inverter questions

[Tex Bigfoot]

I've just about got my mind around the process of changing the gas/120volt /12volt refrigerator that came in our camper out to a 10 cubic foot apartment size unit that is straight 120 Volt .

 

The process is fairly straight forward and I would like to thank all the ones that have been a help to me with this. There are some folks here that really know their stuff.

 

One last question .

I would like for this refrigerator to be able to operate while on the road ,I know that for this I will need an inverter so that is not a problem .

I also know that I will need at least 1 more battery that also is no big deal .

 

The only thing I will need to power is this refrigerator. We don't boondock .

 

With the above in mind can I simply tie the inverter into the breaker box and power the whole box or do I need to run a separate wire to only the plug for the refrigerator?

 

Well ok now something else popped into my mind. Will the inverter drop off line when 120Volt is available or will I need a switch for this?

 

 

[Mark and Dale Bruss]

Part of the answer depends on your shore power: if it is 30 amp or 50 amp.

 

A 30 amp service can run through the Inverter if it is large enough (2000 watts). This would take the place of the Converter, charging the batteries when on short power and switching to generating AC when shore power is not present. The Inverter would need a builtin transfer switch.

 

With a 50 amp service would hook the Inverter to one of the input shore power legs. The output of the Inverter would be connected to a subpanel breaker panel. The refrigerator and other necessary items would be connected to the Inverter Subpanel. The auto-transfer would be the same as the 30 amp service.

 

You want your Inverter to be large enough. Not just for the running current but for the startup current of the refrigerator.

 

There can be skimpier solution others will offer but for a reliable system, do it right.

[Jack Mayer]

You have opened a pandoras box of possibilities here. I suppose I should write a complete article on installing a small inverter for just powering a fridge. Maybe I'll do that in my time off this week.....

 

1) As Mark said, you can put in a whole house inverter. With a subpanel if you have a 50 amp coach; without a subpanel if you have a 30 amp coach. This will pick up the fridge, and other appliances, and typically replace the converter and have an inbuilt transfer switch.

2) A varient of above is to put in a pure inverter - no charge section - and maintain the current converter. In this case you might have to also add a transfer switch.

 

Both of these options are not likely what you want, since you claim no boondocking at all.

 

In that case:

 

1) You can put in a small 1000 watt inverter like the Magnum pure sine wave MMS1012, which has an inbuilt transfer switch to detect shore power and switch to it. Or the Kisae 1000 with transfer switch.

2) or, you can put in a small inverter like you find at Sam's Club, etc without a transfer switch built in, and add an external transfer switch. I don't recommend this.

 

I like the Kisae, if you don't want to fund the Magnum. The newer versions have been upgraded and perform even better than the old ones - which were already good.

 

Now to the wiring....

 

You have to somehow intercept the wire from the current loadcenter and move it to the inverter so that the inverter can select your power source. AND the inverter MUST be mounted near the battery bank. So you are basically going to pull two new Romex lines between the inverter and your main loadcenter. One from the original breaker for the fridge TO the inverter. Then one FROM the inverter to the loadcenter and splice it into the original line feeding the fridge. This in effect puts the inverter "inline" with the fridge, and only the fridge (plus anything else on the original breaker).

 

There are nuances to all this, but that is the basic wiring scheme.

 

Nuances: how to terminate wires in the loadcenter where you splice them; How to run the DC wiring and how heavy is it; catastrophe fusing for the DC side; line protection for the inverter-to-fridge line, etc.

[Darryl&Rita]

Simpler yet. Install a PSW inverter, dedicated to the fridge plug only. Use the inverter to power this receptacle all the time. No transfer switch, no load centre wiring. When travelling, the inverter draws down the battery bank. When parked, the converter charges the batteries back up. If you start doing more dry camping, add some solar to the equation.

[Tex Bigfoot]

thank you both I think I have it .

 

I'm thinking that I can do this fairly easily as I have good access to the battery areas and the breaker box areas . Plus I will need to drop the underbelly in places in order to plug the gas line anyway .

 

Jack one of your comments made me think .

 

Am I correct in thinking that I could just replace my existing converter with a inverter and would have the 12volt for lights plus the whole house would have 120volt as needed?

This statement is taking into consideration that I am and will be short on battery power

[Jack Mayer]

If you replace the converter with an inverter/charger then yes, you can eliminate the converter (or better yet, save it for standby purposes, but unplugged).

