I pointed out something that *COULD* be a problem, and you launched into a tirade!!!

You have amazing abilities to guess what my emotions are. Unfortunately, you guessed wrong.

Members have a certain responsibility to provide correct answers. When one is mistaken, they get results like post #8 #12, #17, and #18

 

You have amazing abilities to guess what my emotions are. Unfortunately, you guessed wrong.

Members have a certain responsibility to provide correct answers. When one is mistaken, they get results like post #8 #12, #17, and #18

 

Is that, "you" just for me, or does it include the other three people that said you are wrong?

 

Is that, "you" just for me, or does it include the other three people that said you are wrong?

I was ignoring the mob rule element.

 

Hi,
I have a 91 Jeep and the gas gauge swings like crazy when ever I hit a bump or turn a corner. Obvoiusly this is the float in the tank responding to the fluid level changing as it sloshes around.
I saw on a Jeep forum that someone added a .001mF capacitor in parallel with the gauge and that slowed down the response to a more civilized movement.
This did not seem to work for me.
By the way, new gauge, new sending unit, new wire from gauge to sending unit and then to ground. 12 volt DC neg ground.
Any ideas?
thanks freicus

Have you ruled out an intermittent connection?

 

Hi freicus, could you clear up a few points, does the gauge flicker or seem to be affected by fuel swirl in the tank, and when the vehicle is stationary does it appear reasonably accurate ?

 

Hi

The sender will have some inductance - all real components do - but it will be small. Any significant a.c. voltage across 100ohm implies significant a.c. power and what is the source of this power? 100ohm provides massive damping.

 

Baffles are usually used in tanks to prevent wild massive movements of the entire contents of a tank.

Does this fuel tank not have them? Is it the original OEM tank?

 

The sender will have some inductance - all real components do - but it will be small. ...

The wire-wound sender might have micro-Henries of inductance; it would take inductances of several Henries to affect the swinging of the gauge. That is one to a million, folks...

 

The wire-wound sender might have micro-Henries of inductance; it would take inductances of several Henries to affect the swinging of the gauge. That is one to a million, folks...

My point was that if it did manage to resonate the 100ohm would damp it to, well, zero

 

You may not have noticed, but they tend not to use WW resistors in RF circuits because the inductance is *VERY* significant. In fact, at RF the spiral on a film resistor is too inductive.

The tank sender has to run stone cold at all times, so it has a lot more turns than most WW resistors, and much larger former diameter. The inductance may not play a big part - but it *WILL* play a part.

I'm jumping on the calling BS wagon too. The physics of the electrical and mechanical component interactions just say there's no way to set up a stable oscillation in the circuit.

These are low current low voltage DC circuits with a fairly low resistance and tiny relative inductance and the fuel gauge needle is a physical mass that has it's own mechanical resonance and limits to it relative swing rate it's capable of simply due to the very limited available power at hand from the whole circuit.

Now given that most wire wound resistors used in fuel sending units are of similar designs to this one,



Most of us here with any basic electronics backgrounds should be able to get a rough calculation of the inductance based on the actual physical dimensions and turn counts and come up with a basic LCR tank circuit calculation from there.

My very generous estimations that most wire wound type sending units would be designed within the parameters of say,

Coil dia = .125" to .5 "
Coil length = 1.25" to 3"
# of turns = 30 to 100

would be in the ~ 1 - 20 uH range.

Given that coupled with a several thousand to tens of thousands of uF capacitor and a 20 - 250 ohm load all being powered by a few tens of ma of current from a maximum DC circuit voltage of several volts at best ........

I have my serious doubts too. The damping effects of the low resistance coupled with it being a low current DC circuit and the inductor itself having a random sweeping change in its inductance as the tank float moves around and there being no switching device let alone a viable feedback loop make it unrealistic that it could ever hit a resonance point that would move the needle in any constant stable pattern.

 

I must be stupid to think there might be physical reason for the wild swings of the sender. Couldn't possibly be a tank with no baffles being used on uneven surfaces. THIS IS AN ELECTRONICS FORUM!
I need to get with the program and figure out the electrical problem with this thing.
Seriously could the OP answer if the tank has baffles or if it is original OEM equipment?

 

Seriously could the OP answer if the tank has baffles or if it is original OEM equipment?

The OP hasn't been here since July 28, the day he posted... Apparently he's no longer interested