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Author Topic: Info Please on ELTEK SMPS 5000 SIL V3 48v/100A, Mains 230vac Charger  (Read 22124 times)
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« Reply #75 on: July 06, 2015, 04:28:07 PM »

I should not drink coffee before posting.

Never earth through a relay.  You have no way of knowing that it ever got re-connected unless you install earth monitoring.  Relay contacts tarnish and go high impedance.  If you were on grid, the prospective Isc would blow the relay apart on a serious fault.

Good to know. The relay I believe you are referring to is a centre-off clunkin' redundancy switch.
Yep.  Switch. 

The dotted line between N & E on the inverter needs to be solid and clearly labelled.  
It's dotted because I'm not sure what to do with it. Is it correct? I'm sure that'll let the smoke outtov a cheapo centre tapped Mod. square waver.

There is no reason to ever remove earth from an appliance, so just bond it all together.

If I tie the inverter neutral to earth downstream of the grid earth neutralising point will this not make smoke? Even if not isn't this creating unsanctioned TN-C-S earthing?
The inverter is floating until it's bonded.  You have to tie one side of it to mains earth, otherwise you've got yourself at IT system.  Earth monitoring for IT systems are eye watering in cost (RCD not adequate) and have onerous maintenance requirements. Same with a genny.  N on them is normally connected to chassis, and we always bond the genny frame to an earth spike as the instructions tell us.
You should never create smoke by connecting the inverter N to earth (effectively TN-C-S), but you create a dangerous situation by not connecting, as you rely on RCD (not permitted) and you'll never clear a fuse on single fault to earth, because there is no path for fault current.
Your double pole switch ensures you don't mix the grid earthing with the inverters.
Depending on the inverter, you may find there is no isolation between mains N and battery 0V. In that case, you've tied the panels to earth.
It's not unsanctioned TN-C-S as you are never connected to the grid. Only the earth is common between systems. The only tricky bit is which colour to use.  Blue link to earth or G/Y to N? Or both to a marked terminal.
Sketch it out and work it through, remembering the inverter is floating, and everything has to have a earth fault path

No real need to earth the panels.   SMA GTI's use earth monitoring on the floating inverter.  However, it wouldnt hurt to link 0V to earth with say a 1M ohm resistor.  This will remove stray current and prevent the panels from floating up - the various power supplies will move the + or - upwards to around 1/2 mains volts ie 110V through filter caps - just enough current to give you a feathery feeling.

What kind of power dissipation does that resistor need?
As it has, theoretically, no current through it, 1/4W. If you find it all smoked out, you know there's a problem.
I've never felt the urge to do it myself, but it's common in electronics design.

What's the size/function of the diode - commissioning protection against incorrect battery polarity?  Needs to be absolutely enormous to clear the fuse.
IIRC the tristar 0V is a link, so connect the panel 0V to the star point? Not sure, as this may introduce unwanted current flow & noise towards the star.

Transient suppressor as recommended in the manual for protection against inductive loads.
Ah yes.  Essential for large contactors too.
It would be a good idea to put some smaller, say 1A diodes across your relay coils too, as you can kill the power supplies with the back EMF. Noisy too.

I'd be tempted to replace the SSR with a relay - personal thing.  If you keep the SSR you don't need a buck converter to go 48v to 24v.  The current input on the SSR is trivial, so 2 x 10k 1/4W resistors would probably do it.

I'm not a fan of mixing voltages in the same panel/instrument. The SSR has zero crossing and is optically isolated between the 24VDC control and 250VAC switched load. I'd prefer that than rely on the isolation of an enamelled coil.
The mixing thing is always tricky.  It happens which ever way. 

As drawn the ammeter will only show charge current.
That's all I want there, positive current = surplus, negative current = discharge.

There are a few manufacturers of AC breakers who will rate them at much lower DC volts/amps.  If you PM clockmanFR he can tell you. You can also use 3 phase breakers and put all 3 in series to get a higher DC voltage breaking as a single pole device. Depends how the budget is holding out on DC breakers/isolators probably should have started a new thread, as this is a good stand alone project.

1.1kWp PV & SB1700. 7kW log burner.
« Reply #76 on: July 07, 2015, 03:57:47 AM » probably should have started a new thread, as this is a good stand alone project.

Bosch!,25187.msg291234.html#msg291234  Grin
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