Last night I powered up the 300 VA toroidal and it is making a quiet hum/buzz. On smaller toroidals this usually means there is a short somewhere, but in my case the buzz persists with the transformer bolted down, or with bolt removed, at a different location, and with bridge+filters connected or not.
Any idea what could be causing this noise?
Any idea what could be causing this noise?
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The total DC current at the pole transformer would need to be zero. But that doesn't mean it cant exist downstream. If one leg pulls a DC current, you get an equal and opposite one forced in the other.
But it's just as likely a high line voltage. It can run 130V (in the US), even if everything is in spec. Get a loose or resistive neutral connection in your breaker box, the two legs can get forced to be unsymmetrical and then it can go really high on one side. You may want to try it at someone else's house - espicially if you've got other symptoms like lights going bright and dim.
There are two smaller toroidals (50VA and 80VA) which are not making this buzzing noise (unless you pull like 90% of their rated current).
There are two fluorescent tubes transformers which are making similar buzzing noise, I suppose for different reasons. The soldering iron station also buzzes when it heats. I presume all those symptoms are unrelated.
The buzzing is mechanical, something is vibrating. Could it be the core is fragmented? Could it be there is a few loose windings ? In either case could this mean the transformer is unsafe and a potential risk?
There are two fluorescent tubes transformers which are making similar buzzing noise, I suppose for different reasons. The soldering iron station also buzzes when it heats. I presume all those symptoms are unrelated.
The buzzing is mechanical, something is vibrating. Could it be the core is fragmented? Could it be there is a few loose windings ? In either case could this mean the transformer is unsafe and a potential risk?
It could be a mechanical issue in the transformer. That happens, and isn't something to be overly concerned about (other than the sound being obnouxious). However, a very small DC component on the mains will easily saturate the core, which results in larger current draw and leaking magnetic field. The larger the transformer the bigger the issue.
Two large low-voltage electrolytics is enough to test that hypothesis. Add two diodes for continous use.
Two large low-voltage electrolytics is enough to test that hypothesis. Add two diodes for continous use.
If is a DC or a saturation issue you should see a measuable currect at the input with no load attached. It may just be that they didn't properly laminate the transformer plates during manufacturing. If that is the case you could request a replacement from the manufacturer or distributor. Another issue could be a short in the primary winding. Try measuring the input inductance to and compare it with the smaller non-buzzing transformers. I would expect the larger transformer to have a slightly lower input inductance. But if its really low then there is a problem.
You can also try vacuum impregnating the transformer (by submerging the entire transformer in varnish inside of a vacuum desiccator) to correct a bad lamination job. By creating a vacuum all of the air is removed from inside the transformer and is replaced with varnish. When the varnish sets it should imobilize everything, preventing vibration noise.
You can also try vacuum impregnating the transformer (by submerging the entire transformer in varnish inside of a vacuum desiccator) to correct a bad lamination job. By creating a vacuum all of the air is removed from inside the transformer and is replaced with varnish. When the varnish sets it should imobilize everything, preventing vibration noise.
First,
power the transformer through a mains bulb tester.
If the bulb stays on you have a wiring fault.
Next, TAKE CARE - the blocker is at mains voltage!!!!
build a mains DC blocker, fit it in the primary, in the Neutral or the Live, but not both. Remember that you must be able to pass AC through the DC blocker and that start up current peaks and abusive usage overloads must also be able to pass without damaging the DC blocker.
All you need are a pair of large low voltage electrolytics (~10mF 10V) and a pair of 400V 1n5404 diodes.
If both wiring faults and DC have been eliminated as the cause and the noise is still heard, then you have a badly manufactured transformer.
power the transformer through a mains bulb tester.
If the bulb stays on you have a wiring fault.
Next, TAKE CARE - the blocker is at mains voltage!!!!
build a mains DC blocker, fit it in the primary, in the Neutral or the Live, but not both. Remember that you must be able to pass AC through the DC blocker and that start up current peaks and abusive usage overloads must also be able to pass without damaging the DC blocker.
