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Old 05-16-2004, 02:45 PM   #1
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???s about Batteries & Solar

I had posted this question in the generator thread but never got an answer. I'm still trying to figure out all the systems in my AS. The manual is not very helpful. I'm not even sure if it's the one that actually goes with my rig. The copyright on it says 1988. But it just seems to cover general topics.

I have a question about running off battery power. When you're using 12V things like lights for instance--BUT you are plugged into shore power (or your shore line is plugged into a genset)--are you drawing 12V off the batteries? Or does it come through the converter straight from the 120V AC bypassing the batteries? I was under the impression when plugged into a 120V line the converter only draws 120V and if the batteries are low from having used the batteries without shore power, or sitting, they will get topped off while you're on shore power.

Another thing I'm wondering is if there is any way to isolate high draw appliances like the A/C, fridge, microwave from lower drawing items like 12V? I'm thinking if you could do that you would be able to keep the batteries charged with a solar panel to run the 12V stuff. It seems like a day's worth of solar charging would get you through the night's 12V needs. At the same time you wouldn't be taking away any power the generator needs to run the higher amp appliances. It could also reduce the size of generator power needed.

If you run the fridge on gas you wouldn't need to use the generator for more than a few hours a day since the A/C would only need to be run during the hottest part of the day which is about 8 hours. If you needed the microwave at night that would take up like 5 minutes of your generator's runtime. I'm also thinking that while you were running the A/C and with the fridge on gas—if you're conservative with your 12V use—you would have your batteries topped off for the night at the end of the day. Is this close to correct?

That makes me wonder about something else. If you are plugged into a generator I'm assuming it will charge your batteries if they are low. What happens if you also have a solar panel? Will it charge the batteries as well? My AS has a solar panel. I THINK mine is set up so you have to switch it on and off. I haven't been able to test it yet and when I bought it no one explained how it works. I know this much though--I had the trailer sitting unplugged and the batteries went dead. So the solar panel wasn't charging. But I found a switch right next to the master battery switch that I'm GUESSING you flip on if you are unplugged so the solar panel can keep the batteries charged. If this is the case I'm wondering if I have to have the solar panel switched off if I'm on shore power to avoid frying something.

Also does anybody know what you need in terms of a solar array? I would like to be able to set up an external power station that I can simply plug my 30 amp into. I've said it before I don't like installing things in my camper that I'll only have to give away later when I sell it. I also don't want to have to rewire my whole unit.

I'm wondering what I need in terms of the number of panels, the batteries, the inverter, generator and so on. It's all pretty confusing to me really. I've read that 100 amps per day per person is the rule of thumb. And then I've read that you want to be able to run for about 3 to 5 days off battery power if you overcast skies. That all sounds good. But how does that translate into the actual equipment you need?

I checked and I can tell you the information available doesn't help you to put together a materials list which is all I want. I don't want to, nor do I have the time, to become a renewable energy specialist to get this done.
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Old 05-16-2004, 03:52 PM   #2
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Check out some of the posts RoadKingMoe has made regarding solar. Also do a forum search on solar power which should answer many of your questions. As far as the switch goes, it could be there to turn on and off the univolt converter because many complain about it buzzing at night. If disconnected from shore power check voltage of your batteries. Go inside and flip the switch and check voltage again. If it went up then I would say that you completed the circuit for your solar array. If nothing happened, connect to shore power and listen for the hummmmm coming from your converter. Flip the switch and see what happens. If it stops then you know what the switch is for.

I have ZERO draw from my batteries by the likes of propane detectors, smoke and CO detectors because those I have are AA battery powered. I have found that a 5 watt solar charger/maintainer will keep my 2 105 amp. hr. batteries topped off if I am an energy mizer. I run only one light at a time and run a fan no more than a couple of hours during the afternoon and for 8 hrs. in the evening. After 3 days of this I am still in the "good" area of the gauge on my control panel. I may leave for 4 days and come back to the batteries topped off and the gauge showing to the right of the "good" area. In April I hooked up a 20 watt panel with Solarex charger and ran 2 fans considerably more often in the afternoon with not much change showing up on the control panel. While the panel is not an exact measurement of what my batteries are doing, I've had them for 3 years now and have never been short of power. I've even run my furnace all night long for 2 nights in a row and the gauge never reached the "fair" area on the gauge.

