MultiPlus-II 3kW for 'UPS' pump power backup, review schematic please?

[KiwiME (Paul)]

Greetings,

I’m in New Zealand and currently have a compliant generator + ATS installed to provide backup power for a stormwater pump. Power outages are rare but I have to cover the possibility to avoid flooding the ground floor of the property. The problem that I’m facing is that the pump only needs to run for a minute every 3 mm rainfall at random intervals so starting a generator each time is not sustainable over many pumpouts due to having insufficient time to charge the 12V starter battery. For example we had 90 mm recently and the pump ran 30 times over 24 hours. The tank filling time ranged between 5 min and 2 hours.

There are other solutions such as installing a larger starter battery or a much larger water tank but it seems that an inverter and LFP battery is not only the cleanest solution but more easily scalable than the others. I may not even need a generator once it’s proven. I’ve calculated that I need only 1 kWh of battery energy per 100 mm of rain. I’d like to design for 250 mm as that’s the local historic record.

This is fairly simple as there is no PV involved. I’ve come up with a schematic which places the inverter + LFP battery after the generator ATS. The idea would be that a 5kWh battery would cover all anticipated rainfall events but the generator could kick-in if needed, if it sees the tank reach a high water level.

My main electrical concern (being new to inverters in general) is to avoid a situation where a pump that’s already running ‘sees’ a sudden change of supply that is out of phase. I know from experience that it can trip a breaker. My existing generator controller handles this by allowing a running pump to fully stop before power is switched back to mains. I’ll just add that there are two pumps, the second is a backup and I anticipate that only one run will operate at any time.

The other concern is intrinsic reliability. If the MultiPlus is not ‘on’ or is not operable, is AC1 still connected to the AC input in to allow grid mains through?

Oh, and do I need the GX model or can it be programmed using a USB cable?

Any comments are appreciated.

Thanks,

Paul

(schematic deleted)

[Craigy]

… after thought…

GX isn’t essential, but important for remote control and support. While the MP has a relay and ACout2 also has a relay, a GX with two independent relays (Cerbo/Ekrano - Ekrano can’t switch 230Vac or 48Vdc) can switch two pumps with contactors. Node Red allows multiple logic considerations, and digital inputs can have a float switch connected so it only pumps when water is detected.

[BjoernK (Björn Kellermann)]

@KiwiME

the MultiPlus 2 is designed having 1 AC_in either for a grid OR for a generator.
For grid usage a grid code has to be selected and the MP2 will do loss of mains probes, e.g. shift frequencies and probably disconnect your generator.
For offgrid usage with a generator on AC_in, you define “no grid code” to accept the generator.

Pls decide either to use

• an MP2 as UPS with grid
• an MP2 for pure offgrid with a generator
• an Quattro with two AC_ins, one for grid the other for generator

Having all loads behind MP2/Quattro, you do not need an ATS. Both do automatic disconnect.

As you seem rely on a proper working system especially during storm with risk of grid loss, I recommend the Quattro.

I personally would go for a bigger Quattro and place it between grid and the house.
You could connect essential loads like the pump on AC_out1 and non-essential loads on AC_out2.
ACA_out2 can be controlled.

The Quattro would serve your house without interruption (20ms). If battery SOC falls below your defined threshold, the GX device would start your generator to recharge.

If you start with Victron either MP2 or Quattro, you will add PV… It’s too easy to extend to not do it.

MP2 /Quattro do not like 30mA RCBO on AC_in, but need them on AC_out to protect people.
In close an 1-0-2-switch on AC_out to switch load directly to grid in case of maintenance of MP2/Quattro.

Pls find my drawing for a 3-phase MP2 setup.

[KiwiME (Paul)]

Thanks for those replies and I very much appreciate you both taking the time out of your day to look at this. It’s clear that I will have to re-scope this system regarding the existing generator.

The point about the MultiPlus-II not accepting an imprecise alternator generator input when configured for a NZ grid is critical.

