Using an Automatic Transfer Switch for a single device?

[bwf]

I am building a custom enclosure to house my MPP Solar 2424 unit outdoors. Inside will be a thermostat controlled heat pad to keep the unit above 0 degrees celcius. In the winter, before I fire up the inverter, I want to power the heat pad directly from the generator first to get the unit up to temp. Then I will turn the unit on which will then supply the power from my battery bank. At which point I would like the power source for the heat pad to switch over to the batteries (energized through a regular outlet coming out of my breaker panel). That way when the generator kicks out because the batteries are charged, the heat pad will still run.

I'm looking for a simple way to achieve this. It looks like this is exactly what an Automatic Transfer Switch does. However all the ones I have found are designed for large loads, like an entire electrical panel. I just want to control one device. There are automatic transfer switches for not a lot of money on Amazon so if they do the trick then I'm happy to go that route. But wondering if someone can recommend something that would fit the bill and not be overkill.

I came across the Xantrex 8080915 PROwatt SW Auto Transfer Switch (https://www.invertersupply.com/index.php?main_page=product_info&products_id=4217) which appears like it would work. I would think I could cut the 3 prong plug off and run "From Utility" to my generator, and "From Inverter" to a wall plug, and then "AC Out" directly into the heat pad. Cutting off the 3 prong plug of the heater unit cable and splicing together with "AC Out" cable. Anyone able to confirm this would work? Or any other recommendations?

FYI this is the heatpad: https://www.amazon.ca/gp/product/B079MHBDNW/ref=ppx_yo_dt_b_asin_image_o04_s00?ie=UTF8&psc=1

Cheers!

 

[FilterGuy]

Your solution will probably work OK. The reason I say probably is that we don't know if the switch switches both Hot and Neutral and I don't know if the generator ties Neutral to ground. Here are the two scenarios to be concerned about.

1) Generator Ties neutral to ground and the switch does not switch Neutral.
In this case, there are two ties between Neutral and Ground: The Generator and the house wiring. If there are no ground-fault breakers in the path, the set-up will appear to work, but there will be current flowing through the ground wire. ... A big no-no.

2) Generator does not tie neutral to ground and the switch does switch Neutral.
In this case, when the generator is providing the power there will be no bond between neutral and ground. This is not considered proper, but it is not the end of the world. In fact, it is no different than plugging the heat pad directly into the generator.

The good news is that most portable gas generators don't tie Neutral and Ground together so scenario 1 might be unlikely.

The pad is 1000W so I assume you won't have it directly in contact with the batteries. I also assume the shed will be insulated enough that 1000W is enough.

 

[Arbee]

I am building a custom enclosure to house my MPP Solar 2424 unit outdoors. Inside will be a thermostat controlled heat pad to keep the unit above 0 degrees celcius. In the winter, before I fire up the inverter, I want to power the heat pad directly from the generator first to get the unit up to temp. Then I will turn the unit on which will then supply the power from my battery bank. At which point I would like the power source for the heat pad to switch over to the batteries (energized through a regular outlet coming out of my breaker panel). That way when the generator kicks out because the batteries are charged, the heat pad will still run.

I'm looking for a simple way to achieve this. It looks like this is exactly what an Automatic Transfer Switch does. However all the ones I have found are designed for large loads, like an entire electrical panel. I just want to control one device. There are automatic transfer switches for not a lot of money on Amazon so if they do the trick then I'm happy to go that route. But wondering if someone can recommend something that would fit the bill and not be overkill.

I came across the Xantrex 8080915 PROwatt SW Auto Transfer Switch (https://www.invertersupply.com/index.php?main_page=product_info&products_id=4217) which appears like it would work. I would think I could cut the 3 prong plug off and run "From Utility" to my generator, and "From Inverter" to a wall plug, and then "AC Out" directly into the heat pad. Cutting off the 3 prong plug of the heater unit cable and splicing together with "AC Out" cable. Anyone able to confirm this would work? Or any other recommendations?

FYI this is the heatpad: https://www.amazon.ca/gp/product/B079MHBDNW/ref=ppx_yo_dt_b_asin_image_o04_s00?ie=UTF8&psc=1

Cheers!

