!!!Working fuel gauge, FOR REAL this time!!!

[RagingMain]

Thatn is the essence of electronics. It never goes as it was planned...


I wonder why?
What wires size did you use?

Same size wire that the OEM gauges come with.
I think it is 18 or 16 gauge wire
Plus I tested the resistance before and after the install of the resistor and it came out as expected.

I think because the 50 ohm is still too much resistance.

 

[Bon-86]

Hey there RagingMain, I'm in England this week but that's not keeping me from following your thread! I'm surprised that the 50 ohm resistor didn't work. Before you try an 8 ohm resistor I think it's a much better idea to try the original bulb instead. If the bulb works then I'll agree that the 50 ohms should be a little less. Eight ohms is way too low though. The fuel bulb is only a 3 watt bulb. The 8 ohm resistor will draw 18 watts which is around 1.8 amps - way too much. Please, try the bulb and if it doesn't work then there is something else that needs to be addressed in your circuit design. Regards!

 

[RagingMain]

Hey there RagingMain, I'm in England this week but that's not keeping me from following your thread! I'm surprised that the 50 ohm resistor didn't work. Before you try an 8 ohm resistor I think it's a much better idea to try the original bulb instead. If the bulb works then I'll agree that the 50 ohms should be a little less. Eight ohms is way too low though. The fuel bulb is only a 3 watt bulb. The 8 ohm resistor will draw 18 watts which is around 1.8 amps - way too much. Please, try the bulb and if it doesn't work then there is something else that needs to be addressed in your circuit design. Regards!

Will Do.
Wont be for awhile though, just put everything together and dont want to take it apart.

 

[satariel666]

Same size wire that the OEM gauges come with.
I think it is 18 or 16 gauge wire
Plus I tested the resistance before and after the install of the resistor and it came out as expected.

I think because the 50 ohm is still too much resistance.

And thats odd.
Better grab about 32ohm resistor first. 8ohm may be little risky.

Hey there RagingMain, I'm in England this week but that's not keeping me from following your thread! I'm surprised that the 50 ohm resistor didn't work. Before you try an 8 ohm resistor I think it's a much better idea to try the original bulb instead. If the bulb works then I'll agree that the 50 ohms should be a little less. Eight ohms is way too low though. The fuel bulb is only a 3 watt bulb. The 8 ohm resistor will draw 18 watts which is around 1.8 amps - way too much. Please, try the bulb and if it doesn't work then there is something else that needs to be addressed in your circuit design. Regards!

I agree. Much much to low.

IMHO messuring the bulb resistance when its cold may be wrong.

 

[RagingMain]

Hey there RagingMain, I'm in England this week but that's not keeping me from following your thread! I'm surprised that the 50 ohm resistor didn't work. Before you try an 8 ohm resistor I think it's a much better idea to try the original bulb instead. If the bulb works then I'll agree that the 50 ohms should be a little less. Eight ohms is way too low though. The fuel bulb is only a 3 watt bulb. The 8 ohm resistor will draw 18 watts which is around 1.8 amps - way too much. Please, try the bulb and if it doesn't work then there is something else that needs to be addressed in your circuit design. Regards!

After doing some calculation I see where you came up with the 50 ohm resistor.
12vdc system with a 3 watt bulb will draw .25 amps of current and 48 ohms total resistance.

When you measure the resistance of the bulb it comes out at 8 ohms

Why the difference???
I think the one BIG thing we are forgeting in the circuit is the OEM Thermirestor as well. Mine measured out per Tech Manual Spec. That is an extra 1000 ohms on the circuit

The bulb only allows the circuit to complete, like the old Christmas tree lights.

Funny thing is when I put the 50 ohm resistor in and measured the total resistance it was right at 48 ohms.

 

[Bon-86]

The bulb filament increases its resistance as it gets hotter. The 8 ohms is the cold resistance. The current initially is initially high and this is why bulbs often blow out at start up due to the high inrush current (and thermal shock). I don't have a good schematic of the thermistor/bulb. Can you point me to one? (Gotta run and catch a plane so I'll check back later!)

 

[RagingMain]

The bulb filament increases its resistance as it gets hotter. The 8 ohms is the cold resistance. The current initially is initially high and this is why bulbs often blow out at start up due to the high inrush current (and thermal shock). I don't have a good schematic of the thermistor/bulb. Can you point me to one? (Gotta run and catch a plane so I'll check back later!)

That makes sense.
But here is a novel idea...
Since the light isnt lit when the small amount of current is flowing and it has a resistance of 8 ohms then an 8 ohm resistors should do the trick

What I am going to do is get a potentiometer and slowly dial down the resistance until I see the fuel pump kick in and see what resistance that is.

As far as a circuit, I know there is one in the tech manual. Just dont remember where

 

[Bon-86]

Okay, I looked at the circuit in the FSM and I think you're onto something. The fuel lamp never does come on at full brightness because there is still a lot of resistance in the thermistor even when it's hot. This means that the bulb's filament is cooler and this means that the bulb's resistance is less than it would be if operated at full voltage. There are several ways to find the correct resistance in that case but your method of inserting a variable resistor will work to find the required value. But be careful because there are several ways this can go wrong. You can burn up the potentiometer, or worse possibly burn up the thermistor, by turning the resistance too low.

