Jump to content

Inverter install questions


4x4ff

Recommended Posts

I just bought a 'new to me' used 1000 Watt Xantrex Prosine 1000 inverter. I only plan on using it to power the residential fridge while traveling. I had a kill-a-watt hooked up to the fridge previously and was very impressed at how it 'sipped' power. I am running 2- 6 volt batteries in my 5er. Anyway on to my question. I currently have my 5er parked several hours away and my intention is to mount the inverter on the back wall of the front compartment. I already have a small xantrex transfer switch wired in and ready to plug in at that location. I am also going to install a marinco on-off switch in the wire from the inverter to the battery along with an ANL fuse.

 

Now my questions:

1) Should I or would it hurt to fuse both the Pos. and Neg. sides?

 

2) Switch between battery and fuse or fuse between battery and switch?

 

3) The inverter is only going to be 4-5 feet horizontal from the batteries (Probably 6-7 feet of wire by the time i route it through switche and fuse). Can I go any smaller that 1/0 wire?

 

I am thinking of mounting everything on a piece of maybe 3/8" plywood and then just screwing that to the back wall. Almost like plug and play. When I install it all I would need is to make my battery connections and plug in my transfer switch.

 

Thanks,

 

Steve

Link to comment
Share on other sites

Hey 4 x 4, my training and background was more in the area of AC Power Distribution Engineering (I didn't do much DC work), but here are my thoughts regardless:

 

 

1) Should I or would it hurt to fuse both the Pos. and Neg. sides?

 

 

I always just fused the POS. If the NEG return were open such that current couldn't be returned in the normal conductor, it may find a path elsewhere.

 

 

2) Switch between battery and fuse or fuse between battery and switch? I'm not sure I understand your question, but here goes regardless?????

 

a) It was always my practice to provide overcurrent protection the protective device (fuse or breaker) was to be at/close to the source of the energy IE the Battery POS terminal. If the overcurrent protection device is NOT there but farther downstream, the conductor between the battery and the fuse IS NOT PROTECTED, an unfused short from the POS conductor to case/frame/NEG (assuming its to frame ground) could yield hundreds of amps and extreme heat generation...........I RECOMMEND THE FUSE BE AT THE BATTERY

 

B) Switch??? You mean an On/Off for DC power to the Inverter ???? Again Id prefer it to be at the Battery + and fuse location. HOWEVER as long as the conductors (to switch and Inverter) are protected by a fuse right at the battery, the circuit and possible downstream short in the conductor or even the switch itself is protected, so an On/Off switch could be placed at a downstream location or Inverter etc. if that is better for easy access as that entire circuit is protected.

 

c) You talking about the AC Transfer (Utility or Inverter AC output to a sub panel) Switch???????? Of course the Inverters DC input is fused and switched as discussed above,,,,,,,,,,I assume the Inverter has its own built in AC output overcurrent protection,,,,,,,,,,,,,Of course the AC from the utility to the AC transfer switch is protected by a breaker in the AC distribution panel.

 

NOTE when you switch/transfer AC power from the Utility to an Inverter or Generator and you switch Ungrounded Conductors (Hots) and the Grounded Neutral, the Inverter or Generator is to be wired and configured as a "Separately Derived Source" with a bonded and NOT floating Neutral. Its when you DO NOT switch the Neutral that it remains floating. I believe an Inverter takes care of that while an onboard Genset has its own internal Neutral to ground Bond. I cant say for certainty absent the diagrams of the Inverter or Generator and the Transfer Switch however, so no warranty, do as the manufacturer suggests.

 

 

3) The inverter is only going to be 4-5 feet horizontal from the batteries (Probably 6-7 feet of wire by the time i route it through switche and fuse). Can I go any smaller that 1/0 wire?

