Mains Fault Detection

[carlosthejackle2001]

Hi

Am currently doing a project for university (in Great Britain) and was wondering if anyone could help me out or put me in the right direction.

The project is on fuel cell technology as an alternative power supply when there is a black out.

The area that am looking into is detecting mains failure & switching to backup supply - I've found plenty information on UPs systems but am not looking for an integrated package. The problem is I can't find any circuits for detecting mains failure and/or switching to backup supply. Are there any?

The idea that I have come up with (with very limited knowledge on power electronics) is to just perhaps use a relay that is energised by the mains and when a black out occurs it changes contacts and backup supply is enabled - have been told that this would be inefficient and also a semiconductor alternative would be preferred so that no spark is created.


Any information/advice would be appreciated


Thanks

 

[JimB]

The relay idea sounds good to me, I have used that for detecting and switching supplies on power failure several times.

Inefficient? OK the relay coil is permanently powered.

Sparks? What is the problem here, explosion protection or EMC considerations? OK if you have explosive vapours then you need a very rigorous approch to the design, if EMC is the problem, given the switching frequency, ie now and again, a switching relay is not a problem.

A relay is cheap, easily understood and provides electrical isolation.
The solid state equivalent will probably be more expensive, more complicated and will not provide complete electrical isolation.

JimB

 

[jkmadsci]

How about a cheap wall wart 120 ac in to 5v dc out. If power goes out, so does 5 volts!!!

 

[chemelec]

The Only problem with Relays is they are Slow.

They will Switch on you backup Supply, NO PROBLEM.

BUT When the Power comes Back on, There will be a "Brief part of a Second" where Both Supplies, "Will be on at the Same Time".

In Some Situations this can Create a Problem.

But I would also just use the Relay. Preferably one that has a 110 VAC Coil.

A Wall Wart is a BAD Idea. It has a rectifier and Capacitor in it. This capacitor storage could Create a LARGE DELAY of a Second or More, in holding in or releasing the relay contacts.

Gary

 

[Nigel Goodwin]

The Only problem with Relays is they are Slow.

They will Switch on you backup Supply, NO PROBLEM.

Simple is GOOD!.

BUT When the Power comes Back on, There will be a "Brief part of a Second" where Both Supplies, "Will be on at the Same Time".

Not if you use a changeover relay!. I've had a generator connected in that way for years, as the generator fires up it turns the relay on, switching from mains to the generator. Even when the mains comes back on the relay keeps supplying power from the generator, until you turn it off.

In Some Situations this can Create a Problem.

But I would also just use the Relay. Preferably one that has a 110 VAC Coil.

Not much use on the 230V mains in the UK 8)

A Wall Wart is a BAD Idea. It has a rectifier and Capacitor in it. This capacitor storage could Create a LARGE DELAY of a Second or More, in holding in or releasing the relay contacts.

Yes, that's a bad idea :!:

 

[JimB]

Exactly what Nigel said.

JimB

 

[carlosthejackle2001]

Sparks? What is the problem here, explosion protection or EMC considerations? OK if you have explosive vapours then you need a very rigorous approch to the design, if EMC is the problem, given the switching frequency, ie now and again, a switching relay is not a problem.



JimB

Explosion protection - I am currently looking into special casing for hazardous environments.

Relay change over time - although it be prefered for it to change in short as time as possible this isn't an issue at this stage - this is because it be only worth while if the generator was up and running already.

Thanks for the replies, they are much appreciated.

 

[tansis]

How much energy does the fuel cell require for start up?

 

[carlosthejackle2001]

How much energy does the fuel cell require for start up?

Am not sure on the energy as I don't have the technical datasheet at hand but it needs 24V battery. Also a computer with specialised software is needed to start it up but this will be supplied by the company.