I think I have a neat, simple and easily implemented idea for a soft start circuit

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Hi,
It looks like the 555 +7476 are sending a continuous logic light level to the opto triac.
Does that mean the opto triac re-triggers itself every zero crossing and this re-triggering then re-triggers the main switch?

yes

A DC controled isolated AC switch.;)

On the output waveform even with a snubber there is a small switching notch of a few volts on each half cycle but I have not noticed a difference in the amp as far as noise related to it, and you do loose a couple of volts to the triac but thats the price you pay for convenience.:rolleyes:
 
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This is the 120VAC line signal to the primary...input 122VAC, output 119VAC, on the DMM. Could be snubbed a bit better, but I'll have to get some higher voltage caps.
 

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Hi,
I didn't know that photo triacs existed. Is Solid State switching more or equal or less reliable than relay?


What you may like to google is SSR or solid state relay.

Possibly more reliable as no moving parts. However, they generate switching noise every zero crossing as they don't conduct below +/- 0.6v. This may or may not get to your amplifier which in turn may or may not have an audible effect. I don't know.

I considered these when desigining my original circuiit as they are very easy to drive, but went with a conventional relay for the reason I mentioned.
 
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That is the issue that I have as well, but it doesn't seem to affect the amplifier with the smaller EI transformers I'm using now. My large toroid just arrived in the mail, I will fiddle with it tomorrow and see if it works and if the switch noise is an issue with it. I'll go with the solid state if there are no real issues, but I would like to test the switching with a heavy load though.

Does 30R for ~6 cycles sound reasonable to limit surge for a 1400VA toroid?
 
... The reset of the 555 and CLE of FF A can be triggered by a logic 'fault' signal from the amplifier circuit via a photo coupler or just a regular transistor reseting the condition of standby, such as measuring if a fuse has blown or DC appears at the outputs.

...

Is triggering the fault signal the only way to get the system to turn off? I haven't played with logic circuits. It would be nice to have something that only needs a single momentary switch to control power.
 
No

One push of the momentary switch turns it on, press it again and both FF's reset, notice the CLE of the FF B is connected to Q of FF A. The fault is just an easy way to automatically reset the circuit with a logic signal in the event of an issue. So yes, the momentary switch turns it on and off.:)
 
re: easily implemented idea for a soft start circuit

For a simple, yet very flexible off the shelf solution, I find these delay on make timer modules combined with a suitable AC relay, PTC thermistor or power resistor to be ideal.

Timer features include:

universal input voltage w/ international safety approvals
selectable digital delay 1 - 1023 seconds
auto reset upon power interuption

The timer module along with a surplus relay costs about 20-$25. They are available from most heating and air conditioning supply houses or on Ebay.

ICM103 DELAY ON MAKE TIMER 1-1,023 SEC. REPL. ICM103B - eBay (item 200469143264 end time Oct-02-10 08:23:36 PDT)

120 VAC RELAY, DPDT 12 AMPS | AllElectronics.com

Or if you require more current:

120 VAC, 40 AMP RELAY | AllElectronics.com

I have used this soft start method on a number power amps with excellent results.

Fast, easy, and inexpensive.

Keith
 

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OK

Now that I finally received the transformer, first thing I did was connect up the primary and see if the soft start circuit worked. It did, but the transformer buzzed loudly. So I connected it directly to the line. It still buzzed but not quite as bad, suggesting the switching of the triac does affect this type of transformer, which I kinda expected. So for simplicity I replaced triac B and phototriac B with a relay.....:rolleyes: Problem solved there. It is still convenient to use a triac to switch the current limiting resistor.

As for the transformer still buzzing while directly on the line, I investigated further. I could feel a couple of windings vibrating and there was a buzz that came from the center of the whole transformer.:( This will obviously not do, so after removing the primary insulation, I discovered several crossed windings on the outsides of the toroid in the primary and that they were not that evenly distributed.:mad: After removing and straightening all of the 11 Ga primary winding, I discovered the iron core coil windings was not fixed in at the center of the coil and were loose.:cuss: I would expect better quality from a US company.:sigh: Still no e-mail response from them about the missing parts.:whazzat: Not only was the transformer kit missing parts, the transformer was obvious cheaply and half-a$sed constructed. Soooooo I set out to rebuild this transformer in a proper way. After all, I did have to pay for it....:rolleyes: An entire day later, it finally works. The soft start circuit works with the relay, although I may play with the logic and see if I can make it work like a soft start/soft stop to prevent any inductance kick back across the relay.

The top of the coil was barely tack welded into place and looked like it could pop loose at any moment. So I broke out the JB weld, cold weld epoxy and used C-clamps to tack down the coil by alternating them around the coil to get it all pressed into place until the epoxy set. Then I cleaned and applied some oil to the sides of the coil as it appeared they had already began to rust.:whazzat: As for the end caps, I only used the part of them that's needed to wrap the wire around the core without cutting it. After hand winding 145 turns of 11 Ga magnet wire (have you ever used 11 Ga magnet wire? ...damn thumbs hurt now:mad: but this time I did not cross any on the outside of the toroid.:cool: ) I connected it to the line and it buzzed no more, silent as a sleeping baby. Now if I can do this by hand, why could not someone at a factory with a winding machine do this?:sigh:

Anyway I added two layers of teflon tape and re-applied the mylar film covering for protection. Now I'm ready to add the secondaries.....finally.:rolleyes:




Oh yeah, and Toroid of Maryland can kiss by sticky Behind, after a hard sweaty day work in the field.:grumpy:
 

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Toroid has a pretty good reputation. I have a couple of their transformers in my system that are dead silent.

Everyone makes a lemon once in a while. I know you were eager to get rolling, but they surely would have replaced your transformer. Did you buy one of their kits?
 
Yes, and still no responce about the missing rubber pads and washers.
I suppose I can solve that issue too, one way or another...:rolleyes:


I would have to pay for return shipping and 20lbs is not a cheap shipment. It doesn't matter now, I have a working transformer.
 
@Hifinerd:

I like your idea to implement a "Power-On Soft-Start" with means of the LM555 very much.

In the meantime I have layouted your idea with the EAGLE software and will etch it.

This is my implementation:





I own a no longer used LAPTOP PSU providing 15.6 VDC at 5A.
I have fed its output to a 12 VDC constant voltage regulator (7812) in my AMP's case and connect the output of the 7812 to connector X2.

It is the LAPTOP's PSU, that I switch on, to switch on the AMP.

In my design of your Soft-Start circuit I use 2 relays: K1, that switches the main's power on as soon as I activate my LAPTOP's PSU and K2,
that switches after the delay determined by the timer IC and C1/R1.

I will use 2 x 20 OHM NTCs to provide for about 5A within the first x00 ms, before they are shorted by K2.

Do you think my circuit will work?

Best regards - Rudi_Ratlos

P.S. The PCB will be very small; about 50 x 70 mm. If you want I will etch another one for you as well.
 
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Just FYI:

I built a soft-start a while back that worked out pretty well, for a pair of mosfet monoblocks. I used 2 supplies, one for the driver circuit, one for the output devices.

The soft-start is only on the main output devices, and the way it works is the circuit detects when the output circuit has risen near enough to the driver circuit (with 3V or so) and then switches on the relays. It's foolproof and has proven safe under all switch on/off etc situations - plus you really shoulf be powering the drivers from a different supply ;)

I.e this soft start has no timer, it just will not switch in the relays unless the voltage difference is low enough not to cause a 'bump'.
 

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