Why automatic transfer switch?

[steveluannj]

I am in the process of upgrading my solar/battery/inverter on my 2022 280RL. I have 2 additional 175W panels, the Li Time 230AH LiFePO4 battery, and am now picking an inverter and transfer switch to let the wife use her hair dryer when boondocking. It seems that with a 200A BMS on the battery, that I am limited to a 2000W inverter, which is fine for the occasional use I expect, but the transfer switch is confusing me. If I had 3000W inverter capacity, I could see cutting the inverter prep wire and making the outlets on that circuit be inverter always. Unless I use multiple high wattage appliances at the same time, the only downside would be efficiency, and who cares if I have shore power. I am planning to use a transfer switch and a 2000W inverter. The cheaper transfer switches seem to have a possible failure mode- I have seen videos where they can connect both sides at the same time, which could be a disaster. I am considering a manual switch. It is a fraction of the price of a good brand automatic, and I would set it to inverter if I am boondocking and need AC power. I don't need it to switch back and forth once I am in place, at least not that I can imagine. Is there a use case I am missing where I need the outlets to switch back and forth from inverter power to shore?

[Jkwilson]

Most probable need for auto switch would be a power failure while on shore power when you were away or asleep and had something on that you didn’t want to shut down. Refrigerator, Crockpot, CPAP, internet device for monitoring status etc..

[Scott'n'Wendy]

I think you have it figured out. They would be very good for someone that NEEDS/DEPENDS on a 120vac device running. Hair dryer probably falls outside that requirement. But a person working out of their trailer may require consistent 120vac. Camping a lot in cold weather to keep the furnace viable through power outages?
From your post I would think the decision between ATS or MTS is only one of convenience. Edit..removed incorrect info

[howson]

Is there a use case I am missing where I need the outlets to switch back and forth from inverter power to shore?

The Victron Multiplus has a built-in ATS. The use case for us is our poodle. The bedroom a/c is tied into inverter so that when we're away if shore power drops the batteries / inverter will continue to run the a/c for up to 4 hours. (We limit our time away to no more than 4 hours anyway when Brody is with us.) I have the 3000W version of the Multiplus. If we're connected to the internet, the Multiplus also sends me a notification that shore power dropped.

The other nice feature of the Victron is PowerAssist. Should there be limited shore power available when moochdocking, the Victron will add it's output to shore power. Example: you're plugged in to 15A of shore power. Assuming the 2000W version of the Multiplus, it will add (approximately) another 15A for a total of 30A. When the demand drops below 15A, the Multiplus immediately switches back to charger mode to top off the battery again.

Victron's not the cheapest...but it is, IMHO, an outstanding product.

Howard

[TedS]

The need for the automatic transfer switch is to prevent multiple incompatible power sources from powering the trailer and to prevent backfeed into the mains should ther be a mains power failure. The frequencies of two independent power sources don't match. Backfeeding a mains source being repaired could electrocute the repairman.

[Scott'n'Wendy]

Backfeeding a mains source being repaired could electrocute the repairman.

While correct, I was thinking he was looking at this from the perspective of boondocking and the gen is off? Not plugged into a post?

[Cate&Rob]

Unless all the outlets you intend to switch back and forth between shore power and inverter happen to be on the same circuit, wiring this without transferring the entire trailer electrical system, will get complicated. Another solution with a small inverter is to install a couple of new outlets wired permanently to just the inverter. Then you can more easily manage what is plugged into the inverter. Works for us . . .

Rob

[howson]

steveluannj



My buddy didn't want to go the Victron route (too much money) and his needs are modest, so we installed his entire system under the bed in his 297RSTS. The inverter is an inexpensive 2000W (1). Goes through a 15A breaker (2) then to a manual plug (3). When he wants to power something (coffee pot, microwave,e tc) he uses an extension cord. One device at a time. The circuit breaker (and extension cord) are his "transfer switch".

Not what I would do...but that's not the point. I show this install to convey there's options based on budget and how the system will be used.

Howard

[Scott'n'Wendy]

Unless all the outlets you intend to switch back and forth between shore power and inverter happen to be on the same circuit, wiring this without transferring the entire trailer electrical system, will get complicated. Another solution with a small inverter is to install a couple of new outlets wired permanently to just the inverter. Then you can more easily manage what is plugged into the inverter. Works for us . . .

Rob

Actually it's very easy to with the special panel GD uses. The 30 amp tie breaker can be used for isolation from the rest.

[Cate&Rob]

Actually it's very easy to with the special panel GD uses. The 30 amp tie breaker can be used for isolation from the rest.

Agreed . . . If the trailer is appropriately wired with this divided panel.

Rob

[Jkwilson]

I think some responses missed a key part of the OP. They are trying to decide if a manual transfer switch will do the job for them, or if they need an automatic one. Not trying to do without one completely.

[TedS]

The automatic or manual transfer switch also prevents a hot shore power inlet when boondocking.

[acoleman43]

steveluannj The transfer switch is needed for specific scenarios.

1- If you have an onboard generator. The ATS will automatically switch from shore power to generator power. It also should have a delay (usually 30 seconds) when the generator is started. This gives the generator time to "warm up" before it has a load. This switch will not allow BOTH shore and generator power to proceed to your main distribution panel providing important protection. You can have a manual switch if desired. An ATS is much more convenient

2-If your AC (alternating current) system is partially inverted (specific circuits/breakers are inverted, not the entire system). This ATS will allow the circuits connected to the inverter to by active BOTH when plugged into shore power (or generator power) AND when inverted. If the ATS does not sense power coming from shore power, it will automatically switch to inverted power. If it does sense shore power, it will not allow inverted power to your main distribution panel. Again, providing protection. You can also use a manual transfer switch if desired, but an ATS is much more convenient.

As howson mentioned, some inverters (like the Victron Multiplus) come with a built-in ATS. If your inverter comes with a built-in ATS, no external ATS or manual switch is needed.

Obviously my preference is an ATS vs a manual switch. I would go even further and make sure your inverter has a built-in ATS. Just my opinion/preference

[Scott'n'Wendy]

I think some responses missed a key part of the OP. They are trying to decide if a manual transfer switch will do the job for them, or if they need an automatic one. Not trying to do without one completely.

Yes, for me if I ever went with an inverter, the transfer switch would be manual. It's not like I need a UPS in the trailer. I've been in CG's when the power went out and some people panic....I usually decide to check back in a few hours. I have nothing pressing that really needs 120v.

[steveluannj]

Thinking I will go manual- it should be more reliable as well as simpler, and I don't see a problem even if I leave the switch in the inverter position and connect to shore power. Less efficient, but no danger to anything. I have inverter prep, so the circuit I am powering is separate from the one that would be connected to shore power or a generator. Thanks for all of your input. This group is helping me a lot.