stormbytes
Wherever I may roam
New Member
Joined: 06/09/2011
View Profile
 Offline
|
I'm planning to hardwire a Xantrex XM1000 in series with a 110 circuit. The main selling point of XM-series inverters, as I understand it, is that they come with built-in transfer switch and dual (12VDC / 110VAC) inputs. I'm trying to gauge the wire requirements (no pun intended).
I'm on a 22' class-A Winnebago. The inverter will be installed inside the dinette bench which also houses my 32A power center. The batteries -- a pair of 220Ah Lifeline 6V in series -- are all the way up front behind the grill. Battery-negative is connected to the chasis and comes up off the chasis at the dinette in a #6ga conductor.
I did a bit of reading and it seems that in "chasis" application (which this is -- as the wire is not isolated from circulating air) a #6ga is good for up to 94Amps. Seeing as the power center maximum draw is around 12A, I thinking I can safely reserve 60A to the inverter (doubtful I'd ever use a third of that).
The XM-1000 is rated for 1000W AC, which I understand to mean a draw of 100A from the DC circuit. I can pick up some #2ga cable and provide for this -- which would be costly, ridiculous, and would require upgrading the chasis-to-power center conductor as well. So I came up with (what I think is) a creative alternative. I'm going to limit the inverter draw to 60A via an inline breaker. That limits the maximum draw on the batteries to around 72A in total and should theoretically solve my design issues.
I'd like a second opinion --
Just to be clear, the load-examples used above are for design purposes only. Anyone pulling 60A from a pair of batteries needs to have their head examined!! The sole purpose of designing for this is so that some girl doesn't burn the down the coach when she plugs in her hair drier 
|
smkettner
Southern California
Senior Member
Joined: 03/21/2005
View Profile
Good Sam RV Club Member
|
I would be inclined to limit power with a smaller inverter instead of an undersized fuse.
You may need a separate transfer switch.
2001 F150 SuperCrew
2006 Keystone Springdale 249FWBHLS
675 watts solar
Send a PM if I missed something
|
stormbytes
Wherever I may roam
New Member
Joined: 06/09/2011
View Profile
Offline
|
smkettner wrote:I would be inclined to limit power with a smaller inverter instead of an undersized fuse.
You may need a separate transfer switch.
Could you share any reasons for doing either?
I've tested the inverter thoroughly and it works as expected. As for limited output, an inverter working at 50% rated power will be leaps-and-bounds more efficient then one rated at less working at its max.
|
smkettner
Southern California
Senior Member
Joined: 03/21/2005
View Profile
Good Sam RV Club Member
|
For instance a ~400w inverter would shut down from overload before the breaker opened.
If you already have the inverter then the 60 amp breaker will protect the #6 wire just fine.
|
shooted
Vancouver
Full Member
Joined: 06/17/2011
View Profile
|
Sizing of the wire in this application is not only for amperage, but also to minimize voltage drop. Voltage drop can be significant even with seemingly light loads at the distance you are suggesting. My Xantrex manual indicated a maximum of 5' from the batteries(complete wire distance and attached directly to), and 2/0 minimum wire. While still operating within current parameters your plan disregards the need of a larger wire to minimize voltage drop.
|
|
|
pianotuna
Regina, SK, Canada
Senior Member
Joined: 12/18/2004
View Profile
 Online
|
Hi Storm,
Breakers are slow to open. A non arcing DC type is required.
The fusing for inverter wiring is usually done for "catastrophic failure" for that size wire. Wiener roasts are fun--but not when your RV is the fuel for the fire. Remember they used to weld with batteries.
The large inverter at small loads may use more "idle" amperage. Since "idle" amps are more or less constant, over 24 day the larger inverter may use more amp hours. The smaller one may work "harder" at full output, but how often is that planned for?
For example a 2000 watt psw inverter may draw 2 amps at idle. So a 100 watt load may in fact draw about 12 amps. A 500 watt load may draw 52 amps,
On a 500 watt inverter the 100 watt load might only draw 10.25 amps and the 500 watt load 52 amps (because the cooling fan will be active right away).
Sizing an inverter is often done at 125% of the maximum planned demand. So on a 1000 watt inverter the maximum continuous load would be around 800 watts. If you are careful on appliance selection that will run quite a few items (one at a time).
You can imagine how nutty the sales folks thought I was when I would wander around testing the items with a kill-a-watt meter. *GRIN*
The wire size was discussed in another thread. Use what the inverter is rated for and use the fuse size they suggest in the manual. Nothing else is prudent.
I don't like transfer switches in general and one built into an inverter would be my last choice.
