Automatic Transfer Switch and Converter Charger

[Aikalowych]

Hello all, I am a new solar owner/installer and stuck in a specific design aspect of my system. I plan on having 400W of solar mounted to the roof of my travel trailer (Springdale keystone mini) with a 40A charge controller and 2000W inverter. My issue is about the concept of transfer switches. I have watched Will’s video on wiring a transfer switch in an RV and I mostly get the concept, however, I’m stuck on one part. To preface - my trailer only has one battery so i plan on the house/cabin battery being the same as the solar battery.

At the end of the video he mentions that you should wire in your own battery charger, bypassing the onboard converter charger, IF YOU DONT WANT to use the converter charger that comes with the RV. I’m not sure if that’s because he’s talking about charging LiFePO batteries? And not sure whether or not you can choose to use the onboard converter charger (WF-8735P in my case).

My question is: Can I wire the onboard converter charger circuit directly to the transfer switch as a way to avoid having the charger active while the inverter is powering the system? Does that make sense/is that possible? Or should I disconnect it altogether and do what he suggests and get a progressive LiFePO battery charger? I’m hesitant to get that battery charger because I might install the system without LiFePO batteries and just upgrade from the sealed lead acids that I currently have a little down the line. So I would like to keep using the converter charger that comes with the trailer.

Bonus question: do you have any recommendations for transfer switches? I was probably going to purchase the go power TS-30 that he showed in the transfer switch video.

Below are some specs:

Onboard convert charger: WFCO model WF-8735P

Battery: Currently 200Ah 12V sealed acid but would like to upgrade to at least 200Ah LiFePO at 12V

Inverter: Renogy 2000W pure sine wave

Charge Controller: Renogy 40A MPPT

Rig: 2021 Springdale Keystone Mini

Draw: main power needs are a mini fridge, an electric kettle once a day, water pump and lights, among charging phones and laptops occasionally. I haven’t done the full calculation but I would guesstimate it to be around 1200Wh of power consumption every day give or take.

Thank you all in advance!!

 

[time2roll]

With 400w solar the converter may not be needed at all. Disconnect power to the converter and let the solar work.
Can reconnect if needed.

My converter has not been used in a decade. Solar provides all 12v power even if plugged in.

 

[Aikalowych]

With 400w solar the converter may not be needed at all. Disconnect power to the converter and let the solar work.
Can reconnect if needed.

My converter has not been used in a decade. Solar provides all 12v power even if plugged in.

Hmmm that’s a great point, I did not think to do this! Would you still recommend using the transfer switch to switch between shore and inverter power?

 

[Tomthumb62]

Can’t answer your question, but since you don’t list your loads or battery capacity, but only have 400W solar, I thought to mention that you’re likely going to struggle with that 3000W inverter. I used to have the 2000W Renogy with 400W solar and the inverter used over 600Wh of battery per day due to its very high idle draw. It was a struggle to keep the battery charged with the high idle draw and only 400W solar, even in full sun, our main load was a small refrigerator. If you don’t intend to power your inverter 24/7, it might not be an issue for you though.

 

[Aikalowych]

Can’t answer your question, but since you don’t list your loads or battery capacity, but only have 400W solar, I thought to mention that you’re likely going to struggle with that 3000W inverter. I used to have the 2000W Renogy with 400W solar and the inverter used over 600Wh of battery per day due to its very high idle draw. It was a struggle to keep the battery charged with the high idle draw and only 400W solar, even in full sun, our main load was a small refrigerator. If you don’t intend to power your inverter 24/7, it might not be an issue for you though.

Oof I made a typo in my specs, I do have the 2000W renogy inverter, however it is the newest version with a power saving mode. Just edited the post to fix that. Thanks for that information!

 

[time2roll]

Would you still recommend using the transfer switch to switch between shore and inverter power?

Transfer switch is required if the inverter is hard wired into the electric system.
Exception would be to plug the main cord into the inverter.

 

[Aikalowych]

Transfer switch is required if the inverter is hard wired into the electric system.
Exception would be to plug the main cord into the inverter.

Okay yeah that’s what I was figuring. So, in your experience, you haven’t had a need for the converter charger to charge the battery? Such as being plugged into shore power but not having sun? And I guess that if that is the case you could just turn the converter charger breaker back on?

