How to Size One Power Supply for Multiple Devices: Complete Industrial SMPS Load Calculation and Distribution Guide

Using one industrial power supply to operate several electronic devices can simplify machine architecture, reduce the number of components inside an enclosure and create a more controlled power system, but only when the shared SMPS is sized from the complete simultaneous load and the output is distributed correctly. The calculation is more involved than simply adding the wattage printed on several devices because industrial equipment can contain loads with different operating patterns, temporary peaks, varying cable lengths and different positions inside the machine. A supply may appear large enough when the individual devices are considered separately but become inadequate when several branches operate at the same time. Conversely, adding every nameplate value without considering machine sequence can produce an unnecessarily oversized design. For buyers selecting an industrial SMPS power supply, the strongest approach is to identify which devices share the same voltage rail, determine the highest realistic combination of loads that can operate simultaneously, calculate the common current and wattage, account for distribution losses and continuous duty, and then select a suitable power class that provides useful operating reserve without excessive oversizing.

The concept is especially important in 5V, 12V and 24V industrial systems because one common SMPS may feed controllers, interface electronics, displays, communication equipment, electronic instruments or several machine subassemblies from a single source. The power supply must support the combined current of all active branches, while every individual branch must also be wired according to its own current requirement. A machine with four 24V devices drawing 1A, 1.5A, 2A and 3A does not require a 3A supply simply because the largest single load is 3A; if all four can operate together, the shared source must support 7.5A plus any justified operating margin. At the same time, if two of those loads are interlocked and can never operate simultaneously, blindly adding all four nameplate currents may overstate the real requirement. This is why power supply load calculation should be based on operating states rather than only on a parts list.

The live MEAN WELL SMPS portfolio available through Kyptec Automation® supports this type of shared-load architecture because the category spans a wide range of current and wattage classes across 5V, 12V and 24V. This allows machine builders to select a compact source for smaller electronic groups or move into a higher-current class when several substantial loads are powered from one common rail. The key is to make the shared supply part of the machine architecture rather than treating it as an isolated component.

Calculate the Combined Load From Simultaneous Current, Not From the Largest Device Alone

The first step in sizing one power supply for multiple devices is to confirm that all of the loads require the same nominal output voltage. Devices designed for 5V, 12V and 24V cannot simply be placed on one common output rail unless the system uses appropriate conversion stages, so the shared-load calculation should begin by grouping equipment according to voltage. All 24V loads belong in one 24V calculation, all 12V loads in another and all 5V loads in their own low-voltage domain.

Once the voltage group is established, current becomes the simplest way to combine the loads. If three 12V devices draw 2A, 1.5A and 3A and can all operate simultaneously, the total current is approximately 6.5A. The associated power is approximately 78W because 12V multiplied by 6.5A equals 78W. A suitable 12V industrial power supply should therefore be chosen from a current and wattage class above this real simultaneous demand rather than simply selecting a 3A source because 3A is the largest individual device.

The same principle becomes more significant at low voltage. Suppose five 5V electronic modules draw 1A, 2A, 1.5A, 2.5A and 1A simultaneously. The total is 8A, which corresponds to approximately 40W. A lower 25W/5A source would be insufficient even though several individual devices fall comfortably below 5A. In this type of application, MEAN WELL LRS-50-5, rated at 5V, 10A and 50W, can represent a more suitable current class if the complete operating conditions and reserve requirements fit the machine.

For compact 5V equipment with much smaller total demand, MEAN WELL RS-25-5 provides 5V at 5A and 25W. A shared electronic assembly whose highest realistic simultaneous current remains around 3A or 4A may fit naturally within this lower class, while the same supply would be inappropriate if several branches together require 6A or 8A. This demonstrates why one power supply for multiple devices must be selected from the combined operating demand rather than from one representative component.

The most important calculation is therefore not the sum of every current printed anywhere in the machine but the sum of every current that can be active during the same legitimate operating condition. Industrial automation often has sequence-dependent loads, and understanding that sequence can significantly improve sizing accuracy.

Use Load Diversity Without Underestimating the Highest Real Operating State

Load diversity describes the fact that not every connected device necessarily reaches maximum current at the same moment. This can prevent unnecessary oversizing, but it should be used carefully because assuming too much diversity can leave the shared supply undersized.

A machine builder should identify the main operating states of the equipment and calculate the current required in each one. If a 24V system contains six branches but only four can operate together because the control logic prevents the other two from being active simultaneously, the shared power supply should be sized from the highest valid four-branch combination rather than the mathematical sum of all six devices. This gives a more realistic multiple device power supply calculation.

The strongest method is to create a simple operating-state table during machine design. Each row represents one machine state and each column represents a connected device or branch. The currents of the active loads are added for every state, and the row with the highest total becomes the key sizing condition. This method is particularly useful when the machine has several valves, controllers, displays or electronic subsystems that do not all run continuously.

