I ordered a 2KVA torroid for my amp - low noise and low magnetising current (30mA no load). When I apply the mains it pops the fuse and sometimes trips the mains circuit breaker. Anyone got experience with big transformers like this - what's the inrush current? I see some people recomend putting a 10 Ohm resistor in series with the primary for a second or two. I had a 220 Ohm 20watt resistor and tried this. Fuse still blew when I shorted the resistor out (with a zero crossing triac switch). Is my series resistor too high in value.
By the way, I sent the transfoermer back to the factory - they checked it and apparently its ok.
Feedback/suggestions appreciated.
By the way, I sent the transfoermer back to the factory - they checked it and apparently its ok.
Feedback/suggestions appreciated.
Banned
Joined 2002
no - I think the primaries are wired correctly. I checked this by wiring a 40W lamp in series. If I measure the seondaries I get 60 - 0 - 60. The lamp is OFF because only the magnetising current is being drawn thru the primary. I short one of the secondaries out and the lamp goes on - I assumed therefore that I had phased it correctly. I checked again with the guy at the factory - I got the primaries right.
I am using a 10A anti surge fuse from Farnell
I spent a fortune on this transformer so I am pretty jerked off that I've got this problem now.
Anyone know what the in-rush (initial magnetising) current is for these things?
I am using a 10A anti surge fuse from Farnell
I spent a fortune on this transformer so I am pretty jerked off that I've got this problem now.
Anyone know what the in-rush (initial magnetising) current is for these things?
For a toroid that huge, you will absolutely need a soft-start circuit.
That is one hyoooge mofo
edit: I see you have one. 220 ohms is too high and probably isn't allowing the transformer's magnetic field to stabilise. Go with a lower value like 68 ohms. Also I didn't see what the primary voltage is in your country.
That is one hyoooge mofo
edit: I see you have one. 220 ohms is too high and probably isn't allowing the transformer's magnetic field to stabilise. Go with a lower value like 68 ohms. Also I didn't see what the primary voltage is in your country.
A soft start is essential and I'm surprised this was not considered already TBH!
220 ohms is too big, you get another inrush when applying full current if the magnetic field has not built up enough. 33-100 ohms is about right, for about 0.5 second delay.
My money is on inrush as this can happen at full whack even under light load. But it's worth doing some checks as furry fighter pilot said.
220 ohms is too big, you get another inrush when applying full current if the magnetic field has not built up enough. 33-100 ohms is about right, for about 0.5 second delay.
My money is on inrush as this can happen at full whack even under light load. But it's worth doing some checks as furry fighter pilot said.
I used this 220 Ohm 20 watt in series but when I short it out I still get the fuse popping. I was wondering if the value was too high, so I did not get the initial magnetising current - this happened when I short it out but this of course blows the fuse. I'll try the 10 Ohm value and see what happens. If that does not work, I'll have to go back to te factory.
I even wondered if the core was cracked - I don't know what these things look like inside - is it powdered iron? Wound laminate?
I even wondered if the core was cracked - I don't know what these things look like inside - is it powdered iron? Wound laminate?
ACR said:
try exactly this lamp (or even stronger one ) as inrush limit resistor -for test.
make decent soft start circ and stop thinking about it;
what you have is common behavior with big donuts.
or use NTC as Pass use.
and-stop playing with it,before you burn primary with unnecessary start-up shocks
It IS residual magnetism ... just found this.
QUOTE:
The excellent magnetic properties of the toroidal transformer and the high remanence of the grain-oriented silicon steel, under certain circumstances, occasionally leads to high inrush current at turn-on. This is particularly true when the circuit is completed at the zero-crossing of the input voltage wave form.
To prevent nuisance interruptions due to blown fuses or supply breaker, some simple precautions should be considered, As the power rating of the transformer increases, the potential effect of the inrush current becomes greater. The following table suggests different types of circuit protection according to the toroid's power rating.
In addition, in those applications where an even lower in-rush current is desired, AMVECO has developed several proprietary construction techniques, Without added circuitry, both the peak value and the duration of the in-rush current can be reduced. As a matter of fact, AMVECO has manufactured toroidal transformers without any inrush current at all. In these cases, AMVECO works closely with the customer to meet the specific requirements of the application. A slight increase in the overall size of the transformer is sometimes necessary to facilitate the lower in-rush current.
Transformer Rating
Suggested Protection
* 15 to 300VA
None
* 300VA to 1.0kVA
Slow-blow fuse in primary circuit
* 1.0 to 2.0kVA
Small value resistor in series with primary circuit
* 2.0kVA and up
Relay momentarily inserts resistor in primary circuit at start-up, or NTC Thermistors
QUOTE:
The excellent magnetic properties of the toroidal transformer and the high remanence of the grain-oriented silicon steel, under certain circumstances, occasionally leads to high inrush current at turn-on. This is particularly true when the circuit is completed at the zero-crossing of the input voltage wave form.
To prevent nuisance interruptions due to blown fuses or supply breaker, some simple precautions should be considered, As the power rating of the transformer increases, the potential effect of the inrush current becomes greater. The following table suggests different types of circuit protection according to the toroid's power rating.
In addition, in those applications where an even lower in-rush current is desired, AMVECO has developed several proprietary construction techniques, Without added circuitry, both the peak value and the duration of the in-rush current can be reduced. As a matter of fact, AMVECO has manufactured toroidal transformers without any inrush current at all. In these cases, AMVECO works closely with the customer to meet the specific requirements of the application. A slight increase in the overall size of the transformer is sometimes necessary to facilitate the lower in-rush current.
Transformer Rating
Suggested Protection
* 15 to 300VA
None
* 300VA to 1.0kVA
Slow-blow fuse in primary circuit
* 1.0 to 2.0kVA
Small value resistor in series with primary circuit
* 2.0kVA and up
Relay momentarily inserts resistor in primary circuit at start-up, or NTC Thermistors
Real big tranny you have got, would be interesting to hear what it's going to feed.
I also think 220Ù is to much especially if you going to have big caps after a rectifier, 47Ù would be better and still safe for fuse.
During your test did you mesure voltage drop over your resistor before shortening it out?
Hov much voltage have you over lamp when it was in series, tranny unloaded?
I think to much voltage drop will also mean phase diff and that can get result in big net voltage diff.
Finally what was your time constant in triac circuit?
I also think 220Ù is to much especially if you going to have big caps after a rectifier, 47Ù would be better and still safe for fuse.
During your test did you mesure voltage drop over your resistor before shortening it out?
Hov much voltage have you over lamp when it was in series, tranny unloaded?
I think to much voltage drop will also mean phase diff and that can get result in big net voltage diff.
Finally what was your time constant in triac circuit?
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