Power switching, mechanical relays or solid state?

Hi,

I'm looking into building a power management unit that monitors a wind turbine, solar cell and generator for battery charging, (switching between each depending on whats available). And switches the load between generator, inverter or mains electricity, depending on what's available.

To cut a long story short, I need to switch a variety of voltages and currents (up to 16 amps at 240 volts) and I'd like some advice on the best way to do the switching. Should I use some simple 12 volt relays, or should I look at power-mosfets or some other solid state solution? I know that solid state is generally more reliable than mechanical, but I've been warned that using solid state devices may lead to electrical noise and interference that may cause problems if I'm using the power to drive a TV or computer.

Note - I'm not looking to build a solar, wind or battery charger, or a 240volt inverter. My plan is buy off-the-shelf units and make an arduino-based controller to monitor and control them.

Thanks

12V relay(which is probably DC) on 240V 16A(which sounds like AC), will blow up in a furry of heat and electricity. Be very cautious before working with high voltages. At that high of power, one little mistake can kill you.

Are the voltages you are controlling AC or DC? AC needs an Optically Isolated Solid State Relay. Here are some nice ones Ive used for some lighting projects. http://www.amazon.com/40A-SSR-Solid-State-Relay/dp/B004HZLMTW

12V relay(which is probably DC) on 240V 16A(which sounds like AC), will blow up in a furry of heat and electricity. Be very cautious before working with high voltages. At that high of power, one little mistake can kill you.

Just to clarify, I was referring to a relay with a 12volt DC coil, switching a 240volt AC supply, here's an example....maplin | the electronics specialist | FREE delivery over £20! | Maplin Why would it blow up in a furry of heat and electricity?

AC needs an Optically Isolated Solid State Relay

Why?

Here are some nice ones Ive used for some lighting projects. http://www.amazon.com/40A-SSR-Solid-State-Relay/dp/B004HZLMTW

They look good, with a control voltage minimum of 3 volts I guess it could be driven directly from an arduino without the need for any driver circuitry.

Oh I didnt realize you were talking about an AC/DC relay. Im not an expert but the purpose of optical isolation is to protect the AC current from getting into the DC current, sorry if my terminology is off. Any AC current through an Arduino pin would certainly cause damage.

Yeah, just plug and play, no need for any additional circuitry. I also use these relays when I need to save space. They are only rated for 125V 8A. Not bad for being 10x smaller. Solid State Relay - 8A - COM-10636 - SparkFun Electronics

OhMyCod:
switches the load between generator, inverter or mains electricity, depending on what's available.

This is something generally referred to as a "transfer switch". If it would be attached to mains, then there will be some specific safety regulations involved. In any event, this is something that has considerable personal safety implications.

If you have to ask on here for advice in this area, you are not qualified to do it.

A transfer switch must, for safety reasons, switch both the hot and neutral lines. You must have provisions for the neutral to be bonded at one place, that corresponds to the source of AC current -- the service entrance, inverter, generator -- and one place ONLY. Thus the need to switch neutral also.

My instinct is that SSRs are unsuited to this application, but I am not all that sure.

If you have to ask on here for advice in this area, you are not qualified to do it.

Sorry, but I really have to pull you up on this one. Having worked in the nuclear industry for many years, this is a really bad piece of advice, never assume that you know everything, always ask for advice, always get a second opinion!

But thanks for your input anyway!

OhMyCod:

If you have to ask on here for advice in this area, you are not qualified to do it.

Sorry, but I really have to pull you up on this one. Having worked in the nuclear industry for many years, this is a really bad piece of advice, never assume that you know everything, always ask for advice, always get a second opinion!

But thanks for your input anyway!

I think he's saying "If you don't know, don't do it.", and while asking for second opinions is a good thing, if you have to ask on THIS forum for advice, then you don't know, and so you shouldn't be messing with mains. If you have a clue, then you won't be asking here :stuck_out_tongue: