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Battery Inverter for future DIY powerwall (and existing PV inverter)
#1
Hi there,

another thread asking about which inverter to buy for a DIY powerwall... Blush

The current situation: 1.9 kWp solar panels installed (but likely to be expanded to 8 kWp in 2-3 years). The 1.9 kWp panels are now connected to a Fronius IG-15, which delivers to 1 phase of the houses 3 phase grid connection.

Now I am planning to build a DIY powerwall using Stuarts DiyBMS v4. So I would need a "ongrid battery inverter", that just charges the battery from the grid whenever the Fronius IG-15 is delivering solar power. And that delivers power from the battery to the (house) grid when there is consumtion but no solar power.

I was looking at the Victron Multiplus II (which has optional a 1 phase current sensor) and also to MPP/Voltronicpower.

And there are some things unclear to me:

1) to level out consumption from grid versus solar production and power delivered from the battery bank, I would need a current sensor that sums up all three phases and tells the battery inverter how much to deliver from the battery bank => the Victron Multiplus II sensor itself can do that only at one phase, no? => does the Victron support some kind of 3 phase current sensor (which would need to be at the houses grid connection)?

2) is there any inverter from Voltronicpower that can also do this levelling out but doesn't have the solar inverter built in (i don't need that and I guess it's better to have things modular... e.g. if the battery inverter breaks, the solar inverter is still delivering to the grid

3) can the Victron Multiplus II handle the battery bank without communication any BMS? (so I would like that the DiyBMS would have a main relay to cut off the battery bank in case of over/undervoltage, but wouldn't talk to the battery inverter)

4) any suggestion which 3 phase current sensor to use at the houses grid connection?

Sorry for asking again the inverter question, but I was reading a lot about this topic and I'm still quite confused how to achieve to level out grid consumption.

Thank you very much!

Manny
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#2
3ph requires 3x metering, plus 3x inverters suitably configured

https://www.victronenergy.com/accessories/energy-meter

https://www.victronenergy.com/live/ess:start
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#3
Sorry if this is a bit blunt...
"I would need a current sensor that sums up all three phases"

Forget looking at inverters. Read up and fully understand how power flows and balances on a 3 phase electrical system and how to calculate power flow on phase to neutral vs power flow between phases. You need to understand 3 phase electrical systems a lot better for the questions your posting. At the moment I would not recommend you install or buy anything without properly understanding a 3 phase electrical system first.

Your 3 phase loads will create some interesting power flows on each phase, which a number of inverters will not he too happy with and create a lot of harmonics, which in turn may lead the local utility to knocking on your door and asking you to disconnect your system.
If you can't quantify how much they cost, it's a deal, I'll buy 5 of them for 3 lumps of rocking horse ......
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#4
(09-03-2019, 12:50 PM)completelycharged Wrote: Sorry if this is a bit blunt...
"I would need a current sensor that sums up all three phases"

Forget looking at inverters. Read up and fully understand how power flows and balances on a 3 phase electrical system and how to calculate power flow on phase to neutral vs power flow between phases. You need to understand 3 phase electrical systems a lot better for the questions your posting. At the moment I would not recommend you install or buy anything without properly understanding a 3 phase electrical system first.

Your 3 phase loads will create some interesting power flows on each phase, which a number of inverters will not he too happy with and create a lot of harmonics, which in turn may lead the local utility to knocking on your door and asking you to disconnect your system.

Indeed a little blunt...

So the house is connected with 50 A per phase, the current sensor of the Multiplus II has maximum 100 A and 13 mm opening (I doubt I can fit 3 x 35mm2 into it). The current sensor delivers max. 50 mA signal to the inverter, and there is only 1 connection for current sensor at the Multiplus II, meaning I can't just use three current sensors and the inverter calculates the sum current => I need a three phase current counter that is somehow connected to the Multiplus II (at least from my understanding)

As an explanation following setup:

Phase 1 => Basement => +500W consumption - 200W solar input (late evening)
Phase 2 => Ground floor => +300W consumption
Phase 3 => First floor  => +400W consumption

If the current sensor of the Multiplus II is hooked over phase 1, it sees 300W consumption and the Multiplus II decides to deliver 300W from the battery. Although it should deliver 300+300+400=1000W from the battery bank. Thats why I'm wondering how people do to level consumption vs. feed into grid.

@ Sean: I don't want to feed in 3 phase. I just want to feed to 1 phase, but matching the consumption of all three phases. Because my utility electricity counter is summing up all 3 phases (saldierend) and decides then whether I'm consuming from or feeding to the grid.

It would be nice if anybody could help me understand how people deal with that (or which three phase counter is used that can "speak" with the Multiplus II telling how much to feed from the bank in order to get the total current blanced.

Or if there are any other battery inverters that can speak in an easy way to a three phase current counter.

Thanks,
Manny
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#5
(09-04-2019, 12:12 PM)manny_286 Wrote: It would be nice if anybody could help me understand how people deal with that (or which three phase counter is used that can "speak" with the Multiplus II telling how much to feed from the bank in order to get the total current blanced.

The 3ph meter has already been linked to above - along with all the info that is currently available regarding DIY 3ph installations.

I strongly suggest you employ the services of a qualified, and suitably experienced company to design, install and commission your project.
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#6
"the current sensor of the Multiplus II has maximum 100 A and 13 mm opening (I doubt I can fit 3 x 35mm2 into it)"

again being blunt and repeating "You need to understand 3 phase electrical systems a lot better for the questions your posting."
If you can't quantify how much they cost, it's a deal, I'll buy 5 of them for 3 lumps of rocking horse ......
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Sean (09-04-2019, 04:03 PM), RikH (09-05-2019, 08:26 PM), intra (09-04-2019, 12:43 PM), winny (09-09-2019, 09:37 AM), 100kwh-hunter (09-06-2019, 04:34 PM), Emiel (09-06-2019, 09:41 AM), stok (09-05-2019, 10:10 AM), EnergyInternet (09-03-2019, 01:36 PM), suntan901 (09-04-2019, 08:00 PM), t3knerd (09-12-2019, 09:53 PM), manny_286 (09-04-2019, 12:12 PM), ajw22 (09-04-2019, 12:21 PM), Solardad (09-05-2019, 03:13 AM), mike (09-03-2019, 12:51 PM), jdeadman (09-04-2019, 05:52 PM), watts-on (09-03-2019, 01:56 PM), Geek (09-06-2019, 03:25 AM), HughF (09-03-2019, 02:00 PM), completelycharged (09-05-2019, 07:34 PM), Riplash (09-04-2019, 05:07 PM), chuckp (09-04-2019, 08:29 PM), clupton (09-03-2019, 12:46 PM), Wolf (09-04-2019, 07:16 PM), DirkB19 (09-04-2019, 09:52 PM)

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