My Bright Green Lamp Limiter

[Mike Watterson]

And a curious BC22 adaptor with two sockets, one of which is switched.

My mum used that so that she could put the lamp into the switched one and the iron into the other.

My dad also used one in the "under the stairs" darkroom for the enlarger. Possibly had a safelight on the switch as the safelight couldn't be used for panchromatic film. He developed medium format film in bowl (120?). I think the tank only took 35mm and maybe 127.

Those were once common especially in rural places that maybe had only a lamp socket in some rooms. Used for the radio.

[ppppenguin]

I've got all sorts of BC adaptors and plugs. I used some fairly recently to rig some temporary lighting with more than one lamp run from a single pendant lampholder.

I keep a lead with a BC plug on one end and 4mm plugs on the other with my lamp limiter. One end into one of the lampholders, the other end into a DMM to measure current. I know I don't the lamp limiting the current when doing this.

[Dave Moll]

And a curious BC22 adaptor with two sockets, one of which is switched.

They were quite common so that you still have the bulb in use (or switched off) while using the iron (or whatever).

And yes, I also have at least one of them in my collection of old plugs and sockets.

[DrStrangelove]

Last night I dreamed about building another one. Ho hum.

It was complicated because I only had a moving coil ammeter, giving rise to some angst & circuit complications.

I was quite relieved when I woke up.

[Mabo5]

I used my new lamp limiter box today for the first time.

I built it over a year ago.

It is blessed with a moving iron voltmeter and a moving iron ammeter.

Trouble is I can't remember if the ammeter shows half or twice the real current since it's calibrated for use with a current transformer.

It looks quite impressive in its bright green plastic biscuit "tin".

Hi,
I've put together a Current Limiter in a panel fronted box, and need a colour wiring plan for it. 
Searches and advice from the ether have proved wrong, edging towards fatal.
The components are a fuse (5A), Digital Volt/Ammeter, four bayonet bulb holders (for 2 x 40W and 2 x 60W bulbs) with on-off rocker switches for each of them, and a bypass switch to override them so power can go directly from the Variac to the Device under test.
It's powered from an Isolation transformer via a Variac using a A 3-pin (UK) plug...
I have two photos of it... 
can you help me out on this at all?
Thanking you,
Peter

 

It's a pity no-one knows how to wire this up, but it was worth a try posting it here as the responses to other radio-based queries are pretty good.

[Doodlebug]

This adaptor is made of porcelain with solid brass fitting. Also an old top pip lamp.
   

[Mark Hennessy]

It's a pity no-one knows how to wire this up, but it was worth a try posting it here as the responses to other radio-based queries are pretty good.

It's partly about liability.

If someone here gives you a wiring plan and you later receive an electric shock, how would they feel? Or worse, what if you - or someone acting on behalf of your family should the shock be fatal - decides to pursue the forum member for damages and compensation?

I feel it might be a good idea to remind folk of our disclaimer: https://golbornevintageradio.co.uk/forum...help&hid=9

To be honest, there's quite a few things that leap out at me about this project.

For example, the neon lamps in all those switches won't come on at lower voltages. Might that be confusing? Probably best to leave the "N" terminal disconnected for the single-pole switches.

The panel meter probably needs a separate supply - is that being fed separately? How to ensure you don't accidentally swap them, which would result in the "full" mains going to your "DUT" (device under test)?

What about the isolation transformer? There is so much confusion about the use of isolation transformers in the vintage radio community - I've lost count of the number of threads I've contributed to over the years, and have been horrified by what some people believe and practice. The addition of an isolation transformer can actually make things less safe in certain scenarios. Generally, an RCD provides better safety, and an isolation transformer will only be needed when you need to connect grounded test equipment to certain areas of certain equipment - they are not a thing to use by default on the false assumption they make everything safe.

With all that said, I think you are correct to not just plough ahead with it. As frustrating as it might feel now, it's best to wait until your knowledge allows you to make your own informed decisions, with full understanding of the implications. Feel free to sketch something up for feedback, and I'm sure you'll get good advice about it, but asking others to do the design work for you is not really fair when there is so much at stake.

Hope that helps,

Mark

[Mike Watterson]

Well said.

