{"id":2889,"date":"2026-07-30T15:00:00","date_gmt":"2026-07-30T15:00:00","guid":{"rendered":"https:\/\/chac-electric.com\/?p=2889"},"modified":"2026-10-14T06:51:40","modified_gmt":"2026-10-14T06:51:40","slug":"ev-high-voltage-dc-contactor-precharge-rfq","status":"publish","type":"post","link":"https:\/\/chac-electric.com\/ru\/blog\/ev-high-voltage-dc-contactor-precharge-rfq\/","title":{"rendered":"Which Pre-Charge Inputs Should an OEM EV System RFQ Include?"},"content":{"rendered":"<div class=\"b2b-article\">\n<p>A pre-charge request that names only battery voltage and contactor current leaves the supplier guessing about the event the device must survive. Charging an inverter&#8217;s DC-link capacitor is different from carrying traction current, and a resistor&#8217;s continuous wattage does not describe its pulse capability. An incomplete specification can therefore produce a circuit that reaches its target once but fails during a hot restart or an unsuccessful charging attempt. The useful starting point is the electrical model and operating sequence. This guide explains the calculation inputs, completion criteria and failure cases an OEM team should supply before selecting a pre-charge resistor and switching device.<\/p>\n<p>The short answer is to specify voltage range, effective DC-link capacitance, initial capacitor voltage, allowable charging time, completion threshold and repetition duty. A <strong>pre-charge circuit<\/strong> limits capacitor inrush before the main path closes. For a simplified passive circuit, its time constant is R times C, while initial current depends on voltage difference divided by resistance. Texas Instruments&#8217; SDAA145A, revised April 2026, describes both passive and alternative active designs. These relationships support early sizing, not approval of a particular <strong>\u0412\u044b\u0441\u043e\u043a\u043e\u0432\u043e\u043b\u044c\u0442\u043d\u044b\u0439 \u043f\u043e\u0441\u0442\u043e\u044f\u043d\u043d\u044b\u0439 \u0442\u043e\u043a\u043e\u043f\u0440\u043e\u0432\u043e\u0434\u044f\u0449\u0438\u0439 \u043a\u043e\u043d\u0442\u0430\u043a\u0442\u043e\u0440<\/strong>. Actual selection also needs switching duty, pulse energy, fault handling and model-specific evidence.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-large wp-image-2810 aligncenter\" src=\"https:\/\/chac-electric.com\/wp-content\/uploads\/2026\/07\/80f72baa-f120-46fa-baee-a26baf190c9f-1024x819.webp\" alt=\"Best AC Contactors Revolutionize Electrical Operations\" width=\"1024\" height=\"819\" srcset=\"https:\/\/chac-electric.com\/wp-content\/uploads\/2026\/07\/80f72baa-f120-46fa-baee-a26baf190c9f-1024x819.webp 1024w, https:\/\/chac-electric.com\/wp-content\/uploads\/2026\/07\/80f72baa-f120-46fa-baee-a26baf190c9f-300x240.webp 300w, https:\/\/chac-electric.com\/wp-content\/uploads\/2026\/07\/80f72baa-f120-46fa-baee-a26baf190c9f-768x615.webp 768w, https:\/\/chac-electric.com\/wp-content\/uploads\/2026\/07\/80f72baa-f120-46fa-baee-a26baf190c9f-600x480.webp 600w, https:\/\/chac-electric.com\/wp-content\/uploads\/2026\/07\/80f72baa-f120-46fa-baee-a26baf190c9f.webp 1402w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><\/p>\n<p>The existing AC-contactor illustrations are general switching-component context, not evidence that an AC contactor is suitable for an EV high-voltage DC circuit.<\/p>\n<nav class=\"b2b-toc\">\n<h2>Contents<\/h2>\n<ul>\n<li><a href=\"#part-1-map-the-pre-charge-function-before-naming-a-contactor\">What must the pre-charge branch accomplish?<\/a><\/li>\n<li><a href=\"#part-2-provide-the-electrical-inputs-that-define-the-event\">Which inputs determine current and charging time?<\/a><\/li>\n<li><a href=\"#part-3-separate-pre-charge-duty-from-the-main-path-duty\">How does pre-charge duty differ from main-contactor duty?<\/a><\/li>\n<li><a href=\"#part-4-define-the-control-and-diagnostic-interface\">How should the controller confirm completion?<\/a><\/li>\n<li><a href=\"#part-5-record-environmental-and-assembly-constraints\">What happens after a failed attempt or hot restart?<\/a><\/li>\n<li><a href=\"#part-6-use-a-structured-rfq-and-evidence-request\">Which evidence should accompany the proposed circuit?<\/a><\/li>\n<li><a href=\"#part-7-choose-the-chac-product-review-route\">How should an OEM review a supplier proposal?