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Old 10-12-2016, 04:13 PM   #1
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Inverters - Thinking big about going small

Question: Does anyone have experience on getting by on a 450 Watt inverter?

Background: I have a 2005 Salem LE 21FB. Like most travel trailers the battery is in the front and the converter/distribution panel is near the middle of the trailer. I've been thinking about my options for off-grid 120v power so I can run my computer and TV for photo processing while I'm boon docking. I've searched this forum on inverter info and read enough threads to realize nearly everyone does it differently.

Originally I was considering a 1500 watt inverter so I could also run the microwave but then I realized that I would have to run thick cables a fair distance to where the inverter would best be located (near the converter/distribution box) or have a short run of thick cables and a long run of AC cable. Then I though why not go small and use the existing #6 AWG cables from the converter to the battery and go with a smaller inverter? According to the user manual for the Magnasine 400W inverter (CSW412), the power lines between the battery and inverter should be #8 for 5-10 foot runs or #6 for 10-15 feet. I'm about at 10 feet straight line so I'm probably actually in the 10-15 foot range.

I would have to do some creative (but safe) wiring to have concurrent 12v to the distribution panel but going small would mean that all the wiring would be localized to the current distribution panel. I plan on replacing my interior lights with LEDs so the existing #6 AWG lines from the battery to the inverter and distribution panel may be able to safely carry the load with no overheating.

For charging I plan on a 100 watt portable solar array with direct connection to the battery. I only have a Group 24 battery so my storage is limited. Other options include:

1. Go lithium and put the battery or batteries under the dinette seat along with a decent inverter/charger and permanently turn off the converter and eliminate the front battery box.

2. Expand the battery storage up front and mount an inverter or inverter/charger in the front pass-through storage space.

3. Use a generator (not very exciting).

So for you electron misers, anyone getting by on 100 watts portable solar, a group 24 battery, and 450 watts inverter power?

By the way, here link to the manufacturer's page on the inverter:

400W 12VDC Pure Sine Inverter CSW Series | Magnum Dimensions

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Old 10-12-2016, 04:38 PM   #2
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With a 400 watt inverter, you'll be limited to about 3 amps. If I were doing it and wanted to maximize my output, I would do a 4 6v battery setup with a 2000 inverter close by, and run the AC line to the converter. A 14-2 line would be enough to carry the load and would be easy to run.

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Old 10-12-2016, 05:01 PM   #3
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You will do just fine with a 400 watt inverter for the TV and computer. I would up the solar to at least 200 watts though and a pair of batteries.

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Old 10-12-2016, 07:58 PM   #4
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Originally Posted by boondocking View Post
You will do just fine with a 400 watt inverter for the TV and computer. I would up the solar to at least 200 watts though and a pair of batteries.
I was thinking about increasing the battery size or solar size. The nice thing about the portable solar kits is that they are easily expandable. Combining two 100 watt solar kits should be relatively easy.
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Old 10-12-2016, 08:08 PM   #5
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Originally Posted by AquaMan View Post
With a 400 watt inverter, you'll be limited to about 3 amps. If I were doing it and wanted to maximize my output, I would do a 4 6v battery setup with a 2000 inverter close by, and run the AC line to the converter. A 14-2 line would be enough to carry the load and would be easy to run.
If I go that route I would have to put the inverter in the front pass through and that space isn't ventilated. The bed is in the front of the trailer so there is a lot of room but no air circulation. I thought about building some sort of ventilated box on the front 'A' part of the hitch. If I went big like that I would go big and put in an inverter/charger up there. The existing 12V lines from the battery to the distribution panel would still be useful but I could shut off the converter.

