Inverter/Load Question

I've moved into a fully off grid subdivision and a couple of my neighbors have warned me off using appliances (e.g. a vacuum and my radial arm saw), not for the grid cannot handle them, but because of the ramp up stress it puts on the inverter.

One man uses his generator (so the load switches to it instead of the array) during these usages, and even suggested using a fridge that runs continually, versus one that starts up and puts a big load on the inverter (as does the well pump, for example).

I'm only a year into this, so I'm curious what others think and do with large, short lived loads, or fridges overall.

Thanks.

Hi Joe;
I've been %100 off grid since 1983.
Depending on your system voltage and capacity.
Large draw items are better to run from a gen set.
Its just easier on the whole system. Never considered it being "tough " on the inverter... more like tough on the battery's.

Having said that they tell me that these "new"  48 volt systems with mppt  charge  controller's can run 240 volt or high draw equip. easily .

At my house we run the genny for microwave, vacuum, blow dryers... anything high draw.

Now refrigerator's,   I have always used propane.    Amish built Diamond brand 17' fridge is highly recomended!
However if my Diamond ever needs replaced, I will go with a Sundanzer 12 volt fridge.
I purchased their 12 vt chest freezer 2 years ago and I love it so much, I preordered another one as soon as the factory is back in production!

Hi Joe. Tell us about your system. The inverter, the battery capacity and the solar array. My inverter is a 4500 watt magnum and any of those loads you mentioned can be started and run off it. It's more a question of the quality of the system then any hard fast rules...

Hey, thought I would throw in my 2 cents. I use a chest freezer with a thermostat control unit as my fridge - its completely plug and play, and a much cheaper route than going with a DC fridge, while still having great insulation. You do have to stack all your stuff in there from the top, which can be challenging at times. Mine is only like 5 cu ft, so the compressor is tiny. It pulls 85 watts or something like that running, so the startup surge is probably only a few times higher than that. Unless you have a monster fridge, the startup is probably not insane.

Big tools will have a much more significant surge, but it is very short, so as long as it falls within the surge rating of the inverter I do not see why it should really be a problem. Some watt-meters will show you the peak wattage, so you could use that to get an idea of what sort of surge you are seeing. I have built up a set of battery powered tools, and that is a great way to go when living off grid. I have enough batteries floating around now that I can get a lot of work done, and just charge the packs when the sun is out. They are not as powerful as corded stuff, but they are light-weight and its nice to not have to dangle cords everywhere when you are working.

As for well pumps, they make "soft-start" motors that ramp the current up slowly. They are a lot more than basic models, but the added electronic brain in it has other benefits. I think they are less likely to burn out if there is no water being pumped, for example. I move water up the hill from a spring to my homestead, so I use a half-horse well pump. It slowly ramps up to 1100watts, and has no problem running on a 1500w inverter that I have dedicated to that load.

Anything with an electric motor that starts under load will have an increased starting surge that's typically between 3 and 5 X the running power.  In the case of my well-pump that I run off-grid, it runs on about 2000W, but startup requires 9100W (3.8X).

A clamp meter with "inrush current" capability can accurately measure this.  If the people in this group are worried about starting power tools, and refrigerators, it's a sign that it's not that well a designed system.  Most likely they cut some corners to get it up and running.

I have a Schneider XW+4868, and I've run my well-pump, a cement mixer, and a circular saw all at the same time.  You could design something for yourself that could have worked better than what they have put together.

Thanks to all for your input. I truly do appreciate it. I felt the same as Michael Q - if you can't run your equipment, you might not have a well designed system.

Others have asked for a bit more data, but the old man I bought the house from lost a lot of food during a crisis here when he ran out of propane and the roads were such he couldn't get any more. So, he beefed up the battery storage and the grid soon before I bought the place. He said he could now run the electric fridge for ten days without any sun. This seems to be about right, by my math and the reserve in my batteries. I am on a 24 volt battery array and was told I have about 24.5 Kwh in reserve.

I do have a separate 220 inverter for the well pump, but I am pretty sure it's just pulling two 110 lines from the regular inverter.

I do run a house vacuum off it, do laundry via a washing machine, and run the shop tools (radial arm saw, table saw, lathe, drill press, etc.) and all seems okay. I use more on sunny days, etc. but I just get warned A LOT by folks out here to use the generator for vacuums and shop tools to save my equipment. Having to use the generator and fuel is a change in where you spend your resources, but not necessarily a savings, per se.

I was also surprised by Thomas R's message that since the 80's he is using a propane fridge. At 1.91 a gallon at the moment, I am curious but would prefer to continue to use the sun.  I only have seasonal road access, so depending upon a trucked in fuel would not make me happy over the long winters we have out here. Nor the cost. I might have to buy new batteries, but it's free in the interim.

Thank you all for the information. I enjoy this site.

Sounds like you are  well set up. Any idea what kind of solar array you have? Older systems undersized the array and oversized the battery. That could lead to the bank living in absorb and never reaching "full". That can shorten battery life. Sometimes a generator run is warranted even if you have enough sun just to do a full absorb and equalize.
So are the batteries approx 19 inches tall and 10 to 11 wide? 8 l16 would be about the size you quoted...

Thanks for that information. I do seem to spend far more time in absorb mode than float, if that's an indicator of such.

I have a 1200 watt array, and I was told it's capable of generating 3.5 to 5.5 Kwh per day based upon angle and where I am. So yes, I have more depth of storage than power to recover from such. As stated earlier, the old man I bought the place from wanted to run his fridge for ten days sans sun. I use between 1.3 and 1.6 Kwh in a normal day, up to 2 Kwh twice weekly.

I've only run the generator a single time in the year I've now been here (a low voltage disconnect), and that was partially my fault in a snow storm, for leaving things on I thought I had powered down. I think I'll take your advice and fire it up and see what happens to the float indicator. I appreciate it!

Joe Garland wrote:

I do have a separate 220 inverter for the well pump, but I am pretty sure it's just pulling two 110 lines from the regular inverter.

That's not exactly how it works.  A standard American home is supplied by three wires (+ ground), L1, L2, and Neutral.  L1 to neutral is 120VAC, L2 to neutral is also 120VAC, but when wired L1 to L2 you get 240V.  That's because L1 and L2 are 180degrees out of phase with each other.

With a 120/240V inverter, the inverter is dividing the outgoing power between L1 and L2.

What you must never do under any circumstances is to apply 120V to L1 and L2 from two different inverters, unless they are physically connected and communicating with each other so their output is in the proper phase.