smoothing out voltage spikes and dips?

[scampo77]

Re: smoothing out voltage spikes and dips?

yes

[budm]

Re: smoothing out voltage spikes and dips?

Good, we are almost done then.

[budm]

Re: smoothing out voltage spikes and dips?

By the way, in the final product, you should install 1/2 fuse, and may be a transient protection device rated at about 35~50V after the fuse.

[scampo77]

Re: smoothing out voltage spikes and dips?

I am just finishing up trying to find out where bottom is and my rheostat in the tank opened. Is this cause I need a resistor larger than 200 ohm. I don't know if this happened from age or from bad circuit design. This happened when I was operating less then 7 ohm.

Other then that it seems to be working beautifully.

[ben7]

Re: smoothing out voltage spikes and dips?

I am just finishing up trying to find out where bottom is and my rheostat in the tank opened. Is this cause I need a resistor larger than 200 ohm. I don't know if this happened from age or from bad circuit design. This happened when I was operating less then 7 ohm.

Other then that it seems to be working beautifully.

It likely burnt out.

[budm]

Re: smoothing out voltage spikes and dips?

There is 200 Ohms resistor in series with the sensor, at worst case with lowest resistance on the sensor, the maximum current will be only 50mA (10V/ 200 = 50mA). Can you get the spec of the sensor? It has to be able to pass enough current to heat up the heating coil of the meter.
http://auto.howstuffworks.com/fuel-gauge1.htm
http://www.aa1car.com/library/fuel_gauge_diagnosis.htm

[ben7]

Re: smoothing out voltage spikes and dips?

There is 200 Ohms resistor in series with the sensor, at worst case with lowest resistance on the sensor, the maximum current will be only 50mA (10V/ 200 = 50mA). Can you get the spec of the sensor? It has to be able to pass enough current to heat up the heating coil of the meter.
http://auto.howstuffworks.com/fuel-gauge1.htm
http://www.aa1car.com/library/fuel_gauge_diagnosis.htm

50mA at 10V is half a watt, so it could have fried it, if it was only 1/4w or 1/8w rated!

[scampo77]

Re: smoothing out voltage spikes and dips?

when i pulled everything apart to fix the tank rheostat, where the failure was it was all blue and discoloured. it looked like a heat failure.

i am getting ready to make a regular board to mount everything to. i bought a circuit board that is just a sheet of copper with no holes in it. is there a chemical i can use to dissolve the copper or can i use a dremel tool to just dig away at parts of copper i dont need? i was just going to draw with a felt pen and then just start digging with a dremel, but i figured i would ask first.

[budm]

Re: smoothing out voltage spikes and dips?

"50mA at 10V is half a watt" that if the the sensor is at 0 Ohm, the 200 Ohms is spec in at 1 Watt. You will not 1/2 W of power on the sensor.
Simple Ohms laws applied here:
Do not forget that 200 Ohms will be in series with the sensor at 7 Ohms, so total resistance will be at 207 Ohms: then current will be 10V/207 Ohms = 48mA.
So you will have 48mA flowing through 7 Ohms, then the power on the sensor at 7 Ohms = 0.016 Watt.
When sensor at 100 Ohms, the current will be 10V/300 Ohms = 30mA.
So you will have 30mA flowing through 100 Ohms, then power on the sensor will be = 0.09 Watt.

1/8 Watt = 0.125 Watt.

My question is: Did you make sure that the 200 Ohms that I have in series is still correctly hooked up per diagram?
You can make even less current flow through the sensor by increassing the 200 Ohms, then just have calculate the max voltage will be fed into the IC, then adjust the Vref High to match that number.
I can also add constant current source to feed the sensor.

[scampo77]

Re: smoothing out voltage spikes and dips?

yes the 200 ohm is inline it seems to measure 200-290ohm.

what should i do next? i am torn between moving forward with board design or redesigning the circuit.

do you think 48mA is enought to melt a thin wire like in a rheostat?

[budm]

Re: smoothing out voltage spikes and dips?

