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Temporary but safe install as a UPS?


Elbow
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Hi everyone,

I have a Replus SineOn IH3KW-48-V inverter that I bought last year when Bonanza was clearing them.  Its still unused.  I also have two Pylontech US2000B batteries on the way.

Eventually I'll put up panels, but in the meantime I'd like to install them temporarily (but safely) to provide an anti-load-shedding UPS for my computers and maybe to feed some lights depending on how long shedding goes on for.

The load on the inverter will be well under 1kW - probably under 500W judging by data from my Openenergymonitor setup.

So I'm looking for some advice.

I have an existing dedicated power circuit running to my study, protected by a 20A C3 curve breaker on the board.  This feeds two red plugs in my study where my gear is connected.

1) Would it be safe to:feed AC input into my inverter from that plug using suitable heavy cable with a red plug on the end?

The inverter user manual says the inverter can draw 17A, the data plate calls for 20A, and the user manual says to protect with a 30A breaker.

SA  socket/plugs are officially rated 15A of course.

But even when charging batteries (25A*53V=1325W) + feeding the load (500W), less some inefficiencies I don't see the load actually exceeding 10A - 2300W at mains voltage.   At 15A I should be able to charge and also supply about 1500W which is far more than I require.

There is a AC filter supplied with the inverter and the docs specifically says it is to dampen surge current.

The main house DB is just a few steps away in the kitchen where there is a breaker to disconnect the supply in case of issues.  Plus, or course, a switch on the socket into which the inverter input is plugged.

I would set the inverter not to feed power back.

2) Can I connect the US2000Bs directly to the inverter?  I ordered the cables.

Do the batteries have adequate protection built in?  Or are external fuses and/or breakers essential?

3) Lastly, can I take the AC output to my computers directly, or is a breaker essential?  This is the area where I feel a bit uncomfortable to not have one since it is possible to have a fault on the supplied gear.

So what advice?

Thanks,
Steve

 

 

 

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22 hours ago, Elbow said:

I have an existing dedicated power circuit running to my study, protected by a 20A C3 curve breaker on the board.  This feeds two red plugs in my study where my gear is connected.

Just saying this ahead of time, you cannot uprate this breaker. 20a is the maximum allowed for plug breakers.

22 hours ago, Elbow said:

1) Would it be safe to:feed AC input into my inverter from that plug using suitable heavy cable with a red plug on the end?

I wouldn't call it safe. But it shouldn't damage the wire of the house. The 20a breaker protects the wire.

But it does not protect the wall socket, nor the plug nor the equipment.

The plug can officially only supply 16a, if you go more than that it will either melt and/or catch fire (both probably, melt first then fire).

I think you already decided to go this way tho, so at least install a 16a circuit breaker between the plug and the inverter. That R42 will be well spent :)

22 hours ago, Elbow said:

But even when charging batteries (25A*53V=1325W) + feeding the load (500W), less some inefficiencies I don't see the load actually exceeding 10A - 2300W at mains voltage.   At 15A I should be able to charge and also supply about 1500W which is far more than I require.

Have you measured this?

More importantly, what if, say your cleaning lady, your wife, children, etc. accidentally plug something in there that exceeds the rating?

I know it sounds silly but my experience that is 99% what usually causes problems in these illegal connections.

Someone who doesn't know about your "dirty little secret" :)

As I said, do the circuit breaker thing above. Also be 10000% percent sure none of the wires can come loose or that anyone can ever get in contact with them.

A dedicated circuit has no RCD protection, so if someone touches that wire they WILL die. No question about it. This isn't America where you can touch a live wire and walk away. A circuit breaker will not trip if a human touches it. I guarantee you that 100% they'll just die.

22 hours ago, Elbow said:

The main house DB is just a few steps away in the kitchen where there is a breaker to disconnect the supply in case of issues.  Plus, or course, a switch on the socket into which the inverter input is plugged.

Well trust me, electrical failures happen so quickly that by the time you realize you need to disconnect it, it has already escalated.

Just my 2c as someone who does a lot of electronics. By the time you realize you need to disconnect it, it is already smoking and probably caught fire or shocked someone to death.

22 hours ago, Elbow said:

I would set the inverter not to feed power back.

If you inverter tries to back feed it is going to explode in your face when Eskom comes back online.

It is like trying to stop the flow of a river with a garden hose with the hose pointed in the wrong direction.

Except in this case the hose explodes.

