How to Select the Right SMPS for an Industrial Control Panel (Sizing, Types & Price)

To select an SMPS for a control panel, match its output voltage to the loads (usually 24V DC), add up their current and allow 20–30% headroom, then choose DIN-rail or enclosed mounting and single- or three-phase input. For example, a 4 A, 24V load needs a 24V 5A unit such as the Mean Well EDR-120-24 (₹2,230).

By Team Voltkart · Reviewed by Amit, Voltkart · Last updated 2 October 2026 · Prices checked 6 October 2026

This guide walks through the five decisions that pick the right power supply for an industrial control panel: output voltage, load current and headroom, wattage, mounting and input. It includes a worked sizing example, 24V price bands from the Mean Well and Selec models we stock, and installation basics. If you already know you want Mean Well and just need to choose a series, go straight to our Mean Well series guide (LRS, MDR, HDR, EDR, NDR, TDR, SDR).

What is an SMPS?

An SMPS (switched-mode power supply) converts the AC mains in a panel into the steady low-voltage DC that PLCs, HMIs, sensors, relay coils and solenoid valves need. It switches the input at high frequency instead of using a large mains transformer, so it is much smaller, lighter and more efficient than an old linear supply. Higher efficiency also means less heat inside the panel, which matters because heat is what shortens the life of electronics in a closed enclosure.

In panel work you will meet two physical forms: DIN-rail supplies that clip onto the same 35 mm rail as MCBs and relays, and enclosed (metal-case) supplies that screw to the mounting plate or a machine body. Both do the same job; the choice is about space, wiring and budget.

The 5-step SMPS selection method

Step 1: Choose the output voltage

24V DC is the standard for industrial control panels. PLC inputs and outputs, proximity sensors, HMIs, relay and contactor-interface coils and most solenoid valves are made for 24V DC. Choose 12V only when the loads need it (CCTV cameras, some LED strips, small OEM electronics), and 48V for telecom equipment and some drives and motor controllers. If a panel genuinely needs two voltages, a second SMPS is usually simpler and more reliable than converting one to the other.

Step 2: Add up the load current and allow 20–30% headroom

List every device that will run from the supply and add up its current at the output voltage, using each device's datasheet. Then multiply the total by 1.2–1.3 (we use 1.25 below). Headroom keeps the supply running cooler, covers devices you will add later, and helps with switch-on surges. An SMPS loaded close to 100% all day in a warm panel will not last as long as one running at 70–80%.

Step 3: Convert to watts and check peak loads

Wattage = output voltage × current. A 24V 5 A supply is 24 × 5 = 120 W, which is why 24V 5 A models carry "120" in their names (EDR-120-24, RPS120-24). After applying headroom, pick the next standard rating up.

Watch for loads that draw much more than their rated current for a moment: solenoid valves and relay banks switching together, DC motors, and capacitive loads such as drive or controller inputs. If several of these switch on at once, size for the peak or stagger them in the PLC program.

Step 4: Choose the mounting: DIN rail or enclosed

A DIN-rail SMPS clips onto the panel rail next to the MCBs, keeps wiring neat and suits most modern control panels. An enclosed SMPS usually costs less for the same power and suits machine bodies, wall mounting and OEM equipment. The comparison table further down shows the trade-offs.

Step 5: Check the input supply

Most panels in India run their control supply from a single-phase 230V AC feed, and every single-phase model in this guide accepts it. The details differ by series, so check them before ordering:

• Wide input, no switch: Mean Well MDR and HDR (85–264V AC), EDR and NDR (90–264V AC) and LRS-35 (85–264V AC), per their datasheets.
• Input selector switch: Mean Well LRS-150, LRS-350 and LRS-600 have a 115V/230V selector (90/85–132V or 170/180–264V AC "by switch" on the datasheet). In India, check it is set to 230V before power-up.
• Two-phase input: Mean Well WDR-120 accepts 180–550V AC, so it can run from two lines of a 415V supply.
• Three-phase input: Mean Well TDR-240, TDR-480 and TDR-960 take 340–550V AC three-phase.

Worked example: sizing a 24V SMPS for a small automation panel

Here is a typical small PLC panel. The currents are example values to show the method; use the datasheets of your own devices.

