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Old 01-20-2020, 11:30 AM   #1
Bob Laps
 
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Default 2 inverters?

I have a question about running 2 inverters....what I want to do is have a large (2000w) inverter powering all my outlets but I also want a small (300w) inverter powering all my outlets for when I’m not running a large load (coffee maker/micro)....not sure if one inverter would “back feed” the other and damage it...thanks

Bob
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Old 01-20-2020, 11:44 AM   #2
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Default Re: 2 inverters?

No problem,

EDIT: as long as you do NOT do the "all outlets" bit.

The inverters' outputs must in effect be isolated from each other.

Which can be done by only having one turned on at a time, but of course relying on human common sense would be stupid.

Many "mostly DC" rigs prefer to dedicate a well-matched smaller unit per appliance so it's only switched on when in use, much better for mostly-solar efficiency than using a big one, especially if left on for hours.

Last edited by john61ct; 01-20-2020 at 04:27 PM.
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Old 01-20-2020, 12:25 PM   #3
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Default Re: 2 inverters?

Awesome...thanks John
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Old 01-20-2020, 02:04 PM   #4
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Default Re: 2 inverters?

Counter point to running two inverters is if you have a quality, 2k watt inverter, it may only be drawing 9 -20 watts at idle. Given such a low draw that may reduce the need for redundancy.
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Old 01-20-2020, 02:46 PM   #5
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Default Re: 2 inverters?

Quote:
Originally Posted by john61ct View Post
No problem, inverters' outputs are in effect isolated from each other.

Whoa whoa whoa - I'd take this with a real grain of salt. Are you suggesting it is OK to parallel asynchronous inverters? And that there are no dangers in doing so?

The "right" way to do this, in my opinion, is with a transfer switch. Not expensive or difficult. Another way would be with a center-off-DPDT switch on the inverter outputs. Both methods will require a good awareness of the overload limits of the smaller inverter. Resettable fuses/circuit breakers on the smaller unit would also be desirable for the occasional overload trip.

Last edited by rollerbearing; 01-20-2020 at 02:56 PM.
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Old 01-20-2020, 03:28 PM   #6
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Default Re: 2 inverters?

Quote:
Originally Posted by rollerbearing View Post
Are you suggesting it is OK to parallel asynchronous inverters?
Wut?

How did you get that idea?

No. Your DC buss is the backbone, use of inverters is intentional as little as possible, most devices are DC native for off grid living, mostly-solar high efficiency.

Inverters are point of load devices, output goes to the appliance each services, or perhaps an AC circuit servicing multiple, but then the user need to be au fait not overloading.

No AC connection between the output side of multiple inverters.
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Old 01-20-2020, 03:55 PM   #7
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Default Re: 2 inverters?

Quote:
Originally Posted by john61ct View Post
Wut?

How did you get that idea?

No. Your DC buss is the backbone, use of inverters is intentional as little as possible, most devices are DC native for off grid living, mostly-solar high efficiency.

Inverters are point of load devices, output goes to the appliance each services, or perhaps an AC circuit servicing multiple, but then the user need to be au fait not overloading.

No AC connection between the output side of multiple inverters.
Carefully read Bob Laps question. He very specifically asked about backfeed on the AC side (implying parallel operation) and your answer gave the impression that there is no concern.


Quote:
Originally Posted by Bob Laps View Post
I have a question about running 2 inverters....what I want to do is have a large (2000w) inverter powering all my outlets but I also want a small (300w) inverter powering all my outlets for when I’m not running a large load (coffee maker/micro)....not sure if one inverter would “back feed” the other and damage it...thanks

Bob
Quote:
Originally Posted by john61ct View Post
No problem, inverters' outputs are in effect isolated from each other.

Many "mostly DC" rigs prefer to dedicate a well-matched smaller unit per appliance so it's only switched on when in use, much better for mostly-solar efficiency than using a big one, especially if left on for hours.
Quote:
Originally Posted by Bob Laps View Post
Awesome...thanks John

Last edited by rollerbearing; 01-20-2020 at 04:08 PM.
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Old 01-20-2020, 04:06 PM   #8
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Default Re: 2 inverters?

Would someone educate me as to why this would be a desirable thing to do?

I always assumed that the larger capacity inverters were just that. Inverters capable of powering up to 2000w (or whatever). So they should easily be capable of powering the lower 300w demand.

What would be the advantage of having two different inverters? A single 2000w inverter would seem to make more sense to me - but I'm here to learn!
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Old 01-20-2020, 04:09 PM   #9
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Default Re: 2 inverters?

I would def not recommend that, why I stated the AC sides should be isolated from each other.

As in physically, each inverter output a completely different circuit, other than chassis reference ("grounding") in common
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Old 01-20-2020, 04:10 PM   #10
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Default Re: 2 inverters?

Spark Plug,

Smaller inverters can have lower idle current. Also, people occasionally supplement a cheap beefy modified sine inverter with a lower cost smaller pure sine wave inverter.

Last edited by rollerbearing; 01-20-2020 at 04:15 PM.
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