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Another inverter question


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Hi everyone,

I peruse this forum often looking for ideas for my trailer. I was reading the other inverter question thread but did not want to hijack that thread http://www.rvnetwork.com/index.php?showtopic=117942

I am going to hook up one of the "Walmart" invertors to run my television. The inverter is from my old trailer and works fine with the television, even though it is a cheapy. Anyway, I am planning to wire the inverter into my system as shown below. Could one of you knowledgeable guys take a look at the attached drawing and tell me if this will be safe? As far as I can tell, it will be, but I would like a second opinion.

In particular I am somewhat concerned about the voltage being applied to the neutral leg of the outlets (alluded too in the other thread) by these cheapy inverters.

post-51177-0-30686000-1432840964_thumb.jpg

 

Thanks,
Dan

 

 

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Dan, as far as "how knowledgeable" my answer is, take it at your own risk lol. Although I'm a retired Electrical AC Distribution Design Engineer (then an attorney after all that) its been a long time so if more current experienced professional electricians or engineers or RV techs or RV experts disagree, better listen to what they say also, YOU GET NO WARRANTY FROM ME (I also have my lawyer hat on now lol)

 

You ask "if this will be safe?" My answer is "probably", however absent the Wal Mart Inverters actual internal wiring design schematic, I don't see how anyone can say with absolute certainty, but I will still ponder a few somewhat educated guesses and proceed.

 

 

1) This is not such a concern with your, I'm guessing small Inverter, maybe a few hundred watts as opposed to a 1000 or 2000 watt, but I usually power an Inverter direct off the batteries (NOT go through any RV DC distribution panel) with a big enough cable as close as possible and if I want to protect the wire from batteries to inverter I place a fuse or breaker right there at the battery energy source. Your diagram shows you are using the DC distribution panel and its fuse which should still work fine, especially with a relatively small Inverter. IT WILL WORK AS YOU HAVE IT even if not how I would wire it (direct to battery). You still obviously want the wires from the panel to the Inverter big enough (even over sized) to reduce voltage drop and safely dissipate the heat without degrading the insulation. Example if you had say a 400 watt inverter, that's around 32 amps at 12.6 volts at power, in which case I would use at least 8 gauge wire SUBJECT TO the distance and voltage drop calculations which may require even bigger wire. A 200 watt inverter could draw around 16 amps in which case Id use at least 12 but more likely 10 gauge wire.

 

2) I see you are using a two pole transfer switch and are, therefore, switching BOTH the Hot and Neutral which is how I would advise, but still SUBJECT TO THE INVERTERS ACTUAL DESIGN AND WIRING DIAGRAM which I don't have.

 

3) I see that you're using a protected circuit from the RV's AC Distribution Panel to the transfer which is obviously safe and correct PROVIDED the overcurrent protection device (fuse or breaker) matches the wire size and the duplex receptacles rating. Typical would be 14 Gauge wire feeding a 15 amp duplex receptacle with a 15 amp fuse or breaker or 12 Gauge wire and a 20 amp breaker.

 

4) Since that duplex receptacle may be fed by the normal utility 120 VAC distribution system, Id have the utility safety third green/bare equipment grounding conductor wired to its Grounding terminal, you only show two wires????????????? But hey home wiring was only 2 wires for years !!!!!!!!! and worked okay right???

 

5) Grounding the case/frame of the Inverter. The Inverter frame, being a non current carrying conductive enclosure similar to junction boxes etc,, I would bond to the Utility equipment Ground (as you show) which happens to be bonded to the RV frame and subsequently the DC Battery Neg.

 

NOW HERE COMES THE RUB WHICH I CAN NOTTTTTTTTTTT ANSWER NOT HAVING THE INVERTER WIRING SCHEMATIC and which in my opinion may not be as safe as if your alternate energy source was a Genset which was configured as a "Separately Derived Source" having a NON floating Neutral which is instead bonded to the gensest case/frame as well as the RV frame THATS A THIRD WIRE GROUNDED NON FLOATING SYSTEM in which case the third wire safety Equipment Grounding conductor is in place that can safely carry fault return current to trip a breaker and clear the fault WHEW LOL A two wire system DOES NOT HAVE THAT ABILITY and can be considered as less safe.

