-cyclops avatar image
-cyclops asked

multiplus - various questions


I'm located in the UK and work from home. With the prospect of blackouts/load shedding/whatever you want to call it - it means that i've been looking at means to stay with power over a duration of 3 hours (as that's what the current rota suggests).

I've been monitoring the consumption of the house for a few months already, so i should have good data on what our house consumes. It's not too much. On a normal day we take about 12 kHw over 24 hours, but this includes cooking (on induction). Our normal load during the day seems to be between 200 and 400watt.

Although the victron systems make me quite greedy, i have realized that a multiplus 800va or 1200va would be enough to handle the normal load (please correct me if i didn't understand this correctly).

But, i wonder a few things:

  • What happens if i do start using more than the multiplus can supply?
  • How is this wired up in a way that it works like a UPS (for the whole house)? Does it mean that all power needs to flow through the device and does it mean that the 800va/1200va is a limit the whole house would be on?
  • To calculate battery size, can i simply take the Ah of a battery and multiple it by the voltage to get the kWh? So for example a 110Ah 12v battery is 1.32kWh ? Of course, it's not 100% effective so you'd end up with (i guess) around 1.2kWh.
  • If i have a multiplus 48v - can i then also charge 24v or 12v batteries?
  • There seem to be different multiplus'es

I am pretty sure about these things from my research, but i just want to confirm here before i start pressing 'order now!' buttons online :-)

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3 Answers
Jason - UK avatar image
Jason - UK answered ·

@_cyclops_ If you pull more than the stated current thought the unit, you will damage the unit but also if you undersize the unit, you wont be able to get the correct cables size to connect to the unit.

If you are looking for an off-grid / UPS solution, you need to take into account the pass-though current - IE the 5kva unit can take 50 amps.

You also need to research the type of battery you are considering and the discharge rate. Lead acid batteries reduce in useable energy the quicker you extract that energy from the battery.

If you are looking for a UPS system for just working form home, in simplistic terms, a 1200va unit connected to a battery serving a single power socket would be a cost effective solution. For a whole house solution, you would need to start looking at the 5kVa units or bigger to cope with the pass-though but also the potential off grid / UPS power loads.

I have my whole house running off a 5kVa Multiplus II GX connected to 4No Tesla Model S car battries. I can run my house for about 2 days solid with no solar or grid supply, and about 20 hours on a weekday in the winter. The missus cooking a Sunday roast (induction hob) with the heating (ASHP) keeping the house warm will empty the batteries in under several hours.

Below is a link to my system. ON the left hand tap is my photos on my install but also a schematic of my system.

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-cyclops avatar image
-cyclops answered ·

Thanks @Jason - UK

That explains a lot for me. I guess i'm going to just get a UPS for the things that need to keep running, as the investment to get the pass-through current is just to high.

Your setup is impressive. What's the reason for you being fully off-grid? Most of the UK is pretty well connected to the grid?

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Jason - UK avatar image Jason - UK commented ·
@_cyclops_ My setup is not aimed for UPS inherently. Its aimed at the ESS to best utilise my solar energy generation. Because of this set up, my energy bill each month is average £10.
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-cyclops avatar image -cyclops Jason - UK commented ·
That make sense. I guess you'll be able to earn that back over a number of years. Great stuff!
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johnone avatar image
johnone answered ·

If it's any help. here's my attempt at an ESS schematic - NB while @Jason - UK's schematic is of an actually working system, I'm just at the design/purchase stage! All comments welcome


ess-schematic.pdf (52.2 KiB)
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