Positive Rectifier To Battery Wire, Fused Or Not?

I think I got a bit lost with pamcopete's comments. Is the reasoning thus:

• With wiring and fuse as per Yamaha: If the fuse were to pop out the power to the bike would be cut including the alternator field winding, but the alternator would continue in a self-exciting mode. Because the regulator has lost its battery reference voltage the output from the alternator via the rectifier is unstable and possibly high in voltage and this is dumped back into the harness where it may damage sensitive electronics e.g. electronic ignitions.
• However, if the rectifier connects via its own fuse to the battery then the unstable power generated by self-excitation gets dumped outside of the harness to the battery where it is isolated from the electronics by the open fuse.

More Questions:

• Does cutting power to the field winding cause continuous self-excitation
• or are we just talking about the time it takes for the rotor's field to collapse
• or is it the residual magnetic field of the rotor
• or am I totally off the plot??

Thank you for any thoughts.

pamcopete said:

RG is correct. The other thing to consider is having the fuse go open circuit which can happen for a variety of reasons. With the fuse coming directly from the battery and the rectifier on the load side of the fuse, the alternator will continue to provide power to the load. However, without the battery in the circuit, the regulator will not have the stabilizing effect of the battery and could go nuts, producing very high voltages which can fry the electrical system without blowing any fuse. So, the best arrangement is to have a separate fuse from the rectifier to the positive terminal of the battery so if the battery fuse goes open circuit for any reason, you will lose all power to the bike but at least you will not suffer a bunch of fried components. A dead short from the load will blow the fuse and disconnect both sources of power from the load although a dead short will also deprive the alternator rotor of the current needed to produce power..

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That's what I was saying, the rectifier would still be exciting the alternator.

16 or 14 gage wire and how many amps on the fuse?

Scott

not to stir the Pot, but for the technical type, Current/i.e. Amperage does not heat anything.... seriously, it's the resistance in the wire that does the heating.... if you take away all the resistance there is NO heat at all.... that is what super conductors taught us !
A diode can some times be used to replace a fuse stopping any flow of electrons in the wrong direction....
..... when I was Young and trying to keep my Honda 90 going and the rectifier burnt out and melted half the wiring harness I repaired the wiring and tried to make a rectifier myself, I had little knowledge at the time on electronics and made one up with 1n4001 diodes
and took it to school with me and asked the electronics teacher if it would work and he said yes but..... it is doubtful it can handle the amperage it will probably just pop the diodes and you'll be back where you started..... so I tried it...... the diodes popped in about 1 minute when I reved it up ! and that was the end of that experiment, my rectifier came in the next day and 3 days later mom went to town and picked it up for me ! ..... I put it on and everything worked great..... charged the battery and I was elated to have my transportation back again ! My older honda 50cc had no battery and I wanted to fix my 90 like that so I wouldn't have to have a battery in it ....but I never could figure out how to do that. I'm sure it can be done but I just don't know how ! perhaps just replacing the battery with one of today's supercapacitors would suffice ! , not sure ! the honda 50 did have a tendency to blow headlight bulbs though when reved real high...
it would be nice if I could do that for the xs and not have to buy another battery next year ! I've looked at the wiring diagrams for batteryless setup for the XS but I like my electric starter ! LOL so I'm undecided !
......
Bob......

Bob Kelly III said:

not to stir the Pot, but for the technical type, Current/i.e. Amperage does not heat anything.... seriously, it's the resistance in the wire that does the heating.... if you take away all the resistance there is NO heat at all.... that is what super conductors taught us !

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That's interesting enough that it was worth scratching my aching head over it a little. The formula for power loss (heat) is current squared times resistance. But at the same time the formula for current is voltage divided by resistance. In the latter formula as R went down, current and therefore heat would go up. One way out of the conundrum is if current is primarily controlled by a different R than the power loss formula R.

So if you had say a DC motor and two wires and a power source, the current in the circuit would be primarily controlled by the resistance of the motor. Now if you think of the current caused by that through just one wire connecting the motor to the power source, the less resistance in that wire the less power loss. So -- if you used a very thin wire there (high resistance) there would be lots of heat. If you used a thick wire, less heat. This is why you need a thick extension cord for high current stuff. So in that case, less resistance means less heat, working on up to the superconductors, whose benefit is low power loss due to very low resistance.

