Fuel Level Switch

[BramF]

Oil pressure and neutral light all word like they should. 

Usually the low fuel light would come on at 250km. I have gotten to this milage a few times recently but haven't dared to ride much further without fueling up, what should be a 'normal' range for the fuel light to turn on?

[LowRyter]

The fuel light on mine would come on at 130-140 mile range.  I can't tell you anymore since the odo reset stem fell out of my speedometer.  I've declined to buy another one and relying on the light now.  

BTW- I purchased a replacement fuel level sensor for my EV and the replacement comes on about 20 miles fewer than the old one did.   I just keep that in mind and know I have a few more miles of gas.  

[docc]

Mine typically begins to glow, off and on, around 150 miles/ 240 km. By the time it is full on and bright, I'm at the roadside performing the Tip-Slosh . . .

[gstallons]

6 hours ago, BramF said:

Oil pressure and neutral light all word like they should. 

Usually the low fuel light would come on at 250km. I have gotten to this milage a few times recently but haven't dared to ride much further without fueling up, what should be a 'normal' range for the fuel light to turn on?

All joking aside , there is no " normal " on ANYTHING involving a MotoGuzzi . 

[gstallons]

FYI .... everyone needs to reread the entire thread on this subject . It would have saved me a lot of trouble TRYING to figure out how it works .

[docc]

On 2/28/2021 at 10:23 AM, BramF said:

Oil pressure and neutral light all word like they should. 

Usually the low fuel light would come on at 250km. I have gotten to this milage a few times recently but haven't dared to ride much further without fueling up, what should be a 'normal' range for the fuel light to turn on?

 

1 hour ago, gstallons said:

FYI .... everyone needs to reread the entire thread on this subject . It would have saved me a lot of trouble TRYING to figure out how it works .

Kiwi_Roy's first post in this thread is very explanatory. Plus, the reminder that the connectors for the Fuel Level Sensor and the Electric Petcock can be switched.

And that is decidedly ungood!

 

[LowRyter]

6 minutes ago, docc said:

 

Kiwi_Roy's first post in this thread is very explanatory. Plus, the reminder that the connectors for the Fuel Level Sensor and the Electric Petcock can be switched. And that is decidedly ungood!

 

Hence, getting  a new sender on my EV.  

[gstallons]

Uhhh , you connected them wrong ?

[Tinus89]

On 2/22/2021 at 3:42 PM, Kiwi_Roy said:

The sensor is a thermistor, no capacitance at all just resistance that changes with temperature, yours read 1.4k because it was reasonably warm then you dipped it in fuel and cooled it down.

I just went through this again with a V7 owner, he took the regular speedo off snd wanted to use a 12 Volt LED in its place.

He tried using the LED directly with his sensor but of course found it was always lit.

I tried to talk him into using an incandescent like the VIIs use but he wasn't having it

Measuring the sensor on my V7 the thermistor is ~1,800 Ohms when cold (it will vary slightly depending on your fuel temperature) When the fuel drops below the sensor the V7 sensor starts to warm slowly until it's only around 90 Ohms.

You have to be really careful not to supply too much current as the sensor will just keep getting hotter and hotter until it fuses in a puff of smoke, the small lamp that the VII comes with is nicely balanced for the sensor, as the current goes up it lights and the current falls back. The V7 dash does a similar thing electronically, it limits the current to 75 milliamps.

 

I worked out that 150 Ohms was a good value to use in series with the sensor, it will pass enough current to warm it up but not enough to fuse it, the 12 Volt LED is wired in parallel with the resistor, it doesn't draw anything when the sensor is cold but is reasonably bright when the sensor warms up

On my V65 Scrambler, I changed all the bulbs (and the whole dash) for LED's. My tank came with a level sensor which I think (but will have to take those measurements) works the same way. This is the gauge: https://www.stein-dinse.com/en/nml-moto-guzzi-petcock-electrically-left-side-mille-gt-sp/item-2-1084757-23105370-.html

So obviously I discovered the light is always on. Reading  your story, would installing a properly sized resistor in series with the fuel gauge be an option, with the LED parallel to the resistor?

