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Old 08-07-2020, 14:32   #1
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The case for multiple small inverters

I had been looking at getting a big inverter (3kw) to run a refrigerator, chest freezer and whatever else, including microwave, dishwasher, washing machine.

The more I have looked into this, the more it seems thatís not the best way to do it.

Large inverters idling can use quite a bit of power.

Instead, Iím looking at getting a few small inverters. One for the refrigerator, one for the freezer, one for the microwave and whatever else, since they donít run simultaneously.

Anyone have any thoughts as to why this is a bad idea?

I would just wire them right in to the DC panel as DC circuits, but near the panel, there would be an inverter, which then runs an ac wire to the appliance.

The other, more general microwave inverter would run normally fully on the AC circuits with a transfer switch.
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Old 08-07-2020, 14:42   #2
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Re: The case for multiple small inverters

No answer but I too am interested in this theory.
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Old 08-07-2020, 14:45   #3
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Re: The case for multiple small inverters

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No answer but I too am interested in this theory.
I guess what Iím looking at is having the ability to scale the inverter(s) for more efficiency. Bringing them online when needed. Shutting them off completely when not needed.

Not possible with one big one.
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Old 08-07-2020, 15:13   #4
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Re: The case for multiple small inverters

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Originally Posted by Chotu View Post
I guess what Iím looking at is having the ability to scale the inverter(s) for more efficiency. Bringing them online when needed. Shutting them off completely when not needed.

Not possible with one big one.
I understand. I have a big honking Magnum that I never use because it almost draws more by itself than charging up my laptop does. So I have a small portable I use mostly.
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Old 08-07-2020, 15:16   #5
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Re: The case for multiple small inverters

Quote:
Originally Posted by Chotu View Post
I had been looking at getting a big inverter (3kw) to run a refrigerator, chest freezer and whatever else, including microwave, dishwasher, washing machine.

The more I have looked into this, the more it seems thatís not the best way to do it.

Large inverters idling can use quite a bit of power.

Instead, Iím looking at getting a few small inverters. One for the refrigerator, one for the freezer, one for the microwave and whatever else, since they donít run simultaneously.

Anyone have any thoughts as to why this is a bad idea?

I would just wire them right in to the DC panel as DC circuits, but near the panel, there would be an inverter, which then runs an ac wire to the appliance.

The other, more general microwave inverter would run normally fully on the AC circuits with a transfer switch.
Assuming you always run fridge and freezer, those should be on one unit rated to run both simultaneously. I would put microwave, dishwasher and washing machine all on another unit rated to run at least the two biggest consumers simultaneously.

Idling two small units isnít better than one unit that replaces both. But the other appliances you can switch it off
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Old 08-07-2020, 16:01   #6
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Re: The case for multiple small inverters

I did this on my boat for the TV. I connected a 400w inverter to the stereo breaker and connected the TV to that. That little inverter had very little parasitic drain but was still big enough to run the TV. If I was going to relabel the breaker panel I would call that one "Entertainment Center".
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Old 08-07-2020, 16:16   #7
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Re: The case for multiple small inverters

Wire the thermostat of the fridge to the on trigger of the inverter.
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Old 08-07-2020, 17:00   #8
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Re: The case for multiple small inverters

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Wire the thermostat of the fridge to the on trigger of the inverter.
Oooh!!!! Wow. Thatís good thinking!!!
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Old 08-07-2020, 17:09   #9
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Re: The case for multiple small inverters

Most modern 3kW inverters have a near zero standby power mode. It works great for fridges and the like. It probably wonít work with tiny loads like a clock on a microwave. A big inverter is very efficient. Also, pure sine wave is often not a feature of small inverters. Pure sine wave will be compatible with everything.

If it were me I would put a big inverter right next to the battery bank if possible.
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Old 08-07-2020, 17:14   #10
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Re: The case for multiple small inverters

also bear in mind you will need an inverter of about 400-500w to start a 100w domestic fridge compressor
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Old 08-07-2020, 19:28   #11
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Re: The case for multiple small inverters

Quote:
Originally Posted by Chotu View Post
I had been looking at getting a big inverter (3kw) to run a refrigerator, chest freezer and whatever else, including microwave, dishwasher, washing machine.

The more I have looked into this, the more it seems that’s not the best way to do it.

