Electrical - wiring Question

[swinada]

How is a inverter wired in to the system? Or do you just keep the inverter handy for when you need it and then plug in what ever you need when you need it?
Here a little drawing of what I'm planning on doing, and if anybody could edit the picture on where and how a inverter would fit in to the picture would be great.

 

[lblampman]

It really depends on the capacity of the inverter and how you want to use it so there's no one answer.

The inverter I most use has a built-in 30-amp transfer switch so the shore power inlet (that is, where outside power comes into the bus) is wired directly to the "AC in" on the inverter; then the AC out goes to the main AC distribution panel. If you're hooked to shore power it just passes through to the AC main panel; if you pull the shore power cable the inverter supplies AC to the main panel. I normally use the Xantrex ProSine 2.0 which has this transfer switch and it also has a charger so you only make one connection to the battery bank (on the DC side). The incoming shore power goes to "AC in" on the inverter and the outgoing AC (from the inverter) goes to the main AC panel. The advantage in this system is that it's simple wiring, it's safe (the PorSine has automatic ground switching), and it's simple to use. The down side is the cost and the fact that without a little due diligence you can turn on more things on the main AC panel than you'd really like the inverter to handle; you do have to pay some attention to the loads.

If you don't have an internal transfer switch you can add an external one (manual or automatic). This presupposes that you have an inverter of a size that will supply most of the loads in the bus and you desire that power to be available in all parts of the bus.

Inverters come in many sizes and are typically either "hard wired" or have GFCI outlets of their own on the enclosure. This alters how the inverter is installed and used. In the simplest system the inveter isn't even interfaced with the onbard AC system; it's simply connected to the batteries on the "DC in" side and you plug whatever you want to run right into the inverter. This can also work by plugging in the shower power cable directly into the inverter (rather than into a power pole); it does mean a trip outside the bus (usually) to plug the shore power into the inverter (but not necessarily).

Another way is to utilize an AC sub panel for the inverter. The idea is this. Your shore power cable comes into your AC main breaker box; all the loads that the inverter can NOT handle (like an electric water heater or an air conditioner) are connected to the breakers on the AC panel. Then all the loads that the inverter CAN handle (or you want to handle) are connected to a AC sub panel for inverter only loads. This sub panel gets it's power two ways: 1) it's connected to the AC main panel to a breaker 2) it's connected to the "AC out" side of the inverter. When the bus is plugged into shore power the breaker on the AC main panel supplies power to the sub panel; when the bus isn't plugged in the sub panel gets it's power from the inverter. If you also have a genset then its output could go to the main panel or to only the sub panel depending on its capacity. You should have a switch in the sub panel input to choose between the main panel (shore power) or the inverter; this can be a manual switch or an automatic transfer switch. I would not rely on just the switch on the main AC breaker box to the sub panel...sooner or later you're going to turn on the inverter and flip that switch at the same time and that will potentially toast your inverter.

I should also add that the AC ground MUST switch with, and follow, the power supply and there can only be ONE point of ground at any given time. When on shore power you must ground the AC system to the power pole and it must disconnect from the inverter. Likewise, when on inverter power the AC ground must be through the inverter and not ground through the shorepower system. A manual or automatic transfer switch designed for this purpose (RV or Marine typically) will accomplish this. The internal transfer switch in some (not all) inverters will also do this but you must check the installation manual. I am not trying to scare anyone here but this is a potentially deadly situation; you need to get it right.

Cheers...

P.S. The inverter doesn't come off the DC main panel as you have it on your drawing unless it's really dinky; otherwise it draws too much power to put through the panel. Most inverters are directly wired to the battery bank with the appropriate inline fuse.

 

[Redbear]

I can't modify your drawing, as I still scribble on napkins and the back side of old reports.

I was working on a reply, pretty much what Les was saying, especially about the "protected" AC sub-panel. I wouldn't try to run the air conditioners off of an inverter, and I wouldn't run the refrigerator off of an undersized inverter.

I hand-drew a sketch with two options and scanned it as a .tif (I can't do .pdfs at this point), but when I tried to attach it, I lost all my comments! I'll have to learn more about this posting stuff. :shock:

There have been a lot of posts here in the past about using a toggle switch to transfer AC loads between the inverter output and the shoreline/genset feed, when using an inverter without an internal transfer.

In reference to your drawing, with a small inverter cut the line from the AC panel to the tv-computer circuit and put the transfer there. Use the fuse or breakers in the unit for protection.

If your inverter is big enough, install a sub-panel on the inverter output and put the protected circuits (tv-computer, fridge-microwave) into this panel. Cut the lines you show going to all these circuits from the main panel. One breaker in the main AC (unprotected) panel will become the main disconnect for the transfer switch and sub-panel.

If you want to see my crude sketch, send a PM and I will attach it to an email.

 

[John-SKO]

In response to Les,

I really appreciate your response. I'm also trying to figure out how to set up the electrical system of my bus. I like the all-in-one idea of the AC and ground being handled by the inverter and even the charging. But I'm also interested in solar panels and am wondering how a charge controller fits into the system. Can it go in parallel with the inverter? In such a circumstance could you charge the batteries on both AC and Solar at the same time?