[docc]

1 hour ago, Tinus89 said:

On my V65 Scrambler, I changed all the bulbs (and the whole dash) for LED's. My tank came with a level sensor which I think (but will have to take those measurements) works the same way. This is the gauge: https://www.stein-dinse.com/en/nml-moto-guzzi-petcock-electrically-left-side-mille-gt-sp/item-2-1084757-23105370-.html

So obviously I discovered the light is always on. Reading  your story, would installing a properly sized resistor in series with the fuel gauge be an option, with the LED parallel to the resistor?

Good question. It would be great to see @Kiwi_Roy back on! Sadly, he hasn't visited in a while  . . .

[Weegie]

If you know the original bulb wattage, I cannot be arsed looking it up, you can easily work out the filament resistance then just wire in a resistor in parallel of the same value and it should work as @Tinus89 has already stated.

No rocket science in the circuit, Ducati did the same thing back in the day, probably other Eye-Tal-yin producers.

Still freaks me out a near empty tank, full of fumes and an electric current passing through a thermistor in the space.

What could possibly go wrong, I mean TWA 800 was a fluke right?

[p6x]

4 hours ago, Weegie said:

What could possibly go wrong, I mean TWA 800 was a fluke right?

Moto Guzzi carefully crafted the system as intrinsically safe. It could never happen. Maybe the tank being in plastic helps?

[Lucky Phil]

7 hours ago, Weegie said:

If you know the original bulb wattage, I cannot be arsed looking it up, you can easily work out the filament resistance then just wire in a resistor in parallel of the same value and it should work as @Tinus89 has already stated.

No rocket science in the circuit, Ducati did the same thing back in the day, probably other Eye-Tal-yin producers.

Still freaks me out a near empty tank, full of fumes and an electric current passing through a thermistor in the space.

What could possibly go wrong, I mean TWA 800 was a fluke right?

CWT's an commercial jets are a million miles away from a motorcycle fuel tank with a lot of various electrical components and wiring inside them and due to their vented to atmosphere nature in the past will possibly contain a flammable mixture. Now days CWT's often use purging systems to prevent the build up of flammable fumes during empty ops.  I suspect the main reason the Guzzi fuel probe uses a plastic housing is to help mitigate any leak to earth/shorting to earth scenarios. Something I'm bearing in my mind when I make my own replacement. I've never heard of a car or motorcycle fuel tank exploding due to a sensor or in tank pump shorting issue and I've seen images of a few in tank pumps that were totally fried and melted and failed.

Phil

[Tinus89]

12 hours ago, Weegie said:

If you know the original bulb wattage, I cannot be arsed looking it up, you can easily work out the filament resistance then just wire in a resistor in parallel of the same value and it should work as @Tinus89 has already stated.

No rocket science in the circuit, Ducati did the same thing back in the day, probably other Eye-Tal-yin producers.

Still freaks me out a near empty tank, full of fumes and an electric current passing through a thermistor in the space.

What could possibly go wrong, I mean TWA 800 was a fluke right?

The original bulb is 1.2W. 

But I am failing to understand how this would work. Adding a resister similar to the 1.2W bulb would only "help" the fuel level sensor in not becoming too hot, right? Would it, in "full" position, still not allow sufficient current to flow through the high resistance in the fuel level sensor to light the LED bulb?

[Weegie]

The TWA 800 remark was made with my tongue firmly in my cheek and I agree.

The idea of mixing components with current passing through them and a potentially explosive atmosphere might sound utterly mad, but could still be safe, it's dependent on a few different variables.  I've never heard of any scenario of a tank exploding due to either a fuel pump or low fuel warning sensor failure either

@Tinus89 am I missing something here?

AFAIK its the properties of the thermistor itself that alters resistance, resulting in a higher current flow for the fixed Voltage across the circuit it has nothing to do with the bulb resistance. The bulb rating is chosen to allow it to be bright enough to be observed, but also to balance/limit the total circuit resistance. If the bulb resistance is too high (i.e. lower wattage) it won't allow enough current to flow and would never light. Too low, would result in too much current and burn out the thermistor.

The Thermistor's resistance lowers as it gets hotter, when it's dunked in fuel it's cold and the resistance is high. When it gets uncovered, fuel below the sensor, the thermistor starts to get hot. When it gets hot the resistance lowers, that will also result in self heating (by how much I don't know).

I don't understand the difference between using a bulb and an LED plus equivalent resistance, in a purely resistive circuit

If I'm talking complete bollocks or missed something feel free to educate me (because I've never been accused of being "the brightest bulb in the building")