"Averaging" fuel level sender??

[nigelmercier]

I'm afraid I can see no way in which adding resistors would affect the sensitivity of a gauge of the type I linked to in my earlier post (ie the type with two coils). Ohms law doesn't have T in it. The only way would be to add capacitance, and as Nigel has pointed out the capacitors would need to be very large...

Quite, it is nonsense.

I don't fully understand the capacitance/resistance discussion so can't really comment...

See above.

The only sensible way to sort this is to contact the manufacturer. I posted a link for you, but here it is again.
http://faria-instruments.com/index.php

 

[wipe_out]

The only sensible way to sort this is to contact the manufacturer. I posted a link for you, but here it is again.
http://faria-instruments.com/index.php

From their website..

"Fuel gauges:
Fuel gauges may at some times seem to "bounce". In most circumstances this is actually caused by the fuel sloshing in the tank and does not necessarily indicate a problem with the gauge or sender."

Basically saying yes we know they bounce but just ignore it..

 

[nigelmercier]

Basically saying yes we know they bounce but just ignore it..

There is a big difference between bounce, which we all get, and "near useless because it swings so wildly". If the fluctuations you are getting are more than half a division, there is something wrong.

 

[wipe_out]

Last weekend in fairly big and frequent swells the gauge was swinging between just under half and full.. So over half the total range of the gauge..

I have another potential cause of the problem.. Apparently the previous owner had an issue with "sludge" in the tank and had someone clean it out.. In order to do this they created an "access" hatch in the aft cabin area floor to get to the tank.. It's a plastic tank so probably didn't have any access holes and I am wondering if they might have somehow cut into the tank to clean it and removed any internal baffles (assuming there were any to start with) at the same time which means the "sloshing" is now not being controlled at all and so causing the gauge "swing".. Is this a likely theory? (I would have to reopen the access holes they created to confirm for sure)..

 

[srp]

It might be. How would you know if there were any baffles fitted originally though. I think that cutting baffles out of a tank through an access hole sounds an almost impossible task. If I was going to clean a tank I would use a vacuum pump and repeated rinses with a small quantity of clean diesel, but who knows what a previous owner would have done.

It sounds as though the bigger potential problem is that the engine could suck air or dirt in if the fuel level was low and it was sloshing about. If that is the case, then a change to or of the tank rather than a modification to the gauge or sender might be in order.

 

[wipe_out]

I'll pull the sender and test it this weekend and also see what I can see through the hole.. Guess this is where one of those fibre optic spy camera goodies you see in the movies would come in handy..

 

[lw395]

If you want to slow down the response electronically, one way would be to use a low pass filter with an op-amp in it, that way you can use sensible size caps.
Damping the fuel in the tank, not in a watery sense, might be more satisfactory.
Racing vehicles put sponge foam in the tanks, dunno if its any good for diesel? Obviously it would tend to get in the way of the sender....

 

[nigelmercier]

I can't speak for your tank, but mine has baffles moulded as part of the walls of the tank. It would be impossible to remove them.

 

[wipe_out]

Pulled the sender today and slowly moved the float up the shaft watching the gauge.. The gauge "clicked" to 4 or 5 different positions across the range, not a smooth movement at all so looks like I need to replace the sender..

Pushed a pipe up the floor of the tank though the sensor hole.. It would appear that there are no baffles in the tank at all.. Tank is about 11" deep in the middle (shaped to the bottom of the hull and about 5ft long.. Without baffles I would imagine even the slightest movement of the boat will have a significant effect on the sender position so fitting the sender probe into a tube to limit the effect is probably what I will try if I can find some suitable tube to fit it into.. Can't find any senders that come that way unfortunately..

 

[srp]

You might have a sender that has a series of switches rather than one long variable resistor, each switch is then connected to its own resistor to give you the 4 or 5 steps you describe. Nothing wrong with that, but as you say, it's the tank shape and lack of baffles that is the problem. What you need is some clever person to think of some way of sticking a baffle in the tank - something like a long strip of springy polythene that you can push through the access hole and it will form a big S shape, held in place by its' springiness against the sides of the tank. Maybe.....

