Fuel Gauge upgrade

[drak130]

Thanks for the suggestions,

We did try lights on/off and it made no difference. Did not try different RPMs.

The airplane does have a goofy magnetic field issue with it where the compass reads 10-15 degrees off on various headings. Tried to swing it myself on a compass rose but did not seem to make any difference. Thought it was my DG drifting so changed it out only to find out that it was the Mag Compass. Different problem or part of the same problem? Too much for this caveman pilot to wrap his brain around.

Given that there are at least two similarly equipped Maules flying around with CiES senders and unshielded wire, my bet is something going on at the alternator. I think we will start there.

Thanks again
Tim

[VA Maule]

Quite often electrical issues are bad ground connections. So before you mess around with what might be a perfectly good alternator try disconnecting cleaning reinstall each ground paying particular attention to the large crimped lugs that attach to the engine mount and firewall (both sides) . Also try re-crimping the large ones with a pair of vice grip pliers wile checking the ohms of each large ground cable firewall forward as well as back to the battery, if the reading changes with squeezing the vice grips corrosion is in the crimp. Any reading much above 0 ohms on those big wires is cause for concern

[drak130]

Fellas,

Checked all the grounds. All good.

CiES insisted on installing shielded wire so we did that. As some of you suggested that shouldn't be the problem and as it turns out, you were correct. No change.

Took Greg and AJ's advice and they were spot on. When powered by a GPU the fuel readings chase any change in the voltage. Currently the battery puts out about 13.5 volts when first turned on and discharges from there obviously. The voltage controller is set at 13.9-14.0 volts.

I suppose we could calibrate at alternator voltage, but then would not get an accurate check on the battery. We could dial the alternator control down to match starting battery voltage but then the accuracy would be in questioned if the plane sits out somewhere during a cross country and it is starting at less than topped off voltage. (it currently sits hangered on a battery minder).

Bottom line is that it sure doesn't seem like it should work this way and now that we know what the issue is, what do we do about it? Any electrical engineers out there? From my college EE classes (only took two) it seemed like there was a device (diode?) that would take varying voltage and put out constant voltage.

Thanks for all the help!

Cheers
Tim

[andy]

You're thinking about a Zener diode. It's part of a voltage regulator circuit but not the only component. The alternator control unit is in charge of controlling the output voltage from the alternator while the engine is running. It's not practical to put a second voltage regulator on the output of the alternator. The alternator is usually capable of providing 60 amps of current and that would require a huge voltage regulator as well as probably not providing a high enough voltage to charge the battery.

I noticed in the CiES installation manual that there are two different frequency output types of senders depending on the AML. Option 1 outputs 1200 Hz - 490 Hz and Option 2 outputs 10 KHz - 64 Hz. Are you sure that you received the correct senders for your aircraft model? You should be using the 10 KHz - 64 Hz version with the EI CGR-30P engine analyzer.

I know that you've checked all the grounds, but you might want to try running a dedicated ground wire into the engine compartment to the point where the alternator and negative battery contactor leads are bolted together. I had some different ground related problems with my JPI EDM 800 and ended up fixing them by doing this.

Section 5.1 Bonding in the installation manual requires burnishing the protective anodizing off one sender attachment screw. Optionally, a ground braid can be attached to the mounting screw and connected to the nearest airframe ground. The resistance measurement with either method should be less than 0.03 Ohms. Your A&P should be able to confirm that. When you measure the resistance, you should measure from the CiES sender attachment ground screw to the ground going to the CGR-30P.

I doubt that there is an interfering magnetic field considering that the sender's electronics and moving magnet are in the same housing far enough away from anything in the airplane that would generate a strong magnetic field.

I would re-check that the wiring is correct on the P5 harness pinout as shown in figure 5.6 of the installation manual for frequency senders.

I would call CiES and have them help you with the calibration procedure for the CGR-30P. It's complex and I read that the engine analyzer manufacturer doesn't always get it right. I think that the calibration process requires the aircraft to be level. I assume that your A&P did that but it would certainly change the fuel level in flight vs. stopped on the ground if it wasn't level.

[drak130]

Folks,
.
Thanks for all the advice. My A&P went to airventure during the frackus with the fuel senders. He got the EI folks and the CiES folks together. They argued for a bit and then came up with some trouble shooting guidance. Turns out it was a bum download from EI. CGR-30s correctly configured and now everything works as advertised. Moral of the story is: even if it is electronic and you just configured it, cycle the power to make sure it took before heading down more labor intensive paths!

Lots of wasted time and extra shielded wire I did not need.

Cheers
Tim

[ajak]

That's great news and thanks for posting the resolution to your problem. I wish all my airplane issues could be solved with a software update!