Building a controller from scratch

[mikesndbs]

Hi, thought I'd post my experiment here just in case others find it interesting.

 

The only thing to add is the PSU needs to have a 33uF capacitor on it's output for filtering so that some coreless motor types are happy.

Otherwise the circuit from Roger Amos is unchanged.

I've used this controller for a good few days now and have been very pleased.

I am going to make another one and install both in an old H&M Duette case if I can get one.

 

Don't skimp on the heatsink! if you limit your input current you reduce any heating.

So far no locomotive or combination has produced any heat outside of the case shown in video 3.

 

Happy to hear your thoughts.

 

Used CPC for all parts.

 

Happy Christmas

 

Mike.

 

 

 

 

 

 

[JohnnyDMonic]

Hi there Mike,

 

Nice work!

 

A couple of suggestions / observations if I may... You have fitted a 1A thermal cutout device, but your power supply is only rated at 500mA so in the case of a short-circuit the power supply would be running at twice its rated load. There are 2 possible outcomes of this: The first is that the power supply gets very hot and melts / is permanently damaged. The second is that some other protection circuitry within the power supply will kick in at 500mA, rendering your 1A device pointless. I would either beef up the power supply to supply 1A safely, or reduce your thermal cutout device to 500mA.

 

Also, if you put the thermal cutout device straight after the rectifier, it would protect against any other mishaps / failures / short-circuits within the controller itself. If I were building this without using an off-the-shelf power supply, I would probably even go so far as to put the thermal cutout device on the AC side before the rectifier to protect against any failures of the diodes in the rectifier.

 

 

[mikesndbs]

On 11/04/2019 at 13:11, JohnnyDMonic said:

Hi there Mike,

 

Nice work!

 

A couple of suggestions / observations if I may... You have fitted a 1A thermal cutout device, but your power supply is only rated at 500mA so in the case of a short-circuit the power supply would be running at twice its rated load. There are 2 possible outcomes of this: The first is that the power supply gets very hot and melts / is permanently damaged. The second is that some other protection circuitry within the power supply will kick in at 500mA, rendering your 1A device pointless. I would either beef up the power supply to supply 1A safely, or reduce your thermal cutout device to 500mA.

 

Also, if you put the thermal cutout device straight after the rectifier, it would protect against any other mishaps / failures / short-circuits within the controller itself. If I were building this without using an off-the-shelf power supply, I would probably even go so far as to put the thermal cutout device on the AC side before the rectifier to protect against any failures of the diodes in the rectifier.

 

 

 

 

Hi, don't know how I missed this.

Thanks for your thoughts.

I use it with a 1.25 amp psu now so all ok there, the 500mA one was just to test and build in some protection.

 

[Crosland]

On 11/12/2018 at 19:33, mikesndbs said:

Don't skimp on the heatsink! if you limit your input current you reduce any heating.

 

The current is determined by what the load draws from the output.

 

The heating will be proportional to the current drawn and the difference between the supply voltage and the output voltage. That is the power dissipation due to the current and the voltage across the output transistor.

 

Limiting the supply voltage to no more than is needed for appropriate full speed will help minimize heating.

[Junctionmad]

There’s a very good review of dc controllers and their waveforms here https://www.scottpages.net/ReviewOfControllers.html

 

Along with some circuits for simple feedback unit