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Yet Another Soft Start Circuit
Yet Another Soft Start Circuit
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Old 8th July 2019, 08:07 PM   #11
johnhenryharris is offline johnhenryharris  United States
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I am looking at removing the power supply from the new case that I made for the power amp. With the amplifier being 24" long and weighing 135 pounds with the upgrade of the toroid from 1kVA to 2.4kVA and the capacitors from 2 at 60K mf to 8 caps with a large inductor in between for a CLC and a total of 632K mf. The original Amp was 16" long by 18" by 90 pounds mono-blocks. Moving the PS and amps to separate case will make it so I can move them easily, if I ever have to after setting them in place. Will replace the Soft start with my new boards as well.
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Old 8th July 2019, 11:00 PM   #12
LongRoad is offline LongRoad  Russian Federation
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Quote:
Originally Posted by johnhenryharris View Post
After looking at a bunch of soft start circuits I decided to design one according to my beliefs as to what is the best way to do it. It may be completely different from your beliefs but there it is.
Enjoy.
There is a soft start working scheme, you can collect it yourself or buy.
Click the image to open in full size.
AIYIMA 1000W Power Supply Delay Power Soft Start Protection Board High Power For Class A Amplifier DIY 30A Relay Protection 220V-in Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group
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Old 9th July 2019, 03:49 PM   #13
johnhenryharris is offline johnhenryharris  United States
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There are a few things about that circuit I do not like. 1. It is overly complicated, but to each their own on that. 2. You have to turn on a switch AND push a button to start the circuit. I did away with that by using the voltage comparator and the controlled cap charge rate. 3. It has the thermistors in both parallel and series, and yes I have even used them that way once but with each parallel device able to carry the whole load. So why parallel them and according to the manufacturers of thermistors it is a no-no to parallel them. Using one higher current rated device instead of two smaller ones in parallel may be more expensive but is far safer, and since I put my design into the public domain I would not share something that could be hazardous.
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Old 9th July 2019, 05:38 PM   #14
johnhenryharris is offline johnhenryharris  United States
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Just for completeness, attached is a print of the PCB layout. The PCB is 3.25" x 3.75". The power transformer and the HD bypass relay take up most of the board real estate.
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File Type: pdf softstart layout.pdf (66.5 KB, 74 views)
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Old 11th July 2019, 11:07 AM   #15
robydream is offline robydream  Croatia
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I developed some time ago SoftStart with push button ON/OFF and delay of cca 2sec with current limiting resistors (4x180R/5W in parallel gives 45R/20W resistor but it better to use 10W resistors to have 40W power dissipation of current inrush limiter).

It have fuse to protect toroid from damage, and it is small and compact..i build three unit until today and all worked perfectly.

[NEW] SoftStart+Push Button V1.0
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Old 12th July 2019, 05:25 AM   #16
johnhenryharris is offline johnhenryharris  United States
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Yes, you definitely should have a fuse on the AC in, not just to protect the toroid but the whole Power supply/Amp. I chose an on/off switch in my design so that I could toggle an tricolor LED from Red for standby to Blue or Green for On, just looks cool to me.
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Old 9th August 2019, 09:12 PM   #17
johnhenryharris is offline johnhenryharris  United States
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For an in-rush current limiter I prefer a thermistor over a resistor. The resistor may be slightly cheaper but if something happens and the bypass relay doesn't pull in then the thermistors with heat up and decrease in resistance allowing the current to flow where as a resistor or set of resistors will just get hot and may limit the current to the amp.
Your thoughts and/or preferences?
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Old 11th August 2019, 12:13 PM   #18
bluerooster is offline bluerooster
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how about something simple?
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Old 12th August 2019, 04:01 AM   #19
johnhenryharris is offline johnhenryharris  United States
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I see relays but I don't see anything controlling them, that's where the differences in design come in. That a whole of relays in the primary circuit, which is fine, it won't affect the sound.
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Old 12th August 2019, 09:55 AM   #20
Ketje is offline Ketje  Belgium
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Quote:
Originally Posted by bluerooster View Post
how about something simple?
You want simple ?
That relais comes in at around 175V~ (without the resistor).
As the NTC gets hot the resistance goes down and the output voltage up.
After a while, when the voltage gets high enough, the relais close the circuit bridging the NTC and holding itself.
With the resistor the threshold can be adjusted to a higher voltage and longer wait.
Mona
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