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<p>We see it at least twice a week: an engineer sends us an email that says <em>"I need a custom coil, can you quote?"</em> — with no drawing, no specs, not even an inductance value.</p>

<p>We reply asking for details. They reply with some. We ask follow-ups. Three weeks later, both sides are frustrated, and the PO still hasn't been placed.</p>

<p>If you've been on either side of that conversation, this guide is for you. Here's how to spec a custom inductor coil the first time — so your supplier can quote accurately in 24 hours instead of 3 weeks.</p>

<hr>

<h2>The 6 Things Every Coil Manufacturer Needs from You</h2>

<p>We've manufactured over a billion coils. Based on that experience, here are the six specifications that separate a 24-hour quote from a 3-week email chain.</p>

<h3>1. Inductance Value (and Tolerance)</h3>

<p>This is the non-negotiable starting point.</p>

<table>
<tr><th>What to provide</th><th>Example</th></tr>
<tr><td>Nominal inductance</td><td>10 μH</td></tr>
<tr><td>Tolerance</td><td>±5% (standard) or ±3% (precision)</td></tr>
<tr><td>Test frequency</td><td>@ 1 MHz (inductance varies with frequency!)</td></tr>
</table>

<p><strong>Common mistake</strong>: Saying "I need a 10 μH coil" without specifying the test frequency. A coil that measures 10 μH at 100 kHz might measure 11.5 μH at 1 MHz due to parasitic capacitance. Always state the frequency at which inductance should be measured.</p>

<h3>2. Wire Specifications</h3>

<table>
<tr><th>Parameter</th><th>Options</th><th>How to decide</th></tr>
<tr><td>Wire type</td><td>Enameled copper / Self-bonding copper / Litz wire</td><td>Self-bonding = no bobbin needed. Litz = lower AC resistance at high frequency.</td></tr>
<tr><td>Wire diameter</td><td>0.01mm – 2.0mm</td><td>Thinner = more turns in same space, higher DCR. Thicker = lower DCR.</td></tr>
<tr><td>Insulation class</td><td>B (130°C) / F (155°C) / H (180°C)</td><td>Based on your device's max operating temperature + safety margin.</td></tr>
</table>

<p><strong>If you're unsure</strong>: Tell us your operating frequency and temperature environment. We'll recommend the wire type.</p>

<h3>3. Coil Dimensions (or Space Budget)</h3>

<p>A drawing is ideal. If you don't have one, provide:</p>

<table>
<tr><th>Parameter</th><th>Example</th></tr>
<tr><td>Inner diameter (ID)</td><td>5.0 mm</td></tr>
<tr><td>Outer diameter (OD)</td><td>≤ 8.5 mm (max allowed)</td></tr>
<tr><td>Height/thickness</td><td>≤ 3.0 mm</td></tr>
<tr><td>Shape</td><td>Round / Square / Rectangular / Oval</td></tr>
</table>

<p><strong>Pro tip</strong>: Give us your maximum allowed dimensions, not an exact number. We often hit your electrical specs in a smaller footprint than you expected — but only if we know the ceiling.</p>

<h3>4. Termination Type</h3>

<p>How will the coil connect to your PCB or assembly?</p>

<table>
<tr><th>Termination</th><th>Best for</th></tr>
<tr><td>Wire leads (tinned ends)</td><td>Through-hole soldering, manual assembly</td></tr>
<tr><td>SMD pads</td><td>Reflow soldering, automated pick-and-place</td></tr>
<tr><td>Pin headers</td><td>Modular designs, socketed connections</td></tr>
<tr><td>Custom connector</td><td>Your own connector spec</td></tr>
</table>

<h3>5. Operating Environment</h3>

<p>This is what separates a coil that lasts 10 years from one that fails in 6 months.</p>

<table>
<tr><th>Factor</th><th>Why it matters</th></tr>
<tr><td>Max ambient temperature</td><td>Determines wire insulation class</td></tr>
<tr><td>Humidity exposure</td><td>May require conformal coating or sealed packaging</td></tr>
<tr><td>Vibration / mechanical shock</td><td>Affects winding tension and bonding method</td></tr>
<tr><td>Chemical exposure</td><td>Some environments degrade standard enamel</td></tr>
</table>

<p><strong>Real example</strong>: A coffee machine manufacturer came to us after their previous supplier's coils corroded within 12 months. The root cause? Standard enameled wire can't handle 85°C / 85% RH cycling. We switched to dual-layer moisture-resistant self-bonding wire — failure rate dropped from 8% to under 3%.</p>

<h3>6. Quantity and Timeline</h3>

<table>
<tr><th>What we need</th><th>Why</th></tr>
<tr><td>Prototype quantity</td><td>10–50 pcs is standard for evaluation</td></tr>
<tr><td>Mass production quantity</td><td>Determines tooling approach and unit cost</td></tr>
<tr><td>Target lead time</td><td>Samples: 3–5 days. Mass production: 7–15 days.</td></tr>
<tr><td>Forecast (optional)</td><td>Helps us reserve capacity for your ramp-up</td></tr>
</table>

<hr>

<h2>The "Spec Phase Trap" — and How We Avoid It</h2>

<p>Here's a pattern we've observed across thousands of custom coil projects:</p>

<p>Week 1: Customer sends vague request → We ask clarifying questions<br>
Week 2: Customer answers 3 out of 10 questions → We ask the remaining 7<br>
Week 3: Customer sends a drawing that conflicts with earlier specs → We flag the conflict<br>
Week 4: Engineering alignment call → Finally, we can quote</p>

<p>Total elapsed time: <strong>4 weeks</strong>. Actual engineering time needed: <strong>2 hours</strong>.</p>

<p><strong>How we solve it</strong>: When you send us your initial request, our engineers respond with a structured checklist based on the 6 categories above. Fill it out once, get a quote within 24 hours.</p>

<hr>

<h2>What Happens After You Send the Specs</h2>

<table>
<tr><th>Day</th><th>What we do</th></tr>
<tr><td>Day 1</td><td>Engineering review — check if specs are internally consistent. Flag conflicts with alternatives.</td></tr>
<tr><td>Day 1–2</td><td>Quote delivery — unit price, tooling cost, lead time, shipping options.</td></tr>
<tr><td>Day 2–5</td><td>Sample production — once you approve, we build evaluation samples.</td></tr>
<tr><td>Day 5</td><td>Samples ship — with full LCR test report for each sample.</td></tr>
<tr><td>Day 5+</td><td>Your evaluation → feedback → mass production.</td></tr>
</table>

<hr>

<h2>Ready to Send Your Specs?</h2>

<p>If you have a drawing, attach it. If you don't, just describe your application and answer as many of the 6 categories as you can. We'll handle the rest.</p>

<p><a href="https://www.jyinductor.com/contact-us/" style="display:inline-block; padding:12px 30px; background:#0047AB; color:#fff; text-decoration:none; border-radius:4px; font-weight:bold;">Send Your Specifications → Get a Quote in 24 Hours</a></p>

<p><strong>Prefer to talk to an engineer directly?</strong><br>
Email: pxsales3@goldeneagle-cn.com<br>
WhatsApp: +86-15907990080</p>

<hr>

<h3>Related Resources</h3>
<ul>
<li><a href="https://www.jyinductor.com/air-core-coil/">Custom Air Core Inductor Coils</a> — Our most popular product line</li>
<li><a href="https://www.jyinductor.com/bobbin-coil/">Custom Bobbin & Solenoid Coils</a> — For industrial and automotive</li>
<li><a href="https://www.jyinductor.com/transformers/">Custom Transformers</a> — High-frequency and low-frequency</li>
</ul>