Topic: WHAT did I do?! - a welding mishap turned into electrical woes

[turkey2143]

So I was welding a cross bar onto the tail of my frame on my 77' CB550 in order to make a bracket for an aftermarket tail light and, to what I thought was cautious enough, I removed the two screw on terminals to my battery. After welding at my neighbor's house, I rode home the 2 blocks to my house and was happy to finally have all my lights working.

After eating a sammich, I went back out to hit the road and before I could pull out of my alley, my main 15A fuse had blown. I put in my spare one and turned the ignition to ON and then watched my new fuse bend, and then break.

So my question to the community is: what did I blow? My voltage regulator? It's only my 15A fuse that keeps blowing each time (2 times and counting). I'm looking at a wiring diagram for my bike, and following the wire leading from my battery. My options seem to be: 1. Starter Magnetic Switch, 2. Rectifier, or 3. Voltage Regulator, and hey why not 4. SSM unit (what is this?)


My guess is the voltage regulator since I've done this before to an old moped.

Any banter/thoughts would be appreciated

[TwoTired]

The 77 Cb550 does not have an SSM.  So, I'd guess you are looking at the wrong diagram.  Probably in the Clymer.  Get a real one from the Honda Shop manual supplements.

It also matters if you have a K model or an F model.

However, both models should have three fuses; Headlight, tail-light, and main.  Main feeds both the head a tail light fuse.  So you could remove those sub fuses as a diagnostic technique.

Make sure you are reading the fuse panel label correctly as the end positions are for spares and the three in the center are actually wired. I fyou put a 7A fuse in the 15A position it won't work with all the lighting on.  Speaking of which, what are you electrical loads?  Are you using more wattage than stock equipment?

Unlikely the Vreg, but if you remove the black wire from it, it is removed from the circuit.

Probabaly the most sensitive component on the bike regarding electrical spikes from welding is the rectifier.  However, that device has no fuses in line with it and is wired direct.  So, it cannot blow the main, though it can muck up the charging of the battery.

Cheers,

[Kevin400F]

Make sure the contacts for the main fuse are clean, bright metal and a tight grip on the fues body. If they're loose/dirty, sometimes there's enough resistance to overheat the fuse and cause it to fail.  But, if this all started when you hooked up a new taillight, try unhooking it.  Maybe its pulling a lot more current than its supposed to.....not quite enough to blow the taillight fuse, but enough than when added to the rest of the bike's electrical load you blow the main.

[754]

Did you pinch, burn through, or move around the taillight or signal wiring?

[lrutt]

Are you sure the rectifier doesn't go  through the regulator then to the battery through a fuse. I'm pretty sure it does. I'm pretty sure Honda would not have designed a circuit that was not fuse protected. Results could be disasterous otherwise.

on a STOCK bike, the ONLY electronic piece is the rectifier, and the common symptom of a bad diode is for it to short. So if that were the case, that could take out the fuse.

Simple enough to test, unplug the rectifier and put another fuse in. If it holds then look at building a new rectifier. Assuming you still have the stock mechanical voltage regulator.

[Spanner 1]

On the SOHC bikes the rectifier is connected directly to the battery, no fuse. Once the battery is installed in the bike it's married to the rectifier !

[TwoTired]

Are you sure the rectifier doesn't go  through the regulator then to the battery through a fuse.

Absolutely.  Any SOHC4 wire diagram will verify.  The regulator and the rectifier are on completely separate power paths to/from battery.  It's far more obvious with the mechanical regulator types.  But even the combined R/Rs have the paths separated internally.

I'm pretty sure it does.

Show me a diagram that concurs.

I'm pretty sure Honda would not have designed a circuit that was not fuse protected. Results could be disasterous otherwise.

When the rectifier shorts, the wiring burns up, provided the battery has enough charged up power do so.
Any SOHC4 wire diagram will, in fact, show this to be true.

Cheers,

[Gaither]

TwoTired

Could a fuse be successfully added to protect the rectifier and/or regulator?

If so, which wire/s and what amp fuse?

Many thanks

Gaither

[TwoTired]

Could a fuse be successfully added to protect the rectifier and/or regulator?

The regulator is already fused at the main. FYI

However, the fuses on these bikes are not really intended to protect the devices, but rather the wiring.

The rectifier is actually more robust than fuses/fuse holders are, unless subjected to abuses such as reverse polarity.

The alternator is incapable of providing more voltage/current than the rectifier can withstand.  It is only the battery that has enough power to hurt it if wired backwards.

If you really needed to protect from reverse polarity battery connections, a fuse could be inserted in the line between the rectifier and the battery at a point electrically before (destination viewpoint) the branch that goes off to the main fuse.

Care would need to be taken so that the fuse connections are isolated from the battery's corrosive out-gassing, if you wish it to remain reliable.  Hermetic sealing would be preferred, or all gold plated contacts.

Note that if the fuse did blow/fail before or while riding, you probably wouldn't know it until the engine quit due to a depleted battery, as there is no charging indicator on the stock bike to tell you the charging system is off-line.

Further, the response time of the fuse would need to be scrutinized.  It would have to blow faster than the rectifier was able to withstand without damage.

All diodes have a "withstand limits" specification.  Some are "never exceed".  A fuse would not prevent the application, only limit the duration of the fault event.  I don't have access to the stock rectifier diode specification.

Does this help?

Cheers,

[bollingball]

Hey boys don't you know he is TwoTired but not asleep!

[Gaither]

TwoTired

It looks as if an additional fuse isn't such a good idea. If it was, you would have already recommended it. Obviously, I continue to almost nothing about wiring, etc!

Thanks for the run-down. I knew you would have the answer. We appreciate your knowledge and your willingness to help. Actually, there are lots of good folks here that help us a lot. Makes this a great Forum!

Thanks again

Gaither

Gaither

[turkey2143]

Source of the problem was (drum roll)... loose taillight wire (green=ground?) was touching the frame

Oh well

[TwoTired]

Source of the problem was (drum roll)... loose taillight wire (green=ground?) was touching the frame

Oh well

I could believe that if the wire was green with a yellow stripe.

Cheers,

[754]

 I win.. I win.. ha.ha.ha...