Variac Testbed Build

[Rontone]

I have been using my variac 'raw' for a while now just using ring terminals to hook up wires and croc clips so its really time to build it into more of a workstation,

Its a hefty beast, Regavolt 15A, it has a really annoying bolt pattern shape underneath so the base will be difficult to mark out and drill for bolting it down, I have some large sheet of paxolin to isolate it from the base of the box

I have looked at sluckeys 'Add a meter to your variac' topic here:- https://el34world.com/Forum/index.php?topic=25028.0

Its going to be fairly large and heavy, but wanted fusing and safety switch on the mains input side, analog and digital meters on the output, RCD panel mount wall socket to plug amps into with a light bulb current limiter mounted on top of the box

Could there be any problem hooking up both analog and digi meters on the same side?

Is it wise to have a meter on the input main side too? I am on UK 240v

[GAStan]

Hello. I'm new to this forum but have been an electronics tech since the '80s so hopefully will give accurate answers.

There is no harm in putting both analog and digital meters on a power line.  I'd be wary of doing this on a circuit as the combined impedance could affect the circuit under test.

The meter for the input would be ok, I don't know how necessary though.  That would depend on the stability/quality of the power in.  For me I would prefer a meter after the light bulb limiter more than on the input power.  As the light bulb limits current the voltage across it will increase dropping the voltage level of the amp, I would want to monitor the voltage actually going to the amp.

Hope this helps.
Glenn

[dragonbat13]

I do not have any answers to your questions but I sure hope you post the progress.

I want to build a similar type thing. I have one of those china bomb variacs, but its a 20 amp.  I would like to house it in a large enclosure with better metering.  I like the one that is often mentioned, but I messed mine up with a stupid move of the drill bit. I have to order another one.

One thing I want to try to install in mine, if possible, is a stand alone heater supply so I can adjust the correct voltage and current to whatever number of tubes I use.

[Rontone]

I finally found a box that is the right height for the variac, I will post some pics soon

I have a PZEM-061 meter on its way and can cut a hole in the panel to fit it in

Just need to work out switching for the bulb to the output socket

[Rontone]

I didn't realise there are different types of RCD, active and passive,

In the instructions for the active one I have it says the device will trip if:-

"A sudden dramatic reduction in, or total loss of, the Mains Supply Voltage (excluding the Passive control circuit devices - see below)"

So for use with a variac output, would a passive be better?

I shouldn't have a sudden reduction in power, unless a fuse blows, but may be dropping the voltage low in some uses or starting low, which may trigger the RCD?

[PRR]

The RCD goes "before" the Variac, no? So it always has 120/240V, and will never drop-out for lack of power (until the drunk Jeep hits my power pole AGAIN).

[Rontone]

The RCD goes "before" the Variac, no? So it always has 120/240V, and will never drop-out for lack of power (until the drunk Jeep hits my power pole AGAIN).

I must fix that steering rack before I go out for a Friday night drink....

I had a single socket with RCD so thought I could use it as the outlet socket on the testbed,

So would it be better to just fit this RCD socket to my home wall socket and simply plug the testbed into that?

[PRR]

> just fit this RCD socket to my home wall socket

Makes sense to me. (Assuming you can do it and live.)

Also protects against ground faults in soldering iron, lamp, etc. I'm not in favor of GFI *everywhere* (got tired of the furnace kicking off) but around water (bathroom) OR bare electric metal (workbench) it makes sense to protect everything in reach.

But maybe others have better thoughts.