Paper shredder - any ideas?

[Shredderama]

Hi all,
hope I can find someone to help out with this one. Paper shredders are of course ten a penny, but I hate throwing stuff away, so here goes...
- the controller board gives next to no d.c. output, just a couple of volts.
- The microswitch, power switch and reverse switch all check out OK.
- The motor is 230 v d.c. according to its label and turns when I put 30 v d.c. from a lab power supply on the terminals.

I'm thinking to myself, how about ditching the controller and just use a bridge rectifier from the 230 v a.c. (I'm in London UK) to give me about 160 v d.c. That should spin the motor up OK. Then I can use a simple relay to reverse.

My question is - What are the flaws in my plan..? How could I improve it?

Thanks for any input you can give here which is much appreciated by a newcomer like myself.
Dan

 

[dknguyen]

230VAC through a bridge rectifier gives a 230Vrms. Which, if smoothed with a big capacitor will give you 230VDC. (ie. when we say VAC we are not talking about the voltage difference between highest and lowest peak).

What does the control board do anyways? Could the motor spin too fast or something without it? Or does it just control a paper sensor or something?

 

[Chippie]

230VAC through a bridge rectifier gives a 230Vrms. Which, if smoothed with a big capacitor will give you 230VDC. (ie. when we say VAC we are not talking about the voltage difference between highest and lowest peak).

What does the control board do anyways? Could the motor spin too fast or something without it? Or does it just control a paper sensor or something?

Usually the motors are geared down...I'd guess the control board allows forward and reverse direction control of the motor and auto stop at paper end..

 

[Shredderama]

Hi and thanks
yes the motor is geared and there's a relay on the board to I think reverse the dc output from the rectifier. The microswitch detects paper present/absent. Other stuff on the board might be (not really sure) - overload protection or something in case the shredder gets really jammed? There is also a simple fuse.
What sort of a capacitor value might I need for this app do you think? 230v dc motor taking the feed from the rectifier.
Many thanks in advance
DB

 

[Hero999]

Just connect the motor to a bridge rectifier with no filter capacitor.

If the motor is designed to work from 230VDC then the unfiltered DC voltage from the rectifier will have an RMS voltage of 230V. If you add a filter capacitor, the RMS voltage will increase closer to 325V which will damage the motor.

 

[Sceadwian]

Unless you use a very large filter cap (relative to the current the motor is drawing) the voltage will never get that high under load. At least a small filter capacitor would smooth out the motor current a bit, generally a good idea, but not necessarily required. For overload protection you could use a simple resettable breaker, or a self reseting thermal fuse. Personally I never understood the need for a micro switch to detect the paper, they get jammed easily and it's just another failure point. A simple on/off switch is all you need.

 

[mneary]

DO NOT add a capacitor if there wasn't one originally. It won't fix the problem, and will create new ones. If the motor was designed to run at 230VDC, a capacitor may make it 330V.

If the board isn't putting out anything, then troubleshoot it. First check the fuse and diodes, then the relay.

 

[Shredderama]

Many thanks for all the input - it must be worth checking the diodes before I go any further. There's no sign of burning on the pcb but this'll give me some practice with the ole meter
If no joy I'll have a tinker with a rectifier
Cheers for now
D