YourDyno can perform Eddy current brake control, for example for a Telma brake. Here you see a customer using YourDyno to control two eddy current hub brakes.
If you have an old eddy current dyno, in most cases you can use your existing power supply. They are controlled using some analog signal or PWM signal. You may connect the power supply’s control signal directly to YourDyno, or at most need to make a small interface to YourDyno. For example, old Bosch eddy current dynos use a 0-10V analog signal. To control those, you just need a simple circuit that converts between a 0-5V signal to a 0-10V signal.
The Eddy current power supply
CAUTION! When working with Eddy current brake control, be aware that high voltages are generated. Take necessary precautions.
In case you do not have a power supply, here are some options.
By far the simplest is to buy a finished off-the-shelf power supply. SportDevices makes a good one that is plug and play with YourDyno: http://sportdevices.com/power-supply-3.x.php. It can output 50V, 75V, 100V and 200V.
It includes all you need. It can be controlled directly from YourDyno using the analog output from YourDyno. SportsDevices have higher power power supplies too, but you need to contact them.
Connecting a power supply to YourDyno
Here is how to connect YourDyno to the SportsDevices power supply. Similar connections apply for other brake supplies.
Other Power supply options for the adventurous
You can also build your own power supply using available components. For example using Semikron:
Two modules are necessary, an SCR (Silicon Controlled Rectifier) phase angle control module (for example Semikron SKPC 200) and the controlled rectifier bridge itself, for example the Semikron SKCH 28 series. The SKPC 200 controls the “firing” of the diodes in the bridge, effectively controlling the rectified voltage (DC) that is applied to the Eddy current brake. The input to the SKPC 200 is an analog signal 0-5V, that is why a filter is necessary on the PWM signal in case of YourDyno v3. YourDyno v4 can control the Semikron directly.
Make sure to select an SKCH that can take your max current and voltage. Also make sure that the bridge has a reverse diode. When the controller turns off power to the brake quickly, the current in the brake continues to flow for some time due to the stored magnetic energy. If there is no diode, the voltage increases until something breaks. The reverse diode solves the problem (make sure it can take the current too). There is also some filtering on the main supply.
Another option is to use a module from NuWaveProducts.com. The circuit is different from the circuit using Semikron modules; instead of using a controlled rectifier bridge, it chops up the AC signal, thereby reducing its energy, and this signal is then rectified using a standard fixed rectifier bridge.
The solution from NuWaveProducts can be controlled directly from YourDyno using a PWM signal. You need a couple of components in addition to the module; a 24V transformer, a current transformer (if you want current limit), plus of course the rectifier bridge itself.
Make sure to order the module with no “soft start”. Soft start is ok for powering heaters and the like, but an eddy current brake needs as low delay as possible for the PID algorithm to be stable. Also make sure to include the Snubber. A Snubber is a filter that protects the components from high voltages when the switches turn off.