--Edit its FM101 not LM101
I’m using a FM101 as per Drew's build. This allows you to calibrate a different sender to match your gauge. In this case a 10/73 ohm sender to a 30/0 ohm gauge . I bought 2 of this units and BOTH are doing the same thing so I am either unlucky or missing something.
Let me start off with the things I have tried on the bench and confirmed with a meter.
Earths are all correct and tied together between FM101, sender and gauge.
Sender reads 11 ohms full and 74 empty and sweeps through that range without dead spots when you move the float.
Gauge reads full to empty when I attach a 30ohm pot in place of the sender. Sweeps through that range smoothly
With sender and FM101 attached, I follow the provided instructions. Done it a few (20+) times now and having also tried to do it incorrectly it’s pretty clear that there is only one way that this unit will program.
Set full on FM101 with sender at 11 ohms - gauge reads F and meter reads 30 ohms. Then the fun starts. Try to set half, with the sender in the middle of its range, and I can only dial the FM101 down to 22.3 ohms before it runs out of range on the trim pot. Setting E is not possible as the trim pot is out of range.
Finish programming and test and the output of the FM101 sits at 30 no matter where you move the sender to.
Maybe the FM101 is confused by the inverse ohms? Proved this is not the case by doing the same test with the 30 ohm pot that I have already used to check the gauge. Same deal. Calibrates 30 ohms fine but will not go below 22 ohms. Static at 30 when set to run.
Both units - same issue. Unfortunately its been so long since I got these that a refund is not an option.
Has anyone other than Drew had success with these? Not sure I want to keep throwing money at this solution.
My alternative mechanical solution to the problem is to strip the sender, flip the resistor and put a 47 ohm resistor in parallel to it between the gauge and ground. That would theoretically end up providing the 30-0 ohm range, but I doubt the sweep of the float would fully cover it. Here are the internals. If I cut a slot in the plastic I should be able to slip it over the float arm arse about. Then I need to cut a square out at the opposite end of the metal holder so I can re assemble. Might work and easier than trying to remove the rivet on the resistor strip and re riviting with the resistor strip flipped (there is a hole already provided).
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Or I just use the sender as is with the 47ohm in parallel and have it read just below half way on the gauge for full and F when empty.
I really hate that idea though.
It took me a couple of senders to get it to work.
