I read with interest the “Forty-Amp Catch-22” article in the December 2017 issue. I recently inspected an RV-6 that had an upgraded 60-amp alternator with healthy #8 wires from the alternator to the bus. However, the wire from the bus to the master relay was only #12 at best. In a high-current battery charging scenario, it could have overheated. So wire sizes need to be looked at, as well as circuit breaker values, when upgrading alternators.
Reader McLagan makes a good point—one that we observe, but forgot to point out. Always check the sizes of wiring throughout a system on a used, older homebuilt when doing an upgrade. You never know what you might find.—Ed.
iPower by iBruteForce
I enjoy Jim Weir’s articles, but I have an issue with “iPower by the iBruteForce Method” in the January 2018 issue. There is nothing wrong with the analog power supply. In fact, other than efficiency, it is preferable to a switching supply used in most chargers. The issue is a lack of bias on the data lines. Apple products require a bias on the data lines to tell the device how much power is available from the charger. Without the bias, they charge at a very low rate or not at all. I learned this after I installed an off-the-shelf DC to DC converter to get 5V DC to charge my iPad. A commercial panel-mount charger replaced the converter, but I then discovered that the noise from the switching power supply swamped the GPS signal to my Garmin 396. Once I figured out the charger was the issue, I put in a metal housing with a ferrite bead on the power-in leads. Problem solved!
Jim Weir responds: It is worse than that. Ralph’s observation is correct…almost. Apple started the whole controversy by completely violating the convention that the most power you can take from a USB port is half an amp (500 mA). Then they went a step further to say that they were putting some electronics into the charging cable to tell the USB port how much power they needed. Then they changed the way that they did that little maneuver. Then the second-gen iPads started sucking 2.1 amps, which nearly all USB circuits couldn’t supply…except those designed by Apple. To top it off (as I now understand it) the current production iStuff takes as much as the USB circuit will allow, and if that isn’t enough to keep the batteries up to speed, the device slowly dies.
To whom this may concern: The SOS article [January 2018] by Myron Nelson was crazy good!
Myron Nelson’s SOS article is Brilliant! Thanks for this. I’ve sent it to several pilot friends.
OMG! MN’s article about acronyms forgot the most important one—TLA (three letter abbreviations). NASA would be shocked.
—Christian von Delius
We heard from many readers about Myron’s story. Glad you liked it! Look for more from Myron in the future.—Ed.
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