Resistance of incandescent light bulbs

[RoGeorge]

Some Python script to control a Rigol DP832 power source, and the measured data points (mA for the given V) from two different models of miniature light bulbs, like the ones used to stabilize the amplitude in a Wien bridge oscillator:

Code: [Select]

import ivi
dp832a = ivi.rigol.rigolDP832A("TCPIP0::192.168.1.4::INSTR")

dp832a.outputs[2].enabled = True

import numpy as np
import time

v = i = r = []

# test voltage: first = 0.5V
#                last = 3.5V
#                step = 0.1V
#
# wait to settle after each voltage step = 5s
#
for v_test in np.arange(0.5, 3.5, 0.01):
   
    # print(i)
    dp832a.outputs[2].voltage_level = v_test
    time.sleep(5)  # wait x seconds for the lightbulb to light up
   
    p3 = dp832a._ask(":MEAS:ALL? CH3").split(",")
    # print (p3)

    r3 = float(p3[0])/float(p3[1])
    v.append(float(p3[0]))
    r.append(r3)
    i.append(float(p3[1]))
   
    # print ("%.3f" % r3, "ohms at", "%.3f" % float(p3[0]), "volts")
    print ("%.3f" % r3, "%.3f" % float(p3[0]))
   
dp832a.outputs[2].voltage_level = 0   




Measured data from miniature light bulb model 1:

Code: [Select]

