Friday, April 2, 2010

On A/C and RPMs

On Monday I received the new beta exciter rings for the newer style RPM sensor. You may remember that the newer style RPM sensor mounts flush to the motor and would allow me to use the remaining portion of the tail shaft on the motor to mount a pulley I can use for the A/C system.

I got to work putting the new sensor in place so that I could run some tests and get some comparison numbers. I thought I'd get a new set of numbers using the old sensor first, and then switch the leads connected to the Zilla to the new sensor and test it. Last time I got readings in first gear at 10, 15, 20 and 25 mph. I wanted to do the same thing this time, but add tests in 2nd and 3rd just to get more data.

Sadly that wasn't to be. When I was putting on the new exciter ring, I knocked the cup for the old sensor that fits over the end of the tail shaft out of alignment, and didn't notice. When I went out to test, I watched the RPMs climb to about 1600 and then the tach went dead. When I got it back in the garage, I found that the magnet inside the cup had been rubbing on the side of the cup and self destructed. *Sigh*

So I took it off and started the test on the new sensor with the new ring to get some new data. Since I had the old data from the older style sensor, I could still compare those two sets. What I found was a slight deviation. At 25 mph, the old sensor reported 4300 RPM, but the new one reports 4600 RPM.

Working with the manufacturer and Ryan at EV Source, we decided to crunch some numbers to see what it really should be. Based on the size of the tires and the final drive ratio in 1st gear, the RPMs at 15 mph should be 2632. The sensor is reporting 2600. I'd say the new sensor is more accurate than the old one.

I took off the old assembly I'd built which was designed to hold both sensors in place, and mounted up the new one. Then I mounted the pulley. I don't have a belt for it yet, so I need to get that next. Then I need to take it down to an A/C shop and find out if they can build new lines for it, and more importantly, if they are willing to. I'm really worried they'll take one look under the hood and say "No way!" In any case, I'm one step closer to A/C.

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