Normally softstart goes before the transformer's primary - see, for instance, the reference power supply design from National. Be careful with the mains voltage, though.
Or, if you want to know where the relay should be powered from, there are different views on that. One way is as per the app note above; another is from a separate "housekeeping" power supply.
Or, if you want to know where the relay should be powered from, there are different views on that. One way is as per the app note above; another is from a separate "housekeeping" power supply.
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I must admit that I am a newby but this is why I am asking these questions. Rough learning curve. Thanks for the danger concern though. So I can assume that this relay is best right after the rectifier and before the reservoir capacitor.
I am using a seperate "housekeeping" transfo for this purpose.
regards.
I am using a seperate "housekeeping" transfo for this purpose.
regards.
greetings
been doing more reading and the relay is used to short the 3 parallel 5W resistors on the main AC before the transfo. The resistors are there to absorb the initial power surge and the relay kicks in after about 200 ms delay. At least this is the way I understand the soft start circuit.
I originally thought this was more of a "mute" type circuit protection.
regards.
been doing more reading and the relay is used to short the 3 parallel 5W resistors on the main AC before the transfo. The resistors are there to absorb the initial power surge and the relay kicks in after about 200 ms delay. At least this is the way I understand the soft start circuit.
I originally thought this was more of a "mute" type circuit protection.
regards.
Necp,
we all want you as a Member.
Learn about the dangers of working with mains electricity before working with mains electricity.
Get someone who is skilled to show you, or take a course at night school, or do a lot of reading and asking.
Soft start is different from slow charge.
To save money and space and time, many try to combine these two functions into one device.
A soft start is to start up a transformer, but to limit the start up current so that it does not blow the fuse, nor trip the breaker.
A slow charge is to charge up the smoothing capacitors slowly enough so that they do not heat up excessively internally and do not exceed their maximum charge rate (V/us)
The soft start is fitted in the mains primary circuit. This is where the biggest danger is.
The slow charge should preferably be placed in the secondary before the capacitors, but it can be either side of the rectifier.
Before you do anything else, build a mains bulb tester, bulb ballast, dim bulb. There are hundreds of references in this Forum and elsewhere. The Dim bulb is in google from wayyyy back. This will be your first mains powered project, get it checked before you plug it in !!!!
Read what it is, what it does to save you blowing up your projects and your self and how cheap and simple it is to assemble.
Learn to use it for starting up every mains powered project. And use it again every time you modify a mains power project.
I recommend you bulb test the wiring to your mains transformer with nothing else attached as the first stage of keeping your self alive.
we all want you as a Member.
Learn about the dangers of working with mains electricity before working with mains electricity.
Get someone who is skilled to show you, or take a course at night school, or do a lot of reading and asking.
Soft start is different from slow charge.
To save money and space and time, many try to combine these two functions into one device.
A soft start is to start up a transformer, but to limit the start up current so that it does not blow the fuse, nor trip the breaker.
A slow charge is to charge up the smoothing capacitors slowly enough so that they do not heat up excessively internally and do not exceed their maximum charge rate (V/us)
The soft start is fitted in the mains primary circuit. This is where the biggest danger is.
The slow charge should preferably be placed in the secondary before the capacitors, but it can be either side of the rectifier.
Before you do anything else, build a mains bulb tester, bulb ballast, dim bulb. There are hundreds of references in this Forum and elsewhere. The Dim bulb is in google from wayyyy back. This will be your first mains powered project, get it checked before you plug it in !!!!
Read what it is, what it does to save you blowing up your projects and your self and how cheap and simple it is to assemble.
Learn to use it for starting up every mains powered project. And use it again every time you modify a mains power project.
I recommend you bulb test the wiring to your mains transformer with nothing else attached as the first stage of keeping your self alive.
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Greetings,
Thanks for the danger tips AndrewT. I am quite aware of mains danger. I've redone all of my home electricity from breaker panel to outlets. Our outlets are mostly 110V but some large appliances are running off 220V. It was a shocking experience (no pun intended). So I am testing my gear from 110V. I'll use your advice testing a lightbulb for my soft start circuit. My PSU is already built and using a 150VA toroidal. I am hearing a thump in my speakers when I turn on the switch. This is what I would like to eliminate. I built the timer circuit on a breadboard and now I am ready to test it through the relay on 110V mains. I will try the lightbulb first.
Nonetheless, I do have another question. Our 110V has one hot, one neutral and one ground wire. So When I connect to the outlet, we are never sure about the hot or neutral wire. Ground is always the middle but sometimes the hot and neutral are reversed from within the outlet.
Does it make a difference on which wire to connect the 3 resistors to main?
Does it always have to be on the hot wire and if so, how do we make sure we are tapping the + side?
Some threads mention to use three 33 Ohm 5W resistors and others go as high as 68 Ohm. What would be the ideal rating for 150VA off of 100V main?
regards.
Thanks for the danger tips AndrewT. I am quite aware of mains danger. I've redone all of my home electricity from breaker panel to outlets. Our outlets are mostly 110V but some large appliances are running off 220V. It was a shocking experience (no pun intended). So I am testing my gear from 110V. I'll use your advice testing a lightbulb for my soft start circuit. My PSU is already built and using a 150VA toroidal. I am hearing a thump in my speakers when I turn on the switch. This is what I would like to eliminate. I built the timer circuit on a breadboard and now I am ready to test it through the relay on 110V mains. I will try the lightbulb first.
Nonetheless, I do have another question. Our 110V has one hot, one neutral and one ground wire. So When I connect to the outlet, we are never sure about the hot or neutral wire. Ground is always the middle but sometimes the hot and neutral are reversed from within the outlet.