7.846 0.010
5.583 0.020
5.172 0.030
5.089 0.040
5.122 0.050
5.137 0.060
5.185 0.070
5.353 0.080
5.500 0.090
5.667 0.100
5.825 0.110
6.066 0.120
6.269 0.130
6.495 0.140
6.740 0.150
6.965 0.160
7.181 0.170
7.442 0.180
7.717 0.191
7.964 0.201
8.234 0.211
8.456 0.221
8.735 0.231
8.981 0.241
9.247 0.251
9.480 0.261
9.734 0.271
9.986 0.281
10.193 0.290
10.434 0.300
10.670 0.310
10.901 0.321
11.128 0.331
11.343 0.340
11.561 0.350
11.733 0.360
11.900 0.370
12.105 0.380
12.303 0.390
12.497 0.400
12.703 0.410
12.893 0.420
13.079 0.430
13.259 0.440
13.402 0.450
13.575 0.460
13.746 0.470
13.916 0.480
14.083 0.490
14.251 0.500
14.407 0.510
14.563 0.520
14.681 0.530
14.832 0.540
14.986 0.550
15.135 0.560
15.282 0.570
15.423 0.580
15.573 0.590
15.709 0.600
15.891 0.610
15.992 0.621
16.123 0.630
16.251 0.640
16.383 0.650
16.510 0.660
16.633 0.670
16.800 0.680
16.922 0.690
17.002 0.701
17.118 0.710
17.237 0.721
17.390 0.730
17.506 0.741
17.617 0.750
17.769 0.760
17.875 0.770
17.979 0.780
18.126 0.790
18.186 0.800
18.291 0.810
18.390 0.820
18.536 0.830
18.636 0.841
18.736 0.851
18.868 0.860
18.967 0.871
19.102 0.881
19.155 0.891
19.246 0.901
19.372 0.910
19.465 0.921
19.596 0.931
19.684 0.941
19.808 0.951
19.894 0.961
20.019 0.971
20.100 0.981
20.181 0.991
20.265 1.001
20.381 1.011
20.459 1.021
20.579 1.031
20.657 1.041
20.775 1.051
20.847 1.061
20.963 1.071
21.070 1.081
21.099 1.091
21.210 1.101
21.278 1.111
21.389 1.121
21.492 1.131
21.556 1.140
21.665 1.150
21.765 1.160
21.828 1.170
21.933 1.180
21.994 1.190
22.055 1.200
22.152 1.210
22.252 1.219
22.349 1.229
22.409 1.239
22.505 1.249
22.609 1.259
22.664 1.269
22.763 1.279
22.860 1.289
22.877 1.299
22.972 1.309
23.065 1.319
23.159 1.329
23.255 1.339
23.307 1.349
23.399 1.359
23.494 1.370
23.585 1.380
23.636 1.390
23.725 1.400
23.774 1.410
23.862 1.420
23.951 1.430
23.998 1.440
24.088 1.450
24.169 1.460
24.256 1.470
24.347 1.480
24.431 1.490
24.476 1.500
24.559 1.510
24.600 1.520
24.682 1.530
24.765 1.540
24.846 1.550
24.928 1.560
24.965 1.570
25.044 1.580
25.125 1.590
25.203 1.600
25.283 1.611
25.360 1.621
25.437 1.631
25.474 1.641
25.545 1.650
25.622 1.660
25.695 1.670
25.771 1.680
25.847 1.690
25.924 1.701
25.992 1.710
26.065 1.720
26.137 1.730
26.208 1.740
26.281 1.750
26.347 1.760
26.379 1.770
26.449 1.780
26.520 1.790
26.589 1.800
26.658 1.810
26.725 1.820
26.792 1.830
26.860 1.840
26.929 1.850
26.994 1.860
27.061 1.870
27.127 1.880
27.152 1.890
27.222 1.900
27.287 1.910
27.355 1.920
27.419 1.930
27.482 1.940
27.545 1.950
27.610 1.960
27.673 1.970
27.737 1.980
27.838 1.990
27.901 2.001
27.960 2.010
27.983 2.020
28.046 2.030
28.105 2.040
28.166 2.050
28.226 2.061
28.286 2.071
28.381 2.080
28.439 2.090
28.498 2.100
28.556 2.110
28.617 2.120
28.674 2.131
28.732 2.140
28.750 2.151
28.846 2.161
28.901 2.171
28.955 2.180
29.011 2.190
29.065 2.200
29.158 2.210
29.214 2.220
29.269 2.230
29.325 2.240
29.375 2.250
29.430 2.260
29.521 2.270
29.576 2.280
29.590 2.290
29.642 2.300
29.734 2.310
29.783 2.320
29.837 2.330
29.889 2.340
29.941 2.350
29.991 2.360
30.080 2.370
30.132 2.380
30.179 2.390
30.230 2.400
30.318 2.410
30.369 2.420
30.379 2.430
30.430 2.441
30.517 2.450
30.564 2.460
30.613 2.470
30.660 2.480
30.743 2.490
30.791 2.500
30.837 2.510
30.884 2.520
30.968 2.530
31.016 2.540
31.063 2.550
31.148 2.560
31.155 2.570
31.202 2.580
31.246 2.590
31.329 2.600
31.374 2.610
31.418 2.620
31.501 2.630
31.545 2.640
31.590 2.650
31.669 2.660
31.713 2.670
31.756 2.680
31.838 2.690
31.881 2.700
31.886 2.710
31.966 2.720
32.008 2.730
32.050 2.740
32.130 2.750
32.174 2.760
32.216 2.771
32.256 2.780
32.336 2.791
32.376 2.800
32.418 2.811
32.495 2.821
32.537 2.831
32.613 2.841
32.653 2.851
32.656 2.861
32.732 2.871
32.772 2.881
32.812 2.891
32.888 2.901
32.925 2.911
32.964 2.921
33.039 2.931
33.076 2.941
33.152 2.950
33.186 2.960
33.262 2.970
33.301 2.980
33.338 2.990
33.412 3.000
33.448 3.010
33.486 3.020
33.521 3.030
33.557 3.040
33.631 3.050
33.667 3.060
33.738 3.070
33.774 3.080
33.843 3.090
33.880 3.100
33.914 3.110
33.984 3.120
34.020 3.130
34.091 3.140
34.124 3.150
34.195 3.160
34.190 3.169
34.224 3.179
34.296 3.189
34.332 3.200
34.402 3.210
34.435 3.220
34.470 3.230
34.539 3.240
34.573 3.250
34.645 3.260
34.676 3.270
34.746 3.280
34.780 3.290
34.811 3.300
34.882 3.310
34.912 3.320
34.945 3.330
34.975 3.340
35.045 3.350
35.076 3.360
35.144 3.370
35.175 3.380
35.242 3.390
35.275 3.401
35.341 3.410
35.372 3.421
35.435 3.430
35.464 3.440
35.530 3.450
35.559 3.460
35.624 3.470
35.653 3.480
35.719 3.490
35.708 3.499
35.774 3.509
35.802 3.519
35.867 3.529
35.894 3.539




Measured data from miniature light bulb model 2:

Code: [Select]