[oldjohnt]

Tex good questions, here are my responses to your specific questions:

 

 

1) I would like for this refrigerator to be able to operate while on the road, I know that for this I will need an inverter so that is not a problem .

I also know that I will need at least 1 more battery that also is no big deal.

 

a) In order to correctly size the Inverter, you need to know the Full Load Amps (FLA) the new fridge draws (or its watts). Then those amps x 120 volts tells you how many Watts are required to operate it. Then the Inverter needs to be rated somewhat higher in watts then the fridge watts since when it starts up the amp draw can for a short period be much higher then its normal running amps. True, the Inverter can have a certain "surge" rating which allows for short term higher amp draw, but in simple laymens terms, I wouldn't size the Inverter right at the same the fridge requires and rely on the "surge: capacity, but instead use an Inverter rated at more watts then the fridge requires. If I knew the fridge watts I could tell you what size Inverter I would use. Regardless, I would size the Inverter to allow for future expansion i.e. do NOT size it so small the fridge is all it can run period. A PURE GUESS would be maybe a 1000 to 2000 Watt PSW Inverter, it depends on the fridges FLA. A 1000 Watt may be plenty, but even if so Id consider a 2000 for future expansion. I have a small dorm size 120 VAC fridge which a 1000 watt Inverter would have powered easy, but I opted for a 2000 anyway. YOUR CHOICE based on fridges FLA mind you.

 

I recommend the use of a Pure Sine Wave PSW Inverter as opposed to a cheaper Modified Sine Wave MSW.

 

 

2) The only thing I will need to power is this refrigerator. We don't boondock .

 

That tells me the ONLY load you need to consider and design for is the fridge instead of the entire RV 120 VAC electrical system

 

3) With the above in mind can I simply tie the inverter into the breaker box and power the whole box or do I need to run a separate wire to only the plug for the refrigerator?"

 

Since you state you don't boondock and the ONLY thing you need to power is the fridge YOU ANSWERED YOUR OWN QUESTION

 

Based on your own statement, I would NOT power the entire breaker box with the Inverter, but instead simply run a 120 VAC Inverter Output 15 or 20 amp Branch Circuit (3 wire, 12 or 14 Gauge depends on fridge power requirement) to the fridge. Also depends on if you have a 30 or 50 amp service!!!!!!

 

TRANSFER

 

a) If its handy to get to you could install the above Inverter powered 15 or 20 amp standard receptacle by the fridge and plug it into the Inverter outlet when you want to run off your batteries and inverter system, orrrrrrrrrrrr plug into the RV breaker Box powered 120 VAC outlet when you're plugged into shore power.

 

Install a Transfer switch to feed the receptacle the fridge plugs into. It has 2 selectable power sources, Inverter or 120 VAC shore power. You just flip it to which power source is required, Inverter while driving or shore power when plugged into shore power. Fairly cheap and easy to install.

 

 

3) Well ok now something else popped into my mind. Will the inverter drop off line when 120Volt is available or will I need a switch for this?

 

YES and NO lol

 

A no frills no auto transfer switch Inverter will only "drop off line" if you remove its 12 VDC battery input power source or you turn it off. It doesn't know or care if your 120 volt panel has power or not.

 

A straight no frills no auto transfer Inverter provides 120 VAC output power anytime its connected to your batteries and its switched ON. If you remove its input power source (your 12 volt batteries) or turn it off, then there's no 120 VAC output to power your fridge WELL DUH

 

HOWEVER If you want to get more automated and fancier (more money) you could have a transfer switch to power the fridge via the RV panel when youre plugged into shore power,,,,,,,,,,, but switch over to the Inverter and battery power when youre not.

 

You can also have an auto transfer that senses when 120 VAC is available and if so the RV panel runs appliances etc but if not (no shore power) the Inverter kicks in and its 120 VAC powers whatever loads are connected.

 

 

NOTE there are a ton of methods and options here depending on your needs desires and budget AND I AM NOT GOING TO COVER THEM ALL. You can get combination Inverter/Chargers that charge your house batteries when plugged into shore power but when not the Inverter draws power from your batteries and supplies 120 VAC loads.

 

CLOSING if all you want to do is power a fridge and you don't boondock I don't see the need nor why you should spend the money for automatic Transfer Inverters or Inverter/Chargers etc etc. Simply install a PSW Inverter close to your batteries and use its 120 VAC output to run the fridge while you're driving. As far as transfer, install a cheap simple manual transfer switch so the fridge can run off battery and Inverter power or 120 VAC utility when plugged in. Or even have 2 receptacles at the fridge. One for RV 120 VAC the other powered by your batteries and Inverter.

