Controlled Mains Test Bench

[solis365]

Hi again everyone

Everyone needs to power their projects, so everyone at some point needs to build something that connects to a wall. I was thinking about building myself a work bench with some form of mains circuitry protection - basically I plug this circuit into the actual wall, and it provides a somewhat safer "mains" level outlet for me.

My thoughts are having a bank of circuit breakers on the board used to set a current limit in case of a short - can you find breakers that will trip at 1A or so? If so, can you get 20 of them and wire the breakers in parallel, only increasing as you know you need additional current? This would prevent the entire wall circuit from tripping.

I would probably also implement some sort of large, easy to press kill switch. Additionally, an isolation transformer.

Though probably not to start, I might eventually add an AC ammeter and voltmeter to the box just to keep tabs on how much power I am drawing.


Does anyone have thoughts on this, or already done something like it? Mains will never be truly safe (i.e., foolproof), but I figure if it's something I'm going to do on a regular basis I might as well make it as safe as possible. This has the added benefit of not having to go to the circuit breaker box every time I blow something, and also not inadvertently shutting down devices connected to the same circuit (I try to experiment on otherwise empty circuits anyway, but...)

 

[Mike_2545]

For any bench AC projects I run the mains through an isolation transformer like this one:

TENMA|72-6670|Isolation Transformer | Newark Canada

 

[solis365]

Thats a very nice product, I might incorporate it into my design as the first stage in protection. I kind of like to DIY (i.e., buy a transformer and make my own) but when it comes to mains safety I would probably use this as it has been tested safe.

Still looking for thoughts on adjustable current breakers (i.e., lots of low-current breakers in parallel, to be switched on and off to adjust current limit.)

 

[BrownOut]

I don't know about circuit breakers, but you can get fuses and inline fuse holders. They are cheap and available.

 

[colin mac]

You can use these.
**broken link removed**

The mains isn't supplied until you close the lid.

 

[JimB]

can you find breakers that will trip at 1A or so?

Yes.

If so, can you get 20 of them and wire the breakers in parallel

Connecting circuit breakers in parallel sounds like a really bad idea.
At the moment I can't give a firm reason why, but it sounds like very bad practice.

JimB

 

[BrownOut]

That's how they are connected in your house

 

[RODALCO]

To control or limit the current in a circuit have a one or two 100 Watt lamps in series with a bypass switch.

A variac is a handy device too to control your voltage from zero to mains voltage.

 

[JimB]

That's how they are connected in your house

My circuit breakers (fuses actually) are connected to a common header rail.
They are NOT connected in parallel.
In a parallel connection, the inputs are connected together and the outputs are connected together.
That is not how a mains distribution box is wired.

JimB

 

[ericgibbs]

My circuit breakers (fuses actually) are connected to a common header rail.
They are NOT connected in parallel.
In a parallel connection, the inputs are connected together and the outputs are connected together.
That is not how a mains distribution box is wired.

JimB

Jim,
Thats the same as most, as you say common rail in, with separate breakers feeding different power/lighting outlets.

 

[BrownOut]

I agree with JimB, you should think carefully before connecting circuit breakers in parallel. I was thinking about a common input bus when I wrote my earlier comment.

 

[KMoffett]

.....A variac is a handy device too to control your voltage from zero to mains voltage.

I agree. Add a current and voltmeter on its output. I found this was the best way to check devices that are blowing fuses. With a good fuse in place in the device, "very slowly" advance the voltage control on the Variac. If the current meter reading immediately starts increasing at only a couple of volts you have short, but have not blown the fuse. Start disconnecting sections of the power feed within the device from the cord inward. Then repeat the procedure. If it doesn't indicate a short, reconnect, and disconnect the the next section further in. Repeat this until you see the short indication again. That will eliminate a lot of possible things. I've never blown another fuse with this trick.

Ken