print out a schematic.
Disconnect and charge the battery
Get a friend in who REALLY knows electrical to help you.

In 20 minutes a guy who knows what he's doing can identify what circuit is shorting out your electrical system. You and I could spend HOURS of back and forth online to reach the same point, spread over several DAYS.

Chances are VERY good you've got a very simple problem that will be easy to rectify. Oh and that gray box is your voltage regulator. It controls the stator/alternator to have it put out a steady 13.8 volts to charge the battery while riding.

Cheers!
 

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Discussion Starter #3
Ok, thank you. Got the schematic and the battery charged. I might end up having to take it into the shop. This is a new hobby for me and most of my buddies know more about cheetos and video games than electrical work.

Thanks again
 

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Give wade a try guy. He's led others through some rough stuff. Yeah, I said that wade.:D
 

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Discussion Starter #5
Give wade a try guy. He's led others through some rough stuff. Yeah, I said that wade.:D
Thanks man, really any advice helps me loads.

...Oh and that gray box is your voltage regulator...

Wade, my question was about the rectifier. Sorry for the unclear description. The one with the cooling fins and bolt in the middle, centered in the last two pictures.

Do rectifiers commonly cause a problem like this? Is it something worth changing on my own?
 

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Unk first you want to establish the problem before you start replacing parts. You said that you were able to start it after jump starting the battery, this sounds like you have either a problem in you charging system or a parasitic draw that is making it so you charging system can't keep up.

First off do you have a multi meter, 2nd is do you know how to use it?
 

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+1 on the charging system suggestion. What voltage do you get at the battery with the bike idling and revved to 3K?

Troubleshooting should always be done with a charged battery.
 

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Discussion Starter #8
Unk first you want to establish the problem before you start replacing parts. You said that you were able to start it after jump starting the battery, this sounds like you have either a problem in you charging system or a parasitic draw that is making it so you charging system can't keep up.

First off do you have a multi meter, 2nd is do you know how to use it?
Yeah the multimeter gave the readings off the battery (12.5v), the draw with everything hooked up and the engine off (~8.5v), and with the rectifier disconnected (0.04v). Check out those pictures.


+1 on the charging system suggestion. What voltage do you get at the battery with the bike idling and revved to 3K?

Troubleshooting should always be done with a charged battery.

Thanks. Due to the resting draw, the bike only fires when directly connected to a stronger power source - car, battery charger, etc. Since my brand new charger quit working, checking the power with the engine running is about impossible. Anyone have a suggestion on where to get a new charger?


- - - -

Going along with what you guys said about the charging system:

Disconnecting the mains (left two multiplugs in the second picture) drops the draw to 0.0. Disconnecting the rectifier (right most multiplug) drops the draw to 0.08-0.04. I agree that there is likely a parasitic draw. Since other sources say that there should be some resting draw, this makes me think it comes from the rectifier. Does this happen with rectifiers? Or what else should be checked?
 

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Unk a rectifier allows current to flow in ONLY one direction. They're used to turn AC produced by a stator/alternator to DC that can charge the battery.

(Fun facts, you CAN run headlights on AC, and some Lincolns with windshield defrosting used "raw" AC because you "lose" a lot of power rectifying AC to DC. Problem was that alternator was a $500 replacement item and non-OEM alternators caused OTHER problems to crop up...)

MOST times when rectifiers die they go open circuit. Pretty rare for one to go to short circuit condition. Not impossible... you should be able to use the diode test on your multimeter to check it if it's indeed JUST a rectifier

If your battery only shows 8.5 volts KOEO (key on, engine off) you've got a dead short in your electrical system. It COULD be the rectifier, but it could also be a dozen other things.

You can accidentally melt a few wires, buy a few parts you don't need, and perhaps eventually stumble onto where your bikes problem lies...

If you're DETERMINED to solve it this way, I'd first inspect every wire on the bike for physical damage --- rubbing through the insualtion, etc...

Then I'd disconnect EVERY pin from every connector until I determined EXACTLY which connection(s) resulted in the voltage dropping to 8.5 V

Then I'd get the schematic out, trace that circuit, see where it's supposed to go...
 

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On frying wires and stuff like that

One thing that I have found to keep the 'magic Smoke" from happening is to use a MANUAL battery charger. mine has settings of two and 10 amps--perfect for a motorcycle. Remove the battery from service and hook the charger up to the battery leads. Now you can test the wires without worry of frying anything.

I have also found that a cheap LED trailer light makes an excellent test light. The one that I have only lights up when the polarity is correct for + and - .

My BIL was at his wits end trying to wire up a trailer to his truck [all the trailer wires were the same color] as he was on a schedule and kept blowing fuses on his truck. It was wire trailer, blow fuse. try another wiring solution. Blow fuse. Only two fuses were left...

We had no multimeter at the house but found an old battery charger and made short work of tracing the trailer ground, running lights,and stop/turn signals once the fuse blowing was eliminated. We used the LED and marked what was what from the trailer wiring. Then we hooked the battery charger in place of the truck battery and set it to 2,then 10 amps and no problems. Put the truck battery back in place and no more blown fuses. Of course,my BIL would never think of a compliment for me after I saved his schedule,but what are in-laws for?

I have also used the battery charger to trace some weird wiring on old houses. Just power the circuit with a battery charger and use the LED or a multimeter to test the wiring.
 

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intimidating electronics

slow down. electrics are slower than you are. so don't slow down too much.

open a connector, check all the wires to ground. almost all black wires are grounded to the frame, if all your tests to black wires are to ground, then try the other ones. usually if you find a ground to one of the other wires, that means it has some insulation rubbed off or it is pinched somewhere. if you trace the circuit, and you can't find the short, then it might be a connector broken somewhere in that circuits wiring somewhere.
which ever connector fixes the drain, thats where your short will be..
if its all of them, the chances are, one of the grounds iin that circuit is loose.
 
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