2.66 A × 1.25 = 3.3 A → choose a 24V 5A (120 W) supply. A 24V 3A unit would run at over 100% once headroom is included, so the next standard step is 5 A. Three good choices:

• Mean Well EDR-120-24: DIN rail, 24V 5A, ₹2,230
• Selec RPS120-24: DIN rail, 24V 5A, ₹1,560
• Mean Well LRS-150-24: enclosed, 24V 6.5A, ₹1,274

Long cable runs: allow for voltage drop

An SMPS holds its own terminals at 24V, but the device at the end of a long cable sees less, because every metre of copper has resistance. At 24V and a few amps, the loss can be enough to upset sensors or stop a solenoid from pulling in. The drop is current × the resistance of both the outgoing and return conductors. Copper is about 0.0172 Ω per metre for each 1 mm² of cross-section, which gives:

Voltage drop ≈ 2 × length (m) × current (A) × 0.0172 ÷ cable size (mm²)

Example: a 24V valve bank drawing 2 A at the end of a 20 m run of 1.5 mm² cable: 2 × 20 × 2 × 0.0172 ÷ 1.5 ≈ 0.92 V. The valves see about 23.1V, roughly 4% low. On a 2.5 mm² cable the drop falls to about 0.55 V.

Ways to deal with it:

• Use a thicker cable for long or heavily loaded runs.
• Put a small DIN-rail SMPS in a field junction box near the loads.
• Trim the output voltage slightly upwards. Most Mean Well units have a "V.ADJ" potentiometer; for example, the 24V versions of the EDR-120, NDR-240 and TDR-240 adjust from 24V to 28V according to their datasheets. Measure at the load after adjusting, and never go above the rated voltage of the devices.

12V vs 24V vs 48V: quick comparison

DIN rail vs enclosed SMPS: quick comparison

Browse DIN rail SMPS or enclosed SMPS.

Single-phase vs three-phase input

Most panels up to about 1 kW run fine on single-phase units such as the Mean Well NDR-480-24 (24V 20A) or SDR-960-24 (24V 40A). Use a three-phase-input supply such as the Mean Well TDR-240-24 (3-phase input) when the panel has no neutral or only a three-phase supply is available, or when you want to spread a large DC load across all three phases. The Mean Well WDR-120-24 fills the gap when only two lines of a 415V supply are available.

Brands we stock: Mean Well and Selec

Voltkart is an authorised distributor of Mean Well and Selec, so every unit comes with a GST invoice and the manufacturer's warranty.

Mean Well

Mean Well is the most widely used SMPS brand in Indian control panels, and we stock around 100 Mean Well models. The enclosed range runs from the small RS series through the popular low-profile LRS series to the high-power RSP series with PFC. On the DIN rail there are MDR (compact, 10–60 W), HDR (ultra-slim step shape), EDR (120 W), NDR (240/480 W, with PFC per the datasheet) and SDR (960 W), plus WDR (two-phase) and TDR (three-phase) input models. Compare them all in the Mean Well series guide and the Mean Well SMPS price list, or browse Mean Well SMPS.

Selec

Selec's DIN-rail supplies are a good-value choice for 24V panels: Selec RP-2M-1.1A-24VDC (24V 1.1A, ₹1,100), Selec RPS60-24 (24V 2.5A, ₹1,342) and Selec RPS120-24 (24V 5A, ₹1,560). See more from Selec.

SMPS price in India: 24V price bands

Live Voltkart prices including GST, checked 2 October 2026. Click a model to see its current price and stock.

All orders ship across India with a GST invoice: typically 2–3 days to Delhi NCR, UP and Haryana and 5–6 days elsewhere. The minimum order value is ₹1,001. For the full Mean Well list (about 100 models) see the Mean Well SMPS price list.

