Soft start circuit - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 16th June 2003, 11:24 PM   #1
Diode is offline Diode  United States
diyAudio Member
 
Join Date: Feb 2003
Location: Oklahoma USA
Default Soft start circuit

Hi all,

I'm sure that this topic has been well covered but to save time in search, I have seen soft start circuits that use one or two MOVs that later get shorted by a relay for full power. I'm looking for a simple circuit that is reliable and places to get parts.
My circuit will be powering an old Peavey transformer from a PV .75K amp that produces 2X +/- 53VAC, current unknown but it powers 2X350WRMS power amps. I will be rectifying both sets of windings and then parallelling them for a 500W amp I'm building. I will have 40,000uF of filtering per rail so I need a good circuit to soft start with.
Can someone please help?

Thanks in advance,
Chris
__________________
The best audio is clean audio!
  Reply With Quote
Old 17th June 2003, 07:24 AM   #2
diyAudio Member
 
EchoWars's Avatar
 
Join Date: Dec 2002
Location: Left of the Dial
Why an MOV? If you are going to short across it, then a decent power resistor will be fine, and IMHO, probably more reliable.

I have built this circuit and added it to several amps. The resistor is an Ohmite 89-Type, aluminum axial, from Digikey.. Very small, very tough.

I show a DPDT switch, with a resistor to discharge the caps. Not necessary in all apps. I also show the relay coil being powered from both rails. Not very efficient with high rail voltages, but keeps current draw even....if these are high-power amps, a 110VDC relay might be a decent idea...less wasted power.
Attached Images
File Type: png inrush_limit.png (3.5 KB, 1998 views)
  Reply With Quote
Old 17th June 2003, 07:28 AM   #3
diyAudio Member
 
EchoWars's Avatar
 
Join Date: Dec 2002
Location: Left of the Dial
BTW, I lucked out finding a couple of good relays at a local surplus shop. I need more, and am SOL so far. If you find a good source of (preferrably) 48VDC relays, I'd like to hear about it.
  Reply With Quote
Old 17th June 2003, 07:38 AM   #4
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
The solution will work but have two disadvantages:

1: Slow reset. Sometimes you get a rather short dip in mains volatge, this can create a heavy current spike (if you use a toroid) even if the smoothing caps are charged.

2: Not allowed in Europe due to safety reasons if you mix mains circuit and secondary side in the same relay. If you choose this solution you must use a relay with increased isolation, for instance ELESTA SIRxxx types
__________________
/Per-Anders (my first name) or P-A as my friends call me
Super Regulator SSR03 Group buy
  Reply With Quote
Old 17th June 2003, 08:26 AM   #5
diyAudio Member
 
EchoWars's Avatar
 
Join Date: Dec 2002
Location: Left of the Dial
Quote:
1: Slow reset. Sometimes you get a rather short dip in mains volatge, this can create a heavy current spike (if you use a toroid) even if the smoothing caps are charged.
Huh? And the spike is smaller with no soft-start?? This sentence makes no sense...perhaps you would care to elaborate...
Quote:
2: Not allowed in Europe due to safety reasons if you mix mains circuit and secondary side in the same relay. If you choose this solution you must use a relay with increased isolation, for instance ELESTA SIRxxx types
He's in Oklahoma. We got half the line voltage you all do.

This is a very commonly used circuit...stolen from an 'audiophile' amp. No magic here. It would be nice to find a decent relay, and a high isolation wouldn't hurt, but most of the HI relays are excessively large. If you got the room, then sure... But for me, at this point anyway, any suitable high-current relay of 48V or better seems to be damn near impossible to find.
  Reply With Quote
Old 17th June 2003, 08:30 AM   #6
matth is offline matth  United Kingdom
diyAudio Member
 
matth's Avatar
 
Join Date: Jun 2003
Location: Bristol
What about this cct. I have made a couple of these and they work great.
http://mitglied.lycos.de/Promitheus/...or_toroids.htm
Attached Images
File Type: jpg delay.jpg (49.5 KB, 1882 views)
  Reply With Quote
Old 17th June 2003, 09:12 AM   #7
Helix is offline Helix  United Kingdom
diyAudio Member
 
Helix's Avatar
 
Join Date: Jul 2001
Location: UK
I have built several of these Elektor in-rush limiters, from 300 to 750 watt trannies with large cap. banks, no problems so far (3 years)
__________________
Ted
  Reply With Quote
Old 17th June 2003, 09:26 AM   #8
HighTec is offline HighTec  Croatia
diyAudio Member
 
HighTec's Avatar
 
Join Date: Mar 2003
Location: Sibenik, Croatia
Hi.

Now it's my turn.This is soft start unit I used in projects with Holton's AV400 modules.The schematic is stolen from Elliott's pages,but I've added some things from a professional unit.
As you see there are two relays.Relay 1 shorts the parallel resistors and he acts in approx. 1,5 sec delay.The relay two acts immediately.In fact he is the main switch and you don't need to use those 10-15A switches.The relays are 12V type.
F2 is a thermo fuse.He blows if Rel 1 fails.The fuse is mounted between the R8 & R9.There must be a contact with them.The best way is to stick them together with a plastic strap.
Q2 is BUZ71.A much less powerfull transistor can do the job very well.I've used this mosfet because I have a whole bunch of them.
Bellow is the schematic and the PCB(in case you decide to build it)
Regards.
Attached Images
File Type: jpg soft start.jpg (52.1 KB, 1940 views)
  Reply With Quote
Old 17th June 2003, 09:29 AM   #9
HighTec is offline HighTec  Croatia
diyAudio Member
 
HighTec's Avatar
 
Join Date: Mar 2003
Location: Sibenik, Croatia
And the PCB.

Bottom layer:
Attached Images
File Type: jpg soft.jpg (37.7 KB, 1729 views)
  Reply With Quote
Old 17th June 2003, 09:34 AM   #10
HighTec is offline HighTec  Croatia
diyAudio Member
 
HighTec's Avatar
 
Join Date: Mar 2003
Location: Sibenik, Croatia
Top silkscreen:
Attached Images
File Type: jpg soft 3.jpg (57.9 KB, 1712 views)
  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
ESP soft start circuit 454Casull Power Supplies 19 29th May 2009 02:06 PM
soft start circuit tsearay Swap Meet 0 8th February 2007 01:18 PM
Soft start circuit for GainClone markiemrboo Chip Amps 23 25th October 2006 05:30 PM
Soft start & Soft Switch circuit: can anybody help? m.parigi Solid State 95 22nd August 2005 03:32 PM
ESP Soft Start Circuit Alcaid Parts 4 25th February 2005 06:56 PM


New To Site? Need Help?

All times are GMT. The time now is 03:06 PM.


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