However, diversity should never be assumed without evidence. If there is any valid machine condition where several loads can operate together, that combination should be included even if it occurs infrequently. A power supply still has to support legitimate short-duration operating states according to its specification.

The same logic applies to startup. Several devices may initialize together even if their steady-state operation is staggered later. A shared SMPS that is sized only from normal running current can therefore fail during startup if the combined initial demand is significantly higher. Startup current should be treated as a separate operating state rather than hidden inside an arbitrary safety factor.

For OEMs, documenting load diversity is particularly valuable because it preserves the reasoning behind the selected power supply. If a later software revision changes the machine sequence so more branches can operate simultaneously, the power calculation should be reviewed because the original diversity assumption may no longer be valid.

Branch Distribution Matters as Much as Total Power Supply Capacity

Selecting a power supply with enough total amps is only the first half of a shared-load design. The second half is distributing that current correctly throughout the machine. A common SMPS may feed several branches, and the electrical path close to the power supply can carry the combined current of every active branch before those paths separate.

Consider a 5V system with four branches drawing 8A, 6A, 5A and 4A. The total simultaneous current is 23A, but each branch carries only its own individual demand after the distribution point. The common output section near the power supply must therefore be capable of carrying the full 23A, while the individual branches can be designed according to 8A, 6A, 5A and 4A respectively. This is the practical meaning of DC power distribution for industrial equipment.

The same principle applies to the common return path. Designers sometimes pay close attention to the positive conductors while underestimating the current carried by the return network. If several branches share one common return conductor, that conductor may carry the sum of all active branch currents. An undersized return path can therefore create voltage drop and instability even when each positive branch is correctly sized.

At high current, branch distribution becomes particularly important. MEAN WELL LRS-200-5 provides 5V at 40A and 200W, making it relevant to systems where one source feeds several substantial 5V branches. In such a machine, it is often preferable to distribute the output near the supply so each branch carries only the current needed by its own electronics rather than routing the full high current over long distances before splitting it.

Connection quality also becomes more critical as total current rises. Every terminal, crimp and connector adds some resistance, and the voltage loss across that resistance increases with current. A shared power supply with ample current capacity can therefore still produce poor voltage at remote devices if the distribution network is not designed appropriately.

This is why a high current industrial power supply should never be evaluated only from its nominal output rating. The complete path from SMPS terminals to every critical load has to support the real current with acceptable voltage drop.

Voltage Drop Must Be Checked at the Most Distant and Highest-Current Loads

A multi-device architecture often places some loads close to the power supply and others farther away. This can cause the devices to receive different voltages even though they share the same nominal rail. The voltage measured directly at the SMPS may remain correct while remote electronics see a lower value because of conductor resistance.

The practical voltage drop is determined by current and total path resistance. The same cable can produce very little loss for a 1A branch but a much larger drop for a 10A branch. This means conductor length and current should be considered together when laying out the shared distribution system.

For a 5V power supply for multiple devices, voltage drop deserves particular attention because even a few tenths of a volt represent a meaningful percentage of the nominal supply. A 0.3V drop from a 5V source leaves only 4.7V at the load, which may or may not be acceptable depending on the equipment specification. The design should therefore be validated at the real load terminals while the machine is operating under its highest relevant current.

At 24V, the same absolute loss represents a smaller percentage of the nominal voltage, which can make distribution across longer distances easier. This is one reason many industrial control systems use 24V for machine-level distribution, while local electronics may operate from lower voltage rails.

The shared power supply should be positioned strategically. If the major loads are concentrated in one part of the machine, placing the SMPS close to that distribution point can reduce long high-current runs. If the loads are widely separated, using several local supplies or local conversion stages may sometimes produce a better architecture than forcing one high-current source to serve every location.

The decision should therefore be based on both electrical capacity and physical machine layout.

One Shared SMPS Is Useful When Loads Share Voltage and Location, but Multiple Supplies Can Be Better in Other Machines

A single shared power supply for multiple devices can simplify industrial equipment when several loads use the same voltage, operate within one enclosure and have a manageable combined current. Fewer supplies can reduce component count, simplify AC input distribution and make the BOM easier to control. One larger supply can also provide a clear central power source for diagnostic measurements and maintenance.

However, one shared SMPS is not automatically better in every machine. If devices are located far apart, a central low-voltage high-current distribution network may create unnecessary conductor size and voltage-drop challenges. In such cases, several smaller supplies positioned near their respective loads may create a more practical system.

Redundancy requirements can also influence the decision. If one common power supply fails, every connected branch loses power. In equipment where separate subsystems should remain independent, multiple supplies may reduce the effect of a single failure. The tradeoff is greater component count, more AC input wiring and potentially more service complexity.

