{"id":20938,"date":"2026-11-06T10:18:47","date_gmt":"2026-11-06T02:18:47","guid":{"rendered":"https:\/\/www.wehopower.com\/news\/dc-fan-polarity-protection-voltage-budget\/"},"modified":"2026-11-06T10:18:47","modified_gmt":"2026-11-06T02:18:47","slug":"dc-fan-polarity-protection-voltage-budget","status":"publish","type":"news","link":"https:\/\/www.wehopower.com\/it\/news\/dc-fan-polarity-protection-voltage-budget\/","title":{"rendered":"24 V DC Fan Polarity Protection: Check the Voltage and Heat Budget"},"content":{"rendered":"<figure class=\"hero\"><a href=\"https:\/\/www.wehopower.com\/it\/product\/75w-power-supply-ac-to-dc-single-output\/\"><img decoding=\"async\" src=\"https:\/\/www.wehopower.com\/wp-content\/uploads\/2026\/11\/hero-22.webp\" alt=\"24 V DC Fan Polarity Protection: Check the Voltage and Heat Budget  title=\" fetchpriority=\"high\" 24 dc fan polarity protection: check the voltage and heat budget title=\"\"><\/a><figcaption>AI-assisted application illustration using original LRS-75-24 artwork. The fan is shown over a vent opening; airflow, concealed fixing and a complete polarity-protection circuit are not verified.<\/figcaption><a class=\"original-link\" href=\"https:\/\/www.wehopower.com\/wp-content\/uploads\/2026\/11\/original-15.jpg\">View original product image<\/a><\/figure>\n<p><strong>Polarity protection for a DC fan branch must be checked at the fan, including the voltage lost and heat produced by the proposed protection circuit.<\/strong> A 24 V supply label does not establish that an attached fan tolerates reverse connection, nor that a protective component leaves enough startup voltage.<\/p>\n<p>For an OEM integrating a candidate LRS-75-24, the practical output is a protected-branch voltage and thermal budget. The fan and protection circuit remain separate products whose specifications must be verified.<\/p>\n<nav class=\"toc\" aria-label=\"On this page\">\n<ol>\n<li><a href=\"#identify-fan-interface\">Identify the fan interface before drawing the branch<\/a><\/li>\n<li><a href=\"#budget-voltage\">Calculate the voltage remaining after the added circuit<\/a><\/li>\n<li><a href=\"#budget-loss\">Treat conduction loss as a local thermal load<\/a><\/li>\n<li><a href=\"#check-signal-return\">Check tachometer and control returns as well as power<\/a><\/li>\n<li><a href=\"#validate-the-assembly\">Validate the selected fan and circuit as one assembly<\/a><\/li>\n<\/ol>\n<\/nav>\n<section id=\"identify-fan-interface\">\n<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_86 counter-hierarchy ez-toc-counter ez-toc-grey ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">Sommario<\/p>\n<span class=\"ez-toc-title-toggle\"><a href=\"#\" class=\"ez-toc-pull-right ez-toc-btn ez-toc-btn-xs ez-toc-btn-default ez-toc-toggle\" aria-label=\"Attiva\/disattiva Sommario\"><span class=\"ez-toc-js-icon-con\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Attiva\/disattiva<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewbox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewbox=\"0 0 24 24\" version=\"1.2\" baseprofile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/span><\/a><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/www.wehopower.com\/it\/news\/dc-fan-polarity-protection-voltage-budget\/#Identify_the_fan_interface_before_drawing_the_branch\" >Identify the fan interface before drawing the branch<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/www.wehopower.com\/it\/news\/dc-fan-polarity-protection-voltage-budget\/#Calculate_the_voltage_remaining_after_the_added_circuit\" >Calculate the voltage remaining after the added circuit<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/www.wehopower.com\/it\/news\/dc-fan-polarity-protection-voltage-budget\/#Treat_conduction_loss_as_a_local_thermal_load\" >Treat conduction loss as a local thermal load<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/www.wehopower.com\/it\/news\/dc-fan-polarity-protection-voltage-budget\/#Check_tachometer_and_control_returns_as_well_as_power\" >Check tachometer and control returns as well as