Transfer Switch Wiring Help for OffGrid System with Generator Backup

[kalebcrafts]

Hi All, I'm pretty new to this solar thing. I'm not a licensed electrician. I'm a DIY guy trying to build an offgrid cabin. I've got a 3700 watt solar array (10 370 watt panels) with (2) Rich Solar 3000 watt inverters and (2) 5.3kw BigBattery Li batteries. I don't have a massive power load (the cabin is pretty small). However, I do want to have a propane generator to backup the solar when it's hot and I run a little window AC or if it's cloudy for a few days, etc. I'd also like the generator to not just power the loads, but to charge the batteries when the sun can't. The generator I've got is a 14kw Kohler Propane Generator.

So, my question is what is the best to set this up to be automatic and pain free. I was thinking I'd need an automatic transfer switch. My thought was to run the AC output from the solar inverters to the supply side of the transfer switch so it is the primary power source. Then if the voltage coming from the inverters/batteries drops the transfer switch would engage and the generator would kick on and begin power the loads. Am I thinking through this correctly?

My only concern would be, how do I then have the generator also charge the batteries in the solar setup? I'm thinking i would need an additional panel/circuit that is only powered when the generator comes on that powers an AC charger that I can wire to the batteries?? How would I do that? Or is there a better way to do this? Thanks in advance!

 

[time2roll]

The transfer switch should come with a wire diagram that shows generator vs inverter(utility) inputs and output to your loads.

If the generator has multiple outlets I would just plug the charger into the generator direct.

 

[DIYrich]

Transfer switch is expensive, plus the cost of something like a chargeverter to charge the batteries.

Consider switching to something like the eg4 6000xp. It can do what you want.

Although if the AC puts you over 6000 watts, you may have to put it on the generator side, and not through the 6000xp. Then you would have to manually start the generator whenever you start the AC. Or you could parallel a second 6000xp.

 

[DIYrich]

So, my question is what is the best to set this up to be automatic and pain free. I was thinking I'd need an automatic transfer switch. My thought was to run the AC output from the solar inverters to the supply side of the transfer switch so it is the primary power source. Then if the voltage coming from the inverters/batteries drops the transfer switch would engage and the generator would kick on and begin power the loads. Am I thinking through this correctly?

You are missing what happens next. ATS transfers to generator (with a glitch in power). With load disconnected from inverter, the voltage recovers, and ATS switches back. Cycle repeats every few seconds (or whatever delay period the ATS has to switch back to primary). Not good.

 

[50ShadesOfDirt]

An ATS is there to sense grid-down, and switch on the generator for power, and then reverse the process when grid-up, all automatic operation.

What OP has is off-grid, so I see these choices:

1. what is the inverter, and does it support auto-gen-start; if it doesn't, could it be made to do so?
2. kohler probably already supports auto-start, so look at their diagrams/docs for 2-wire start or similar
3. what (alternative) mechanism to sense the need to start the gen (usually, in off-grid, it's to recharge the battery-bank)

For 1., if you can get your inverter to sense low battery-bank and start the gen, and you've got the kohler hooked up to do so, that's the desired end-state. As other post indicates, maybe OP inverter doesn't support this, and another brand/model would do it much better, at the cost/headache of an inverter replacement.

For 2., normally, ATS is provided by generator manufacturer, so the two work together really well. What does kohler offer, and can you get that ATS offering to sense the need to recharge the battery-bank. Does their offering play well in off-grid scenario?

For 3., you could, if running a huge load, just fire up the kohler from it's control panel (if it was like my old generac, just take out of auto-mode, and fire it up in manual-mode), or perhaps find a "remote start" kit, if offered. If you really want "automation", then perhaps the huge field of arduino-like solutions might allow some cobbling-up of automation, once you've sorted 1. and 2.

For various reasons, I had to bail on Generac's, and I've settled on Westinghouse propane gens ... cheaper, easier to maintain, auto-choke, auto-start, remote fob start, smart-port (for a westinghouse external ATS box) which allows me to put them in "vacation mode" where the gen senses the need to come on, recharge battery-bank for a period of time, and then shut down.

Hope this helps ...

 

[Snaketzu]

For 1., if you can get your inverter to sense low battery-bank and start the gen, and you've got the kohler hooked up to do so, that's the desired end-state. As other post indicates, maybe OP inverter doesn't support this, and another brand/model would do it much better, at the cost/headache of an inverter replacement.

This is the most desirable end state, in my opinion. You want an inverter that can handle managing the generator, which generally means sending a start signal when the battery state of charge reaches a programmed low point and uses it to charge the batteries back up and then shuts it off (of course it will assist with loads while it is running, adding to the pool of available current). As a bonus, this negates the need for (and expense of) the transfer switch.
DO NOT put a grid tied solar system downstream of a standby generator transfer switch. I can't speak to every single inverter model out there, but most inverters don't have the capability to tell whether the incoming power is actually grid or the generator, and generators ARE NOT meant to be backfed. Bad things will happen and you won't like them.
Whatever equipment the OP has or may otherwise prefer is immaterial. Use the right equipment for the job at hand. If you want a backup generator, you need the correct equipment to make use of it.

 

[kalebcrafts]

Thanks everyone for your help. After some research it seems my inverters actually do have an auto start gen feature and I can set the voltage of the batteries for cut in and cut out. Then I just have to wire that to the 2 wire start for the generator.

Also, 50shades, I think you are right that if I know I'm going to run a larger load and us an Mini Split for the afternoon I could just manually start the generator to supply the additional power needs and set the inverter to use utility/generator first and charge the batteries simultaneously.