At 07:07 PM 07/13/08, you wrote: >Laryn, > >Your thinking is good. A simple relay, 3 pole/double throw would do >what you want and power the relay coil with your normal AC >power. When it goes the relay drops out and connects the repeater >to the RED emergency outlet. > >As someone else suggested switch all 3 wires of hot, neutral and >safety ground just to make sure you are not connecting something >that you should not. > >Some suggest runing the repeater on the RED emergency outlet and all >else on the normal outlet. You need to check to see if this RED >outlet is powered all the time and not just when the gen/emergency >power is running. Since it goes to the generator it might not >be. Easy to check by plugging a lamp under normal power conditions. > >The only problems I see is the sudden switching back and forth that >might occur quickly serval times in a short period. Like turning >on/off the repeater power supply rapidly, but don't think this would >be an issue. > >73, ron, n9ee/r
I long long time ago.... no, wrong story. More years than I want to think about I was at a local 2-way shop trying to beg a cabinet... the owner pointed at a old Moto 6 foot one in the corner and said "clean it out, leave me the radio, take the rest". So here I was, stripping down a radio cabinet that had come out of a hospital elevator room. It turned out to be a Motrac series 90w high band paging station. The power wiring was exactly as this comment thread was describing, with two power plugs (one labeled "Normal" and one labeled "Generator"), and a 4PDT contactor relay that made the entire cabinet jump an inch when it pulled in with a BANG (the contacts were 440vAC 50a rated on a 120vAC coil). The overall design had a clock-motor-driven timer that used a cam and a roller microswitch that implemented a 15 minute delay between generator power and normal power. In other words, a switchover from normal to generator was instantaneous, but normal power had to be on for 15 minutes before the radio system was switched back to it. The box the contactor and timer were in had a rotary switch labeled "normal", "generator" and "automatic", with a note saying "For bench test use generator cord and set this switch to generator". But this is old technology. Modern electrical practice is that the red outlets are hot all the time, and the white outlets die during a power failure. So the relay is totally un-necessary. Just plug the system into a red outlet, and design it so that a short (one minute or so) outage does not cause any discontent (maybe have an AGM battery in the bottom of the rack). One last comment - the hospital electrician may be keeping a list of what is on the generator outlets. Or maybe the administrative people are. Or maybe there are some other rules. Maybe the local inspectors has their nose in the hospitals electrical business. If I were in your shoes I'd get permission in writing from someone in the hospital before I plugged into that red outlet. I can envision a future situation where someone does a red-outlet-audit and finds your box, and it turns out that the recently-retired electrician gave you verbal permission a year ago, and the new guy has no idea who you are. Then the waste matter hits the rotary airfoil. I'm mentioning this because a friend works at a local convalescent hospital... they recently did a red-outlet-audit (the first in several years) and discovered that they are at 93% of generator capacity... they thought (guessed?) they were at 45-50%. Right now they are seeing what can be shed... i.e. moved from red to white, as a generator upgrade would be a political and financial nightmare (they would have to replace the underground diesel fuel tank with one that is much larger, and that would require major permits / costs / demolition / costs / installation / costs / certification / costs - and that is just for the tank. Then you have to fill it at over $5 a gallon. Then you have the same merry-go-round on upgrading the generator and it's controls and the load transfer switch. Mike WA6ILQ
