If you want a really cheap soft start just buy a "sprung" toggle switch (ie. the kind which only stays on while you depress it). Wire this, plus a suitable high wattage resistor (my 10ohm 200W wire-wound cost 20 cents surplus) in parallel with the main switch.
Simply depress the toggle 2-3 secs prior to setting the main switch, then release. Very simply, very cheap ...... actually works too 🙂
mark
PS: .... don't forget to turn-on the main switch, else the poor little 200 watter may start smokin'
Simply depress the toggle 2-3 secs prior to setting the main switch, then release. Very simply, very cheap ...... actually works too 🙂
mark
PS: .... don't forget to turn-on the main switch, else the poor little 200 watter may start smokin'
you could use this
220V -----------R1----------C1---------------Bridge----------------
...................................I---R2---I.................I..I.....I......I.......I
..................................................................I..I.....C2..Z1.....RE1
..................................................................I..I.....I.......I......I
..................................................................I..I------------------
..................................................................I..........................
0V--------------------------------------------------..........................
R1 390R 2W
R2 1M 2W
C1 0,47µF 600V
C2 1000µF/35V
Z1 24V 1,3W
RE1 16A 24V relay
This will give the relay about a 3-5sec delay.
220V -----------R1----------C1---------------Bridge----------------
...................................I---R2---I.................I..I.....I......I.......I
..................................................................I..I.....C2..Z1.....RE1
..................................................................I..I.....I.......I......I
..................................................................I..I------------------
..................................................................I..........................
0V--------------------------------------------------..........................
R1 390R 2W
R2 1M 2W
C1 0,47µF 600V
C2 1000µF/35V
Z1 24V 1,3W
RE1 16A 24V relay
This will give the relay about a 3-5sec delay.
FYI
Mark,
No Biggie, just an FYI. This is called a Momentary Switch.🙂
I know, the first thing to go is the memory,... I forgot what was the second thing to go.
Rodd Yamashita
Mark,
No Biggie, just an FYI. This is called a Momentary Switch.🙂
I know, the first thing to go is the memory,... I forgot what was the second thing to go.
Rodd Yamashita
This kind of bridge failure should not have happened;
that is to say it never happens to me 🙂
I recommend trying a different bridge.
The light bulb in front of the transformer on the AC line
seriously limits the input current. I would use a higher
voltage, higher wattage, as the 24 volt lamp gets pretty
abused on turn-on.
that is to say it never happens to me 🙂
I recommend trying a different bridge.
The light bulb in front of the transformer on the AC line
seriously limits the input current. I would use a higher
voltage, higher wattage, as the 24 volt lamp gets pretty
abused on turn-on.
Bridge Failure?
Peter,
You mentioned in you post that the bridge failures happened on two different amps. Were both bridges from the same source or did you obtain them at different times?😕
Regards,
Rodd Yamashita
Peter,
You mentioned in you post that the bridge failures happened on two different amps. Were both bridges from the same source or did you obtain them at different times?😕
Regards,
Rodd Yamashita
Happened on four amps. I obtained them from the same source but at different times. They rated 25 and 35 amps 200V and 600V.
Bridge Failure?
Peter,
You say, 4 failures, 2 different bridge ratings, 2 different amps, 2 different purchase times. This doesn't eliminate a source related problem, but it makes it highly unlikely.
How often do you turn your amps off-and-on?
Rodd Yamashita
Peter,
You say, 4 failures, 2 different bridge ratings, 2 different amps, 2 different purchase times. This doesn't eliminate a source related problem, but it makes it highly unlikely.
How often do you turn your amps off-and-on?
Rodd Yamashita
I've built my first pair of A75 monoblocks in 1992. Since I liked the amps I built another 2 pairs which I'm still using in my main system. The first pair is for sale now. In 1994 when Zen article appeared in Audio Amateur I jumped on the project and built 3 of them. Two I'm still using, one is sold. So summing up in the last 10 years I've been using 2 pairs of A75 monoblocks almost every day and 2 Zen amps from time to time. I recall replacing bridges once in ea. Zen amp and at least 3 times randomly in A75s. I always switch the amps off overnight. The bridges I used where from the same store, however, bought at few different ocasions, whenever needed.
So far I didn't consider that as something unlikely since my capacitor banks where quite high. There is 0.1u cap across AC pins of each bridge.