 

 

If the Inverter has a 1000 watt output, and since its NOT 100% efficient, it could draw (lets use an OVER conservative figure for safety) lets just say1100 watts from the batteries, and 1100 watts at lets just use 12 volts, equates to 92 amps. At 6 to 7 feet I don't envision any excess voltage drop or over ampacity concerns with 1/0 cable and yes you can likely go even smaller (subject to class and type of insulation and temperature and if in conduit or in free air etc etc etc) BUT I WOULD HAVE TO TAKE THE TIME TO RUN THE NUMBERS THROUGH A DC CABLE AMPACITY AND VOLTAGE DROP CHART/CALCULATOR > I would size the conductors so there's even less then any allowable 3% voltage drop since you're only starting at 12 volts to begin with subject to battery state of charge. BIGGER THE BETTER WITHIN REASON OF COURSE. NOTE AC versus DC and class and grade of insulation and temperature and location and jacketed or in raceway or in free air etc etc all affect ampacity, so if you use a chart or calculator HAVE YOUR GLASSES ON AND READ ALL THE FINE PRINT LOL

 

 

4) I am thinking of mounting everything on a piece of maybe 3/8" plywood and then just screwing that to the back wall. Almost like plug and play. When I install it all I would need is to make my battery connections and plug in my transfer switch.

 

Sure that will work. In such cases if I have my "druthers" I prefer to mount on metallic surfaces for better heat transfer away from the devices and to provide case/frame grounding. Running cables through rubber grommet protected holes isn't all that difficult.

 

Nuff said, John T Too long retired and rusty Electrical Engineer so noooooooooooo warranty

Link to comment
Share on other sites

1) Should I or would it hurt to fuse both the Pos. and Neg. sides?

 

2) Switch between battery and fuse or fuse between battery and switch?

 

3) The inverter is only going to be 4-5 feet horizontal from the batteries (Probably 6-7 feet of wire by the time i route it through switche and fuse). Can I go any smaller that 1/0 wire?

 

1. It's not necessary as one fuse will provide protection along the entire circuit, but it sure wouldn't hurt anything if you did both. 1a. That's debatable, but with an inverter I always opt to go with the side with the most current "potential" (most likely to have an over current condition). The pos. side. However, there is some school of thought that, when connecting directly to a 12v source (battery) then you should fuse on the neg. side. Just my own personal choice... but I don't necessarily agree.

 

2. I would place my disconnect on the upstream side of the fuse. Does that make sense? So disconnected at the switch.. there should be no current flow to the fuse or inverter. If you've already purchased your gear then it's no biggie, but my preference is generally to use a stand alone switched breaker rather than a separate switch and in-line fuse.

 

3. So.. you'll need to calculate that for a round trip.. 4' = 8'. At 7' (14' actually.. ) with 1/0 you'll have around a 2.33% current loss (.28 volts).. so I certainly wouldn't go any smaller that 1/0. That's allowing for 100amps. You're inverter shouldn't ever pull more than around 80, but I always like to apply a 125% rule to my calculations.

 

Pushing fewer amps will allow for less loss.. so in day to day usage.. you could realistically plan on around less than .5% loss on 1/0 @ 14'. and call it 15amps (?). That's right about where I would want to be.

 

Other than that.. it sounds like you're good to go! Plug n play away!!

 

On edit: I wasn't necessarily recommending that particular switch for your application.. just so you would know what I was talking about. You would want to purchase one in the appropriate voltage and fuse rating.

Link to comment
Share on other sites

 

1. It's not necessary as one fuse will provide protection along the entire circuit, but it sure wouldn't hurt anything if you did both. 1a. That's debatable, but with an inverter I always opt to go with the side with the most current "potential" (most likely to have an over current condition). The pos. side. However, there is some school of thought that, when connecting directly to a 12v source (battery) then you should fuse on the neg. side. Just my own personal choice... but I don't necessarily agree.

 

2. I would place my disconnect on the upstream side of the fuse. Does that make sense? So disconnected at the switch.. there should be no current flow to the fuse or inverter. If you've already purchased your gear then it's no biggie, but my preference is generally to use a stand alone switched breaker rather than a separate switch and in-line fuse.

 

3. So.. you'll need to calculate that for a round trip.. 4' = 8'. At 7' (14' actually.. ) with 1/0 you'll have around a 2.33% current loss (.28 volts).. so I certainly wouldn't go any smaller that 1/0. That's allowing for 100amps. You're inverter shouldn't ever pull more than around 80, but I always like to apply a 125% rule to my calculations.

