power supply

[conntaxman]

Im trying to make a power supply to run a treadmill.I have 2 treadmills both don't work. I tried to use a light dimmer and a Full wave bridge rectifier 40amp.But the motor just started up on fast speed .The motor is 90vdc and 20amp and has brushes.
Next I was going to use the transformer from the other machine use light dimmer into the transformer, them to the bridge rectifier. would that work?
tks
John

 

[Resqueline]

Motors are inductive and thus requires a better "dimmer" than a light dimmer. Does the motor have permanent magnets btw.?
Yes, if the transformer is the ordinary simple iron-cored tpe you can do that, except you'll have to use a dimmer made for inductive loads there too.

 

[climatex]

Check if the dimmer is a simple diac-triac circuit powered directly from mains. If it is, check if there's a RC circuit in parallel with the anode and cathode of the triac, adding it will protect the SCR/triac from blowing up.

If it ain't that simple, try my schematic...

and put the triac on a heatsink.

No problems regulating an angle grinder with this one. Just beware you mustn't use a capacitive load, or else the triac might short out, in some cases violently.

Best regards climatex

 

[duke37]

Running a transformer or other inductive load from a light dimmer is not considered good practise since it is possible to get saturation if equal positive and negative pulses are not obtained. It can work if the load has a fairly high resistance but here you are driving quite a large power motor.

Motors come in all shapes and sizes, you say that the motor is DC and has brushes. In order to control the speed, it is necessary to maintain the field at a constant level and to vary the armature supply. Dropping the field and armature together would not change the speed if there was no friction, all you do is drop the torque available.