I’m also seeing that the Quattro is not type-approved (yet) for our network according to their list of approved units. I believe it could be done but would need the electrician to make a specific application to the regional grid network owner, Unison.

I’m in a flat above two small shops in a small commercial building (that I own) and have very limited space for equipment. The 9m x 9m pyramid-shaped roof area and shade from the adjacent building limit the space and effectiveness of PV panels. I have allocated space for the equipment that’s optimal in location but limited in size, see the image in the new schematic. The intent was to install a steel double-door electrical enclosure (already on order) and fit everything in that.

As I mentioned, my required scope is to provide backup power for the pump station. Overall, grid power here is reliable here but I need to cover the possibility of failure as it’s happened twice in 20 years but both events were during the last 5 years.

The power and energy requirements needed are fairly well understood as I’ve been tracking this for years.

There are many solar installers around but once I engage any I’m on a roller coaster of sales talk and pressure. I’d like to be prepared from a technical perspective before opening that door.

I need 0.7 kWh of 230VAC energy per 100 mm of rainfall including start-ups. I want to handle a maximum of 250 mm in one rain event, so that’s 1.75 kWh. I don’t know exactly how much to allow for inverter efficiency and depth of discharge but let’s estimate 95% and 60% DoD, so the battery capacity requirement is now 3 kWh.

So, to move ahead, at least in terms of this post, I can simply discard the option of using generator power as an alternative AC input to a MultiPlus-II. I’d probably remove all the existing associated equipment other than the small controller that logs pump activity and can alert me to any problems such as the primary pump failing to operate.

The intended enclosure seems adequate for a MultiPlus-II 3kW and a 5kWh LFP battery, plus switchgear. The box can be modified if needed for cooling but I don’t see that being higher than a 150 W heat load. Plus, the pump typically only runs for 1 minute each time, so it won’t even get warm unless I use the off-grid power for other purposes like a refrigerator.

Here’s a relevant schematic. It wasn’t clear to me if the MultiPlus still transfers AC from the input to AC-1 when the unit is off but I’ll assume it doesn’t. As such can I add a bypass switch if the Multiplus is not operational so that the pump can still run off mains when needed?

I don’t need the MultiPlus to act instantly to a loss of grid-mains. I have high-level float switches installed in the tank that could be used as a signal to enable the inverter if that’s advantageous to minimise standby power draw.

(schematic deleted)

[BjoernK (Björn Kellermann)]

Hi @KiwiME

this looks better although I am not familiar with NZ requirements.

You can discharge a LFP battery to 10% SOC.
I would set “minimum SOC” (until grid failure) to 90% SOC. This would keep you battery on 90% SOC. If grid failes, the MP2 3kVA GX will draw some 15W. Your 5kWh battery will provide with a delta of 80% appr. 4kWh minus the 0,4 kWh/day the MP2 draws.

Please mind the MP2 3kVA is VA not W. If your loads are 80% real power, e.g power factor of 0,8, the MP2 3kVA becomes a MP2 2.4 kW.
Pls double check your pumps.

When configuring the system oks reach out about “dynamic shutdown” if MP2 in Ve.Configure. The MP2 has a battery monitor. You can define shutdown current to protect your battery. On starting heavy loads, like pumps, the cut off might be to height as the voltage might drop significantly on start. But Victron knows about those stuff and has parameters to adjust to your needs.

If you want to keep the generator, you can build an isolated system with generator, MP2 and the pumps. An additional telco PSU could recharge battery from mains. Though only the PSU is connected to mains and recharge battery at 52V DC the battery. Eltek Flatpack 2 for 150 EUR at eBay is one choise. You could put all this into one 19” mobile rack giving you a 3kVA/5kWh mobile power station.

Search for Victron “hybrid generator”:

Hybrid Generators | Victron Energy

[KiwiME (Paul)]

Thank you for the suggestions, in particular the interesting hybrid idea.

I don’t see any power factor information in the pump specifications but I did measure the startup current of a spare pump, out of water, see image below. With additional effort I could do the same while submerged.