I have managed to find the reference were I read about certain problems leading to the production of high voltages by the alternator. The Book is Automotive Electronic Systems by Trevor Mellard. The electronic version can be viewed at:

https://books.google.co.uk/books/ab...onic_Systems.html?id=rDYvBQAAQBAJ&redir_esc=y

Of particular interest is Chapter 5 Page 44: Right-hand column and second paragraph down. We have the mention of additional protection being required to deal with over voltage caused by such things as regulator failure, switching off high inductive loads, loose contacts and breaks in conductors. Power loss to the regulator or loss of the battery as a voltage reference for the regulator (the latter was mentioned in Entry 57 by Pamcopete) is effectively regulator failure.

Getting back to Mrtwowheel's original question, Yes there is an advantage to be gained by wiring the rectifiers +ve terminal via its own fuse directly to the battery's +ve terminal rather than sharing the XS's 20A fuse. As we add more and more modern electronics to our bikes this wiring scenario becomes more beneficial in ensuring voltage stability.

Cool Paul, thanks very much for your input.

Thank you Pamco Pete, you always show up at the right time, and it's great to know that there is a better way to wire this and why.

Scott

If our regulator needs the battery to "stabilize" it, the diagram Gary posted in #3 prevents the problem -- since if the single fuse the reg and rec are on blows, there will be no power anywhere on the bike, incl. from the generator.

I think the post #3 diagram is a very good one, the more I look at it. If you want to do something different I suggest you draw it up first of course, but take a picture of your drawing and post it in this thread. Not so we can tear it apart but to help you guarantee you have what you want.

A blown fuse will cut the power to the field winding and the alternator will stop working. In general terms that is true. However the field winding is an inductor so when it has its power cut the magnetic field around the inductor collapses and this can induce unacceptable voltages into the harness that may damage electronic circuitry. This magnetic field collapse occurs very quickly and may put circuitry at risk for a millisecond or so. This senario should be designed into a modern regulator with a diode added to dump any induced current to ground. In a similar manner high voltages at the rectifier end should also have been dealt with, perhaps with a zener diode.

So is it necessary to reroute the rectifier output via a separate fuse? Maybe Yes, maybe No:

• If you have a points ignition and no modern electronic circuitry such as GPS/Phones/Voltmeters connected then I do not see what harm a millisecond or two of rough electricity is going to do.
• If you have just a $2 Chinese voltmeter fitted and oneday a rough bit of electricity burns it out then you probably would not be too bothered. You could live with that.
• If you have modern electronics running such as electronic ignition you may want added protection or just be happy with the protection built into your modern rectifier/regulator - This is probably my view.
• However, if you are building a harness for your bike and you want the maximum protection for your modern electronics then you may make the changes to the rectifier/battery wiring. You may even add a few more protection devices at the same time.

Each person will make there own decision based on what risks they consider to be unacceptable or improbable. We know the potential risk in this case but do we individually feel it necessary to rush out and cut into our harnesses????? I will not be, but I may consider doing this if circumstances changed.

Personally I am glad the question was raised, I learnt a little bit more. I better understand why people recommend ditching that old XS fuse box in favour of the blade fuse system and its better contacts.

^Blowing the fuse at the battery wouldn't be any different than turning the key off.

I agree, and the regulator has circuitry built in to dump the induced current. So I will not be making any changes. But some people like to go a little further with their projects, self-satisfaction or peace of mind or best practice?????

My Current Stock Fuse box really does SUCK.... intermitant contacts pleg it even though I cleaned it about 3 months ago , it started giving me trouble again last week so I took it all apart and cleaned it again, the problem with them are the fuse clips in the manifacturing proccess they bent the clips in a stamping operation, and over time that thin crushed corner brakes leaving one side of the clip broken off so I have been cleaning them and putting them back together in their plastic base which holds them together bending the clips for better pressure on the fuse is a must after they brake like that, so Obviously, it needs replaced..... I was going to get the standard 4 bay bladded fuse holder but may get a 6 bay just so I have extra places for fuses to go , if I want to add something.
my question is , if I added a fuse for the regulator/rectifier red wire , what fuse should I use in it ? a 20 amp like the one before it ? or perhaps a 15 amp ?
.... I haven't done the math on it and I don't know how much the Reg/rec. draws anyway.... should be minimal so a small fuse should do the trick !
.... your thoughts ?

