Should sense wire of Honda R/R be grounded?

[amontyg]

I blew a main fuse the other day and have been spending some time trying to figure out why.

I recently installed a R/R from a Honda (Not sure what make and model it cam off of, I can find out if required) and have noticed that the sense wire I was instructed to connect to a switched power source is grounded to the negative battery terminal.

Is this correct? I am testing this by connecting one lead from my meter from the end of the sense wire to the positive battery terminal which reads 12 volts.

What would happen if I disconnected the sense wire and ran without it?

[koolaid_kid]

So, you have a 6 wire R/R, correct?
Green is ground
Red is 12V output
Black is the sense wire and needs to go to a 12V switched wire.
The other 3 go to the stator.

[amontyg]

That is correct.

I am disconnecting the sense wire from the 12V switched source. I am then getting 12V between the sense wire and positive battery terminal. Leading me to believe that the sense wire is grounded. Should the sense wire be grounded?

[koolaid_kid]

That is correct.

I am disconnecting the sense wire from the 12V switched source. I am then getting 12V between the sense wire and positive battery terminal. Leading me to believe that the sense wire is grounded. Should the sense wire be grounded?

Nope. Connect as I directed and you will be fine. Anything else will invite disaster.

[amontyg]

Thanks Koolaid_Kid, but does the observation of getting 12V between the sense wire and the positive terminal mean that my R/R is bad?

[koolaid_kid]

Not at all. In fact, some run the sense wire to the positive terminal of the battery. It works as well, though it does have a constant, tiny drain on the battery when it is not running.

[BassCliff]

Hi,

I recently installed a R/R from a Honda (Not sure what make and model it cam off of, I can find out if required) and have noticed that the sense wire I was instructed to connect to a switched power source is grounded to the negative battery terminal.

This has me confused (which is easy to do). A switched power source would not be connected directly to the negative battery terminal. That would be a direct short in the electrical system and cause a few problems. The sense wire should not be connected to the negative terminal either. It is permissible to connect it directly to the positive battery terminal (i.e. for testing purposes) but this causes a small current drain.



I have my sense wire connected to the tail light wire at the rear brake light switch. The tail light is on with the switch and is a 12v source. There are others. Some members have installed a relay or two to handle extra switched 12v connections.

System Relay Modificiation (PDF by Koolaid_Kid)



Thank you for your indulgence,

BassCliff

[Steve]

If you connect the sense wire to a ground point, the R/R will do its best to try to get the voltage at that ground point to about 14 volts.

Although it is best to connect straight to the battery, there is a very, very small drain, as K_K mentioned. If you ride every day, it probably won't matter much, but if you only ride on weekends, you might want to keep the bike on a Battery Tender.

If you connect the sense wire to a switched wire, like a tail light or brake light feed, check the voltage at the point where you plan on connecting. Some have found almost 2 volts difference between that point and the battery. What would happen in that case is that the R/R will adjust the output until the sense point is at 14 volts, but the battery will actually be close to 16.

That is why it is best to go straight to the battery, or at least use a relay to provide a switched terminal. The relay can be switched by the tail or brake light feeds, it won't care that the voltage is a bit low.

.

[ekabil]

The sense wire is grounded to the negative battery terminal through the RR ground. That's how it senses the voltage. Current must pass through the sense wire. Because voltage doesn't change across two parallel components, but current is divided, the RR is able to detect voltage identical to the voltage of whatever wire the sense is connected to, while drawing a much smaller current.

[koolaid_kid]

If you connect the sense wire to a ground point, the R/R will do its best to try to get the voltage at that ground point to about 14 volts.

Although it is best to connect straight to the battery, there is a very, very small drain, as K_K mentioned. If you ride every day, it probably won't matter much, but if you only ride on weekends, you might want to keep the bike on a Battery Tender.

If you connect the sense wire to a switched wire, like a tail light or brake light feed, check the voltage at the point where you plan on connecting. Some have found almost 2 volts difference between that point and the battery. What would happen in that case is that the R/R will adjust the output until the sense point is at 14 volts, but the battery will actually be close to 16.

