Topic: CB550 Blowing Main Fuse

[pavlis]

My original problem was a charging system that wasn't charging. In the process of trying to figure that out, I ended up swapping out the existing solid state voltage regulator and replacing it with an old stock vreg---which looked clean inside and had factory point and core gaps.

The battery finally began to get charge with the swapped vreg and I thought the problem was resolved.

Next morning, the first ride with the "repaired" charging system ended after about 3/4 of a mile. Main fuse blown. I swapped in a spare and it blew the instant I turned the key on. And from that moment the main would blow every time I turned on the ignition. Immediately.

In the effort to find what I assumed was a short, I discovered that if I removed the black wire connection to the (OEM) vreg, everything on the bike worked (except, of course, the charging system) the engine ran, lights worked, horn worked.

So now I have:

• a solid state vreg that doesn't charge the battery but also doesn't blow fuses
  
• an original equipment vreg that (for one brief moment) did charge the battery---until it started blowing fuses.
  

Any idea what's going on? Any ideas about what I should try next?  Thanks.

[bryanj]

Try disconnecting the white wire and replacing the black, if fuse blows the reg is at fault if not the white wire or field coil is shorted---usually the wire as coils tend to be bulletproof

[pavlis]

Thanks.

Did that and the fuse did not blow. I'll see if I can find a short in the white wire.

[Gene]

This is why I love this forum.

[pavlis]

Can't find any short in the white wire or field coil.

While checking I got the following resistance values between terminals:

• black terminal-white: 9.9 ohms
• black terminal-green: 36.2 ohms
• white terminal-green: 46.2 ohms

Sound reasonable? I'm assuming if there was a short the resistance would be the big "-1".

[scottly]

Those readings are all way off! With the wires disconnected from the stock regulator, it should read "-1", or zero ohms between the black terminal and the white terminal. A higher resistance reading here is not the cause of the blown fuse.

[bryanj]

Black to white should not connect when not on reg box white to green is the field coil and should be low resistance

[pavlis]

Thanks, Guys. And please pardon my stupidity, but do the resistance readings mean the regulator is toast? And to follow up; any thoughts as to what might have toasted it?

Thanks again.

[scottly]

I'm assuming if there was a short the resistance would be the big "-1".

Wait a second. The big "-1" may actually mean an open circuit, not a short circuit. With the meter set to the lowest ohms scale, connect the two meter leads together and note the reading; this is what your meter will display with zero ohms, or a "dead short". With the white wire disconnected from the reg, measure the resistance between the white wire and the battery negative terminal, and subtract the reading with the leads connected together. For a 550, IIRC, the field resistance is about 5 ohms. If the white lead is somehow shorted to ground, it may have burned the contacts in the reg, causing the 9 ohms you read between the black and white regulator terminals, as well as blowing the fuse. 

[pavlis]

Thanks, Scott.

This is what I got:

• probe-to-probe --- 0.2
• white wire at vReg to batt neg --- 0.4

So the resistance from battery negative to the terminal end of the white wire (not connected to the vReg) is 0.2 ohms; which seems OK.

It's pretty clear something (in the charging system?) fried the vReg --- any ideas what?

These are the numbers I get from the alternator:

• stator (yellow-to-yellow) --- 1.0, 1.0, 1.0 ohms
• white to battery neg --- 0.2  (with the probe-to-probe 0.2 ohms subtracted)
• green to battery neg --- 4.5

[bryanj]

green to battery neg should be zero, sounds like you have a high resistance connection somewhere

[scottly]

Thanks, Scott.

This is what I got:

• probe-to-probe --- 0.2
• white wire at vReg to batt neg --- 0.4

So the resistance from battery negative to the terminal end of the white wire (not connected to the vReg) is 0.2 ohms; which seems OK.

It's pretty clear something (in the charging system?) fried the vReg --- any ideas what?

The white wire having only 0.2 ohms to the negative battery terminal is NOT OK! That should be the reading on the green (ground) reg wire.
The 4.5 ohms is what the reading on the white wire should be.
Is this a stock harness??

[pavlis]

Guys, thanks for your help.

Have been delayed by a bit of "unraveling" --- as every time I touch the harness I find a bad wire or corroded connector.

At the moment I'm unable to run current through the system. Will get back to the post as soon as the situation changes. (Waiting for a 6-position connector block (ignition) and some blade connectors looking for a new battery-to-ground cable.)

Soon.