 

[Tomthumb62]

Oof I made a typo in my specs, I do have the 2000W renogy inverter, however it is the newest version with a power saving mode. Just edited the post to fix that. Thanks for that information!

Curious how the power saving mode on the Renogy works, have you tried it yet? At the time, I couldn’t find how to adjust those settings…it appeared to be factory set and not adjustable.

On the Victron inverter I replaced it with, the default power saving “eco mode” settings didn’t work for my case. However, they are highly adjustable and I got it dialed in perfectly. My idle draw went from about 644Wh on the Renogy to about 100Wh on the Victron. This makes a huge difference in how long I can go without much sun and not need to fire up the generator.

Anyways, if the power saving mode on the Renogy isn’t adjustable then it may or may not be a selling point.

 

[Aikalowych]

Curious how the power saving mode on the Renogy works, have you tried it yet? At the time, I couldn’t find how to adjust those settings…it appeared to be factory set and not adjustable.

On the Victron inverter I replaced it with, the default power saving “eco mode” settings didn’t work for my case. However, they are highly adjustable and I got it dialed in perfectly. My idle draw went from about 644Wh on the Renogy to about 100Wh on the Victron. This makes a huge difference in how long I can go without much sun and not need to fire up the generator.

Anyways, if the power saving mode on the Renogy isn’t adjustable then it may or may not be a selling point.

They claim it uses <5W in eco mode. I haven’t tested it yet so I’ll have to see!
I’m curious if you or anyone else has had experience with wiring the onboard converter charger to the transfer switch circuit, to avoid having to manually shut off the converter charger when powered by the inverter?

 

[Tomthumb62]

They claim it uses <5W in eco mode.

That’s the issue I had with Renogy—their claims never added up to reality. So when you do test it, please report back because maybe they actually got this one right. But if the eco settings are not adjustable (iirc, they aren’t), then it’s a crap shoot as to whether the eco mode is actually useful to you or not.

I’m curious if you or anyone else has had experience with wiring the onboard converter charger to the transfer switch circuit, to avoid having to manually shut off the converter charger when powered by the inverter?

As for wiring up a switch, I ended up in a similar boat. However, I chose to NOT go the automatic transfer switch route. Instead I wired up a manual switch. It was confusing as heck to wire it but I learned a lot and it worked on the first try. Maybe someday I’ll change it to an auto switch, but I manually switch so rarely that it doesn’t seem worth the cost or complexity. And the auto switches are physically much larger and I have a very tight space to work in.

With the manual switch, the left position provides 120v house power from the inverter/battery/solar, center is OFF and right position the power is from shore power. When plugged into shore power, the Victron 120v battery charger also powers up, which both charges the battery and provides 12v house power. This charger acts very similar to a standard “RV converter”, but has no switching ability, hence the manual switch.

It works wonderfully and I loved all I learned wiring something like this up. Would be child’s play for an electrician, but that’s not me. I had to draw out the wiring plans over and over before I was confident I had it correct. And it was a slow process actually wiring it up because I kept double checking it over and over, which saved my butt at least once because I had gotten things backwards. Like anything DIY, double and triple check if you have any doubts and do it too even if you don’t have doubts!

 

[Tomthumb62]

They claim it uses <5W in eco mode. I haven’t tested it yet so I’ll have to see!

Found this in the Renogy user manual:

▇ ECO Mode
ECO mode is a battery saver mode. When on, the inverter will search for a load by sending
a pulse every 2~3 seconds to the AC outlets. The Power LED will also pulse. Loads that are
50Watts or less will not be powered on and the inverter will remain in this mode until 50W or
greater is detected or until it is manually shutdown.

Italics are mine. So this confirms that the ECO mode is preset and not adjustable. Which means if you want the inverter to power on from eco sleep with less than 50W load, your outta luck.

So it really depends upon your use case as to whether the eco mode will be useful to you.

On my system, my lowest inverter load is 15-20W. I have my Victron inverter eco settings set to wake up at 10W or greater. This means my inverter wakes up for any and all inverter loads in my house. The Renogy would not work on my case because those settings are not user adjustable like the Victron.

If you intend to use the eco mode on your Renogy, ask yourself if you have any loads under 50W? If so, you might become extremely frustrated that you don’t have power when you want it.

 

[time2roll]

Okay yeah that’s what I was figuring. So, in your experience, you haven’t had a need for the converter charger to charge the battery? Such as being plugged into shore power but not having sun? And I guess that if that is the case you could just turn the converter charger breaker back on?