.....
Bob.........

I PM'd pamcopete about the fuse size, hopefully he will post a suggestion on this thread. I'm just guessing that a 10 amp fuse might do it, just guessing. It would be terrible to set up an intermittent fuse blowing situation.

Scott

that would happen if you used too small of a fuse, otherwise it should be fine,....
I like the idea of a Zener diode to catch the excessively high voltage that we get every once in a while on these bikes, something to shunt say 16 to 17 volts off to ground or perhaps help the regulator do a better job ...as their fairly sloppy in real life.... 14vdc to 15vdc
is in the ball park but seen people with complaints of 17vdc when revved up ... and that's hard on everything !
i think mine puts out 15.5 vdc at 3 grand RPM and that's fairly high.....
.....
Bob....

On the XS D-model and later the alternator rating is 16A at 5000rpm so the fuse needs to deal with 16A output to the battery at times. Already the harness has a 20A fuse to protect against short circuits including the red wire to the rectifier. Therefore a 20A fuse will be my choice as it reproduces what Yamaha already has in place.

My priority is really to fuse the blue wire to the tail light as this has been highlighted in the past as a common source for a short circuit with the effect of shutting down the whole bike as it is wired directly to the 20A fuse:

http://www.xs650.com/threads/79-fuse-diagram.2128/
(See Entry 8 by Pamcopete)

Fitting a fuse here is a more practical and proven issue rather than fusing the rectifier to battery which strikes me as a somewhat more academic/theoretical and nice to do kind of thing. But if I were making my own harness I would do it.

Paul, with the condition of my drivers license at this moment in time, I would rather my bike not run, instead of blowing a separate fuse for the taillight.

Scott

Bob Kelly III said:

that would happen if you used too small of a fuse, otherwise it should be fine,....
I like the idea of a Zener diode to catch the excessively high voltage that we get every once in a while on these bikes, something to shunt say 16 to 17 volts off to ground or perhaps help the regulator do a better job ...as their fairly sloppy in real life.... 14vdc to 15vdc
is in the ball park but seen people with complaints of 17vdc when revved up ... and that's hard on everything !
i think mine puts out 15.5 vdc at 3 grand RPM and that's fairly high.....
.....
Bob....

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If you have a proper stock type charging system, you will never get high voltages, unless the regulator loses its sensing voltage. Now if you have a PMA and capacitor system......................yes the voltage can swing very high and low. I use an automotive VR-115 regulator, and the voltage never exceeds 14.2 volts. Your bike's voltage should never exceed 14.5 volts. Any voltage above 14.5 volts is hard on the battery. Any voltage above 15 volts is hard on bulbs and ignition systems. Yes, if your bike goes to 15.5 volts a 3000 rpm, you badly need a new regulator.

Paul quote:
"Fitting a fuse here is a more practical and proven issue rather than fusing the rectifier to battery which strikes me as a somewhat more academic/theoretical and nice to do kind of thing. But if I were making my own harness I would do it."

Yes, Pamcopete's suggestion to fuse the rectifier independently and directly to the battery, is based on a rare theoretical event occurring. Very low priority in my mind. However, its not uncommon to hear of bikes having electrical short circuits in the tail light circuit. I'll be fusing my tail light very soon.

retiredgentleman said:

However, its not uncommon to hear of bikes having electrical short circuits in the tail light circuit. I'll be fusing my tail light very soon.

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This is another good example of a fuse providing something besides protecting the wiring.

The box will be mounted low on the hardtail. The main harness, starter cable and ground cable will enter the box through the grommet on the lower front of the box. There are drain holes in every compartment. There will be a black vinyl cover for the box with faux straps and buckles and fringe. The battery strap is not mounted yet. In the box are the battery, starter solenoid, regulator, fuses and safety relay. Every connector is crimped and soldered.

Scott