<\/a><\/li>\n<li><a href=\"#faqs\">\u0427\u0430\u0441\u0442\u043e \u0437\u0430\u0434\u0430\u0432\u0430\u0435\u043c\u044b\u0435 \u0432\u043e\u043f\u0440\u043e\u0441\u044b<\/a><\/li>\n<\/ul>\n<\/nav>\n<h2 id=\"part-1-map-the-pre-charge-function-before-naming-a-contactor\">What must the pre-charge branch accomplish?<\/h2>\n<p>A discharged capacitor initially presents a demanding charging load. A passive pre-charge branch introduces resistance to limit current, allowing capacitor voltage to approach battery voltage before the low-resistance main path takes over. The circuit diagram must identify the branch, main contacts and voltage-sensing points.<\/p>\n<p>There is no universal sequence that can be copied into every EV. Provide the actual positive\/negative switching arrangement and controller states. TI&#8217;s reference diagrams explain particular architectures, not a substitute for the vehicle&#8217;s safety and fault-management design.<\/p>\n<h2 id=\"part-2-provide-the-electrical-inputs-that-define-the-event\">Which inputs determine current and charging time?<\/h2>\n<p>For a constant source Vb, initial capacitor voltage V0, resistance R and capacitance C, the idealized voltage is Vc(t) = Vb &#8211; (Vb &#8211; V0) exp(-t\/RC). Initial current is (Vb &#8211; V0)\/R. State which loads remain connected during charging; a load drawing current can invalidate the simple unloaded calculation.<\/p>\n<p>As an illustrative calculation, 400V charging an initially empty 1,000uF capacitor through 100 ohms gives 4A initial current and a 0.1s time constant. After three time constants, the capacitor reaches about 95% of source voltage, leaving approximately 20V across the main closing path. Its final stored energy is 80J. These are ideal calculations, not a recommended component rating or a universal completion target.<\/p>\n<table>\n<thead>\n<tr>\n<th>Input<\/th>\n<th>\u041f\u043e\u0447\u0435\u043c\u0443 \u044d\u0442\u043e \u0432\u0430\u0436\u043d\u043e<\/th>\n<th>Required limit or condition<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Battery and initial capacitor voltage<\/td>\n<td>Sets initial voltage difference<\/td>\n<td>Minimum, maximum and residual-charge cases<\/td>\n<\/tr>\n<tr>\n<td>Effective capacitance<\/td>\n<td>Sets charging time and energy<\/td>\n<td>Installed total and tolerance<\/td>\n<\/tr>\n<tr>\n<td>Resistance<\/td>\n<td>Trades current against charging duration<\/td>\n<td>Tolerance and temperature dependence<\/td>\n<\/tr>\n<tr>\n<td>Completion criterion<\/td>\n<td>Limits stress when the main path closes<\/td>\n<td>Allowed voltage difference and validation basis<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h2 id=\"part-3-separate-pre-charge-duty-from-the-main-path-duty\">How does pre-charge duty differ from main-contactor duty?<\/h2>\n<p>The branch device closes into a charging event; the main device carries a different operating load and may face different opening requirements. Ask for making, carrying and interruption evidence at the actual DC voltage and current. An ampere marking alone does not establish these duties, polarity constraints or fault interruption capability.<\/p>\n<p>A <strong>pre-charge resistor<\/strong> also needs a pulse-energy review. For an ideal initially discharged capacitor charged from a constant source through resistance, the energy dissipated in resistance over a complete charge equals one-half C Vb squared. Cable resistance and other components share losses in a real circuit. Confirm how the selected resistor&#8217;s pulse curve, voltage rating, cooling and repetition limits apply.<\/p>\n<h2 id=\"part-4-define-the-control-and-diagnostic-interface\">How should the controller confirm completion?<\/h2>\n<p>A fixed timer cannot distinguish successful charging from an open resistor or failed branch contact. Define the voltage measurements and plausibility checks used to permit main-path closure. Account for sensor error, stale data, timeout and inconsistent feedback.<\/p>\n<p>Document which faults inhibit closing and how the system reaches a controlled state. Command feedback alone does not establish capacitor voltage, welded-contact detection or absence of hazardous voltage. Those functions need their own documented diagnostic design.<\/p>\n<h2 id=\"part-5-record-environmental-and-assembly-constraints\">What happens after a failed attempt or hot restart?