 

The thing is, not having the inverter diagram, I "suspect" its output is the same as an isolation transformer i.e. a 2 wire device transformer that has 120 VAC across its 2 output terminals BUT NO NEUTRAL. Its MY GUESS its pure 120 VAC Line to Line, NO Neutral, NO center tap, NO grounded leg like a 120/240 volt utility transformer ITS A FLOATING SYSTEM. If its a true floating isolation transformer, in theory and absent capacitive or inductive effects, there would be ZERO VOLTS FROM EITHER L1 OR L2 TO CASE OR FRAME OR RV GROUND

 

BUT I DO NOT KNOW THAT WITHOUT A SCHEMATIC SO NO FREAKING WARRANTY

 

If I had the Inverters schematic I could advise further, but suspecting its a floating isolation transformer output 120 VAC Line to Line with no Neutral nor Center Tap nor case/frame grounding of one leg of the AC, I HAVE TO PASS UNTIL I KNOW MORE

 

THAT BEING SAID, for the most part subject to my wire size advise above and using the panels distribution and protection, , its probably safe and likely how many out there are wired from the factory and will work just fine. But I still don't like NOT knowing how its wired internally and am reluctant to advise about something I cant be sure of, that's just how I'm wired and configured, SO IF SOMEONE KNOWS FOR SURE tell us and I may change my advise. IT ALL HINGES ON HOW THE INVERTER IS DESIGNED AND IF IT EVEN HAS A NEUTRAL AND IF SO IF ITS FLOATING OR CENTER TAPPED OR BONDED TO ONE LEG. A genset usually has a true Neutral and I know how to handle that situation safely, but I just dont know the Inverters circuitry

 

John T

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Thanks John T.

That was just the kind of detailed answer I was looking for.

I will ohm out the system and check the grounds. I will also measure the inverter output and see if I can determine if it is setup like a normal 120VAC line with a true neutral, or it is split with +/-60VAC.

I will have to check how the wires are routed to see if I can get a higher gauge wire back there from the battery. I did measure the current draw when it was installed in my old trailer, it only draws about 5Amps when running the tele, which is normally all it is used for. However, as you noted, if I load it down with more stuff, it could draw quite a bit more.

Thanks

Dan

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Dan if the load is only 5 amps, or even if it were to double, and assuming the run isn't much over 20 feet I DONT SEE A "MAJOR" PROBLEM even with 14 gauge wire although Id sill prefer 12 or even 10 subject to length

 

I still doubt your Inverter even has a center tapped Neutral (or any Neutral for that matter, center or end line tapped) with 60 VAC line to Neutral and if it does I will re think my advise. I also doubt there will be continuity from either Line to the case/frame UNLESS it happens to have a Neutral which is ALSO like a genset and non floating but bonded to case/frame.

 

Again I just don't know, maybe some of the good gents here know how they are configured (or at least ones they own)

 

Best wishes, I think you are fine wired as shown

 

John T

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Looks doable to me. I 'might' suggest a more direct path from your battery bank to your inverter. I'm always trying to look forward at potential upgrades, keeping my cut-offs localized, maximize efficiency, and what's going to make the most "sense" to the next owner.

 

To that end, I'm a firm believer in "wire once". I would probably beef up the run from my battery bank to a surface mount circuit breaker near the inverter and then tie into that line rather than routing it through the power distribution panel. It doesn't need to be as fancy as the one linked, but you get the idea. If you ever choose to upgrade your inverter setup you're pretty much plug'n'play.

 

Just a thought. ;)

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X2 on the more direct path to the batteries, unless your power panel is already close to the batteries. In fact, the best advice is to locate the inverter within a couple feet of the battery (but not in the same compartment due to battery gasses), connect it directly to it with an appropriate fuse in the positive lead, and then route the 120 VAC to the TV outlet.

 

Inverters (even the small ones) have a low voltage cutout so they will shut down before the battery is fully drained. The problem is there's only a few tenths of a volt difference between a mldly discharged battery's working voltage and the point where the inverter shuts down.

 

If you have too much wire loss, the inverter will shut down from low voltage even though you have plenty of charge left in the batteries.

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Yo Yarome,

 

I always enjoy your postings. When I was asking questions about my Solar set up some months back you and others provided me with some great information, THANKS AGAIN

 

Regarding your comment ".... I would probably beef up the run from my battery bank to a surface mount circuit breaker near the inverter...." I would take a different approach.

 

I would install the circuit breaker (which is to protect the wire in case of a short or overload) right at the energy source (Battery Bank) NOT the downstream Load/Inverter.

 

The purpose of the overcurrent protective device (breaker) is to protect the feed wires leading FROM the battery TO the LOAD/Inverter, plus prevent a catastrophic battery overload in case of a dead short. THEREFORE, I would install it right at 1) The source of the energy and 2) Right where the feed wires begin NOT somewhere downstream at the LOAD/Inverter.

 

If the breaker is located far downstream from the batteries like at the LOAD/Inverter, but there's a dead short in the wires after/downstream of the batteries but before the breaker, THERES NO PROTECTION and a short there WILL NOT TRIP THE BREAKER.

 

HOWEVER if you install the overcurrent protective device (to protect wires) right at the batteries, there's little chance of leaving any portion of the circuit unprotected.

 

Any wire from the batteries BEFORE THE BREAKER is NOT protected and if a dead short occurs there, the breaker doesn't do its job, it doesn't see that high current.

