Simple solar question... May 11, 2010, 09:19:39 pm Yahoo Message Number: 112500Looking at solar charge controllers and panels leaves me a little confused. I'm trying to set-up a charging system for a 12 trojan deep cycle I use when rving to power my drywasher. What I'm having trouble is how much panel and controller I need. Suppose my drywasher runs 4-5 hours a day using a little under 3 amps an hour. That would mean I used between 12-15 amps. How many watt panel will put it back in a normal summer day in the mojave desert ? And how many amp panel will I need ?
Re: Simple solar question... Reply #1 – May 11, 2010, 10:30:29 pm Yahoo Message Number: 112501Jim, If your "Drywasher" draws 3 Amps at 13.3 Volts, it is using 40 Watts of power at any instant. If you figure a solar system is 50 percent efficient, (varies a lot on time of day, angle of the panel to the sun, temperature, etc. etc. so 50 percent is probably a good guess for any given day in the desert) you would need an 80 Watt panel to keep it running without running down your battery. Any extra would be used to charge your battery. To figure the size of a controller, divide the power rating of any panel you buy by 13.3 and make sure it is rated to handle that amount of current. For example, if you ended up with 200 watts of solar panel(s) you would need a controller capable of 15 Amps. (200 divided by 13.3 = 15) This is really simplified, but I hope it gives you some idea of what you might need. And remember, bigger is better, just more expensive.Rich Gort - 2000 MB - Birch Bay, WA
Re: Simple solar question... Reply #3 – May 12, 2010, 12:12:42 am Yahoo Message Number: 112507"The drywasher simply uses 3 amps when it's running. And it better be able to run on 12 Volts. Otherwise, it's a whole new ball game." Alex brings up a crucial point here, and I want to emphasize what he said. If your drywasher has to plug into 120VAC--if you were planning to run it from an inverter--that changes the whole picture. Three amps at 120V equal THIRTY amps at 12V! (More, actually, because the inverter is only going to be about 90% efficient.) Or putting it another way, 3A at 120V = 360W. Since solar panels rarely deliver more the half their rated capacity, that would call for 600W or more of solar panels--a huge investment. Bottom line: before you get any further into speccing out your system, make very sure you know which situation you're dealing with. Read the manufacturer's placard on that drywasher carefully and see what amperages, voltages and wattages it specifies.Andy Baird http://www.andybaird.com/travels/
Re: Simple solar question... Reply #4 – May 12, 2010, 01:21:16 am Yahoo Message Number: 112510As I stated the dry washer runs from a 12 volt trojan battery I am using. The motor on it draws 2.5 amps I'm told . So I think that means it should run for about 50/2.5 =20 hours.....{conservative guess here} But I want to setup a solar panel on a plywood sheet for support to charge it. In the desert I get good sun for about 12 hours and could move the plywood sheet to adjust the angle as needed. So could 50 watt panel put most of what I use back into the battery? even at 50% maybe 2 days running it and 1 day rest ? So a 50 watt panel would create roughly 50/14.3=3.49 3.49 *6 hours= 20.94 at 50% = 10.47 going back into the battery ? Does that sound right ? Could it all work with just a 30 amp controller ? The panel and controller will someday make it inside the motor home.
Re: Simple solar question... Reply #5 – May 12, 2010, 01:32:34 am Yahoo Message Number: 112511Yes, my 1982 lazyy daze has (1) 12 volt battery under the hood. but the battery I used is a spare I carry in it's own case. And Since I have 12 volt batteries I see no good reason to switch to 2 six volts in the current configuration of my rv.... When my Mom passes on and I get to go back to full timing We shall see.
Re: Simple solar question... Reply #6 – May 12, 2010, 02:31:22 am Yahoo Message Number: 112513QuoteAs I stated the dry washer runs from a 12 volt trojan battery I am using. The motor on it draws 2.5 amps I'm told . So I think that means it should run for about 50/2.5 =20 hours.....{conservative guess here} But I want to setup a solar panel on a plywood sheet for support to charge it. In the desert I get good sun for about 12 hours and could move the plywood sheet to adjust the angle as needed. So could 50 watt panel put most of what I use back into the battery? The unit of charge is A-hr, so a solar panel supplying a current of 3A for 1 hr will return 3 A-hr of charge back to the batteries - neglecting losses. A panel rated at 50W and 17V at max power will produce 50/17 = 2.9A - under full sun, in the tropics, cooled to room temperature, that is what it will do. Mounted on a board, and aimed directly at the sun in summer in a CA desert at midday, it will produce probably about 2.5A. Now if you manually adjust it constantly to track the sun, you might get about that for about 4-5 hours, and average half that for the remainder of the day. So, for your 12-hr day, you might get about (2.5 X 5) + (1.25 X 7) = 21 A-hr of charge. If your dry-washer is consuming 2.5A during that entire period, it will have used 2.5 X 12 = 30 A-hr. So, you would be down at least 10 A-hr. In the winter on a sunny day, expect half the charge capacity from solar. Note this assumes you are vigilantly adjusting the solar panel all day long for both azimuth and direction.Steve
Re: Simple solar question... Reply #7 – May 12, 2010, 10:02:51 am Yahoo Message Number: 112518"the dry washer runs from a 12 volt trojan battery... The motor on it draws 2.5 amps" OK, then it's a low-power device (30 watts), and your scheme sounds workable. You could probably run it with an 80W panel if that were the only thing you wanted to power from the sun... but what about your interior lights, sound system, etc.? You may want more panels, or a larger one. Plan for the whole coach, not just that one device."Could it all work with just a 30 amp controller?" A 30A controller can handle up to 360 watts, so it certainly can deal with one or more 80W panels. :-)Andy Baird http://www.andybaird.com/travels/
Re: Simple solar question... Reply #8 – May 12, 2010, 10:48:16 am Yahoo Message Number: 112521rving to power my drywasher. >WHAT is a "drywasher"?
Re: Drywasher? Reply #9 – May 12, 2010, 11:24:33 am Yahoo Message Number: 112522Roger, I didn't know either, but Google has the answer. "There's gold in there them hills!" It's used by gold prospectors. A link: http://www.thompsondrywasher.com/index.htmAlex Rutchka, SE #4 '05 MB
Re: Simple solar question... Reply #10 – May 12, 2010, 12:42:10 pm Yahoo Message Number: 112526Here's another tip to help juggle your money. When shopping a charge controller, look for one that will handle your future needs with the best efficiency. That would be an MPPT controller - but at 300W capacity, it will be expensive. An alternative, for now, is to decide what your initial solar panel needs are, then purchase an inexpensive shunt controller that will handle the current. Shunt controllers are not quite as effective as others for keeping the batteries fully topped off, but they are just as good as PWM controllers in bulk charge mode, where it seems you will be operating most of the time. Also, compared to other charge controllers, they draw no current at all after dark.Steve
Re: Drywasher? Reply #11 – May 12, 2010, 12:42:10 pm Yahoo Message Number: 112527Thanks for looking it up. there are 2 basic kinds of drywashers. Constant air. which use something like a leafblower to sopply air to blow off the finer/lighter material and a puffer which has a motor driving a bellows. I use the puffer type which is often powered by a motor like a window motor from a car. If I can keep the battery charged from a solar panel. I will not be using my portable generator as much to recharge that battery.
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