 

Pushing fewer amps will allow for less loss.. so in day to day usage.. you could realistically plan on around less than .5% loss on 1/0 @ 14'. and call it 15amps (?). That's right about where I would want to be.

 

Other than that.. it sounds like you're good to go! Plug n play away!!

 

On edit: I wasn't necessarily recommending that particular switch for your application.. just so you would know what I was talking about. You would want to purchase one in the appropriate voltage and fuse rating.

 

 

I like the switched breaker idea. Saves some extra wiring connections. For my setup do you think 100 Amp would be appropriate?

Link to comment
Share on other sites

Hey 4 x 4, my training and background was more in the area of AC Power Distribution Engineering (I didn't do much DC work), but here are my thoughts regardless:

 

 

1) Should I or would it hurt to fuse both the Pos. and Neg. sides?

 

 

I always just fused the POS. If the NEG return were open such that current couldn't be returned in the normal conductor, it may find a path elsewhere.

 

 

2) Switch between battery and fuse or fuse between battery and switch? I'm not sure I understand your question, but here goes regardless?????

 

a) It was always my practice to provide overcurrent protection the protective device (fuse or breaker) was to be at/close to the source of the energy IE the Battery POS terminal. If the overcurrent protection device is NOT there but farther downstream, the conductor between the battery and the fuse IS NOT PROTECTED, an unfused short from the POS conductor to case/frame/NEG (assuming its to frame ground) could yield hundreds of amps and extreme heat generation...........I RECOMMEND THE FUSE BE AT THE BATTERY

 

B) Switch??? You mean an On/Off for DC power to the Inverter ???? Again Id prefer it to be at the Battery + and fuse location. HOWEVER as long as the conductors (to switch and Inverter) are protected by a fuse right at the battery, the circuit and possible downstream short in the conductor or even the switch itself is protected, so an On/Off switch could be placed at a downstream location or Inverter etc. if that is better for easy access as that entire circuit is protected.

 

c) You talking about the AC Transfer (Utility or Inverter AC output to a sub panel) Switch???????? Of course the Inverters DC input is fused and switched as discussed above,,,,,,,,,,I assume the Inverter has its own built in AC output overcurrent protection,,,,,,,,,,,,,Of course the AC from the utility to the AC transfer switch is protected by a breaker in the AC distribution panel.

 

NOTE when you switch/transfer AC power from the Utility to an Inverter or Generator and you switch Ungrounded Conductors (Hots) and the Grounded Neutral, the Inverter or Generator is to be wired and configured as a "Separately Derived Source" with a bonded and NOT floating Neutral. Its when you DO NOT switch the Neutral that it remains floating. I believe an Inverter takes care of that while an onboard Genset has its own internal Neutral to ground Bond. I cant say for certainty absent the diagrams of the Inverter or Generator and the Transfer Switch however, so no warranty, do as the manufacturer suggests.

 

 

3) The inverter is only going to be 4-5 feet horizontal from the batteries (Probably 6-7 feet of wire by the time i route it through switche and fuse). Can I go any smaller that 1/0 wire?

 

 

If the Inverter has a 1000 watt output, and since its NOT 100% efficient, it could draw (lets use an OVER conservative figure for safety) lets just say1100 watts from the batteries, and 1100 watts at lets just use 12 volts, equates to 92 amps. At 6 to 7 feet I don't envision any excess voltage drop or over ampacity concerns with 1/0 cable and yes you can likely go even smaller (subject to class and type of insulation and temperature and if in conduit or in free air etc etc etc) BUT I WOULD HAVE TO TAKE THE TIME TO RUN THE NUMBERS THROUGH A DC CABLE AMPACITY AND VOLTAGE DROP CHART/CALCULATOR > I would size the conductors so there's even less then any allowable 3% voltage drop since you're only starting at 12 volts to begin with subject to battery state of charge. BIGGER THE BETTER WITHIN REASON OF COURSE. NOTE AC versus DC and class and grade of insulation and temperature and location and jacketed or in raceway or in free air etc etc all affect ampacity, so if you use a chart or calculator HAVE YOUR GLASSES ON AND READ ALL THE FINE PRINT LOL

 

 

4) I am thinking of mounting everything on a piece of maybe 3/8" plywood and then just screwing that to the back wall. Almost like plug and play. When I install it all I would need is to make my battery connections and plug in my transfer switch.

