power supplies

[simbarb1]

hi all,a mundane question no doubt apart from those that know! been looking at a 775 dc motor,12-24v. would i be able to power it with a 12v battery,or what should i look for in specs
thanks for any advice

[Bob225]

Lower voltage - less torque and rpm are you going to use it with a speed control and/or gearbox ? What are you using the motor for ??

[simbarb1]

hi bob and thanks even i see the rpm is a tad high! basically i want a small disc sander 3" for models so nothing meaty. as for speed control that would be good to have but i dont know about about gearboxes so any advice would be great,thank you

[Bob225]

Proxxon do a small disc sander - i paid about £95 for mine, but they seem to have gone up horrendously, Parkside seem to do a clone of the proxxon

[ericmark]

With DC the stronger the field the lower the speed and the higher the torque, using an old dynamo as a motor for a trolley we could start with full field which would get us moving then reduce the field and speed would increase, very like notching back on a steam engine.

But in the main we don't have independent field and armature supply, so next we look at toy trains, typically 12 volt DC, with a variable resistor, as you decrease the resistance the engine starts to move, however it tends to jump from around zero to half speed as it starts to move, we get back EMF, so the voltage raises.

So if we use a voltage regulator then the start up is far smoother, however it still tends to jump from zero to quarter speed.

So next is send a pulse then measure the back EMF which until it moves is zero, as it starts to move the back EMF increases so we can get a very smooth take off, however with a wound field this works well, but with a permanent magnet field the pulses destroy the permanent magnets, so engine requires a new motor.

I have used a 2N3055 transistor to control model trains with a steady voltage very successfully, used the same circuit to charge batteries with a very well regulated supply, in the main to supply a radio transmitter, but although good fun, in real terms with the advent of integrated circuits, not worth while as a commercial venture.

You can buy ready made motors and controllers for far less than one can make them. And the use of DC motors are things of the past, using an inverter we can vary the frequency and voltage to an AC motor and get far better control to what we could with a DC motor.

As a project good fun, but likely better buying some thing ready made.

[Bob225]

Only issue I see with 75mm sanding disc the max sanding area will be 20-25mm as you only use 1 side (downward stroke of the disc) the upward stroke will rip up the object pulling it away from the rest

iirc Dremel used to do a small sander

this may be of interest

https://www.instructables.com/Dremel-Di ... and-Cheap/

https://www.etsy.com/uk/listing/8893828 ... attachment