 

[captainboo]

The gauge "clicked" to 4 or 5 different positions across the range, not a smooth movement at all so looks like I need to replace the sender

I have this style of sender:

http://www.asap-supplies.com/marine.../dip-type-liquid-level-sender-euro-resistance

It works with a series of reed switches inside the column and when the float is raised and lowered the gauge does move in a series of steps from one side to the other so your gauge and sender may be normal.

 

[wipe_out]

I see.. Is that common to have a "stepped" sender with only 4 or 5 points? I could understand about 10+ points but if its 5 you only have positions for full, 3/4, 1/2, 1/4 and empty (although I don't remember if that's specifically where they were lining up)..

My thought was to fit the "probe" into a piece of aluminium tube with small holes on the top and bottom.. The flow restriction should average the sender.. The rest of the tank would still be "sloshing" around but the float will be gently moving up and down in the tube "averaging" the level.. Just need to find a friendly and cheap engineering shop because if the baffle costs too much to make it would be easier to look at the ultrasonic senders that have "damping" build in electronically..

 

[wipe_out]

I have this style of sender:

http://www.asap-supplies.com/marine.../dip-type-liquid-level-sender-euro-resistance

It works with a series of reed switches inside the column and when the float is raised and lowered the gauge does move in a series of steps from one side to the other so your gauge and sender may be normal.

That's like the one I was looking at actually (just the US version).. Does your gauge only have about 5 steps or do you have more?

 

[captainboo]

I honestly can't remember but I don't think it is more than 5 - Empty, 1/4, 1/2, 3/4, and Full as the gauge only has small sweep range and indicating between those positions would require another 4 switches to make the steps uniform and it certainly hasn't got that many positions.

 

[wipe_out]

I honestly can't remember but I don't think it is more than 5 - Empty, 1/4, 1/2, 3/4, and Full as the gauge only has small sweep range and indicating between those positions would require another 4 switches to make the steps uniform and it certainly hasn't got that many positions.

Thanks, that's interesting.. Perhaps I will just try and "baffle" the existing sender and see what happens because the swing between 1/4 and full makes the gauge useless at the moment..

 

[nigelmercier]

http://www.asap-supplies.com/marine.../dip-type-liquid-level-sender-euro-resistance
It works with a series of reed switches inside the column...

I believe you are mistaken, it says: Resistance: 10 ohms empty, 180 ohms full which is the European standard for resistance gauges. I think you might be confused with your water gauge, which are often stepped.

Pulled the sender today and slowly moved the float up the shaft watching the gauge.. The gauge "clicked" to 4 or 5 different positions across the range, not a smooth movement at all so looks like I need to replace the sender...

Looks like you have a dirty or broken resistance track.

 

[wipe_out]

Looks like you have a dirty or broken resistance track.

I have a "probe" type.. Not a "float" type sender so there isn't a resistance track just a magnet that slides up and down a shaft..

 

[nigelmercier]

I have a "probe" type.. Not a "float" type sender so there isn't a resistance track just a magnet that slides up and down a shaft..

You mean like the one linked above at ASAP?

It is a resistive sender, it must have a resistance track somewhere.

 

[wipe_out]

You mean like the one linked above at ASAP?

It is a resistive sender, it must have a resistance track somewhere.

captainboo's post above suggests that there are a series of switches at points in the shaft which "switch" the resistance in "steps" over the length of the shaft which would explain the response I saw on the gauge when I manually moved the float along the length of the shaft..

 

[captainboo]

captainboo's post above suggests that there are a series of switches at points in the shaft which "switch" the resistance in "steps" over the length of the shaft which would explain the response I saw on the gauge when I manually moved the float along the length of the shaft..

Correct - and the senders are in my fuel tanks, I don't have any contents indication in my water tanks! The gauge I have goes from 10 - 180 ohms and the sender uses the reed switches to add different resistors to the circuit and hence vary the resistance overall. You'll find there is a magnet in the external float part.