"So you will have 48mA flowing through 7 Ohms, then the power on the sensor at 7 Ohms = 0.016 Watt" As I indicated, when the sensor is at its lowest resistance, he power on that 7 Ohms section is only 0.016 Watt.
Can you get another sensor? if you can:
1) hook it up outside the tank that way you can read the voltage on the sensor when you move the viper from minimum resistance to maximum resistance.

2) Add another 200 Ohms in series with the original 200 Ohms, this will limit the maximum current to 20mA (10V/ (200+200+100) = .020A.
This will make the highest voltage to the input of the IC to be about 2V, you will have to change R3 from 1500 Ohms to be 500 Ohms to allow you to adjust the Vref HI to around 2V for #10 LED to be on (full tank).

[scampo77]

Re: smoothing out voltage spikes and dips?

yes i have another sensor and i have also fixed the old sensor. i can pull it out to measure voltage. i will do this tmrw and report back.

i need to be more clear so i am understood. i was trying to find bottom on my tank so i was peeling around with the wiper at 2-10ohm for days. it failed but where it failed was at the top near 89 ohms, this is past the range of my gauge anyway. i took the top 10% of the rheostat, unwound it and put it tn the garbage and took the bootm 90% and just shorted it out to the top. it DID cook due to a heat failure but it did not physcially open at the 7 ohm spot. the rheostat seems to be working just fine i just dont want to blow it up a second time, next time i may not be as lucky.

the other sensor is in the second tank has been unused this whole time and in future use will be almost always sitting at 0-3 ohms. that tank is almost always empty.

when i am testing voltage on the wiper i just jab it anywhere on the wire? then move the wiper up and down? if this is true i will try it with the resistors i have in place already.

i wanted to see if it was getting warm so i hooked it up outside the tank and put the wiper at 0 ohm and it didnt get hot. i guess i had it backwards i will try the same thing tmrw with the wiper in the full position. and report back

[budm]

Re: smoothing out voltage spikes and dips?

When the sensor is at its minimum resistance, that when you will have the most current flowing through the 200 Ohms and the sensor, the 200 Ohms will be dissipating most of the power which does not make sense why the sensor is damage, and when the sensor is at 98 Ohms, the current flowing to the 200 Ohms and the sensor will be even less, at a bout 0.03A ) or 30mA.
So something is not making sense here.
What you can do also is to try using 10 Ohm 1/4W in place of the sensor and see how hot it gets. I have a feelings some thing is not connected right.
How many wires are there from the sensor, it should have only 1 wire since on end of the sensor will be already tied to the metal housing of the sensor assembly, any pictures of the sensor unit?

[budm]

Re: smoothing out voltage spikes and dips?

"yes the 200 ohm is inline it seems to measure 200-290ohm." What do mean by that? it is 200 Ohms or it is not.

[budm]

Re: smoothing out voltage spikes and dips?

So what did you find so far?

[scampo77]

Re: smoothing out voltage spikes and dips?

so this is how i have wired up this circuit. im not sure if its wrong or not. i am trying to figure out how to draw these circuit boards. so i dont have to use mspaint anymore.

[budm]

Re: smoothing out voltage spikes and dips?

The left leg of the cap has to go to ground, see post78.

[scampo77]

Re: smoothing out voltage spikes and dips?

Ooops my mspaint has failed me again. The cap goes from pin5 to ground

Is my 200 ohm resistor in the correct parking spot?

[budm]

Re: smoothing out voltage spikes and dips?

Yes, it still does not explain why the sensro failed with only 30mA flowing throug it.

[scampo77]

Re: smoothing out voltage spikes and dips?

well i am willing to chaulk it up as it must have been an old sensor. also i am hoping that once i get off a breadboard and onto a PCB it will eliminate any rogue wires that may have touched down or possibly shorted out the sensor.

now that the LED display seems to work, atleast in prototype. can i ask about the second part of this circuit or should i start a new thread?

in brief i need a comparitor window to activate a 555 timer to engage a pump to transfer liquid. i can explain more here or i can start a new thread.