30 amp inverter in a 50 amp rig - RV-Dreams Community Forum

Loki · RV-Dreams Family Member

30 amp inverter in a 50 amp rig

Jack Mayer · RV-Dreams Family Member

If I'm visualizing it correctly you can do that....I think I have a schematic of something similar on my website....

But to be sure it would be nice if you put a drawing here.....I'm not sure I'm visualizinng your test correctly.

The key is to ensure that 50 amps does not pass through the inverter transfer switch on a continual basis....since it is only rated for 30 amps. And, typically it only has a single service leg.

Loki · RV-Dreams Family Member

Jack, I searched your website and found it - it is called Conceptual Design 2. Too bad I can't patent my idea anymore ! I have a schematic but don't know how to include it in the post. Copy and paste doesn't work because the graphic elements are not pasted. What I plan to do is running both legs of the shore/generator AC through 2 30 amp breakers into an inverter with a dual transfer switch, like the Freedom SW 3012, and the output AC through 2 other 30 amp breakers to the external 50 amp transfer switch, and from there to the existing load center. The advantage of this design is that I can install the panel with the 4 additional breakers at a place where I have ample space, e.g. next to the inverter, and the wiring is much easier than relocating circuit breakers from the main panel to an inverter subpanel. Disadvantage is that I have to get out in the rain and close the breaker that tripped because DW turned the AC on while inverting... wink

Jack Mayer · RV-Dreams Family Member

If you email me your schematic I'll loook at it....I'm really bad with descriptions....too easy to go wrong.

-- Edited by Jack Mayer on Thursday 26th of January 2012 02:38:39 PM

charles · RV-Dreams Family Member

OK, What am I missing, you want to plug a 50 amp rig into a 30 amp outlet,is that correct?

IF that is the case why not a 30amp plug what 50amp receptacle and plug your 50a line into that?
I must be off somewhere. Please advise.

Loki · RV-Dreams Family Member

Charles, my question is only about using the inverter when dry camping. Because there are no 50 amp inverters available (at least according to my research), only 30 amp, using an inverter in a 50 amp rig is less trivial than I would like it to be. What I usually would have to do is removing the breakers that I want to be powered by the inverter (like your 110V outlets and the microwave) off the main panel and put them on a subpanel that is fed from the inverter. Unfortunately, that's easier said than done, because in most cases there is not enough space next to the main panel to install a subpanel, so I would have to rewire the circuits to the place of the new panel. Feasible, but could be pretty complex, and I wanted to find an easier solution.

Bill Adams · RV-Dreams Family Member

If you want to have a bunch of fun, some of the newer 50 amp coaches have 2 30 amp inverters installed allowing for the use of most anything you like on any circuit (just not all at the same time). I have also seen 8K alternators installed on the engine so there would not only be power everywhere, but enough power to run the A/C units while on inverter and driving! If you've got enough money you can do almost anything you like!
I know, I know, off topic! Sorry, I couldn't help myself.

Jack Mayer · RV-Dreams Family Member

Bill I did a 5er with stacked Outback inverters for split phase 120/240 volt power. And over 2000 amphours of battery storage. The truck that pulled it had a 12 kw generator a couple of high output alternators and a bunch of other goodies. But no solar - yet. Pretty much all electric - had a gas cooktop, but also induction.

Bill Adams · RV-Dreams Family Member

The 8K alternator I saw on a Prevost (with dual 4000W inverters) reduced the engine output by an estimated 50HP! I guess if you have lots of HP to spare that's not a big deal but if you don't think that alternator was HUGE you are seriously mistaken!

Loki · RV-Dreams Family Member

Oh my goodness, what a power plant! That battery bank alone must be over 500 lbs!

Bill Adams · RV-Dreams Family Member

It would be at least that. I have 4 - 156# Lifeline 8-D batteries in my coach.

Jack Mayer · RV-Dreams Family Member

Gee, Bill, you have the same thing I'm putting in my new coach. 4x8D Lifelines..... We think alike.... ;) I also have 820 watts of solar...

Bill Adams · RV-Dreams Family Member

I could really use that! The bad news is that the batteries are really, really expensive. The good news is that I bought these in QZ in Jan. 2003 for $300 each. Today you will be lucky to get them for twice that price. However, at any price, they are now 9 years old and still going "pretty" strong. We can tell they don't have the capacity that they used to but they have enough and I am not really in a position to spend $2400 to replace them.

Jack Mayer · RV-Dreams Family Member

Bill, I'm assuming you already have an inverter.....so if you want solar and we cross paths I'll be glad to "help" you put it on. As long as you have a place near the battery bank for the controller, and a way to get the wires to the roof, you are "good to go". On your roof (I'm guessing a little) I'd bet we could just use 3M 5200 to attach them...no penetrations. (Although with the work you already do I doubt you need any help to do this...)

-- Edited by Jack Mayer on Sunday 29th of January 2012 10:41:26 AM

Bill Adams · RV-Dreams Family Member

It would be quite easy to route good quality cables from the roof to the battery bank. There is room in the battery compartment for "stuff" or it could be located in a cabinet about 4' above the bank in the bedroom. It's the cost that scare me but it would cut down on the amount of time I have to run the generator a bit. Since I need the most power at night (when there's no sun) the genny would still be on but I might be able to start it later and maybe not have to run it very long in the morning.

Jack Mayer · RV-Dreams Family Member

Morningstar MPPT 60 at around $500 for the controller. Around $125 for the remote panel.

Sun Electric panels (205 watt panels) at $1.34 a watt. $275 each plus shipping (which is reasonable, or if in Phoenix pick them up).

Wire and connectors around $200

Bill Adams · RV-Dreams Family Member

Ouch, $2000+ for solar is a big hit and my 9 year old batteries would likely need to be replaced at the same time ($2400).

Loki · RV-Dreams Family Member

What about placing electronic equipment like an inverter or a controller in the battery compartment, like suggested above? Manufacturers of inverters and other equipment advise against that, because of the danger of igniting hydrogen from the battery bank. I always doubted that the hydrogen concentration could ever be large enough to create an explosive mixture with air, because of the ultralow weight of hydrogen.

bjoyce · RV-Dreams Family Member

Personally I don't want to be a Darwin Award winner by deciding I am more of an expert than the manufacturer.

Bill Adams · RV-Dreams Family Member

Let's see....Hydrogen gas in an enclosed space and an electronic spark.....Isn't that the formula used by the Hindenburg?

Trabuco · RV-Dreams Family Member

I agree Bill & Bill I would find another location for your inverter. Better to be safe.......

Loki · RV-Dreams Family Member

The flammability limit of hydrogen in air is 4 vol-% which is a lot given the fact that hydrogen quickly disappears through all cracks and crevices. Also, hydrogen is only formed while charging the battery and only in considerable amounts at the end of the charging cycle or when overcharging. When fully charged, the hydrogen formation rate is 0.000267 cubic feet per minute and charging amp and cell. Charging 4 12V batteries with 10 amps in a battery compartment of 20 cubic feet brings you to the flammibility limit in just 12 minutes - if the compartment is gas-tight (which is inlikely under realistic conditions). That leaves you with three options: a) a very well ventilated battery compartment; b) no electric or electronic equipment in the compartment; c) a good insurance.

Jack Mayer · RV-Dreams Family Member

Besides the flamability issue, you also have a corrosion issue. Even with AGM batteries there can sometimes be outgassing - although with AGMs this is not common, but a response to something wrong. It is simply not a good idea to put an inverter in a battery compartment. However, if you can divide the compartment properly and make the battery side into a separate area then that would be a solution. The key is good ventilation.