 

Sure that will work. In such cases if I have my "druthers" I prefer to mount on metallic surfaces for better heat transfer away from the devices and to provide case/frame grounding. Running cables through rubber grommet protected holes isn't all that difficult.

 

Nuff said, John T Too long retired and rusty Electrical Engineer so noooooooooooo warranty

 

 

John,

 

Thanks for your input. I had previously installed http://www.amazon.com/Xantrex-Inline-Transfer-Relay-PROwatt/dp/B004S5Y158?ie=UTF8&keywords=xantrex%20transfer%20switch&qid=1461538122&ref_=sr_1_1&sr=8-1

this transfer relay on the circuit for the fridge. This then plugs into the inverter and switches to the inverter when park power is lost. Is this okay???

 

Steve

Link to comment
Share on other sites

I agreed with Yarome right to the end of #3. (current calc). And we are probably talking the same thing.

 

My contention is that it would take 15 amps more power with the loss. I work it back from the inverter as I figure the inverter is a 'constant load'. Using some really fuzzy math to illustrate it - your fridge uses 1 amp at 120 volts = 120 watts. Inverter is 90% efficient. 120 watts /.9 = 133.3 watts.

 

And here is where it gets 'fuzzy'

 

This is going to be a 'constant' load whether it is @ 12.8 volts or 12.5 volts (the difference being the wire size losses (smaller wire)).

 

With the larger wire, you have 12.8 @ the battery, 12.4 at the inverter, and 10.7526 amps of current.

 

With the smaller wire, you have 12.2 @ the inverter and a current of 10.9289.

 

I assume Yarome used 1000watt and then the numbers really get much more sideways. Power loss is a square of the current. P(loss)=I(current)^2*R(resistance) --- 10 times the current has 100 x the loss for the same piece of wire.

 

On rereading his post, I where he is referring to it as a loss, he's right, it's a system loss (gain in current) so your still losing more power with a smaller wire.

Link to comment
Share on other sites

4 x 4, that relay you showed should work fine as I'm sure it switches the Hot and Neutral.

 

As I'm sure you're aware, just because you're using a 1000 watt Inverter to power the fridge and assuming no other big loads YOU WONT BE PULLING ANYWHERE NEAR 1000 WATTS OUT OF THE INVERTER which makes your chosen 1/0 wire size adequate (subject to length and temperature and insulation and enclosure, but if a conductor is in free air its ampacity is increased). Now, if you're going to be adding relatively large loads and are approaching 1000 watts from your inverter I would run a voltage drop calculation. I don't like much over a 2% drop even where 3% is permissible.

 

Sounds like you're doing fine. Even though my small fridge only consumes 35 amp hours to run 24 hours, I purchased a 2 KW PSW Inverter. My buddy runs a fridge of similar size off a 600 watt and has no problems.

 

PS Heat energy loss in conductors is I Squared R, but R is relatively low in a 1/0 cable remember.

 

John T

Link to comment
Share on other sites

I like the switched breaker idea. Saves some extra wiring connections. For my setup do you think 100 Amp would be appropriate?

 

Exactly. Fewer connections to maintain and fewer points of resistance.

 

Fuse size is based on a couple of different factors. I wouldn't do less than 100a. You 'could' go up to 150a though. With just your reefer on it, you won't go near that (or even close to 100), but your prosine does have a surge rating of 1500watts. As a general rule of thumb.. I always try to wire/fuse to the full capacity and ratings of the equipment.. even if you don't have any intention of maxing it out. KWIM? No telling how you might choose to use it in the future.

 

100/150.. your call.

Link to comment
Share on other sites

Do you guys think this breaker would work. It's Type III and appears to be switchable.

 

That'll do. Looks like 1/4" terminal posts so you'll need appropriately sized wire lugs with a nice tight fit. Are you making your own cables or having a local shop do them for you? It's important to ensure both conductors are of equal length so you'll want to account for the actual breaker and additional set of lugs when taking measurements. If it's an older inverter.. I don't know for sure what size of lugs you'll need... but they are 'probably' 5/16" (8mm). It should say in your manual.