That is why it is best to go straight to the battery, or at least use a relay to provide a switched terminal. The relay can be switched by the tail or brake light feeds, it won't care that the voltage is a bit low.

.

Correct. I went through this with my GS and Redman is currently (no pun intended) going through it with his GK. I ended up putting a relay on mine, and I believe he intends to do it with his. The main issue seems to be the ignition switch. I had over 2V difference, he has 1.5V.

The sense wire is grounded to the negative battery terminal through the RR ground. That's how it senses the voltage.

Well, sort of. To be more correct, the sense wire detects the difference in potential in order to determine voltage. Think of how your voltmeter works. You have to place the black wire to a ground and the red wire to the 12V wire being investigated.

Current must pass through the sense wire.

While technically correct, a very tiny amount of current passes through the wire. It is really concerned about voltage, not current. That is why it has such a small current drain.

Because voltage doesn't change across two parallel components, but current is divided, the RR is able to detect voltage identical to the voltage of whatever wire the sense is connected to, while drawing a much smaller current.

This would be a bit confusing to the uninitiated, but is technically correct.

[Steve]

The sense wire is grounded to the negative battery terminal through the RR ground. That's how it senses the voltage. ...

The only problem with that is that the R/R ground is (or should be) ZERO volts. What is it going to sense? The R/R will then do its best to try to raise that to its set-point (about 14 volts), but, because it is a GROUND reference, it will be unable to do so. In the process, it will be putting out well over 15, 16, whatever volts in the effort to try to rasie the voltage of the GROUND point.

NO, the sense wire goes to a POSITIVE voltage point, not a NEGATIVE (or GROUND) point.

OK reading through the statement a few more times, it might be technically correct in that the sense wire is grounded through the R/R ground, but that is not where it should be connected.


.

[amontyg]

I have the sense wire attached to the orange wire right before the brake light switch. When the ignition is on and the bike is not running I get 12volts from this point to the positive battery terminal. If I disconnect the sense wire from the orange wire I get 12 volts from the orange wire to the negative battery terminal. Does this make sense? Should this point see a complete reversal in polarity when the sense wire is connected?

Just to be clear I have the green wire running right to the negative battery terminal. The red wire is connected to the original red lead for the original R/R. I have then run one of each of the three wires from the stator into one of the three yellow wires in the R/R. All connections have been soldered.

[Steve]

If it is "reversing the polarity" like you say, it would be blowing fuses in the process.

You have something screwy going on there.

A couple of quick tests, if you please:
1. Remove the sense wire connection, let it float free
Start the bike, read the battery voltage at idle and at 3-4000 rpm.
2. Leave the bike running, connect the sense wire to the positive battery terminal, record the BATTERY voltage at the same engine speeds.
3. One final test, connect the sense wire to the negative battery terminal, record the BATTERY voltage a the same engine speeds.

Please let us know what you see, but I think a quick look at your results will tell you where to have your sense wire connected.

.

[amontyg]

Thanks Steve, I can't seem to get the bike started at the current moment, although I'm suspicious of the battery being slightly low as the culprit for this. My bike seems to be very sensetive to battery voltage. Also, it's dark now, which is a problem for us apartment dwellers, so I will have to work more on this tomorrow.

I'm not questioning the instructions about where to attach the battery terminal, but I am beginning to wonder if maybe my new R/R is bad?

[Steve]

..., but I am beginning to wonder if maybe my new R/R is bad?

"Begin to wonder" all you want, but if you do the simple tests that I have asked you to do, you will KNOW in about two minutes.


OK, to clarify just a bit, I asked you to do the tests, but did not tell you what you are looking for.

Test 1. Voltage might be anything, but will probably be high, maybe 12-14 at idle and over 15 at speed.

Test 2. Voltage should be between 12-14 at idle, no more than 14.5 at speed.

Test 3. Voltage should DEFINITELY be high, maybe 12-14 at idel and over 15 at speed.
Basically the same as #1, but with the uncertainty factor removed.