Automatic grid to renewable switch design

Re: Automatic grid to renewable switch design

I have not looked up the switches you are using... But my questions would be:

1. You have the Blue (N) connection common between the AC mains and the Inverter. I would probably prefer to have switch both the L and N connections (double pole, single throw type switch). Keeps any surges from the mains further away from your inverter/battery setup (running on mains, the inverter is 100% isolated behind relay).

2. The switches you have--can you guarantee that they are "Break before Make" type connections? They appear to have 2 independent control inputs--I would be concerned that you may have a race condition where one switch stays on while the other switch is connecting--and for a split second, both the inverter and mains are connected together--not my idea of "fun".

My question is "why" are you doing this? Emergency automatic or manual power transfer (which one)? Or are you going to turn on the inverter manually--so could you use a manual transfer switch instead (double pole, single throw, break before make).

Also, what are your loads... Lighting and appliances--or a computer and you are making a large UPS--where a 1/2-1 cycle transfer glitch can cause the computer to crash.

If you are working with the mains (AC connection from power company)--transfer switches are safety critical devices and are not something you should wire up yourself. Any problems--and you might be open for big problems.

If you are working with a large 2-3+ kWatt TSW (True Sine Wave) Inverter--may include their own transfer switches (and even AC battery Chargers)... So the designs can get sort of complex to make sure they remain safe.

If this is, for example, running from a generator on your farm, and sharing with solar power--a bit less of a liability issue--but still, may be worth looking at an off-the-self transfer switch (north American product here).

-Bill

Re: Automatic grid to renewable switch design

Boy--I am not sure I have the time to look into what Digital Relay would work well for you--you can get those in SCR (which will turn off at a phase crossing) or other styles (with coordinated or random on/off timing).

My fear is that you turn on one relay instantly and the other (SCR type) turns of at the next zero voltage crossing. So, you could end up with both relays on for 1/2 a cycle--Not a good thing for synchronized inverter/grid connection. Might blow a fuse or a FET/Transistor very easily.

You can certainly find 240 VAC DPST 24 volt mechanical relays--that would take about 1.2 watts to hold "on"... I cannot tell if it is a From C (common connection break before make relay or not from what I have seen so far)...

The Prosine 1,000 has a 15 amp transfer switch option (don't know if it is a factory or field install option)--this was listed for the North American version--don't know if available for Europe or not.

You might have to browse through the relay catalogs or call a supplier to see if they can direct you to the appropriate part quickly or not.

Since you are in the UK--anything that I find for a standard AC Transfer switch is probably going to have issues in your country.

-Bill