All you need are a pair of large low voltage electrolytics (~10mF 10V) and a pair of 400V 1n5404 diodes.
If both wiring faults and DC have been eliminated as the cause and the noise is still heard, then you have a badly manufactured transformer.
Hi,
if you decide to implement the DC blocker for some or all of your toroids then the caps must be a series pair of back to back polarised electrolytics.
For 50Hz the cap impedance of two 1000uF back to back is Imp = 1/2/Pi/F/C = 6.3ohms
The peak voltage across the caps will be sqrt(2) * 1.5A * 6.3ohms = 13.5Vpk.
The caps for 1.5Arms need to be about 20 times bigger to get the voltage below the Vf of the single diodes.
You can use pairs of series diodes in each direction to double the voltage capacity of the blocker but that still leaves you needing 10mF+10mF and 4diodes for 1.5Arms @ 50Hz.
DC on the mains is a slight misnomer.
An unsymetrical waveform where the area of the +polarity half waves is not equal to the area of the -polarity half waves is an effective unbalance in the current flowing through the transformer that is not pure AC.
That is the equivalent to adding a variable DC component to the AC component.
if you decide to implement the DC blocker for some or all of your toroids then the caps must be a series pair of back to back polarised electrolytics.
For 50Hz the cap impedance of two 1000uF back to back is Imp = 1/2/Pi/F/C = 6.3ohms
The peak voltage across the caps will be sqrt(2) * 1.5A * 6.3ohms = 13.5Vpk.
The caps for 1.5Arms need to be about 20 times bigger to get the voltage below the Vf of the single diodes.
You can use pairs of series diodes in each direction to double the voltage capacity of the blocker but that still leaves you needing 10mF+10mF and 4diodes for 1.5Arms @ 50Hz.
DC on the mains is a slight misnomer.
An unsymetrical waveform where the area of the +polarity half waves is not equal to the area of the -polarity half waves is an effective unbalance in the current flowing through the transformer that is not pure AC.
That is the equivalent to adding a variable DC component to the AC component.
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The primary inductance should be much lower than your other transformers. I assume you have a multimeter that can measure inductance? The other way is to measure input current on the primary using an amp meter. You can use a clamp amp meter so that no voltage flows through the meter since it use the magnetic field generated by the current.
Image of Clamp Amp meter:
http://www.edmo.com/modules/products/xarimages/Large/FLUKE_336.jpg
Try measuring the coupling capacitance between the primary and secondary and compare it with your no-buzz transformers. Set your multimeter to Capacitance and connect one probe to one of the primary leads and the other to one of the secondary winding leads. If its much higher, your probably S-O-L because is a poor transformer design, vacuum impregnating the transformer may reduce the noise, but I don't think it will eliminate it.
FWIW: Your only real chance of eliminating the noise is if one of the core laminations is loose, vacuum impregnation should fix that issue. You may also have luck by encasulating the transformer using tranformer potting resin. The only issue is that resin will restrict heat dissipation, if you encapulate then derate to about 70% to 80% of the transformers max power output.
resin for potting transformers
http://www.ellsworth.com/display/productdetail.html?productid=1221
Thanks I have printed your suggestions and will try them later. Farnell tech guy said a quiet buzz is quite normal, unless the transformer is getting hot (over 60 C). I have not let it run for anything over 2-3 mins at a time, so I do not know yet. I will post more when I have run those tests.
Just experienced some humming around my gear
It had not been there before
I narrowed it down to one monoamp
Humming was only audible when standing close to amps
Not when listening close to amp
A bit strange
Remedy was VERY simple
I just loosened the mounting screws
Humming gone
btw, its mounted on rubbers
It had not been there before
I narrowed it down to one monoamp
Humming was only audible when standing close to amps
Not when listening close to amp
A bit strange
Remedy was VERY simple
I just loosened the mounting screws
Humming gone
btw, its mounted on rubbers
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