Electrical noise and load interaction can also matter in specialized applications. One rapidly changing branch can affect the common supply rail seen by another sensitive branch if the distribution architecture is poor. Correct wiring and local filtering may solve this, but in some machine designs separate power domains can be preferable.

The buyer should therefore avoid treating centralization as a goal by itself. The strongest architecture is the one that balances total load, physical distance, serviceability, failure impact, voltage drop and machine layout.

For many compact industrial machines, one appropriately sized MEAN WELL supply can provide a clean solution. For larger distributed systems, the same category can support several independent rails using different capacity classes according to the physical design.

Select the Final SMPS From the Highest Simultaneous Load Plus Justified Operating Reserve

Once the simultaneous-load calculation and distribution architecture are understood, the final step is choosing the appropriate SMPS capacity. The power supply should provide enough current for the maximum legitimate combined load, enough wattage for the resulting power demand and an appropriate amount of operating reserve for continuous duty, thermal conditions and future expansion.

Suppose a 12V system has a highest simultaneous current of 10A. The base power requirement is approximately 120W. The designer should then determine whether the machine will operate near this condition continuously, whether startup demand is higher, whether the enclosure runs warm and whether future devices are already planned. The final supply class should be chosen from that complete picture rather than simply selecting exactly 120W.

A 24V machine with 8A combined simultaneous current requires approximately 192W. If the system operates continuously near that level, the designer may choose a higher practical class than a supply whose maximum is almost identical to the load. The additional capacity should serve a defined engineering purpose rather than become arbitrary oversizing.

For OEM production, this calculation should be documented clearly so purchasing and service teams understand why the chosen model is required. The approved output voltage, combined current, maximum simultaneous load, branch arrangement and expansion allowance should become part of the machine documentation.

Once the electrical architecture has been validated, Kyptec Automation® also provides an OEM industrial power supply route for repeat production requirements, allowing manufacturers to standardize a suitable MEAN WELL supply across recurring machine builds.

Frequently Asked Questions About Using One Power Supply for Multiple Devices

1. Can one power supply run multiple industrial devices at the same time?

Yes, one supply can operate several devices when they require the same output voltage and the combined simultaneous current remains within the selected SMPS capacity. The correct calculation should include every device that can operate together during the highest-demand machine state rather than simply checking the largest single load. The branch wiring and common return path must also be designed for the real current being distributed.

2. How do I calculate the total amps for several devices on one power supply?

Add the current of every device that can operate simultaneously on the same voltage rail. If four 24V devices draw 1A, 2A, 2.5A and 1.5A at the same time, the total is 7A. If one of those loads can never operate with another because of the machine sequence, the valid operating combinations should be calculated separately and the highest legitimate total used for sizing.

3. Should I add the maximum current of every device even if they do not run together?

Not automatically. The power supply should be sized from the highest realistic simultaneous load, not necessarily from the mathematical sum of every connected device. However, diversity should only be used when the machine logic genuinely prevents certain loads from operating together. If simultaneous operation is possible, those currents should be included.

4. Can I mix 5V, 12V and 24V devices on one power supply?

Not directly from one single-output rail unless the system includes suitable voltage conversion stages. Devices should normally be grouped according to their required operating voltage. A 24V SMPS should feed 24V loads, while 12V and 5V equipment require their appropriate voltage sources or properly designed downstream conversion.

5. Is one large SMPS better than several small power supplies?

It can be better when the loads share the same voltage, are located reasonably close together and the central distribution network is practical. One supply reduces component count and can simplify the BOM. Several supplies may be preferable when loads are widely separated, require greater independence or would otherwise create long high-current cable runs.

6. Does every branch need the same size cable when one supply powers several devices?

No. Each branch should be designed for the current it actually carries, while any common conductor before the branches separate must be capable of carrying the combined simultaneous current. The return network deserves the same consideration because shared return conductors can carry the sum of several branch currents.

7. Can one 10A power supply run two 5A devices?

Mathematically, two devices drawing exactly 5A each require the full 10A capability of the supply if they operate simultaneously. Whether that is an appropriate continuous design depends on the exact product specifications, operating environment and desired headroom. A larger current class may be preferable if both devices genuinely remain near 5A for long periods.

8. Can a 20A power supply run four devices drawing 4A each?

The combined current is 16A, so a suitable 20A supply can potentially support the load if the voltage matches and all four devices operate within the expected conditions. The remaining 4A provides some nominal current reserve, but continuous duty, temperature and startup behavior should still be considered before final approval.

9. How do I account for startup current when several devices share one SMPS?

Treat startup as a separate machine state and identify which devices initialize simultaneously. Add their startup demands rather than relying only on steady-state current. If startup is staggered by the control system, calculate the actual sequence instead of assuming every device reaches its maximum at once.

