What Wattage rating for lamp limiter?

[pwdrive]

High power resistors/rheostats can be expensive unless you already have them to hand, one of the cheapest high power resistors is the filament bulb itself perhaps.

Lawrence.

[SurreyNick]

It occurred to me that a domestic dimmer switch might fit the bill as they have to dissipate anything up to 100W. I know some of the modern ones use electronics to turn the power on and off though and so won't work. I need to do some research. There's no point investing more than a few quid in this exercise as it was only an idle thought to include an easy reference table in the instructable - certainly not a requirement.

I like the solution of two 40W bulbs in series being able to switch between one or both. I had thought about doing a second instructable for a deluxe series lamp limiter which would include three bulbs of different wattage and a selector switch to choose the desired one. I was also going to add an RCD to this version too. That's a future project though and perhaps the subject of a new thread aka "What would you include in a deluxe series lamp limiter?"
We'll see.

Nick

[Nick]

It occurred to me that a domestic dimmer switch might fit the bill as they have to dissipate anything up to 100W. I know some of the modern ones use electronics to turn the power on and off though and so won't work. I need to do some research. There's no point investing more than a few quid in this exercise as it was only an idle thought to include an easy reference table in the instructable - certainly not a requirement.

All domestic dimmers use phase control to vary power - its not a voltage control like a resistive load. Forget domestic dimmers

The main way to vary voltage is to use a variac (a type of auto-transformer) - here's my REAL power controller using a variac & RCBO, MCBs, filtering and a meter: 



The schematic is here: 
  Variac Protection.pdf (Size: 40.39 KB / Downloads: 28)

The TDK RFI filter I used is really quite complex internally - needed because I didn't want the RFI from the stuff I was driving to get back into the mains...

   

[SurreyNick]

Now, that's a variac on steroids Nick! I have a much simpler version in the pipeline.

I'm probably just going to drop the idea of the quick reference table. It's too much trouble for too little benefit. I got the answer to the main question, which was what wattage bulb to use to get partial illumination with a 50mA device and that's good enough. The reference table idea was just a flight of fancy. I would have done it if it was quick and easy.

I note your comment that all domestic dimmers use phase control. I thought you could still get variable resistance types! Oh well, I really am out of touch.

Nick

[Refugee]

I built my lamp limiter in the 1970s.
It has a double pole switch that shorts out the lamp and also the neon bulb that is a crude leakage test. The ammeter terminals are in parallel with the lamp.

[SurreyNick]

It's surprising how many variations there are on the theme of the lamp limiter. I can see a deluxe version coming on....
I'm going off topic now though, so must stop.
Nick

[Alan Douglas]

My variac has a 3A ammeter. There's a series lamp too, a 500W halogen but that's only there to protect from dead shorts, and can be switched out if I actually need a lot of current.