Switching between shore power and Inverter power for 120 AC

[RetchedOne]

I'm trying to figure out how this is supposed to work...

PD4045 w/battery minder (charger)
30amp 120v when hooked up at the camp site, no need for the power inverter.

When NOT hooked up to shore power, the inverter may be used to power misc small items and possibly a small dorm fridge...
(I'm not buying a DC fridge)

However, the PD4045 has a battery charger... So when it has 120v supplied to it from shore power it charges the batteries... which are running the inverter... which are feeding the power inverter...

This seems like an issue...

I know you can get a manual "ATS" to switch between power sources, but what about the inverter...
I don't want the inverter running when on shore power, but i dont want to have to move my "fridge" to a different plug...

Then there are the solar panels, i'm assuming they go straight to the battery (well, through other stuff, but that's where they end up).

[Wobbly Wheels]

You aren't going to harm anything running the inverter while on shore power. On boats, on board AC systems are typically fed from the inverter and the shorepower connection is only for battery charging (save for the occasional hardwired dockside loads like a hot water tank element). The added advantage is that the batteries will buffer any spikes in the line voltage before they get to your electronics.

[MtnDon]

We use an ATS, automatic transfer switch, that switches the trailer AC power from inverter to shore whenever the shore power is connected. However I wired up a circuit that is for the shore 120 VAC only which is where the air conditioner is plugged into. I did that so there would be no danger of forgetting and running the air conditioner off the inverter and batteries. All the other outlets can be used at any time as the ATS seamlessly switches from external to internal power. The shore power can also be plugged into a generator for boondocking.


Be selective when choosing a dorm type fridge. Some are real power hogs, some are not.

[RetchedOne]

The shorepower and inverter feed into an ATS.
The ATS feeds the PD4045
The PD4045 feeds 120v circuits and 12vdc and the battery minder... Charging the same batteries feeding the inverter... feeding the PD4045...

Seems like a loop...

[GuitarPhotog]

With a PD 4045 you don't need a battery minder. The PD contains a 4-stage smart charger.

<Chas>

[RetchedOne]

But that's the thing. Won't that use the 120v from the inverter to charge the batteries... running the inverter?

[Wobbly Wheels]

The shorepower and inverter feed into an ATS.
The ATS feeds the PD4045

That sounds like the issue right there.
The 4505 and the inverter need to feed into the transfer switch and the switch output runs to your AC bus. That way, when shorepower is NOT energized, the inverter will be the 'default' AC source and plugging into shorepower will switch you over to the 4505.

[Socal Tom]

Don't plug the entire trailer into the inverter, just the devices you want to use.
Tom

[RetchedOne]

But those devices will already be wired to the 4045 AC bus, so how do I easily switch them between shore and inverter.

[RetchedOne]

I guess I could wire up the "Top outlet" to the inverter, and the "bottom" outlet to the 4045... I'd have to swap the fridge over to a different outlet... but that won't happen all that often...
That may be the cleanest...

[Wobbly Wheels]

Don't plug the entire trailer into the inverter, just the devices you want to use.
Tom

I don't get why you wouldn't use the inverter to feed the AC system rather than as a separate outlet. That way, the inverter can be located close to the batteries to reduce the 12V voltage drop (shorter cables) and you can run AC outlets to wherever you need them.
Otherwise you'd need one 12V circuit to power an inverter for your TV/phone charger, etc in the cabin and another to run the blender in the bar...I mean 'galley'.

[Socal Tom]

Don't plug the entire trailer into the inverter, just the devices you want to use.
Tom

I don't get why you wouldn't use the inverter to feed the AC system rather than as a separate outlet. That way, the inverter can be located close to the batteries to reduce the 12V voltage drop (shorter cables) and you can run AC outlets to wherever you need them.
Otherwise you'd need one 12V circuit to power an inverter for your TV/phone charger, etc in the cabin and another to run the blender in the bar...I mean 'galley'.

In my case I have. 200 watt inverter, it runs my tv and some small other things. It seems a lot of trouble to feed all the outlets when I don't need them. I don't have a 4045 so maybe I'm missing something?
Tom

[Wobbly Wheels]

To each their own, Tom. 200W means you can plug them into a standard 12V 15A outlet and in that case I can see having one inverter and moving it around as needed. For the bigger, hardwired units (1000-1500W) the voltage drop would necessitate some pretty heavy cabling to put the inverter where you want the outlets (eg, in the galley with the batteries on the tongue). By running the 110 to the back of the trailer rather than 12V, you are wasting fewer of your precious Amp*hours making heat.

[Socal Tom]

I guess I can see that. I would expect that in a large RV. It's a little surprising to me in a TD. I think a simple inexpensive option could be adding a regular wall switch between the 4045 and the invertor, so you could switch it off if not on shore power.
Tom

[Wobbly Wheels]

I would expect that in a large RV. It's a little surprising to me in a TD.

Unfortunately, DC doesn't travel well. That's especially true when you're trying to move the 125A that a 1500 W inverter needs from the tongue box to the galley and back. I was looking at mounting mine in the galley cabinet of my 4X8 build but the routing quickly added up to 25' to the batteries and back. To keep a maximum voltage drop of 10%, that means 4AWG cable.


By keeping the inverter close to the batteries and running the AC back, I can use 6AWG...but more because of the maximum allowable current in the conductor (125A) rather than the length of the run. Based solely on voltage drop, I could run 16AWG over that short a distance but obviously the 125A would turn it into a fusible link pretty quickly


Then you can run the AC wherever you want to with no voltage drop at all. All of the usual practices apply when working with AC, as well as keeping it separate from DC, but it's far more efficient to move AC than DC. That's especially true when you see how quickly wire lengths start to add up when you start pulling them. I got 100' rolls of red & black 16AWG for DC but I'm thinking now that it might not be enough

Still, there's something to be said for K.I.S.S.