If you’ve ever browsed through the back of a piece of industrial equipment, a medical device, or even a compact consumer electronics system, you’ve likely run into one of our open frame switching power supplies—they’re the no-frills, space-saving workhorses that convert AC wall power to the regulated DC voltage almost every modern electronic needs. As a supplier who’s spent the last decade designing, testing, and shipping these power supplies to engineers around the world, one question comes up more often than any other: “Can I wire open frame switching power supplies in series to get a higher output voltage?” Open Frame Switching Power Supply
At first glance, it seems like a straightforward solution. If one power supply puts out 24V DC, wiring two in series would give you 48V—perfect for that custom machine tool prototype, that specialized medical imaging sensor, or that industrial control panel that needs a higher voltage than standard off-the-shelf supplies offer. But here’s the thing: it’s not as simple as just connecting the positive of one supply to the negative of the other and calling it a day. Over the years, I’ve seen engineers get this wrong more times than I can count, leading to blown components, failed tests, and even a few late nights troubleshooting at a customer’s facility. Let’s break this down the way I explain it to every customer who asks, using real-world scenarios and hard lessons we’ve learned in our own test lab.
First, let’s start with the basics of how an open frame switching power supply works, because that’s where most of the confusion starts. Unlike linear power supplies, which use a bulky transformer to step down AC, switching supplies use high-frequency transistors to switch the input on and off rapidly, then rectify and regulate that signal to get a stable DC output. For an open frame unit, this circuit is housed in an exposed metal or plastic frame—no enclosed casing, no built-in overvoltage protection for the output, and no built-in “talkback” between multiple units wired together. That last point is critical: most standard open frame power supplies are designed to operate as standalone units, not as part of a series-connected chain.
The biggest challenge with series wiring is voltage matching and load sharing. When two power supplies are in series, each one is responsible for a portion of the total load. If both supplies are identical (same model, same output voltage rating, same current capacity), that’s a good start—but even then, they won’t split the load evenly. Let’s say you have two 24V, 5A open frame supplies wired in series to get 48V total. If the connected load draws 5A, theory says each supply should supply 5A, right? Wrong. In reality, tiny manufacturing tolerances in the switching transistors, output capacitors, and feedback circuits mean one supply will take on slightly more load than the other. Over time, that imbalance adds up: the overloaded supply will run hotter, its output voltage will drift, and it could eventually fail, taking the other supply with it. I remember a customer in the agricultural equipment industry who tried this with two of our 12V, 10A open frame supplies for a 24V LED lighting array. Six months later, they came back to us with both supplies dead—turns out one had been carrying 12A for months because of a tolerance mismatch, burning out its output rectifier.
Wait, you might be thinking, what if I use identical supplies and add an external load-sharing circuit? That’s a common workaround engineers suggest, but here’s the catch: most open frame power supplies don’t have a remote sense pin or a load-sharing terminal built into their circuit. Those features are standard in higher-end enclosed power supplies, especially those designed for parallel or series operation, but open frame units are optimized for cost and size, not advanced interconnection. We once tested this with three of our 24V, 15A open frame supplies—we tried adding external resistors to balance the load, and while it worked for a short time, the resistors heated up, added unnecessary bulk to the compact frame, and created a voltage drop that made the output unstable at low loads. For applications where every watt and every cubic inch matters, that’s not a tradeoff anyone wants to make.
Another risk I see all the time is ground loop issues and safety compliance. Open frame power supplies have a single ground reference tied to their input AC neutral, right? If you wire two in series, you’re connecting their outputs together, which links their grounds. Suddenly, you have two different voltage references sharing a common ground, creating a loop that can cause noise in the system. That noise might not be a big deal for a LED array, but it can ruin sensitive medical sensors or cause a motor in an industrial machine to misfire. Worse, series-wiring open frame supplies often runs afoul of safety standards like UL 60950 for industrial equipment or IEC 60601 for medical devices. Those standards require that every power supply meet strict isolation requirements between input and output, but when you connect two units in series, you’re creating new voltage paths that weren’t tested by the manufacturer. We had a medical device customer a few years ago who failed a third-party safety audit because they’d wired two open frame supplies in series— the auditor pointed out that the combined output voltage exceeded the maximum isolation rating for either unit’s internal circuitry, even though each was rated for 24V. That delayed their product launch by three months, and cost them tens of thousands of dollars in rework.
