Small Home ongrid, get AC offgrid

[trad]

They don't offer an isolation transformer.
Used from places like Ebay is the cheapest option.
You're looking for a 240v input (most commonly 480v/240v) and a 240v/ 120v output single phase transformer.
Size should be 5kva per Growatt SPF-5000-ES.
So, 10kva for 2 stacked Growatt's.

Like this?

5kva transformer

This looks perfect, but sadly the forklift doesn't come with it.

Is this typical size and weight for a 5kva?

 

[timselectric]

Like this?

5kva transformer

This looks perfect, but sadly the forklift doesn't come with it.

Is this typical size and weight for a 5kva?

You don't need hospital grade. (Extra large and heavy) And that one doesn't have an enclosure. (You need it enclosed)
But, it is a hell of a good price.

 

[timselectric]

Something like this would work.

Hammond Power C1F005LES 5KVA Transformer Pri 240-480V Sec 120-240V 3R | eBay

Find many great new & used options and get the best deals for Hammond Power C1F005LES 5KVA Transformer Pri 240-480V Sec 120-240V 3R at the best online prices at eBay! Free shipping for many products!

www.ebay.com

 

[Hedges]

Also, unless you have 208V and want 120V, don't know what good that transformer would do you.



What are you trying to accomplish? Start with single-phase 240V from an inverter which sometimes has grid L1/L2 passing through, and create isolated 120/240V?

Standard power transformers don't play nice with inverters. They have no-load current about 10x what is desirable, because they are sized allowing core to go part way into saturation every cycle (saves money and weight).

They are much better behaved at 1/2 of rated voltage. Easy to use 240/480 primary as 120/240V autotransformer. But to make an isolation transformer I would need two. 240/480 primary in series gets 240V from inverter. 120/240V secondary makes 120V L1 for load. A second transformer wired similarly makes the other 120V L2 for load.

 

[Zwy]

I use about 1000kwh per month, but the bulk of that is AC here in S Texas. The goal is to put the 3T 240v AC on solar while the sun is shining. When the sun goes down, the AC can switch to the grid.

I will make this investment looking for a quick payback, so large battery banks are out. I have room for 100 solar panels if necessary but I need to choose an All in One inverter, solar charge controller. What is the best 240v AIO that can use as little battery as necessary and seamlessly switch over to grid power when there isn't enough sun?

(the EG4 6500ex is awesome, but wouldn't that be overkill for this small load?)
(would this be a good use case for the much maligned Growatt 5000 ES ?)

Why not have batteries?

 

[trad]

Why not have batteries?

Yeah, I'll slide down that slippery slope just like the rest of you. The other thing I wasn't going to do was go grid tied and net metering. The arguments above make a great case for doing the whole thing right and not going for just the AC.

 

[trad]

For a split-phase output.
an Autotransformer is fine, for no grid connection.
If also connected to grid, an isolation transformer is the best option.

Thanks for the pointer to an ebay option here. But I still have one question. I understand, the isolation transformer has safety features for old style non polarized radios and tv's. But I have non of these things and don't forsee any legacy non polarized equipment connected to solar. Is there some other reason you recommend an isolation transformer for 120v loads with a grid connected Growatt 5000 ES US?

And finally, if I install an isolation transformer, will my 120v loads be backed up by the grid. For example will my 120v fridge automatically switch to grid when the sun goes down?

All this assumes I never want to grid-tie and go net metering. At some point I will want to install batteries to capture excess solar over and above what my usage is. Nothing we have done here will pass electrical inspection, correct?

 

[timselectric]

Thanks for the pointer to an ebay option here. But I still have one question. I understand, the isolation transformer has safety features for old style non polarized radios and tv's. But I have non of these things and don't forsee any legacy non polarized equipment connected to solar. Is there some other reason you recommend an isolation transformer for 120v loads with a grid connected Growatt 5000 ES US?

The only reason why I suggest an isolation transformer. Is to isolate the grid from your system.
To avoid your system from trying to balance the neighborhood. (Can happen with an autotransformer)
And to remove the N/G bonding issues.

