What size generator?

[RCinFLA]

I believe Victron LF inverters do have user setting for maximum AC input current allowed. (load shaving)

Charging from AC input will be limited by charger parameter settings or maximum AC input allowed.

When AC output exceeds user set AC input limit, AC output will be supplemented by battery power through inverter. This is great for smaller generator operation.

AC output load has first priority on limited AC input power. As AC output load increases there will be less overhead AC input power available for battery charging. This is a smooth transition from charging battery to drawing from battery to support greater AC output loads.

The AC output load can exceed what generator or inverter is capable of individually by combining power from both sources.

There is a small response time in the order of 10-20 msecs for AC output surge loads before inverter/battery picks up any excessive AC output surge load current. This can cause generator to momentarily bog down from momentary surge current, causing a shift in its AC frequency output, which causes inverter to release from generator. As long as inverter can support AC output load, the inverter will not shut down for overload and the inverter will resync and reconnect to generator again after a 20 sec to minute gap.

 

[photomankc]

LOL... this adds a wrinkle. Kind of a both worlds thing:

https://a-ipower.com/products/gxs7101ird-remorte-dual-fuel-inverter-generator

My inlet is 240V capable. I COULD use a generator like that to get two branches of juice. Break the hots out and send one to the outlets and the external chargers. Then one to the inverter. That would leave the full 30A capacity of one leg for cabin loads via bypass and up to 19A to power the chargers. That means no consumption from battery during generator run time and plenty of juice even to likely start an AC while charging.

That assumes the charger on the 6500 can be disabled or can co-exist at lowest setting with the other charger/s.

So that leads to another question... are parallel chargers okay? One 30 or 35A is hard to find but two 18A would do the job assuming they can coexist.

 

[photomankc]

Alrighty. I thought you said 5K watts, not 3, but maybe I wasn't paying attention. On my off toad trailer, I have 200watts solar, + 600 portable in needed, 206Ah LifePo4 + 2000 watt inverter if needed. Obviously, I don't run the 13K AC off the batts, and rarely the micro. Water heater and furnace are propane, as is the fridge.

I'm not the OP and I think you are correct, he referenced a 5000W inverter and a recommendation he got for a 10KW generator.

Yeah, I get it. I am no EE, just trying to compare your interesting project with a somewhat similar use case. It seems to me that with a "Tiny" house you have a huge advantage over any travel trailer or camper in that you can insulate to whatever specs you want. Travel trailers are mostly all very poorly insulated. I am just speculating but from what I know, good insulation isn't cost prohibitive, and can make a large difference in energy consumption. Sounds like low hanging fruit to me, anyways.

I'm 2x4 walls and going to use a lot of rock-wool insulation. Still R13 or so but adds quiet. Way better than trailers but still not amazing. Heat will be propane though and cooling is really a very once-in-a-while thing. Not much fun to be outdoors near Arkansas in late June/July/August so I just stay away.

Do you mean an RV style water pump, or this a pump part of the combi unit? My RV pump doesn't use much power. Hard to avoid the power drain from the micro, but I don't use mine much, so not a problem for me off grid. But it's understandable that you want to include that.
I do all of my cooking with propane, it sounds like you need/want electric. That's cool.

Probably a 1/2HP shallow well pump and tank. I looked at continuous run pumps too but think I'd prefer the pump/tank. Electric for cooking is limited to microwave and kettle/coffee pot mostly. The kettle I kind of got attached to. Getting 1.5L of boiling water in very short time is really nice, and I don't have to break out the camp stove and pots. Microwave is nice because I bring leftovers to warm up most construction trips. Again, convenient to just pop in and eat vs cooking after swinging a hammer all day.

It really didn't sound like you were refuting my comments, I was just expressing my interest in your project. It sounds like fun to me.

It is fun. Having the lights on without a generator running for the first time was GREAT!

