Electric machines design and production

Subsea motor, Downhole motor, Electric vehicle motor, ROV motor, Special motors, Electric ship/boat motor, permanent magnet motor, renewable energy permanent magnet generator.

Karsten Moholt have long experience with overhauling, rewinding and production of electric machines.
An electric machine is a converter from electricity to mechanical power (motor) or from mechanical power to electricity (generator) or from one electric power to another (transformer).
In today’s market there are a lot of standard electric machines, but sometimes it is necessary to make new machines for special applications. Standard machines are made for use in standard environments and are normally made for standard frequency and voltage (50/60 Hz. 230/400/440/690V).
Sometimes it is need for machines working under other conditions, or at different frequency and/or voltage. Karsten Moholt have the knowledge of how to make design special designed for your needs.

As an example, a standard motor made for 50 Hz, can be speed controlled with a frequency inverter, but when the frequency is increased over 50Hz, the torque will be reduced. Karsten Moholt can design and produce motor running at full torque all the way up to maximum frequency.

What we make

Karsten Moholt can design and produce electric machines for use under water (subsea motors down to 6000m depth), into oil well or other places where it will be necessary to make special design for environments with high pressure, high temperature etc.

Motor power solutions

For control of motors we can offer complete solution for direct start, soft start or for frequency inverter-controlled motors, direct connected at low voltage machines up to 690 VAC or in combination with transformer and necessary filter for use at higher voltage. Typical up to 4,2 kV AC.


Typical power/size/speed for the most common motors: (Induction motors for subsea)


This is the standard size, but all motors can be made with other dimension if required.


Permanent magnet machines:

For some application where high torque is required, we can provide a solution utilising a permanent magnet motor. By doing this we can create motors with high torque which are connected directly to the load without the aid of a gearbox We can also produce permanent magnet motor solutions to meet high effi ciency low and or low weight requirement scenarios.

KM do all design and calculation for these motors. Magnets are custom made, to make an optimal motor for right temperature and performance. Normally we use Neodymium-IronBoron (NdFeB) magnets, the most powerful and advanced commercialized permanent magnets today.
They can be made with different quality depending on temperature and energy product (BH).

For high temperature (up to 350 ºC) motor we use Samarium Cobalt (SmCo) magnets. The advantages are superior resistance to high temperature. Excellent resistance to corrosion, no coating is needs for surface protecting. High working temperature. SmCo is suitable for machines with high magnetic requirements and good for strict working environment requirement. They are more expensive and about 90% of the energy product (BH) compared to NdFeB.


Permanent magnet module motors:

Karsten Moholt is working with a module-based series of permanent magnet motors. The idea by this concept is to be able to make a fl exible motor-concept, where it is possible to add modules to reach the needed torque. Each module length is as standard, 50mm. The diameter of the stator core is four dimensions. D65mm(1Nm/module), D95mm(2,5Nm/module), D120mm (14Nm/module) and D170mm (42Nm/module). Custom sizes can be created on demand.
The Nm/module value is just an indication. It might change depending on environment temperature, speed/frequency, operating time etc. As an example, if the application needs 7 Nm, it can be 7 modules of D65mm (total 350mm-length) or 3 modules of D95mm (150mm-length). To find the total length of the motor, the stator end-winding and the bearing house must be added. The output power for the motor will depend on the motor rpm. and can be calculated by use of this formula:

Where P is the power in W and M is the torque in Nm.

Typical size for D95mm motor with one and three modules, will be approximately like this:


These motors are made with a bigger distance between the rotor and the stator than standard motors. We do this so that we can install a barrier inside the stator to prevent pollution from the rotating parts to damage the winding. For use under water these motors will be compensated with oil for pressure compensation, lubrication and cooling. By use of this barrier, the pollution from IPM-motor KM-PM-D450-L250 SPM-motor KM-D95-8p-9s-1 module KM-D95-8p-9s-3 module the rotating part or water ingress will not affect the winding, and even if the motor is fi lled with water, the winding will not be destroyed.


Our motors can be delivered with rotation feedback built in. Sometimes it is only need to have a feed back for the motor rpm, feedback for running the motor in Close loop, or if position is important for robotic operation we can customise this based upon your requirements. For use in subsea applications we have solutions that work reliable under high pressure and operating in oil.



Power cable/connectors:

Depending on the environments, it might be necessary to use special cable solutions. We can help to fi nd an optimal solution, by cooperating with cable manufacturers or find standard cables that can be used. We can also deliver different solution for connection of the motor by use of connectors or by direct connection.

Power Cable Connectors

Monitoring and analysis:

All our motors and generators can be delivered with monitoring and analysis solutions. Examples of parameters that can be monitored are temperature, vibration, mechanical speed, motor voltage (When use of long cables!) and water in oil sensors for oil filled motors. For motors used with long cable/under water, motors can be delivered with integrated motor monitoring PCBs for use with CAN-Bus, Ethernet or RS485.

Monitoring and analysis

Hydraulic compensators:

For machines made for use under water. The machine will be fi lled with oil for cooling and for compensating for the pressure. We can help specified size and/or deliver compensators which are suitable for the actual design. If you require an extra barrier we can advise/design an optimal solution for your requirements.

Hydraulic compensators

Hydraulic Pumps (HPU):

Our motors can be designed for interface to customers pump, or we can deliver a complete solution with motor and pump. For shaft interface, we prefer spline shaft, but can also deliver motor shaft with wedge. For need of hydraulic pump, we can cooperate with specialists that can deliver optimal pumps and valve solutions. Normally the motor can be fi lled with the same oil as the hydraulic oil used in the hydraulic pump and this will be easy to combine. No need for mechanical seal.
We can also deliver solution with centrifugal pumps, piston pump, screw pump, or other pump solutions. Examples of combination of KM-motors and Hawe hydraulic pump. Please contact us for other configurations.

Hydraulic pump HPU

Configuration hydraulic pumps

Mechanical seals:

For shaft running in other medium than the medium inside the motor, it is sometimes necessary to use mechanical seals. Our motors can be custom developed to your medium and pressure requirements.

Mechanical Seal

Gear box:

If you need a gearbox to accompany your motor, we can offer an interface to match your gearbox or a gearbox integrated within the motor. We can offer various forms of gear box including planetary gear, angle gear or harmonic gear solution. Other solution can also be delivered if preferred.

Centrifugal pump:

Our motors can be designed to run at optimal speed for use on centrifugal pump. Normally standard motors are made for 50/60Hz, but our motors can be delivered for frequency up to 200Hz as a standard. However, we can produce higher frequency on request.

Centrifugal pump

Interface to other components:

Our motors are produced according to customer’s needs; this also includes interfaces for equipment that will be assembled to the complete machine. Just let us know your needs, and we will fi nd a good solution. As relevant example we can deliver motors with interface for thrusters, ball screw/roller screw actuator for linear movement.

Thrusters and ball screw