It's actually a lot easier to not connect the grid to the AC input. And use a Chargeverter for the grid backup.
This option removes all of the issues with grid backup.

 

[timselectric]

And finally, if I install an isolation transformer, will my 120v loads be backed up by the grid. For example will my 120v fridge automatically switch to grid when the sun goes down?

They would.

All this assumes I never want to grid-tie and go net metering.

This is not a grid-tied capable unit.

At some point I will want to install batteries to capture excess solar over and above what my usage is.

Batteries can be added at any time.

Nothing we have done here will pass electrical inspection, correct?

Correct
This is not UL listed equipment.
Unlikely to get it through an inspection.

 

[Zwy]

Yeah, I'll slide down that slippery slope just like the rest of you. The other thing I wasn't going to do was go grid tied and net metering. The arguments above make a great case for doing the whole thing right and not going for just the AC.

I went from desiring backup power to load reduction to complete off grid power with batteries.

Didn't spend a dime thankfully until I decided to just start out with complete off grid power with batteries. Best choice is to just go all in. This way you can develop a master plan.

 

[trad]

It's actually a lot easier to not connect the grid to the AC input. And use a Chargeverter for the grid backup.
This option removes all of the issues with grid backup.

If using a Chargeverter, you still need either a autotransformer or an isolation transformer to make a neutral for 120v loads, correct? Does the isolation transformer provide any additional benefit over the auto transformer in this case?

You keep taking me down wild and wonderful rabbit holes. Thanks for the ideas.

 

[Hedges]

Thanks for the pointer to an ebay option here. But I still have one question. I understand, the isolation transformer has safety features for old style non polarized radios and tv's. But I have non of these things and don't forsee any legacy non polarized equipment connected to solar. Is there some other reason you recommend an isolation transformer for 120v loads with a grid connected Growatt 5000 ES US?

The 240V inverters were designed for European 240V L/N power, not US 120/240V L1/N/L2. There are some long threads here about excessive current draw from the grid (attempting to rebalance, as Tim mentions) and various safety issues depending on what non-UL, non-NEC compliant attempt to use it.

I don't think any compliant way to use them was ever described, except that an isolation transformer appears to solve all the technical issues, leaving just "not UL listed".

SS does offer an auto-transformer for use with this (or similar?) model.

"Took some thinking to make a Neutral ground bound with the inverters being 240 Volt. But works well and a triple 20 Ampere breaker can make this a safe setup."
Apparently meaning that a breaker can protect the transformer from overload and simultaneously disconnect downstream 120V loads to protect them from damage caused by lost neutral.

Growatt 5kW Split Phase Transformer | ATS 5000T-ES

Signature Solar provides solar panels, off-grid solar systems, grid-tie, and hybrid systems. Quality solar inverters, bifacial solar panels, complete solar kits, solar batteries. Featuring brands such as EG4 Electronics with their solar battery, LifePower4 and EG4 LLifePower4 and EG4 LL

signaturesolar.com

The proper solution is to select an inverter which supports split phase, possibly a pair of stackable 120V inverters.

If using a Chargeverter, you still need either a autotransformer or an isolation transformer to make a neutral for 120v loads, correct? Does the isolation transformer provide any additional benefit over the auto transformer in this case?

You keep taking me down wild and wonderful rabbit holes. Thanks for the ideas.

Chargeverter eliminates issue of autotransformer trying to rebalance grid, and you can properly bond the derived neutral to ground.

Autotransformers are often undersized, can't handle full power on a single 120V leg. If autotransformer disconnected by fuse or breaker, lost neutral can burn up 120V loads. Victron offers one with suitable protection, although I'm not convinced it can be safe and proper, without trying to rebalance grid when grid feeds through inverter.

If using isolation transformer, you are forced to get one large enough to transfer the power, and standard use of breakers protects it.

But like I wrote earlier, if you try to get an isolation transformer, I think it will be a nasty load for the inverter. Most transformers are designed assuming the grid will power them, and optimized for cost. I tested a 25kVA transformer, and when driven with 240V it drew 4A no-load. That is 1000VA. You would likely get a smaller transformer, but it will still demand excessive current from the inverter 24/7.