Does it make a difference on which wire to connect the 3 resistors to main?
Does it always have to be on the hot wire and if so, how do we make sure we are tapping the + side?
Some threads mention to use three 33 Ohm 5W resistors and others go as high as 68 Ohm. What would be the ideal rating for 150VA off of 100V main?
regards.
A soft start will not get rid of a turn on thump (that is amp related, not power supply related). Also, you really don't need a soft start on a 150VA transformer, the inrush current draw is low enough.
It's always better to put all of the switches, fuses, and other current limiting devices on the hot mains wire. Standard outlets here have 2 slots and the ground pin. The wider slot is neutral - trace it back to the IEC socket (if you are using one).
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Does that equate to polarised plugs and sockets?
One cannot insert the plug top the "wrong" way around.
They are polarized - a 2 prong, double insulated unit will only plug in one way.
Some older equipment still has the non-polarized version of 2 equal width prongs. I can't recall when they changed it, but I do know it was in my lifetime.
This is getting old already.
You said you have experience and rewired your house - did you install new, polarized receptacles?
What type of power cord are you using? It should be 3 conductor: hot, neutral and ground. This will only go in ONE WAY. If you are using a 2 prong plug (you certainly shouldn't be) then this should be polarized too - one prong is wider!!!! Neutral is wider!
You said you have experience and rewired your house - did you install new, polarized receptacles?
What type of power cord are you using? It should be 3 conductor: hot, neutral and ground. This will only go in ONE WAY. If you are using a 2 prong plug (you certainly shouldn't be) then this should be polarized too - one prong is wider!!!! Neutral is wider!
Both the Neutral and the Live must be considered as dangerous.
The Live and Neutral inside the amplifier must both be protected from inadvertent interference to the same insulation/isolation standard.
In the UK, we are required to use 2pole mains switches to ensure that both Live and Neutral are switched OFF together. Just to avoid the risk that some eejit has wired up the house wiring incorrectly or another eejit has wired up a rewire-able plug top the wrong way.
The Live and Neutral inside the amplifier must both be protected from inadvertent interference to the same insulation/isolation standard.
In the UK, we are required to use 2pole mains switches to ensure that both Live and Neutral are switched OFF together. Just to avoid the risk that some eejit has wired up the house wiring incorrectly or another eejit has wired up a rewire-able plug top the wrong way.
I rented a USA house once where the few 3 prong outlets and big blade small blade outlets installed were backwards, with the big blade hot and the small one neutral. This mattered as I was trying to fix a 1975 television, as the entire chassis was hot. Many times 3 prong outlets are installed because that is all they sell, but the walls contain 2 wires. Two prong houses wired should not be "grounded" internally, but let the electric company do it outside at the pole. The big blade is neutral, white, and closer to earth potential than the black. Amateur wired houses from the thirties to fifties often have the black wire as the lower potential side and the lamp base ring, as black is used in automotive electricity (which came to the country first) as the frame or return side. This is incorrect.
Most audio equipment does not tie the chassis to the neutral side, and is "double insulated". Other designs with an exposed metal chassis tie it to the rounded safety ground pin. I find the fear of mains voltage a bit strange, as most of us have rewired lamp switches or appliance cords long before we ever touched a piece of audio gear. Rule 1 is, don't touch the metal with the cord plugged in. Audio devices contain energy storing capacitors, so that brings up rule 2, which is don't touch any metal until you prove it is less than 25 VDC to the chassis or safety ground. And rule zero is "don't work alone".
Three prong outlets and 3 wire Romex were available when My father & I wired a room in 1962, but none of my Dynakit equipment (ST120 designed 1966) nor my Hammond organs (design 1968) had 3 prong plugs. The chassis in this equipment is not tied to either blade of the power plug. However, certain replacement capacitors might have grounded cases, and may inadvertantly tie one side of the DC power to a power blade. This has to be thought out carefully. TV's always had a grounded chassis, and my mother's 1954 philco TV would bite due to the cardboard insulation between the chassis and the steel enclosure, if the humidity was high and the non-polarized plug was in "backward."
Most audio equipment does not tie the chassis to the neutral side, and is "double insulated". Other designs with an exposed metal chassis tie it to the rounded safety ground pin. I find the fear of mains voltage a bit strange, as most of us have rewired lamp switches or appliance cords long before we ever touched a piece of audio gear. Rule 1 is, don't touch the metal with the cord plugged in. Audio devices contain energy storing capacitors, so that brings up rule 2, which is don't touch any metal until you prove it is less than 25 VDC to the chassis or safety ground. And rule zero is "don't work alone".
Three prong outlets and 3 wire Romex were available when My father & I wired a room in 1962, but none of my Dynakit equipment (ST120 designed 1966) nor my Hammond organs (design 1968) had 3 prong plugs. The chassis in this equipment is not tied to either blade of the power plug. However, certain replacement capacitors might have grounded cases, and may inadvertantly tie one side of the DC power to a power blade. This has to be thought out carefully. TV's always had a grounded chassis, and my mother's 1954 philco TV would bite due to the cardboard insulation between the chassis and the steel enclosure, if the humidity was high and the non-polarized plug was in "backward."
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I'd never get a damn thing done, if I lived by this rule.
Fact is, any of our homemade audio equipment should be grounded to safety earth. If the receptacle is wired incorrectly, you should have allowed for that possibility in the build (as Andrew says, double pole switch, insulate both hot and neutral).
Does it make a difference for normal operation if your soft start is on the hot or neutral? No, strictly speaking it does not.
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