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Open Roads Forum  >  Tech Issues

 > Inverter, automatic transfer switch – bypass charger?

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JohnKoz

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Posted: 07/30/10 07:20pm Link  |  Print  |  Notify Moderator

Hi folks,

I had a seemingly basic question about how 120vAC utility power is routed coming into an RV with an automatic transfer switch and an inverter.

It seems to me that the battery charger (converter) should be always run off of the street/utility power and never off the inverter, for obvious reasons (ok, in case it isn’t obvious you don’t want the charger to charge the battery from the inverter which is depleting the battery, kind of an electrical circle).

So that would mean there is some kind of special load center or other transfer/breaker boxes that has 2 circuits, one that goes through the transfer switch and the other that doesn’t. I’d want some circuits to be NEVER fed through the inverter, like the battery charger, electric hot-water heater.

How is this usually wired, and with what configuration of breaker boxes and transfer switches?

Thanks a bunch

-John


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smkettner

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Posted: 07/30/10 08:10pm Link  |  Print  |  Notify Moderator

You need a sub panel. Usually the existing panel would feed the sub panel through the inverter. All non inverter circuits stay where they are. Circuits to be powered by the inverter go on the sub panel.

Single circuit there is no extra panel needed with extra breakers to split the power. You could even do two transfer switches for two circuits to avoid the sub panel. If you did two I would get an inverter without one. Three or more circuits you probably want a sub panel and even with two.

So now map out exactly what is on each breaker and if it should be on the inverter or not. Some are shared with other stuff like converter and fridge.


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ShapeShifter

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Posted: 07/30/10 08:26pm Link  |  Print  |  Notify Moderator

JohnKoz wrote:

How is this usually wired, and with what configuration of breaker boxes and transfer switches?

There are many different ways to wire an inverter, it will vary greatly from one manufacturer and model to another.

On my rig, 50 amp power comes in through the automatic transfer switch (which selects between shore power or generator) and to the main breaker panel. One of the breakers (30 amp) from that panel feeds the inverter/charger. The inverter has it's own automatic transfer switch inside of it, and has two outputs: one with a 20 amp breaker that feeds most of the outlets in the rig, and one with a 15 amp breaker that feeds the microwave.

Another common way to do it is as smkettner mentioned: feed the output of the inverter to a sub panel, either directly (if the inverter has a power feed-through) or through another transfer switch (if the inverter has no feed-through.)

The simplest way is to just plug the shore cord into the output of the inverter, but then you have to worry about feeding the charger and other large loads that might overload the inverter. (But you already know this, or you wouldn't be starting this thread!)

A variation of this last method is to place an additional transfer switch between the main gen/shore transfer switch and the main breaker panel. This eliminates the need to plug the shore cord into the inverter, but does nothing to mitigate the other issues of feeding the charger or other high loads.


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MrWizard

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Posted: 07/30/10 08:35pm Link  |  Print  |  Notify Moderator

Rv's that come with the inverter built in, usually have a combination unit that does both jobs , when no 120vac is available the converter section does not operate, the shore power pass thru transfer switch for that circuit built into the combo unit

Installing a stand alone inverter means you can wire dedicated circuits or switch of the.converter

Some people simply plug the shore cord into the inverter and switch off the converter, and set the fridge and WH to propane 'manual mode' not auto mode
The proximity of the inverter to the batteries and shore cord is a consideration put it greatly simplifies the wiring needed

* This post was edited 07/30/10 09:18pm by MrWizard *


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dougrainer

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Posted: 07/30/10 08:38pm Link  |  Print  |  Notify Moderator

Most Inverters LARGER than 400 watts for RV use have a Auto pass thru 120 relay. That means IF the Inverter is on INVERT and 120 is supplied to the Inverter (Shore or APU), then the Inverter INVERT function is turned OFF ( automatically goes to Standby mode), and the appliances that are powered from the Inverter are now powered by the Shore or APU supplied current. You NEVER connect a CONVERTER to a Inverter powered output. Like you mentioned, there is NO free power. The power used by the Inverter in Invert to POWER the Converter is more than most Converter's can re-supply. Otherwise you would have the elusive perpetual power supply. If you have a W/H powered by a Inverter (which is NOT the best way to power a W/H), then you would have to have at minimum a 1500 watt Inverter. Which will usually have the Auto transfer 120 relay. They do make 500 to 1500 watt Inverters without the auto transfer relay. Doug

JohnKoz

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Posted: 07/31/10 04:44am Link  |  Print  |  Notify Moderator

MrWizard wrote:

Rv's that come with the inverter built in, usually have a combination unit that does both jobs , when no 120vac is available the converter section does not operate, the shore power pass thru transfer switch for that circuit built into the combo unit…

I think this is the bottom line where I was going; I already have the inverter (non-switching strait inverter) and the automatic transfer switch installed, except it’s switching entire main panel. I like the sub-panel idea, so one panel is strait shore-power and the other is switched between shore/inverter.
I was hoping there was some kind of “combination unit” available that basically had 2 circuits in it, so I could just replace my main panel and not have to add another sub-panel.
Any idea where I might find a “combo unit”?

