Shore/Inverter & Shore/Solar transfer

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ryancousins

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Apr 19, 2019
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I have a small trailer with a 30 amp converter/charge controller. I?d like to add an inverter, and I know I?d need a transfer switch. However, I?d also like the ability to add solar panels and when I?m not running on shore power and hence my battery is not being charged from the existing charge controller, I?d like it to switch to being charged by the solar panel. I have been searching the forum but haven?t found anyone talking about the exact same scenario. Is there a device that can handle both transfers at the same time or would I need two separate switches? I?ve read on here that you don?t have to worry about a transfer switch with solar because the charge controller you?d get with the solar panel will take care of that but I?d just assume not have to have another charge controller when I already have one built in. In my mind, it seems like the solar would be wired in upstream of the camper?s existing charge controller at the same point as the output of the existing converter and there would be a transfer switch at this point? But if I did just buy a separate charge controller I?m assuming if my existing controller is charging the battery, the solar controller, hooked up parallel to the other controller would see the voltage coming from the other controller and automatically assume the battery is charged?
 

HueyPilotVN

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First , Welcome to the Forum.

You probably have a convertor/charger that provides 12 volts and charges the batteries.  This is different that a Solar charge controller.  a solar charge controller is powered by the DC from the panels and manages how much of that goes to the batteries.

A transfer switch is usually used to manage the transfer of two A/C sources, usually the shore power connection and a generator.  With your current setup you probably choose the source by switching the plug on your power cord if you have a generator.

Hooking up a Solar power system so that the connection is at the same point as the input from your convertor/charger is the normal way to connect solar, (usually at the battery bank itself).

You can do this without problem just like you can use two garden hoses to fill a swimming pool at the same time.

The Invertor if used connects to the output of your battery bank and does not need a transfer switch.

This is kind of a simple explanation but it will get you started in understanding how these things interelate.
 

ryancousins

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Apr 19, 2019
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But I?d would still need a solar charge controller, right? I couldn?t just hook up the solar panel directly to the battery because the battery could backfeed the panels plus anytime there is sun it would apply a voltage to the battery, even if it?s fully charged.
 

HueyPilotVN

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You need a solar charge controller to manage the rate and amount of current going into your batteries.

Some very small panels that just provide a trickle charge can be used to charge the battery but they are not very good for much more than just maintaining a small charge.

There are very many good posts an this Forum about Solar.

Use the search function above and type in Solar and you will find lots of discussions to go thru.
 

Lou Schneider

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ryancousins said:
I have a small trailer with a 30 amp converter/charge controller. I?d like to add an inverter, and I know I?d need a transfer switch. However, I?d also like the ability to add solar panels and when I?m not running on shore power and hence my battery is not being charged from the existing charge controller, I?d like it to switch to being charged by the solar panel.

Welcome to The RV Forum!

The basic rule of thumb is you can have multiple DC sources active at the same time without causing any problems.  To do what you want, i.e. charge with solar when shore power isn't available, all you need to do is connect the output of the solar system to the batteries along with the existing converter.

You will need a solar controller, both to regulate the output of the solar panels so they don't overcharge the batteries and to keep the batteries from backfeeding into the panels at night.

However, with AC power you can only use one source of power at a time.  Thus you'll need for a transfer switch to select between shore power or the output of the inverter.

I have been searching the forum but haven?t found anyone talking about the exact same scenario. Is there a device that can handle both transfers at the same time or would I need two separate switches? I?ve read on here that you don?t have to worry about a transfer switch with solar because the charge controller you?d get with the solar panel will take care of that but I?d just assume not have to have another charge controller when I already have one built in.

You don't have an existing charge controller, you have a converter.  A converter takes in 120 VAC and outputs DC voltage to keep the batteries charged.

This is different than a solar charge controller which takes in DC power from the solar panels.  So yes, you really do need a separate charge controller for the solar panels.

In my mind, it seems like the solar would be wired in upstream of the camper?s existing charge controller at the same point as the output of the existing converter and there would be a transfer switch at this point?

No, the output of the solar system is added downstream of the converter, at the batteries.  There is no provision to add it "upstream" of the converter as the voltage at that point is 120 VAC.
But if I did just buy a separate charge controller I?m assuming if my existing controller is charging the battery, the solar controller, hooked up parallel to the other controller would see the voltage coming from the other controller and automatically assume the battery is charged?

Both the solar controller and the converter will be supplying voltage to the batteries. They will only absorb as much current as they need, from whichever source has the higher voltage.
 

John From Detroit

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How much inverter do you want and how much battery do you have?

Now if all you want is to run a Television.. A small (200-300 watt Pure or True sine wave) can be used to do that full time. Most converters (If you have more than say 30 amps) will keep up with it. not as efficient as a transfer switch but.. Well other advantages.