22.326 0.500
22.364 0.510
22.600 0.520
22.742 0.530
22.970 0.540
23.301 0.550
23.525 0.560
23.746 0.570
24.062 0.580
24.284 0.590
24.490 0.600
24.801 0.610
25.016 0.620
25.313 0.630
25.510 0.640
25.802 0.650
25.996 0.660
26.286 0.670
26.574 0.680
26.653 0.690
26.938 0.700
27.111 0.710
27.392 0.720
27.663 0.730
27.835 0.740
28.105 0.750
28.264 0.760
28.530 0.770
28.793 0.780
28.949 0.790
29.204 0.800
29.462 0.810
29.606 0.820
29.867 0.830
30.118 0.840
30.267 0.851
30.507 0.860
30.540 0.870
30.787 0.880
31.028 0.890
31.163 0.901
31.393 0.910
31.636 0.921
31.765 0.931
32.000 0.941
32.227 0.951
32.350 0.961
32.577 0.971
32.803 0.981
32.920 0.991
33.146 1.001
33.360 1.011
33.579 1.021
33.693 1.031
33.909 1.041
34.019 1.051
34.119 1.061
34.330 1.071
34.530 1.081
34.625 1.091
34.832 1.101
35.038 1.111
35.242 1.121
35.325 1.130
35.523 1.140
35.724 1.150
35.913 1.160
35.997 1.170
36.196 1.180
36.385 1.190
36.573 1.200
36.760 1.209
36.837 1.219
37.024 1.229
37.210 1.239
37.173 1.249
37.368 1.259
37.547 1.269
37.735 1.279
37.806 1.289
37.994 1.299
38.175 1.309
38.349 1.319
38.416 1.329
38.599 1.339
38.776 1.349
38.951 1.359
39.131 1.370
39.193 1.380
39.368 1.390
39.540 1.400
39.598 1.410
39.768 1.420
39.936 1.430
40.109 1.440
40.163 1.450
40.215 1.460
40.382 1.470
40.553 1.480
40.716 1.490
40.880 1.500
40.930 1.510
41.086 1.520
41.245 1.530
41.406 1.540
41.563 1.550
41.608 1.560
41.761 1.570
41.915 1.580
42.074 1.590
42.227 1.600
42.379 1.610
42.419 1.620
42.567 1.630
42.719 1.640
42.860 1.650
42.899 1.660
43.046 1.670
43.085 1.680
43.233 1.690
43.380 1.700
43.517 1.710
43.660 1.720
43.803 1.730
43.944 1.740
43.975 1.750
44.110 1.760
44.248 1.770
44.389 1.780
44.527 1.790
44.665 1.800
44.802 1.810
44.825 1.820
44.958 1.830
45.093 1.840
45.230 1.850
45.361 1.860
45.386 1.870
45.516 1.880
45.647 1.890
45.673 1.900
45.806 1.910
45.938 1.920
46.067 1.930
46.193 1.940
46.321 1.950
46.450 1.960
46.469 1.970
46.595 1.980
46.721 1.990
46.845 2.000
46.970 2.010
47.093 2.020
47.219 2.030
47.341 2.040
47.463 2.050
47.584 2.060
47.707 2.071
47.821 2.080
47.721 2.090
47.841 2.100
47.959 2.110
48.082 2.120
48.199 2.130
48.318 2.140
48.435 2.151
48.548 2.160
48.666 2.171
48.774 2.180
48.888 2.190
49.002 2.200
49.007 2.210
49.231 2.220
49.234 2.230
49.348 2.240
49.453 2.250
49.566 2.260
49.676 2.270
49.784 2.280
49.895 2.290
50.004 2.300
50.113 2.310
50.216 2.320
50.220 2.330
50.329 2.340
50.436 2.350
50.542 2.360
50.647 2.370
50.755 2.380
50.855 2.390
50.962 2.400
51.066 2.410
51.169 2.420
51.272 2.430
51.375 2.440
51.479 2.450
51.581 2.460
51.682 2.470
51.781 2.480
51.875 2.490
51.977 2.500
52.075 2.510
52.176 2.520
52.273 2.530
52.373 2.540
52.473 2.550
52.573 2.560
52.668 2.570
52.657 2.580
52.754 2.590
52.850 2.600
52.945 2.610
53.040 2.620
53.135 2.630
53.232 2.640
53.435 2.650
53.523 2.660
53.616 2.670
53.709 2.680
53.804 2.690
53.896 2.700
53.988 2.710
54.078 2.720
54.171 2.730
54.261 2.740
54.354 2.750
54.446 2.760
54.537 2.771
54.627 2.780
54.716 2.791
54.804 2.800
54.895 2.811
54.981 2.821
54.961 2.830
55.050 2.841
55.135 2.850
55.224 2.861
55.310 2.871
55.396 2.881
55.482 2.891
55.565 2.901
55.650 2.910
55.735 2.921
55.926 2.930
56.008 2.940
56.091 2.950
56.169 2.960
56.254 2.970
56.338 2.980
56.421 2.990
56.503 3.000
56.585 3.010
56.664 3.020
56.747 3.030
56.826 3.040
56.907 3.050
56.987 3.060
57.063 3.070
57.145 3.080
57.115 3.090
57.299 3.100
57.378 3.110
57.453 3.120
57.531 3.130
57.609 3.140
57.685 3.150
57.761 3.159
57.834 3.169
57.913 3.179
57.989 3.189
58.069 3.200
58.147 3.210
58.221 3.220
58.298 3.230
58.371 3.240
58.450 3.250
58.633 3.260
58.704 3.270
58.781 3.280
58.857 3.290
58.929 3.300
59.005 3.310
59.077 3.320
59.151 3.330
59.220 3.340
59.294 3.350
59.263 3.360
59.336 3.370
59.406 3.380
59.477 3.390
59.552 3.400
59.622 3.410
59.693 3.420
59.758 3.430
59.826 3.440
59.894 3.450
59.962 3.460
60.133 3.470
60.202 3.480
60.269 3.490