The generator controller I have can disable either pump (of 2) and knows when either are running. As such, even when the MP2 is active it can be easily modified to ensure that either:

• only one pump can run at any time, or
• that only one can start at any time.

At 230 x 5.2A = 1.2 kW each, but only knowing that these are capacitor-start induction motors, do you think the ‘3kW’ MP2 can start a second pump while one is already running? I don’t expect to actually see that scenario being required as each can handle 180 mm/h of rainfall, a significant rate and not one seen here historically.

Thanks again for your interest.

[BjoernK (Björn Kellermann)]

The datasheet states 11A output for MP2 3000 and 19A for the 5000. Additionally the units have a temperature derating.

You measured dry startup of 22A @230V which is 5000VA. With a running pump, your peak would be 28A or 6500W.

I would go for the MP2 5000 and limit startup to one pump at a time.

The MP2 5000 can deliver 9000W peak, which appr. 170A @ 55VDC. 6500W is appr. 120A.
Please check peak current of your battery.

[Jeroen2 (Jeroen Kuijf)]

Good morning,

Thank you for sharing your setups.

Setup 1 cannot be done as you do with the second MEN connection.

Its ok when running on the gen alone, but when you switch to main then 2 MEN connections are active, only one is allowed not to have current/voltage swings between the 2 MEN connections and unnecessary tripping of RCDs.

The second setup ok (Bjorn is right, I would also go for a “heavier” Victron, why not a Quattro (2 inputs, gen and grid)), the mains has the fixed MEN, so in pass-thru mode of the Victron thats active and that connection serves for all loads, however in inverter mode alone then you must switch the internal ground relay of the Victron to create the MEN, don´t forget to activate that in VE-config (just checking the box to “ON”), some RCDs behave different without a proper MEN, test yours with a 5K Ohm resistor to trip an RCD of 30mA and test with a 500 Ohm resistor a 300mA RCD.

When you use your generator, the fixed MEN can be made inside the Generator connection box, so, also in Passthru of the Victron the internal ground relay opens, using only 1 MEN at the time, very important!

Regards, Jeroen.

[KiwiME (Paul)]

Thanks for the comments so far. The support has been outstanding.

After considering many options I have a new proposal (attached) where an MP2 (48/5000/70-50 AU-GX) is wired to a dedicated 20A circuit from the main switchboard with AC1 feeding the ‘mains’ input of the existing ATS changeover switch. The MP2 maximum AC current draw would be set to 20A.

The purpose of this arrangement is to allow the generator to take over supply to the pump, if for any reason the MP2 fails to provide 230VAC power. It’s obviously not going to charge or support the battery but I believe I can live with this scenario, in part due to the MP2’s low on-battery standby drain.

Proposal A.pdf (162.0 KB)

As I’ve mentioned, space is tight, loss of grid power is rare, and I’m not looking to overcomplicate the goal of this installation. The only purpose is to support the pump with as close to 100% reliability as practical.

In the longer term, if the inverter/battery combination proves reliable I can remove the generator and optionally the ATS switchgear (except the RCBO).

The 48V 100Ah DaH Solar LFP battery has a specified 100A maximum which in conjunction with inverter bus capacitance I hope will be sufficient to start one pump reliably. I’d like to have some confidence that it will, please? I won’t have room for a larger battery.

My existing home-made pump controller will be configured to only allow one pump to run at any time, so that the only load is 23A for 0.25 second starting and 5.2A running, per the graph I posted earlier.

I’ll just add, since it’s been commented on twice, NZ electrical standards require that the M-E-N is re-established at the generator input to the ATS in the case where that is located some distance away from the main switchboard. The primary MEN is not connected to the load when the generator is running. This detail is notably different from Australia, whose regulations are otherwise identical. In this latest wiring configuration the second MEN does not impact the MP2 as it never sees it.

One last question: what is the basic difference between these versions? Or at least which one do I use? I have no intent to backfeed power to the grid or use PV.

Thanks!

AC switchgear will be in an adjacent MCB enclosure to the right of the steel box.