power<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/www.wehopower.com\/it\/news\/dc-fan-polarity-protection-voltage-budget\/#Validate_the_selected_fan_and_circuit_as_one_assembly\" >Validate the selected fan and circuit as one assembly<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-6\" href=\"https:\/\/www.wehopower.com\/it\/news\/dc-fan-polarity-protection-voltage-budget\/#Fan-branch_protection_assessment\" >Fan-branch protection assessment<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-7\" href=\"https:\/\/www.wehopower.com\/it\/news\/dc-fan-polarity-protection-voltage-budget\/#Sources_and_further_reading\" >Sources and further reading<\/a><\/li><\/ul><\/nav><\/div>\n<h2><span class=\"ez-toc-section\" id=\"Identify_the_fan_interface_before_drawing_the_branch\"><\/span>Identify the fan interface before drawing the branch<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>A two-wire fan, a three-wire fan with tachometer and a four-wire controlled fan are not interchangeable wiring tasks. Read the fan manufacturer\u2019s pinout, voltage limits, startup demand and signal-interface instructions. Wire colors and a similar plug are insufficient identification.<\/p>\n<p>IL <a href=\"https:\/\/www.wehopower.com\/it\/product\/75w-power-supply-ac-to-dc-single-output\/\">LRS-75 product table<\/a> lists a 24 V variant with a 0\u20133.2 A current range. Its photograph shows that exact suffix. Those facts establish a candidate source; they do not authorize a particular fan, reverse-current path or external semiconductor.<\/p>\n<figure id=\"fig-original\" class=\"product-original\"><a href=\"https:\/\/www.wehopower.com\/it\/product\/75w-power-supply-ac-to-dc-single-output\/\"><img decoding=\"async\" src=\"https:\/\/www.wehopower.com\/wp-content\/uploads\/2026\/11\/original-15.jpg\" alt=\"24 V DC Fan Polarity Protection: Check the Voltage and Heat Budget  title=\" loading=\"lazy\" 24 dc fan polarity protection: check the voltage and heat budget title=\"\"><\/a><figcaption>Manufacturer image showing the WEHO LRS-75-24; the photograph identifies the pictured unit and does not establish equipment-level suitability.<\/figcaption><a class=\"original-link\" href=\"https:\/\/www.wehopower.com\/wp-content\/uploads\/2026\/11\/original-15.jpg\">View original image<\/a><\/figure>\n<\/section>\n<section id=\"budget-voltage\">\n<h2><span class=\"ez-toc-section\" id=\"Calculate_the_voltage_remaining_after_the_added_circuit\"><\/span>Calculate the voltage remaining after the added circuit<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>For the proposed branch, use <strong>Vfan,min = Vsource,min \u2212 Vprotection,max \u2212 Vcable,max \u2212 Vother,max<\/strong>. Use the fan\u2019s required voltage at startup as well as during running. A protection device whose voltage drop depends on current or temperature must be evaluated at the relevant operating point.<\/p>\n<p>In a hypothetical example, the minimum source voltage is 23.5 V, the protection drop is 0.55 V and cable plus connector drop is 0.35 V. The fan receives <strong>22.6 V<\/strong>. If its documented startup minimum is 23.0 V, the proposal fails that initial screen even if its running minimum is lower.<\/p>\n<p>Do not turn up the supply automatically to hide the missing margin. Other receivers on the same output must remain within their voltage limits at every permitted setting. A branch redesign may be necessary.<\/p>\n<figure id=\"fig-diagram\" class=\"diagram\"><img decoding=\"async\" class=\"technical-desktop\" src=\"https:\/\/www.wehopower.com\/wp-content\/uploads\/2026\/11\/diagram-22.svg\" alt=\"24 V DC Fan Polarity Protection: Check the Voltage and Heat Budget  title=\" loading=\"lazy\" 24 dc fan polarity protection: check the voltage and heat budget title=\"\"><img decoding=\"async\" class=\"technical-mobile\" src=\"https:\/\/www.wehopower.com\/wp-content\/uploads\/2026\/11\/diagram-mobile-22.svg\" alt=\"24 V DC Fan Polarity Protection: Check the Voltage and Heat Budget  title=\" loading=\"lazy\" 24 dc fan polarity protection: check the voltage and heat budget title=\"\"><figcaption>Hypothetical voltage budget; not a component-selection or wiring diagram.