Toroid soft start - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 21st April 2005, 01:56 AM   #1
diyAudio Member
 
Join Date: Nov 2003
Location: NW Washington
Send a message via MSN to officeboy
Default Toroid soft start

It's time to finally get moving on another project.
I have a 750VA piltron that needs to make some beautiful (loud) music.

This will be my highest power project yet, and first off I need a soft/delay start.
I plan on using something simple like http://mitglied.lycos.de/Promitheus/...or_toroids.htm
But I have 2 worries/questions.

1) To me it looks like this circuit needs 2 legs of AC, will the 120 that we have around here do the trick? (With neutral going into the bottom of B1)

2) The 4 10ohm, 5W resistors, this will give 40ohms resistance, and at 120V this is 3A. A 750VA transformer can draw greater then 6A, is this the intent, to only allow about 1/2 of the needed power to get through? Or do I need to increase this rating to give my amp more power to be able to start up (some of this is what has me confused, specifically "To determine the power rating for the ballast resistor, which is 125% of the transformer power rating at full power ..."
Also why 4 resistors? I could see if they were parallel to help spread dissipation, but in a case like this wouldnít a single 40ohm work just fine?
  Reply With Quote
Old 21st April 2005, 02:47 AM   #2
diyAudio Member
 
mpmarino's Avatar
 
Join Date: Jun 2004
Location: Crunchville, where I don't fit in.
I'm interested in this circuit as well. It seems to me that:

1. yes, it would be fine I think, but you could reduce c2 and 3 or r1/r2 to get similar timing.

2. I see your point. At 120v it would seem to be best at 20 ohms, not 40 ohms for the same rate of inrush.

Also, isn't using 4 resistors is series spreading dissipation as 4 resistor bodies are being used somewhat equally? If in parallel and not perfectly matched, wouldn't one current hog?


My question...

Why not put, say, 24v or so of zener just before the relay coil? Wouldn't this more decisively and consistently fire the relay closed?

please flame me if I'm wrong on any of this.

Marc
__________________
Crazy Yankee.
  Reply With Quote
Old 21st April 2005, 03:12 AM   #3
diyAudio Member
 
Join Date: Aug 2004
Location: Illinois
What happens if the 24VDC relay sticks "open?" Won't the voltage supplied to it continue to rise beyond 24VDC when C2 and C3 become charged?

If the relay sticks "open" what will be the DC voltage supplied by B1, assuming a 120 VAC house supply? Won't it eventually rise to 168VDC (1.4 X 120VAC)?

Am I wrong on this? Or, do R1,2,3 and R4,5,6,7 function as a voltage divider circuit?
  Reply With Quote
Old 21st April 2005, 03:23 AM   #4
diyAudio Member
 
mpmarino's Avatar
 
Join Date: Jun 2004
Location: Crunchville, where I don't fit in.
Dick,
I see your point. However, I think voltage is limited at the coil by the resistor 'ladder' created by R1,2,3 and the relay coil. The resistance of the coil will be unchanged whether the relay sticks or not. R4,5,6,7 arent really a part of the circuit.

I think the voltage would spike if the relay coil went open..even then, no harm done.

Please notice I say "I think" a lot here

Edit: I have a feeling that large variations in the resistance of different brands/styles of relay coils could cause a problem..I THINK.

The more I look at this circuit, the more I like it. Thanks for bringing it up!
__________________
Crazy Yankee.
  Reply With Quote
Old 21st April 2005, 03:27 AM   #5
diyAudio Member
 
Join Date: Nov 2003
Location: NW Washington
Send a message via MSN to officeboy
Quote:
Originally posted by mpmarino
Also, isn't using 4 resistors is series spreading dissipation as 4 resistor bodies are being used somewhat equally? If in parallel and not perfectly matched, wouldn't one current hog?
After a little more reading on the basics of resistors yes Iíve found that resistors can be beefed up by using them in parallel or in series.

