Pro Power OnBoard with Autotransformer -- to work around the bonded neutral issue?

[v2h8484]

Has anyone used Pro Power OnBoard with an autotransformer to work around the bonded neutral issue?

I see reports of success with neutral transfer switches but I have used autotransformer with bonded neutral generators in the past and wondered if the same can be done with Pro Power OnBoard. Autotransformer has the added benefit of automatic load balancing between the 120V legs.

Sponsored

 

[Maquis]

Do you mean isolation transformer? I can’t visualize how an autotransformer would work here.

 

[v2h8484]

No. I mean autotransformer or perhaps more accurately neutral forming autotransformer. Specifically, only connecting the L1 and L2 from a 240V power source (e.g. generator) and connect L1, L2 and neutral without ground bonding from the autotransformer to loads.

 

[TaxmanHog]

Some thing like this?

https://shop.pkys.com/autotransformer.html

I looked up via google for single phase 7.5 KW versions, kind of pricey 1500 to 3000 bucks!!

 

[Fastnf]

Enphase uses a neutral forming transformer in their smart switch. Both their back up batteries and the input from solar are 240 volt with no neutral. I haven’t tried it but it would seem like you could connect pro power in the same manner. I am a month or so from getting my Enphase system operational. Once’s it up and running I will be looking at options to use pro power to charge the Enphase batteries during extended outages with low solar input (ie snow storms).

 

[v2h8484]

Some thing like this?

https://shop.pkys.com/autotransformer.html

I looked up via google for single phase 7.5 KW versions, kind of pricey 1500 to 3000 bucks!!

Yes, that's a diagram for the Victron autotransformer. You can get a UL compliant Growatt 11.4kW autotransfomer with built-in ATS for ~$500.

 

[Maquis]

Some thing like this?

https://shop.pkys.com/autotransformer.html

I looked up via google for single phase 7.5 KW versions, kind of pricey 1500 to 3000 bucks!!

The problem here is that the derived neutral will be bonded to ground in the home’s main panel. Since the truck’s neutral is also bonded to ground, it doesn’t address the original issue.
Also, unless the 120-0-120 of truck matches exactly that of the transformer, there will be high circulating currents in the windings with the neutrals connected.

That transformer is intended for use with a generator with a 240V only output.

 

[v2h8484]

Also, unless the 120-0-120 of truck matches exactly that of the transformer, there will be high circulating currents in the windings with the neutrals connected.

That's one of the things I was wondering about with Pro Power OnBoard. Is there actually significant circulating current to cause problems (e.g. GFCI tripping)?

 

[Maquis]

That's one of the things I was wondering about with Pro Power OnBoard. Is there actually significant circulating current to cause problems (e.g. GFCI tripping)?

The circulating current won’t affect the GFCI. But it will turn the auto transformer into a big heater!

 

[v2h8484]

The circulating current won’t affect the GFCI. But it will turn the auto transformer into a big heater!

Theoretically yes. However, it has not been an issue in my experience with 240V split-phase neutral bonded generators. It's probably because the the loads on the 120V legs are never perfectly balanced anyway and the autotransformer has very high rating for neutral imbalance rating.

 

[Maquis]

Theoretically yes. However, it has not been an issue in my experience with 240V split-phase neutral bonded generators. It's probably because the the loads on the 120V legs are never perfectly balanced anyway and the autotransformer has very high rating for neutral imbalance rating.

Circulating currents have nothing to do with loads.

If one of these is used successfully with a split phase, neutral bonded generator, I’d bet that only 2 wires - the 240V phases - are connected to anything.

This would also work with ProPower, but simply omitting the transformer, and not running the ground wire from the truck accomplishes the same thing.

 

[v2h8484]

Circulating currents have nothing to do with loads.

If one of these is used successfully with a split phase, neutral bonded generator, I’d bet that only 2 wires - the 240V phases - are connected to anything.

This would also work with ProPower, but simply omitting the transformer, and not running the ground wire from the truck accomplishes the same thing.

Hmm ... maybe we are saying the same thing. The main purpose of the autotransformer is automatic load balancing between the 120V legs. I don't think you get that connecting directly to Pro Power OnBoard. This is the setup I have used with 240/120V generators without problems:

The diagram is from https://shop.pkys.com/autotransformer.html.

I am interested to know if there is anything in the Pro Power OnBoard that would make it not work in the same setup.

 

[Maquis]

Hmm ... maybe we are saying the same thing. The main purpose of the autotransformer is automatic load balancing between the 120V legs. I don't think you get that connecting directly to Pro Power OnBoard. This is the setup I have used with 240/120V generators without problems:

The diagram is from https://shop.pkys.com/autotransformer.html.

I am interested to know if there is anything in the Pro Power OnBoard that would make it not work in the same setup.

It does load balance by presenting the 120V loads to the genny as a single 240V load.
But it’s not going to solve GFCI tripping.

 

[v2h8484]

But it’s not going to solve GFCI tripping.

That's one thing I would like to certain about Pro Power OnBoard. Typically, 240/120V generators only have GFCI on the 120V outlet circuits.

 

[d2blake]

Enphase uses a neutral forming transformer in their smart switch. Both their back up batteries and the input from solar are 240 volt with no neutral. I haven’t tried it but it would seem like you could connect pro power in the same manner. I am a month or so from getting my Enphase system operational. Once’s it up and running I will be looking at options to use pro power to charge the Enphase batteries during extended outages with low solar input (ie snow storms).

Have you been able to do this? I’d like to know if I can install a transfer switch between utility and the smart controller2. Then have a micro grid with the truck and enphase battery system/solar.

Sponsored