Tech Tip
OVERLOAD AND DERATING CHARTS FOR AVTRON POWER RESISTORS
GENERAL FORMULAS
OHM’S LAW
V = I x R (Volts = Amps x Resistance)
POWER CALCULATIONS
P = V x I (Power = Volts x Amps)
P = V2/R (Power = Volts squared / Resistance)
P = I2 x R (Power = Amps squared x Resistance)
SINGLE SHOT OVERLOADS (cool to ambient between cycles)
| TIME ON |
MULT. AMPS BY |
MULT. WATTS BY |
| 1 sec. |
8.0 |
64 |
| 3 sec. |
7.0 |
49 |
| 5 sec. |
6.0 |
36 |
| 10 sec. |
4.5 |
20 |
| 30 sec. |
3.0 |
9.0 |
| 60 sec. |
2.0 |
4.0 |
REPEATING DUTY OVERLOADS
| NEMA CLASS |
ON TIME/OFF TIME |
MULT. AMPS BY |
MULT. WATTS BY |
| 110 |
5 / 75 sec. |
2.5 |
6.2 |
| 130 |
10 / 75 sec. |
2.0 |
4.0 |
| 140 |
15 / 75 sec. |
1.8 |
3.2 |
| 150 |
15 / 45 sec. |
1.6 |
2.5 |
| 160 |
15 / 30 sec. |
1.5 |
2.2 |
| 170 |
15 / 15 sec. |
1.4 |
2.0 |
| 90 |
continuous |
1.0 |
1.0 |
DERATING FOR AMBIENT TEMPERATURE
| AMBIENT TEMP. |
MULT. AMPS BY |
MULT. WATTS BY |
| Up to 40 C |
1.0 |
1.0 |
| 50 C |
0.96 |
0.92 |
| 60 C |
0.95 |
0.90 |
| 70 C |
0.94 |
0.88 |
| 80 C |
0.92 |
0.85 |
| 90 C |
0.90 |
0.81 |
| 100 C |
0.88 |
0.77 |
| 120 C |
0.86 |
0.74 |
| 150 C |
0.80 |
0.64 |
DERATING FOR ALTITUDE
| ALTITUDE |
MULT. AMPS BY |
MULT. WATTS BY |
| 0 - 6000’ |
1.0 |
1.0 |
| 6000’ - 15000’ |
0.86 |
0.75 |
| above 15000’ |
|
consult factory |
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avtron_tip (orig.-8/1/02)
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