Fuel Gauge needle moving with revs issue

[plugsandsparks]

Phew, thats better. Let me look for a proper rectifier and suitable regulator to give a consistent DC voltage, you may have to play around with the resister to get a full scale reading when talk is full, or you may want to get an empty indication when the tank is very low, its often hard to get both without alot of playing around.

 

[mainline]

There is no rectifier, and no flasher relay either (no turn signals). I posted the diagram to show that the current wasn't transformed on its way to the gauge. The rectifier was fitted to some models for the horn for some markets, but not on mine.

The only alterations to the wiring were to add a brake switch to the handlebar in line with the foot pedal brake switch; also, the brake pedal is fed through the main circuit instead of having its own wiring, and the rear light has its own wire coming from the regulator. Nothing that interferes with the gauge circuit as far as I can tell.

A battery could always be fitted, but the point of this bike being all AC is to keep it simple and easy to repair and maintain. I'd rather avoid that route.

Try shorting the diode out and see how it reacts.

Connected correctly, the coils will balance, leaving only the variation in the sender resistance to unbalance it and move the needle.

 

[plugsandsparks]

Just had a look and the proper Vespa rectifier is cheap enough and at least it is designed for the frequency range

Regulator / Rectifier 4-Pin for Vespa PK 50, PX 80, PK 125, P 200, PX 200, Cosa, XL2

Regulator / Rectifier 4-Pin for Vespa PK 50, PX 80, PK 125, P 200, PX 200, Cosa, XL2

euroscooterparts.co.uk

 

[Tarlow]

Try shorting the diode out and see how it reacts.

This particular gauge didn't have a diode at first. When connected to AC, no reaction at all. When connected to a battery, it would move with the float.

 

[Tarlow]

Just had a look and the proper Vespa rectifier is cheap enough and at least it is designed for the frequency range

Regulator / Rectifier 4-Pin for Vespa PK 50, PX 80, PK 125, P 200, PX 200, Cosa, XL2

Regulator / Rectifier 4-Pin for Vespa PK 50, PX 80, PK 125, P 200, PX 200, Cosa, XL2

euroscooterparts.co.uk

Isn't that for a battery model? There are 4 pins, and I only have 3 wires for the regulator.

 

[mainline]

This particular gauge didn't have a diode at first. When connected to AC, no reaction at all. When connected to a battery, it would move with the float.

Did it move the gauge correctly. ?
Is the AC fuel gauge not available ?

You could use a bridge rectifier and variable voltage regulator circuit, but better to get the one suggested.

 

[DPG]

I think I'd just lift the filler cap and have a look

 

[Tarlow]

Did it move the gauge correctly. ?
Is the AC fuel gauge not available ?

You could use a bridge rectifier and variable voltage regulator circuit, but better to get the one suggested.

It seemed to more or less, but this was off the bike, with no revs to affect it.

The AC fuel gauge acts exactly the same on this bike. It also has a diode and a resistor, which is why I fitted a diode to this one (which as a DC unit originally, didn't have one) to see if it would work.

The regulator suggested is for battery models apparently, and has 4 pins, while my circuit is just ground, hot wire from the stator, and wire out.

 

[Tarlow]

I think I'd just lift the filler cap and have a look

Haha it certainly would be more simple, but I'm not acrobatic enough to do all that whilst driving

 

[plugsandsparks]

Isn't that for a battery model? There are 4 pins, and I only have 3 wires for the regulator.

The diagram you posted for the non battery model has 4 pins, there are only 2 wires to the regulator and what looks like 2 wires to the outputs of which one is the horn. For what it costs, its got to be worth getting it , connecting the 2 wires to the regulator as per diagram and then measuring the DC output using your meter as per diagram. If you get around 10VDC solid through the rev range , then jobs a good un.. you just then need to adjust the resistor to get the correct readings on the gauge- OR take a road trip to Derbyshire England and i do it myself....

 

[Tarlow]

The diagram you posted for the non battery model has 4 pins, there are only 2 wires to the regulator and what looks like 2 wires to the outputs of which one is the horn. For what it costs, its got to be worth getting it , connecting the 2 wires to the regulator as per diagram and then measuring the DC output using your meter as per diagram. If you get around 10VDC solid through the rev range , then jobs a good un.. you just then need to adjust the resistor to get the correct readings on the gauge- OR take a road trip to Derbyshire England and i do it myself....

The link you posted is for a regulator/rectifier. Do you mean I should somehow hook it up as per the diagram to the current 3 pole regulator, or just replace the 3 pole with this 4 pole?


In which case the hot wire incoming from the stator would connect to either G, and the wire going to the circuit (and gauge) to the A, correct? I might actually be able to borrow a similar regulator from a different scooter to try it out.

 

[plugsandsparks]

There does appear to be an issue with the diagram as the fuel gauge looks to be fed by AC, as i think (its hard to tell and someone has used a highlighter on it which makes it difficult to check colours BUT a regulator/rectifer is much more useful than separate items for sure. It sounds like you have a regulator but not a rectifier, hence you get a nice even AC voltage but very little DC. Its certainly doable to get rid of your exiting regulator and replace with a combined device like the one mentioned. You will need the instructions that come with the device to ensure the correct wires go to the correct terminals, the one in the picture i think tries to help but i cannot make it out.
Also the diagram appears to show a low fuel light - but cannot be sure.

 

[Tarlow]

Yes, the fuel gauge is fed by AC, and the diode keeps the current going one way.

There is a low fuel warning light, whose circuit closes once the float reaches the lowest point of the sender range. That works fine.

Here's the diagram without the highlights: