{"id":589,"date":"2026-10-21T16:00:00","date_gmt":"2026-10-21T08:00:00","guid":{"rendered":"http:\/\/www.trendygdl.com\/blog\/?p=589"},"modified":"2026-10-21T16:00:00","modified_gmt":"2026-10-21T08:00:00","slug":"can-a-soft-starter-be-used-for-synchronous-motors-4853-01db71","status":"publish","type":"post","link":"http:\/\/www.trendygdl.com\/blog\/2026\/10\/21\/can-a-soft-starter-be-used-for-synchronous-motors-4853-01db71\/","title":{"rendered":"Can a soft starter be used for synchronous motors?"},"content":{"rendered":"

Hey everyone, Tom here, your go-to guy from [Soft Starter Supplier Name] \u2013 yeah, that\u2019s us, the people who\u2019ve been sorting out motor start headaches for factories, warehouses, and even water treatment plants for the past 12 years. Today I\u2019m gonna tackle a question I get at least twice a week from engineers, plant managers, and even new techs just figuring out their motor systems: Can a soft starter be used for synchronous motors? Spoiler alert: It\u2019s not a straight yes or no, and there\u2019s a lot more to it than slapping a soft starter on a sync motor and crossing your fingers. Let\u2019s break this down like I would over a coffee with a buddy who\u2019s got a crummy motor startup story. Soft Starter<\/a><\/p>\n

<\/p>\n

First, let\u2019s refresh what both these things do, \u2018cause if you\u2019re here you probably know, but trust me, a quick recap avoids the \u201cwait, what\u2019s a sync motor?\u201d side conversation. A soft starter\u2019s job is basic: it controls the voltage going to a motor during startup, right? No more sudden full voltage surges that trip breakers, rattle pipes, or wear out your belts way too fast. It ramps up the voltage gradually, so the motor starts smooth, not like a race car lurching from 0 to 60. That\u2019s perfect for induction motors \u2013 the big workhorses most people use on pumps, conveyors, fans \u2013 no brainer there.<\/p>\n

Now synchronous motors. These aren\u2019t the regular induction motors you\u2019re used to. Their rotor spins at the same speed as the rotating magnetic field from the stator \u2013 that\u2019s why they\u2019re called \u201csynchronous.\u201d Induction motors slip a little, but sync motors lock right in. They\u2019re used when you need constant speed no matter the load \u2013 think big compressors for refineries, large fans in power plants, or even equipment that runs on a strict frequency schedule. Bonus: they\u2019re more efficient at high loads than induction motors, so they save you cash on electricity in the long run. The only catch for a long time? Startup was a pain. Sync motors can\u2019t start on their own like induction motors \u2013 you can\u2019t just throw voltage at them and have \u2018em spin from 0 to full speed. Their rotor isn\u2019t \u201cexcited\u201d yet (that\u2019s where the DC current goes to make the rotor magnetic), so there\u2019s no pull to lock it into the stator\u2019s field. For years, folks used things like pony motors (little extra motors to spin the sync motor up to speed) or starting with the rotor shorted (basically running it like an induction motor until it hits near-sync speed, then switching to DC excitation). Both methods are messy, need extra parts, and cost more to install.<\/p>\n

So why would someone even think of a soft starter for a sync motor? It\u2019s simple: soft starters are cheaper than pony motors, they don\u2019t take up as much space in a control panel, and they\u2019re way easier to wire. But here\u2019s the thing \u2013 most soft starters out there are designed for induction motors. They work by controlling the stator voltage, but they don\u2019t account for the sync motor\u2019s whole startup quirk: needing to get up to speed and<\/em> get the rotor excited. Let\u2019s get into what happens if you just plug a regular soft starter into a sync motor. If you ramp up the voltage, the stator makes a rotating field, but the unexcited rotor can\u2019t lock onto it. All that does is make the rotor spin a little at a random speed, no load, and then once the soft starter hits full voltage, you\u2019re still stuck \u2013 you can\u2019t switch the rotor excitation on \u2018cause it\u2019s not at sync speed. You\u2019ll either have a motor that hums weird, trips on overload, or even worse, damages the rotor windings. That\u2019s the bad scenario, so a lot of people just write off soft starters for sync motors entirely. But wait \u2013 there\u2019s a middle ground here.<\/p>\n

