Xantrex XM1800 PRO Series Inverter

[waterdog]

I am about to install an XM1800 with built in transfer switch.   It's a nice looking unit.   The price was right - it's good to have a friend in the business. 

The part that kills me is the requirement to run 2/0 cable no longer than 5 feet.   I'm going to use this thing to run a tiny microwave for a maximum of 2 minutes at a time and the occasional light load.   So as far as sizing the cable goes, I could probably use an even smaller cable and extend it to ten feet which would allow me to put it under the nav station where I want it.   But...

One day I'll sell the boat or brother in law will be out for the weekend and somebody will no doubt plug in a shop vac and run it continuous for a half hour.  So I shall go out and buy cables that will exceed the cost of the inverter and the battery monitor.   

Of course the alternative is to locate close to the battery and run the AC cables over the longer distances.   I've looked at all the threads on inverters and there doesn't seem to be a satisfactory location near batteries.  Am I missing something?   Are people really running > 2/0 cable over to the nav stations?

The real issue on cable sizing is actually heating with high currents, is that correct?  The recommended size is always based on continuous operation, is that right?   When you get to large cables there is some thermal mass and a time constant that would suggest that heating is not an instantaneous event.   Are there therefore any protection devices, (fuses, circuit breakers) that will trip based on the time&current or cable temperature? 

I know the correct answer is always follow the manufacturers recommendation, but I'm interested in the boundary condition.     

[Craig Illman]

Steve -

Well, it's certainly not to ABYC standards, but my 1000W inverter was thin enough to lay on top of the Starboard water tank. I installed a separate mini battery switch and fuse for it. I was considering mounting a Prosine in the rear starboard cubby just forward of the galley.

Craig

[Stu Jackson]

The concept is that the inverter wiring takes 12V OUT of the batteries, so the amperage draw of the inverter "working" can be huge, even for "small" loads.  Our small microwave takes 82 to 86 amps when it is running for short periods of time, based on our Link 2000 readings.  That's DC amps coming out, going to the inverter to be swapped for 120V power.  If you do the sizing on amperage for distance of the flow from the batteries to the inverter for its maximum load carrying capacity at 3% drop, 2/0 seems about right. 

Our Freedom 15 is under the nav station, located on the outboard wall of the foot-well.  It is a 1500 watt inverter, and our older Freedom unit came with the 2/0 wires installed solidly to the unit.  The newer Freedoms have bolts to attach your own wiring.  We ran the 2/0 wiring through two holes in the aft vertical wall to the holding tank compartment and under the sole to the battery compartment.  I would strongly recommend following directions.  I agree with your logic about future owners, plus it's always right to install it correctly.  I wouldn't mess around with time/current/heat issues, just size the wirng correctly for the distance and load its gotta carry and run.  You're right, theoretically, but...all that's built into the wire sizing tables and charts.  The only thing I know of that derates wiring is being in (high) heated (i.e., engine) compartments.

Conversely, if that's all you plan to operate, why such a big inverter?   

[waterdog]

Conversely, if that's all you plan to operate, why such a big inverter?   

I was paying half of retail.  I couldn't afford not to get the big inverter

The fun part of all of this is that I can do calculations on loads and wire sizes and heating and cable lengths and voltage drop etc., but the likely practical limitation on all of this is that an 1800W inverter (assume 180A input at at 85% efficiency)  running full out will suck the life out of my little battery bank and drop below 11V threshold and trip out before cable of any reasonable size will heat to the point of damage / safety concern.

It would actually be fun to test and gather data with a bunch of different cable sizes / loads / lengths etc.  if one had the time and money...   

But there are more important things like applying my new name graphics that will be ready tomorrow...





 

[Bill Asbury]

Awesome graphics, Steve!

[waterdog]

Thanks.  My kids picked the name and the little dragon hung out on the last boat for 40 years.  My only job was to pick a font consistent with the ancient family heritage of Celtic terrorism...   

[Ken Krawford]

Steve,

Have you thought about using welding cable.  It's a fraction of the price of marine grade wire and much more flexible.   I was able to purchase some at a local Ace Hardware.  As Ron would say, "Just a thought".

[Jon Schneider]

Best deal on cabling that I've found: bestboatwire.com.  One third or less the price of Defender or WM.  No connection to me other than I've bought a lot from them.

[waterdog]

Thanks for all the input.   I've gone with the big cables.  And of course I've run out of time to pursue internet sources as we are just about to pop down to Seattle for a few days and then off on the boat for a month.  In the end I got the cables from the little marine store next to my marina.  They may not be cheap like bestboatwire.com, but they let me hang out and have coffee and use their crimper.   And their inventory of 2/0 cable was really old so it was almost half the price of the local volume chandleries!  I have to keep these guys in business because they are the ones that are there for me when I need 2 feet of hose or a couple of #10 by 3/4 stainless whatevers...

[efiste]

What about the battery interconnect and wire before and after a battery monitor shunt? I won't that need To be the same size (2/0)? I am working on a similar project on my C34.