 

SURE as you mentioned the breaker will trip (if short is after the breaker) and the portion of the wires AFTER THE BREAKER is protected, but if the breaker isn't located right at the energy source, a section of the wire (before the breaker at the Inverter) isn't protected at all.

 

Anyway, that's the way I was taught in engineering school plus several NEC Seminars I had to attend each year in my career, but that's no guarantee its right and/or that your way is best, and I believe people have the freedom to do as they please lol. I just believe its much safer to install the breaker at the energy source NOT somewhere downstream where the load is located such that the entire run of wire is protected.

 

PS in your home are the circuit breakers located in the main distribution panelboard (where wires begin) orrrrrrrrrrrr in the kitchen where the toaster plugs in (where wires terminate at the load) ???? Think about it!!!!!!!!!

 

Take care Yarome, and thanks for all your help

 

John T Longgggggggg retired and rusty on this stuff, so as always, NO WARRANTY

Just because I was NEC trained to place the breaker at the source and beginning of the circuit (versus out at the load) don't mean its

the best method, do as yall please.

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Any wire from the batteries BEFORE THE BREAKER is NOT protected

 

Hey John!

 

No.. you're absolutely correct. Didn't you know though? You're expected to read my mind and see the same wiring and equipment setup I'm picturing in my head? :P

 

In the above I had in mind we're talking somewhere in the neighborhood of a 2'-5' run to the inverter. In that case.. mounting a surface breaker near the inverter would probably put you within 3' or so of the battery or terminal post connection. Possibly a compromise, but neglegable for the sake of convenience and maybe a little "cleaner" install.

 

Your remarks are valid though. It is important and appreciate you making sure the OP has the best possible information available.

 

~ Cheers on ya :D

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Yarome, yep I do tend to go OVERBOARD at times lol. I couldn't count how many times I've seen short cable runs from say a battery to a load with NO PROTECTION AT ALL, but if the cables are well insulated and well supported with no place in sight where they may get together or short up against a conductive frame member etc., what are the chances?? I cant help but to point things out just because maybe some electrically challenged new gents here (present company excluded) may learn a thing or two. Look at big battery cables on cars and truck, they don't have overcurrent protection yet wind and snake around engines and frames and high temperature. Under my RV frame there are tons of typical wire runs and any place any are close to the frame or to each other I split 1/2 rubber heater hose to cover them and zip tie them, is that what they call type A personality or something that sounds worse lol

 

Best wishes, take care now

 

John T

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I do tend to go OVERBOARD at times lol.

 

Not at all, John. It's not always safe to "ass"ume and great there are folks out there that are making sure of adding their experience for those just starting out.

 

If you want to see "overboard".. :P I don't often show my setup.. especially pic 2 with my "octopus hole".

 

001_zpszrxo7goq.jpg

 

003_zps8bztvnf1.jpg

 

One of these days I'll get that all cleaned up.

 

Appreciate your input.

 

~ Mikk

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GEEEEEEEEEEE that's a "pretty" installation MUCH better then anything I've done, I don't always practice what I preach, its like I tell my kids, do as I say NOT as I do. But good quality safe proper electrical RV installations sure makes a body sleep better, especially if your grandkids are spending the night inside.

 

John T

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Yarome, that is not "overdone". That is the right way to do it.

 

One of the reasons I stopped doing installations is that there were too many "customers" that argued with the cost of doing it right. Seems like many people want it done "on the cheap". And I simply will not do that. It got to the point that it was not fun anymore so I simply stopped doing it. :)

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One question - what current does your inverter draw when there is no 110v load? You are switching the 110v lines but that still leaves the inverter still "on" and that will be a constant drain on your batteries. Is there a switch on the 12v side that I am not seeing?

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One question - what current does your inverter draw when there is no 110v load? You are switching the 110v lines but that still leaves the inverter still "on" and that will be a constant drain on your batteries. Is there a switch on the 12v side that I am not seeing?

 

Actually, I'm not switching my 110v.. that line at the terminal block is 12v. The back end of the inverter is fused and no need for a seperate disconnect (since I can simply flip it off). There is a manual switch built into the inverter that I leave on and have remote control panels for the inverter/charger and solar controller mounted in a different location.

 

With no load on it burns 25 watts, but in "search mode" that drops down to 7 watts. It's always off though unless I intend to use it. The 110vac line runs out the back and through the floor and over to the subpanel (which can't be seen). It's tied into all of the 110vac with the exception of the A/C and water heater.

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One of the reasons I stopped doing installations is that there were too many "customers" that argued with the cost of doing it right. Seems like many people want it done "on the cheap". And I simply will not do that. It got to the point that it was not fun anymore so I simply stopped doing it. :)

 

I hear ya, Jack. I don't lay hands on too often anymore myself. If I show a fella my setup and their eyes pop out for using 2/0 on 10" runs I kinda figger he'll be doing all of his own work. :lol::P

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  • 2 months later...