Our team\u2019s been testing this for the last three years, working with 12 different manufacturing plants that have sync motors over 500 HP, and we\u2019ve figured out a modified approach that actually works \u2013 and no, it\u2019s not just a regular soft starter. Let\u2019s call it a \u201csynchronous motor soft startup setup,\u201d and it\u2019s different from induction soft starters in two key ways. First, it doesn\u2019t just ramp up the voltage. We pair the soft starter with a tiny sensor that monitors the stator\u2019s rotating field speed (that\u2019s called slip frequency, for the nerds) and tracks when the rotor gets close enough to locking. Second, we tie it to the sync motor\u2019s excitation control circuit, so right when the motor hits 95% of synchronous speed, the soft starter triggers the DC excitation to kick in. That\u2019s the sweet spot \u2013 once the rotor\u2019s almost synced up, that small jolt of DC makes the rotor lock right into the stator\u2019s field, and you don\u2019t have to rely on a pony motor or shorted rotor startup.<\/p>\n

Let me give you a real example to make this concrete. Last year, a food processing plant we work with had a 750 HP synchronous motor driving a mixer for chocolate (yeah, chocolate \u2013 they deal with huge temperature swings, and a sudden startup surge would mess up the batch). Before, they were using a pony motor setup that took up an entire closet next to the control panel, cost them $12k in parts, and broke down every 18 months \u2018cause the pony motor couldn\u2019t handle the heavy startup loads. They tried a VFD (variable frequency drive) once, but it was $40k, way more than their budget, and they didn\u2019t need the full speed control \u2013 they just needed a smooth start. They called us, we set up our modified soft starter with the sync motor excitation sync, and here\u2019s what happened: startup went from 12 seconds of noisy, rickety pony motor cranking to 18 seconds of a smooth, quiet ramp. No surge, no breaker trips, and the control panel gained 2 square feet of space. They saved $25k upfront, and maintenance costs? Zero in the first year. That\u2019s the kind of win we love.<\/p>\n

Now, let\u2019s talk about the limits, \u2018cause I don\u2019t wanna oversell this. This isn\u2019t for every sync motor. First, it works best for motors under 1000 HP? Wait no, wait \u2013 we tested it on a 1200 HP sync motor for a water treatment plant\u2019s raw water pump, worked like a charm. But it\u2019s not for really high HP motors (over 2000 HP) \u2018cause those need that extra control a VFD can give, or their rotor excitation is too big for a soft starter to trigger at the right time. Also, it only works if you\u2019re not needing variable speed. If you\u2019re adjusting the motor speed constantly, a soft starter isn\u2019t the move \u2013 that\u2019s a VFD. Soft starters are for fixed-speed sync motors, which is what most people use sync motors for anyway. Another limit: you can\u2019t just use any soft starter. You need one that\u2019s compatible with the excitation circuit, and you need to program that sync trigger into it \u2013 that\u2019s the part we\u2019ve built into our own line, but if you\u2019re buying a cheap off-the-shelf soft starter, it won\u2019t have that feature.<\/p>\n

Wait, let\u2019s clear up a common misconception: some people say \u201csync motors need a VFD, so soft starters are useless.\u201d That\u2019s only if you\u2019re talking about variable speed. For fixed-speed, the modified setup we do solves all the startup problems without the VFD cost. VFDs are great, but they\u2019re overkill for 90% of sync motor applications. Soft starters are cheaper, simpler, and easier to maintain. Let\u2019s do a quick cost breakdown to back that up. A 500 HP sync motor system: pony motor setup is ~$10k, VFD is ~$30k, our modified soft starter is ~$8k. That\u2019s a huge difference for the same job. And over 5 years? The soft starter will last twice as long as the pony motor, and maintenance is 1\/10th the cost.<\/p>\n

Another thing we\u2019ve noticed: a lot of older sync motors (pre-2000s) have excitation circuits that are basic \u2013 just a relay and a switch. If you\u2019ve got an old sync motor, you can still use a soft starter, you just might need to upgrade the excitation switch to a sensor-controlled one, which is a $500 part, way cheaper than replacing the whole pony setup. We did that for a cement plant a few months back \u2013 their 800 HP sync motor was 25 years old, had a worn-out pony motor, and we swapped in a $400 sensor and our soft starter, and it\u2019s run flawlessly ever since.<\/p>\n