 

This is your money your RV and your choice. I tried to ONLY answer your questions, but if you get deeper into this and want to start thinking Inverter/Chargers and Auto Transfer Inverters etc. etc. post back.

 

DISCLAIMER Im a long retired EE and rusty on this stuff so no warranty and there are several fine gents here more current and RV experienced then myself, so don't bet the farm on anything I say lol

 

John T

[Tex Bigfoot]

Based on the comments I have now installed a Hailer 10.1 CF home type refrigerator.

it was a nice fit and an easy install. Next week I will be picking up a 1000 watt inverter and setting that up on a circuit to power the new unit. turns out in my load center the refrigerator was on a circuit with only it and one other plug.

Max load is 6 amps on startup then the load drops to 2 amps, 6 amps X 120 volts = 750 watts so in my mind 1000 should do the job......please check my math as I have been know to ....lets see how should I say this .......tea totally screw it up before ....yep that pretty much says it all.

 

I had been trying to get my head around this for sometime now and it finally came together .Thank you all so much for the help .

[oldjohnt]

Tex, if the brief start up current is 6 amps (6 x 120 = 720 Watts) while the normal run current is 2 amps (2 x 120 = 240 Watts), a 1000 Watt Inverter "should" do the job. Of course its NOT 100% efficient (some heat losses) but its big enough even for the max short term 720 watt surge with room to spare for any inefficiency factor.

 

So, all you have to do is wire up the Inverters 120 VAC output and a transfer method (manual is easy and cheap) so you can select RV utility power when plugged up or Battery/Inverter power while driving down the road. I'm talking about a no frills non auto transfer straight Inverter mind you. With a 1000 watt inverter and if the existing RV branch circuit already has one additional non fridge receptacle, you may consider retaining that for small power ( a few hundred watts) battery/inverter powered loads such as phone and elec device and computer charging etc. That way while driving you have a ready made battery/inverter powered 120 VAC receptacle you can plug small 120 VAC devices into. The 1000 watt inverter can run the fridge PLUS say a computer and phone chargers etc.

 

A 15 amp rated branch circuit will suffice for that Inverters 1000 watt 120 VAC output, that means 14 Gauge 3 conductor (Hot, Neutral, Ground) wire (14/2 w ground romex) protected with a 15 amp overload protection device. I don't know what type of internal thermal overload protection the inverter has built in, but that should protect the unit itself.

 

The 1000 watts at 12 VDC corresponds to around a 83 amp load (not counting inefficiency heat losses) on your batteries, but that's if you drew the entire 1000 watts which it appears you will seldom do. Regardless, Id still size the DC input (battery to Inverter) feeders for an ampacity of no less then 100 amps and still subject to wire length and voltage drop if needed. Closer to batteries the better BUT NOTE ALL OUR RECENT DISCUSSION REGARDING POTENTIAL PROBLEMS WITH AN INVERTER IN THE SAME LOCATION AS BATTERIES !!!!!

 

I also have a Haier but only a small dorm size fridge, and it sips power at the rate of around 30 Amp Hours per day. With my 460 Amp Hour battery storage bank and 400 watts of solar panels (and Onan genset if ever needed) I can dry camp and run that fridge till the cows come home lol

 

You're getting there, congratulations

 

Again, see what more current more RV experienced gents have to say, I may be all wet grrrrrrrrrrrrrrrrr

 

John T

[4x4ff]

I am going through this exact scenario myself right now. My goal like you is not for boondocking but to power the fridge during travel and the occasional campground power outage. I asked a very similar question here myself just a week or so ago. I purchased the Whirlpool WRT 111 series refrigerator and am very pleased with the additional room and how little power it sips. I am at least initially trying be as 'cost effective' as I can. I am a firm believer in the 'buy it nice or buy it twice' type of mentality but right now I just don't have the funds to go 'high end' so I am trying to go something reasonable and affordable.

 

I found the circuit that the fridge is on and pulled it out of the breaker box. I am going to wire in this http://www.amazon.com/dp/B004S5Y158/ref=wl_it_dp_o_pd_S_ttl?_encoding=UTF8&colid=3TZJ10L3BICA5&coliid=I3BK449YAE9H1Z transfer switch and probably use this http://www.amazon.com/dp/B002I04A74/ref=wl_it_dp_o_pC_S_ttl?_encoding=UTF8&colid=26H6379GZVYXT&coliid=I2JRPJ4RZWL7LI&psc=1 Inverter. I am also going to install this http://www.amazon.com/dp/B002W87JNO/ref=wl_it_dp_o_pC_nS_ttl?_encoding=UTF8&colid=26H6379GZVYXT&coliid=I1G362UGNYM63D&psc=1 remote switch for the inverter. I already purchased the transfer switch and in fact started wiring it in today. I have not purchased the inverter yet. I wanted to get the transfer switch wired in and ready while I had some other issues I was fixing and had everything accessible.

