Fuel gauge testing

[Kool48]

Ok here's the latest.  Just left Farm and fleet.   Bought a 6 volt lantern battery.  I'm down to 2 gas gauges now.   I've cleaned both with Deoxit 5.  1st gauge test (only gauge to 6 volt battery. Needle does sweep to full when connected directly to batterys  + side and gauge stud #2.  And sweeps back to empty on gauge stud # 1.   So I'm assuming this gas gauge is functioning properly.    Now the 2nd fuel gauge,  testing the exact same way.   It will sweep but instantly start smoking at the top of the Bi- metal blades  ( heated ).   So I'm assuming it's at a faulty stage about to go ?    No sending unit connected at this time.  Any inputs , does #1 gauge sound good as far as this test ?

[_shel_ny]

...

Edited October 21, 2016 by _shel_ny
already figured out torch = lantern

[maok]

You need to have the sender unit (variable resistor) connected. It limits the current going through your meter.

[maok]

Regarding having it run on 12v, you need to put a small resistor inline, probably the same as the maximum value of your sender unit. Experiment by using your fluke (wow!) DDM in AMP mode and see what current is running through your circuit with the 6 volt battery. 

Edited October 21, 2016 by maok
Spelling

[Kool48]

Here's my latest updates on gauge testing.    I went a bought a cheap 6volt lantern battery.      Came home , I tested this way.   Ground from  battery to the sending unit body only.  Positive of  battery to the SW ING stud go gas gauge then jumper wires to 1&2 of gauge to 1&2 of sending unit    Finally I have movement.    It seems to be working ok , it only goes back to a 1/4 of a tank mark on gauge.   But goes past the full mark.    Is there a way to calibrate the gauge or tweak the heating bars so it reads closer than it is now.      I still don't get what I was doing wrong before.    But my Runtz reducer is trashed now.    So I need to buy a new reducer before it goes into car.    Outta 3 gauges.  1 is just junk.   1 works but starts smoking as soon as power is applied but does sweep.   The 3rd is the one I'm working with now that needs calibrated.   If it can't be then I'm back to square 1 again lol.    

[maok]

Forget the voltage reducer. It doesnt look like anyone has had any success with these on a meter.

Just use a resistor before the +ve input of your meter.

[Kool48]

51 minutes ago, maok said:

Forget the voltage reducer. It doesnt look like anyone has had any success with these on a meter.

Just use a resistor before the +ve input of your meter.

So If I'm understanding you correctly , I can use a good 30 ohm 1/2 watt resistor between power source and gauge and that's it ? As far as the Fluke goes , I have a couple.  Never really checked amperage with either.    But I'd like to learn as much as I can .   I used to do vintage home audio restorations for myself not as a business.     But I'm a member of a ver good audio site.  Learned a lot from those guys regarding audio.    But I'm by far a tech or a professional when it comes to electronics and how it all works.   My own projects come out pretty good of course I had a lot of online help.   Just like hear.    When it comes to 60s 70s muscle car stuff I fairly good at those.         I do thank and appreciate everyone here for there' help and inputs.    

[maok]

It should do the trick. If the 30ohm is not quite right, try alittle more or less.

When measuring the current with the fluke, it needs to be in series (inline) not parrallel.

[Kool48]

1 hour ago, maok said:

It should do the trick. If the 30ohm is not quite right, try alittle more or less.

When measuring the current with the fluke, it needs to be in series (inline) not parrallel.

Thanks I'll give it a try , I have a bunch of resistors around here someplace . Been a long time since I worked on electrics . I have to dig my old stuff out.    I'll play with the DMM also.  

[maok]

Oh, don't put the battery across the terminals of the meter, it will/may smoke.

Good luck.

[Kool48]

59 minutes ago, maok said:

Oh, don't put the battery across the terminals of the meter, it will/may smoke.

Good luck.

Gotcha.   Thanks 

[maok]

How did you go?

[Kool48]

8 minutes ago, maok said:

How did you go?

Well , I'm still scratching my head a bit.   I haven't dug out my old electronics stuff yet.  It's buried in garage Attic lol.   So where I'm at now , is as I mentioned before a few post back.   Testing with 6 volt battery.      My thing is now , I have 1 outta the 3 gauges that may be good .   I know 1 is total loss.  The other smokes.   So the 3 rd gauge , seems ok it sweeps all the way to the left (empty) and all the way to the right ( full ) when gauge has nothing connected at all.    Now if I connect to only the 6 volt  battery and ground either stud 1 or 2 out on the  battery it will sweep both ways depending on which stud I'm on.    So then I test it with sending unit.   6 volt battery connected to the sw ing stud of gauge.   Battery ground to sending unit housing and jumper wires from 1&2 of gauge to sending unit.    Lift float up to where it looks like it even with the sending unit flange or at full position , needle sweeps past full.  Let float down slowly and gauge starts coming down.   It's not super smooth ,it kinda hesitates and then moves a bit more towards empty.   I kinda think that's still ok.   My thing is even with the float completely down , the gauge will not read less than about a 1/4 of a tank and just stays there.    Disconnect everything then it'll go on down to empty .    So is the problem with the gauge ?   Or the sending unit ? 

[maok]

Why are you connecting 1 AND 2 to the sender unit? It should be only one of them, the one that is not connect to battery power.

[Young Ed]

15 minutes ago, maok said:

Why are you connecting 1 AND 2 to the sender unit? It should be only one of them, the one that is not connect to battery power.

Nope this is a 2 wire system. To work there are 2 posts on the gauge and 2 on the sending unit that need to be hooked up plus a third on the gauge for power

[maok]

Is there a circuit diagram I could look at?

