Old 6 volt auto headlight in series with 1154 on 12 volts

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SUMMARY

Connecting a 1154 automotive lamp and an old 6-volt headlamp in series on a 12-volt supply results in the same current flowing through both bulbs. The 1154 lamp, with specifications of 16.8W/5.3W and 2.63A/0.75A, will not cause all current to flow through the lower wattage bulb, as both lamps share the same current in a series circuit. The voltage drop across each lamp will not be equal due to differing filament resistances, and measuring current draw and voltage drops is essential for understanding the behavior of the circuit.

PREREQUISITES
  • Understanding of series circuits and current flow
  • Basic knowledge of incandescent lamp specifications
  • Familiarity with measuring electrical current and voltage
  • Knowledge of resistance and its effect on filament temperature
NEXT STEPS
  • Research the electrical characteristics of incandescent lamps, focusing on filament resistance
  • Learn how to measure current draw and voltage drops in a circuit
  • Explore the implications of connecting different voltage-rated lamps in series
  • Investigate the thermal behavior of incandescent lamps under varying voltage conditions
USEFUL FOR

Electronics enthusiasts, automotive technicians, and anyone interested in understanding the behavior of incandescent lamps in series circuits.

John1397
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If one hooks a 1154 and an old 6 volt automotive headlamp in series and powers it with 12 volts will the headlamp being that it
is higher wattage cause all the current flow thru the smaller wattage bulb causing it to burn out?
 
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John1397 said:
... will the headlamp being that it is higher wattage cause all the current flow thru ...
All the current? If they are in series, the same current flows through them.
 
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An 1154 lamp (I'm assuming this is what you mean by '1154') has two filaments. Which one of these are you referring to?
Sylvania specs - 16.8W/5.3W, 6.3V/7.0V, 264 lumen/38 lumen, 2.63A/0.75A.

What is the rated wattage of the "old 6 volt automotive headlamp"?

Generally speaking, each of the two incandescent lamps connected in series acts as a variable resistor with their resistances determined by their filament temperatures. Disabuse yourself of the notion that 6 volt rated lamps will drop 6V across each of them when connected in series across a 12V supply. If they have the same part number and contain nearly identical filaments then their voltages will be nearly identical, but lamp voltage drops won't be when two radically different filaments are connected in series.

Can you measure the current draw and voltage drops?
 
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