RC51 Forums banner

1 - 11 of 11 Posts

·
Registered
Joined
·
23 Posts
Discussion Starter #1
How does the stock fuel guage run? Is it only two wires?

Does it send power through the float to sense level?

Need to know if it's compatible with the existing fuel guage on my lower tank of my '85 Shadow..

Sent from my SM-G930W8 using Tapatalk
 

·
Registered
Joined
·
23 Posts
Discussion Starter #4
Ahhh, grooooovy. I'll fab up a way to keep the OEM guage. Thank you ☺

Sent from my SM-G930W8 using Tapatalk
 

·
Registered
Joined
·
1,580 Posts
The negative from the dash indicator goes to the thermistor in the fuel tank, which is in turn connected to ground. There is always current in the circuit, but not enough to light the dash lamp when the thermistor is cold. So long as the thermistor is submerged in fuel, it stays cold and its resistance stays high, keeping the light extinguished.


When the fuel level goes below the thermistor, the small amount of current in the circuit heats the thermistor which reduces its resistance. As it gets warmer and less resistive the circuit current increases until the dash lamp illuminates.



This is why, even with very low fuel, it takes a minute for the low fuel light to turn on when you first turn on the bike.

It's also why you should not fill your tank immediately after turning the bike off if the fuel light was on. Best to let the thermistor cool off for a bit before shocking it with cold fuel.
 

·
Registered
Joined
·
1,580 Posts
i had a headache with it because i had to build my own fuel light when i changed my dash out for my new unit. it's tricky to get an LED to stay out just with the thermistor as they need SFA to light them up. i ended up running the thermistor circuit through the coil on a relay, and the LED off the contacts. the coil will pass enough current for the circuit to work, but not so much that it will latch the contacts.
 

·
Registered
Joined
·
8,663 Posts
The negative from the dash indicator goes to the thermistor in the fuel tank, which is in turn connected to ground. There is always current in the circuit, but not enough to light the dash lamp when the thermistor is cold. So long as the thermistor is submerged in fuel, it stays cold and its resistance stays high, keeping the light extinguished.


When the fuel level goes below the thermistor, the small amount of current in the circuit heats the thermistor which reduces its resistance. As it gets warmer and less resistive the circuit current increases until the dash lamp illuminates.



This is why, even with very low fuel, it takes a minute for the low fuel light to turn on when you first turn on the bike.

It's also why you should not fill your tank immediately after turning the bike off if the fuel light was on. Best to let the thermistor cool off for a bit before shocking it with cold fuel.
This is what it looks like.
 

Attachments

1 - 11 of 11 Posts
Top