Need advice: looking for split phase battery backup system, generator-style

[diso12]

Context:

Where I live, the power sometimes goes out and [natural gas] heating goes down with it because fans stop working. I have a 240V split-phase generator inlet with manual transfer switch, which works fine but it's loud and we have to turn it off at night. I am now looking to also have an extra battery-backed power supply I can fall back to.

I want to end up with a split-phase 240V system, which I would plug into a generator inlet and manually transfer power. I want to charge it from the wall plug.

What I would like to know:

I ordered 2x12V ampere time batteries to keep in a heated area. I now need either all-in-one or an inverter+charger. The one I originally ordered was 220V, but it turned out to be european style, not split-phase like they do in USA. I am scanning internet for other options, do not see any sane ways to run the system on 24V, everything I see is unreasonably expensive. I really don't need the system to be much powerful, just enough to sustain house during off-peak time. Typical energy used is around 500W, so I would imagine 2KW system would do nicely.

So, should I just go ahead bite the bullet and buy LV6048 and two extra batteries to end up with 48V system, or is there some options which would allow me to run backup power on 24V yet provide split phase 240V output?

 

[snoobler]

Welcome to the forum.

Anything with a motor may have a high surge current, and any inverter must be selected to handle that surge. Surge is typically 4-10X the run power.

Ampere time batteries are 100Ah 12V LFP, that's 2 * 12.8V * 100Ah = 2560Wh, which would provide about 4 hours at 500W and retain about 20% reserve for max battery cycle life.

NOTE that LFP is not good for standby power as they shouldn't be stored for long periods at full charge. They will degrade. If you expect several outages a month, no worries. One every month or two? Then lead-acid is probably the better choice.

This beast:

Welcome to Electric Car Parts Company - ...Specializing in Lithium Batteries, Chargers, Solar Storage <br> <br> (801) 566-5679 9am-5pm or (801) 449-0681 5pm-9am MDT

has absurd surge capability and can be ordered for 24V or 48V and output 120/240VAC split phase.

It's essentially identical to the AIMS line.

 

[diso12]

Welcome to the forum.

Anything with a motor may have a high surge current, and any inverter must be selected to handle that surge. Surge is typically 4-10X the run power.

Ampere time batteries are 100Ah 12V LFP, that's 2 * 12.8V * 100Ah = 2560Wh, which would provide about 4 hours at 500W and retain about 20% reserve for max battery cycle life.

NOTE that LFP is not good for standby power as they shouldn't be stored for long periods at full charge. They will degrade. If you expect several outages a month, no worries. One every month or two? Then lead-acid is probably the better choice.

This beast:

Welcome to Electric Car Parts Company - ...Specializing in Lithium Batteries, Chargers, Solar Storage <br> <br> (801) 566-5679 9am-5pm or (801) 449-0681 5pm-9am MDT

has absurd surge capability and can be ordered for 24V or 48V and output 120/240VAC split phase.

It's essentially identical to the AIMS line.

Quite an expensive item at $900... I'm debating now if I should just go ahead and get 48V going if I'm already splurging on inverter

 

[snoobler]

LOL. $900 6kW LF inverter "expensive." You are too accustomed to cheap, mediocre products.

Whatever you decide, if you're considering Lithium batteries, you shouldn't use them unless you expect FREQUENT outages. You're paying a premium for something you're going to damage.

 

[diso12]

LOL. $900 6kW LF inverter "expensive." You are too accustomed to cheap, mediocre products.

Whatever you decide, if you're considering Lithium batteries, you shouldn't use them unless you expect FREQUENT outages. You're paying a premium for something you're going to damage.

I understand your point... In my defense, I have been looking for much less powerful than 6k inverter.

Thanks for warning me on battery degradation problem. I'm wondering if there is mitigation for liion batteries, since I already ordered these. Keep them at 80% charge?...

 

[snoobler]

That will help a little, but reliably charging them to 80% may be difficult to consistently accomplish. Any long term storage should be conducted at 40-50% SoC, and since this is a standby system, what's the point of only having 40-50, or 80% of your capacity available when you want all of it?

Cheaper AGM batteries will likely perform better unless you have blackouts every few days.

 

[Supervstech]

I understand your point... In my defense, I have been looking for much less powerful than 6k inverter.

Thanks for warning me on battery degradation problem. I'm wondering if there is mitigation for liion batteries, since I already ordered these. Keep them at 80% charge?...