<\/h2>\n<table>\n<thead>\n<tr>\n<th>Case<\/th>\n<th>Design question<\/th>\n<th>Evidence to request<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Repeated start<\/td>\n<td>Has the resistor cooled sufficiently?<\/td>\n<td>Pulse repetition and thermal limits<\/td>\n<\/tr>\n<tr>\n<td>Charging timeout<\/td>\n<td>What prevents continuous branch heating?<\/td>\n<td>Inhibit and timeout response<\/td>\n<\/tr>\n<tr>\n<td>Residual capacitor voltage<\/td>\n<td>Does the voltage difference change direction?<\/td>\n<td>Permitted initial conditions and polarity<\/td>\n<\/tr>\n<tr>\n<td>Sensor or feedback fault<\/td>\n<td>Can closure occur with invalid evidence?<\/td>\n<td>Plausibility checks and defined safe response<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>Include enclosure temperature, mounting, vibration, creepage\/clearance requirements and service access. Do not evaluate resistor heating from a single cold attempt. An active pre-charge alternative also needs its own controls, losses and fault analysis; TI&#8217;s 2026 application note is a useful architecture comparison, not proof that an active solution is always preferable.<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/chac-electric.com\/wp-content\/uploads\/2026\/06\/01-cqc6-600x600.webp\" alt=\"\u041f\u0440\u043e\u0438\u0437\u0432\u043e\u0434\u0438\u0442\u0435\u043b\u044c \u043f\u0440\u043e\u043c\u044b\u0448\u043b\u0435\u043d\u043d\u043e\u0433\u043e \u043a\u043e\u043d\u0442\u0430\u043a\u0442\u043e\u0440\u0430 \u0441 \u043f\u0435\u0440\u0435\u043c\u0435\u043d\u043d\u044b\u043c \u0442\u043e\u043a\u043e\u043c \u0441\u0435\u0440\u0438\u0438 CQC6\" \/><\/p>\n<h2 id=\"part-6-use-a-structured-rfq-and-evidence-request\">Which evidence should accompany the proposed circuit?<\/h2>\n<p>Request the annotated circuit, component references, pulse calculations, switching-duty data and controller state sequence. List test conditions covering electrical tolerances, temperature, repeated attempts and identified faults. A standards reference must match the actual component and intended market; do not infer automotive or functional-safety approval from a low-voltage industrial product listing.<\/p>\n<h2 id=\"part-7-choose-the-chac-product-review-route\">How should an OEM review a supplier proposal?<\/h2>\n<p>CHAC&#8217;s <a href=\"https:\/\/chac-electric.com\/ru\/high-voltage-dc-contactor\/\">\u0412\u044b\u0441\u043e\u043a\u043e\u0432\u043e\u043b\u044c\u0442\u043d\u044b\u0439 \u043f\u043e\u0441\u0442\u043e\u044f\u043d\u043d\u044b\u0439 \u0442\u043e\u043a\u043e\u043f\u0440\u043e\u0432\u043e\u0434\u044f\u0449\u0438\u0439 \u043a\u043e\u043d\u0442\u0430\u043a\u0442\u043e\u0440<\/a> category is the relevant family entry point. Its STE2 <a href=\"https:\/\/chac-electric.com\/ru\/product\/ste2-series-high-voltage-dc-contactor-round-epoxy-sealing\/\">DC contactor<\/a> page provides a real model-family record for a supplier discussion, not an established match to this pre-charge event. Provide the branch and main-path duties and approve only an exact proposed model with supporting DC duty data. The existing AC-contactor photograph is not a product recommendation for this application.<\/p>\n<h2 id=\"faqs\">\u0427\u0430\u0441\u0442\u043e \u0437\u0430\u0434\u0430\u0432\u0430\u0435\u043c\u044b\u0435 \u0432\u043e\u043f\u0440\u043e\u0441\u044b<\/h2>\n<h3>Is 95% voltage a universal completion threshold?<\/h3>\n<p>No. Select the allowed closing voltage difference from the actual main-path duty and system validation. The calculation above uses 95% only as an illustration.<\/p>\n<h3>Can a larger resistor always make the circuit safer?<\/h3>\n<p>No. It lowers initial current but increases charging time and can affect timeout behavior. Evaluate current, time and thermal duty together.<\/p>\n<h3>Does continuous wattage describe pulse capability?<\/h3>\n<p>No. Obtain the resistor&#8217;s pulse-energy and repetition data for the event and cooling conditions.<\/p>\n<h3>Can an AC contactor replace a high-voltage DC contactor?<\/h3>\n<p>Not without explicit model-specific DC switching evidence. Similar appearance or a matching current number is insufficient.<\/p>\n<h3>Should a failed pre-charge attempt immediately repeat?<\/h3>\n<p>Only under the validated fault and retry logic. Identify the failure and thermal conditions before permitting another attempt.<\/p>\n<h3>Is a timer enough to prove the capacitor is charged?