Soft Starter header

AuCom EMS 4 and EMS 45 AuCoStart Soft Starters

Background of the EMS soft starters.

The AuCom EMS series soft starter was an early generation soft starter designed in the very early 1980s and manufactured for approximately 12 years. The circuitry was based on analog technology driving power SCRs which were reverse parallel connected on each phase. - three phbase full wave control.
The EMS series soft starter were a constant current starter with a current ramp option. They included I2t overcurrent protection and vector sensitive phase imbalance protection.
The electronics cards were usable over a wide range of starters and were programmed by a DIP switch. THere were a number of optional cards providing current ramp, soft stop and trip indication functions.
The EMS soft starters were available either as a chassis mount unit, or a totally enclosed unit ranging from 7.5HP to around 600HP with larger units made to order. The largest EMS starters manufactured were 1.6MW 440 volt 60Hz.
There are many of the original EMS soft starters still operating today. While AuCom Electronics, the original manufacturer or the EMS soft starters no longer supports this family, support is still available via Advanced Motor Control in Christchurch, New Zealand.


There are essentialy six different main control pcbs for the EMS series of soft starter.

They are as follows:

  1. EMSC05 - small standard duty (single SCR modules)
  2. EMSC15 - small Heavy Duty (single SCR modules)
  3. EMSC06 - medium standard duty (parallel SCR modules)
  4. EMSC16 - medium heavy duty (parallel SCR modules)
  5. EMSC07 - Large standard duty (Hockey puck SCRs)
  6. EMSC17 - Large heavy duty (Hockey puck SCRs)

The standard duty pcbs can be set for a starting current of between 100% and 300% of the motor rated current. The heavy duty pcbs can be set for a starting current of between 350% and 550% of the motor rated current.

The motor rating is set on a DIP switch according to a chart on the door of the starter. The start current ratio is also set on a DIP switch according to the chart on the door of the starter.

Like pcbs can be exchanged between starters provided that the DIP switch is set up to suit the attached motor. The pcb does not have any "model" settings so an EMSC05 from a 7.5HP starter can be used in a 40HP starter and vice versa. The current weighting on the DIP switch settings is determined by the CT ratios.
This can be useful in determining if there is a pcb fault. Swap the pcb between starters and see if the problem moves.

A heavy duty rated pcb can be used in place of a standard duty pcb if the start current needs to be set higher than 300%, however the start current DIP switch settings for the heavy duty pcb are different from the standard duty settings. - You will possibly overload the starter if you set the start current too high. This can result in fuse failure, or in SCR failure over a period of time.

It is not possible to swap pcbs from different groups. i.e. an EMSC06 can not be used in place of an EMSC05 or EMSC07.


Testing the SCRs in an EMS series soft starter.

To test the SCRs in the EMS units, there are two simple tests to apply.
Disconnect the inputs and Outputs of the starter,
Unplug the white firing loom plugs from the pcb.
Measure the resistance of the SCRs on each phase by measuring input to output on each phase.
If the resistance is greater than 100K, the SCRs are probably OK.

Connect three 100W lamps to the output of the starter in star connection with the star point floating. The lamps should be rated at the phase - neutral voltage of the incoming three phase.
Connect the three phase supply to the input and the control voltage to the control input.
Set the starter to start.
All lamps should ramp up to full brightness at an equal rate. If one lamp is not as bright, or flickers, there could be an SCR issue, a contact issue or a control pcb issue. Swap the firing loom plugs around. If the problem stays with the same lamp, the problem is with the firing loom or the SCR. If the problem stays with the same socket on the pcb, the problem is with the control pcb.