Battery Sensor bypass question.

Hi, new here, have an XJ750 Seca.

Found this site looking for battery sensor fixes and found the one about putting a 2K resistor in series with the wire. Since the computer expects to see 6 volts I was about to make up a voltage divider using 2 equal value resistors from ign to ground, feeding the middle junction to the computer.

A single 2K resistor is much simplier, but I'm curious if this is based on knowledge that the computer is measuring the voltage across an internal 2K resistance resulting in 6 volts. Has anyone actually measured the voltage going to the computer after the resistor?

 

No, but the assumption is that TTL logic chips are being used and +5 is the common biasing. Check out one or all of the other circuit inputs to satisfy this question for yourself. Report your findings if you can. My 82 isn't up and running yet or I'd post.

 

I'd also like to know what you find. I'd love to get rid of the blinking light.

 

The following info is from.... http://www.geocities.com/MotorCity/Speedway/7795/

If the battery is working correctly, the electrode will sense between 4 and 6 volts.

The Yamaha trouble shooting manual on the computer (found on the XJCD) is using 12 volts to check if light goes out.

 

i tried a few resistors and went with 5.9K
if the key is on for a few minutes and then the the bike is started the light will stay on a while, maybe till the choke comes off
on a normal start it goes off right away
this is with a good battery and good alt. brushes
never did any voltage checks, it just seemed to be a good value to monitor the battery, so thats where i quit

 

The sensor battery I just replaced is still good enough to test with, so I'll hook it up and measure it along with the voltage using a 2K resistor this weekend and post the result. I understand ohms law and how to use it, but that's about as far as my electrical knowledge goes.

 

Over the weekend, I connected a 2.1K resistor between the Ign fuse and the computer's battery sensor wire. Started the bike and the battery test passed immediately, just like it would with a sensor battery. Hit the check button multiple times and it cycled through just fine. I measured the voltage between the battery ground and the sensor wire and got 2.8 to 3 volts with the battery voltage running 14.5 to 14.8 volts from idle to 2,000 rpm. Since the resistor is dropping almost 12 volts, the current is something like 5 ma. I may have messed up or had a poor connection somewhere and I have no idea what the monitor expects, since logic circuits, computers, etc., are black boxes to me. It was too hot to charge, change, and measure it with the old battery, which is too feeble to start the bike. I need to make up a proper wire with bullet connector, etc., so I'll try measuring again if this makes no sense. I'd guess a smaller resistor ~1K would raise the voltage, but would double the current but again I have no idea what might cause potential damage to the computer.

 

Jeepers.... since I originally owned my seca in 1997 the wire has always just had the sensor cut off and a lead running to the (aftermarket) fuse panel (wired into a fused 12v supply on the draw side - not supply).... no resistores and has worked fine?!?!