I need help from an electronics genius.
Road Warrior
Joined: Jun 2014
Posts: 1,357
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From: Michigan
Just so we are clear the resistor needs to be 5.5K not 400 in parallel, in the name of attempting to answer first I made an error and corrected it with an edit, by the way those gauges will look real good as long as they aren't too bright at night.
Last edited by HardRider1; Jan 27, 2016 at 06:58 PM.
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Road Captain
Joined: Jul 2015
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From: Billings, Montana Out in the Wild West.
Ok, 5.5K it is, thanks again.
Last edited by madsonp; Jan 27, 2016 at 07:12 PM.
Seasoned HDF Member
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From: Charleston, SC
That would add ten more to the total from his stock sender.
OP, you could run it the way it is. Worst case scenario, if the high number is full and low number is empty, it'll read full longer and won't reach completely empty on the gauge. If you want to do the math, you might find a resistor value that when hooked in parallel would bring the overall impedance down. The problem is, it will do this as a ratio to the total resistance.
This site has an online calculator.
Using that calculator, you would need a 5.5k ohm resistor in parallel with the sending unit to make the 251 come down to 240. But that would barely reduce the 39.8 below 39.5 ohm. To make the low side 39.8 come down to the 33 ohms you're after you'd need a 193 ohm resistor. This will have a much larger effect on your high end resistance, it would drop to 109 ohms. If I were you, I'd try it the way it is, the difference is minimal. It can't be any worse than the gauge that came with the bike from the factory.
OP, you could run it the way it is. Worst case scenario, if the high number is full and low number is empty, it'll read full longer and won't reach completely empty on the gauge. If you want to do the math, you might find a resistor value that when hooked in parallel would bring the overall impedance down. The problem is, it will do this as a ratio to the total resistance.
This site has an online calculator.
Using that calculator, you would need a 5.5k ohm resistor in parallel with the sending unit to make the 251 come down to 240. But that would barely reduce the 39.8 below 39.5 ohm. To make the low side 39.8 come down to the 33 ohms you're after you'd need a 193 ohm resistor. This will have a much larger effect on your high end resistance, it would drop to 109 ohms. If I were you, I'd try it the way it is, the difference is minimal. It can't be any worse than the gauge that came with the bike from the factory.
I thought the fuel sender was a simple DC circuit and not AC (impedance) and the OP's sender changes state from 251.5 - 39.8 ohms.
I figured adding 10 ohms (or thereabouts) to a 240-33 ohm circuit would give him 250-43 ohms which would be close to the range. Hell I forget.
A resistive decade box would be useful here...lol
Grand HDF Member
Joined: Aug 2014
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From: Eastern Ohio
It's really been a long, long while since I was an electronics technician so forgive my weak attempt.
I thought the fuel sender was a simple DC circuit and not AC (impedance) and the OP's sender changes state from 251.5 - 39.8 ohms.
I figured adding 10 ohms (or thereabouts) to a 240-33 ohm circuit would give him 250-43 ohms which would be close to the range. Hell I forget.
A resistive decade box would be useful here...lol
I thought the fuel sender was a simple DC circuit and not AC (impedance) and the OP's sender changes state from 251.5 - 39.8 ohms.
I figured adding 10 ohms (or thereabouts) to a 240-33 ohm circuit would give him 250-43 ohms which would be close to the range. Hell I forget.
A resistive decade box would be useful here...lol
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From: Utah
Reciprocal formula for parallel resistance: 1 / (1/x (R1) + 1/x (R2))= RT
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Road Captain
Joined: Jul 2015
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From: Billings, Montana Out in the Wild West.
Seasoned HDF Member
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From: Ottawa, Ontario
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