Inverters - Thinking big about going small

KevK · 10-12-2016, 04:13 PM

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

AquaMan · 10-12-2016, 04:38 PM

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.

boondocking · 10-12-2016, 05:01 PM

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.

KevK · 10-12-2016, 07:58 PM

Quote:

Originally Posted by boondocking

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.

KevK · 10-12-2016, 08:08 PM

Quote:

Originally Posted by AquaMan

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.

bob caldwell · 10-12-2016, 08:37 PM

Pure sine wave style.......tv will love it...using a 800 watt....ran 4 lengths of 10 gauge wire, 2 lengths for pos and 2 for negative.......works just fine.....run of wire was about 10'

markb422 · 10-13-2016, 12:46 PM

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.

lugoismad · 10-13-2016, 01:02 PM

Here's an idea. Skip the inverter.

Buy a 12 volt charger for your laptop

https://www.amazon.com/ZOZO-Universa.../dp/B012FREMNG

watch TV on the laptop with a USB TV Tuner.

https://www.amazon.com/MyGica-A681-A.../dp/B0084363Z6

Photo Lab · 10-13-2016, 01:05 PM

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!

WolfWhistle · 10-13-2016, 05:20 PM

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).
WW

NorSnrub · 10-13-2016, 07:29 PM

I run my led tv with a 150 w pluged in the lighter plug. Don't run high wattage stuff. Just tv or computer. No microwave or toaster. Use the gas stove.

KevK · 10-13-2016, 08:08 PM

A thanks to all for their input so far and some more information from me.

My TV is an older 20" Sony LCD with a fluorescent backlight. According to the information on the back of it, it draws 55 watts. My laptop died years ago and I have been using a 2012 mini Mac for my computer needs. The mini Mac is rated at 11 watts idle and 85 watts max so I don't need very much AC power at all. I don't have a great need for a lot of TV but when the weather is bad it is nice to have something to keep me occupied.

On my trip this past summer I had an idea for TV on the down days but it had one major flaw - no AC power unless I was in an RV park. The idea? I downloaded several movies rentals on iTunes to my mini Mac to watch later when I had no TV reception or there was nothing worth watching on TV. With Apple's iTunes you have 30 days to watch a rental you downloaded and 24 hours to finish watching it once you start watching it. The rental price is the same as if you were watching it immediately after renting it. As you have 30 days to start watching the rental you really only have to have good internet once a month. I downloaded several movies before leaving on my trip and one or two more during the wee early morning hours when I was in an RV park with good wifi.

I only have one 12V outlet in the camper and that is a part of the TV antenna booster. Unfortunately it is 8 amps max which gives me between 80 and 96 watts if you factor in an inverter efficiency of 80-90% and even less when the battery voltage drops. That is cutting it close but if I swap out the spinning disk drive in the mini Mac with a solid state drive that would reduce the computer power needs if I don't do anything CPU intensive. I already added one SSD to the Mac and run off that so other than power on, the spinning hard drive isn't used. Mark, where did you get your 150W PSW inverter? I may give that a try before I start making modifications. If the combo blows the 8 amp limit, I could switch to a laptop for photo processing and rented movie watching.

=================

More info. The parts cost to add more battery storage and electronics isn't a big issue for me but I want to dip my toe into the water before diving in with modifications. A schematic of my RV is below. As is typical, the Group 24 battery box is up front between the propane bottles and the front of the trailer. The power distribution center and converter is below the refrigerator. I was going to put the 450w inverter in the space under the stove/oven which has convenient access to the existing 6 AWG wire from the battery to the converter. I figure it is sized at #6 for the battery charging and little is used for other 12v uses.

If I were to go all out, I was thinking of putting in two Relion Lithium Ion batteries under the dinette and put an inverter charger in the same space. I would probably have to vent the space to handle the inverter charger heat but the lithium batteries like a more climate controlled space. That would put the system close to the power distribution system. But I'm leaning towards baby steps for now.

Great input guys. I appreciate it. My plan right now is to get a small cigarette lighter inverter and give that a torture test to see my real world needs.

PSU Turf · 10-13-2016, 08:26 PM

I would not feel comfortable boon docking for more than 2 days with a single battery. And that's before adding an inverter and running more things off of the battery. I have a Power Max battery box mounted on the frame behind the propane tanks. It looks like your trailer would have room for the same box. It has room for 4 batteries. I divided my box so I have (2) 6 volt batteries on one side. The other side has a Samlex 600 watt pure sine wave inverter, Trimetric battery monitor, Bogart solar charge controller, and a couple of bus bars for connecting the cables. There is divider with a rubber gasket to divide the box and keep any sulfur gas, from the batteries, away from the electronics. Input power is supplied by (3) 100 watt panels. If I am in a campsite that gets full sun all day I could probably get by with 1 panel but usually there is a fair amount of shade. Over engineering or over powering means less chance for disappointment down the road. Like many others on this forum I have become addicted to the mods but it is fun. Hope you enjoy your mods.

pmsherman · 10-15-2016, 07:36 PM

Converting from 12VDC to 110VAC then back down to 20VDC (computer) and probably 12VDC for the television isn't the most efficient way to maximize battery life. As already recommended, a 12VDC power supply for your computer will get that running directly from the battery. If you can't find one that has an appropriate power plug, you can use my solution - cut the power cord and put it back together with PowerPole connectors. Put the same connectors on a DC power supply and you can switch the computer's power plug from AC to DC easily.

