Minimum resistance of NTC thermistor when connected series with bulb

Thread Starter

MrsssSu

Joined Sep 28, 2021
26
Hi, just curious,
A bulb (30 Ohms , 100W) is connected in series with NTC Thermistor (200 Ohm at room temperature). Since the ohmic resistance of NTC Thermistor will decrease over time, how long does it take normally for a thermistor from 200Ohm to reach close to 0 Ohm) which means all power is transferred to the bulb. From experience, what is the minimum resistance of NTC thermistor it can reach normally when connected with series with a (30 Ohms , 100W) bulb?

Thank you for reading
 

Audioguru again

Joined Oct 21, 2019
3,670
Many years ago an NTC thermistor was sold to be screwed into a light bulb socket to reduce the high current surge when it is turned on to increase the lifetime of the bulb.
But today incandescent bulbs are not used anymore because they waste too much power making heat.
 

Thread Starter

MrsssSu

Joined Sep 28, 2021
26
Many years ago an NTC thermistor was sold to be screwed into a light bulb socket to reduce the high current surge when it is turned on to increase the lifetime of the bulb.
But today incandescent bulbs are not used anymore because they waste too much power making heat.
Hi, how many percent of power supply energy does NTC consume normally when connected to bulb ? My guess would be less than 5% because when it has high temperature, it has very low resistance (low power usage). Is there any article which says its percentage of power consumption? Seached many articles online, found none:))
 

Alec_t

Joined Sep 17, 2013
12,261
Welcome to AAC!
Thermistors come in various physical shapes and sizes. The bigger they are the longer they take to heat up.
100W bulbs come with various voltage ratings. The higher the voltage the lower the current and hence the longer to heat up.
 

Ian0

Joined Aug 7, 2020
3,517
The more power it wastes, the hotter it runs. That reduces the resistance so it runs cooler and wastes less power.
Unless you know the ambient temperature around the thermistor and its thermal resistance, you can't work it out.
If the lamp is run "cap up" (as in a ceiling pendant luminaire) the answer will be different from the case where the lamp is run "cap down" (as in a table lamp).
 
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