Have you asked Nelson on the Pass forum? I've got 2x600VA toroids (1 each channel) and use the soft-start from Rod Elliot.
poobah said:ACR & choky,
What's weird is that "inrush" doesn't happen EVERY time you power on... it's luck of the draw... and if it occurs, it is only for the first half cycle. Seems that ACR's is tripping every time he powers up!
that's because -in case of OP ,current is AC and doesn't know for few milliseconds which side of current circ to choose....
it really depends of core and turns in primary; all 1KW donuts are not the same; I remember that one 450VA donut take me more time for fine tuning of soft start ,then all even bigger toroids later........
Yeah, I put a 500VA dual secondary 30V toroid and two bridge rectifiers with 10mF (6800uF and 3300uF parallel) of smoothing on each rail into my guitar amp, and I can see the lights dim when I turn it on. Those toroids make a heck of a big magnetic field, and they put a lot of power into it- and then they charge the caps up. I'm running a 6A SB fuse in the hot line, and that makes me a bit nervous- but I tried a 5A and it blew. I've wondered about mag field collapse and kickback when it shuts down, but apparently it dissipates it all into the secondary- it takes 10 seconds or so before all the lights go out and the sound stops on the amp after I shut it down. Some of that's the caps, of course, but you have to wonder how much power it pumps into those caps while the field is collapsing.
A few years ago I bought a 1kva torroid, 50 + 50 v secondaries - 120v primary, brand new. Hooked it up a few months ago and found out it would sometimes trip the breaker, even with the secondaries disconnected. Otherwise it works fine, correct voltages, low idle current, low heat, etc. But every third or second time it will trip the breaker, with loaded or unloaded secondary. I figured it was a intermittant short in the primary or secondary windings. I threw it in the scrap pile (I think its still there!), I don't really trust it and it was worth piece-of-mind to get it out and get another transformer in its place. I got an E core transformer to replace it (got a way better deal on a surplus E core) and never had a breaker problem since.
Hi,
your 2kVA transformer will draw about 9.1A maximum (on 220Vac) when run at full output. Using a T10A fuse is admirable but you may have to increase the fuse value by 30% or even as high as 100% to ensure a reliable soft start up.
The transformer start up current can peak at 240*2^0.5/(primary + cable resistance). This could approach 1kApk if you use low resistance cabling.
You need a soft start. I think you could benefit from using a progressive soft start, say 50r for 300mS, 30r for 600mS and 20r for 1Sec.
You can use SS switching and even zero crossing but relay switching will work just as well, although possibly, for a shorter lifetime.
There is some doubt in my mind about whether zero crossing helps or exacerbates your problem. It depends on whether the transformer is behaving as an inductor for the first few mSec after switch on, in which case zero voltage crossing = maximum current crossing. Once on line the transfomer behaves substanstantially as a resistive load with a relatively low phase angle.
The light bulb coming back on when you connect the secondary, confirms you have wired the light bulb soft start correctly and that the transformer has successfully started. It also confirms that the bulb wattage is too low for this size of transformer.
Try 60W, 100W and 150W bulbs to see which allows the transformer to slowly charge a test capacitor bank. This will be the bulb rating you will use to start your amplifier when you have completed the mods.
I suspect that the 150W bulb may be too small for the 2kVA and you may have to try a larger bulb or parallel a pair for successful testing.
your 2kVA transformer will draw about 9.1A maximum (on 220Vac) when run at full output. Using a T10A fuse is admirable but you may have to increase the fuse value by 30% or even as high as 100% to ensure a reliable soft start up.
The transformer start up current can peak at 240*2^0.5/(primary + cable resistance). This could approach 1kApk if you use low resistance cabling.
You need a soft start. I think you could benefit from using a progressive soft start, say 50r for 300mS, 30r for 600mS and 20r for 1Sec.
You can use SS switching and even zero crossing but relay switching will work just as well, although possibly, for a shorter lifetime.
There is some doubt in my mind about whether zero crossing helps or exacerbates your problem. It depends on whether the transformer is behaving as an inductor for the first few mSec after switch on, in which case zero voltage crossing = maximum current crossing. Once on line the transfomer behaves substanstantially as a resistive load with a relatively low phase angle.
The light bulb coming back on when you connect the secondary, confirms you have wired the light bulb soft start correctly and that the transformer has successfully started. It also confirms that the bulb wattage is too low for this size of transformer.