Have not really used the converter in years even with the 4x GC2. Now with a lithium battery I can generally run a week without a worry. By then I am moving on. Certainly the converter is there if difficult conditions persist.

 

[Aikalowych]

That’s the issue I had with Renogy—their claims never added up to reality. So when you do test it, please report back because maybe they actually got this one right. But if the eco settings are not adjustable (iirc, they aren’t), then it’s a crap shoot as to whether the eco mode is actually useful to you or not.


As for wiring up a switch, I ended up in a similar boat. However, I chose to NOT go the automatic transfer switch route. Instead I wired up a manual switch. It was confusing as heck to wire it but I learned a lot and it worked on the first try. Maybe someday I’ll change it to an auto switch, but I manually switch so rarely that it doesn’t seem worth the cost or complexity. And the auto switches are physically much larger and I have a very tight space to work in.

With the manual switch, the left position provides 120v house power from the inverter/battery/solar, center is OFF and right position the power is from shore power. When plugged into shore power, the Victron 120v battery charger also powers up, which both charges the battery and provides 12v house power. This charger acts very similar to a standard “RV converter”, but has no switching ability, hence the manual switch.

It works wonderfully and I loved all I learned wiring something like this up. Would be child’s play for an electrician, but that’s not me. I had to draw out the wiring plans over and over before I was confident I had it correct. And it was a slow process actually wiring it up because I kept double checking it over and over, which saved my butt at least once because I had gotten things backwards. Like anything DIY, double and triple check if you have any doubts and do it too even if you don’t have doubts!

Wow! yeah that all makes sense. Congrats on getting it right the first try! I’ve gone back and forth and I think the auto switch is the way to go for us, due to us having to switch frequently (currently hooked up to intermittent shore power). I am mechanically inclined and look forward to the wiring process though I know I’ll have to spend time drawing it out and making sure everything is correct.

Hopefully I’ll have things installed by the end of next week so I will report back on my experience with the inverter. Thank you for your feedback and sharing your experience.

This may be a dumb question, but how do know how much power your inverter is consuming when idling? Would a battery monitor tell you or the unit itself?

 

[time2roll]

This may be a dumb question, but how do know how much power your inverter is consuming when idling? Would a battery monitor tell you or the unit itself?

Most will list the idle draw in the spec sheet. Many are close to 1% of rating.

 

[Tomthumb62]

This may be a dumb question, but how do know how much power your inverter is consuming when idling? Would a battery monitor tell you or the unit itself?

No dumb questions here!

A battery monitor would tell you. As would a clamp meter.

There is at least one thread here where people measure their actual idle draw. You have to read between the lines because of human error, but it’s a useful read nonetheless.

 

[beeg86]

I have a very similar setup. 400w renogy solar and a 2000w renogy inverter and 4 6v 230ah lead acid batteries, but my inverter is the old version. I went the simpler route and plug my trailer into the inverter using the shore power cable. I then flick the converter off in the breaker panel so it doesn't try and charge the batteries from the converter. I'm in northern BC Canada and the solar charges my batteries from Mid 70% in the morning all the way to 100% and I leave my inverter on 100% of the time when I'm camping on weekends. I also hooked my panels up in series and did have an issue with my charge controller throwing a code for over voltage on a cool sunny morning. I had hooked it up in series to make use of the fuse that came with the kit I bought and renogy told me after to hook it up in series/parallel. I had however already mounted the panels on the roof in a way that the cables wouldn't reach in that way. I was able to hassle them for a free 60 amp Rover and kept the 40 amp. Early spring and late fall I use the converter to charge once in a while as my panels are flat mounted and we get very limited sun at those times.

 

[Sprinterman]

Hi, I have a class C with the same wfco 55 amp distribution panel. I bought the same inverter and trying to have the inverter run everything without the need of propane frig. The problem is the refrigerator still needs a 12v source, as well as the slide, lights and others I am sure. All I want to turn off is the charging of the batteries from the converter. I am looking for the solution. All I can figure is wire the 12 volt distribution directly to lithium house batteries, and the converter would only charge the batteries. I already have a transfer switch for the generator and the shore power. I was going to install another from those two sources and the inverter. I have seen some people say put a subpanel, but looking for advice. Thanks in advance!