Here's what confuses me.

While I agree that you need a transfer switch so as to energize the heating pad first with the generator, and after some time with the battery, why do you seek this transfer switch to be automatic if--or so it would seem--many other parts of this process seem to involve manual steps on your part anyway?

If, on the other hand, you would like free advise on how to start the generator (provided it has a cranking battery) based upon a certain condition (e.g. time of day), and turn off based upon a certain amount of time and/or heating blanket temperature I can help you with that--in which case an automatic transfer switch will make sense. Getting a self cranking generator to turn on or off based on a whole host of measurable conditions (you name it, temperature, time, water level, humidity, degree of outdoor light, voltage, etc.) is not hard.

There are plenty of inexpensive automatic switches for the RV world. They are not though UL 1008 listed and as a result not designed for home use. I can't recommend them for use beyond the RV world.

Here's an example of one: https://www.ebay.com/itm/POWERMAX-P...602003?hash=item468399bf53:g:kcUAAOSwD0lUiffk

If, on the other hand you want advise on a small and reliable indoor manual transfer switch I recommend those from Reliance.

http://www.reliancecontrols.com/easy-tran.aspx

 

[bwf]

Thanks for your responses.

Filterguy - Sorry I should have mentioned, the generator is a Honda EU3000IS. From what I've read, it has a 'Floating Neutral'. The ground and neutral are not bonded together. I'm guessing that means that Possibility #2 you mentioned would be more likely to occur? I do have to admit though, you did find another flaw in my design. I was scratching my head when you mentioned my heater was 1000w. I was under the impression I was buying a 24w heater. I didn't realize the thermostat was such a big draw until seeing your post. So I'll be returning that, and was going to try and test one of these in its place https://www.amazon.ca/gp/product/B074HVYDV1/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

The heat pad is to maintain temp above 0 degrees C in the winter for my all-in-on MMP Solar unit in an outdoor enclosure, not my batteries. My batteries are Kilovault CHLX series, so they have their own built in heater and BMS.

Arbee - You are right to wonder why I'd go to the effort if other steps in the process were manual. But this is just one piece of the puzzle I was hoping to sort. The next step would be the auto start generator. I haven't gone deep into it yet, but I have found this

HONDA EU3000is-P GenStart Wireless & 2-Wire Start System

- Start and Stop your EU3000is with any switch, 2-Wire AutoStart control or automatically from your off-grid inverter. - Start and Stop your EU3000is with our Wireless Transmitter from up to 1000 meters away! - NEW Cold Climate Technology Choke Control for dependable starting at any...

genstart.ca

and it appears that it will do the job at first glance. But I would also be very grateful for your offered free advice if you have already been down that path and can ease my frustrations before they occur I also appreciate your suggested transfer switches, but don't they seem a bit overkill? Again, this transfer switch is ONLY to manage the power source for the heat pad, as it needs power before the inverter turns on. The invert has it's own transfer built in to manage the transfer of power from my generator to main breaker panel.

 

[FilterGuy]

Yup, if the Honda leaves neutral floating, it should be OK.

What Inverter are you using? You need to know how the internals work so you ensure your house 1) Always has a Neutral-Ground bond and 2) Never has more than one Neutral-Ground bond. Since the Generator does not have a bond, the chances are good you will never have two bonds, but if the inverter does not do the bonding, you will likely get into a situation with no bonds..... and that is pretty dangerous.

 

[bwf]

It is the MPP Solar - PIP LV2424 MSD 24V 2.4kW, 120V Output, 2kW Solar Input 80A Mppt

I bought a grounding plate that I plan to bury and connect with #6 wire to the electrical panel. Correct me if I'm wrong, but I think the electrical panel is the only thing I need to connect to the ground plate?

 

[FilterGuy]

It is the MPP Solar - PIP LV2424 MSD 24V 2.4kW, 120V Output, 2kW Solar Input 80A Mppt

I bought a grounding plate that I plan to bury and connect with #6 wire to the electrical panel. Correct me if I'm wrong, but I think the electrical panel is the only thing I need to connect to the ground plate?