But wait—this isn’t a hard no. There are scenarios where series-wiring open frame switching power supplies works, if you’re willing to jump through the right hoops. Let’s be clear: we don’t recommend it for critical applications, but for low-stakes, non-safety-critical projects, it can be done safely if you follow strict guidelines. First, only use identical, brand-new units from the same production lot. Manufacturing tolerances are lowest when units are made at the same time, so load imbalance will be minimal. Second, add external load balancing circuits—we’ve had success with simple current-sharing modules that monitor each supply’s output current and adjust its internal feedback to keep the load evenly split. Third, test for voltage drift over temperature: run the supplies at full load for 24 hours, monitor each unit’s output voltage to make sure neither drifts outside its rated tolerance. And fourth, consult a safety engineer if this is for a commercial product—don’t just rely on your own tests, because a safety failure can be catastrophic.
That said, let’s talk about a far better alternative for most applications: using a single higher-voltage open frame power supply. Over the last five years, our team has expanded our line to include higher-voltage open frame models, from 36V up to 120V, with current capacities ranging from 1A to 20A. These units are designed with the same space-saving, high-efficiency design our customers rely on, but with built-in overvoltage and overcurrent protection, tighter tolerance matching, and compliance with global safety standards. For example, our 48V, 10A open frame supply is half the size of two 24V, 10A units, has a 92% efficiency rating (versus ~85% for two series units), and comes with a three-year warranty. We designed these specifically to eliminate the need for custom series wiring, cutting down on design time, testing costs, and safety risks for our customers.
I always tell engineers that the best part of working in this industry is that there’s almost always a better solution than a workaround. A few months ago, a customer who made custom 48V lithium-ion battery chargers for electric golf carts reached out to us—they’d been wiring two of our 24V, 15A open frame supplies in series for their chargers, and were tired of the load imbalance and short lifespans. We walked them through our new 48V, 20A open frame supply, and they switched immediately. Their production yield went up by 25%, their testing time was cut in half, and their end customers reported fewer failures. That’s the kind of solution I love delivering, because it solves a problem without the hassle of custom wiring and testing.
Now, I know some of you are going to push back—you have a prototype that needs 60V right now, and you can’t wait six weeks for a custom 60V unit. If that’s the case, here’s what you need to do before you wire two open frame supplies in series. First, isolate the outputs: use a high-voltage isolated diode between the two supplies to prevent reverse current, which can happen if one supply’s voltage drifts lower than the other. Second, add individual overvoltage protection diodes to each output, set to the rated voltage of each supply—this will blow a fuse before a unit’s output exceeds its limit. Third, test thoroughly: run at minimum load, maximum load, and every load in between, test at high and low temperatures, and have a third party check your safety compliance. We’ve tested this setup ourselves in our lab, and it works for short-term prototypes, but I still recommend moving to a single dedicated supply once you move to production.
At the end of the day, open frame switching power supplies are versatile, but they’re not one-size-fits-all. As a supplier who’s on the front lines of customer problems every day, I want you to make the right choice for your application. Series wiring can work, but it comes with significant risks: load imbalance, safety compliance issues, noise, and shorter supply lifespans. For most projects, a dedicated higher-voltage open frame power supply is the smarter, safer, and more cost-effective choice.
If you’re working on a project that needs a custom or higher-voltage power supply, or if you have questions about whether series wiring is right for your setup, I’m here to help. We’ve spent years refining our open frame designs and testing interconnection solutions, so we can guide you through every step—from prototype to production. Don’t let a bad power supply choice derail your project; reach out to discuss your needs today.
Enclosed Switching Power Supply References
- Texas Instruments. (2021). Understanding Load Sharing in Switching Power Supplies. Application Report SLVA892.
- Underwriters Laboratories. (2020). UL 60950-1: Information Technology Equipment – Safety – Part 1: General Requirements.
- International Electrotechnical Commission. (2018). IEC 60601-1: Medical Electrical Equipment – Part 1: General Requirements for Basic Safety and Essential Performance.
- Linear Technology. (2019). Series Operation of Switching Regulators: Theory and Practice. Design Note DN076.
Guangzhou Kaihui Electronics Co., Ltd.
Guangzhou Kaihui Electronics Co., Ltd. is one of the most professional open frame switching power supply manufacturers and suppliers in China, specialized in providing the best customized service. We warmly welcome you to buy high quality open frame switching power supply made in China here from our factory.
Address: 2F BLDG8, Standard Ind.Park, Dongchong Town, Nansha District 511453, Guangzhou, Guangdong, China
E-mail: amy@gzkaihui.com
WebSite: https://www.kaihuipowersupply.com/
