Avtron, Avtron Power Resistors
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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