The bond between Neutral and the Ground wire is a different thing and a different purpose than tying the ground wires to earth ground.

The Green or bare copper wire that runs throughout the house is called the Equipment Grounding conductor and it is there to provide a current path if any power wire gets shorted to non-conducting metal. The shorted current goes from the hot at the breaker box, through the breaker, out to the short circuit back through the equipment grounding conductor, through the bond between the equipment Bonding jumper and neutral. This is a very low resistance path, so the current will be very high a quickly throw the breaker. (This is known as clearing the fault).


Notice that clearing the fault would happen even if the system was not tied to ground. However, even if the home system was not tied to ground, the utility ties Neutral to earth ground so there is still the shock hazard. (Some people will tell you the earth ground is necessary to clear the fault or that it makes the breaker trip faster or other such things, but it is not true.)

The next logical question would be why do we (and the utility) tie to ground at all? Why not just leave the 120V float? Then you have less shock risk...right? It gets a bit complicated, but if the system is allowed to float, you can get problems with imposed voltages from static build-up and nearby lighting strikes. Supposedly these build ups can be large enough to be a safety hazard, but more often the build-ups will cause equipment damage.

I am working on a paper that talks about all of this (The graphic above is from the paper). I am having some folks review it and hope to publish it to the resource section in the next week or two.

 

[FilterGuy]

I looked up the manual for your inverter and found this:

11. GROUNDING INSTRUCTIONS This inverter/ charger should be connected to a permanent grounded
wiring system. Be sure to comply with local requirements and regulation to install this inverter.

And this:



As with so many inverters, the description of how it deals with the neutral-ground bond is almost criminally negligent.

I *think* this means it never ties Neutral and ground. However, it can use the dry contacts to signal an external switch to do the bond if it is not on external AC Power. ( If I am correct, you would not use this signal.)

Since neither the Honda generator or the MPP does the Neutral/Ground bond, You would do a permanent tie external to the inverter.

My silly wild A$$ guess is that the grounding of the MPP is as shown below: (I have seen similar on other inverters)

You really need to confirm what the MPP Does..... DO NOT assume my guess is correct.



Notice that I am guessing that the Grounding lug, AC-In ground wire and ac out ground wire are all just tied to the inverter chassis. In this case I would either use AC out ground or the Grounding lug to tie to the common grounding point. (This avoids ground loops)

 

[Arbee]

Thanks for your responses.

Filterguy - Sorry I should have mentioned, the generator is a Honda EU3000IS. From what I've read, it has a 'Floating Neutral'. The ground and neutral are not bonded together. I'm guessing that means that Possibility #2 you mentioned would be more likely to occur? I do have to admit though, you did find another flaw in my design. I was scratching my head when you mentioned my heater was 1000w. I was under the impression I was buying a 24w heater. I didn't realize the thermostat was such a big draw until seeing your post. So I'll be returning that, and was going to try and test one of these in its place https://www.amazon.ca/gp/product/B074HVYDV1/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

The heat pad is to maintain temp above 0 degrees C in the winter for my all-in-on MMP Solar unit in an outdoor enclosure, not my batteries. My batteries are Kilovault CHLX series, so they have their own built in heater and BMS.

Arbee - You are right to wonder why I'd go to the effort if other steps in the process were manual. But this is just one piece of the puzzle I was hoping to sort. The next step would be the auto start generator. I haven't gone deep into it yet, but I have found this

HONDA EU3000is-P GenStart Wireless & 2-Wire Start System

- Start and Stop your EU3000is with any switch, 2-Wire AutoStart control or automatically from your off-grid inverter. - Start and Stop your EU3000is with our Wireless Transmitter from up to 1000 meters away! - NEW Cold Climate Technology Choke Control for dependable starting at any...

genstart.ca

and it appears that it will do the job at first glance. But I would also be very grateful for your offered free advice if you have already been down that path and can ease my frustrations before they occur I also appreciate your suggested transfer switches, but don't they seem a bit overkill? Again, this transfer switch is ONLY to manage the power source for the heat pad, as it needs power before the inverter turns on. The invert has it's own transfer built in to manage the transfer of power from my generator to main breaker panel.

bwf: it sounds like ideally you'd love the whole thing to be automated but might be willing to tackle each step manual at first and then introduce automation for these steps with time, especially in mind of your budget.

