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G2gobig

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Posts: 2
Reply with quote  #1 
Good evening everyone.

I am trying to design a solar system for my small fiberglass camper. I am very good at most tasks, but electronics is not one of them...

My fiance inherited a camper and I have been re-doing it for a couple months now. The idea is to take advantage of the sun we have in Florida and use a solar system to power the majority of things in the camper. I know I will have to have a generator for supplemental power, but would like to use it as little as possible. The camper wouldn't be making extended stays anywhere but be more of a short trip type use. 

I already have three 280W solar panels that will most likely be flat mounted, unless I get creative with my fabrication skills.
Max Voltage - 32V
Max Power Current - 9.91A
VOC - 39.1V
Short Circuit Current - 9.47A

I was planning on getting a Victron MPPT 150/35 for the charge controller.

I was also planning on purchasing four Trojan T-1275 batteries for power. 150AH @ 20-hr. Two pairs wired in parallel to get 24V.

The inverter I want to use is an AIMS 2000W inverter/charger. I may have to pony up to the 3000W model, but I am not sure yet. 

What I want to power is a mini-fridge, some LED lights, minimal use of water pump, charge a laptop/phones/portable music devices/gps/electronic dog collars ect. If possible I would like to also run a small AC unit for short periods of time.

The AC unit says it draws 700W or 6.2A, the mini-fridge (< 4cubic ft) I am assuming would be just under a 1000 watts for the day, LED lights would be no more than 200 watts a day if using them heavily at night. I am not too sure about the draw on the batteries when charging my miscellaneous items. 

What I am having a hard time doing is calculating how much run time I would have if running the AC and mini fridge on a sunny day where I can get good sun on the panels. How much run time would I have before I drain the batteries to the point of needing to be charged again either by generator or shore power?

Any help would be greatly appreciated. Or if you think any of the components should be changed, by all means I am open to second opinions. I have been trying to research this as much as possible but between work and everything else, I just dot have the time or patience. I need to have this thing back together for a trip in November, and I have a TON of work to do... 

Thanks again
-Bill






stmbtwle

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Reply with quote  #2 
Hi Bill welcome to the Forum.

To be honest I'd probably go with 12v as opposed to 24v, I know 24v is slightly more efficient but your camper is probably already set up for 12v, and 12v accessories are probably cheaper and easier to find.  The Victron charge controller can't handle the current at 12v, but the Midnight Solar 150 Classic can.  Don't know how it compares price wise though.  You'd also need a different inverter.

The fridge shouldn't be a problem but I'm not so sure about the AC.  You have about 3 kwh of battery storage of which you should only use about half, or 1.5 kw.  Your AC draws .7 kw so that's about 2-3 hours on the batteries.  While the solar panels MIGHT give enough power for a couple hours in the middle of the day they won't be able to run the AC and fridge AND charge the batteries at the same time.  You might get away with it for a while but sooner or later you'll have dead batteries.

I'd look at a "Fan-tastic Vent". They replace a standard RV roof vent and move a LOT of air, for only about 3 amps at 12v. With the fan on exhaust and the windows open just a bit your rig will stay pretty liveable (been there done that).  I've had 4 I think and love them.  Price about $130 to $250 or so, depending on frills.  Plan on using the genset when running the AC, you probably won't hear it over the AC, anyway.

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
Rick H Parker

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Reply with quote  #3 
I already have three 280W solar panels that will most likely be flat mounted, unless I get creative with my fabrication skills.
Max Voltage - 32V
Max Power Current - 9.91A
VOC - 39.1V
Short Circuit Current - 9.47A

More information on the panels would be helpful. Make and model number?


I was also planning on purchasing four Trojan T-1275 batteries for power. 150AH @ 20-hr. Two pairs wired in parallel to get 24V.

The camper already has a 12V system and 120V system, If you add a 24V system your complicating things. If your having trouble sorting two voltage system, think what it would be like with three voltage systems.


The inverter I want to use is an AIMS 2000W inverter/charger.