 

[sunshine_eggo]

I believe Victron LF inverters do have user setting for maximum AC input current allowed. (load shaving)

Yes. One needs:
USB-MK3 + VEConfig or Victronconnect
VE.bus smart dongle + victronconnect (can only change the AC input value but monitor all others)
External control panel that allows one to set AC input with a dial.

Charging from AC input will be limited by charger parameter settings or maximum AC input allowed.

Yep. First one hit establishes the limit.

When AC output exceeds user set AC input limit, AC output will be supplemented by battery power through inverter. This is great for smaller generator operation.

Yep, and the inverter is AGGRESSIVE in protecting AC input. It will initially supply DOUBLE the overage to prevent exceeding AC-in even momentarily. If load stabilizes, it dials back to 1.0X. This is a programmable value that defaults to 2.0.

AC output load has first priority on limited AC input power. As AC output load increases there will be less overhead AC input power available for battery charging. This is a smooth transition from charging battery to drawing from battery to support greater AC output loads.

Confirmed. Power loads with AC-in and charge with surplus up to AC input limit or charger output limit. It is smooth, but you hear it when it happens. She growls.

The AC output load can exceed what generator or inverter is capable of individually by combining power from both sources.

Confirmed. One has to size Victron AC output wires for the max AC-in + PowerAssist.

FWIW, If powerassist is not enabled, one can readily overload the generator regardless of the AC input setting.

There is a small response time in the order of 10-20 msecs for AC output surge loads before inverter/battery picks up any excessive AC output surge load current. This can cause generator to momentarily bog down from momentary surge current, causing a shift in its AC frequency output, which causes inverter to release from generator. As long as inverter can support AC output load, the inverter will not shut down for overload and the inverter will resync and reconnect to generator again after a 20 sec to minute gap.

I'm guessing that's the "growl" I hear...

 

[photomankc]

Yep, and the inverter is AGGRESSIVE in protecting AC input. It will initially supply DOUBLE the overage to prevent exceeding AC-in even momentarily. If load stabilizes, it dials back to 1.0X. This is a programmable value that defaults to 2.0.

Yeah that's awesome. The cheap-o's just slam the generator with the whole load then shrug their shoulders when it falls over.

 

[sunshine_eggo]

Yeah that's awesome. The cheap-o's just slam the generator with the whole load then shrug their shoulders when it falls over.

Exactly what the Victron does if PowerAssist is disabled... Learned that for myself.

 

[RCinFLA]

Inverter is 60Hz (or 50Hz) so control sensing is dealing with a sinewave that is 16 msecs long. This limits reaction time to about half to one cycle of AC depending where a sudden surge current hits in the sinewave cycle. Then there is a little time for inverter control to readjust PWM sequencing in inverter feedback control to the LF transformer drive to feed greater AC supply current to the AC output current.

This is why up to a couple of AC cycles of a sudden AC surge current, like a single phase motor starting up, may make it through inverter to generator. Usually, it is just a small bump in the road to the generator. Single phase motors take about 0.3 to 0.5 seconds to spin up so most of any starting surge beyond inverter AC input current limit will be covered by inverter/battery.

 

[12VoltInstalls]

If I was the OP I would omit supplying all that stuff and just say the thing is "solar ready" or some such nonsense.

If people want an offgrid teenyhome they should learn how to live offgrid. If they need a generator they can buy one.

folks I know with very large 5th wheel RV's and other large TT's all seem to get by quite well with no more than <=4500 watt gennys when boondocking. (including PV, of course). With my own small (18ft) trailer, I run the 13K AC and micro with a 2200 honda

cuz you know how to manage and not be dumb

 

[12VoltInstalls]

Having the lights on without a generator running for the first time was GREAT!

It weirded me out for a few years (and still does!) that I can do whatever I want without a grid connection (within limits but the limits aren’t a big deal). I have no generator either.

 

[Checkthisout]

It weirded me out for a few years (and still does!) that I can do whatever I want without a grid connection (within limits but the limits aren’t a big deal). I have no generator either.