A proper inverter is the best solution. One that is UL listed is more likely to be designed and built correctly.

 

[Vigo]

"Took some thinking to make a Neutral ground bound with the inverters being 240 Volt. But works well and a triple 20 Ampere breaker can make this a safe setup."
Apparently meaning that a breaker can protect the transformer from overload and simultaneously disconnect downstream 120V loads to protect them from damage caused by lost neutral.

I have broken a few things with lost neutral, i admit..

I do have a 3-pole breaker in my setup but i was also going to add a 3-pole contactor with a 120v coil so that if i lose 120v i interrupt all 3 automatically.

 

[Hedges]

I do have a 3-pole breaker in my setup but i was also going to add a 3-pole contactor with a 120v coil so that if i lose 120v i interrupt all 3 automatically.

Care to present that design as a schematic?

so we can "critique" it ?

 

[trad]

But like I wrote earlier, if you try to get an isolation transformer, I think it will be a nasty load for the inverter. Most transformers are designed assuming the grid will power them, and optimized for cost. I tested a 25kVA transformer, and when driven with 240V it drew 4A no-load. That is 1000VA. You would likely get a smaller transformer, but it will still demand excessive current from the inverter 24/7.

A proper inverter is the best solution. One that is UL listed is more likely to be designed and built correctly.

To begin with I wrote (the EG4 6500ex is awesome, but wouldn't that be overkill for this small load?)

Now it seems we are heading towards something like a dual 6500ex solution for 240v or an EG4 18KPV. This could allow so many more options in the future like net metering, big battery bank, massive solar array. (net metering needs more investigation)

I was starting out wanting to get very quick payback, but.... If you start cheap, it will just cost you more in the long run.

 

[timselectric]

If using a Chargeverter, you still need either a autotransformer or an isolation transformer to make a neutral for 120v loads, correct? Does the isolation transformer provide any additional benefit over the auto transformer in this case?

You keep taking me down wild and wonderful rabbit holes. Thanks for the ideas.

With the chargeverter, you don't have a direct connection with the grid. So an autotransformer is fine.

 

[timselectric]

To begin with I wrote (the EG4 6500ex is awesome, but wouldn't that be overkill for this small load?)

Now it seems we are heading towards something like a dual 6500ex solution for 240v or an EG4 18KPV. This could allow so many more options in the future like net metering, big battery bank, massive solar array. (net metering needs more investigation)

I was starting out wanting to get very quick payback, but.... If you start cheap, it will just cost you more in the long run.

Yes, you definitely need to decide what you want. Before you start buying things.
This seems to have grown from just powering a 3T A/C unit from solar, during the day.
It's ok, solar can be very contagious. lol

 

[Vigo]

Care to present that design as a schematic?

so we can "critique" it ?

Uh oh, sounds like you've already spotted the hole in my plan..

But im scared to post the details, because what if someone makes an excellent point that causes my house to lose power!

In all seriousness, i really should focus more on human safety vs 'functional'. The contactor idea was more to protect the hardware in my house from ME!

 

[Hedges]

A 120V coil might not drop out even if L1 is reduced to 60Vrms, leaving L2 with 180Vrms.
Or, if it sees 180Vrms, it might survive long enough to witness death of the other devices.

I wanted to see your design to know if that's all it relied on, before gleefully bursting your bubble.

You would need a voltage monitor with tighter tolerances than just a relay coil.


A 2 pole circuit breaker protecting auto-transformer L1/L2 and disconnecting loads as well would work, but limits 240V pass through.

A 3-pole breaker (ganged breakers) could protect neutral and disconnect L1/L2 poles that carry higher current.

A 2-pole circuit breaker could protect neutral with one pole and disconnect relay coil with the other.

Victron I think has an active monitoring circuit that controls relay.

 

[Vigo]

Excellent point, i'll reconsider with that in mind! I was just assuming 120 would essentially be all or nothing in the fault scenarios i was envisioning, but you're right that in the absence of anything that limits imbalance things could get pretty far out of whack before the contactor dropped out. Thank you.