[Mabo5]

It's a pity no-one knows how to wire this up, but it was worth a try posting it here as the responses to other radio-based queries are pretty good.

It's partly about liability.
If someone here gives you a wiring plan and you later receive an electric shock, how would they feel? Or worse, what if you - or someone acting on behalf of your family should the shock be fatal - decides to pursue the forum member for damages and compensation?
I feel it might be a good idea to remind folk of our disclaimer: https://golbornevintageradio.co.uk/forum/misc.php?action=help&hid=9
To be honest, there's quite a few things that leap out at me about this project.
For example, the neon lamps in all those switches won't come on at lower voltages. Might that be confusing? Probably best to leave the "N" terminal disconnected for the single-pole switches.
The panel meter probably needs a separate supply - is that being fed separately? How to ensure you don't accidentally swap them, which would result in the "full" mains going to your "DUT" (device under test)?
What about the isolation transformer? There is so much confusion about the use of isolation transformers in the vintage radio community - I've lost count of the number of threads I've contributed to over the years, and have been horrified by what some people believe and practice. The addition of an isolation transformer can actually make things less safe in certain scenarios. Generally, an RCD provides better safety, and an isolation transformer will only be needed when you need to connect grounded test equipment to certain areas of certain equipment - they are not a thing to use by default on the false assumption they make everything safe.
With all that said, I think you are correct to not just plough ahead with it. As frustrating as it might feel now, it's best to wait until your knowledge allows you to make your own informed decisions, with full understanding of the implications. Feel free to sketch something up for feedback, and I'm sure you'll get good advice about it, but asking others to do the design work for you is not really fair when there is so much at stake.
Hope that helps,
Mark

Hi Mark,
THank you for our reply.
Yes it does.
The design comes from an existing DBT; the schematic the chap can't locate as it was quite some time ago, and it was constructed with a Variac built in to the panel for his own practicality on the testing bench. 
I was just pitching it here to see if it was 'straightforward' to an electrician... 
I use a Variac via an Isolation Transformer for repairs and restoration but a DBT like this provides (IMO) some 'finer control'.
The AC powered panel meter itself the digital panel meter itself requires a direct AC mains voltage connection (typically 80V to 260V AC) to power its internal circuitry and illuminate the display, and comes with a 100A split-core current transformer. 
Best Regards,
Peter

[Mark Hennessy]

Hi Peter,

I'm sure you'll get there

Noting you're using the US term ("Dim Bulb Tester"), if you haven't already, it might also be worth searching for "Lamp limiter", which I think is the more common term in the UK. That should bring in some more results.

You might have already seen it, but here's a really simple version: https://www.vintage-radio.com/projects/l...miter.html

And there is a very well documented build of that here on this very forum: https://golbornevintageradio.co.uk/forum...p?tid=4781

It's a good starting point. As you want to have multiple lamps of different powers, I'd just put them in series with the bypass switch across each. As mentioned, you probably can't make use of the neon bulb within, unless you think it might actually give you some useful information about the voltage seen at that point in the chain and Neutral.

Definitely carry the Earth across. On those occasions when you wish to use an isolation transformer (and you *know* why it's necessary), then I'd place it between the lamp limiter and the DUT. Remember that your RCD prior to this unit will no longer offer you protection on the output side of the transformer. For the transformer itself, do not carry the Earth through. You can read about transformers separately in this document: https://golbornevintageradio.co.uk/forum...?aid=11638

Not having the variac in the same box is a complication because, as mentioned, it means you'll need two mains inputs to get the meter powered. I know you've made the opening for it, but I'd be inclined to drop it as the variac markings will give you a close enough idea of the input voltage and the behaviour of the bulb will let you know what the load it doing. Obviously the rating of the selected bulb will give you a decent idea of the current flow. This is all quite imprecise in nature - the idea being to know when it's safe to skip the bulb once the basics of the DUT are established - so accurate current measurements are "nice to have" in a lamp limiter. More valuable on the variac itself, arguably.

Some of those voltage/current meters can be a bit sketchy - here's one that I tested and ended up modifying quite substantially: https://www.markhennessy.co.uk/mdu/

All the best,

Mark