---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Tue 11/21/17: 3 ---------------------------------------------------------- Today's Message Index: ---------------------- 0. 09:54 AM - Coming Soon - The List of Contributors - Please Make A Contribution Today! (Matt Dralle) 1. 09:37 AM - Re: Re: voltage fluctuations (Robert L. Nuckolls, III) 2. 12:50 PM - Re: Re: voltage fluctuations (Robert L. Nuckolls, III) ________________________________ Message 0 _____________________________________ Time: 09:54:18 AM PST US From: Matt Dralle Subject: AeroElectric-List: Coming Soon - The List of Contributors - Please Make A Contribution Today! Each year at the end of the List Fund Raiser, I post a message acknowledging everyone that so generously made a Contribution to support the Lists. Its my way of publicly thanking everyone that took a minute to show their appreciation for the Lists. 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Best regards, Matt Dralle Matronics Email List Administrator ________________________________ Message 1 _____________________________________ Time: 09:37:54 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: voltage fluctuations I was able to work on this last weekend and found that there was indeed some voltage loss between main bus and master switch. Got that taken care of, got rid of the jumper between pins 3 and 6 on voltage regulator and added a dedicated bus voltage sense wire, and then monitored voltage at a number of locations with the engine running using my trusty Radio Shack multimeter: 14.08 V at battery; 14.06 at battery bus, 14.05 at main bus, and 13.31 at e-bus that is fed through a diode. With the e-bus alternate feed switch turned on, e-bus voltage jumps to 13.96. Voltage readings are now steady at the battery and bus locations. Very good. This validates our hope that there are no problems with the hardware. EIS and two EFIS screen voltage values are only indicated in tenths of volts on the screens, and these values seem to fluctuate by 0.1 or 0.2 V; not sure why that is, but perhaps that isnt really a concern. ALL digital dispalys are subject to some degree of 'bobble' in the least significant digit. Which has to do with the manner in which DC votlages are filtered, sampled and converted to binary values for furhter processing. Then there are the effects of naturally occuring variations in the bus votlage itself. Unless the designer has gone to the trouble to oversample, do running averaging or perhaps convert to more digits and toss out the last one . . . you're going to see this bobble. As much as plus or minus two counts in the least significant digit is of no concern. Back in the days when the best voltmeters installed might look like this: [] You couldn't see the fluctuations . . . but they were still there. EIS (fed from e-bus) = 13.5 V pilot EFIS, primary power source (fed from e-bus) 13.4 V pilot EFIS, secondary power source (fed from main bus & TCW power stabilizer =13.8 V. So looks like my intended secondary power source for covering engine-start brown-outs is actually serving as my primary power source due to its higher voltage. Copilot EFIS, primary power source (fed from e-bus) = 13.2 V (a bit low) There is no secondary power source connected for the copilot EFIS. So, all good overall, although thinking I should adjust the voltage regulator until I get 14.2 V at the battery so that it recharges a bit faster. 14.4 volts is not out of line. Reading from the Hawkjer-Enersys manual on Odyssey batteries: Emacs! It sounds like the power management philosophy for the 'secondary power sources' could use some refinement. Without detailed schematics describing just how electrons are being herded through the system, it's not possible to offer a detailed assessment. The take-away from this exercise was predicted by one of my heros: "When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the stage of science, whatever the matter may be." -Lord Kelvin- 1864 Bob . . . ________________________________ Message 2 _____________________________________ Time: 12:50:41 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: voltage fluctuations I almost forgot . . . >So, all good overall, although thinking I should adjust the voltage >regulator until I get 14.2 V at the battery so that it recharges a bit faster. > > 14.4 volts is not out of line . . . When setting your voltage regulator, adjust for the desired magnitude AT THE REGULATOR'S SENSE POINT. In this case, at the main bus. Adjusting for voltage at the battery does not account for inevitable VARIATIONS in voltage drop between the sense point and the battery. If the battery is taking a charge, current through the charge path DEPRESSES voltage at the battery . . . which approaches zero as the battery charges. A fully charged battery's terminal voltage and the sense point at the bus will be essentially equal. So while cranking on the little screw, measure from the bus. 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