10. Why does voltage drop become worse when several devices share one power supply?

The common section of the distribution network can carry the combined current of all active branches. Higher current produces greater voltage loss across the same conductor resistance, so a shared system can experience significant drop if common cables or terminals are undersized. Measuring voltage at remote loads under full simultaneous demand is therefore important.

11. Can one branch affect another branch connected to the same power supply?

Yes, particularly if the shared supply or common distribution path is poorly sized. A large change in one branch current can influence the common rail voltage seen by other devices if the source or wiring has insufficient capacity. Proper distribution, low-resistance connections and suitable power-supply sizing help reduce this interaction.

12. Should each device have its own protection when several devices share one SMPS?

Branch-level protection can be useful in many industrial systems because it helps isolate faults and makes the distribution architecture easier to manage, but the exact protection method should follow the machine’s electrical design and applicable requirements. The shared SMPS rating alone does not determine the protection strategy.

13. Can multiple low-current devices use one much larger high-current power supply?

Yes, when the voltage is correct and the complete architecture is compatible, but excessive overcapacity should still have a reason. The devices will normally draw according to their own requirements, yet an unnecessarily large product can add physical size and cost without improving the machine. A proportionate current class is generally preferable.

14. How should I size the common return wire for several devices?

The shared return path should be evaluated for the maximum combined current that can flow through it before the branches separate. If four active branches return 3A, 2A, 4A and 1A through one common conductor, that section may carry approximately 10A. Treating the return as a low-current path can therefore create avoidable voltage drop.

15. What happens if one device fails short on a shared power supply?

A fault on one branch can potentially affect the common power system depending on the supply and protection architecture. This is one reason machine designers often use suitable branch protection and structured distribution rather than connecting every load directly to one uncontrolled common node. The exact fault strategy should be part of the machine electrical design.

16. How much extra capacity should I leave when one SMPS powers many devices?

There is no universal percentage. The appropriate margin depends on maximum simultaneous load, continuous duty, startup demand, temperature, load variability and planned expansion. Calculate the real combined requirement first, then select the nearest practical capacity class that provides useful operating reserve without unnecessary oversizing.

17. Should OEMs use one common power supply across several machine variants?

They can when the machine variants share the same output voltage and the common supply comfortably supports the highest legitimate load among them. Standardization can simplify purchasing, production and service, but the chosen model should not become excessively oversized for smaller variants unless there is a clear commercial or engineering reason.

18. What is the best way to size one SMPS for multiple industrial devices?

Group devices by voltage first, then identify every valid operating state and add the current of all loads that can operate simultaneously. Calculate the corresponding wattage, include legitimate startup demand and known future expansion, review common conductors, return paths and voltage drop, and then choose an industrial SMPS power supply from Kyptec Automation® whose MEAN WELL current and wattage class supports the complete system with appropriate operating reserve. The final decision should also consider physical location, serviceability and whether one centralized supply or several local supplies produce the stronger machine architecture.

Conclusion

Sizing one power supply for multiple devices requires more than adding nameplate wattages or choosing a product larger than the biggest individual load. The correct design begins by grouping devices according to output voltage, identifying which loads can operate simultaneously and calculating the highest legitimate combined current. That number establishes the real electrical requirement of the shared rail.

The next step is understanding how the current is physically distributed. The common section near the power supply can carry the total current of all active branches, while each individual branch carries only its own load. Common return paths must be treated with equal care because they can also carry the combined current and create voltage drop if they are undersized.

Machine sequence and load diversity can reduce unnecessary oversizing, but only when the operating logic genuinely prevents certain devices from being active together. Startup conditions should also be checked separately because several devices may initialize simultaneously even if their steady-state operation is staggered later.

Voltage drop becomes especially important in low-voltage high-current systems. A shared 5V architecture can carry tens of amps, making conductor length, connection resistance and branch location central to reliable operation. A correctly sized SMPS cannot compensate for poor distribution, and an excellent distribution network cannot compensate for a source whose total current capacity is too small.

The final power supply should therefore be selected from the highest realistic simultaneous load plus justified reserve for continuous duty, temperature and known expansion. The live MEAN WELL SMPS range available through Kyptec Automation® provides multiple 5V, 12V and 24V current classes, allowing machine builders and OEMs to match one shared supply to the actual combined load rather than relying on an arbitrary oversized source.

A well-designed shared SMPS architecture can reduce component count, simplify the machine and create a clear power-distribution structure, but only when the combined load, branch currents, common return, voltage drop and operating sequence are engineered together. When those factors are treated as one system, one power supply can operate multiple industrial devices efficiently and predictably without becoming either undersized or unnecessarily oversized.