So a split power supply on two chassis with the transformers and diodes and some filtration on one and the final filters ETC on the circuit chassis would work if properly done. What would be the major areas of causes of problem doing it this way. Cost not a major one being it is DIY .
Just the usual practical issues, wire R losses, wire inductance leading to RFI pickup... shielding/twisting of the cables/wires if long, etc.
-RNM
I've been working on some controlled switch-on circuitry and have also the experience that when you switch off the toroid while it is carrying appreciable current, the surge current at the next switch-on can be very high and blow the fuse.
As to the zero-crossing switch-on, that doesn't really draw so much secondary current as one would think.
The caps have zero charge but the secondary voltage (and current) rise relatively slowly and the caps charge in concert.
The secret for controlled switch-on is that you switch on at the same point on the wave were you switched off last time. Where that point is, is immaterial (disregarding secondary load current for the moment).
You just have to survive the very first switch-on, after that you're home free.
jan
I'm not in agreement. I suspect a different mechanism is at work.
The current being drawn is in 2 parts, the core magnetization current, and the secondary current bucking the magnetization.. So the nomenclature may be in play as well.
I'd really like to see the test setup, what is being said isn't consistent with what I believe.
Course, I don't know magnetics very well.
jn
It is possible to have approximately a 100A surge, if you catch the AC signal wrong, with fairly small power supply capacitance, like 10,000 uf or so. That is why we have some form of slow start on all of our larger amps with big transformers.
Industrial power supplies are usually equipped with this too, especially 'tranformerless' power supplies.
Industrial power supplies are usually equipped with this too, especially 'tranformerless' power supplies.
Or better use a starter circuit:
1) resistor in series with primary winding
2) resistor is shunted by power relay contact after a couple of seconds.
The 45 amp one is good for 270 amps inrush.Zero-crossing opto isolated SSR is not good to turn on a big toroidal transformer. Been there
Did you use the versions with zerovolt turnon?
And it controls the off.
I am only concerned that the inrush due to core saturation or magnetization may be based on not controlling the on time.. I still do not see significant magnetization as the culprit. Does anybody have coercivity numbers for typical toroids we are talking about?
jn
If you want to limit inrush into a transformer you should turn on at the peak of the line, see:
http://relays.te.com/appnotes/app_pdfs/13c3206.pdf
Zero crossing turn on is OK with capacitor inrush limiting.
G.
http://relays.te.com/appnotes/app_pdfs/13c3206.pdf
Zero crossing turn on is OK with capacitor inrush limiting.
G.
If you use a triac controlled by an opto, you need to switch ON as the current ( which is 90 degrees out of phase with voltage) passes through zero. The white goods guys have been doing this for years with motors and they make millions of them every year.
I doubt that the switch off cycle has anything to do with the fuse popping next time power is applied. The magnetizing current generates a field and when you turn the transformer off, it just collapses - any current generated by this just dissipates into the load - usually the secondary.
Certainly, if you do not use soft start from 500 or 600 VA upwards, you will be popping fuses, tripping the breaker and generally causing mayhem, and especially so where you have a bank of filer caps that need to be charged up. On a big supply, this can easily be 400A peak. Plus of course the torroid in rush current.
For soft start, I use a series resistor which is then shorted out after a short period by a relay. I have never had any problems with this.
I doubt that the switch off cycle has anything to do with the fuse popping next time power is applied. The magnetizing current generates a field and when you turn the transformer off, it just collapses - any current generated by this just dissipates into the load - usually the secondary.
Certainly, if you do not use soft start from 500 or 600 VA upwards, you will be popping fuses, tripping the breaker and generally causing mayhem, and especially so where you have a bank of filer caps that need to be charged up. On a big supply, this can easily be 400A peak. Plus of course the torroid in rush current.
For soft start, I use a series resistor which is then shorted out after a short period by a relay. I have never had any problems with this.
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Its interesting that others have found the same issue with turn on surges with big transformers. My experience was that its intermittent. If it were simply big turn on currents it should pop every time.
The charge cycle is pretty quick and I used a DC relay scaled to the target DCV of the of the supply to short out the series resistor on the primary and a diode to ensure it discharges. Worked fine, simple retrofit and future production had no issues.
Toroid core material
Here is a clip I found in the interwebs:
Material: Unisil M089-27N (27M4)
Maximum loss 0.89w/kg @ 1.5T.50Hz, 1.7T.60Hz.
Widths 10 - 80mm
All material supplied to BS EN 10107:2005
Toroidal cores available from stock
Maximum OD 200mm Maximum ID 100mm
G.O.S.S. has been manufacturing toroidal cores since 1996 on high speed automatic core winding machines (shown above).
transformer core manufacturers,toroidal cores,manufacturer of strip wound cores,manufacturer of magnetic cores,magnetic cores
I don't know if it gives a clue into the core or its ability to retain a field. It seems they use M4 and it won't have a gap. It mentions 1.7T flux so thats a lot (and way over JN's limit). Hopefully JN can derive some meaning from this.
The charge cycle is pretty quick and I used a DC relay scaled to the target DCV of the of the supply to short out the series resistor on the primary and a diode to ensure it discharges. Worked fine, simple retrofit and future production had no issues.
Toroid core material
Here is a clip I found in the interwebs:
Material: Unisil M089-27N (27M4)
Maximum loss 0.89w/kg @ 1.5T.50Hz, 1.7T.60Hz.
Widths 10 - 80mm
All material supplied to BS EN 10107:2005
Toroidal cores available from stock
Maximum OD 200mm Maximum ID 100mm
G.O.S.S. has been manufacturing toroidal cores since 1996 on high speed automatic core winding machines (shown above).
transformer core manufacturers,toroidal cores,manufacturer of strip wound cores,manufacturer of magnetic cores,magnetic cores
I don't know if it gives a clue into the core or its ability to retain a field. It seems they use M4 and it won't have a gap. It mentions 1.7T flux so thats a lot (and way over JN's limit). Hopefully JN can derive some meaning from this.
I knew you'd say that
I'm working on an article, all will be revealed in the fullness of time.
jan
Even wiki describes toroidal transformer inrush current peak ....
Einschalten des Transformators ? Wikipedia
Toroidal behaves different than EI.
Einschalten des Transformators ? Wikipedia
Toroidal behaves different than EI.
I am not a big fan of semiconductor switches used for audio power control. The dead zone around the zero crossing makes more noise than a real switch. In practical circuits this has been enough to be clearly heard.
The remnance in a toroid core needs to be as little as 10% to have the switch on surge. At 30% it is a giant problem. What is interesting is that I have not seen the issue in unloaded transformers.
The question is if I cut open a core and measure that will the result be distorted?
JN think core memory used toroid cores for a reason.
The remnance in a toroid core needs to be as little as 10% to have the switch on surge. At 30% it is a giant problem. What is interesting is that I have not seen the issue in unloaded transformers.
The question is if I cut open a core and measure that will the result be distorted?
JN think core memory used toroid cores for a reason.
I'd be interested to hear jn's view on the remnance stuff.
Are we saying this is after the core had been disconnected from the supply for some time, and then reapplying power gives the issue? I would expect the remnance is related to the magnetizing current, and on a torroid ( especially a big one) this would be very low. Not enough to pop fuses the way some people are suggesting.
Ahh the joy of . . . Magnetics
Are we saying this is after the core had been disconnected from the supply for some time, and then reapplying power gives the issue? I would expect the remnance is related to the magnetizing current, and on a torroid ( especially a big one) this would be very low. Not enough to pop fuses the way some people are suggesting.
Ahh the joy of . . . Magnetics
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