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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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UPS gives funny voltages - why?
I have a Conext (by APC) model CNB-325 battery backup power supply (not
a real UPS) that shows funny voltages when the power cord is disconnected. Backup supply plugged into AC outlet; hot-neutral: 120 VAC hot-ground: 120 VAC neutral-ground: 0.7 VAC Backup supply unplugged from AC outlet, computer used as load: hot-neutral: 115 VAC hot-ground: 58 VAC neutral-ground: 58 VAC Backup supply unplugged form AC outlet, no load: hot-neutral: 115 VAC hot-ground: 19 VAC neutral-ground: 60 VAC A different model Conext, model CNB-300, behaved similarly, only the no-load voltage on battery power was 90 VAC neutral-ground and 40 VAC hot-ground. I didn't get such wierd voltages on battery operation with a much older APC BK-300 (much larger battery, all-metal case); hot-neutral and hot-ground both measured 118 VAC, neutral-ground was slightly under 1 VAC. I measured with both a Fluke 73 digital meter (true RMP) and an analog meter with 10K/volt sensitivity. The analog meter gave very different voltages with each backup supply running off battery, but I assume it was caused by the AC not being a real sine wave. |
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