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Old 12-04-2006, 07:14 PM   #1
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1964 26' Overlander
Alameda , California
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Post Planning new wiring with inverter

I'm thinking I may redo the electrical system from scratch. Here's what I'm thinking so far, roughly:

30A inlet
...#10 cable to...
30A main breaker
...#10 cable to...
Prosine 2.0 inverter charger
...#10 cable to...
load panel

20A GFCI breaker
...#12 cable to...
air conditioner

15A GFCI breaker
...#14 cable to...
bathroom outlet

15A GFCI breaker
...#14 cable to...
kitchen-counter outlets, outside outlet

15A GFCI breaker
...#14 cable to...
outlet behind fridge & all other outlets

Does that sound right? This is leaving aside all the 12V wiring for now.

I would never run the air conditioner on inverter power, but for the Prosine's power-sharing to work correctly, it seems like it has to be on the load panel tied to the inverter. Otherwise (as far as I can tell) you'd need to set the Prosine to think you only have 20A shore power, instead of the 30A you really have when the A/C is not running. And in fact, if you happen to be drawing 20A (battery charger taking 10A, microwave another 10A, eg) and the A/C starts up and pulls 15A, you could trip the shore breaker anyway, it seems to me.

The external power ground and the battery negative terminal should both be connected to the shell, correct? Do I need to connect that ground to the frame as well?

One more question - the neutral & ground should not be tied at the main breaker in the trailer wiring, as they'll be tied wherever the shore power is being provided, correct?

Prior to buying & installing the Prosine & batteries I can just connect from the main breaker to the load panel with #10 cable, and put the current 12V charger on a circuit on the load panel. (I don't want to get into a discussion of the merits or otherwise of an inverter just as yet; I just want to do all the wiring so installing one won't be difficult later).

I'm thinking I'll probably get a generator too anyway, but carry it in the truck bed and just plug it into the shore power connector when stopped.
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Old 12-04-2006, 07:29 PM   #2
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Can you provide a diagram?
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Old 12-04-2006, 08:17 PM   #3
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The Prosine inverter runs off the battery not the ac. It produces ac from12 volt battery. Run # 2/0 welders cable from your battery to the Prosine. Run # 10 from the main ac Airstream input plug than back to your main breaker. See post below.
I put in a 3.0 Prosine in several years ago and it works great. I put one Concord 305 amp AGM battery under the couch and three more concord batteries in the tow vehicle. The concord batteries in the tow vechile work because I put a plug in one of the two empty battery boxes in the Airstream and another on the tow vehicle using a 15 foot #2/0 welders cable. We run the air conditioner at rest stops when needed. Works from four to six hours. Be sure to fuse everything properly.
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Old 12-04-2006, 08:22 PM   #4
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I forgot. You need to run the main input ac line to the prosine than back to the main breaker so the inverter can switch using the internal transfer switch for the 120 volts ac and or battery when your Airstream is plugged in.
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Old 12-04-2006, 08:52 PM   #5
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I'll put together a diagram when I get home. I was leaving out all the 12V wiring for now. I would have a separate main panel for the 30A breaker right after the 30A inlet. From there it goes to the inverter, which also acts as a transfer switch between shore power and inverting, and then the inverter output goes to the load panel with the breakers for the trailer circuits.

The inverter of course connects to the batteries for inverting or charging.

I wasn't really intending to get onto the details of inverters yet, but isn't 2/0 cable a bit small for a 3kW inverter (especially with a 15 foot run)? I was planning to use 4/0 cable with the 2kW unit and that's with the batteries being right next to the inverter...
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Old 12-04-2006, 09:50 PM   #6
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Since all the 120 ac passes through the inverter you only need one main breaker box. 2/0 welders cable is the right size and flexable. In a twenty foot run there is less than a one volt drop while running the air conditioner.
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Old 12-04-2006, 10:09 PM   #7
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I have been considering adding a inverter/charger and using it instead of my converter. Do you have any idea about battery longevity lead acid mat or gel? Do you know what the difference if any is between a kW and a 1.5 or 2.0 if the load is light maybe only 200 watts or so. I don't know if a larger inverter is any less efficient if the loads are the same. Do you use a gen. also? Do you only charge boon docking with your TV or do you have any solar or ? Is it silent on hookups or does the charger still hum? My converter is still working any comments on leaving it on a dbl. through switch or do you think the 3 or 5 stage chargers are plenty without the redundancy? Has anyone herd about any lithium batteries coming on the market for these applications for weight savings?
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Old 12-05-2006, 12:20 AM   #8
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Well, I'm not an expert on this, but the manual for the Prosine 3.0 specifies 3/0 for marine installations, 4/0 for RV installations. The ampacity of that 2/0 cable is roughly 220-300A, but the Prosine 3.0 can presumably draw about 250A at 3kW load, 330A at 4kW surge, and they specify a 450A breaker, so it seems a bit small to me.

The manual suggests 500MCM cable for a 15ft run. A 3.3% voltage drop on a 120A charging current over 15ft of 2/0 cable seems pretty high to me, for a charging circuit. But maybe you don't charge the batteries over that 15ft cable.
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Old 12-05-2006, 10:06 AM   #9
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Get 4/0 or even 250mcm cable unless you can use the wires resistance as heat in sub-zero weather.. (can you tell it is 5°F outside now?)

A 12 volt 15' 2/0 circuit drawing 200 amps will drop .48 volts as losses, current x voltage = power so that is 96 watts being used to heat the copper conductor. True, that 200 amps is only seen on start-up surges but the device will be drawing its normal current plus the losses every second of operation. Stepping up to 4/0 would save 30 watts losses, up to 250mcm would save 50 watts - you paid extra for best trailer ever made so don't skimp on wiring

And as Jacobwellcom points out the losses are in both directions, charging and load so on top of the 15+% losses of the batteries add in double your calculated line losses for everything ever used from the system.

There isn't great instaneous payback putting large copper conductor in but think of it as every twelfth charge as free and done for you while you sleep by the keebler elves' maintance section
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