John

 

[Redbear]

Yes, you can place an inverter/charger in parallel with a charge controller. If they are simple fixed-voltage devices, just calibrate them to the same cut-off, or plan one to stop just before the other. If you use "smart" multi-charge rate devices, you will have to control the interaction between them. For example, If the shoreline/genny is filling up a low battery, and the sun comes out, the charging voltage from the PV might be misundestood by the AC charger as a battery that is nearly full. The best way to control interaction is to get two units that talk to each other.

My wife and I are looking at possible going off-grid in our planned retirement home. (Any skoolie will have to wait till that's done It's trailer camping for now. ). I also inherited two off-grid communications sites using older PV technology. I have been doing a LOT of reading, including here.

A good, well written place to start is "The 12-volt Side of Life" http://bart.ccis.com/home/mnemeth/12volt/12volt.htm by Mark Nemeth, an RV full-timer. Another reference is in the electrical info found in "Poop Sheets by phred"http://www.phrannie.org/phredex.html. The "Poop Sheets" deal with various aspects of living in homes on wheels.

One line of inverter/chargers and charge controllers is Outback. http://www.outbackpower.com/ These are the ones I hope to use. Many people think these are the Cadillac of inverters. With their components, you can install a HUB communications box and MATE remote display/controller, and the units will share battery charge and temperature information and act as one. Download the manuals and take a look. The appendix in the MX-60 charge converter manual has very good information on battery charging.

There are lots of other brands out there, too. Most of the off-grid homes my wife and I have toured http://www.nesea.org/buildings/openhouse/listings.php have used the Trace/Xantrex line, which I understand are the sucessors to the Heart line used in many RVs. (If you see a home listing near you in VT, drop them an email. The official tours are Columbus Day weekend, but many or most are proud to show off their homes by invitation as well.)

Take a look at Home Power magazine http://www.homepower.com/home/, Download the sample issue in .pdf, and check out the advertisers' web sites.

John, are you a hiker? One of the off-grid comm sites is 2.5 miles up a hiking trail about 40 miles west of you, north of Whitehall. I'll be up there several times this summer supervising contractors, and can show you briefly how the solar, wind and AC genny work together as chargers in old technology. (You would have to enjoy the walk and the view of Lake George, or it would be a lot of work for a little bit of information.)

 

[John-SKO]

Redbear,

I love hiking. Thanks for all your information. The main plan is to invest in some nice equipment now, with the plan of moving said equipment into a sustainable home after the life of the bus. So I consider a lot of this equipment to be an investment rather than a cost.

Sorry I hijacked your thread Swinada, I'll PM about Whitehall.
John

 

[swinada]

Sorry I hijacked your thread Swinada, I'll PM about Whitehall.
John

No problems its all good info.

I got one of those.

But since I'm not gonna have a Geni right away did I think i could just wire the Inverter in to the Geni side of the box. Then if
I need to run off the batteries I just throw the switch. If I get a Geni I can just plug the shore power cord in to the Geni if I need to run it. That should work, shouldn't it?
(the plug in for the generator is covered up and can be directly wired to the 20 AMP breaker)

 

[Redbear]

But since I'm not gonna have a Geni right away did I think i could just wire the Inverter in to the Geni side of the box. Then if I need to run off the batteries I just throw the switch. If I get a Geni I can just plug the shore power cord in to the Geni if I need to run it. That should work, shouldn't it?

It looks good. I can't blow up the picture, but it appears there's a locking bar, and the transfer from shore to "genny" takes place by turning off one 'main' breaker, and then turning on the other. The locking bar keeps you from back-feeding the grid or the grid backfeeding the local source. That's a not uncommon means of transfer.

Using an outlet on the genny instead of direct wire, and plugging a short piece of shoreline into it is a common and very foolproof way of switching. Automatic transfer relays last thousands of cycles, but do sometimes fail. If you plug your own cord in, there is no question about the power source. If a connector ever goes bad, grab another from the hardware store.

The convenience of an ATS is if the power fails in the middle of the night, and you have a remote genset start by the bed, you roll over and punch the button, instead of going out and switching cords.

The genset input to your panel CAN be used for the inverter output. Since it appears this will switch the whole bus, be careful about adding up your loads. A shoreline or genset can typically supply more current than an inverter; or if the inverter is big enough, the batteries aren't.

 

[swinada]

yes it has a locking bar.

This prewired generator transfer switch is ideal for powering essential appliances with a portable generator during a power outage. It accommodates 6 to 10 household circuits, and can be used with any portable generator up to 5000 watts (continuous). Ideal for powering your furnace blower (gas only), refrigerator and kitchen circuits, well pump, lights, and television. If your needs change, you can easily expand this transfer switch to up to 10 circuits just by adding more circuit breakers. The enclosure can be surface mounted indoors, and allows hardwired or plug-in generator connections. Prewiring means it's faster to install! Because it was designed with off-the-shelf circuit breakers you don't have to search high and low for replacements, and your installer can reconfigure the breaker combinations to suit your family's needs. This transfer switch includes a L14-20 male power inlet and dual wattmeters to help you balance generator loads to prolong generator life. Includes two 15-amp 1-pole breakers, two 20-amp 1-pole breakers, and one 2-pole 20 amp breaker. UL 1008 Listed. Listed with Siemens, Square D, Cutler-Hammer and GE interchangeable type breakers.