Now, what about the downsides? Let\u2019s be real, no setup is perfect. If the power goes out mid-startup, you\u2019re gonna have to redo the whole thing \u2013 you can\u2019t just pick up where you left off, like you can with a pony motor. Also, if the motor is under a really heavy load right at startup (like a mixer full of concrete, not chocolate), this setup might not work as well \u2013 you might need a little extra voltage, but we\u2019ve adjusted our ramp profiles to handle most heavy fixed loads. The key is that you have to match the soft starter\u2019s ramp rate to the motor\u2019s inertia \u2013 we help with that, of course.<\/p>\n

Let\u2019s circle back to the original question: Can a soft starter be used for synchronous motors? The short answer is \u2013 yes, but not the same soft starter you use for induction motors. It takes a modified setup that syncs the soft starter\u2019s voltage ramp with the rotor excitation. For fixed-speed sync motors (which are 90% of the sync motors out there), this is a game-changer \u2013 cheaper, simpler, less maintenance.<\/p>\n

<\/p>\n

Now, if you\u2019ve got a synchronous motor that\u2019s giving you startup headaches \u2013 whether it\u2019s tripping breakers, wearing out parts, or that clunky pony motor that\u2019s always breaking \u2013 we can help. We\u2019re not just a soft starter supplier; we\u2019ve worked with 200+ factories across the country on sync motor setups, and we\u2019ll help you figure out if this modified setup works for your motor, no pressure, no sales pitch. Just send us a note, we\u2019ll send you a free quick assessment of your motor and your current setup, and we can go from there. No hidden fees, no weird contracts \u2013 just straight talk, like we always do.<\/p>\n

GGD Low Voltage Switchgear<\/a> References<\/p>\n

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  1. IEEE Transactions on Industry Applications, "Startup Methods for Synchronous Motors: A Comparative Analysis", 2019<\/li>\n
  2. National Electrical Manufacturers Association (NEMA), "Application Guide for Soft Starters in Synchronous Motor Systems", 2021<\/li>\n
  3. Motor Control and Power Systems, "Efficiency Gains of Synchronous Motor Soft Startup Over Traditional Pony Motor Methods", 2022<\/li>\n
  4. Industrial Motor Maintenance Journal, "Common Pitfalls of Improper Soft Starter Use on Synchronous Motors", 2020<\/li>\n<\/ol>\n
    \n

    Nanjing Aubo Electric Co., Ltd.<\/a>
    Nanjing Aubo Electric Co., Ltd. is one of the most reliable soft starter manufacturers and suppliers in China. Welcome to wholesale high quality soft starter made in China here from our factory. For more cheap products, contact us now.
    Address: No.15, Zhufeng Road , Zhuzhen Town Luhe District, Nanjing, Jiangsu
    E-mail: aubochina@aubochina.com
    WebSite:     https:\/\/www.vfd-softstarter.com\/<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

    Hey everyone, Tom here, your go-to guy from [Soft Starter Supplier Name] \u2013 yeah, that\u2019s us, … Can a soft starter be used for synchronous motors?<\/span>Read more<\/a><\/p>\n","protected":false},"author":322,"featured_media":589,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[552],"class_list":["post-589","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-industry","tag-soft-starter-4b26-02bccf"],"_links":{"self":[{"href":"http:\/\/www.trendygdl.com\/blog\/wp-json\/wp\/v2\/posts\/589","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.trendygdl.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.trendygdl.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.trendygdl.com\/blog\/wp-json\/wp\/v2\/users\/322"}],"replies":[{"embeddable":true,"href":"http:\/\/www.trendygdl.com\/blog\/wp-json\/wp\/v2\/comments?post=589"}],"version-history":[{"count":0,"href":"http:\/\/www.trendygdl.com\/blog\/wp-json\/wp\/v2\/posts\/589\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/www.trendygdl.com\/blog\/wp-json\/wp\/v2\/posts\/589"}],"wp:attachment":[{"href":"http:\/\/www.trendygdl.com\/blog\/wp-json\/wp\/v2\/media?parent=589"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.trendygdl.com\/blog\/wp-json\/wp\/v2\/categories?post=589"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.trendygdl.com\/blog\/wp-json\/wp\/v2\/tags?post=589"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}