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Garage Wiring, Coffee Roasting, Voltage Drop and Solar

Fultonius
Hi Folks,


I do a little coffee roasting. It's a 1300w machine, with a 230v heater element (40 Ohm - upgraded from a 240 / 44 ohm version). When running, it's drawing 5 amps and the voltage is dropping to 221v (around 229v before connecting).


Annoyingly, this means long roasting times in summer, and very long in winter! (not ideal)


So, here's my dilemma. I'm trying to consider the effects of voltage rise if I have batteries and an inverter. Obviously, I could get a variable output 1.5kw pure sine inverter and run it islanded. I have 7 x 16 ah 12v batteries redirected from going to the scrappies, which would have plenty juice to run this. I've been thinking for a while about putting a few solar panels on the roof and that's where it gets complicated.


Obviously the wiring from the house to the garage (at the bottom of the garden, so maybe 30m of wire) is a bit underspecced for what I need. Upgrading this would give me more chance of getting the correct voltage, and would probably make sense if I plan to put any "unused" power back to the grid. If the panels/inverter were grid-tied, what voltage would I end up with in the garage while running the roaster? My assumption is the amps will flow from the inverter to the roaster, and the grid will not have any effect? However, that's where my concern is - if my local voltage is higher, will that then default to pushing back to the grid and pull my voltage down?
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    I'd be looking very hard at the cabling if adding a 5 A load really loses you as much as 8 or 9V - that suggests the best part of 2 ohms in series in the loop.

    It's not  ' a bit underspecced ' it is 'woeful' .Consider a length of 2.5mm or ideally 4mm SWA as the most sensible minimum for even a couple of sockets and a light at that sort of distance.

    Is it running on a length of old lawnmower flex or something ? Even 1mm2 cable (the thin lighting stuff) would be about half that. (1mm2 is about 16-18 milliohms per core per metre, depending how hot or cold it is and how near the minimum of the production tolerance. )

    Any attempt to generate and push power back towards the meter with that sort of resistance in the way is pretty much doomed to fail, as the solar inverters cut off if their generation voltage rises too high. If you have 230V at the meter (and it sounds like you do more or less) then if the solar panels tried to generate say 10A, then the voltage at the panels would need to exceed 250 - and around then the over-voltage trip kicks in to protect the electronics  and any grid connected kit.
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    I'd be looking very hard at the cabling if adding a 5 A load really loses you as much as 8 or 9V - that suggests the best part of 2 ohms in series in the loop.

    It's not  ' a bit underspecced ' it is 'woeful' .Consider a length of 2.5mm or ideally 4mm SWA as the most sensible minimum for even a couple of sockets and a light at that sort of distance.

    Is it running on a length of old lawnmower flex or something ? Even 1mm2 cable (the thin lighting stuff) would be about half that. (1mm2 is about 16-18 milliohms per core per metre, depending how hot or cold it is and how near the minimum of the production tolerance. )

    Any attempt to generate and push power back towards the meter with that sort of resistance in the way is pretty much doomed to fail, as the solar inverters cut off if their generation voltage rises too high. If you have 230V at the meter (and it sounds like you do more or less) then if the solar panels tried to generate say 10A, then the voltage at the panels would need to exceed 250 - and around then the over-voltage trip kicks in to protect the electronics  and any grid connected kit.
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