If your television has a 110 cord that plugs directly into it, it's probably connected to a DC converter inside to provide 12V power for the television electronics. It should be easy to tap into the output of the internal power supply to run a DC power in line for use off of the battery. You could also add a buck/boost converter to the television power line to stabilize the voltage supplied to it, making it independent of battery voltage.

Phil

KevK · 10-16-2016, 01:06 PM

Phil, my computer is a mini Mac which is not a laptop and only has a AC cord to it. Yes there is a transformer inside but there isn't a lot of space to mess around in it and other than shielding the bluetooth antenna, swapping out the hard drives with solid state drives, and upgrading the memory, I'm not going to modify it to see if I can get it to run on 12v. And since I'm not modifying the computer, I may as well leave the TV alone.

I've decided to go with a 150 watt pure sine converter from Go Power. I found a good deal on eBay for an unused one and I'm going to give the setup a try while my trailer is here at home. If it doesn't work out, I haven't put much $$ into the project and can modify as necessary but with only a 150 watt inverter being on when I need it, I'm not drawing a lot of juice.

I'll update this thread to let others know how I get along. Thanks all!

Kevin

markb422 · 10-16-2016, 03:57 PM

Kev, it looks like it may be a little late for you but this is the inverter I bought from Amazon for $106.
Samlex PST-120-12 Pure Sine Wave Inverter 120 Watts AC DC 120 VAC USB Port 12V
Nice compact unit that I hung right on the back of the tv wall mount with a couple wire ties. Plugs into the 12v acc outlet of the booster. Works great with my Furrion 32" led and direct tv receiver. The combined draw for both is around 100 watts. It also has a usb for charging phones.

KevK · 10-16-2016, 10:00 PM

Thanks Mark but I already paid for the Go Power on eBay. That does look like a nice compact unit.

KevK · 10-23-2016, 07:35 PM

Apparently my lighter plug isn't up to snuff. The TV is 55 watts max and the computer 85 watts max, 11 watts idle. The 150 watt inverter should have no problem handling the load. I've tried starting the TV then computer after a minute or so and the reverse order. In both cases I can hear some clicking in the inverter/12v outlet area and then the computer or tv or both will shut down. As it is an eBay inverter, I thought it may have been a return item that had problems so I brought the inverter, tv, and computer to my car for a test run. It worked flawlessly so the inverter doesn't appear to be the issue.

For me this means either install a dedicated 12v outlet near the distribution panel or consider getting a 12v tv and a laptop. I could also install a 115v AC outlet near the distribution panel that dedicated to the inverter. Then I don't need to worry about wiring a transfer switch or do any more involved electrical system modifications.

As I have the winter to sort things out, my next test is to spend an evening on the tv/computer with the inverter wired directly to the battery in a standalone configuration to confirm that the inverter can handle the load and the battery has adequate capacity.

SidecarFlip · 10-23-2016, 08:21 PM

In my case I look at more batteries = more weight and I have a truck camper so I want my weight in necessities, not batteries.

I opted for a 3000 watt Xantrex Pro Sine, way more output than I will ever need but, you need to look at one, the idle current usage (all inverters whether being used or not, consume current (called idle current consumption), unless the inverter is equipped with a remote shutdown. The Pro-sine ships with a remote shutdown and the 3000 watt Xantrex has a very low idle current consumption as well.

Typically, the larger output the inverter is, the less the idle current consumption is.

I run a single Group 31 seep cycle and the battery easily powers the inverter all night supplying my Cpap machine the 50 platry running watts it needs.

I went with the big PSW inverter as a hedge against future upgrades One other nice thing about running a big output power PSW inverter is residual heat from operation is a non-issue. The fan never comes on and the case never even gets warm. That allowed me to put the inverter very close to the battery in the compartment with the FW tank and battery box, as space is very limited in a TC. I used welding cables for the power leads as well and crimp on solid copper lugs for the cable ends.

I ran the output via Romex to a dedicated outlet labelled 'Inverter Only'.

NorSnrub · 10-24-2016, 01:21 PM

If your battery is down a volt or so the inverter drops out.

You may also like: