AS Series INRUSH CURRENT LIMITERS For this application note, let us limit our discussion Thermistor Protection for Precharge Circuit on Lithium Ion Batteries to the selection of the Thermistor When a battery is connected to a load with capacitive input, there is an Inrush current SELECTION OF surge as the capacitance is being charged to the battery voltage. The Input current depends on the input capacitance the larger the batteries and the more powerful the THE THERMISTOR load, the larger the input capacitance. A large Inrush current (in the precharge circuit, The minimum resistance of the thermistor is without protection) can cause the following: determined by the following: Damage to input filter capacitors 1. Ambient temperature Blowing of the main fuse if asked to carry the inrush current without protection 2. Input capacitance value Contact failure (as well as reduction in current carrying capacity) (of the precharge circuit) due to arcing and pitting that results from high inrush current 3. Battery voltage Damage to the battery cell, which is not rated for inrush current The precharge surge current reaches 63.2% (1/e) of its initial value after a time = RC. A typical precharge circuitry for battery operation is below with the timing diagram, showing how the circuit operates. (Courtesy of Lithium -ION BMS) In the selection of the thermistor, we consider a time value of five time-constant when the R1 capacitances are fully charged and the surge current reaches the normal operating current. 10 K1 For the purpose of our design, let us assume the following quantitative values: PRECHARGE Precharge time: 20 millisecond + Ambient operating temperature: Varies between BATTERY HV OUT K2 10C to 50C. + Battery voltage: 100 volt B= CONTROLLER K1+ Capacitor bank : 50,000 F K1+ K1 5 = RC K1+ K3 K1+ R = 5 / C = 5 (0.02 sec) / 0.05F = 2.0 . K1 B- Now, look at the at R-T curves for Ametherm thermistor at ambient of 50C. The material V Cexhibits Load Voltage R 50C/ R 25C = 0.412 R 10C / R t 25C = 1.70 A Precharge Surge Therefore, minimum resistance 25C = 2.0 / Battery Normal Operating Current Current 0.454 = 4.40, so our standard part has 5.0 t ohm nominal resistance K1 At 10C, the standard part will have a resistance K1 of 5.0 x 1.70 = 8.50 , which will meet our K1 t minimum resistance. Off Pre On Off charge Determine the energy the thermistor needs to handle with out self-destruction, In its most basic form, the Precharge circuit operates as follows: E = C V2 = (0.05) (100) 2 = 250 Joules. OFF: When the system is OFF all relays / contactors are off. Precharge: When the system is first turned on, K1 and K3 are turned on to The steady state current is not calculated because in most precharge circuits the steady state current Precharge the load, until the Inrush current has subsided. R1 shows the location goes through the contactor. of Thermistor in the Precharge circuit. ON: After Precharge, contactorK2 is turned on (relay K1, must be off to save The part, which would meet your specification, is AS32 5R020. coil power)AS Series INRUSH CURRENT LIMITERS Key Benefits of Ametherm AS Inrush Current Limiters Lower current density (as compared to traditional types of inrush current limiters) Faster reset time D No hot spots from fatigue, because of lower current density and uniform temperature gradient throughout the disc Wider temperature range of operation with out de-rating L A ELECTRICAL SPECIFICATIONS S R 25C MAX I HOT R MAX ENERGY Max Cap Cooldown R -T DC Body Temp Part ( ) (A ) ( ) (JOULES) 680VAC time (sec) curve mW/C Max SSI (C) Number *AS32 0R530 0.50 30 0.011 300 650 120 A 78.20 199 0.50 36 0.009 300 650 120 A 78.20 199 *AS32 0R536 *AS32 1R030 1.0 30 0.013 300 650 120 B 79.40 215 T *AS32 1R036 1.0 36 0.010 300 650 120 B 79.40 215 AS32 2R025 2.0 25 0.020 300 650 120 C 78.20 220 AS32 5R020 5.0 20 0.027 300 650 120 G 78.20 255 10.0 15 0.052 250 500 120 H 85.20 185 AS32 10015 AS32 20010 20.0 10 0.095 250 500 120 I 58.00 192 C AS32 50006 50.0 6 0.380 250 540 120 M 78.20 212 AS35 0R550 0.50 50 0.0074 800 1730 200 A 129.44 210 AS35 1R040 1.0 40 0.0113 800 1730 200 B 127.00 212 B 2.0 35 0.0147 700 1500 200 C 119.20 210 AS35 2R035 3.0 30 0.0135 600 1300 200 C 116.40 215 AS35 3R030 5.0 25 0.0288 600 1300 200 G 112.2 208 AS35 5R025 AS35 10018 10.0 18 0.0556 500 1080 200 I 122.80 220 PAD LAYOUT 20.0 10 0.1760 500 1080 200 M 101.10 177 AS35 20010 Y MECHANICAL SPECIFICATIONS D T S L A B C X Y Part Number (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) X *AS32 0R530 30.0 7.8 17.1 22.0 2.2 4.8 0.8 17.1 4.8 30.0 7.8 17.1 22.0 2.2 4.8 0.8 17.1 4.8 *AS32 0R536 *AS32 1R030 30.0 7.8 17.1 22.0 2.2 4.8 0.8 17.1 4.8 *AS32 1R036 30.0 7.8 17.1 22.0 2.2 4.8 0.8 17.1 4.8 AS32 2R025 30.0 7.8 17.1 22.0 2.2 4.8 0.8 17.1 4.8 T: 800-808-2434 AS32 5R020 30.0 8.2 17.1 22.0 2.2 5.4 0.8 17.1 5.4 AS32 10015 30.0 9.0 17.1 22.0 2.2 6.8 0.8 17.1 6.8 775-884-2434 AS32 20010 30.0 8.5 17.1 22.0 2.2 6.4 0.8 17.1 6.4 (Outside the US and Canada) AS32 50006 30.0 8.2 17.1 22.0 2.2 5.4 0.8 17.1 5.4 F: 775-884-0670 AS35 0R550 36.0 6.4 19.0 22.0 2.2 3.4 0.8 19.0 3.4 www.ametherm.com AS35 1R040 36.0 8.5 19.0 22.0 2.2 5.5 0.8 19.0 5.5 info ametherm.com AS35 2R035 36.0 8.5 19.0 22.0 2.2 5.5 0.8 19.0 5.5 AS35 3R030 36.0 8.5 19.0 22.0 2.2 5.5 0.8 19.0 5.5 AS35 5R025 36.0 8.5 19.0 22.0 2.2 5.5 0.8 19.0 5.5 3111 N. Deer Run Road AS35 10018 36.0 8.5 19.0 22.0 2.2 5.5 0.8 19.0 5.5 Carson City, Nevada AS35 20010 36.0 8.5 19.0 22.0 2.2 5.5 0.8 19.0 5.5 89701 USA *(UL Approved)