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Discussion Starter #1
Hello!

I have a CX500 from 79 with CDI.

It has a problem where the battery is suddenly out of charge. Sometimes its when I come out to the garage in the morning, sometimes when I want to leave a gas station after a fill-up. It seems random and doesn't seem to correlate with the bike sitting or long drives. However, if I bump start it to leave the gas station and get home, it will have enough power to start when I get home. This symptoms could point to a faulty battery, but when I measure the battery (from the guide in the wiki) everything seems okay. It even charges the battery well when testing.

But I decided to test the stator. Here is my results:

1/5 113
2/5 96
3/5 224
4/5 117
6/5 97
7/5 221
9/5 437
9/8 87

A/B 0
B/C 0
C/A 0

A/Ground yes
B/Ground yes
C/Ground yes

As you can see, EVERYTHING is within spec EXECPT the 3 yellow wires (under saddle) which all had continuity to ground. This means a broken stator, right?

It need to have the idle set to a minimum of 1500 rpm, otherwise it won't idle, but that can be carb related. Otherwise it runs great, except suddenly the battery is almost flat (lights work, but not enough power to crank the engine)

Can someone diagnose what is wrong with the bike? Also, what does each yellow wire do?

Thanks in advance!!
 

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You have continuity between the yellow stator wires and ground? That's fubar if so. Generally they'll maintain a low charge in that condition.

What voltage do you see at the battery at 3,500 RPM?

Test the yellow wires back to pin 9 for continuity and tell us what you have. Continuity here will give running problems.

But the poor idle could be anything.
 

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Looks like you have a short to ground on the stator charging coils. Check the yellow wires and make sure you dont have a short to ground on the yellow wires from where it leaves the engine right up to the connector (sometimes I wire will wear and touch the frame). If the wires are all good then the coil is shot and you will need to replace the stator
 

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Discussion Starter #4
The three yellow wires also had continuity back to 9...

Battery voltage at 3500 rpm topped at 14,30
 

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That's your problem. The insulation has failed allowing the battery charging ground to short to earth fubaring the charging. Though your charge seems to be reasonable considering.They have also shorted to the CDI power coils upsetting those.

I think the problem here is mixing unrectified AC with DC.
 

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Discussion Starter #6
After like ten minutes of sitting the battery voltage was down to 12,30. Started it at charged up to 14,30 again.. Is this a battery problem/shot battery?
 

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Discussion Starter #7
Thanks! Could the battery be draining slowly when sitting due to the connection to ground?

Also, can you try to explain the AC DC issue to me?
 

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Your battery also sounds suspect.

I'm not an electrics boffin but..... the 15 coils are arranged in 3 groups {that's why 3 yellow wires}. These groups are phases and they're generating 3 phase AC power. This is rectified in the regulator/rectifier into DC that will charge your battery and power the components.

The 2 coils that power the CDI are individual coils {though linked, this is why the 8/9 reading} and would generate DC.

This is where I'd like someone with more electrical nouse to chime in? What do you get when you mix AC with DC fellers?

Anyway, the pin 9 to yellow short probably doesnt effect your battery charging - but the yellows shorted to earth do. Pin 9 to yellow short does seem to have an effect on power to the ignition system though.
 

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Your battery also sounds suspect.

I'm not an electrics boffin but..... the 15 coils are arranged in 3 groups {that's why 3 yellow wires}. These groups are phases and they're generating 3 phase AC power. This is rectified in the regulator/rectifier into DC that will charge your battery and power the components.

The 2 coils that power the CDI are individual coils {though linked, this is why the 8/9 reading} and would generate DC.
You don't get DC out of a coil, you get DC out of a rectifier. The rectifier is an arrangement of diodes, that force the voltage in the right direction and then followed by filters to smooth out the level, to make it smoother.

This is where I'd like someone with more electrical nouse to chime in? What do you get when you mix AC with DC fellers?

Anyway, the pin 9 to yellow short probably doesnt effect your battery charging - but the yellows shorted to earth do. Pin 9 to yellow short does seem to have an effect on power to the ignition system though.
If you mix AC and DC you get AC with a DC offset. For example if the AC voltage is from + 20 to - 20 V, and the DC its mixed with is +5, the AC voltage will remain unchanged, but range from -15 to +25V. If the DC component is way bigger than the AC, then you'll probably call it DC with noise.

TF
 

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Cool. You understand this stuff. I've got stator faults worked out but barely understand electrical items of this type. It's cause and effect repeated at nauseum I understand.

Now, taken as a given the CDI coils are not meant to be in continuity with the battery charging coils what do you think would be upsetting the ignition system when there is continuity? ;)
 

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Depending on where the short actually is will determine what the effect will be, but suffice to say any short between the CDI coils and charge coils WILL screw the ignition system up big time.
 

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Cool. You understand this stuff. I've got stator faults worked out but barely understand electrical items of this type. It's cause and effect repeated at nauseum I understand.

Now, taken as a given the CDI coils are not meant to be in continuity with the battery charging coils what do you think would be upsetting the ignition system when there is continuity? ;)

I don't believe that a bike with the yellow wires shorted to ground can also have 14.3 battery V at 3500rpm, unless somebody is mixing up infinity ohms and 0 ohms.

TF
 

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Maybe what someone else said regarding the insulation being shot might be true. I would test that by measuring the resistance of the yellow wires to ground, and moving the bundle of wires from the stator around to see if there is a spot where the they are truly grounded. I would use my meter on beep mode to test this.

When I read through this again, it also sounds like the battery won't hold a charge. I would test that by taking it off the bike, and charging it fully, then letting it sit overnight and measuring it in the AM. If its low then the battery is junk. Just to be sure, I'd also check the sense wire for the regulator. If that's got an intermittent bad connection, the bike could be unintentionally overcharging the battery, which ruined one of my batteries.

TF
 

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I don't believe that a bike with the yellow wires shorted to ground can also have 14.3 battery V at 3500rpm, unless somebody is mixing up infinity ohms and 0 ohms.

TF
He stated they are not shorted to ground, but to one of the coils, which may still allow the battery to charge but would effect the CDI unit and/or spark control.
 

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Ah, well find it really hard to imagine the charger putting out 14V with a ground short. Only way I can see that happening is if both ground points (bike chassis and stator, and the battery -ve) were isolated from each other (floating ground). If both are joined as one, the system would be incapable of charging.
 

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Discussion Starter #19
Its wierd.. From the testing I have done its defently charging. But what is wierd to me is the inconsistensy... Sometimes the bike will sit for a week and start right up, with plenty of charge. Sometimes its doesnt have enough charge to start the engine..
Sometimes I will pull into the gas station and then it cant start again because of low charge. If I bump start it at the gas station and drive for 5 minutes, it will have enough charge to start again.

I will also note if I drive with the lights off, the low charge problem seems to appear less. So maybe it can barely charge the battery enough and turning the light off gives it that extra enough power. Someone said that the shorts to Ground i have will make the bike maintain only a low charge...
 
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