Best way to use two inverters for one load?

HRTanner

I have been noticing several people have a "Daytime" system and "Night" system, which really intrigues me. As several people have noticed I have an inverter/charger that is way overboard for my daily load, but I don't want to get rid of it because it handles everything I would want to run at one time, as long as the sun is up. When the sun goes down the inverter "uses" more power than the house, just to stay on.

So I'm thinking I may just put together a "Night" system to power just my LED lights and Satalite TV/Internet, using a much smaller and more efficient inverter. This would be powered by a 2/2 configuration of 12v-200ah batteries, and charged by a 2/2 config of 285w PV panels.

So the question is, how to hook both inverters to my house power panel, whithout causing any feedback or anything else I don't know would happen?

Any expert advice is greatly appreciated.

mcgivor

Thiss can be accomplished with an auto transfer switch with the main inverter on normal power and the smaller on standby. This could be timed, which is how I do it, by programming an invert block period, not possible with many inverters, but with some creative thinking almost anything is possible, or the inverter could be manually turned off. This is the transfer switch I use for reference 

 https://www.aliexpress.com/item/ATS-2P-63A-230V-Micro-Circuit-Breaker-Dual-Power-Automatic-transfer-switch-Auto-transfer-switch/32868401442.html?

HRTanner

Awesome, that's exactly what I need, as I plan to have the larger inverter as the main so I can just turn on the smaller inverter and turn the main off. Simple.
Thank you very much.

Estragon

I have multiple circuits that can be run from either the big inverters, or a small 300w Morningstar, so I used a panel like this:

https://www.homedepot.ca/en/home/p.60-amp-generator-panel-with-18-spaces-36-circuits-maximum.1000722301.html

Another regular panel has the circuits running stuff like pumps that can only run on the big inverters.

BB.

You can also get manual genset transfer panels... You can wire the main panel to your main AC inverter... And the small inverter to the "generator" input... And switch circuits between Main/Small inverter as needed.

Personally, I highly suggest that if you do have a large/small AC inverter (eventually, you should change out the big inverter to something a bit nicer).

And that you only have one battery bank/Solar array/solar charge controller(s).  Keep the one bank happy is difficult enough--Having two banks and solar arrays+chargers--Now you have 2-4x the number of issues.

Finding "smaller" 48 VDC inverters can be a bit difficult... But I believe you will be much happier.

Cotek (and Samlex) inverters are pretty decent inverters (Quality/$$)... Here are some 48 VDC input inverters from our host NAWS:

https://www.solar-electric.com/residential/inverters/off-grid-inverters.html?nav_inv_input_voltage=439

-Bill

t00ls

HRTanner said:

. As several people have noticed I have an inverter/charger that is way overboard for my daily load,
When the sun goes down the inverter "uses" more power than the house, just to stay on.

what...how is the inverter using more power than what loads are on...very inefficient or something is wrong with it

BB.

In general, a "small" (few hundred Watt) AC inverter can use 6 Watts just turned on a running (Tare Load).

Larger inverters (in the 1,000's of watts) can use 20-40 Watt just turned. Seen some of the large, less expensive, AC inverters use even more.

40 Watts * 24 hours per day = 960 WH per day

A  very conservation minded home/cabin can use as little as 3,300 WH per day (fridge, lights, washing machine, well pump, TV, laptop).

So--For smaller systems, yes, Tare Losses can be a significant load for off grid solar power systems. 40 Watt Tare Load is about the average load for a Energy Star rated full size refrigerator (1,000-1,500 WH per day in moderate climate).

-Bill

t00ls

never mind...I see it now
Input Specifications

• Nominal Input Voltage: 48.0Vdc
• Low Battery Alarm: 42.0Vdc-44.0Vdc
• Low battery Trip: 40.0Vdc-42.0Vdc
• High Voltage Alarm: 64.0Vdc
• Low battery Voltage Restart: 62.0Vdc
• Idle Consumption: 200 Watts
• Power Saver Mode Idle Consumption: 40 Watts
• Automatic transfer switch - 63A @ 220/230/240V
• Bypass - 63A @ 220/230/240V
  
  idle consumption is 200 watts.....wow...I would get rid of that thing
  

Estragon

An inverter may have  85-90% peak efficiency, but be near zero with a very light load relative to capacity.  My Outbacks use ~35w just being on, so 45w to run (eg) 10w load.  Run that 24hr, and it's 1000 watt-hrs for a 240wh load.  Mine are master/slave, so another ~200wh to keep the slave on standby, and becomes a fridge magnitude load which needs to be considered in planning.

I turn the big inverters off when not needed overnight etc.

Tecnodave

I'm doing much the same but both inverters can run on either bank, Big inverter is MagnaSine MS-4024AE 120/240 4 kW , the smaller one is either a Cotek SK-1500 or a Exeltech 1100 watt unit. Cotek is for general duty and Exeltech is much quieter EMI wise and is used for communications. I use Square-D QO line generator transfer panels to switch in units used , 2 of them. One switches big/small the other switches between small inverters. I don't have breakers in those I use Square D QO Line switches meant for air conditioner cut off switches......Part QO 200..... note 2 pole 00 amp.  (they are not breakers so no amp trip rating)  These switches are rated 60 amps and are very rugged.

Bit it of added info. Generator transfer panel is Square D QO 4/8 panel with solid copper busses. Most all small panels have tin plated aluminum busses. This panel will only take 2 double space 240 volt breakers and those are occupied by the QO line switches. My breakers are in separate QO line panels. 

david

jonr

Don't judge new inverters based on inverter size - check the actual minimum consumption while working (not stand-by idle).

westbranch

Dave you lost me somewhere...

Are you running 2 of your Inverters constantly or when/where/how do you shut off the unused Inverters ie DC feed.

tks

Tecnodave

WB,
No I normally run the MagnaSine day times and the Cotek when there is little load. The Cotek is more efficient at small loads than the MagnaSine, and I don't need 120/240 most times. The inverters are turned off when not used. Switching from bank to bank is done with MidNite 4 gang switches found in MidNite garage sale. These were 4 switches 150 volt 156 amp wired in series for an early birdcage project that was scrapped. I machined copper plate to gang them in parallel , walla a 150 volt 624 amp switch for $10.00 plus labor.  The little inverter is very quiet EMI wise and is used during radio programs that are faint here. No I'm not a ham. Just a broadcast junkie that does not want to hear the same music again . Shortwave radio.

David

Tecnodave

WB,

Littlr edit for clarity,
The inverters are turned off at the inverter control panel itself....I leave the DC on to not shock the caps at startup. Easier on the gear.

david

Tecnodave

Estragon,

I am sure that with only a 10 watt load your outback is using way more than idle plus load. The 85-90 percent effenicy is at 60-80 percent of full load .  Most 4kw inverters are about 30-40% efficiency at 10 watts so maybe 70-100 watts from battery to power that 10 watt load.

david

Saipro

My 4kVA MustPower/PowerStar uses about 100W idle consumption. The higher the load, the less it burns on its own. Not a good inverter for night time loads. I had a smaller nameless Chinese brand for night time (about 30W) then switched to a hacked APC inline UPS. Victron MultiPlus 5kVA for daytime loads has an idle 25W consumption (had to retire it due to a fault which forced the fans at full revs constantly thus raising idle consumption to 50W. Returned to the MustPower). The Victron Phoenix for critical and night time loads has an self-consumption of roughly 10W in use thus perfect. Both are wired to the same bank. I use knife switch to switch between them. That way both can never feed the same circuits at the same time.