Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 11 replies
  • Subscribers 32 subscribers
  • Views 1013 views
  • Users 0 members are here
Options
You may also be interested in
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

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?
Parents
  • 0
    It's probably simplest to think of the grid-tied inverter as being a "negative" load.


    So if the PV was producing 1A and the roaster was drawing 5A, then 4A would be drawn into the garage from the house. (Load = 5A + (-1 A))


    If the inverter was producing 6A then the overall load would be -1A - i.e. 1A would flow from the garage back to the house.


    Voltage drop would be in proportion to the load (in both magnitude and direction) . If you're losing 8V with a 5A load you, reducing the load to 4A would reduce the voltage drop to 6.4V so you'd have something like 222.6A instead of 221V (ignoring any voltage drop within the garage for simplicity). With a -1A load you'd have a -1.6V voltage drop in the garage supply - i.e. an increase of 1.6V from house to garage giving you something like 230.6V.


    That said, the practice might not be as simple as the theory suggests. Ordinary PV inverters don't produce a nice constant current just when you want it, but vary considerably with the intensity of the sunshine. You'd probably need rather more than a garage roof full of PV panels to get anything like a reliable 5A even during clear days. Adding batteries might seem attractive but makes things much more complicated - how would you regulate the output from a battery driven grid-tied inverter - when the connected load includes the national grid?  If battery driven, an islanded system that only supplies your loads is probably more practical - but then you probably want a mains supply to re-change the batteries when the PV isn't sufficient. There comes a point where replacing the 30m of cable with something more sensible starts to look attractive....


    Actually 8V v.d. for a 5A load over 30m feels like rather a lot - that would imply a cable with a loss of more that 50mV/A/m - which would suggest it's rather smaller than 1mm² - which feels rather unlikely. Perhaps you've a loose connection or corroded joint somewhere that's the real cause of your problem.


       - Andy.
Reply
  • 0
    It's probably simplest to think of the grid-tied inverter as being a "negative" load.


    So if the PV was producing 1A and the roaster was drawing 5A, then 4A would be drawn into the garage from the house. (Load = 5A + (-1 A))


    If the inverter was producing 6A then the overall load would be -1A - i.e. 1A would flow from the garage back to the house.


    Voltage drop would be in proportion to the load (in both magnitude and direction) . If you're losing 8V with a 5A load you, reducing the load to 4A would reduce the voltage drop to 6.4V so you'd have something like 222.6A instead of 221V (ignoring any voltage drop within the garage for simplicity). With a -1A load you'd have a -1.6V voltage drop in the garage supply - i.e. an increase of 1.6V from house to garage giving you something like 230.6V.


    That said, the practice might not be as simple as the theory suggests. Ordinary PV inverters don't produce a nice constant current just when you want it, but vary considerably with the intensity of the sunshine. You'd probably need rather more than a garage roof full of PV panels to get anything like a reliable 5A even during clear days. Adding batteries might seem attractive but makes things much more complicated - how would you regulate the output from a battery driven grid-tied inverter - when the connected load includes the national grid?  If battery driven, an islanded system that only supplies your loads is probably more practical - but then you probably want a mains supply to re-change the batteries when the PV isn't sufficient. There comes a point where replacing the 30m of cable with something more sensible starts to look attractive....


    Actually 8V v.d. for a 5A load over 30m feels like rather a lot - that would imply a cable with a loss of more that 50mV/A/m - which would suggest it's rather smaller than 1mm² - which feels rather unlikely. Perhaps you've a loose connection or corroded joint somewhere that's the real cause of your problem.


       - Andy.
Children
No Data

Community Rules & Guidelines