Once you start lighting up the entire trailer, running all fans and tuning into the TV then you will definately need that solar array you have. I don't think my 20 + 5 watts would be able to keep up.
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Old 05-16-2004, 06:51 PM   #3
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Quote:
Originally Posted by joossens
I have a question about running off battery power. When you're using 12V things like lights for instance--BUT you are plugged into shore power (or your shore line is plugged into a genset)--are you drawing 12V off the batteries? Or does it come through the converter straight from the 120V AC bypassing the batteries? I was under the impression when plugged into a 120V line the converter only draws 120V and if the batteries are low from having used the batteries without shore power, or sitting, they will get topped off while you're on shore power.
The system is set up so it puts out what is commonly called 12 volts. It is called that because it is more like 12.25-14.75 volts.
The system is set up so when plugged in, it will have a voltage, of, say, 13.5 volts. If you turn on a light, that drops the voltage, the regulator will put out a little more to keep the voltage at 13.5. It will continue at the higher rate until you turn off the light, it will then reduce its output so it is again at 13.5 volts.
What that means in English is that you are using power from the battery, and the Univolt is replacing it as you use it.
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Old 05-16-2004, 08:49 PM   #4
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Most things in your trailer operate off "12VDC." Lights, radio, water pump, vent fans, furnace fan, thermostat, circuit boards (and possibly ignitor) in furnace, water heater, and refrigerator, the anti-condensation element around the refrigerator doors, perhaps even a heating element to operate the refrigerator if it has 12VDC capability, LP detector, brakes, tongue jack, and possibly stabilizer jacks. Your trailer may also have a CO detector powered by "12VDC." These things can typically operate on a DC voltage between 10.5-11.0 and 14.6 volts.

These things can operate off your batteries, which are "the source," and when they do, these things are "the load." Electrons run from the negative battery terminal through the loads that are turned on, back to the positive terminal of the battery, and within the battery from the positive to the negative terminal. The voltage that these loads operate on is the battery voltage, which depends on the batteries' state of charge, but generally between 10.5 (dead) and 12.6-12.7 volts (fully charged).

When you plug your trailer into 120VAC, whether it comes from campground power or a generator, a "converter" takes some of that AC, converts it to a DC voltage higher than that of the batteries' (generally between 13.2 to 14.6V), and applies it across the batteries. Since the voltage is higher than the batteries, the converter becomes "the source" and the batteries become part of "the load." The negative terminal of the converter is outputting electrons and its positive terminal is collecting them. Electrons now run from the negative post to positive post inside the batteries, and they are being charged by the converter voltage, which is also supplying the power to all the other things in "the load."

A "solar controller" fed by solar panels can perform the same function as the converter fed by campground power or a generator, but at a much lower level. As David says, I and others have written extensively here on solar power in the past years. These writings are all available to you through the Forum's Search feature.

An absorbtion RV refrigerator normally operates off propane on the "Gas" setting, but can operate off 120VAC in the "Auto" setting. (in either case, the circuit board and anti-sweat element (if it is turned on) still use 12VDC). In the Auto setting, the refrigerator switches to 120VAC when it is present, and switches to propane when it isn't. Absorbtion refrigerators cool by heat.

The refrigerator is not much different than the RV water heater, which usually operates off propane, but may have a 120VAC heating element that can be used instead of, or in addition to, propane.

The air-conditioner and microwave oven are 120VAC only. The refrigerator and water heater don't have to be 120VAC because they have the propane option.
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Old 05-16-2004, 09:13 PM   #5
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Ok so let's see if I have this straight:

1 - Using any 12V DC items goes through the battery rather than 120V when plugged into shore power?

1 - Unless I run things like the fridge and water heater from gas I cannot isolate them while on 120V?
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Old 05-16-2004, 10:13 PM   #6
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12VDC items get their power from the converter, not the batteries, when plugged into shore power or generator. The batteries are also charging during this time.

12VDC items get their power from the batteries when not plugged into shore power.

When not plugged into shore power, if there is/are solar panel(s) outputting DC:

1. If the 12VDC load is less than solar controller output, the 12VDC load uses some of solar controller output, and the rest of the solar controller output charges the batteries.

2. If the 12VDC load is greater than the solar controller output, the 12VDC load uses all of the solar controller output, and the batteries contribute the rest of the power to the load.

Whether you run the water heater and/or refrigerator on gas or 120VAC, their circuit board(s), ignitors, and the anti-condensation element (if turned on), are 12VDC items and get power as described above.
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Old 06-01-2004, 10:51 AM   #7
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Our As came with a switch to turn off/on the microwave, so you wouln't forget and run it when something else was drawing a lot of power.

The "Real GOODS" solar techs will design you a system for your RV. Or look at the catalogue for systems ready to go for RV's. silver suz
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