Maybe that's wrong: and right or wrong it's fine.

Q1) What is the condition for which to get this whole thing going (i.e. the generator started)? Is it the two fold condition of a certain amount of lumens (i.e. the sun has come up) and the presence of temperatures below freezing?

Q2) Is the heating requirement there to keep the MPP Solar 2424 at above freezing temperatures before energizing it? Is the factor that indicates it okay to energize the MPP Solar 2424 the presence of ambient 1 degree C temperature or higher?

Q3) When it's indicated to energize the MPP Solar 2424, is its sole source of power your battery bank or are other things energizing the MPP Solar 2424, and if so what (e.g. the generator)? When you wrote: "Then I will turn the unit on (the MPP Solar 2424??) which will then supply the power from my battery bank." did you mean to say that the unit will be supplied power from your battery bank?

I'm not trying to play word games...I just want to understand so I can help you.

Q4) Is the presence of current on the line from the MPP Solar 2424, which is designated to power the heating blanket the condition by which not only power for the heating blanket is switched from the Generator to the MPP Solar 2424, but is this the same condition that turns off the generator (buzz speak: grounds the magneto)?

Q5) If temperature remains above freezing you need not involve the generator or heating blanket, correct? In fact you need to have the MPP Solar 2424 energize the heating blanket, correct?

Q6) What happens if, while the MPP Solar 2424 is operating, the temperature dips below freezing. Do you want to close the circuit from the MPP Solar 2424 to the heating blanket? If so at what temperature do you want this to happen (e.g. 5 degrees C)?

Q7) What happens once the heating blanket brings things above freezing? Is there a temperature where you want the heating blanket to cut out?

Q8) What turns off the MPP Solar 2424, the lack of sunlight?...the lack of above freezing temperatures if the heating blanket doesn't work? Both, neither, something else?

Q9) What fuel do you plan on running the generator with?.. Gasoline? Do you have access to propane or piped in natural gas?

Q10) Is this the sole purpose for the generator?

There are cheaper automatic transfer mechanism to come by. The won't though be up to the US home standard of UL 1008 for automatic transfer switches. I don't know the Canadian equivalent much as I strongly suspect one that's comparable exists.

The link to your autostart device is not only an expensive unit, but just a manually starting device from a distal location. If you run gasoline you still may need to physically visit the generator to fuel up...not to mention manually engage other parts of this process.

A GSCM or GSCM mini from Atkinson Electronics can start or stop your generator based on shorting its pins 5 and 6, or stopping the generator by unshorting these points on the device. Sensors that measure things like temperature, lumens, time of day, or voltage etc. could be attached as indicated. One customer of US Carburetion, who sells gasoline to propane/gasoline/natural gas conversion kits for generators, fired up their generator from a large propane tank in the field, based upon the level of water in an animal drinking trough, energizing the pump to supply more water. In that case it was cheaper than having the utility draw another power line from a pole. My point is pretty much anything that's measurable can serve as the reason to turn on or off a generator with battery crank. Some customers have their systems set up to crank the generator simply if its cranking battery runs low, so as to power up it's own battery.

~~~~~~~~~~~

If I'm correct, this setup is all about insuring that the MPP Solar 2424 is not energized below freezing, correct? If so, is a larger battery bank to solely energize the heater, and possible more solar panels not feasible as a solution, bypassing the MPP Solar 2424 until above freezing temperatures have been reached?

 

[teotwawki.je]

Bit of a diversion from your initial plan but why not use low voltage DC heat pads (E.g. as used in 3D printers) powered by a PID from the battery? That's what I've built for a 48V barge installation. The only time this would not work is if you drain the battery completely while below freezing.

Also, if it's a Lithium Ion chemistry, you can use the battery while below freezing - E.g. to run the heat pads. It's just that you can't charge it while below freezing.