electronics, repairs, service manuals and datasheets discussion community for the repairs professionals and technicians
FAQSearchMembersGroupsRegisterProfilePM'sLogin/Out
How do I limit voltage?

 
Post new topic   Reply to topic    Electronic equipment repair and service manual search discussion Forum Index -> Electronics General
View previous topic :: View next topic  
Author Message
conmgt



Joined: 08 Apr 2008
Posts: 1
Location: Philadelphia, PA USA

PostPosted: Tue Apr 08, 2008 4:09 pm    Post subject: How do I limit voltage? Reply with quote

Hello,
First, I am new to this forum and am not savvy in electronics but I am an electrician.
I have a commercial grade wood planer that is 2 years old. There is a large flat metal table that moves up and down by way of 4 spiral shafts chain driven by a 24VDC motor made by Elra. The machine itself is fed by 240VAC 3 phase. There is a small transformer for the DC motor which has an output of 30VAC +/- 4V. Attached to it is a simple PC board with a rectifier (4 posts) and a 50V 10,000mF capacitor. That's it.
The problem is that at one point the 30VAC into the PC board produced 50+ VDC and burned out that 24VDC motor...$400! Now the output is down to 30VDC again. The question is, how did this happen? More important, how do I prevent it? Can I add something between the rectifier and the motor to prevent anything over 30VDC from passing through? I'm thinking some sort of a diode. Should I limit the VDC to 24?
Let's keep it in laymans terms. Thanks
p.s. how did I add an image to this?
Back to top
View user's profile Send private message Visit poster's website
torbjorn



Joined: 07 Jun 2007
Posts: 370
Location: Sweden

PostPosted: Thu Apr 10, 2008 4:54 pm    Post subject: Reply with quote

I suppose that it is a single phase transformer ? Then, one possible way that it has delivered a too high voltage is that the primary is intended for connection between one phase and the neutral conductor, but then by mistake was connected between two phases. In this case, the secondary voltage will raise to 1,73 times the rated voltage. A such overvoltage will also burn out the transformer within a short time, unless its core is designed with very large margins to saturation.

A good overvoltage protection is a so-called crowbar circuit, with a SCR connected across the output of the bridge rectifier, and its gate connected to the anode via a suitable resistor and zener diode.
Recommendations regarding the design of such circuits can be found in application notes at the major semiconductor manufacturer's (ST Microelectronics, NXP, SanRex and so on) web sites.
Make sure that you have a fuse at the primary side of the transformer and that the transformer's short circuit current is high enough to blow the fuse within one second.
Back to top
View user's profile Send private message
buljko



Joined: 15 Apr 2008
Posts: 4

PostPosted: Mon Apr 21, 2008 9:35 pm    Post subject: Reply with quote

Back to top
View user's profile Send private message
buljko



Joined: 15 Apr 2008
Posts: 4

PostPosted: Mon Apr 21, 2008 9:51 pm    Post subject: Reply with quote

http://www.voguehost.com/ims/u/buljko/buljko/protection.jpg
Back to top
View user's profile Send private message
buljko



Joined: 15 Apr 2008
Posts: 4

PostPosted: Mon Apr 21, 2008 9:55 pm    Post subject: Reply with quote

BTW, How I can edit my post or attach picture? I do not see this options.
Back to top
View user's profile Send private message
Mon1018



Joined: 22 Apr 2008
Posts: 2

PostPosted: Tue Apr 22, 2008 2:24 pm    Post subject: Reply with quote

You can edit in the Profile.
Back to top
View user's profile Send private message Visit poster's website
vtech



Joined: 08 May 2006
Posts: 1264
Location: USA

PostPosted: Tue Apr 22, 2008 7:40 pm    Post subject: Reply with quote

use "img" tags

Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    Electronic equipment repair and service manual search discussion Forum Index -> Electronics General All times are GMT
Page 1 of 1

 
Jump to:  
You can post new topics in this forum
You can reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Електроника София - Service Manuals Free Download - Prikachi - Service Diagrams

Free TV Schematics Download - HARDW.net - Pinout Master - Jabse Search - Jabse.InK  - Pulsator

Connector Pinout Forum - Новини - SnimkiOt.com - безплатен DNS - Whois разузнаване - Poblizo.com : пътешествия