My choice would be to use a voltmeter that has an ammeter setting. I'd put the meter in series with the bulb (while the gas is low) and measure the current through the bulb. I'd then remove the ammeter from the circuit and set the meter up to measure the voltage across the bulb with the meter in parallel (again while the gas is low). Now that you know both the voltage (V) that the lamp is seeing and the current (I) running through it you can calculate the actual filament resistance using Ohm's law. V/I = R. I'd go with a little lower resistance than what you calculate because you don't want the revised circuit not to work on a cold day. This is more work but you'll know what the correct value is and won't risk frying something.

 

[RagingMain]

Okay, I looked at the circuit in the FSM and I think you're onto something. The fuel lamp never does come on at full brightness because there is still a lot of resistance in the thermistor even when it's hot. This means that the bulb's filament is cooler and this means that the bulb's resistance is less than it would be if operated at full current. There are several ways to find the correct resistance in that case but your method of inserting a variable resistor will work to find the required value. But be careful because there are several ways this can go wrong. You can burn up the potentiometer, or worse possibly burn up the thermistor, by turning the resistance too low.

My choice would be to use a voltmeter that has an ammeter setting. I'd put the meter in series with the bulb (while the gas is low) and measure the current through the bulb. I'd then remove the ammeter from the circuit and set the meter up to measure the voltage across the bulb with the meter in parallel (again while the gas is low). Now that you know both the voltage (V) that the lamp is seeing and the current (I) running through it you can calculate the actual filament resistance using Ohm's law. V/I = R. I'd go with a little lower resistance than what you calculate because you don't want the revised circuit not to work on a cold day. This is more work but you'll know what the correct value is and won't risk frying something.

Good Idea
Once I feel like pulling it all apart I will do that.
If I use the potentiometer I will keep an ammeter installed as I dial down the resistance and never go below the OEM bulb of 8 ohms.

 

[marecki]

The resistance is 47ohm on Koso units, you have to partially go based on the gauge you're using and what you're ligting up.

 

[MaxMidnight]

Was the optimal value for the fuel level warning light resistor established?

 

[Biker Dash]

This is something I very much want to do. I was thinking that the tach location would be an ideal spot for the gauge, where as I want to mount a tach up where the speedo is (with matching speedo of course)

Maybe I might make up a powerpoint instruction presentation using the info gathered here.

 

[wildweasel_pt]

Make it happen. ANd welcome...

 

[Suave Cowboy]

Brilliant! I don't think I'm comfortable enough in my wrenching abilities yet to attempt it myself but I've always wanted a fuel gauge. Very impressive, great work!

 

[frank5079]

This is something I very much want to do. I was thinking that the tach location would be an ideal spot for the gauge, where as I want to mount a tach up where the speedo is (with matching speedo of course)

Maybe I might make up a powerpoint instruction presentation using the info gathered here.

Interesting...may be you can fab out this gauge cluster from a Vmax snowmobile

 

[Bayoublaster]

What length flexible sending unit should I order from Centroid for the VMax tank? It is the three wire version that you used correct? I have a KOSO RX-2N Speedo that already has the fuel gauge built into it so all I had to do is order a Fuel Gauge Wizard 500 to put in line between the speedo and the sending unit, calibrate the Wizard 500 for the low end and top end and will be good to go. I just don't know what length flexible sending to order and I'm on an oil rig in the Gulf of Mexico right now and would like to place the order from them now so I will have it next week to work on while I'm on vacation. Appreciate any help. Thanks again as I would have never even thought about installing a working fuel gauge without this thread.
On another note, it's amazing how much info there is out there in the marine sector about just this type of install, but on the other hand I have a built in fuel gauge on the KOSO so I won't have the problem you've run into. Wish Ya all the luck as I know Ya gonna figure it out. This is what the Wizard 500 looks like on the inside:

 

[KJShover]

I used a two-wire unit, this one. If I remember right I ordered the 12" length. You can trim it to the length you need.

I think I ended up with removing about 1.5-2" from it. I padded the end (kept it open) with about 1/2" of fuel safe rubber to prevent accidental grounding. My knock off speedo has a built in fuel gauge and being I'm bypassing the Vmax wiring all together I got to keep my fuel light functionality.

Here are the instructions you can reference.

 

[one2dmax]

I am setup as a dealer for them and not sure if i can save you any costs when you get figured out what you want.

 

[Bayoublaster]

I looked at both models (2 wire and 3 wire) and the only difference seems to be that the 3 wire model requires switched power. I'm sure there is a reason behind that, but I haven't been able to get anyone on the phone over at Centroid Products and Sean's busy right now and i can't leave a # for him to call me back as I don't have a call back # out here on the rig. KJShover......got any thoughts on the diffeence between the two models as I'm leaning towards the 2 wire model myself. Thanks

 

[KJShover]

KJShover......got any thoughts on the diffeence between the two models as I'm leaning towards the 2 wire model myself. Thanks

The speedo I have (Koso knockoff) already has power to the fuel gauge, so a keyed-on source wasn't needed as it powered up when you turn the ignition on. The guy I bought it from suggested the 2-wire model.

As you can see it works and quite well I might add (install was the same as the write up). I topped it off a few days ago, then in the middle of a ride I reset the trip. That's why I'm at a little under 3/4 of a tank but only in the 30's km. Like I mentioned earlier, being it's independent of the Vmax wiring, the low fuel light works as it should (Although I did replace mine with a flashing red LED, as for the resistor, I have no idea what I used. I had a handful and kept swapping them out until I found one that works, somewhere in the forum is a pt # for the proper LED, I looked at my instrument panel but All my connections are soldered and then covered with heat shrink tubing, so I couldn't see the colors of the bands).