6KW is pretty much the lowest split phase inverter size of much use... most any 240V appliance is going to need over 4KW...
if you were looking for less than 6KW, what were you planning to operate on split phase output?

 

[diso12]

6KW is pretty much the lowest split phase inverter size of much use... most any 240V appliance is going to need over 4KW...
if you were looking for less than 6KW, what were you planning to operate on split phase output?

I was just looking to hook the house through generator inlet. I don't really even need to power anything that runs on 220V.

I wonder if it would be a problem if I simply bond two phases together given that house will not be on main power when inlet in operating, and even if somehow main power gets turned on despite interlock, there's still breakers, and I can probably install additional fuse for that specific case.

Do you think this would work?

 

[Hedges]

I was just looking to hook the house through generator inlet. I don't really even need to power anything that runs on 220V.

I wonder if it would be a problem if I simply bond two phases together given that house will not be on main power when inlet in operating, and even if somehow main power gets turned on despite interlock, there's still breakers, and I can probably install additional fuse for that specific case.

Do you think this would work?

That is commonly done with recreational vehicles - they have a 50A 120/240V plug, and and adapter to 30A 120V.
Any 240V appliance sees zero volts so doesn't try to run.

It can work for a house, but there is a problem the way wiring is often done. If the inverter is only 2500W or smaller, not a problem.

We use Romex wire with red, white, black, and bare conductors. Bare is ground. White is neutral. Red and black are for the two hot wires of a 120/240V split-phase system.
With 120/240V split phase, white only carries the difference between red and black. If two 20A breakers are connected, red and black are protected to 20A max, and white never sees more than 20A.

If a 5000W 120V inverter or generator was connected to both red and black, their two breakers would each carry 20A, and white would carry 20 + 20 = 40A, causing a fire.
If only 2500W 120V inverter, only 20A available so no problem.

If you want to use an inverter or generator to power the house when grid is down, either wire in a transfer switch or get an interlock that lets one breaker backfeed the the panel only when main breaker is off.
If you do this without a transfer switch or interlock, when power comes back on it will burn up your inverter. If a lineman works on the utility grid he could be electrocuted.

 

[diso12]

That is commonly done with recreational vehicles - they have a 50A 120/240V plug, and and adapter to 30A 120V.
Any 240V appliance sees zero volts so doesn't try to run.

It can work for a house, but there is a problem the way wiring is often done. If the inverter is only 2500W or smaller, not a problem.

We use Romex wire with red, white, black, and bare conductors. Bare is ground. White is neutral. Red and black are for the two hot wires of a 120/240V split-phase system.
With 120/240V split phase, white only carries the difference between red and black. If two 20A breakers are connected, red and black are protected to 20A max, and white never sees more than 20A.

If a 5000W 120V inverter or generator was connected to both red and black, their two breakers would each carry 20A, and white would carry 20 + 20 = 40A, causing a fire.
If only 2500W 120V inverter, only 20A available so no problem.

If you want to use an inverter or generator to power the house when grid is down, either wire in a transfer switch or get an interlock that lets one breaker backfeed the the panel only when main breaker is off.
If you do this without a transfer switch or interlock, when power comes back on it will burn up your inverter. If a lineman works on the utility grid he could be electrocuted.

I do indeed have an interlock, so that's taken care of, but I should probably think of installing some sort of inline fuse to protect inverter from over-current. Although, don't inverters typically have internal fuses/breakers?

So... given that, what would be an appropriate inverter to get? It would be preferable if it doubles as charger...

 

[FilterGuy]

This beast:

Welcome to Electric Car Parts Company - ...Specializing in Lithium Batteries, Chargers, Solar Storage <br> <br> (801) 566-5679 9am-5pm or (801) 449-0681 5pm-9am MDT

has absurd surge capability and can be ordered for 24V or 48V and output 120/240VAC split phase.

It's essentially identical to the AIMS line.

That *looks* like yet another rebranded Sigineer inverter but it is a much lower price than the other 6KW Sigineer re-brands.

 

[Hedges]

I do indeed have an interlock, so that's taken care of, but I should probably think of installing some sort of inline fuse to protect inverter from over-current. Although, don't inverters typically have internal fuses/breakers?

So... given that, what would be an appropriate inverter to get? It would be preferable if it doubles as charger...