Link to comment
Share on other sites

the circuit and possible downstream short in the conductor or even the switch itself is protected, so an On/Off switch could be placed at a downstream location

 

John knows his stuff. He's not wrong about switch placement "downstream" of the fuse.. especially if it's for convenience.

 

As mentioned.. I generally go "upstream" with a disconnect. It's not protected, but it's a simple device likely not affected by over current, the cost of a switch is fairly minimal and I prefer to have no current at the fuse itself for ease of maintenance. The possibility for 'user error' when popping/replacing/wiring in-line fuses is much greater on a "live" conductor.

 

There are no hard and fast rules for switch placement, though.. it's simply personal preference. With a switched breaker it becomes a moot point and all around better idea, IMO.

Link to comment
Share on other sites

Good looking combination switch/ breaker, if one is chosen that is rated for 100 amps (or your load) DC and its withstand voltage is sufficient (which I'm sure as its only 12 volts) it should do just fine.

 

Back to the math: If your battery bank has to supply 1100 watts (which is over but lets use it) to power a 1000 watt rated Inverter, that computes to 92 amps at 12 volts.

 

I always size conductors to have an ampacity of 125% of the "maximum continuous current" or 1.25 x 92 = 115 amps

HOWEVER note the technical definition of "maximum continuous current" depends on the load and duty cycle and if you're

only running that small fridge its NOT 92 amps. IE you need the actual load or else of course you can assume full inverter

capacity "continually" and design for that condition, not a problem. To allow for future expansion its good to go ahead and

design for a full load now versus having to rewire later.

 

This is only a couple of the literally hundreds of web sites regarding cable ampacity for 12 VDC, and note its different from

the more typical AC charts and again, single conductors in free air has a much higher ampacity then if enclosed.

 

http://www.engineeringtoolbox.com/amps-wire-gauge-d_730.html

 

http://www.offroaders.com/tech/12-volt-wire-gauge-amps.htm

 

Still it never hurts to oversize cables to reduce voltage drop and I Squared R heat energy losses and I usually end up in an

over kill over engineered situation just to be safe REGARDLESS what a chart indicates. HOWEVER and as Yarome speaks

of it seems some Inverters Ive seen often DO NOT have big enough lugs and studs to accommodate say 1/0 wire gauge

terminations!!!!!!!!!!!!!!!!!!!!!!!!

 

BACK TO LOCATING THE OVERCURRENT PROTECTION DEVICE.

 

I was taught to never leave a conductor un protected from overcurrent. That's why the overcurrent protection device (fuse or

breaker) MUST be located at the energy source (Battery POS in this case) NOT somewhere downstream fed by an UN

PROTECTED CONDUCTOR. If you run a cable from the battery POS to your switch and if that cable were to short out

THERES NO OVERCURRENT PROTECTION so extreme current and extreme heat is the result until such time the cable

melts open or the energy is depleted. I HAVE TO STRONGLY ADVISE any cable from the battery to a load or switch or your

combination switch/breaker have adequate overcurrent protection which means a fuse or breaker RIGHT AT THE

BATTERY

 

NOTE first you compute the LOAD,,,,,,,,,Then you size the conductors to have an ampacity of 125% greater then the "max

continuous load",,,,,,,,, Then you size the overcurrent protection device TO PROTECT THE CONDUCTORS and to protect the

conductors the fuse has to be at the Battery

 

ALSO you don't want to size the fuse any greater then the conductors ampacity (there may be some exception related to

available fuse sizes), that defeats the whole purpose of over current protection!!!!!!

If a conductor has a max ampacity of 100 amps, its to be protected by a 100 amp fuse, not higher. There are, however,

exceptions related to motors protected by thermal overload to allow for the initial high inrush current thereby allowing them to

start.

 

 

That's my story n Ima stickin to it lol

 

 

Have we beat this topic to death yet??????????? Engineers, especially engineer attorneys just cant give a short simple

answer, its NOT in our DNA, sorry we just do the best we can

 

Old John T

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...