Adjusting Fuel Gauge And Sender Resistances - Page 1
Forum section: electronics / projects

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: June 10, 2024, 04:01:59 pm
content: Greetings.Suppose you had a Fuel Gauge manufactured to operate in the 0 to 190ohm range where 0 ohms = Empty and 190 ohms = Full.Now suppose you have a Fuel sending unit which provides a resistance range of 0 ohms when empty and 90 ohms when full.Is there any way to use resistors in parallel or series to compensate so that the gauge can work properly with the available sender mentioned?I guess that basically you want to convert across the entire range so that as the Fuel Sender reaches it's full resistance of 90 ohms, the Gauge actually sees 190 ohms of resistance.Assume a negative grounding system.Thanks

author: David Hess
author_rank: Super Contributor
timestamp: June 10, 2024, 04:34:20 pm
content: With just resistors, the resistance range can be lowered, but not increased. Increasing the range will require active circuitry of some kind.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: June 10, 2024, 07:39:18 pm
content: I think that's what I want to do......Lower the resistance range of the Gauge ?

author: floobydust
author_rank: Super Contributor
timestamp: June 10, 2024, 08:03:44 pm
content: You could use an op-amp and power transistor etc. to convert the sender resistance, to about 3x.Something reliable is a bit awkward because older vehicles have dirty power and fuel tank ground is electrically noisy (esp. if there's an electric fuel pump) compared to the instrument cluster.There are $20 conversion modules out there that use a microcontroller to convert any fuel tank sender resistance to any fuel gauge. It might be worth looking at because old senders are being changed to modern ones and if your 90 goes then what? Hassle is the UI is gross to calibrate empty/full tank.https://www.aliexpress.com/item/1005006992275033.htmlhas instructions, picshttps://www.aliexpress.com/item/1005006419104858.htmllow priceIt's just how much time you want to spend on it. There's some American makers of these converter modules but pretty expensive.

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: June 11, 2024, 01:08:44 am
content: Quote from: floobydust on June 10, 2024, 08:03:44 pmAwesome!Thank you for that!

author: Smokey
author_rank: Super Contributor
timestamp: June 11, 2024, 01:28:59 am
content: I think you want to think about this like a current source, not directly a voltage or resistance thing.If it's an old school gauge then it's probably responding to the amount of current. That's what moves the needle (magnet in a coil).

author: amyk
author_rank: Super Contributor
timestamp: June 11, 2024, 03:50:18 am
content: Quote from: Smokey on June 11, 2024, 01:28:59 amThus roughly halving the voltage to the gauge may also work, and was my first thought on how to solve this.

author: Poroit
author_rank: Frequent Contributor
timestamp: June 11, 2024, 09:12:43 am
content: Have a look at these sites,https://www.squarebirds.org/gauges/HeatActivated/http://www.mgb-stuff.org.uk/fuelgauge.htm#typesI think you have a thermal sender

author: ThermallyFrigid
author_rank: Frequent Contributor
timestamp: June 15, 2024, 05:52:32 am
content: The actual Fuel Tank Sender resistance range in this case is 368ohms (empty) to 90ohms(full)So this vehicle has a 368 - 90 Fuel Tank Sender (very unusual)even if I reversed the wire wound plate in this sender to reverse the empty and full ends the 368 is too far out of normal range.StandardFuel Gauge ohm ranges are listed here....... (empty to full)0 - 900 - 1900 - 18010 - 180240 - 33240 - 30Here is the device I ordered to be able to use any fuel gauge with any fuel sender. I hope it works. I want to use Sender 368 - 90 ohm with Gauge 240 - 33 ohm.https://www.aliexpress.us/item/3256803576994211.html?spm=a2g0o.order_list.order_list_main.5.78c61802eWSkZ1&gatewayAdapt=glo2usa

author: floobydust
author_rank: Super Contributor
timestamp: June 15, 2024, 06:12:42 pm
content: What make/model vehicle is it? It looks like you've got a huge offset 60-90Ω compared to the usual senders.Important is the 1/2 tank reading, newer sensors can have non-linear fuel tank shape corrected for in the resistance curve. They seem to first design a car and then stuff in the fuel tank at the last minute and some are really weird shaped and giveThere was also a problem with Shell fuel additives damaging plastics, I had a car the float or resistance track got wrecked.