Often they don't have protection on output. They may have protection on battery terminals but usually not high-performance fuses. Your interlock (if interlocked breaker) could provide some protection.

Wide range of performance, quality, price.

Here's my favorite, but you'll choke on the price: $5000 msrp, many being liquidated on eBay right now for $2000 more or less.

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Depending on what you want to run you may find choices from $300 and up.

It should be pure sine wave, not "modified sine wave" which can cause overheating of motors.
At least 2000W so it can start a refrigerator (needs to put out 5x nameplate rating of any motors.)
Some have internal transfer switch, can act as a UPS to keep loads running. Or you can use your interlocked breaker (don't forget to turn off breaker feeding inverter/charger so it doesn't try to power itself)

 

[Supervstech]

Keep in mind that if you feed both lines with a 120v inverter, and the hots are tied together, if utility power EVER is turned on, you could have a fairly exotic explosion...
Make sure you tie the hots into the inverter side downstream of the utility interlock.
Another option would be to get a 3KW split phase inverter from them.
Should be a lot less money, and you wouldn't overload any circuits if something failed...

 

[diso12]

Another option would be to get a 3KW split phase inverter from them.

You lost me here.... Which 3KW inverter are we talking about?

 

[snoobler]

That *looks* like yet another rebranded Sigineer inverter but it is a much lower price than the other 6KW Sigineer re-brands.

It absolutely is. I received confirmation from both Sigineer and ECPC.

 

[diso12]

What ticks me off in that inverter price is that I can get 8750W inverter generator for $800 - which already has split phase inverter built in, more power and cheaper than inverter alone, and you get an extra generator for bonus. Da heck.

 

[Hedges]

What ticks me off in that inverter price is that I can get 8750W inverter generator for $800 - which already has split phase inverter built in, more power and cheaper than inverter alone, and you get an extra generator for bonus. Da heck.

Chinese sourced ICE and generator doesn't cost much. But 8kW sine-wave inverter too, I know what you mean.

Rather than having a 48V battery and having to boost it, what they are doing is having the generator output rectified to produce > 340 Vdc, then implementing a high-frequency inverter to make 120/240V split-phase.

Compared to the battery inverters we have linked, it doesn't include high current transistors and a boost circuit from 12V or 48V to 400V.

A desirable DIY hack would be to add PV with MPPT to supply its DC rail, so generator can stay at idle most of the time.
Adding battery, BMS, battery charger adds cost and complexity.

There are 400V battery inverters, for instance 6kW Sunny Boy Storage ($2500) which produces 240V but not 120V except with external transformer.
A 10kW battery for it is $6500.

I've been thinking that PV to an inverter-generator or to a VFD would be good.
My VFD (on pool pump) can be connected to either 240V single-phase or 208Y 3-phase. It has 6 rectifier diodes. With possibly some internal rearrangement I could feed it from grid and also from PV string. Would have to design string so Voc doesn't exceed ratings.

 

[Supervstech]

What ticks me off in that inverter price is that I can get 8750W inverter generator for $800 - which already has split phase inverter built in, more power and cheaper than inverter alone, and you get an extra generator for bonus. Da heck.

Wow..
Seriously? I haven't seen an inverter generator over 3000 watts less than 800, and that was 120V!
Crazy!

 

[Hedges]

Wow..
Seriously? I haven't seen an inverter generator over 3000 watts less than 800, and that was 120V!
Crazy!

And electric start, at that (says so in the title but I missed it)

"ABOUT THE BATTERY 1. The lithium-ion battery supplied with your generator is only partially charged, in order to maximize its service life. The battery may not have enough charge to start the engine during its first use. If this is the case, connect the battery according to the instructions below, and start the generator using the recoil starter, according to the instructions below. The battery will receive charge when the generator is running. 2. Lithium-ion batteries are subject to a natural aging process. The battery must be replaced at the latest when its capacity falls to just 80% of its capacity when new. Weakened cells in an aged battery are no longer capable of meeting the high power requirements needed for the proper operation of your generator, and therefore pose a safety risk."

Hmm, what's the safety risk? It fails to crank?
Or ...


Manual appears to have been written here, rather than being a bad translation.

"With the help of a friend or trustworthy foe, such as one of your in-laws, carefully remove the generator from the packaging and place it on a sturdy, flat surface."

 

[diso12]

Manual appears to have been written here, rather than being a bad translation.

I think wen is legit as far as business go.