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Old 08-21-2007, 01:25 PM   #1
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How to? Solar Charge

Im hoping you can shine some light on the electric system for my upcoming project. What I want to do is rig up the electrical system in my short bus.

Ultimately, Im going to want to be able to power a small air conditioning unit. Also, I want to power one or two of: laptop, television, a small radio, and very low wattage lighting. Additionally, but not simultaneously, at some point I may need to power an electric burner or cookware of some type.

Realizing a small air conditioning unit may draw 10 amps max over 8 hours max (80Ah) and that I do not want to discharge my deep cycle battery beyond 50% at any time if at all possible, that puts me in the 160Ah range. Add another 100Ah to that for other applications and Im leaning towards the Concorde Sun Xtender PVX-2580L AGM Sealed Battery rated at 255Ah, 12Volt. Even if overkill, better too many Ah than too few Ah, especially if dependant on solar power, no?

Im fairly sure Ive sized my battery appropriately, so Id like to build the system around that. I want three available methods of charging this battery.

A) I want to mount a Sanyo 200 Watt HIT Solar Panel to the roof. Ill have room for more than one, seeing as how the dimensions are roughly 4.3 feet X 2.9 feet, but maybe not the budget for more.

B) A Honda EU2000i or EU1000i lightweight generator will come along for the trip

C) Id like to be able to charge the battery off of 120v AC whenever I can find some juice around.

Now I plan to spend the majority of my time in Florida, Texas, and the southwestern areas of the US, hence the desire for solar charge. Like I said, I may have room for more panels, but not the budget...so

Question 1) How likely is it that I will need a second panel at all?

I need a charge controller between the PV unit(s) and the battery, that much I know. Where Im somewhat confused leads to

Q2) How do I determine what I need the charge controller to be rated at?

The two AC methods would probably be primarily for backup during cloudy spells or in the event of a high depth of discharge etc. So I need a multistage battery charger between the shore power/ generator and the battery bank. Similarly

Q3) How do I determine what the charger needs to be rated at?

Also, Im very open to additional methods of charging the battery, but very unsure as to how anything else might work. Ive heard I can rig a special alternator to generate charge, but not sure of the costs of this method, and really would like to keep this electric system seperate from the vehicles own primary electrical system. I think the solar power along with said backups should be a good set-up.

Great, now that the battery is juiced up, its time to run the show. I plan on having every appliance using 120v AC power. Of all the appliances I think I might run, the measuring stick for the inverter should be the sum of the wattages of the appliances running simultaneously, or the wattage of the highest drawing appliance thatd Id run by itsef.

Most likely the first scenario has me running a 600 watt AC unit, and maybe a 100 watt laptop plus a few lightbulbs. Less than 1000 watts total. The second scenario has me running either a 1000 watt microwave or a 1200 watt cooking device by itself so lets go with a Samlex 1500 Watt 12 Volt Sine Wave Inverter.

EDIT: Oh- and if anybody can speak a bit about where ill need my fuses and meters, and what type, thatd be great!

So theres my system, as I see it. If you see any gross miscalculations or oversights, please let me know. Ive researched this topic fairly well, but am by no means an expert in the field so its likely theres alot that I dont understand and before I go about purchasing thousands of dollars in equipment, I need to know its all going to work smoothly.

Thanks!
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Old 08-21-2007, 09:35 PM   #2
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Re: How to? Solar Charge

Before attacking any of those other questions we need to clear up some math here. I'm thinking there is a unit conversion missing.

You said a small air conditioner draws about 10 amps. That is reasonable enough...but at what voltage? 10 amps at 120 volts is 1200 watts. To get 1200 watts on the 12 volt battery side after the inverter has done its thing you're looking at 100 amps of draw. Your battery isn't going to hold out long with that draw.

Now I could be completely mistaken here. If you have found an air conditioner that will run on only 120 watts (10 amps at 12 volts) please DO let us know. Cooling is a constant battle for all of us.
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Old 08-22-2007, 04:37 PM   #3
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Re: How to? Solar Charge

Ok, yeah

There was a very clear and major miscalculation running through that whole first post that I realized. I didnt take into account the amperage its going to draw at 12v DC, just at 120v AC. Essentially missing the 0. And throwing off everything by ten fold. Damn.

Never to fear. So a major revamp of the plan needs to be made here. If things are gonna be drawing 10x more than what I anticipated, heh, Im doubling the battery bank. And going with a cheaper gel battery as opposed to the AGM in order to compensate.

So the bank will be in the neighborhood of 500Ah.

Air conditioning. Gonna have to scale it down. So as oppposed to that 7000 BTU ac unit I may have to go with a personal space air conditioner such as the Amcor Personal Air Conditioner APC2000E. Power Consumption: 250W/2.1A. So 2.1 Amps at 120v will draw 21 amps at 12v. Thats not too bad.
or
FREECOMŽ RCS-M1000T 4,000 BTU. Power Consumption: 4.1 Amps at 120v so 41 at 12v, also not bad.

But the bigger unit, the freecom, is rated for 100 square feet. The smaller unit is designed to be a personal space air conditioner. Dinky units. Ill have to change up the way I was gonna use them. These things will have to be right in my face as Im sleeping. Not too big of a problem really, just mount it closer to the bed. And possibly change the way I wanted to work them. As opposed to having AirC for the duration of the night, it may need to be on an as needed basis.

Nevertheless, even if I wanted to run it solid....20 amps over 8 hrs= 160Ah. Same as before, I dont wanna draw the bank down too much. 160 x 2 = 320Ah. Good. Even though the inverter is gonna suck up its percentage, with a 500Ah bank I should be good to run it all night if neccessary without croaking. I basically just had to settle for a smaller unit. Itll suffice.