Hi everyone,

 

I peruse this forum often looking for ideas for my trailer. I was reading the other inverter question thread but did not want to hijack that thread http://www.rvnetwork.com/index.php?showtopic=117942

I am going to hook up one of the "Walmart" invertors to run my television. The inverter is from my old trailer and works fine with the television, even though it is a cheapy. Anyway, I am planning to wire the inverter into my system as shown below. Could one of you knowledgeable guys take a look at the attached drawing and tell me if this will be safe? As far as I can tell, it will be, but I would like a second opinion.

In particular I am somewhat concerned about the voltage being applied to the neutral leg of the outlets (alluded too in the other thread) by these cheapy inverters.

attachicon.gifInverter.jpg

 

Thanks,

Dan

Hi all,

I just wanted to follow up and let you know the outcome of my inverter installation.

In the end, I wired it almost exactly like my original diagram shows. Note that as oldjohnt mentioned, my drawing does not show the ground connection to the duplex outlets, however it is connected.

I checked various breakers until I found one that provided AC, only to non-gfi outlets. On my trailer the air conditioner and microwave are not on the outlet breaker, so no worries there.

 

The inverter I used was the cheapy shown below.

 

This is the second one of these I have purchased. I left the first one in my last trailer. They seem to drive my televisions fine and their standby current is very low (< 0.1A) and they seem to recover from standby mode as soon as even a small load is detected.

This inverter DOES split the power between hot and neutral as oldjohnt mentioned. So you measure about 60VAC to ground on both legs and 120vac hot to neutral. Before I installed it, I verified that there was no neutral/gnd bond inside the trailer.

The relay I selected was an NTE R04-11A30-120 availible on Amazon. It is a 30A DPDT with 120VAC coil. I used the 120VAC coil because I did not want to "waste" battery power energizing the relay coil. This is an open frame relay so I mounted it inside of a handy box.

Dan

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Hi all,

I just wanted to follow up and let you know the outcome of my inverter installation.

In the end, I wired it almost exactly like my original diagram shows. Note that as oldjohnt mentioned, my drawing does not show the ground connection to the duplex outlets, however it is connected.

I checked various breakers until I found one that provided AC, only to non-gfi outlets. On my trailer the air conditioner and microwave are not on the outlet breaker, so no worries there.

 

The inverter I used was the cheapy shown below.

 

This is the second one of these I have purchased. I left the first one in my last trailer. They seem to drive my televisions fine and their standby current is very low (< 0.1A) and they seem to recover from standby mode as soon as even a small load is detected.

This inverter DOES split the power between hot and neutral as oldjohnt mentioned. So you measure about 60VAC to ground on both legs and 120vac hot to neutral. Before I installed it, I verified that there was no neutral/gnd bond inside the trailer.

The relay I selected was an NTE R04-11A30-120 availible on Amazon. It is a 30A DPDT with 120VAC coil. I used the 120VAC coil because I did not want to "waste" battery power energizing the relay coil. This is an open frame relay so I mounted it inside of a handy box.

Dan

For some reason I can no longer figure out how to attach files. Even though I managed to do it when I started this thread. So the inverter part number is not showing up.

It was a Schumacher model X141B.

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Thanks for the update.

 

FWIW Your statement "This inverter DOES split the power between hot and neutral as oldjohnt mentioned. So you measure about 60VAC to ground on both legs and 120vac hot to neutral." surprises me. When I talk of splitting power, I was thinking more along the lines of 120/240 volt with a center tapped Neutral instead of 120 line to line still center tapped. Until I have some actual Inverter internal electrical diagrams, I'm going to remain reluctant about how to wire them, other then do what the manufacturer says lol. I'm quite familiar with transformer or wound non inverter genset wiring configuration and Neutrals and Grounding etc., but when the output is a floating non grounded system absent a true Neutral I'm gonna sit back until I have some diagrams to look at. At our Naval Facility way back when floating Deltas were common in the forties and fifties but starting in the sixties and in my day we preferred grounded systems.

 

John T

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I purchased an invertor that auto switches over when A/C is lost and wired several outlets to its output, including the TV/ Easy to do since I had lots of room behind my convertor where all the runs terminate. i did buy a true sine wave model however. easier on electronics. It was already a rats nest back there. The circuit breaker in the photo has been replaced with a better quality resetable one. Since my convertor is a fair ways from the battery, I made sure the circuit breaker will trip well before the battery leads reach capacity. I only use it to power the TV, a CPAP, a water pik, maybe portable fans & a laptop. never all of them at once. Its a 40 amp invertor but I have it fused at 25 amps. With all LED lighting, there is not much additional draw from any 12v sources. Still in true paranoid fashion, I loaded it to the hilt and checked the leads for any heat.

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