<\/figcaption><a class=\"original-link\" href=\"https:\/\/www.wehopower.com\/wp-content\/uploads\/2026\/11\/diagram-22.svg\">Open full-size technical illustration<\/a><\/figure>\n<\/section>\n<section id=\"budget-loss\">\n<h2><span class=\"ez-toc-section\" id=\"Treat_conduction_loss_as_a_local_thermal_load\"><\/span>Treat conduction loss as a local thermal load<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>For a series element with a 0.55 V drop at 0.8 A, the hypothetical conduction loss is <strong>P = VI = 0.44 W<\/strong>. This is heat in that element, not the total fan input power or the supply loss. Its actual temperature depends on package, copper, enclosure, airflow and neighboring heat sources.<\/p>\n<p>A MOSFET-based circuit has different drive, reverse-connection and startup requirements from a simple diode. <a href=\"https:\/\/www.ti.com\/document-viewer\/lit\/html\/SSZT974\/GUID-B8E8F13F-7B11-4710-8ABE-5FF16750FE46\" target=\"_blank\" rel=\"noopener\">TI\u2019s motor-driver discussion<\/a> illustrates that reverse-supply protection depends on the circuit architecture; its featured FET arrangement is not a ready-made circuit for any fan.<\/p>\n<p>Selecting a component by its headline current alone leaves voltage rating, transient conditions, thermal resistance and failure behavior unresolved. Confirm the complete circuit with the responsible designer.<\/p>\n<\/section>\n<section id=\"check-signal-return\">\n<h2><span class=\"ez-toc-section\" id=\"Check_tachometer_and_control_returns_as_well_as_power\"><\/span>Check tachometer and control returns as well as power<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<div class=\"table-scroll\">\n<table>\n<thead>\n<tr>\n<th scope=\"col\">Interface<\/th>\n<th scope=\"col\">What can be missed<\/th>\n<th scope=\"col\">Verification<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Fan power pair<\/td>\n<td>Protective element changes the available voltage<\/td>\n<td>Voltage at fan during defined states<\/td>\n<\/tr>\n<tr>\n<td>Tachometer output<\/td>\n<td>Receiver has its own pull-up and reference requirements<\/td>\n<td>Fan and receiver interface documents<\/td>\n<\/tr>\n<tr>\n<td>PWM\/control input<\/td>\n<td>Its reference may be disturbed by an improvised return-side device<\/td>\n<td>Allowed reference and signal levels<\/td>\n<\/tr>\n<tr>\n<td>Other branch sources<\/td>\n<td>Signals can create an unintended path when power is absent<\/td>\n<td>Authorized power-off interface assessment<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>This is an interface review, not a recommendation to put a diode in any particular wire. Do not use PE as a fan return or assume a signal wire is protected because the main positive conductor has a protective element.<\/p>\n<\/section>\n<section id=\"validate-the-assembly\">\n<h2><span class=\"ez-toc-section\" id=\"Validate_the_selected_fan_and_circuit_as_one_assembly\"><\/span>Validate the selected fan and circuit as one assembly<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Record startup from the specified temperature and supply conditions, steady operation, commanded speed changes and the approved fault checks. Observe the voltage at the fan and component temperatures using a defined method. A quiet spinning fan is not a complete acceptance result.<\/p>\n<p>Keep the fan part number, protection-circuit revision, source setting and wiring record together. A replacement fan can change startup current or signal behavior even when its 24 V label looks identical. Reuse this budget when evaluating the replacement, rather than carry forward an unsupported compatibility statement.<\/p>\n<\/section>\n<section class=\"cta\">\n<p>Send the <a href=\"https:\/\/www.wehopower.com\/it\/product\/75w-power-supply-ac-to-dc-single-output\/\">LRS-75-24 fan-branch enquiry<\/a> with the fan model, startup-voltage requirement, proposed polarity-protection device, PWM\/tach references and measured voltage-loss record. Request the supply\u2019s applicable operating limits, then review the fan interface and protection loss against the actual assembly.