 

Steve

[4x4ff]

Tex, if the brief start up current is 6 amps (6 x 120 = 720 Watts) while the normal run current is 2 amps (2 x 120 = 240 Watts), a 1000 Watt Inverter "should" do the job. Of course its NOT 100% efficient (some heat losses) but its big enough even for the max short term 720 watt surge with room to spare for any inefficiency factor.

 

So, all you have to do is wire up the Inverters 120 VAC output and a transfer method (manual is easy and cheap) so you can select RV utility power when plugged up or Battery/Inverter power while driving down the road. I'm talking about a no frills non auto transfer straight Inverter mind you. With a 1000 watt inverter and if the existing RV branch circuit already has one additional non fridge receptacle, you may consider retaining that for small power ( a few hundred watts) battery/inverter powered loads such as phone and elec device and computer charging etc. That way while driving you have a ready made battery/inverter powered 120 VAC receptacle you can plug small 120 VAC devices into. The 1000 watt inverter can run the fridge PLUS say a computer and phone chargers etc.

 

A 15 amp rated branch circuit will suffice for that Inverters 1000 watt 120 VAC output, that means 14 Gauge 3 conductor (Hot, Neutral, Ground) wire (14/2 w ground romex) protected with a 15 amp overload protection device. I don't know what type of internal thermal overload protection the inverter has built in, but that should protect the unit itself.

 

The 1000 watts at 12 VDC corresponds to around a 83 amp load (not counting inefficiency heat losses) on your batteries, but that's if you drew the entire 1000 watts which it appears you will seldom do. Regardless, Id still size the DC input (battery to Inverter) feeders for an ampacity of no less then 100 amps and still subject to wire length and voltage drop if needed. Closer to batteries the better BUT NOTE ALL OUR RECENT DISCUSSION REGARDING POTENTIAL PROBLEMS WITH AN INVERTER IN THE SAME LOCATION AS BATTERIES !!!!!

 

I also have a Haier but only a small dorm size fridge, and it sips power at the rate of around 30 Amp Hours per day. With my 460 Amp Hour battery storage bank and 400 watts of solar panels (and Onan genset if ever needed) I can dry camp and run that fridge till the cows come home lol

 

You're getting there, congratulations

 

Again, see what more current more RV experienced gents have to say, I may be all wet grrrrrrrrrrrrrrrrr

 

John T

 

John T,

 

With a 1000 watt inverter located say 4' run (may be less) from the batteries what size wire would you recommend as a minimum and what size and type of 'catastrophe' fuse should I put inline???

 

 

Steve

[oldjohnt]

4 x 4,

 

You ask "With a 1000 watt inverter located say 4' run (may be less) from the batteries what size wire would you recommend as a minimum and what size and type of 'catastrophe' fuse should I put inline???"

 

Well call me Mr. Conservative and I admit I tend to over size (less voltage drop) so with that being said:

 

PS with such a short 4 ft run (with adequate conductors) voltage drop isn't much of a concern, but I still over design, just an old habit that's hard to break ( I had a conservative very NEC compliant Boss way back when) and how I'm wired lol

 

 

(A) INVERTER DC INPUT

 

I would use 2 Gauge Copper THWN conductors. 4 Gauge would get you buy and "work", but you asked and that's what I would use. I'm NOT saying that's NEC (which indicates certain MINIMUM sizes) I'm ONLY saying its what I would use even if YES its over sized. Use whatever you please, For only 8 feet of wire it likely wont bust the budget to use bigger then necessary wire I hope????

 

NOTE Im sure people could post "By Golly I have a 1000 watt inverter and used 4 Gauge or even 6 Gauge etc and NEVER had a problem" and that's fine and all well and good. Ive used BIGGER then necessary or NEC sized wire before and I never had a problem either lol

 

As far as protecting the big No. 2 copper feeders FROM the batteries TO the Inverter input, at the energy source (batteries) you would normally size it to match/protect the conductors ampacity which is 115 amps. NOTE the overcurrent protection device (like a fuse at the battery energy source) is to protect the feeders NOT the Inverter. However, since the Inverters rating is more like 83 amps on its DC Input, if you wanted to limit its input current you could use an 80 amp fuse which still protects the feeders PLUS limits current the Inverter can draw. I would assume the Inverter has its own built in thermal protection. I didn't take the time to look up type and rating and fuse classes etc for this application.