Installation and wiring basics

• Protect the input. Feed the SMPS through its own MCB, sized for the input current and inrush shown on the datasheet.
• Protect the DC side. Split the 24V output into groups (PLC and HMI, field sensors, valves) with fuses or DC circuit breakers, so a short in one field cable does not drop the whole PLC.
• Leave space for air. Keep the clearance above and below the unit that the datasheet asks for, and do not mount it directly above a heat source such as a drive.
• Check derating. Every Mean Well datasheet has a derating curve showing how much current the supply can deliver at higher ambient temperatures. In a hot panel, size with that curve, not just the nameplate rating.
• Set the input switch. On LRS-150, LRS-350 and LRS-600, confirm the 115/230V selector is on 230V.
• Earth and 0V. Connect the SMPS earth terminal to the panel earth bar, and follow your site's policy on earthing the 0V rail consistently across the panel.

For a step-by-step wiring walk-through, see how to wire a DIN rail SMPS, and our control panel components guide for the rest of the panel.

Features worth checking on the datasheet

• PFC (power factor correction): on larger supplies it keeps the input current closer to a clean sine wave, which helps where many supplies share a feeder. The Mean Well NDR, SDR, TDR and RSP series include active PFC according to their datasheets; the smaller LRS and MDR models do not need it.
• DC OK signal: a relay contact or terminal that changes state if the output fails, so a PLC can raise an alarm. The Mean Well MDR-60, SDR-960 and TDR-240 datasheets list a DC OK relay contact.
• Output adjustment: a front potentiometer to trim the output slightly up or down, useful for voltage drop on long runs (see above).
• Derating: the curve that shows how much load the supply can carry as panel temperature rises. Always size against it for hot panels.

Common SMPS problems

• No output: check the input MCB and the input voltage at the terminals, then disconnect the loads. If the output comes back with no load, a short or overload on the DC side is tripping the supply's protection.
• Voltage drops under load: the supply is undersized or derated by heat, or the DC cables are too thin or too long. Measure the voltage at the SMPS terminals and at the load to tell which.
• Trips at switch-on: large capacitive or inductive loads switching on together exceed the supply's short-term capacity. Stagger the loads or choose a larger unit.

How to make sure your Mean Well is genuine

Buy from an authorised distributor, and check that the label, model number and serial number are printed clearly and match the datasheet. Voltkart is an authorised Mean Well distributor, so every unit comes with a GST invoice and the manufacturer's warranty.

Final checklist

• Output voltage matches the loads (24V for most control panels)
• Total load current added up from device datasheets
• 20–30% headroom added, then rounded up to the next standard rating
• Peak and switch-on loads checked
• DIN rail or enclosed, to suit the panel layout
• Input type correct (single, two or three phase), and the 230V switch set where fitted
• Derating checked against the datasheet for the panel temperature
• Input MCB and DC-side protection planned

Frequently asked questions

Which SMPS voltage is standard for control panels?

24V DC is the standard for PLCs, sensors, relays and HMIs in industrial panels. 12V appears in CCTV and small OEM equipment, and 48V in telecom and some drives.

How much headroom should an SMPS have?

Size it 20–30% above the total continuous load. For example, a 4 A load needs a 5 A supply. Running an SMPS continuously near 100% shortens its life, especially in a hot panel.

How do I calculate SMPS wattage?

Multiply output voltage by current: 24V × 5 A = 120 W. Add up the load current first, apply the headroom, then pick the next standard rating.

DIN rail or enclosed SMPS: which is better?

A DIN-rail SMPS (Mean Well MDR/HDR/EDR/NDR, Selec RPS) clips onto the panel rail and saves space and wiring. An enclosed SMPS (Mean Well LRS/RSP) costs less for the same power and suits machine bodies and wall mounting.

What is the price of a 24V 5A SMPS in India?

On Voltkart, a Mean Well EDR-120-24 DIN-rail 24V 5A costs ₹2,230 and a Selec RPS120-24 costs ₹1,560. The enclosed Mean Well LRS-150-24 (24V 6.5A) costs ₹1,180, including GST.

Is Voltkart an authorised Mean Well distributor?

Yes. Voltkart is an authorised distributor of Mean Well and Selec, and ships across India with a GST invoice.

Related guides and products

• Mean Well series guide (LRS, MDR, HDR, EDR, NDR, TDR, SDR)
• Mean Well SMPS price list
• How to wire a DIN rail SMPS
• 12V/24V SMPS power supplies
• DIN rail SMPS · Enclosed SMPS

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