Battery Sensor? We Don't NEED No Stinkin' Battery Sensor!

Got a Question here.
I am finishing up the overhaul of my '82 XJ750RJ, and I understand there is supposed to be some sort of battery sensor.
The warning light and display don't show any problems.
I had a look and there is no extra wires, ir dangling sensors in the battery area.
There is a small white with red tracer wire hooked to the battery side of the solenoid, with a distinctly un-Yamaha connector.
I was unable to locate a wiring diagram on the XJCD, so I was wondering if someone could see if their battery sensor wire is white w/ red.
If this is the case, is there any problem leaving it connected to 12v +?

Any insight is greatly appreciated.

Nachoman :twisted:

 

The sensor wire is the red w/ white one. By hooking it up to a power source you are just bypassing the sensor (lol something I need to do with mine actually). One the XS models it is suggested that you wire in a resistor too though. If you want the sensor you can still get them from Yamaha for about $20, it screws into the battery to check the fluid level. The problem is you need to have a battery with screw in plugs not push in. I have a sensor but forgot to order the Yusa battery; I think they are the only ones that have the screw in plugs.

 

I get my batteries from Wal-Mart, and they have a separate hole for the sensor apart from the fill holes/caps.

 

Hey Nacho, I posted the bypass diagrams in the Photo Gallery (that is of course if that is what you want to do). Otherwise, spring the dough for the Yuasa and buy the sensor. There was an extensive discussion on this topic a few months back, hit the back pages. Nick knows how to search our forums for particular topics. I hope that he'll educate me at some point. Good luck!

 

Right, so a 2000 ohm resistor, with a 1/2 watt rating inline should protect the circuit?
I believe the current mod was done a long time ago.
That said, how critical do you think the resistor is?
Am I frying the "computer"?

Nachoman

 

As long as you don't run too far out (+/-10%) you should be ok. I would try to keep it at or slightly below5 VDC. As for frying, I wouldn't be knowing, I expect not. I just bought the correct battery to begin with and left it at that. The red/white wire is your sensor wire by the way, sorry that I failed to mention it in my last post.

 

http://www.xj4ever.com/HCP14180 battery sensor bypass.pdf

 

Wow.....talk about dredging up the past! 11 years----

 

Some thought and speculation as I see it and subject to change as noted by the XJCD or other knowledgeable members. Note I have been running with the 5.6k resistor for the past month with no issues noted.

The original battery sensor installed in the 4th cell from negative battery supplied approximately 6.4 volts to the CMS for battery monitoring - 3x a fully charged battery where each cell would equal approximately 2.13 volts. The original setup was mainly a check for electrolyte level as the voltage decrease to set a fail would equate to a battery voltage of 6.6 volts, well below a useful voltage monitoring spec.

Installing a 2.2k resistor is really only useful for eliminating the battery warning, as that value combined with the internal components of the CMS would not detect a battery low voltage until the battery dropped to approximately 5 volts. Once again too low to be considered a useful voltage monitor.

The more appropriate size of the "bypass" resistor with wiring and switches that are in good working order is 5.6k, which will set the battery warning at approximately 10.8 volts, a warning that would be set in time before the bike would stop running from lack of voltage to power the TCI and ignition coils.

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Quote robbo from another thread:

"battery voltage at resistor when running is 2.7v."

This is really close to what it should be. With no wiring / switch issues the calculated voltage using a 2.2k resistor is 2.88 volts at a battery voltage of 12.8 volts. If the battery warning is intermittent with the resistor then the most likely cause is what Len mentioned earlier, a downstream issue with the ignition switch contacts or wiring causing a momentary open or increased resistance. This should also be visible in the failed condition as a voltage much higher than 2.7 volts. A solid reading of 2.7 volts or so with the constant battery warning would be a bad sign as it would point to internal to the CMS.

CMS internals:

 

So, to be clear, the circuit above is how it's already implemented, except the 5.6k resistor? So, to set this up yourself, you only need a 5.6k ohm resistor between the white/red wire and 12v+ from the battery, correct?

 

yes or any hot connection available

http://www.xj4ever.com/HCP14180 battery sensor bypass.pdf

 

Yeah, saw that, just wasn't sure if the "Sensor Bypass Device" was just a 5.6k resistor or anything more as well, as Rooster's schematic above shows a lot more - which I understand to be the CMS circuit.

 

Is there somewhere to buy the "sensor bypass device kit" from the attached PDF?

 

Upper right hand corner; click the XJ4Ever icon and start a PM with Chacal.

 

Correct. It shows the portion of the CMS that interacts with the battery sensor.

 

Chacal sells the premade setup, or you can make one REALLY cheap - the resistor cost me $1, but came in a 20 pack from Active Electronics here in Calgary, I think they have one in Edmonton too.

Then it's just a wire from the positive battery terminal (or the battery side of the starter relay that's right beside the battery) to the resistor, then from the resistor to the white with red strip wire that should be close to the top of the battery.

If I were to do it again, though, I'd try with a lower resistance. 5k or so. Mine tends to get grouchy at low RPM's, which triggers the blinky red light of annoyance. Maybe there's something wrong with my charging system (though I've never had the slightest bit of a problem in that department) or maybe my resistor is a bit higher resistance than it says on the tin stripes, but I hate that blinky red light.

 

I'd suspect either your particular resistor, or that your altenator brushes are short (or some other low-voltage issue). I'm using a 5.6 K Ohm resistor and never have a blinking light.

 

I would not suspect the resistor (you could measure it to be sure) or the charging system (which is also easily verified) if you are having no issues starting. The more likely cause is the switch contact in the ignition switch that routes the battery voltage to the CMS - it likely needs a good cleaning.

I was thinking you were using the 6.2K, which sets the battery sensor fail at 12V rather than the 10.8v as with the 5.6K. I had thought of suggesting the higher value, but was concerned with the losses (like Wintersdark) that might occur and potentially create false fails. If everything is in good working order, the 6.2K would actually be the better choice.

 

Now that I think about it, you are correct. I do have the 6.2 K installed still. I had forgotten about that conversation. I appreciate the corrrection.

 

hmmm, this sounds pretty plausible. Ignition switch has been exposed to the elements for a very long time and probably never cleaned (I did the handlebar switches but not the ignition switch)... Will have to pop out open and give it a good cleaning and hit with dielectric grease.