I have a generator and it still weirds me out, especially when it's stormy and all power is out, trees are down and I get the recreational property and everything is normal as it is any other time. Internet works (cellular) . All lights on etc.

 

[AstroBob]

It weirded me out for a few years (and still does!) that I can do whatever I want without a grid connection (within limits but the limits aren’t a big deal). I have no generator either.

But it's a nice weird to have, ain't it?

 

[RCinFLA]

Saw this video on Victron's 'dynamic assist' feature that provides a 'rate of change' limiting on AC input. This feature is probably most useful for inverter-generators in ECO mode where generator rpm is modulated based on AC output load on generator.

The difference between 'limiting AC input current' and 'dynamic assist' is limiting AC input does not start the inverter reaction time until AC input current limit is reached, while the 'dynamic assists' starts the inverter supplement as soon as AC input current starts to rise before AC input current limit is reached, then gradually backs down inverter supplementing assist to let AC input take the limit of AC input. This gives the inverter feedback control a jump on covering a sudden surge, not having to wait until AC input limit is reached before it gets involved. This should reduce initial surge leak-through to generator, like starting an air conditioner.

The obvious advantage to inverter-generator variable rpm ECO mode is lower generator noise and some fuel savings.
Disadvantage is, in response to a step increase in AC load, the inverter-generator has to increase its engine rpm which takes a second or two. During this rpm ramp up, the generator's alternator is unable to supply the peak load current so the output AC sinewave voltage peaks from inverter-generator's inverter are clipped.

For a conventional synchronous fixed 3600 rpm generator there is a lot more stored mechanical energy reserve in the 3600-rpm rotating engine flywheel. Just need a good stable engine speed governor control that does not vary with generator loading to keep generator AC output frequency from varying too much, which if more than about 0.3% per second wobble, will cause inverter to be unable to track phase with generator and causes inverter to release from generator.

 

[OffgridMatty]

I ordered the eg4 30A charger from Signature Solar. It’s permanently connected to my bus bars and charges my two 24v Lifepower4 batteries without issues. I use a Honda EU 2000 generator when charging.

 

[John Frum]

I ordered the eg4 30A charger from Signature Solar. It’s permanently connected to my bus bars and charges my two 24v Lifepower4 batteries without issues. I use a Honda EU 2000 generator when charging.

Do you not have an inverter_charger or all_in_one?

 

[OffgridMatty]

All in one. Growatt 3kW Stackable Off-Grid Inverter | SPF 3000TL LVM-24P

 

[John Frum]

All in one. Growatt 3kW Stackable Off-Grid Inverter | SPF 3000TL LVM-24P

I'm curious why you would use a dedicated charger when your Growatt has an ac2dc charger built in?

 

[OffgridMatty]

I guess I didn’t trust the growatt. I also bring the batteries home in the winter and wanted to option to charge at home with my grid ac. I leave the growatt at the cabin year around. Still figuring it out and probably making mistakes along the way. I just bought the cabin this season so over time I’ll probably fine out what works best.

 

[photomankc]

I'm curious why you would use a dedicated charger when your Growatt has an ac2dc charger built in?

Wouldn't it have the same issue we are discussing above though? That is if he uses the all-in-one to charge then his AC loads through the unit are also attached to the generator?

 

[John Frum]

Wouldn't it have the same issue we are discussing above though? That is if he uses the all-in-one to charge then his AC loads through the unit are also attached to the generator?

The efficiency is lower for the ac loads with a dedicated charger.

With the all_in_one charger the ac loads are powered by the generator and the battery is charged by the all_in_one's charger.
There is no conversion loss for the ac loads and ~80% conversion efficiency for the battery charger.

With the dedicated charger there is ~80% efficiency for the charger(ac to dc conversion) and a compounded 85% efficiency for the inverter(dc to ac conversion).

That is ~68% overall efficiency for the ac loads vs 100% efficiency for ac bypass.

 

[photomankc]

That's great... if you have the watts to do both. If you have 1800 running watts to charge and supply the cabin you don't have a lot left over. Efficient or not.