Four 6V batteries would be a bit overwhelming on my little trailer. I can easily pull it but I'm thinking it is more than I need.
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Old 10-12-2016, 08:37 PM   #6
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Pure sine wave will love it...using a 800 watt....ran 4 lengths of 10 gauge wire, 2 lengths for pos and 2 for just of wire was about 10'
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Old 10-13-2016, 12:46 PM   #7
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Depending on the computer and tv you could probably get away with a smaller inverter. I use a 150 watt psw inverter to power my 32" led tv and direct tv receiver. I think the tv draws 60 watts and the receiver 40. I plug it into the 12v outlet at the tv booster. I plan to add a 1500 watt msw inverter near the batteries next year to power small appliances.
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Old 10-13-2016, 01:02 PM   #8
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Here's an idea. Skip the inverter.

Buy a 12 volt charger for your laptop

watch TV on the laptop with a USB TV Tuner.
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Old 10-13-2016, 01:05 PM   #9
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Inverter experiences

Lots of good suggestions here, but I thought I'd throw in my two cents worth, and draw on my not-always-good experiences.

Inverters are kind of funny critters, not all of them being efficient, although the market is now offering better units at lower prices. Having said that, the probability of your DC cables overheating isn't the primary consideration in cable sizing, more critical is voltage drop. Like bank balances, bigger is nearly always better in wire size. As for choice of the actual wire, my favorite is welding cable...very flexible, tough insulation and pure copper. For a 400-450 watt inverter, you will need to be able to furnish it with 45-50 amps at 12 volts, with 41.6 amps being the theoretical current draw if 100% efficient, which can't be done. As for batteries, I personally went with two 6 volt golf cart batteries in my Sunseeker, which adds up to 250 amp hours at 12 volts. I would have gone with more batteries, but space was limited. If your space situation demands it, you can go with a group 27 deep cycle battery. The thing to remember is keep the 12 volt wires short as practical, and #6 wire is actually none too large, although the 50 amp capacity of #6 seems to meet the need rather well. Best test would be to measure the voltage at the inverter input terminals. Most inverters will shut down if the voltage is too low, generally around 10 volts.

A word on the need for sine wave inverters: Since virtually all electronic devices operate on DC, the AC input to the power supply used is much less important, and it also offers robust surge protection, which is a big plus. Since many of these power supplies are presently what is known as "switching regulators" the DC output remains stable over a wide range of AC input. (Look at the label, which usually says something on the order of "70-250 volts input") That is what you want to see! Also, most flat panel
TV sets actually use a 12 volt power input from their little in-cord power supply. Check on this, too. This is also the case for many computer monitors, which often have 12 volt connections even when they have the typical 120 volt cord connection. Knowing this may well save the amount of inverter capacity you actually need. For some reason, many laptops use an input voltage of around 20 volts DC...I'm not really certain why, but am going to experiment with using 12 volts and see what happens!
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Old 10-13-2016, 05:20 PM   #10
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Sorry for chiming in, but this is my take.

1) Magnum PSW 1000W. @ about $500 ... Although 600W is enough.

2) Located near the batteries as practically possible.

3) Consult the manual to pick wire gauge from batteries to inverter don't listen to me or anyone else, read and learn; the Magnum manuals are excellent.

4) Provide a proper breaker disconnect between the two.

5) Run two #12 or #14 ga Romex to two dedicated outlets inside, where ever you need them and simply wire up 3 prong plugs and plug them directly to the inverter. Obey the electric code. By doing this you will avoid ground loops etc.

6) A pair of 6v 230Ah from Batteries Plus about $110 each. That is 115Ah usable if you never go below the 50% which drastically lengthens the life of the batteries. A pair of 12v true deep cycle would be okay if it makes sense to do so.

7) Trimetric TM-2030 monitor for me is essential; even if you use another brand of SCC although a SC-2030 with the TM is a nice pair. You will need a 100A shunt if the load is below 600W or 500A if the load is above. Easily wired between batteries and everything else.

8) If you replace the Ah with solar you will need at least two 100W panels more like two 120Ws. Not knowing anything about your rig. Rule of thumb you need xx Watts of panel for xx Amps of battery... so, 220Ah of battery relates to about 220W of panel, but that is just a rule of thumb.

9) If you sometimes use the converter to charge on shore or gen power, get an IOTA with IQ4 or Progressive Dynamics with Charge wizard (if you haven't already).

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