Try 60W, 100W and 150W bulbs to see which allows the transformer to slowly charge a test capacitor bank. This will be the bulb rating you will use to start your amplifier when you have completed the mods.
I suspect that the 150W bulb may be too small for the 2kVA and you may have to try a larger bulb or parallel a pair for successful testing.
Listen to Andrew, he's talking sense.
Zero crossing is the worst thing you can do. A starting up transformer ALWAYS acts as an inductor, because that's exactly what it is.
A soft start made from a relay shorting a resistor will be reliable for a long time as there is no arcing or real high current breaking/making.
AndrewT said:
Zero crossing is the worst thing you can do. A starting up transformer ALWAYS acts as an inductor, because that's exactly what it is.
A soft start made from a relay shorting a resistor will be reliable for a long time as there is no arcing or real high current breaking/making.
Zero Crossing NO NO!
at the zero voltage point current is at its MAXIMUM! Yes it sounds weird but its true, I use a relay with power resistors for soft starting anything over 300VA with or without load. The initial current surge on a 2KVA toroid is truly staggering. Transformers are not quite to simple easy to understand devices most people assume them to be, they have complex personalities!
RC
So Long Syd Barrett
at the zero voltage point current is at its MAXIMUM! Yes it sounds weird but its true, I use a relay with power resistors for soft starting anything over 300VA with or without load. The initial current surge on a 2KVA toroid is truly staggering. Transformers are not quite to simple easy to understand devices most people assume them to be, they have complex personalities!
RC
So Long Syd Barrett
Wow - lots of advice/feedback - thanks guys.
Here are notes etc in reply to some of the questions raised above.
1. Supply voltage is 235VAC - England
2. Soft start consists of 2 triacs - soft start triac with 220 Ohm in series with primary (I'll now change that to 22 Ohms or 33 Ohms based on dialog above). Main triac is wired across soft start triac and resistor.
3. The triacs are controlled by a micro. I switch them on at the zero crossing point in both cases since I figurred that initially Vac = 0 so Iac = 0. However, as noted above, situation is different once the transformer is magnetised - is 0 crossing for the main triac the correct thing to do here? Maybe I need to model it.
4. Someone asked does the fuse pop every time? Its only anecdotal, but it seems it does not pop for the first 1 or two times (here I am taling about when I've removed the softstart and am connected directly to the mains via a switch) but after this it pops every time. Leave it overnight, and the story repeats - ok for 1st on or 2 turn ons, and then it pops the fuses again.
5. I have 100k uF 100V waiting to be connected to the output rectifiers when I can get the popping fuse solved.
6. The transformer is from Airlink and I asked them to specially wind it to be quiet - no buzzing etc since the 1KVA ones from RS buzz like a chain saw. On the occasions when I got it going without blowing the fuses, it buzzes for about 1-2 seconds and is then very quiet - you have to put your ear right on the core to hear a very faint noise - I would say from that aspect it is very good indeed - even if it does weight 16Kg!
7. Application is a big 300W/ch amp. I'll post photos once its working.
8. The soft start is in for about 6 seconds. I can change it in the software to value.
NB - I see this thread is marked 'Moved' - am I in the wrong forum?
Here are notes etc in reply to some of the questions raised above.
1. Supply voltage is 235VAC - England
2. Soft start consists of 2 triacs - soft start triac with 220 Ohm in series with primary (I'll now change that to 22 Ohms or 33 Ohms based on dialog above). Main triac is wired across soft start triac and resistor.
3. The triacs are controlled by a micro. I switch them on at the zero crossing point in both cases since I figurred that initially Vac = 0 so Iac = 0. However, as noted above, situation is different once the transformer is magnetised - is 0 crossing for the main triac the correct thing to do here? Maybe I need to model it.
4. Someone asked does the fuse pop every time? Its only anecdotal, but it seems it does not pop for the first 1 or two times (here I am taling about when I've removed the softstart and am connected directly to the mains via a switch) but after this it pops every time. Leave it overnight, and the story repeats - ok for 1st on or 2 turn ons, and then it pops the fuses again.
5. I have 100k uF 100V waiting to be connected to the output rectifiers when I can get the popping fuse solved.
6. The transformer is from Airlink and I asked them to specially wind it to be quiet - no buzzing etc since the 1KVA ones from RS buzz like a chain saw. On the occasions when I got it going without blowing the fuses, it buzzes for about 1-2 seconds and is then very quiet - you have to put your ear right on the core to hear a very faint noise - I would say from that aspect it is very good indeed - even if it does weight 16Kg!