Or by "combination unit" do you mean an inverter/converter with automatically switched output?

Thanks

-John

dougrainer

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Posted: 07/31/10 07:11am Link  |  Print  |  Notify Moderator

JohnKoz wrote:

MrWizard wrote:

Rv's that come with the inverter built in, usually have a combination unit that does both jobs , when no 120vac is available the converter section does not operate, the shore power pass thru transfer switch for that circuit built into the combo unit…

I think this is the bottom line where I was going; I already have the inverter (non-switching strait inverter) and the automatic transfer switch installed, except it’s switching entire main panel. I like the sub-panel idea, so one panel is strait shore-power and the other is switched between shore/inverter.
I was hoping there was some kind of “combination unit” available that basically had 2 circuits in it, so I could just replace my main panel and not have to add another sub-panel.
Any idea where I might find a “combo unit”?

Combination unit is a Inverter/CHARGER. It Inverts and has a high amp Charger built in, which is the best way to use an Inverter.

Or by "combination unit" do you mean an inverter/converter with automatically switched output? Are you stating that the COMPLETE RV shore power goes thru the Inverter you have now???? If so, that is NOT correct. Please list the Brand and Model of the Inverter you have now and its wattage rating. Doug

Thanks

-John


ShapeShifter

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Posted: 07/31/10 08:25am Link  |  Print  |  Notify Moderator

JohnKoz wrote:

I was hoping there was some kind of “combination unit” available that basically had 2 circuits in it, so I could just replace my main panel and not have to add another sub-panel.
Any idea where I might find a “combo unit”?

I've seen such combination breaker boxes, but I'm having a heck of a time finding them right now.

One option I can find is part of an Intellitec Energy Management Unit, which is probably a lot more complex than you want to get. This is a system that monitors your power usage, and automatically sheds loads (like a second A/C, water heater, washing machine, etc) if the load gets too high, and turns them back on as the load is reduced. I have one of these systems (without the inverter panel) and it is wonderful, but probably more than you're looking for.

The manual for it is HERE and a description of one fellow installing on is HERE. Here's a photo of the panel from that last link, note the main shore power breakers on the right, and the smaller group of inverter breakers on the left:



Note that with a system like this, you will still need some sort of transfer switch, if there isn't one built into your inverter. In your case, you say you have an automatic transfer switch, you would just have to change it around a little: the input to that transfer switch would be fed from a breaker on the main panel, and the output would go to the smaller inverter panel.

If you have a 50 amp system, adding the EMS could be a valuable (although expensive?) addition -- it sure makes dealing with limited power a lot easier. if you have a 30 amp system now, this panel would be overkill.

MrWizard

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Posted: 07/31/10 10:51am Link  |  Print  |  Notify Moderator

I am referring to inverter converter combo
Such as xantrex or the FREEDOM_10 that came with our DP

the easiest thing for you might be one of the prosine models with the pass-thru/transfer built in,
Place the unit near the power panel wire a female cord end into the breaker, plug in the inverter, put a male plug on the OEM romex and plug it into the inverter
only that one circuit will have power from the inverter when shore power is not connected,
shore power will be used when available

No sub panel needed no changing the power panel

* This post was last edited 07/31/10 11:58am by MrWizard *   View edit history

smkettner

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Posted: 07/31/10 12:32pm Link  |  Print  |  Notify Moderator

JohnKoz wrote:

I already have the inverter (non-switching strait inverter) and the automatic transfer switch installed, except it’s switching entire main panel. I like the sub-panel idea, so one panel is strait shore-power and the other is switched between shore/inverter.
I was hoping there was some kind of “combination unit” available that basically had 2 circuits in it, so I could just replace my main panel and not have to add another sub-panel.


All you need is a second transfer switch and rewire what you have.

Remove the existing transfer switch and put the main power feed back to the main breaker the way it was.

Remove the romex from the panel that feeds the circuit you want on the inverter and connect it to the load (output) side of the transfer switch. Get a new piece of romex and connect the now open circuit breaker to the inverter input. The inverter is still connected to the other input and you are good to go.

When you get the second transfer switch do the same thing with the second circuit. Just jump the inverter to provive power to both transfer switches. Or use a cord with plug from each transfer switch and plug them both into the inverter.

This avoids replacing and rewiring a new panel or adding a subpanel with breakers that need access.

On mine I used IOTA transfer switch and put both switches in one box to save space.

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