Regards, Don
Kustom Koach Class C 28'5" 256 watts Unisolar, 875 amp hours in two battery banks 12 volt batteries, 2500 MSW watt inverter.
|
stormbytes
Wherever I may roam
New Member
Joined: 06/09/2011
View Profile
Offline
|
shooted wrote:Sizing of the wire in this application is not only for amperage, but also to minimize voltage drop. Voltage drop can be significant even with seemingly light loads at the distance you are suggesting.
The batteries are wired to the chasis with what appears to be a 1/0 cable. The chasis serve as a common bus wich, to my understanding, essentially extends the battery terminal all the way down to where the 'receiving' conductor (#6ga) picks up the current. The length of that conductor is less then 5'. I spoke with a Xantrex technician several days ago and he made no mention of any concerns in this configuration. Do you disagree?
shooted wrote:
While still operating within current parameters your plan disregards the need of a larger wire to minimize voltage drop.
The load ratings and conductor diameter were taken directly from the AWG standard. Despite that, you are correct in saying that voltage drop was not directly considered.
Where do you fee an appreciable voltage drop might be encountered in the described configuration and how might I test for these? What improvements would you recommend I consider?
|
stormbytes
Wherever I may roam
New Member
Joined: 06/09/2011
View Profile
Offline
|
Hey Pianotuna!
Good of you to chime in...
To follow up on your comments:
pianotuna wrote:
Breakers are slow to open. A non arcing DC type is required.
The fusing for inverter wiring is usually done for "catastrophic failure" for that size wire. Wiener roasts are fun--but not when your RV is the fuel for the fire.
You make some valid points. The breaker I'm considering are used in high-end, high-power audio amplifier applications. How about a 50A breaker instead?
pianotuna wrote:
Remember they used to weld with batteries.
They still do! Though not always intentionally
pianotuna wrote:
The large inverter at small loads may use more "idle" amperage. Since "idle" amps are more or less constant, over 24 day the larger inverter may use more amp hours. The smaller one may work "harder" at full output, but how often is that planned for?
For example a 2000 watt psw inverter may draw 2 amps at idle.
The XM-1000 idles at just under 0.4 amps. Another positive about this model is the detachable (twisted-pair, RJ-11) recessed control plate that can be installed as a wall panel (intended use). I have no intention of idling the inverter aimlessly so idle draw, while valid, is less of a concern.
pianotuna wrote:
Sizing an inverter is often done at 125% of the maximum planned demand. So on a 1000 watt inverter the maximum continuous load would be around 800 watts. If you are careful on appliance selection that will run quite a few items (one at a time).
I purchased the XM-1000 for a number of reasons, not the least of which was getting a great deal. I have no intention of going over 200W so planning of maximum draw is taken from a purely precautionary angle -- hence all the talk about breakers, limiting current, etc.
pianotuna wrote:
You can imagine how nutty the sales folks thought I was when I would wander around testing the items with a kill-a-watt meter. *GRIN*
Been there. Done that. Exactly the kind of thing I can see myself doing. I'd follow up with draw measurements with my Fluke 374 cuff.
pianotuna wrote:
The wire size was discussed in another thread. Use what the inverter is rated for and use the fuse size they suggest in the manual. Nothing else is prudent.
If you're referring to the "other thread" where we discussed my solar setup (yes-- the thread that ultimately cost me $345 **BIGGER GRIN**) I decided to dedicate a thread to the inverter/wire-gauge question as I felt it warranted some more specific address.
(joking about the cost... I'm **VERY** glad you steered me towards the ROGUE 3024. Probably the best decision I made in regards to the solar installation!)
pianotuna wrote:
I don't like transfer switches in general and one built into an inverter would be my last choice.
Control freak!
|
shooted
Vancouver
Full Member
Joined: 06/17/2011
View Profile
|
I would never argue with the manufacturer. I would suggest you do your install in accordance with the manual and/or based on your conversation with the technician.
My understanding from my manual was a maximum distance with a minimum wire size attached directly to the batteries. There was no allowance mentioned in using any type of distribution(i.e., chassis, D.C. dist. block, etc.).
* This post was
edited 04/28/12 07:28pm by shooted *
|
stormbytes
Wherever I may roam
New Member
Joined: 06/09/2011
View Profile
Offline
|
shooted wrote:I would never argue with the manufacture. I would suggest you do your install in accordance with the manual and/or based on your conversation with the technician.
My understanding from my manual was a maximum distance with a minimum wire size attached directly to the batteries. There was no allowance mentioned in using any type of distribution(i.e., chassis, D.C. dist. block, etc.).
I'd guess that a large percentage of RV installations involve calculated allowances that deviate from a manufacturer's recommendations. While I'd love to follow the manual to a tee, practical needs demand cautious, thought out improvisation.
|
|
|
