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Re: Fuel gauge sender project...the start of it...
Jon G #1415202 Mon Jun 28 2021 03:37 PM
Joined: Mar 2014
Posts: 2,475
J
Jon G Offline OP
'Bolter
You can do that, Craig. At least it is certainly worth a try. I wasn't certain why you had suggested a 45 ohm resistor...have been wondering if there was some trick I never learned. And that's possible, I ought to add. I've studied this stuff off/on since late 1957, and sometime in the early 70s I disabused myself of thinking I'd ever understand it completely.


Email me your postal address (my email address is jon_goodman@yahoo.com). I don't have a 60 ohm resistor here, but I do have 4 180 ohm resistors and I'll be happy to send 3 of them to you. Run 3 of those in parallel and you'll have 60 ohms (60.3 by my meter). That should help things.


Jon

1952 1/2 ton with 1959 235
T5 with 3.07 rear end
Re: Fuel gauge sender project...the start of it...
Jon G #1415207 Mon Jun 28 2021 03:55 PM
Joined: Mar 2007
Posts: 1,271
T
Crusty Old Sarge
Jon,
59 Fleet (Mark) suggested the 45 Ohm resistor, he has used that with his project and seemed to have good luck. I have however found a 1w 60 Ohm resistor on Amazon and ordered 2 of those. I don't profess to being an electrical genius, I do have a background in Power Generation so I am following your tests closely. I had thought about adding a resistor prior to doing a search for the sending unit subject. I was happy to find your thread and how detailed it was. My thinking was that "I can't be the only one that has encountered this problem", that thinking was right and led me to your post.

I will wait for the 60 Ohm resistor to be delivered and do some testing on my own, and of course I'll be sure to post the results. I thank you for the education.


Craig

Come, Bleed or Blister something has got to give!!!
59' Apache 31, 327 V8 (0.030 over), Muncie M20 4 Speed, GM 10 Bolt Rear... long term project (30 years and counting)
Re: Fuel gauge sender project...the start of it...
Jon G #1415216 Mon Jun 28 2021 04:42 PM
Joined: Mar 2014
Posts: 2,475
J
Jon G Offline OP
'Bolter
Thanks Craig. The 1W 60 ohm resistor should be fine. Power Generation, eh? Interesting. Evidently we could use a lot more of that than we currently have here in Northern Texas. Or at least we could learn to manage it better.


Jon

1952 1/2 ton with 1959 235
T5 with 3.07 rear end
Re: Fuel gauge sender project...the start of it...
Jon G #1418537 Wed Jul 28 2021 07:28 PM
Joined: Mar 2007
Posts: 1,271
T
Crusty Old Sarge
Jon,
Please check my math. Using a 45 Ohm resistor should get me close if I'm figuring this correctly. Ohms law says that should work. 1/90+1/x=1/30 or 1/30-1/90=1/x.


Craig

Come, Bleed or Blister something has got to give!!!
59' Apache 31, 327 V8 (0.030 over), Muncie M20 4 Speed, GM 10 Bolt Rear... long term project (30 years and counting)
Re: Fuel gauge sender project...the start of it...
Jon G #1418538 Wed Jul 28 2021 07:43 PM
Joined: Mar 2014
Posts: 2,475
J
Jon G Offline OP
'Bolter
That looks right, Craig. 1/30 - 1/90 = 1/45 or put another way it would be .02222222 and that would be the same as 1/45.


Jon

1952 1/2 ton with 1959 235
T5 with 3.07 rear end
Re: Fuel gauge sender project...the start of it...
Jon G #1418550 Wed Jul 28 2021 09:31 PM
Joined: Mar 2014
Posts: 2,475
J
Jon G Offline OP
'Bolter
Or in case the teacher wants to see our calculations...
9/270 -3/270 = 6/270 or 1/45.


Jon

1952 1/2 ton with 1959 235
T5 with 3.07 rear end
Re: Fuel gauge sender project...the start of it...
Jon G #1418597 Thu Jul 29 2021 07:06 AM
Joined: Jan 2019
Posts: 98
F
'Bolter
The problem with using the 45ohm resistor (or any parallel resistor) is going to be one of linearity.