Did you check the whole camper out, it may already have an inverter. Can you get 120V without the generator running?


the mini-fridge (< 4cubic ft) I am assuming would be just under a 1000 watts for the day
.

Watts (W) is a rate, watt-hours (wh) is a quantity.

My suggestion is, do a full inventory of the camper's electrical system then plan around what is already there.








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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
G2gobig

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Posts: 2
Reply with quote  #4 
Thank you for the responses.

1. There is no existing electrical system in the camper. I am starting with a fiberglass shell and a trailer. I just got the trailer lights in this weekend, so that is all it has for wiring. 

2. The solar panels are made by BG in Canada. I dont have the model number. A friend of mine gave me these three panels and i figured i would try to use them. The sticker on the back says:
Module Power: 280W
Maximum Power Voltage: 32.0V
Maximum Power Current: 8.91A
Open Circuit Voltage (VOC): 39.1V
Short Circuit Current (ISC): 9.47A
Maximum System Voltage: 1000W
Module Efficiency: 17.4

3. I cant properly size the amount of loads I will be drawing because I don't have the mini-fridge, water pump, lights, ect. yet. I have a shell and a trailer with some  tail lights. I am trying to get my all my stuff together so that I can make sure i plumb everything nicely and have the infrastructure to support the system.

4. I was planning on getting a 24v to 12v converter to run all the LED lights and water pump. That is pretty much the only two things I can think of that I would run with the 12v.

5. Batteries say that they have 1.99 KwH of energy. So wouldn't that mean I would have closer to 4KwH of energy in the batteries?

6. The camper will be used many times for baseball tournaments, mountain bike outings, ect. where there is an hour or two between games or taking a break from riding to cool off. and get out of the sun. In the summer time here in FL, if you use a fan to move air, you are just moving around a bunch of hot air and it doesn't do much to cool anything off. I figured I would have to run the generator while using the AC, but even if i could use it for two hours without the generator going, it would be great. Then it could re-charge over the next couple days, as it would likely not be used consecutive days in a row. Even if it was, i have a nice little honda generator that will power everything just fine. 




stmbtwle

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Reply with quote  #5 
As far as I know batteries are rated as to TOTAL energy.  So yes, 50% of 4 x 1.99 is about 4 kwh.  I think Trojan has a chart comparing DOD (depth of discharge) to cycle life.  If you're planning on only running the AC for a couple hours you should get away with it, but bear in mind a camper that's been sitting the sun all morning is already pretty hot and it will take that much more energy to cool it down.  A fan that exhausts hot air will do a lot better than one that just stirs it up, and you already know the difference between leaving your car windows up or down in the parking lot.  You might do well to ventilate, then close up and run the AC. There are so many variables involved, sun, shade, insulation, etc etc, that a realistic prediction is almost impossible.  However you DO have the genset for backup, so go for it.

My fridge (7 cu ft) uses about 1 kwh (1000 watt hrs) per 24 hr day, so I think your estimate of 1000 watts (watt hrs) per day should be good.  Pump is negligible.  LED lights also (compared to the fridge and the AC).

Your idea of running a 24v-12v converter should work fine.



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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
Rick H Parker

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Reply with quote  #6 
5. Batteries say that they have 1.99 KwH of energy. So wouldn't that mean I would have closer to 4KwH of energy in the batteries?

1.99 KwH of energy capacity at the 100 hour discharge rate. Which is a 20W load. 20W * 100 hour = 2000Wh = 2.00 kWh. Energy capacity for higher rates of discharge will be lower the 2.00 kWh.
For Flooded Lead Acid you should use 50% or less for a reasonable battery life span.
For Absorbent Glass Mat (AGM) 80% or less for a reasonable battery life span.

4. I was planning on getting a 24v to 12v converter to run all the LED lights and water pump. That is pretty much the only two things I can think of that I would run with the 12v.

That would work well.

I figured I would have to run the generator while using the AC, but even if i could use it for two hours without the generator going, it would be great.

I think you could run an AC all day long on battery+solar panels. Two hours on battery alone with the other loads would be right on the edge of doable. 





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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
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