neon indicator light in a series circuit

[whiterabbit]

First thanks for helping,

I am rigging a wire harness which will power 7 lamps connected in a series.

The harness is connected to a variable transformer so that I may raise or lower voltage thus allowing me to control color temperature of the light.

The lights will normally operate between 12 and 15 volts AC so my transformer will be dialed to output around 84 to 105 volts.

Now if one of the lamps burns out, I dont want to have to test each one to see which is the burned out lamp. Somebody offhandedly mentioned I could hook a neon up in parallel as an indicator light.

I am having a hard time figuring this out. If somebody could do a quick sketch for me that would be great.

Thanks

JP

 

[Phasor]

It's pretty simple - I've done a quick sketch - you'll have to excuse my poor drawing skills

**broken link removed**[/img]

 

[whiterabbit]

Thanks very much, its exactly what I needed.

jp

 

[mechie]

Series Resistor ?

Sorry if this sounds like nit-picking,
but should'nt each neon have a current-limiting resistor in series with it?

 

[whiterabbit]

Thanks for this observation. It would not be obvious to me,

This current limiting resistor, is it possible that these resistors can be purchased already built into the lamp.

Is it going to matter in any way that I will be stepping voltage down to between 84V - 105V.

Off the subject:

Can anyone refer me to an on-line resource for wire harness components. I am not having much luck beyond finding plugs or computer connectors. What I am looking for is a circular 3 way T junction for 8 - 10AWG wire.

Or if you know of any wire harness mfg, that can do short run this would be great as well. Est. annual qty. 100-500 pieces.

Thanks.

 

[kinjalgp]

Yes ofcouse small neon lamps do require current limiting resistros. Do use them if you are not interested in watching fire-cracker show :wink:

Kinjal

 

[mechie]

Neon Mains Indicators

Yes, neons can easily be bought with its resistor, all neatly packaged up in a plastic housing, ready for panel mounting.

The value of the resistor should be chosen to give the correct current to the neon, which is voltage dependant.
As you will be varying the voltage from 85 to 105V you should ideally get neon indicators designed for 110v operation, but if 'push comes to shove' you can happily get away with 240v indicators (they will be dimmer and flicker more but still serve the purpose).

 

[whiterabbit]

Great, I was hoping that would be the case, thanks.

 

[Phasor]

Correct me if I'm wrong, but don't most neons only strike at around 80V anyway? - therefore, for 80-110V operation, one shouldn't really need a resistor.

 

[mechie]

Neon Series resistors

The specs for neon lamps will vary from type to type but in general they require something between 0.25mA and 0.6mA.
These devices are CURRENT operated, Not VOLTAGE -- Beware :twisted: I agree they will require a high (!) voltage to strike (value depends on type), but they need a much lower voltage to run :shock:
If there is no current limiter in the circuit they will go --B-A-N-G--; the current will reach some scary value and will blow a 5Amp fuse easily.

I would expect a 220K resistor to be about right for the proposed application.

As an aside ...
Old electric organs used neons for the oscillators -- charge a small capacitor (0.1uF) from 100V DC via a large resistor (1M0) and the neon (connected in parallel with the cap) will flash at a steady rate, producing a sawtooth waveform. This is a relaxation oscillator.
A similar circuit; when one lead is hand-held and the other lead offered towards the emitter, will test an electrostatic ioniser. The flash rate depeding on distance from the ioniser and its emitter's efficiency. 8)