7. Application is a big 300W/ch amp. I'll post photos once its working.
8. The soft start is in for about 6 seconds. I can change it in the software to value.
NB - I see this thread is marked 'Moved' - am I in the wrong forum?
Hi
you're in the correct forum now, the Moderators must have been awake today
From your last post it appears you are one of the few who actually reads replies and from the sound of it you are about to action some of the recommendations.
You could end up being a friend of the Forum. Is that what you want?
How easy to disable the zero crossing check?
Have you tried a higher wattage bulb yet.
BTW. the build up of the transformer magnetic field happens in tens of mS. You do not need seconds of delay, that simply overheats the soft start system.
Finally, how about trying to be helpful with your location. Try not to copy some other idiots that think it is humerous to hide their location.
Some may do it to hide their real intention obtained by browsing the intellectual property that appears here. Work that out.
you're in the correct forum now, the Moderators must have been awake today
From your last post it appears you are one of the few who actually reads replies and from the sound of it you are about to action some of the recommendations.
You could end up being a friend of the Forum. Is that what you want?
How easy to disable the zero crossing check?
Have you tried a higher wattage bulb yet.
BTW. the build up of the transformer magnetic field happens in tens of mS. You do not need seconds of delay, that simply overheats the soft start system.
Finally, how about trying to be helpful with your location. Try not to copy some other idiots that think it is humerous to hide their location.
Some may do it to hide their real intention obtained by browsing the intellectual property that appears here. Work that out.
Hi ACR,
If you're gonna hang 100,000uF off the secondary, think of the peak current thru the bridge rectifier. With that much capacitance the rectifier will be asked to supply VERY large pulses of current at the peak of each mains cycle.
I would suggest experimenting with an L-C filter on the secondary side instead of just dumping straight into the caps. The inductor will limit the peak charging current into the caps which will also improve the reliability of your bridge rectifier.
Also the low-pass effect of the L-C will reduce harmonics of mains frequency on the secondary supply, I've seen this generate audible noise in wiring (!) due to the large magnetic fields.
Many years ago I found a large capacitor bank (something like 8 x 33,000uF) at a surplus store. Wired this into my beloved Tilbrook 5000 mosfet amp (hey, it was the 80's low-THD was everything!) and was delighted to find the amp would run for up to a minute after pulling the mains plug out!!
However it did go thru fuses on a regular basis...
Good luck and keep us updated,
Len.
If you're gonna hang 100,000uF off the secondary, think of the peak current thru the bridge rectifier. With that much capacitance the rectifier will be asked to supply VERY large pulses of current at the peak of each mains cycle.
I would suggest experimenting with an L-C filter on the secondary side instead of just dumping straight into the caps. The inductor will limit the peak charging current into the caps which will also improve the reliability of your bridge rectifier.
Also the low-pass effect of the L-C will reduce harmonics of mains frequency on the secondary supply, I've seen this generate audible noise in wiring (!) due to the large magnetic fields.
Many years ago I found a large capacitor bank (something like 8 x 33,000uF) at a surplus store. Wired this into my beloved Tilbrook 5000 mosfet amp (hey, it was the 80's low-THD was everything!) and was delighted to find the amp would run for up to a minute after pulling the mains plug out!!
However it did go thru fuses on a regular basis...
Good luck and keep us updated,
Len.
AndrewT said:Hi
you're in the correct forum now, the Moderators must have been awake today
From your last post it appears you are one of the few who actually reads replies and from the sound of it you are about to action some of the recommendations.
You could end up being a friend of the Forum. Is that what you want?
How easy to disable the zero crossing check?
Have you tried a higher wattage bulb yet.
BTW. the build up of the transformer magnetic field happens in tens of mS. You do not need seconds of delay, that simply overheats the soft start system.
Finally, how about trying to be helpful with your location. Try not to copy some other idiots that think it is humerous to hide their location.
Some may do it to hide their real intention obtained by browsing the intellectual property that appears here. Work that out.
I couldn't have said anything better myself, any or all points. The location bit is a pet hate of mine too
I would not recommend experimenting with an inductor in the supply line. For class-b amps the nonlinear load is an unfriendly factor, but the worst thing is the potential to create massive resonant peaks due to the 2nd-order resonance at cutoff, and there is another possible resonance due to the LCR interaction creating a resonant circuit. Both of these nasties will be right up in the high frequency range where you don't want them. This can drive amps into instability.
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