What Wattage rating for lamp limiter?

[SurreyNick]

I have a 100W bulb in my lamp limiter which doesn't illuminate at all when put in series with a component bridge drawing just 50mA. That isn't surprising when the bulb requires 417mA to fully illuminate and about 300mA to partially illuminate it i.e. the sort of current drawn by a valve radio.

Is this percentage, i.e. 70-75% of a bulb's normal current, what I need in order to get a dull glow with the limiter? If not, what level of current will get some noticeable illumination in daylight? For example will a 40W bulb partially illuminate with a 50mA current? It'll take 167mA to illuminate it fully. How about a 60W bulb? That requires 250mA. Will 50mA even register on the filament?

I'm trying to work out what wattage bulb to buy for my limiter to test my 50mA component bridge, without having to fork out for several bulbs to find the right rating.

Thanks

Nick

[boater sam]

I use a 40w for most radios which are 40w to 65w appliance draw, 60w for a TV or something over  100w draw, 100w for bigger stuff.
40w will glow with a definite amount of light output with a 50w appliance. With 60w bulb you will be able to see the filament. 100w will barely warm up.
It matters little really, any wattage between 40 and 100 will limit the current with practically all radios and serve to prevent fuses blowing due to shorts which is the main reason for using a bulb limiter anyway..
If you need to control the current you really would be better using a variac.

[Yorkie]

I tend to use Poundland 60 Watt clear glass ones.

You get a direct view of the filament rather than with opal glass ones. (Obviously).

As Sam says, most domestic radios tend to range from 40 - 65 Watts or thereabouts, depending on the valve line-up.

The ubiquitous Bush DAC90A for example is listed by Bush as consuming 35 Watts.

[pwdrive]

Nick here's a link to show hot and cold resistances of a 40, 60 and 100 watt filament light bulbs (I've not checked it's accuracy, no facilities at the moment) anyone on here checked the resistances in practice?....Just out of interest.

http://www.electronicsfaq.com/2013/11/me...-cold.html

Lawrence.

[Yorkie]

That's a neat and well thought out presentation Lawrence.

Well spotted.

[tiv48]

I agree with the others for radios I use 40 watt
for tv and some amps 60 or 100 watts.
on colour tvs you have to disable the degaussing circuit.
some S.M.P.S don't like to start with a lamp limiter because of the need for a start up supply.
Rob T

[pwdrive]

That's a neat and well thought out presentation Lawrence.

Well spotted.

David,yes, I've been trying to find on the web some plotted curves for various voltages versus current/resistance when applied to a 230/240 volt filament bulb, didn't find anything on my first trawl but that link I posted came up, from that it might be able to establish a general prediction curve for higher and lower wattage bulbs not covered in that link, why?...dunno, I just find some odd things interesting.

Lawrence.

[SurreyNick]

OK, I got my answer - 40W should do it. My thanks for that.

What I should have explained but neglected to include in the OP was that I want a degree of bulb illumination because it's for a photo I want to take. I am preparing an instructable on assembling a series lamp limiter for beginners and it includes a number of photos of the limiter in use. One of the photos I want is showing a bulb partially illuminated indicating the device under test doesn't have any serious problems. Hopefully a 40W bulb will oblige with my 50mA component bridge.

As David said, that presentation on the hot and cold resistances was interesting Lawrence. It has given me the idea of perhaps creating a quick reference table to include in my instructable showing what sort of illumination one could expect with a current draw at 50mA increments up to 500mA for bulbs of 25W, 40W, 60W, 100W etc. I wonder if a beginner would find that a useful aid to selecting the bulb wattage for the device they want to test? I imagine I should be able to determine the answers using a simple device comprising a 0-500mA AC meter along with a fixed 470 ohm resistor in series with a 0-5000 ohm pot. If I plug that into the lamp limiter I should be able to vary the current from 44mA to 511mA.

Nick

[Refugee]

You will need a big powerful pot if it needs to pass 500ma.

[Nick]

My lamp limiter has two 40w bulbs in baton holders in series - each bulb has a switch in parallel with it - i.e. depending on the switch settings you can have no load in line, 40w or 80w - I used a standard twin gang light switch and wall box for this. Obviously this scheme can easily be extended as required...