Solar Help from EEs and Others Please - Page 2 - Fiberglass RV


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Old 03-25-2014, 05:46 PM   #15
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It looks like your ac outlets, air conditioner and microwave all have to run off of the inverter/battery bank. As mentioned above, there is no way an inverter/battery will be able to keep an a/c on for long, even with an huge charger. You might want to incorporate running the a/c off of the shore power only and have pairs of outlets, one from the shore cord & breakers, the others from the inverter, for your utility ac use.

BTW: Just how big are those 100 watt solar panels?
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Old 03-25-2014, 05:55 PM   #16
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The flexible Renogy panels are 41" x 21", and the Lil Snoozy roof is plenty big - might even be big enough for 6, but I think that would be WAY overkill.

Since I have lots of time to plan, I'll figure out a way to bypass the batteries when on shore power, though I doubt I'll need it that much.
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Old 03-25-2014, 06:07 PM   #17
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duplicated from above
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Old 03-25-2014, 06:46 PM   #18
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Fuses... a quick look on line shows max circuit amperage rating times 1.35 = fuse size, bumped up to the next common size. Your 45A controller x 1.35 = 60A. Make sure they are rated for DC.

http://assets.bluesea.com/images/products/20010.jpg
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Old 03-25-2014, 06:53 PM   #19
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Thanks Bob - good formulas!
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Old 03-25-2014, 08:00 PM   #20
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I'm afraid there's a lot in your picture that doesn't make sense, like having a 12v fuse panel that doesn't connect to all your 12v devices, missing things like your solar controller and inverter, and an inverter circuit that feeds all your 120V appliances as well as a shore power connector that doesn't. Perhaps a better approach for you -- and us -- would be to tell us what you're looking for and thinking of buying, and asking someone here to draw it up for you.

As for the solar set up:
* You've got four panels on your drawing and an MPPT controller, but it looks like all four panels are wired up in parallel. To get the biggest bang for your buck out of your MPPT controller, you really ought to wire them up as two sets of two panels in series, what many people would call a "24 volt" setup. Wiring them up this way will make maximum use of your MPPT controller's capabilities while still minimizing the effect of having a panel or two parked in the shade. It'll also allow you to use a smaller, lighter, lower-cost, 30-amp controller.

* You should ask yourself this question: Do I really want to run my A/C off my 12v system? In most cases, the answer to that question would be no, because you'd need a lot of both batteries and solar panels to actually be able to do that. The system you've described isn't up to the task.

* Even a microwave is pushing it. Deep cycle batteries work best when their discharge rate doesn't exceed 50% of their rated capacity, e,g, a 100AH battery shouldn't be asked to provide more than 50 amps of power at any given time. To run even a 900w microwave you need a battery bank with, at the very minimum, 150AH batteries.

If you decide you only need these appliances when you have hookups, youll need some wat to switch between shore and inverter power. You can use a simple A/B switch (ours is a standard "3-Way" light switch), which is very simple and inexpensive, or you can get an inverter that does the switching for you.

One thing you don't really need is a "transfer switch." Most trailer owners don't have one; they simply plug their shore line into their generator when they're using it.
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Old 03-25-2014, 08:07 PM   #21
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Deborah,
Not a solar expert or EE, just a solar user.
I am using 2 100W portable panels with a 45a MPPT controller. The system works really well, and often we don't need to put out both panels to recharge our single group 27 battery in just 2 hours. You may find that the need for 4 panels is too much for the single battery. You could add more battery capacity or reduce the number of panels depending on how far north you are and how much tree cover you have at the camping area. There are ways to size this stuff published on line.
You can connect the negative lead from your onboard charger to the shunt as well, to monitor its output on the Trimetric.
Sizing fuses is to protect devices and the wire. If your controller is 45a, you could protect that with a 60 amp fuse, and the wire if sized to carry 45a could be protected with 45 amp fuse, but you will want to upsize the wire to lessen voltage drop which improves charging. If you upsize the wire you would size the fuse to protect it, and it may be well above the 60 amp fuse needed to protect the controller, so you would be fine with the 60 amp for both.
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Old 03-25-2014, 08:24 PM   #22
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Thanks Peter - I've been all over the map trying to figure out what to do, since there doesn't seem to be a packaged system that meets my needs. Added to that, there's a lot of conflicting info.

Didn't know how to draw the solar panel setup - I want to duplicate what you did (from an earlier post) and what you just described.

I want the A/C and the microwave only for hooked up applications - and will be in that situation only rarely. But I do want the option.

I'm looking at a pair of 6V 200 AH batteries, so in series, shouldn't I have 400 AH? Actually, I don't even need a microwave, but want the capacity to add one in the future.

My biggest energy users will be the 12V fridge, my computer, 12V lighting and pump, and a Keurig mini (doesn't continuously heat water). I will have a TV, but I rarely watch, so it's occasional use. Composting toilet, if I decide to go that way, has a solar fan, so no electricity or water.

Great advice on the transfer switch. I opted for drawing it, because several web sites said it was necessary, and what do I know?
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Old 03-25-2014, 08:47 PM   #23
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Despite the issues raised, drawing out a schematic for critique is an excellent way to get your hands around a problem and find out how to solve it.

Don't get discouraged, start reworking what you have and, long before your Lil' Snoozy is in the driveway, you will have an electrical system all laid out that will do everything you want.

And that's a whole lot better than depending on Joe at Acme RV to do what you want to accomplish, and to do it right the first time.
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Old 03-25-2014, 08:51 PM   #24
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Thanks for the encouragement Bob. That's exactly what I intended.
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Old 03-25-2014, 10:13 PM   #25
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Start by first determining your projected energy usage.. It can be done with a spreadsheet available from many sources. You can figure out the consumption for your appliances manually either with generic figures readily available online, or calculate it using owners manual information and compliance stickers on item.
You can also by an inexpensive kill o watt meter such as this and measure actual consumption (these numbers might surprise you.. Especially the mini Keurig)

http://Amazon.com/gp/aw/d/B00009MDBU...&pi=SY200_QL40
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Old 03-25-2014, 10:46 PM   #26
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Deborah, based on your projected items using DC power, I would say that 200W would be plenty. Two panels of 100W each, plus a controller, going into a pair of batteries. 2 6V golf cart batteries in series would work well. BTW, when you wire them in series you will get 6+6=12V, but the 200A will stay the same. (If wired in parallel, you'd retain 6V but get 400A; however, 6V won't run your 12V appliances, so that's out.)
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