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I seem to have sorted the unstable resistance from my fuel sender and the gauge now reads correctly and the needle doesnt jump erratically, but it reads slosh. it will go from half tank to empty depending on if your turning, braking, uphill etc. It only reeds correct on flat ground either stationary or going forward.
I can find nothing wrong with the system so I can only assume this is how they are.
Anyone solved this? I'm not going to be foaming/baffling the rank!
I did find one place that sells a gadget but £30 and not in Stock anyway.
Any other options?
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colnerov
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Posts: 2,869
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Hi, Yes it's partly down to the tank not being baffled and partly down to the type of gauge used. Some manufacturers used voltmeters but most used bi-metal strips, the be-metals strips are a lot slower reacting to the voltage change from the fuel moving about.
Colin
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bortaf
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Posts: 4,549
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Yeh the bi metalic type has a built in damper (the time it takes for the temp to alter and bend the strip) you could insert a drilled baffle around the sender if there is access ? most senders now sit inside the swirlpot and/or are part of the pump/puickup so swing about even less, i spose you could dampen the float arm? no idea how though ?
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R.I.P photobucket
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This gauge works with coils, one on the positive side, one on the negative side and the usual variable resistance (0-30 in this case) of the sender.
No real access in the tank. don't want to drop it again anyway. But it would probably require cutting the tank open.
Not sure how I could dampen the sender arm but again, its a proper struggle to even get the sender out without dropping the tank.
Needs solving electrically I think.
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How old is the car (electronic dash or old school) ? The explanations above about the gauge reacting quicker than you want make sense, rather than damp it mechanically I'd experiment with damping the electic signal to the gauge. An "Electrolytic Capacitor" costs pennies, fit one in the tank sender circuit (to earth? across the sender? across the gauge?) and hope for the best (think of it like a storage tank - little ripples in the power signal will take a while to affect the power stored in the tank )
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Last Edit: May 1, 2017 19:37:48 GMT by nomad
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Vehicle is 1979 and very much old school dash I have capacitors, i have seen the same thing mentioned elsewhere but no one seemed to know how to wire them or if it will work. Easy to try I guess though.
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Bit of reading and I found some info on running a capacitor, some good, some bad.
So it will work to damp the gauge, but might give a possibility of sparking in the tank!
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What's the resistance on your sender? From memory older stuff is like <1000 ohms so to make any real difference you'd need a load of capacitance, in the region of 10,000uf+ to damp out sloshes from cornering.
If you've got two coils and a wiper resistor, wire the caps across each coil, obviously minding the polarity.
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Sender is 0-30 ohm. I'm trying to find any more references to a capacitor causing arcing in the tank. I think the theory was when sender goes to 0 the stored charge could go back through the sender, or something like that. Ive built a few amplifier circuits but physically building a circuit from a schematic doesn't mean I understand what its all doing
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Oh if it's 30 ohms there's just too much current flowing for any reasonable sized capacitor to make much of a difference if fitted directly on the coils.
You'd need to make a buffer circuit really to totally isolate the gauge from the sender and filter the signal, but it quickly starts getting complicated
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I stand corrected - it was worth asking the question but it sounds like it's not going to be a simple plug-and-play fix
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Its not the first time ive tried a bit of research on this and havent found an easy way out yet, so maybe there isnt one.
Ill message the people that make the anti slosh modules and see if they will be making more. They also can only say it will work with vdo/lotus stuff as thats all they have been used on.
If not, I may either have to live with it, or try and fit a different mech onto my gauge face. No doubt ill also have to change sender which is a pain as tank is unusual 6 bolt.
I have been told they did this from new. I cant believe, even in 1979, you could buy a new car with a fuel gauge that sloshed about as you drove!
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The gauge in my 88 t25 varies by 1/4 of a tank depending on which way you're turning or accelerating, it's definitely just one of those things.
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Been trying to get on the module companies site (spiyda) but seems to be a security issue. Might phone them tomorrow, see what they say.
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I wonder if it's the shape of the tank that exacerbates the problem? Mine is similar stuff being from the same manufacturer and roughly the same time, and I don't have major issues such as you describe. I do have a problem where the gauge reading seems to drop if I open the drivers window, but I presume that's just my imagination.
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Cf tank is roughly 2'x2.5' and 6" deep. I guess the low height means there is not much sender throw so smaller movements make a bigger difference.
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fad
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Posts: 1,781
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Right this is a nice and easy fix. So you have 0-30 Ohms as your output from the sender. As said, a capacitor would do it were the impedance of this much smaller. But you can't do that here. You would traditionally smooth with a circuit as above (it's usually used for D-A conversion but it would work here, you want to slow the response down). But either way... You need an intermediary circuit. Try it and see though... The values would be experimentation, but anyway... Don't worry about a spark in your tank. You'll never know about it if it does it :lol: A simple sure-fire way of doing this would be with an analogue to digital converter with a high sample rate, and then a digital to analogue converter with a low sample rate, with some sort of averaging going on and smoothed outputs. There are various ways of achieving this, and if it's a route you want to go down let me know and I will put a little time into designing something for you when I get a chance
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Last Edit: May 2, 2017 10:47:33 GMT by fad
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colnerov
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Hi, Yes, don't worry about a spark in the tank for the simple reason that the atmosphere in there is far too rich to ignite.
Colin
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fad
Posted a lot
Posts: 1,781
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Hi, Yes, don't worry about a spark in the tank for the simple reason that the atmosphere in there is far too rich to ignite. Colin Unless the tank has been left empty for a while and had time to vent
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Well, if were sure the R/C is safe and not going to blow up the van, I can try easily.
I have lots of resisters in many values and a fair few capacitors kicking about.
Any guess on values to start with?
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