Variation resistance on voltage of a halogen bulb

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izentrop
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Re: Variation of resistance on voltage of a halogen bulb




by izentrop » 19/04/20, 09:20

Macro wrote:The calculators of diesel engines measure the combustion temperatures, using glow plugs (a simple resistive element) they manage to determine injection faults with this principle ... So it must be quite possible
In advanced electronic management, there must be a thermistor incorporated, because the temperature is not current or voltage
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Exnihiloest
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Re:




by Exnihiloest » 20/04/20, 19:29

Christophe wrote:Arf trap question!

For me the joule effect is the opposite: creation of heat by the circulation of an electric current.

Yes

Obviously the more resistance there is, therefore of T °, ​​the more there is joule power ... it's a vicious circle


All false.
U = R * I, P = R * I², P = U² / R, P = UI: these are all the relationships between voltage U, current I, resistance R and power P.
What we have constant and imposed is the tension. The simplest is therefore to use P = U² / R: the more the resistance increases, the more the power decreases.
It is all the more obvious that a very high resistance is like an open circuit, therefore little or no power, and that a low resistance is like a short circuit, therefore theoretically infinite power which will cause the short to burn out. -circuit or jump the circuit breaker.

So when we light a filament lamp, there is a pulse overcurrent at the start, then the resistance increases because of the heat, so the current decreases and stabilizes at the value I = U / R where R is the resistance at nominal operating temperature.
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paul_f5hpq
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Re: Variation of resistance on voltage of a halogen bulb




by paul_f5hpq » 21/04/20, 14:44

Hello,
To confirm these last statements, the overcurrent of the departure is neither more nor less than the rise in temperature of the filament.
As a reminder, the halogen lamp or any filament is a VDR, resistance depending on the voltage.
It is a non-linear component, the measured curve which appears in the first graphs (low hat in passing; o)
highlights it.
Small tip: to use it as a "load bank" (to unload or test a power supply), I use such a compatible component 5 and 12V.
A simple 12V 5 / 21W car bulb (pilot / stop).
The 5W filament consumes 5,2W in 12v and 1,5W in 5V.

The logic of proportionality would like that if you have 1,5W in 5V, you get 13,5W in 12V. Well no !
Indeed, the filament is barely orange under 5V and dazzled in 12v, we realize that the "light temperature" is not the same!

In any case, this little bulb allows me to have a consumer of about 0,3mA under 5V to test the capacity of the "power banks" (which are great scams in terms of mAh ...) and to be able to "shoot" a little less than 0,5A on small 12V power supplies to assess their possibility (again 8 to 15v, with or without filtering, great scams ...).

Experiment, you will discover a thousand and one things worthy of interest, which allow us to understand the technological environment that surrounds us.

Kind regards.
Pol
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paul_f5hpq
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Re: Variation of resistance on voltage of a halogen bulb




by paul_f5hpq » 21/04/20, 14:59

Hello Isentrop,
Let's avoid mixing "thermistor, varistor and resistance".
The diagram presented in your post uses a thermistor mounted on a divider bridge to be measured by a microcontroller.
Its resistance varies in large proportions (NB: it is only linear over a small well identified range) with the surrounding temperature. If the range is exceeded, the processor uses a conversion table, very practical to go further or lower; o)
Namely: CTN resistance decreases when the temperature increases, CTP resistance increases with temperature.
Moreover, designers must ensure that the current flowing through it generates little self-heating so as not to generate measurement errors. (which says current & resistance => developed power, even femtowatts is heat!

The world of non-linear resistances is unsuspected, I am sure that you will discover in their study of beautiful things and very unsuspected applications.

Kind regards.
Pol
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