Your inverter will essentially act as a low impedance dead short.

There are videos online of noobs that try to back feed followed by explosions.

22 hours ago, Elbow said:

2) Can I connect the US2000Bs directly to the inverter?  I ordered the cables.

Do the batteries have adequate protection built in?  Or are external fuses and/or breakers essential?

Definitely need a disconnector and fuse. The low voltage high current part of the install (DC side) is the part of the install with basically no shock risk but very high fire risk.

I have one of those disconnectors and they are solid.

That type of fuse is the best but quite expensive (200kA breaking capacity), there are some cheaper options available. But they have lower breaking capacity (lower kA ratings). Basically the breaking capacity determines how much the fuse can stop without exploding in your face. So maybe if you keep it away from your face it could be ok to go cheaper.

22 hours ago, Elbow said:

3) Lastly, can I take the AC output to my computers directly, or is a breaker essential?  This is the area where I feel a bit uncomfortable to not have one since it is possible to have a fault on the supplied gear.

It depends on your inverter, was it designed to output power directly to appliances?

If yes then yes, if no then no :)

The engineer who built your system is going to know better than I do about what safety they have in it.

What does the manual say?

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It sounds like you want to make a suicide cable to get power into that circuit? The answer to that is always no. Simply no, do not do it. It is much safer (though still questionable) to go to your DB board, find the live and neutral for that circuit, pull them out of the DB and temp-hack them into your inverter. And then add a 20A breaker to protect the cable, and an RCD because it is feeding sockets.

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2 hours ago, plonkster said:

It sounds like you want to make a suicide cable to get power into that circuit? The answer to that is always no. Simply no, do not do it. It is much safer (though still questionable) to go to your DB board, find the live and neutral for that circuit, pull them out of the DB and temp-hack them into your inverter. And then add a 20A breaker to protect the cable, and an RCD because it is feeding sockets.

No, certainly not.

I’m not feeding anything back to the board.  I’m effectively making an ordinary plug in UPS setup with the output to a socket into which I will plug my switch, router, server.

 

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1 minute ago, Elbow said:

I’m not feeding anything back to the board.  I’m effectively making an ordinary plug in UPS setup with the output to a socket into which I will plug my switch, router, server.

Then I don't see a reason for concern. Just put a breaker and an RCD on the output, and make sure it is properly earthed.

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9 hours ago, plonkster said:

Then I don't see a reason for concern. Just put a breaker and an RCD on the output, and make sure it is properly earthed.

 

So I decided to try to do a proper job with an eye to the future.

 

IMG_20181209_195845.thumb.jpg.2a1aa8ef219f127db090ba66b6312009.jpg

 

Left to right on the board:

  1. double pole isolator for the incoming mains power
  2. 32A circuit breaker for the mains power going to the inverter (install document says 30A; but in any event the dedicated cct into which I will plug it has a 20A breaker).  I used the 32A because I will get the electrician to pull a suitable supply over from the main board and connect it up properly.
  3. 20A circuit breaker for the power coming out of the inverter
  4. Hager break before make changeover switch - up connects the output side to inverter out; down connects to input mains
  5. RCD for the power coming out of the changeover switch
  6. 1 x 20A and 2 x 10A for output from the inverter.

For now I'm just going to put a dedicated power socket alongside and connect it to one of the 10A breakers.  Much more than I need and well within the capacity of the inverter.

Elbow

 

 

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That's perfect as far as I am concerned. When you redo it later, get a bigger box (I hate working in cramped boxes) and just transfer the breakers.

Also, you can stick wires through behind the DIN-mount bar, there is usually a bit of space there. That way you don't have to route everything around or between breakers. A trick I learnt from my sparky.

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11 hours ago, Elbow said:

No, certainly not.

I’m not feeding anything back to the board.  I’m effectively making an ordinary plug in UPS setup with the output to a socket into which I will plug my switch, router, server

There are quite a few companies who sell solutions like this with inverters like the Axpert. Easiest would be to get a pre-wired DB with plugs (like they use at pools) and connect the inverter output to the DB mains

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6 hours ago, plonkster said:

That's perfect as far as I am concerned. When you redo it later, get a bigger box (I hate working in cramped boxes) and just transfer the breakers.

Also, you can stick wires through behind the DIN-mount bar, there is usually a bit of space there. That way you don't have to route everything around or between breakers. A trick I learnt from my sparky.

Thanks for the hints!

 

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