Quote:
Originally posted by Dick West
What happens if the 24VDC relay sticks "open?"
If the relay sticks, then I think you will have some very hot resistors on your hands.
But the relay sticking should have no effect on B1 as the electro magnet will still be drawing power and trying to close the circuit.

As to the voltage potential of B1 I wish I could tell you. I know that there is some voltage dropping happening, but I canít seem to get this to work in LTSpice.
  Reply With Quote
Old 21st April 2005, 01:54 PM   #6
...truth seeker...
diyAudio Member
 
Ed LaFontaine's Avatar
 
Join Date: Feb 2004
Location: where the Appalachians rise from the Blue Grass
Default An elegant solution

Look at what Coulomb has done with Maxhawk's soft switch, found here:

http://www.diyaudio.com/forums/showt...330#post624330

Pretty neat!
  Reply With Quote
Old 21st April 2005, 02:00 PM   #7
sek is offline sek  Germany
diyAudio Member
 
sek's Avatar
 
Join Date: May 2003
Location: Berlin
Hi officeboy,

this topic has been discussed many times before. There is a multitude of alternatives available, please do the search.

You will find discussions about pros and cons of the circuit available at Promitheus' website. Also, circuits by Rod Elliot (recommended) and others, even by many forum members (e.g. peranders, available as PCB if I'm not mistaken).

Sebastian.
  Reply With Quote
Old 21st April 2005, 03:36 PM   #8
diyAudio Member
 
Join Date: Nov 2003
Location: NW Washington
Send a message via MSN to officeboy
Quote:
Originally posted by sek
this topic has been discussed many times before. There is a multitude of alternatives available, please do the search.

You will find discussions about pros and cons of the circuit available at Promitheus' website. Also, circuits by Rod Elliot (recommended) and others, even by many forum members (e.g. peranders, available as PCB if I'm not mistaken).
There are a few threads here about soft starts, but none i could find with these specifics. My electronics knowledge is quite simple, and i like to learn as i go along. So i would not want to build this till i could as least see why things are doing what they do.

There are many better documented circuits available, but the cost is a bit higher, and my budget is about $5 (but I have lots of old broken electronic things to rob parts from)
  Reply With Quote
Old 21st April 2005, 06:02 PM   #9
diyAudio Member
 
Join Date: Nov 2003
Location: NW Washington
Send a message via MSN to officeboy
Page 6 of this PDF has basically the same circuit, but with a little more discussion.

http://www.edn.com/contents/images/30702di.pdf
  Reply With Quote
Old 21st April 2005, 06:52 PM   #10
Bakmeel is offline Bakmeel  Netherlands
diyAudio Member
 
Bakmeel's Avatar
 
Join Date: Jan 2002
Location: The Netherlands
The simplest thing would obvious be the thermistor trick as you all know. When they heat up, the resistance falls and you have an instant soft start. But then you have these bloody hot things stuck in your cirquit and you don't want that. You conceive a brilliant plan to use resistors you switch on and off, basically stepping the input current.

How about you replace the resistors in your smart soft-start circuit with thermistors and get the best of both? At switch-on the thermistors will have about 10 ohms resistance each, dropping as the current increases. You measure the time delay it takes to get to full current, and set this delay in your soft-start relay. The relay shorts the thermistors, taking over the current softly, as the thermistors cool down again.

It's what I plan to do for my Aleph 2 1KVA trannies. I haven't implemented it yet.

Cheers,
Bouke
__________________
More Power Igor! More Power!
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
B+ soft start Gluca Tubes / Valves 2 3rd September 2007 02:04 PM
Need a soft start? maxpou Solid State 19 18th April 2007 10:23 PM
Does 300VA toroid need soft start circuit? orthoefer Power Supplies 26 18th May 2006 11:41 AM
Soft start & Soft Switch circuit: can anybody help? m.parigi Solid State 95 22nd August 2005 04:32 PM


New To Site? Need Help?

All times are GMT. The time now is 08:17 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2