 

( INVERTERS OUTPUT

 

Again the Inverter may have its own built in protection, but a 1000 Watt inverter can supply around 8 amps at 120 volts. Therefore, for a 120 volt circuit fed by the Inverter output I would use 14 Gauge 3 conductor (Hot, Neutral, Ground, 14/2 w/Ground Romex or other wire, sure its oversized WELL DUH you know me lol)

 

 

 

John T

[4x4ff]

Thanks John,

 

The inverter is a Xantrex 806-1210 PROwatt 1000 PSW inverter. I'm glad to hear about the #2 wire. I was thinking I would have to use 0 or maybe even 2/0. Any particulars on the fuse?? Type, style, model etc.???

 

 

Steve

[Jack Mayer]

Use the size wire the inverter manuf. recommends, or one size heavier. And use the size fuse they recommend. ALL manuf. include this information with their product installation instructions.

[oldjohnt]

Hey there Jack,

 

I enjoyed that portion of you post where you stated "or one size heavier" we must be cut from the same mold. Hey, as long as I can afford a few more bucks if bigger wire will reduce voltage drop (more critical in longer runs) and reduce the I Squared R heat losses, plus be a bit safer, IM ALL FOR IT (within reason) and would rather err on the side of safety.

 

As far as installation instructions, I would also follow them UNLESS (1) They are incorrect or (2) Not in compliance with NEC minimum standards. If either of those were the case, then I would do what is engineering and NEC correct, safe and proper. But, of course, the instructions are most likely right on.

 

Nice chattin with ya, take care and safe travels

 

John T

[4x4ff]

Use the size wire the inverter manuf. recommends, or one size heavier. And use the size fuse they recommend. ALL manuf. include this information with their product installation instructions.

 

Thanks Jack,

 

I had downloaded the manual but missed that section somehow until I reread it. According to the manual for for the 1000 Watt I should use a minimum of "0" cable for lengths of up to 6' along with a 150 amp ANL fuse.

 

I guess that answers that.

 

 

 

Oldjohnt,

 

Thank you for your input. As you said I guess it is better to go more robust than under.

 

 

Steve

[oldjohnt]

4 x 4 You're doing good and you're welcome.

 

Hey you will NEVER hear me complain about using wire BIGGER then necessary wire based on current draw or even if bigger then the NEC might require. That's less voltage drop,,,,,,,,,less I Squared R heat losses,,,,,,,,,,safer.

 

Here's a bit more info from the AWG Ampacity Chart I had handy. NOTE, factors such as Temperature, Insulation, Enclosures or Jacketing, Free air or buried in earth or in conduit etc etc etc ALL changes the amp rating and could necessitate even bigger wire (or smaller if in free air).

 

 

If a 1000 watt Inverter operates at say 12.6 volt input, that's 79 amps. At 12 volts it would draw 83 amps (bigger wire = less voltage drop so better)

 

HOWEVER No Inverter is 100% efficient (heat losses) so to extract 1000 watts at 120 Volts OUTPUT, YOU WOULD NEED MORE THEN 1000 WATTS ON THE INPUT, the 79 and 83 amp approximations above may be LOWER THEN ACTUAL, therefore, the Inverter could draw maybe 85 to 90 + amps (depends on efficiency). I don't have that Data but bet the manufacturer does!!!! YET MORE REASON TO USE BIGGER WIRE TO BE ON THE SAFE SIDE

 

# 2 Copper THWN at 75 Degrees is rated at 115 Amps (per my chart absent all the data, so may be inaccurate)

 

# 0 Copper THWN is rated for 150 Amps (per my chart absent all the data, so may be inaccurate)

 

BOTTOM LINE I BET 0 GAUGE 150 AMP RATED WIRE IS BIG ENOUGH (if DC INPUT is in the 79 to even 100 amp range as noted above) and since the manufacturer states such, to be on the safe side and especially WARRANTY, Id use that instead of my earlier 115 amp rated 2 Gauge wire recommendation. BIGGER IS BETTER. If you drop voltage on the input wiring (because wire is too small) that affects operation and its best NOT to do that

 

Congratulations, you're getting there

 

John T