Homemade Multi Drill

[MaxHeadRoom78]

Things I extracted from all discussions:
- motors draw a lot more current when they work connected than when idle
- if the current drawn from motors exceeds power supply output current, power supply will burn out
- same for voltage, if more voltage than motors are made for is applied, motors will burn out

Not quite so, with a off load DC brushed motor, as the supply voltage increases so does the rpm and also the BEMF which counters the opposed voltage, so the current remains virtually the same in this state across the no load rpm range, a higher voltage, within reason does not damage the motor, as load is applied for a given voltage the rpm will drop and so will the generated DC which in turn results in a increase in current.
The highest current is for a motor with full voltage applied at zero rpm and will be decided by the armature resistance, which can be measured empirically.
Those bridge rectifiers will be more than ample.
Max.

 

[Cosmosus]

Not quite so, with a off load DC brushed motor, as the supply voltage increases so does the rpm and also the BEMF which counters the opposed voltage, so the current remains virtually the same in this state across the no load rpm range, a higher voltage, within reason does not damage the motor, as load is applied for a given voltage the rpm will drop and so will the generated DC which in turn results in a increase in current.
The highest current is for a motor with full voltage applied at zero rpm and will be decided by the armature resistance, which can be measured empirically.
Those bridge rectifiers will be more than ample.
Max.

Awesome, thanks for clarification! I'm saving all of this info, might very well need to use it in the future.

So this transformer + rectifier is better option than Switching regulated power unit (links were provided), even if it has enough output for motors to work and not get PS burned out?
Here's another, nicer packaged transformer: https://www.ebay.co.uk/itm/Vigortro...935043&hash=item2140d226f2:g:cycAAOSwWHZbFVCo

And I found another motor, this one is geared: https://www.alibaba.com/product-det...?spm=a2700.7724838.2017115.337.2e6778carS2cMw higher torque, but only 12v supply and significantly lower on speed (RPM)


edit: Switching supply, but with more output current - 30A and 360W BUT only 12V - so that means lower speed of the motors right? Is it worth to sacrifice speed if the motor (https://www.banggood.com/775-Gear-M...tail-top-buytogether-auto__2&cur_warehouse=CN) have such a high RPM range?

 

[Nigel Goodwin]

I would suggest you order ONE motor, and have a play with it - use a car battery to power it (for 12V), or a couple in series for 24V. See if it drills OK without a gearbox, and measure the current it takes - you can then move on from those results.

 

[Cosmosus]

Awesome, thanks for clarification! I'm saving all of this info, might very well need to use it in the future.

So this transformator + rectifier is better option than Switching regulated power unit (links were provided), even if it has enough output for motors to work and not get PS burned out?

And I found another motor, this one is geared: https://www.alibaba.com/product-det...?spm=a2700.7724838.2017115.337.2e6778carS2cMw higher torque, but only 12v supply and significantly lower on speed (RPM)


edit: Switching supply, but with more output current - 30A and 360W BUT only 12V - so that means lower speed of the motors right? Is it worth to sacrifice speed if the motor (https://www.banggood.com/775-Gear-M...tail-top-buytogether-auto__2&cur_warehouse=CN) have such a high RPM range?

I would suggest you order ONE motor, and have a play with it - use a car battery to power it (for 12V), or a couple in series for 24V. See if it drills OK without a gearbox, and measure the current it takes - you can then move on from those results.

OK, I will do that.

About transformers, I need really high power rating if I'm gonna be using 24V on secondary and would like somethhing like 30A output, therefore 30A*24V=720VA!! These are very expensive!!
(If we're not looking in China, with chassis etc)

 

[MaxHeadRoom78]

As already suggested here and other multiple forums, the best way is to do some empirical testing, this way you can come up with some valid data in order to order right parts and components.
Max.

 

[Cosmosus]

As already suggested here and other multiple forums, the best way is to do some empirical testing, this way you can come up with some valid data in order to order right parts and components.
Max.

OK, I'll try 2 different methods, with transformer and bridge and also with 30A power supply and soft start circuit to eliminate inrush current as much as I can.

I'll come back to share the results for anyone who might do similar project in the future.

Thanks everyone! You've helped me a lot!