The sender unit must be working just like a potentiometer. 

It's possible that your sender unit is faulty, does not register a good contact to the swept arm before 1/4 mark.

 

[_shel_ny]

8 minutes ago, maok said:

Is there a circuit diagram I could look at?

The sender unit must be working just like a potentiometer. 

It's possible that your sender unit is faulty, does not register a good contact to the swept arm before 1/4 mark.

 

Diagram in the download section.

[maok]

Thanks.

Quote

Lift float up to where it looks like it even with the sending unit flange or at full position , needle sweeps past full.  Let float down slowly and gauge starts coming down.   It's not super smooth ,it kinda hesitates and then moves a bit more towards empty.   I kinda think that's still ok.   My thing is even with the float completely down , the gauge will not read less than about a 1/4 of a tank and just stays there.    Disconnect everything then it'll go on down to empty .

To test the sender unit, connect both the terminals of the sender unit to the red wire of your fluke and the black wire to the chassis of the sender unit. Switch your fluke to ohms and see if you get consistent ohm readings through out the range of the sender unit. If my guess is right, you should get values that vary from middle to the top of the sender unit and also middle to the bottom of the sender unit.

If you don't get smooth consistent readings and you can open the 'can' of the sender unit up easily try giving the internals a clean.

 

[maok]

I'm now thinking that you probably don't need that 30ohm resistor before the main power to the meter. But it wont hurt.

What is happening is that you have 2 coils inside the meter that are receiving current (amps) based on the where the resistance (ohm) value of each side of the sender.

ie. when sender is at full, one coil inside the meter is receiving full amps and the other is receiving very little amps, and vice versa, when the sender is at empty. When the sender is half way then both coils are receiving the same amount of current to balance the needle in the middle of the meter.

Essentially the meter needle has opposing forces applying in proportion to the position of the sender arm in the tank. I think....:)

Edited October 27, 2016 by maok
spelling error

[Kool48]

4 hours ago, maok said:

I'm now thinking that you probably don't need that 30ohm resistor before the main power to the meter. But it wont hurt.

What is happening is that you have 2 coils inside the meter that are receiving current (amps) based on the where the resistance (ohm) value of each side of the sender.

ie. when sender is at full, one coil inside the meter is receiving full amps and the other is receiving very little amps, and vice verse, when the sender is at empty. When the sender is half way then both coils are receiving the same amount of current to balance the needle in the middle of the meter.

Essentially the meter needle has opposing forces applying in proportion to the position of the sender arm in the tank. I think....:)

Thanks Moak ,   I did as you asked.  Red wire from Fluke to both 1 & 2 post of sending unit.   Ground to body of sending unit.   I get .4 ohms either all the way up or all the way to bottom about 6.7 ohms in middle of sweep of float arm.  So yes it's consistent.  Smooth also.      As far as taking this particular sending unit apart to clean I'm not sure.   Looks to me to be sealed .   The arm has a jam nut holding pivot point to body.    But I don't think you can pull the inner parts out this small hole.    So I haven't even tried it.   And if I did what would you reseal it with.   It's just odd that with sending unit connected to gauge I can't no lower than a 1/4 of a tank.   But gauge sweeps fine both ways using just a 6 volt battery.    I suspect that the sending unit being at fault here. But doesn't make sense.    The sending unit and gauge both have 1&2 post and gauge has 3rd post for power input.   So yes it's a 2 wire system.   I marked sending unit housing with blue sharpie at full , half and empty marks.    Tank is 8 "s deep   gauge has more Swing than 8 "s though.    This sending unit was used on 38 to 48 plymouth.  It's a Atwater Kents sender.    

[maok]

Yeah, I wouldn't worry about pulling the sender unit apart, no chance of resealing it.

Try 2 more tests.

1. Connect everything back together but reverse the connections on the sender unit. See if this gets you a range from empty to 3/4 full. Opposite to what you got before.

2. Check each of the terminals on the sender unit separately for ohms. Move the sender arm very slowly and check if there is erratic resistance values.

The two tests above should confirm (or deny) that you have a faulty sender unit. Either replace it or enjoy it the way it is. After all, its not a bad policy to fill up at about 1/4 full.

 

I wish my 1928 Chrysler  fuel gauge has as much movement (about 1/4 movement) as yours. My meter unit has mechanical issues - pot belly metal base is collapsing. They are a bugger to work on.

Anyone have a spare?

[dale]

I switched a 47 plymouth over to 12 volts way back when I didnt know better and never changed the sender unit nor the gauge and it all worked fine.  Not much on electronice so does the sender need a reducer from 12 volts or not as Kool48 was asking ?

[dale]

I see on e-bay a sender unit for a 1955-1956 Plymouth and 1955s were 6 volt and 1956s were 12 volt so does voltage matter ?

[maok]

The voltage does not matter in these cases. But if you go too high ie. say +24v you will get too high a current running through the meter and may burn it up if using the same sender unit as a 6v setup. The wire in the coils of the meter is very fine. So going from 6v to 12v will double the current running through the coils which I would think would be okay.

 

The '12v sender' may have higher resistance values (twice) which would mean that you would have half the current running through the coils of the meter. This shouldn't affect the way the meter works. Or, the manufacturers simply labelled them as a '12v sender' to sell you another to make money. But I couldn't say either way.

Edited October 27, 2016 by maok
spelling error

[dale]

Using the sender I got with a new tank I got out my other gauge, ran some emerycloth thru the gauge points, sprayed some brake cleaner on it, hooked it up and its working perfectly.  (so far)  12 volts straight thru.  Looks to be accurate.  Got to make sure you have a good ground.