Danfoss MCD Soft Starters, New Zealand

Danfoss / MCD soft starters

A soft starter is not a drive. It controls the start and then hands the motor to full mains. If someone has asked for a soft starter because they want speed control, they want a VLT instead.

MCD is the Danfoss soft starter range, on pumps, compressors, fans and conveyors across New Zealand plant. The older MCD 200 and MCD 3000 units are the ones we are asked for most.

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The ranges

Range	Position	Status
MCD 100	Compact. Small motors, minimal settings	Mature
MCD 200	The volume range. Set by potentiometer and DIP switch	Discontinued
MCD 500	Full featured. Keypad, parameter set, protection functions	Mature to discontinued
MCD 600	Current generation	Current
MCD 3000	Earlier full featured range	Long discontinued

The MCD 200 and MCD 3000 are where most of our enquiries sit, because they are out of production and still starting motors on plenty of sites.

What a soft starter actually does

Worth being clear about, because it decides whether the part is even the right answer.

	Soft starter	Variable speed drive
During start	Ramps voltage or current to limit inrush and torque shock	Ramps frequency and voltage together
While running	Motor is on full mains at full speed	Speed is controllable throughout
Speed control	None	Yes
Energy saving at part load	None	Substantial on a fan or pump
Cost and panel space	Lower	Higher

So a soft starter is the right part where the problem is the start and not the running. Mechanical shock on a conveyor, water hammer on a pump, supply limits on a large motor, belt slip on a fan.

If the requirement is to run the machine slower, or to save energy at part load, the answer is a drive. Tell us the problem and we will say which one you want.

Bypassed or not bypassed

The most consequential thing about a soft starter, and it is visible in the model number.

The semiconductors that control the start also carry the run current unless something bypasses them.

	Not bypassed	Internally bypassed
After the ramp	SCRs keep conducting	A contactor takes over
Heat in the panel	Continuous. Needs ventilation and derating	Much lower once running
Panel space	Smaller unit, bigger panel	Bigger unit, simpler panel
Long term reliability	SCRs run hot for their whole life	Better

A third arrangement exists: an external bypass contactor in the panel, wired around a non-bypassed starter and closed by the starter's own output once the ramp finishes.

So if there is a contactor next to the soft starter that closes a few seconds after starting, that is the bypass. Replacing the starter with an internally bypassed unit changes that arrangement, and replacing an internally bypassed unit with a plain one puts continuous heat into a panel that was not designed for it.

Tell us which of the three you have.

In line or inside delta

The wiring question that changes the rating, and the one most likely to produce a wrong part.

	In line	Inside delta
Conductors to the motor	Three	Six
Starter carries	Full line current	Phase current, lower than line
Starter size for the same motor	Larger	Smaller
Configuration	Set in the starter	Set in the starter, and it must match the wiring

Inside delta is how a smaller starter drives a bigger motor, and it is common where panel space or budget was tight. It needs six conductors to the motor and the motor's delta connection broken out.

Two things follow, and both cause real problems:

A starter set for in line on inside delta wiring, or the reverse, does not work correctly. The configuration and the wiring have to agree.

And a starter sized for inside delta is undersized for in line duty. Swapping the same model onto a three wire installation may put it beyond its rating.

Count the conductors going to the motor before ordering. Three or six answers the question, and it is the fastest check on this page.

Sizing is by duty, not by kilowatts

Where soft starter quotes go wrong when only the motor rating is supplied.

What decides the size	Why
Motor current	The starting point, not the answer
Start current limit	A higher limit means more heat in the SCRs
Ramp time	A longer ramp means longer at elevated current
Starts per hour	The one people forget. Heat accumulates
Ambient temperature	Panel internal, not outside air
Load type	A loaded conveyor or a crusher is not a fan

A starter rated for a light duty start will trip on thermal overload doing a heavy one, and that is correct behaviour rather than a fault.

So if a starter is tripping on overload after a few starts in quick succession, the duty may have changed rather than the starter having failed. A wastewater station that has gone from four starts an hour to twenty is the classic case.

Send the motor current, the starts per hour and what the load is, and we will size it properly.

The classic failure is a shorted SCR

Worth recognising, because the symptom looks mechanical.