At the two end points (30ohm and 0ohm), the math works out. A 90 and a 45 in parallel does equate to a 30. A 0 and a 45 equates to a 0.

But in the middle, it will not be correct because one resistor is changing and the other is not. Take half a tank as an example: the effective resistance *should* be 15ohms. The resistance of the sender will be 45ohms (halfway between 90 and 0), but the parallel resistor will still be 45ohm as well. So the effective resiatance of the whole thing will be 22.5ohms. At 1/4 tank, the sender will be 22.5 and the parallel will be 45ohms for a total of 15ohms instead of the 7.5ohms it should be.

I realize this is similar to your comments on the 45 ohm idea, but that post *appears* to be implying that the % change in effective resistance would be constant across the entire range. If I misunderstood your meaning, I apologize for repeating you.

It probably wouldn't be amy easier than a custom solution, but if you took 3 0-90 ohm senders and hooked them up in parallel, that would do the trick because the effective resistance would always be 1/3 the sender resistance.

Last edited by Fibonachu; Thu Jul 29 2021 07:11 AM.

58 Apache, long bed fleetside, V8 w/SM420
Drivable but the rear axle needs work.

59 Apache, long bed fleetside, half of an L6, 3 on the tree
Bought by my dad out of a field for $100 to build with my brother. He never touched it, so now it is mine if I can figure out how to get it down from Alaska.
Re: Fuel gauge sender project...the start of it...
Jon G #1418598 Thu Jul 29 2021 07:17 AM
Joined: Jan 2019
Posts: 98
F
'Bolter
Have you considered getting a PCB made with the "coil" printed on it? The one I put in my truck was that design. The copper is thin enough that you can tune the resistance of the trace by adjusting the trace width and coil length. You can get the PCB pre-machined with your mounting holes and in the curvature that you want.

I could help design that pcb if you were interested. The picture I have in my head is a replacement board that matches the original design so anyone could just replace the coil in their existing sender with it.


58 Apache, long bed fleetside, V8 w/SM420
Drivable but the rear axle needs work.

59 Apache, long bed fleetside, half of an L6, 3 on the tree
Bought by my dad out of a field for $100 to build with my brother. He never touched it, so now it is mine if I can figure out how to get it down from Alaska.
Re: Fuel gauge sender project...the start of it...
Jon G #1418610 Thu Jul 29 2021 12:16 PM
Joined: Mar 2007
Posts: 1,271
T
Crusty Old Sarge
Fibonachu, Jon...
I realized just as you said the resistance would not change equally across the the band as such the gauge would only be accurate at full and empty. I found a product for Classic Instruments that allows the sending unit and gauge to be compatible. Cost is the factor here, the module is $135.00.

https://shop.classicinstruments.com/sn34


Craig

Come, Bleed or Blister something has got to give!!!
59' Apache 31, 327 V8 (0.030 over), Muncie M20 4 Speed, GM 10 Bolt Rear... long term project (30 years and counting)
Re: Fuel gauge sender project...the start of it...
Jon G #1418624 Thu Jul 29 2021 02:00 PM
Joined: Mar 2014
Posts: 2,475
J
Jon G Offline OP
'Bolter
Hi guys, I probably oversimplified things in my linear sweep comment. I'm known to do that when talking about things like insurance or electronic theory. Mainly because those 2 topics are dangerous to discuss. At any point parts of the audience can doze off and bang their head on their desktop. But yes, preserving linearity is important and even with a carefully made variable resistor coil, that isn't always as simple as it seems it should be. That is one of the reasons I've been impressed with the sender unit sold by "renbusan" on eBay. As for the coil on the PCB, please tell me more about what you're thinking. The image below is the best I've come up with so far and I do have one thing about it I need to change. I've been meaning to incorporate a ball bearing between the wiper lever and body. The project isn't dead by any means, but just stalled a bit while I think about it.

Attached Files
new design 2.JPG (17.92 KB, 14 downloads)

Jon

1952 1/2 ton with 1959 235
T5 with 3.07 rear end
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