Where is there a good place on series circiuts to go and get to help understand how to get the lights to all be the same brightness?

Welcome to the forum. Can you provide a little more info on what you are looking for? In a series circuit and if all the bulbs are the same make, model, and wattage, they are should be the same brightness.

Yes we are using the same size bulb, we have the series with the on lamp bright and the others dim. How do we make them all the same brightness?

I believe you're asking about Ohm's law. Each light is essentially a big resistor. A 30W bulb is a 0.25 Ohm resistor. A 60W bulb is a 0.5Ohm resistor. Etc.

More here:
http://science.howstuffworks.com/circuit1.htm


...this isn't a homework question by any chance, is it?

The bright bulb is different from the dim ones. It's resistance is lower.

Higher?

The best example of this is the old "all American five" tube radio where they had tube filaments ranging from 12v to 50v and they all used 150MA but the effective resistance was selected so they could take 120v line power in series to light them all up.
(The octal set was 12SA7 converter, 12SK7 IF amp, 12SQ7 audio detector and signal amp, 50L6 audio power, and 35Z5 rectifier).
Later they came out with a 100MA "miniature" string but it worked the same.
That was what we had in your basic table radio until the late 60s early 70s when transistors took over. I still believe the tube radios were better at pulling in distant stations and sounded better but that is just old guy nostalgia.

Greg LOL.
Skeeter, another good example: You have a 24 volt power supply. But you do not have any 24 volt bulbs. But you do have 12 volt bulbs. If you put two 12 volt bulbs in series with the 24 volt supply you will have 12 volts at the mid point between the bulbs and the supply. But you still have 24 volts output at the supply.

Darwin? sorry I digress.

If they are the same wattage AND the same voltage rating, then the bulbs should be the same brightness. If they are then you may just have a bad bulb. I would let both bulbs cool off and ohm them out and see what you get.

Yes the series circuit we had had 3 130V 25w lamps. THe firs bulb was brighter than the other 2.

Wasn't the circuit wired in parallel?

Skeeter

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Basic Circuits #1: Series Circuits

Basic Circuits #3: Ser/ Par + Voltage Divider

Series AC Circuits

Series-Parallel AC Circuits

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We had a discussion in the Electrical Theory area some time ago, which covered connecting several Incandescent Lamps in Series.

As I remember, there were at least 3 Lamps - each rated for 120VAC, connected in Series.
One Lamp was a lower wattage than the other two - something like One (1) 60 Watt Lamp, in Series with Two (2) 100 Watt Lamps.
The System Voltage used to drive the Lamps was 120VAC.

The preliminary query was why the lower wattage Lamp was brighter than the other two higher wattage Lamps.

The discussion covered basic Ohms Law, which described the reason for the lower wattage Lamp's higher intensity was due to that Lamp's higer Resistance (or since the supply was AC, more correct term would be higher Impedance) - and therefore the 60 Watt Lamp's Filament had a higher Voltage across it.

Since it carried the sum total current of all three Lamps, and had a higher Voltage across it, the highest level of Wattage was transduced in the Lamp with the lower wattage rating - therefore making it the brighter Lamp.

That is the key factor here: the Lamp with the higher Resistance (or Impedance in this case), has the highest Voltage measured across it, and therefore will draw the most Wattage from the Power Supply.

From this example, it should be easy to see why the smaller loads (read most crucial and $$$ loads) lose smoke when an "Open Neutral" situation takes place.

ooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo

In your last reply, you mention that all three Lamps are the same wattage and rated Voltage, yet one is brighter than the other two.

This would mean the one brighter Lamp:

* 1: Might be connected in Parallel,

* 2: Might be of a different rating (wattage and or voltage),

or

* 3: Might have an initially higher Cold Resistance than the other Lamps.

If they are all the same types, and connected in Series, they should all be the same intensity (brightness).

Are they all clear, or is the brighter Lamp clear?
Any of the Lamps Frosted? (non-clear)

Try running the Lamps separately - across 120VAC, and see if the brightness is uniform or not.
If uniform brightness is experienced in the separation test - AND your Series test circuit IS connected correctly in Series, time to look for a good excorcist!!!

Else, adjust accordingly - finding at least Three (3) Lamps with uniform intensity, and verify the test circuit is indeed connected in basic Series fashion - as described below:

*** One side of the 120VAC circuit connects directly to one side of the "first" lamp;
* The other side of the "first lamp" connects directly to one side of the "second" lamp;
* The other side of the "second" lamp connects directly to one side of the "third" lamp;
*** The other side of the "third" lamp connects directly to the other side of the 120VAC circuit.

Basic, Crude ASCII Schematic below:

(120Va)......_(L1)_......_(L2)_......_(L3)_......(120Vn)

Key:
(120Va) = 120VAC Circuit - Ungrounded Conductor
(120Vn) = 120VAC Circuit - Grounded "Neutral" Conductor
...... = Circuit Conductors between Lamps
_(L1)_ = Lamp # 1
_(L2)_ = Lamp # 2
_(L3)_ = Lamp # 3

Please let us know of the outcome

Scott
edited for spelling

Referring to the last post, "ohming them out" after they cool will only tell you if there are working or not (Continuity). The cold filament resistance is significantly less then the resistance it is when its "on". Eg. 120V, 60W bulb draws 0.5 A,--> 120/0.5 = 240 ohms (hot)

That was common in Britsh radio and TV equipment of the era too, although with supplies of 200 to 250V the typical table radio with five tubes had to employ a series dropper resistor as well.

In fact the Mullard valve coding system used by tube manufacturers here had the first letter denote the heater characteristics, and some were specifically reserved to designate tubes intended for series connection: P was 300mA, U was 100mA, and so on, the latter being very common on domestic radios of the era (UCH81 converter, UL84 output pentode, etc.).

During the immediate post-war period we imported quite a number of those "All American Five" designs too, modified for U.K. use. One method of adapting the series filament chain for 200-250V was to use a very long power cord which had a nichrome resistance element as one conductor to act as the extra series resistance.

Apparently it worked quite effectively -- Until somebody decided that he didn't like the 9 or 10 ft. cord and tried to shorten it.

They had radios in the US with resistor cords too (not AA5). I tried one with with lamp cord and a couple of tubes got real bright for a second.