<\/h3>\n<p>No. It indicates elapsed time, not successful charging. Completion requires the documented measurements and plausibility checks.<\/p>\n<h2 id=\"references\">\u0421\u0441\u044b\u043b\u043a\u0438<\/h2>\n<ul>\n<li><a href=\"https:\/\/www.ti.com\/lit\/an\/sdaa145a\/sdaa145a.pdf\" rel=\"nofollow noopener\" target=\"_blank\">Texas Instruments SDAA145A: DC-Link Capacitor Pre-Charge Designs in Automotive Systems<\/a>, revised April 2026, especially sections 1-3.<\/li>\n<li><a href=\"https:\/\/www.ti.com\/lit\/wp\/slvaf35a\/slvaf35a.pdf\" rel=\"nofollow noopener\" target=\"_blank\">Texas Instruments SLVAF35A: pre-charge switching and contactor-driver discussion<\/a>.<\/li>\n<\/ul>\n<p>A useful specification describes the charging event and the evidence required before main-path closure. Establish voltage difference and capacitance first, calculate current, time and pulse duty, then review the device and resistor against both normal and abnormal operation. Completion logic, hot retries and sensor failures deserve as much attention as nominal ratings. Do not substitute an illustrative calculation, a category listing or an AC product photograph for high-voltage DC validation. CHAC&#8217;s product-family information can help direct the supplier discussion, while exact duty documentation governs the eventual selection. <a href=\"https:\/\/chac-electric.com\/ru\/%d1%81%d0%b2%d1%8f%d0%b6%d0%b8%d1%82%d0%b5%d1%81%d1%8c-%d1%81-%d0%bd%d0%b0%d0%bc%d0%b8\/\">Contact CHAC<\/a> with the circuit, event inputs and required evidence for a model-specific review.<\/p>\n<p>\u0414\u043b\u044f \u043f\u043e\u043b\u0443\u0447\u0435\u043d\u0438\u044f \u0434\u043e\u043f\u043e\u043b\u043d\u0438\u0442\u0435\u043b\u044c\u043d\u043e\u0439 \u0438\u043d\u0444\u043e\u0440\u043c\u0430\u0446\u0438\u0438 \u043f\u043e \u0441\u043e\u043e\u0442\u0432\u0435\u0442\u0441\u0442\u0432\u0443\u044e\u0449\u0435\u0439 \u043a\u0430\u0442\u0435\u0433\u043e\u0440\u0438\u0438 \u043c\u0430\u0442\u0435\u0440\u0438\u0430\u043b\u043e\u0432 \u0441\u043c. <a href=\"https:\/\/chac-electric.com\/ru\/blog\/plug-in-distribution-box-rfq\/\">Which Pre Charge Inputs Should<\/a>.<\/p>\n<p>Continue with this related guide: <a href=\"https:\/\/chac-electric.com\/ru\/blog\/voltage-protector-keeps-tripping-how-to-protect-refrigerators-and-appliances\/\">Voltage Protector Keeps Tripping How<\/a>.<\/p>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>A pre-charge request that names only battery voltage and contactor current leaves the supplier guessing about the event the device must survive. Charging an inverter&#8217;s DC-link capacitor is different from carrying traction current, and a resistor&#8217;s continuous wattage does not describe its pulse capability. An incomplete specification can therefore produce a circuit that reaches its [&hellip;]<\/p>\n","protected":false},"author":10,"featured_media":2810,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[],"class_list":["post-2889","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-blog"],"blocksy_meta":{"styles_descriptor":{"styles":{"desktop":"","tablet":"","mobile":""},"google_fonts":[],"version":8}},"acf":[],"_links":{"self":[{"href":"https:\/\/chac-electric.com\/ru\/wp-json\/wp\/v2\/posts\/2889","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/chac-electric.com\/ru\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/chac-electric.com\/ru\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/chac-electric.com\/ru\/wp-json\/wp\/v2\/users\/10"}],"replies":[{"embeddable":true,"href":"https:\/\/chac-electric.com\/ru\/wp-json\/wp\/v2\/comments?post=2889"}],"version-history":[{"count":5,"href":"https:\/\/chac-electric.com\/ru\/wp-json\/wp\/v2\/posts\/2889\/revisions"}],"predecessor-version":[{"id":4846,"href":"https:\/\/chac-electric.com\/ru\/wp-json\/wp\/v2\/posts\/2889\/revisions\/4846"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/chac-electric.com\/ru\/wp-json\/wp\/v2\/media\/2810"}],"wp:attachment":[{"href":"https:\/\/chac-electric.com\/ru\/wp-json\/wp\/v2\/media?parent=2889"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/chac-electric.com\/ru\/wp-json\/wp\/v2\/categories?post=2889"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/chac-electric.com\/ru\/wp-json\/wp\/v2\/tags?post=2889"}],"curies":[{"name":"\u0432\u043f","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}