Re: 48-50 Bimetal Senders Retrofit Project

Posted by humanpotatohybrid On 2024/5/3 15:20:09

Thanks. It's surprisingly non-linear, but maybe that's how the gauges read to begin with.

Since you have 0.2A at 20 sender ohms, then with a 5V regulator that implies the gauge has a 10 ohm resistance. This checks out with the 50 and 100 ohm values also. So we see that about 22mA is required for the gauge to read 0; and open circuit is required for the gauge to read 100. I can easily make something that will convert linear-linear. Following the exponential decay curve could be difficult, but might not really be necessary as you can just calibrate the gauges to what looks good. For example, where normal coolant temp and oil pressure read right in the middle, and where the gas gauge reads perfect near empty. Will have to think more on a design that could replicate this curve well.

David please confirm, the "gauge percentage" of 0 is like your empty tank, no oil pressure, and cold engine; and "gauge percentage" 100 is full tank, high oil, and high temp?

P.S. Howard, I think that's what I'm getting at. I can make something where a 10-70 ohm sender will pretend to be a 20-120 ohm or whatever. Of course, if the range only needs shifted then a simple inline resistor would do the trick. But for these, even though a 10 ohm would make a 10-70 sender read correct when low, it would never read about more than about 85% high.