The Great Battery Sensor Elimination Mystery Finally Solved

I had been enjoying the good fortune of being one of the few XJ owners to still have a functional battery fluid level sensor, and then a few weeks ago I was topping-off on battery water; and my 26 year-old plastic sensor was lodged quite firmly into the fill port. In the process of extracting it I successfully destroyed it. I did a quick search of the site here, assuming that there would be some instructions for a quick fix; considering that dealing with bikes that are decades old my problem was probably a common one. I quickly discovered that there was some debate as to the voltage the sensor was supposed to return to the computer in order to avoid the highly annoying phantom warning light. After checking my Yamaha shop manual, where the computer is only shown as a black-box (no schematics of its internal wiring), I decided that it was my moral obligation as and XJ lover and electrical engineer to solve this problem once and for all. After opening my computer up and checking out it's internal configuration I determined the sensor connected directly to some type semi-conductor switch, which essentially reads an input voltage and based on the reading turns a switch on or off. Semi-conductor switches have a trigger voltage, if the chip gets a reading below that voltage the switch is "off," above that voltage its "on". The funny thing about semi-conductor switches is that no current flows into them via their input terminals (Think about measuring battery voltage with a multi-meter; no current flows through the meter). For this reason you don't have the be concerned about overloading the chip with its input voltage. Since the bike runs on a 12v electrical system it can easily be assumed that the input voltage the computer was looking for has to be less than 12v; therefore connecting the sensor lead directly to 12v will solve the phantom warning light problem.

So in short, if your battery sensor is broken, tie the sensor wire directly to the +12v terminal of your battery and you won't have to worry about the annoying warning light anymore; and it will not harm your computer. I've ridden nearly 1000 miles since doing so with no problems. There is no need for resistors or soldering; simply tie it off to the +12v battery terminal.

I've enjoyed being able to come here for information about my XJ and I'm glad I can finally contribute something to help other XJers,

Jay

 

I tied mine into the outgoing side of a fuse in the new fuse panel. It's worked fine for years!!

 

Sweet!
I'll be doing that soon.

 

Re: The Great Battery Sensor Elimination Mystery Finally Sol

Damnit! I just did the resistor installation. Not that it really takes that much more time than just pigtailing the sensor into a b+ wire; but still! :x

 

Ok Jay, what family of chips were in there? I surmised the TTL logic systems were used given the age of the construction. This would put the logic levels at about 5 volts. I understand that the TTL is a very hearty chip and will take high voltage but I am concerned about long term reliability. A quick and dirty voltage divider network isn't that hard to create and gives me a bit of piece of mind (I haven't opened up my computer yet, mayhap I ought to).

 

Re: The Great Battery Sensor Elimination Mystery Finally Sol

Robert, the only thing I was really looking for when I checked out the computers internal wiring was that sensor didn't connect to either a diode or transistor, because in in both of those cases current does flow into them from their input terminals, but with binary logic chip no current enters through the input terminals. They have 5 terminals, + input, - input, + power, - power, and output. Current can flow in and out through the latter 3 terminals but not the inputs. Since there is no current flow, putting a voltage divider between the +12 batt. terminal and the computer doesn't really do anything, as ohms law states that voltage drop is V=IR, no current, no voltage drop. So even with the divider in there your computer is most likely still 'seeing' 12v.

Jay

 

awhile ago i got rid of the sensor too, but realized that the light went on only if the battery was gone, not good
after playing around for awhile i found that a 5900 ohm resistance would let the light turn on for about 30 seconds, after started with a low battery
like when i forget to turn the key off while working on something else
seems to me this is better than just knowing i still have a battery
if you don't want the light to come on, take the bulb out and save it, their all the same

 

Seeing that you've been in there and I haven't, I'm in no position to disagree with you Jay. I have to remedy that, I've got the instrument cluster off right now (got to replace the weather stripping on the glass). Glad you've taken the time to provide first-hand information of considerable value to our population, thanks a bunch!

 

I can't believe the timing of this post. I just bought my first bike, a 82 750 Maxim on Saturday(Aug 25). VERY thankful for all the info the forum members provide.

 

Welcome Kurtman, you've just received precisely what this forum is all about, helping to get XJ knowledge out to those in need. Glad to hear of your recent aquisition, pictures? Price? How many miles? Any funny story behind procurement of said XJ?

 

Re: The Great Battery Sensor Elimination Mystery Finally Sol

Here is my bike. 24Kms

Any funny story behind procurement of said XJ?
I will get back to you on this..

Hopefully the image shows.

I tried the white with red stripe to pos on the fuse box. Battery warning did not go off. Hmmm. Must be something else wrong.

 

After reading a few more posts, maybe I should check my alternator brushes...

 

Well, I have to thank you all again. Measured the brushes (11mm), cleaned the copper plate the brushes make contact too. Put it all back together, walla, 14.5 volts at the battery and the throttle is SO snappy now it's unreal. AND if it doesn't get any better, the BATTERY warning light is OFF.

BIG THANKS..AGAIN

 

The first part of this post should be a sticky.

 

Kurtman, she is beautiful! Great score! Now get the most for your money and get that thing ColorTuned and syncronized. You think she is happy now, just wait 'till you unleash the beast within!

 

Re: The Great Battery Sensor Elimination Mystery Finally Sol

Kurtman,
That is a very sharp looking ride. Just remember, your XJ is like a woman, you treat her right and she'll treat you right (probably more true for XJ's than women). Welcome aboard.

Jay