A 2-pole 60-amp main breaker must be installed in existing load center (not included).

Protected by US Patent 6,861,596 B2 and other patents pending.

Dimensions: 9.25 W x 11.125 H x 3.375 D.

Optional flush plate available (Model 50329) for flush mounting (Sold separately).

Would the watt meters still work properly even if I have the inverter hooked up to the line?
I dont think i will have to big a loads since I dont plan on much. AC i dont have and I'm not sure if I want one. Really all that will be running of the inverter will probably be a TV or computer may be a Microwave. But with the computer I'll probably go for a 12V DC powersupply anyway.

here is a bigger picture.

 

[Redbear]

Would the watt meters still work properly even if I have the inverter hooked up to the line?

I saved and blew up the picture to see what you have. I think it's a GenTran 2026. I downloaded the instruction sheet at http://www.gen-tran.com/content/support/installation_instructions.asp.

The pre-wired connectors are poorly drawn. The schematic looks like all the hot inputs and outputs are shorted together. You have to read the text or look at the wire colors in the main panel to decode that Black/Black/White are your commerical power inputs, and blue wires are your protected outputs.

The installed "wattmeters" (actually measuring amps) measure the two 110-volt legs coming in from the 220-volt socket. They feed the two 30-amp breakers that act as the emergency generator input. The meters will always read zero when the mains are switched back to 220-volts 'commercial' power.

If you use the genset socket for the inverter feed, and the 60-amp breakers for the shoreline or genset input, the meters will only read the draw on the inverter when it's the source. If you were always and forever going to limit your bus to 30 amps total at 110 volts, the Gen Tran could be rewired so that one "wattmeter" measured the 110-volt shoreline, and the other measured the 110-volt inverter.

(Replace the 60-amp commercial main with a 30-amp main breaker, remove and discard the black input wires, and disconnect the wire from 'Y' on the genny socket to use as a shoreline input. Trace the 'Y' wire through its meter to one side of the 30-amp genset main, move that end over to feed one side of the new 30-amp commercial main. Wire the inverter to the 'X' pin of the socket connector, and leave the 'Y' pin disconnected.)

If you use 220-volts for any of the three sources, you would have to install other metering, or use this device only as a breaker panel and not a transfer switch. It cannot safely be modfied to measure both inputs at 220 volts.

 

[swinada]

Thanks for that detailed reply. I dont plan on running 220V in my bus. that 30Amp main braker would only get one wire coming from the shore? the black one to the breaker and the white one would go to the neutral bar, the green to the ground stud, right?
Just to make sure I understood this right. is this what you meant?

could it be straight wired like this? Just to get rid of that plug and prevent anybody coming along and plugging something into it.

 

[Redbear]

The second drawing looks like it. The instructions say there is a cover plate included to fill the hole when the plug is removed.

The first drawing is also correct, except it shows the plug pin "Y" screw being used as the tie point between the shoreline and the meter. DON'T DO THIS AS PICTURED! Leave the plug pin un-connected, and use a wire nut to joint the two wires inside the box. If you use the male pin as a tie point, there would be hot 110 volts for someone to poke their finger into if the inverter was unplugged and the shoreline feed was live. I think you were just using this as a convenient place to modify the drawing, yes? I don't see any problem with either plan with this correction.

One thing to consider when using a 220-volt panel on 110 volts, is that every other breaker will be dead in a simple install like drawing #2. There are two 'hot' bars in the back of the box, one for all the odd numbered ('A') breaker positions, and one for all the even ('B') ones. One side of the double main powers each bar. In drawing #2, all the even 'B' circuit breakers will be dead.

If there are already more breakers on the odd bar than you need, then just use them and ignore the even ones.

If you need more breakers, there may be lugs on the ends of the bars not shown in the drawing, to be used as power inputs in some other configuration of the box. If this is the case, loop a jumper of #10 or larger wire between the two lugs to power the second bar from the first bar and thus power all the breakers.

If there are no lugs, and you connect the feed from the meter to both poles of a double main, then you could draw 30 amps on the 'A' side and 30 amps on the 'B' side before it trips. Even if the shoreline and the lead-in can handle it, you are drawing up to 60 amps through the 30 amp meter. Not a good thing. Using a dual 15 will protect the shoreline and meter, but will cripple how much you can draw from each pole.

Breaker 6A/6B looks like a double pole 20-amp unit. If you jumper the two outputs and turn it on, you would have four branch circuits: 4A, 4B, 5A, and 5B. 4B abd 5B together would have to draw less than 20 amps. I think you were thinking about 4 circuits, so this may work. Another option is to replace the full-size breakers with half-width ones, but why buy all new breakers if you already have them?