On Fri, 11 May 2001 12:03:31 EDT ChrisAtUpw@....... writes: > In a message dated 11/05/01, twleiper@........ writes: > > > Except you want the 5 HP engine to put away at about 1500 RPM with [edited] > > > > Since we are considering fairly high power systems, providing > two 12 V > storage batteries for a 24 V system and two 750 W alternators to > charge them [edited] > 1,500 W is probably OK for the computer and other > equipment > being considered, but it is not a lot of power to run a whole house > as well. > The 24V is a very attractive option, but you quickly get back into serious money unless you are quite lucky. 24V inverters are not easy to come by, and two 12v ones are probably cheaper. About ten years ago I WAS lucky in that I could tell that a non-descipt box with a giant cannon receptacle on one end was, in fact, a 2KW inverter used to power the accessory/shaver outlets in an airliner. This is a very nice unit with sine wave output, excellent regulation (including load controlled cooling fan speed), buss syncronization and all weighing about 10 lbs. It run on 24 volts as well. I bought it for $20 and, after reverse-engineering it by drawing out schematics, put it to use in my SWL /seismo shack to power almost the same loads Larry is talking about. A couple computers and 160W of flourescent lighting. The average load is about 500W if my 20" Sun monitors are off, 1KW otherwise. The battery bank consists of two 110 AH PowerOne Gell cells in series, and is also used to power an R-392 military tube receiver that has been on for ten years. I charge the batteries and power the radio with a 5 amp current limited power supply. When power is interrupted, a simple adjustable "delay-on" relay "falls off" and switches the load. The inverter runs at all times and, thanks to its "sense" input, remains syncronized with the line. It draws little power in the no-load state, and the relay is easily fast enough for the switching supply in the computers. When power is restored, the relay times out about a minute and then switches the load back to the line. I also have a simple lightning / static detector amplifier system that will switch to the inverter and cut the modem lines when thunderstorms are nearby. For the rest of the house I have a very conservatively rated 5 kw military four cylinder water cooled gas generator from 1960 with a Hercules engine and Leyland generator. It is 120V, and, before I built my automatic transfer switch, I had a manual transfer switch that powered both legs in parallel, thus cutting out all the big loads like the range, oven and dryer. Being military, the generator has a 24v charging and cranking system which I could use to charge the inverter batteries, but I don't. The inverter just keeps the computers going while the generator starts. Later, I installed a 100A sub panel with just the standby loads so the generator could start automatically without being over-loaded. The generator gets regular exercise under load of about a half hour every other week in the summer and every week during the winter. Actual outages average about 15 hrs a year, but there are years where the actual time may have only been minutes, and one Nor'easter year it ran 80 hrs for one storm alone. The 5KW generator easily powers a fridge, a freezer, oil fired boiler, well pump, hot water circulator (heat water with oil and/or 80 gal electric) a large TV and a couple computers, as well as enough lights to move around in the 6,000 sq ft home. I have a KWH meter on the generator, and the cumulative average load has been 2.1 KW at night and half that during the day. The only caution in this example is the fact that this particular generator has greater than average capability to start motor loads because of the high torque of the four cylinder (13HP) engine and rather large rotating mass...the whole thing weighs 750 lbs. A "lawn mower" type generator of the same 5KW size would probably require you to stagger your motor loads. One load you should avoid is ceiling fans. These are series-wound and draw an amazing amount of current while starting, as does the the oil burner blower motor. If the head pressure has not had enough time to bleed down, your fridge will hammer down a small generator as well. In any event, having worked with both these power sources for many years, and helped friends and family members design and install or restore similar systems, I would not recommend the inverter for anything other than what Larry started this thread about...resistive and light inductive loads. Certainly no motors beyond drills and sewing machines. But you will be suprised what you can do with 1 KW of load, and that would easily be supported by the 12V 80A alternator and putt-putt Briggs Stratton. And if you want to power intermittent bigger loads just get a 2 to 3 KW inverter and plenty of battery (current) capacity. Then you can use the hair dryer, hot plate, electric frying pan (remember them?) or coffee maker. The putt- putt will deliver its kilowatt and the batteries the rest. Speaking of batteries, my favorite local scrap yard has main-frame UPS pulls that are Gel in the 80 to 100 AH range for about $20 each. Some of these are rated for a ten year service life and may only be half used. They have skids of them. Sorry for the long post, but trust me, it will work. Tom __________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>