This is such an interesting thread that I decided to bench-test my hypothesis posted earlier. Using a DuraComm LP-14N switching power supply set for 13.8 VDC output, a variable AC power source, and an electronic load, I tested the power supply to see at what input voltage it would falter, at various loads. Here are my findings:
At 1 ampere DC load, faltered at 74.2 VAC input At 2 ampere DC load, faltered at 76.1 VAC input At 3 ampere DC load, faltered at 76.9 VAC input At 4 ampere DC load, faltered at 78.0 VAC input At 5 ampere DC load, faltered at 80.2 VAC input At 6 ampere DC load, faltered at 80.8 VAC input At 7 ampere DC load, faltered at 81.3 VAC input At 8 ampere DC load, faltered at 83.2 VAC input At 9 ampere DC load, faltered at 84.4 VAC input At 10 ampere DC load, faltered at 85.9 VAC input Even at a 10 ampere DC load, the AC input current was only 3.03 amps. If you are provided 85 VAC at a maximum of 4 amperes AC, a switching power supply appears to be the ideal solution. I have no doubt that switchers made by Samlex, Astron, and others will offer similar performance- but, as always, YMMV. 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Eric Lemmon Sent: Sunday, February 14, 2010 11:17 AM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] 85VAC to 12 VDC? AJ, The obvious solution is to connect a commercial switching power supply- definitely NOT a linear supply- across the AC source. Most Samlex, Astron, and DuraComm switchers can work wonders in such an environment, where conventional linear power supplies will surely fail. Don't use a larger (higher capacity) power supply than you really need; in this case, larger is not better! 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> [mailto:Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> ] On Behalf Of AJ Sent: Sunday, February 14, 2010 10:22 AM To: Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> Subject: [Repeater-Builder] 85VAC to 12 VDC? We've been given the opportunity to setup a remote receiver at the end of local local cable television provider's plant on the hill to help with coverage. Powering is the only issue we're running in to - currently the only power available within 6 pole spans is the 90 V AC plant power across the CATV coax. They've offered to cut in a power inserter at this location to feed up to 4 amps of 90 VAC to us (roughly 85 VAC at that point in the plant) - what is out there for a reasonable cost effective solution to convert this to 12 VDC? This stub of plant does not have RF across it, nor will it any time soon (RF removed when fiber backbone was overlashed on the same pole line). Our first concern was leakage but that shouldn't be an issue. 73, AJ, K6LOR