IF you want to run the MIcrowave you will need at least 1500-2000 watts. Many inverters like teh Xantrex Freedom XC have a built in transfer switch. I will line draw how those work

SHore--Breaker box---30 amp line to inverter--- Second breaker box (Sub panel)---Loads

You only put the MIcrowave and other loads you want on the sub panel (TV/ELectronics and GFCI chain) THe Water heater. fridge and Air Conditioenrs remain on the main panel (The first breaker box).
 

Gary RV_Wizard

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I've written two beginner-level articles on adding an inverters that may be useful.  Both were paid for by others, so can only be found on those websites.

https://www.vehq.com/rv-inverter/

http://www.doityourselfrv.com/rv-inverter-install-diy/

 

ryancousins

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Apr 19, 2019
Posts
21
Lou, when I say my "existing controller", I am referring to the circuitry built into the converter that regulates the recharging of the battery. I'm learning in RV world when someone says converter they imply that it also charges the battery, but in my  more generic electronics mind a converter simply goes from one voltage to another and is essentially just a power supply. It has no intelligence about properly charging a lead-acid battery. However I know that in the RV world the converters are almost always going to have the "charge controlling circuitry" built in. That's why I said my existing charge controller, because I do in fact have an existing one, even if its just built into the converter.

I was thinking I could get away with not buying a charge controller with any solar panels I'd like to buy, but I think it would be a lot easier to buy a stand-alone controller and hook that up to the battery in parallel with the converter. But technically, it should be possible to hook up the raw output of the solar panels to the point in the converter where the converted 12 volts is on it's way to the battery for charging and have a switch to go between the converter and the solar panels, but that would be a lot more work I think.

Since you can apparently safely hook up the solar system to the battery even though there is already a charging circuit connected to the battery, then that would be simple and installing an inverter and transfer switch for the AC circuits I'd like to power when off of shore power should be simple.

 

ryancousins

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Apr 19, 2019
Posts
21
John from Detroit:

At this point the only thing I want to run on the inverter for sure is the canopy lights, but I just think it would be nice to have 110 available at the outlets for really small items. So I would just transfer the outlet circuits for inverter use, and nothing else. I know I wouldn't want to run all of the AC from the inverter, especially considering the converter itself would then be inline and that certainly wouldn't be a good thing!
 

Drewd

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Feb 17, 2016
Posts
76
Couple of things to make your inverter experience better:
1.  Purchase one with a remote on/off switch so you don't have to go outside to flip a switch.
2.  Purchase a trimetric or equivalent battery monitor.  Using an inverter without a battery monitor is like purchasing  a car without a gas tank gauge.
3.  Buy a commercial grade inverter.  I have a Samlex commercial grade inverter which is twice the size of an equivalent non-commercial inverter.  It will last longer.
4.  Inverters are more efficient at loads near max capacity  Inverters also use electricity in standby mode.  Sizing an inverter is important so you don't waste unnecessary battery capacity.  For example, a 3000 watt inverter can have up to 1 amp/hour of power usage in standby mode while a 1500 watt one may have .5 amp/hours of idle draw.   
5.  Some cheaper inverters have fans that come on regardless of how little power is being inverted.  This can be noisy and fans do draw battery power. My inverter's cooling fans are controlled by a thermostat and never come on on loads <50 of rated capacity.

An auto-transfer switch really makes things easy.  I wouldn't own an inverter without one.  Running 20 amp outdoor Romex under your camper isn't difficult and you won't regret doing it. 

Don't be tempted to save $$$ by using a modified sine-wave inverter.   

I used a jumper wire in my 50 amp auto-transfer switch so all of my power distribution circuit panels are "hot' with inverter power.  Before you use your inverter, make sure your hot water heater is on propane (it can use 1500 watts/hour) and your fridge is switched to propane as it can use 300 watts/hour t 120 volts AC.  Both of those loads can add up quickly.  Also ensure your thermostat is set so your air conditioner doesn't come on by itself as the load can trigger a fault in your inverter if it isn't rated for the start up surge.

How will you be recharging your batteries?  If using a generator or shore power via your converter, I found that many RV's have their converters 15-30 feet away from the batteries attached to often undersized wire.  This causes unacceptable voltage losses, 0.5 volts in my case, which reduced voltage to the point I was not getting an absorption charge on my batteries.  Moving the converter within several feet of my batteries literally cut my generator time in half each day. 
 

grashley

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May 7, 2015
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Location
Western Kentucky
Welcome to the Forum!

It sounds like you are getting it figured out.

You are actually looking at two SEPARATE projects. The Solar project is a stand alone project, complete with its' own controller with output directly to the battery bank.

The inverter is also a stand alone project.  My way to describe this is to select the circuits in your current power panel you want to power with the inverter.  REMOVE these circuits from the main panel and move them to a sub box.

Incoming shore / generator power goes to the main panel, through a breaker, to the ATS in the inverter, and power passes straight through to the sub box when on this power source.  All circuits work as they do now.  Some breakers are relocated.
Battery power goes to the ATS in the inverter.  When no shore / generator power exists, the battery / inverter provide 120V power TO THE SUB BOX.  Other circuits, like A/C and converter are NOT powered.
 
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