<\/p>\n<\/section>\n<section id=\"worksheet\" class=\"sheet\">\n<h2><span class=\"ez-toc-section\" id=\"Fan-branch_protection_assessment\"><\/span>Fan-branch protection assessment<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<div class=\"sheet-row\"><label>Supply and setting<input aria-label=\"Supply and setting\"><\/label><label>Fan part number<input aria-label=\"Fan part number\"><\/label><label>Protection circuit revision<input aria-label=\"Protection circuit revision\"><\/label><label>Fan startup voltage limit<input aria-label=\"Fan startup voltage limit\"><\/label><label>Thermal conditions<input aria-label=\"Thermal conditions\"><\/label><\/div>\n<div class=\"table-scroll\">\n<table>\n<thead>\n<tr>\n<th scope=\"col\">Operating state<\/th>\n<th scope=\"col\">Fan current evidence<\/th>\n<th scope=\"col\">Voltage at fan<\/th>\n<th scope=\"col\">Protection loss\/temperature<\/th>\n<th scope=\"col\">Decision<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td contenteditable=\"true\" aria-label=\"Worksheet cell\"><\/td>\n<td contenteditable=\"true\" aria-label=\"Worksheet cell\"><\/td>\n<td contenteditable=\"true\" aria-label=\"Worksheet cell\"><\/td>\n<td contenteditable=\"true\" aria-label=\"Worksheet cell\"><\/td>\n<td contenteditable=\"true\" aria-label=\"Worksheet cell\"><\/td>\n<\/tr>\n<tr>\n<td contenteditable=\"true\" aria-label=\"Worksheet cell\"><\/td>\n<td contenteditable=\"true\" aria-label=\"Worksheet cell\"><\/td>\n<td contenteditable=\"true\" aria-label=\"Worksheet cell\"><\/td>\n<td contenteditable=\"true\" aria-label=\"Worksheet cell\"><\/td>\n<td contenteditable=\"true\" aria-label=\"Worksheet cell\"><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>Blank project worksheet. Enter verified project data; example calculations above are not measurements.<\/p>\n<\/section>\n<section class=\"source-list\">\n<h2><span class=\"ez-toc-section\" id=\"Sources_and_further_reading\"><\/span>Sources and further reading<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<ol>\n<li><a href=\"https:\/\/www.wehopower.com\/it\/product\/75w-power-supply-ac-to-dc-single-output\/\">WEHO LRS-75 product information<\/a><\/li>\n<li><a href=\"https:\/\/www.wehopower.com\/wp-content\/uploads\/2025\/07\/LRS-75-a07.pdf\">WEHO LRS-75 specification<\/a><\/li>\n<li><a href=\"https:\/\/www.ti.com\/document-viewer\/lit\/html\/SSZT974\/GUID-B8E8F13F-7B11-4710-8ABE-5FF16750FE46\" target=\"_blank\" rel=\"noopener\">Texas Instruments: Six Weird Ways to Design with a Brushless-DC Driver<\/a><\/li>\n<\/ol>\n<\/section>","protected":false},"excerpt":{"rendered":"<p>Assess an external fan-branch polarity-protection proposal using receiver voltage, conduction loss and the exact fan interface rather than the supply wattage.<\/p>","protected":false},"author":2,"featured_media":20926,"parent":0,"menu_order":1,"comment_status":"","ping_status":"","template":"","format":"standard","meta":{"_acf_changed":false,"_joinchat":[],"footnotes":""},"news_category":[284],"class_list":["post-20938","news","type-news","status-publish","format-standard","has-post-thumbnail","hentry","news_category-product-articles","entry"],"acf":[],"post_mailing_queue_ids":[],"_links":{"self":[{"href":"https:\/\/www.wehopower.com\/it\/wp-json\/wp\/v2\/news\/20938","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.wehopower.com\/it\/wp-json\/wp\/v2\/news"}],"about":[{"href":"https:\/\/www.wehopower.com\/it\/wp-json\/wp\/v2\/types\/news"}],"author":[{"embeddable":true,"href":"https:\/\/www.wehopower.com\/it\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.wehopower.com\/it\/wp-json\/wp\/v2\/comments?post=20938"}],"version-history":[{"count":0,"href":"https:\/\/www.wehopower.com\/it\/wp-json\/wp\/v2\/news\/20938\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.wehopower.com\/it\/wp-json\/wp\/v2\/media\/20926"}],"wp:attachment":[{"href":"https:\/\/www.wehopower.com\/it\/wp-json\/wp\/v2\/media?parent=20938"}],"wp:term":[{"taxonomy":"news_category","embeddable":true,"href":"https:\/\/www.wehopower.com\/it\/wp-json\/wp\/v2\/news_category?post=20938"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}