Transfer switch fabrication

[O C Diver]

Ok, let me explain my logic:

I want to keep powered supplied to the refrigerator.

In the order of preference.

Shore power is first as it's a negligible cost and dosen't require battery charging and power invertering from 12 VDC to 120 VAC. Probably the least amount of failure points and complexity.

Generator is second as it's running to either do climate control or recharge batteries. Otherwise, this is the same as shore power with a higher energy cost.

The Magnum Energy inverter is third as it always invertering power except when saving battery capacity is important. Using an inverter requires recharging the batteries which adds more complexity / failure points.

The Victron inverter is fourth as it's the backup in case all else fails or I need to optimize battery capacity.

The transfer switch was the only piece needed to complete the power switching.

Ted

 

[Circumnavigator]

Unless you want to be able to run the reefer on a source other than what the boat is running on, it's simpler than you think, because whatever power the boat is running on is probably what you want the reefer running on.


If that works for you, then you need only one relay, a DPDT
Feed: Reefer
NCedicated inverter
NO:Boat power
Coil:Boat power


If there's AC power on the boat, the coil pulls in and the reefer uses it. If not, the relay drops out and it takes power from the dedicated inverter.


Jim

 

[twistedtree]

i'll agree there's a benefit for the mechanical interlock. i will also say that the closed contacts are designed to de-energize a few milliseconds before the open ones begin to close. with proper circuit protection it would be perfectly safe.
this problem has almost an infinite number of ways to manage it. i will let myself out of the conversation. there's enough engineers on it without me.

A double throw switch is inherently mutually exclusive. Just be sure it's break before make, but that's what they all typically are.


Ksanders described it a few pages ago.


Here are a few example SPDT relays, 15A, 120VAC.



https://www.mouser.com/c/electromec...5 A&relay contact form=1 Form C (SPDT-NO, NC)


With these you would switch only the line wire, not line and neutral. Use a DPDT relay to switch both line and neutral.

 

[twistedtree]

You can also look at the Finder Series 62 relays. They offer 16A, 120VAC contacts, and 120VAC coil, DPDT (other configs too). Also available are DIN rail mounted sockets with screw terminals. I have used quite a few Finder relays of various sorts.

 

[ksanders]

I think everyone is over-complicating this. The transfer switch only needs to switch 2 sources based on the original description. It just needs to switch between what we'll call "ship's power" and "dedicated inverter". The switching for shore / gen / inverter on the "ship's power" side sounds like it's already handled upstream of the transfer switch.

One relay will do the job, but in traditional TF fashion he now needs a PLC.

 

[Choices]

Not make before break! That means a bumpless transfer in synched or DC. Not for this application. A small few second time delay is best.

 

[twistedtree]

Not make before break! That means a bumpless transfer in synched or DC. Not for this application. A small few second time delay is best.

Sorry, did I say that wrong? Probably. Break before make. Disconnect from one side before you connect to the other. A little lesdyxia creeping in.

 

[O C Diver]

Lots of good information in this thread. Have formulated a design and will report back on how it works.

Ted

 

[freedomwaters]

Lots of good information in this thread. Have formulated a design and will report back on how it works.

Ted

can't wait . my brain is fried trying to figure all this out. lol thanks for the help so far.

 

[MVDarlin]

Blue Seas sells a switch for $400. I have one for a siimilar application. I eventually abandoned the idea and connected a 3,000 watt inverter to the house AC with a 4 position Blue Seas AC source switch. Off/Shore/Gen/ Inverter. It cost about $450 10 years ago. It is a lot more efficient to run AC power long distance and mount inverter close to battery bank with heavy DC cables.

 

[Robnmelissa]

You may wish to use a 3 pole relay to properly direct your ground conductor. Keep in mind the ground and neutral are combined at the “power source”. This means at the generator and inverter outputs (when inverting).

But… During inverter pass through, this neutral to ground cross connect is opened (internally at the inverter pass through relay), so that the neutral to ground cross connect ends up back in the shore side distribution panel.

Thus, depending on whether all your AC loads are downstream of your inverter,, you may have two grounding busses. One for inverter loads, and another for non inverter loads like air conditioning or larger electric heaters.

If you don’t keep your ground paths correct, it may cause AC leakage onto your bonding system and accelerated zinc depletion.

Rob