So far I didn't consider that as something unlikely since my capacitor banks where quite high. There is 0.1u cap across AC pins of each bridge.
It is no wonder that the bridge or fuse blows at turn on, with the very large cap banks being talked about here. If the inrush current for the first half cycle is calculated for the 600,000uf cap value talked about it comes out to 350 amps or so depending on transformer DCR and inductance, the impedance of the cap at 50/60 Hz and the on resistance of the diode bridge.
The real question is not what parts to use that can take this punishment. The question is how to limit the inrush current. Others have offered suggestions on how to do this and I have no doubt that they would work.
The method I have used in the past is to use a 3 pole high current relay with a 120 VAC coil and a resistor, value to be determined by amount of current limiting required, a standard 120 VAC light bulb could also be used.
1. The coil of the relay is wired in parallel with the transformer primary
2. The resistor / light bulb is wired in series with the hot side of the transformer primary.
3. Pole #1 of the relay is wired to short the resistor / light bulb when the voltage on the relay coil rises high enough to close the relay contacts.
4. Poles #2 and #3 are in series with the + and - outputs of the power supply and close when the relay contacts close.
The reason this circiut works because the resistor in series with the transformer will limit the current when the cap bank is at 0 volts. As the voltage on the caps starts to rise the current demand from the transformer will decrease and less voltage will be dropped across the series limiting resistor. As The charge current for the caps drops the voltage on the transformer primary and relay coil will rise. When the voltage on the relay coil reaches 80 to 95 volts (this depends on the relay) the contacts will close and full power will be supplied. The + and - output of the power supply need to be open while the caps are charging or the load of the amp may prevent the realy from closing.
I have used this system for years and it works great as long as the resistor value is correct, but this is easy to do. Just start out with a high value and reduce the value until you get the delay needed.
The real question is not what parts to use that can take this punishment. The question is how to limit the inrush current. Others have offered suggestions on how to do this and I have no doubt that they would work.
The method I have used in the past is to use a 3 pole high current relay with a 120 VAC coil and a resistor, value to be determined by amount of current limiting required, a standard 120 VAC light bulb could also be used.
1. The coil of the relay is wired in parallel with the transformer primary
2. The resistor / light bulb is wired in series with the hot side of the transformer primary.
3. Pole #1 of the relay is wired to short the resistor / light bulb when the voltage on the relay coil rises high enough to close the relay contacts.
4. Poles #2 and #3 are in series with the + and - outputs of the power supply and close when the relay contacts close.
The reason this circiut works because the resistor in series with the transformer will limit the current when the cap bank is at 0 volts. As the voltage on the caps starts to rise the current demand from the transformer will decrease and less voltage will be dropped across the series limiting resistor. As The charge current for the caps drops the voltage on the transformer primary and relay coil will rise. When the voltage on the relay coil reaches 80 to 95 volts (this depends on the relay) the contacts will close and full power will be supplied. The + and - output of the power supply need to be open while the caps are charging or the load of the amp may prevent the realy from closing.
I have used this system for years and it works great as long as the resistor value is correct, but this is easy to do. Just start out with a high value and reduce the value until you get the delay needed.
As they say (whoever they are?) ......
The best solutions are the really simple ones 🙂
Very clever!
mark
The best solutions are the really simple ones 🙂
Very clever!
mark
Deja vu. Earlier in this thread.HarryHaller said:
PedroPO, are you listening? This is the best solution.
Isn't a thermistor a 10 ohm resistor which "disappears" after the caps are fully charged? I would say that this is the best and the simplest solution with only one part being used. Big relays are sometimes hard to place in the amp and the delay circuit and resistor take additional space, than there are all the wires... I wouldn't like to use relay after the caps. It complicates the circuit. The only limit for using thermistors might be the excessive capacitance.
HPotter said:
given the thermal time constant of the thermistor, a large capacitor may not be sufficiently charged before the thermistor becomes a low resistance hence still causing a large surge .... they dont disappear but they do drop to about 0.3ohms or less which is of little net effect.
Maybe I'm missing something, but it seems to me that if the coil of the relay is wired in parallel with the transformers primary, it would see the full 120VAC as soon as power is applied and energize immediately. This would close all the contacts, by-passing the current limiting resistor and connecting the supply outputs to the amp.