Large inverters idling can use quite a bit of power.

Instead, I’m looking at getting a few small inverters. One for the refrigerator, one for the freezer, one for the microwave and whatever else, since they don’t run simultaneously.

Anyone have any thoughts as to why this is a bad idea?

I would just wire them right in to the DC panel as DC circuits, but near the panel, there would be an inverter, which then runs an ac wire to the appliance.

The other, more general microwave inverter would run normally fully on the AC circuits with a transfer switch.
I have a 3Kw pure sine inverter with ability to supply 6kW for 5 min and 9kW for 30 seconds. When idle it draws ~2 to 4 amps (at 12 Volt, the higher value is when fans are still going), but if no load is detectable for a period (time can be preset) it goes to sleep, and idle/sleep current is then around 1 Amp. On my unit the threshold of detectable load is adjustable from 1 to 99 Watts.

If one would install several smaller inverters, I would not be surprised if the combined idle currents of all the inverters would add up more than 1 Amp.
Furthermore, a lot of smaller (cheaper) units might not have sophisticated features, like sleep mode.
BUT..... an idle/sleep current of 1 Amp is still 24 A/h a day, still quite a draw if battery capacity is limited.

I just brought secondhand a second inverter (600 W also pure sine), its main use is for the little shelf where I charge all the electronic toys/tools. Idle current is only 0.2 to 0.3 Amps. The big inverter is usually switched off. Likely the small inverter will remain on 24/7.
Lastly, I use USB and USB-C charger points on that little shelf, directly powered by the 12 Volt house battery, no need for an separate inverter.
Computer is powered directly (hmmm, via a bucks converter, with an idle current of 80 mAmp) from the 12 Volt house battery, no need for an inverter there either.
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Old 08-07-2020, 19:36   #12
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Re: The case for multiple small inverters

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Most modern 3kW inverters have a near zero standby power mode. It works great for fridges and the like. It probably wonít work with tiny loads like a clock on a microwave. A big inverter is very efficient. Also, pure sine wave is often not a feature of small inverters. Pure sine wave will be compatible with everything.

If it were me I would put a big inverter right next to the battery bank if possible.
I agree with this. If you can't afford the small amount of standby power loss, you need to look at your battery bank harder. Also, when in economy mode, it only draws 15 watts / hour while allowing your clocks and small loads to operate. I have to use this as my refrigerator needs constant power to run it's controller. Even smaller inverters will still have a similar draw.
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Old 08-07-2020, 23:00   #13
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Re: The case for multiple small inverters

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also bear in mind you will need an inverter of about 400-500w to start a 100w domestic fridge compressor
I donít think this is right.

Inverters are sold based on their continuous output oddly enough. Most can handle near double their rating for brief intervals like the LRA of a compressor.

So a 300 watt model is supposed to be able to deal with the lra of 600 watts, yes?

Wouldnít that work just fine for the compressor startup?
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Old 08-07-2020, 23:05   #14
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Re: The case for multiple small inverters

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Originally Posted by Palarran View Post
I agree with this. If you can't afford the small amount of standby power loss, you need to look at your battery bank harder. Also, when in economy mode, it only draws 15 watts / hour while allowing your clocks and small loads to operate. I have to use this as my refrigerator needs constant power to run it's controller. Even smaller inverters will still have a similar draw.
Ok, what inverter is this, so I can compare?

Edit: found it. It’s the victory 2kva.
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Old 08-07-2020, 23:24   #15
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Re: The case for multiple small inverters

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Originally Posted by Palarran View Post
I agree with this. If you can't afford the small amount of standby power loss, you need to look at your battery bank harder. Also, when in economy mode, it only draws 15 watts / hour while allowing your clocks and small loads to operate. I have to use this as my refrigerator needs constant power to run it's controller. Even smaller inverters will still have a similar draw.
Where are you getting 15 watts?

I see 36 watts as the absolute lowest the 2kva unit uses when itís completely off and looking for current to turn on.

Next level is AES mode and thatís 7 amps or 84 watts on standby.

24 hours of power completely off with no clocks on is 72 AH wasted.
24 hours of that AES is 168 AH wasted.

These are big numbers to just waste no matter how large your battery bank is.

This type of inefficiency is what Iím trying to avoid.
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