Now, as far as cooking goes, a 1200 watt electric frying pan will draw 100 Amps out of the DC. Ouch. Umm... I guess we can work with that. Its not like ill be running the frying pan for hours on end. 25 Minutes at the most. Still feasible.

Plus I can get an 800 Watt microwave, 66 amps at 12v thatll run for all of what? 4 minutes?

Um. What else. The TV and laptop and radio will draw what they draw, cant really downsize in that area but the doubling of the battery bank will compensate. I didnt intend on using those for an extended period of time either.

So, fixed up the draw calculations and adjusted accordingly. Im still confused in one major area:

How do I determine what the solar charge controller and the shore power charger will need to be rated at???

Matter of fact the whole charge process confuses me. I really need to look into this.

At what pace will a 200watt solar panel at full power charge a battery?
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Old 08-22-2007, 04:49 PM   #4
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Re: How to? Solar Charge

Quote:
Originally Posted by p0p633
At what pace will a 200watt solar panel at full power charge a battery?
Well if you had the 500Ah bank then in a perfect world:

200 W / 14 Volts = 14.286 Amps | 500AmpHours / 14.286 Amps = 35 hours

which sounds about right, of course that number is if the battery was completely discharged which it wouldn't be. My solar panels would take forever to charge my batteries and so I rely on the engine or my charger to recharge the system when I have returned home.

The charger in my bus (which is also the inverter) can charge at up to 50 Amps(AC) (6000W) with a switch to let you select 30, 20, 15, or 5 depending on how big the incoming circuit is.
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Old 08-22-2007, 05:19 PM   #5
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Re: How to? Solar Charge

Quote:
Originally Posted by Steve
200 W / 14 Volts = 14.286 Amps | 500AmpHours / 14.286 Amps = 35 hours
ok. THANK YOU. Thats how I figured it to work. And like you said, the battery would never be discharged beyond 50% in our perfect world full of sunshine and bikinis. So 250Ah / 14.2 amps = 17 hrs.

yuck. Id be lucky to get 17 hours of good solid sun over 3 days. Looks like if I added a second 200W panel, it would cut it down to 8.5 hours which is at least a more realistic amount of sun to get in a day. Albeit all this is under perfect circumstances and the sun doesnt shine at full strength for more than like 4 or 5 hours.

It at least builds a good base charging system that I can easily supplement with a generator and shore power.

I need to look at the specs on these panels and on the generators Im looking at.
More to Come....

Chime in here, folks.
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Old 08-22-2007, 05:26 PM   #6
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Re: How to? Solar Charge

I think for me the benefit of solar, unless you change your lifestyle to live within small power consumption, is that the panels will maintain your bank as long as your bus is stored outdoors which means you do not have to keep it plugged in. If you have your bank hooked to your alternator you can always use your engine to charge it back up quick if the solar isn't able to keep up.
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Old 08-22-2007, 07:02 PM   #7
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Re: How to? Solar Charge

Have you considered other ways to reduce your power consumption? A gas grill and a gas range/oven can replace the microwave and electric frying pan and will probably give better results. Heck, you could even use the stove to heat water for a french press for coffee in the morning. No, propane isn't free, but it's relatively inexpensive in bulk and is predictable. I also can't help but think it will give better cooking results than an electric frying pan.

Just some food for thought. My electrical demands are minimized down to just entertainment and a dorm fridge really. I use fluorescent lights throughout, etc. The benefit in reducing electrical demand is that you reduce charging demand. Using my alternator to recharge the batteries every 36 hours (that's the typical go-no-more point) I could last an awful long time boondocking. Typically I am not parked that long so perhaps I have that going for me. I also like campgrounds with shower facilities versus a solar shower outdoors, but my bus is based on my needs just as yours will be based on your needs.
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Old 08-23-2007, 04:46 AM   #8
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Re: How to? Solar Charge

Quote:
Originally Posted by the_experience03
Have you considered other ways[gas] to reduce your power consumption?
Yes. Yes I have. I very well may. In addition to propane I want to contruct/purchase a solar cooker to leave in the sun. Or even a small old fashion straight charcoal grill. I think the frying pan and microwave that ill have will be last ditch methods, actually. I just like to have them factored in.

Quote:
Originally Posted by the_experience03
I also like campgrounds with shower facilities versus a solar shower outdoors, but my bus is based on my needs just as yours will be based on your needs.
Well, true. My needs will likely place me somewhat near beach shower facilities most of the time so I dont worry about the shower as much. However I will do the solar shower bag thing and like it. Or soap in the ocean.

Quote:
Originally Posted by the_experience03
Using my alternator to recharge the batteries every 36 hours
Quote:
Originally Posted by Steve
If you have your bank hooked to your alternator
This is something I am very unfamiliar with. Im not factoring this into my project at all. Perhaps I should if its that easy. Guess Ill set some time aside to learn the workings of this rigup.
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Old 08-26-2007, 12:27 PM   #9
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Re: How to? Solar Charge

Remember, The figures given by manufacturers, amps, volts or watts or whatever are for ideal lab conditions. This means you will most of the time get less than the rated output. AND most of the links ( batteries, inverters, chargers etc. ) in the electrical chain are only about 80% efficient. That's a considerable loss which cannot be ignored if you want to be happy with your system. The bottom line is you need a lot more in real life than it looks like on paper.
Go for it. it feels good to be on your own.
Good luck
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