Inrush current for some other 3 more types of slightly bigger incandescent light bulbs:

[bob91343]

I was taught that the cold resistance of a typical incandescent lamp is about one-tenth of its hot resistance.

[Alti]

Also worth noting that with R at 25oC it means the peak current reaches sqrt2*Urms/R only when the turn on happens to be at exactly 90 degrees phase angle (at peak voltage). At all other turn-on times, with such tremendous powers pushed into light filament (adiabatic heating), it is already going to be preheated near peak voltage.
Halogens have super high R_hot/R_cold, some around 16-17. But when you measure inrush when powering at voltage zero crossing, you realize Irms_cold/Irms_hot rarely reaches 13 in practical circuit.

[aiq25]

I had to do that while working on a DC to AC (12V to 110AC) inverter because it was the best load to try in terms of inrush current.

[Benta]

So what's the question?

[RoGeorge]

No question, just some measurements.

Good for example to make a light bulb simulation model, or to make a rough approximation of the expected current when the voltage is lower than nominal, things like this.  I measured mine to find the expected resistance of the light-bulb when used as an amplitude stabilizer in a Wien bridge generator like this one:
https://en.wikipedia.org/wiki/Wien_bridge_oscillator

[mawyatt]

Interesting measurements, wonder if someone has used a PTC Fuse in place of the bulb for the WB Oscillator?

Best,

[NiHaoMike]

I had to do that while working on a DC to AC (12V to 110AC) inverter because it was the best load to try in terms of inrush current.

I always thought that motors tend to be the most difficult sort of load to deal with, although that is solved to some extent with V/Hz ramp up.

Interesting measurements, wonder if someone has used a PTC Fuse in place of the bulb for the WB Oscillator?

Those are extremely nonlinear with respect to resistance over temperature. It would be difficult to get it to stabilize.

[RoGeorge]

Interesting measurements, wonder if someone has used a PTC Fuse in place of the bulb for the WB Oscillator?

Thanks    those are measurements from a couple of years ago, posted now because somebody was asking in another topic about the SPICE model of light bulb, to simulate a WB oscillator, so I thought those two measured charts would help making a rough approximation of what to expect from a miniature incandescent filament (light bulb of about 5mm/0.2inch diameter and 3.5V nominal or so).



I would be curious, too, to see the comparison in terms of a Wien Bridge distortions when the amplitude of the oscillator is stabilized using a light bulb vs a PTC Fuse.   

As a wild guess, I would expect to see better result with the light bulb, simply because most of the WB schematics I've seen use either a light bulb, a FET, or the more elaborated servo method of Jim Williams described in the "Max Wien, Mr. Hewlett, and a Rainy Sunday Afternoon".

The advantage of the light bulb is that it has a big thermal inertia, while I was measuring I noticed that the filament needs 3-5 seconds to reach its final light intensity.  I would expect a fuse to be optimized for fast time response, therefore low thermal inertia.

Another concern would be the I-V curve, where the light bulb is very close to a pure resistor (the filament resistance is in fact a temperature controlled resistor, and the temperature of the filament is constant for fast voltage variations) therefore a linear element (an LTI system can not change a spectrum, so no distortions added).  I suspect that, temperature aside, a complex material like the one used in making a PTC fuse might have a V-I curve with more non linearities than the filament, a metal alloy, might have.

Again, no idea if the above guesses will hold when tested in practice.