Symptom	Likely cause
Motor hums and will not turn, or turns slowly	Shorted or failed SCR. The motor is single phasing
Starts on some attempts and not others	SCR or gate drive
Overload trips after repeated starts	Duty, not a fault
Trips immediately on start	Wiring, configuration, or a locked rotor
Runs fine but the panel is hot	Bypass not operating, or no bypass fitted
Nuisance phase loss or sequence fault	Supply side, before the starter

A humming motor that will not accelerate is usually a starter fault rather than a motor fault, because one phase is not being switched. Testing the motor in isolation shows nothing wrong, which sends people the wrong way.

Semiconductor fuses are a separate part and are required in some configurations. If a starter has failed hard, check whether they went with it.

Where the settings live

This decides whether a replacement is a swap or a commissioning job, and it differs across the range.

Range	Settings	On a replacement
MCD 100, MCD 200	Potentiometers and DIP switches on the unit	Copy the physical positions. Photograph them before removal
MCD 500, MCD 600	Keypad and a parameter set	Parameters entered or transferred
MCD 3000	Keypad and parameters	Parameters entered

On an MCD 200 the settings are visible and physical, which is good news. Take a clear photograph of the dials and switches before the old unit comes off the wall and the replacement is set in a minute.

That photograph is the thing people forget, and once the unit is in a skip the settings are gone. It costs nothing and it is the single most useful habit on this range.

Before ordering a replacement

Symptom	Check first
Motor hums, will not accelerate	The starter, not the motor. Likely a failed SCR
Overload trips after several quick starts	Starts per hour against the rating. May not be a fault
Panel running hot	Whether the bypass is closing
New starter behaves oddly	In line against inside delta. Count the motor conductors
Starter failed hard	The semiconductor fuses
Wanting speed control	You want a drive, not a starter

What to send us

The model number off the unit.

The motor current and rating.

Three or six conductors to the motor. That settles in line against inside delta.

Starts per hour and what the load is. Pump, conveyor, fan, crusher.

Whether there is a bypass contactor in the panel.

A photograph of the dials and switches, on an MCD 100 or MCD 200.

Whether it is on a soft stop duty as well as soft start. Pump stations often are, to control the check valve.

What we can supply

Current production. MCD 600 across the ratings, plus accessories and communication modules.

Mature and discontinued. MCD 100, MCD 200, MCD 500 and MCD 3000. New old stock, surplus and tested used.

Parts. Semiconductor fuses, cooling fans on the larger frames, and communication and I/O modules where the range supports them.

Sized to duty. Send us the load and the starts per hour rather than just the kilowatts and we will quote something that lasts.

Soft starters are good spares

Worth stating, because they are cheaper to hold than drives.

On an MCD 100 or MCD 200 the configuration is physical, so a shelf unit set to match is genuinely ready to go. No parameter set, no software, no laptop.

One starter per rating you run, plus the photographs of the settings, covers a site cheaply. On a wastewater network with a dozen identical stations that is a very small investment against a pump out of service.

We buy Danfoss MCD

MCD 200 and MCD 3000 units hold value, because the plants running them cannot buy new and the alternative is a panel rebuild.

Keep bypass contactors, semiconductor fuses and any communication modules with the starter, and if you can, note the dial settings before it comes off the wall. A starter with its settings recorded is worth more to the next plant. See Sell To Us.

Common questions

Can you get a part that is not listed on your site?
Usually. The site shows what we hold, not what we can source.

Can a soft starter slow my motor down?
No. It controls the start and then the motor runs at full speed on the mains. Speed control needs a drive.

Can I fit the same model onto three wires instead of six?
Not safely. A starter sized for inside delta is undersized for in line duty, and the configuration has to match the wiring.

My motor hums and will not start.
Suspect the starter before the motor. A failed SCR single phases the motor and the motor tests fine.

Why does it trip after a few starts?
Thermal capacity. Check starts per hour against the rating. That is often the duty rather than a fault.

Do you supply used equipment?
Yes, where new is not available, tested and clearly described.

What is the lead time?
Ex stock items ship the next working day within New Zealand. We give you a firm lead time with the quote.

Do you quote in NZD?
Yes, in NZD including GST for New Zealand customers.

Send us your model numbers

Count the conductors going to the motor and tell us the starts per hour. Those two answers size the starter correctly. Quotes in NZD including GST.

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Industech is an independent supplier of new, surplus and used industrial automation equipment. We are not an authorised distributor of, approved by, sanctioned by, or affiliated with Danfoss. Danfoss, VLT and MCD are trademarks of Danfoss A/S. All trademarks, brand names and model numbers are the property of their respective owners and are used here for identification purposes only.