Also, a 10ohm resistor (or thermistor) will allow 12Amps to flow with a 120Volt input (24Amp on 240Volts). On the output of the transformer, this current is multiplied by the secondary-to-primary ratio. This means that if your transformer has +-25Volt secondaries, the in-rush current through the secondaries and bridge will be 4.8 X 12Amps or 57Amps (114Amps in Europe)!!
This current level will drop off as the voltage builds on the supply caps, but the greater the capacitance of the supply caps, the longer it will take for the current to drop off. This could be a few seconds or more with the larger supplies. If you turn the amp on and off every day, sooner or later a 25Amp bridge will have to fail.
The small caps across the diodes of the bridge will only protect against voltage spikes not high in-rush currents.
Rodd Yamashita
roddyama
quote:
1. The coil of the relay is wired in parallel with the transformer primary
Maybe I'm missing something, but it seems to me that if the coil of the relay is wired in parallel with the
transformers primary, it would see the full 120VAC as soon as power is applied and energize immediately. This
would close all the contacts, by-passing the current limiting resistor and connecting the supply outputs to the
amp.
Maybe this will help.
The resistor is in series with the transformer primary and the relay coil until the relay contact closes and shorts the resistor. I would start out with 50 ohms as the series resistor. If the delay is too long decrease the value but not lower than 25 ohms.
Bruce
quote:
1. The coil of the relay is wired in parallel with the transformer primary
Maybe I'm missing something, but it seems to me that if the coil of the relay is wired in parallel with the
transformers primary, it would see the full 120VAC as soon as power is applied and energize immediately. This
would close all the contacts, by-passing the current limiting resistor and connecting the supply outputs to the
amp.
Maybe this will help.
The resistor is in series with the transformer primary and the relay coil until the relay contact closes and shorts the resistor. I would start out with 50 ohms as the series resistor. If the delay is too long decrease the value but not lower than 25 ohms.
Bruce
Paulb:
Thanx
I will try without the relay circuit first to see if it works fine and to find the power of the resistor with 20 ohm resistor since I've got 220V.
Pedropo
Thanx
I will try without the relay circuit first to see if it works fine and to find the power of the resistor with 20 ohm resistor since I've got 220V.
Pedropo
I've just made a "soft start" circuit that works very well.
It is based on the information that all you guys shared, that I thank you.
It consists on a lamp (220V 150W) in series with the primary of the transformer connected on the "live" wire. The voltage of the secondary drops to 11.8V.
I attached a switch in paralell with the lamp, so when closed the full 30.0V go to the amp.
Positive things:
- cheapeast resistor you'll ever find;
- If it burns, screw another one( you can paralell a couple of bulbs in case of one fails;
- Free light, since you allready paid the heat;
- variable tension limiter-if you wan't less power in your amp and don't have the money for a variac, just screw a less powerfull lamp (220V 60W gives you a tension of 7V);
- No timer needed-if you like leave the lamp on, I guess it wont hurt anyone.
- IF YOU HAVE A LITTLE OVERHEATING PROBLEM, (like me) here is the solution while the new heatsink arrive.
Negative side:
- It limits the maximum tension of the amp if you don't turn off the light.
- I guess that now is the lamp holding on the current inrush, so she's not going to last 2000 hours as written on the box
Give me your thoughts on this.
Pedro
It is based on the information that all you guys shared, that I thank you.
It consists on a lamp (220V 150W) in series with the primary of the transformer connected on the "live" wire. The voltage of the secondary drops to 11.8V.
I attached a switch in paralell with the lamp, so when closed the full 30.0V go to the amp.
Positive things:
- cheapeast resistor you'll ever find;
- If it burns, screw another one( you can paralell a couple of bulbs in case of one fails;
- Free light, since you allready paid the heat;
- variable tension limiter-if you wan't less power in your amp and don't have the money for a variac, just screw a less powerfull lamp (220V 60W gives you a tension of 7V);
- No timer needed-if you like leave the lamp on, I guess it wont hurt anyone.
- IF YOU HAVE A LITTLE OVERHEATING PROBLEM, (like me) here is the solution while the new heatsink arrive.
Negative side:
- It limits the maximum tension of the amp if you don't turn off the light.
- I guess that now is the lamp holding on the current inrush, so she's not going to last 2000 hours as written on the box
Give me your thoughts on this.
Pedro
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