Posted: 4/3/2007 10:31:18 AM EDT
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I found this article the other day, and it sounds like a good plan for getting a backup power system going. It did leave me with a two questions right off the bat. The first one is in step one; is installing a transfer switch a DIY project, or something best left to a pro? My second question is how to figure out what size inverter/charger to get and how many batteries am I going to need? During an emergency I just want to keep the fridge cold a light or two going and the radio working. After I get a ham license I'll be adding another radio to the list. |
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As far as the transfer switch, it depends on how much of the house you want to power up. There are a few "transfer switches" that are just 2 breakers that cant be turned on at the same time, all the way up to the more commercial types that use 2 wire start. If you just want to run the fridge and a light, then get a good size portable. then just run an extention cord. If you want to spend more then a LP/NG or diesel is the way to go. Any thing that is permanent mounted should be installed by a "pro" and not just any electrican either. There is alot more to it than just hooking up a few wires. The NG line (if thats what you get) needs to be properly sized. If you go with something like a Generac that is avalble at homedepot or the like, you may want a "factory trained" tech to perform the start up so you dont run into warranty and other installiation issues down the road. I have worked with generators for the last 13 years and see more problems caused by inpropper install by customers then all others combined. As far as an inverter you would have to dertrmine the load amount then how long you wanted the batterys to last with out being recharged, then get the approprate inverter and ammount/size batterys. Keep in mind that some chargers dont like long charge times and are not designed to charge battery banks... I hope that I didnt muddy the water to much... |
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All good points! If you're trying to size power needs -- get a Kill A Watt meter. Thirty dollars or so. Tells you voltage, hz, indicated amps, VARS, watts, power factor, total time running and total kw-hours consumed. Name plates on appliances are useless, nothing more than guidlines. A KillAWatt meter takes the guess work out. Well worth it. As far as batteries go, they must be deep cycle. The starter type battery in a typical auto is designed for very brief high loads and a quick recharge. These will die very quickly if used for deep cycling. Once you've figured the load you want to run in total kw-hrs e.g. couple of small flourescent lights and a deep freeze for 48 hrs at 130 watt = 6.24 Kw-Hrs. Bump that up by 10% to account for typical inverter losses = 6.86 kw-hrs of storage if you were going to drain these batteries completely dead. BUT! Don't do that! Because lead-acid batteries do not like being discharged more than %50 --( a shallower cycle is even better. ) now figure on doubling that capacity to roughly 14 kw-hrs of storage. Rough and ready conversion example.... Say I've got a 12 volt battery rated at 95 amp-hrs. Keep in mind the standard rating is this load spread over 20 hours, higher loading yields a smaller total output and a smaller load would stretch this. But just raw numbers, 12 volt times 95amp-hrs equals 1.14kw-hrs 14kw-hrs divided by 1.14kw-hrs per battery eqauls 12 batteries. That's a pile of batteries. Now you do double check of your requirements...just 24 hour run time would only need 6 batteries for a %50 discharge. Maybe you can live with that for starters. Same math hold true if you were using 6 volt batteries. In this case you'd be wiring them in series-parallel. For grins, lets assume a 220 amp-hr battery at 6 volts. So each battery yields 1320 watt-hours or 1.32kw-hr per battery. So to have 14kw-hrs (48 hour run time, %50 depth of discharge) needs 10 of these... This is the balancing act. If you were going to recharge these say every 12 hours, then the batterries would only need to be 1/4 the total. Or go the other way..1_BIG_BUNKER planned big and he's got nearly 60 kw-hrs of storage. His thinking was never draw the batteries down more than 10 or 20 percent and they'll last a lot longer. Read this www.jobrelatedstuff.com/forums/topic.html?b=1&f=123&t=521243 Inverter and Battery storage test and upgrade at BOL. Pics added... Right up the line your talking about |