OK, I'm a bit desperate here right now..
I have a 600 VA Toroid (Antek) wired for 220V on the primaries (I'm in Europe).
I have buildt a soft-start circuit that's supposed to be good for up to 1kVA.
I've decreased the shunt resistance from 40 Ohm to 33 Ohm and beefed up the wattage rating quite well. (from 5 to 17W resistors, four off)
Now, this is what happens:
I throw the switch and when the relay closes and bypasses the resistors after approx 1 second, the 10A glass fuses go with a spectacular green flash.
The resistors get quite nice and hot, so current is being drawn before the relay closes.
To the best of my understanding, this shouldn't rerally happen. What is wrong??
One thing though, I have wrapped the outer diameter of the toroid with a strip of permalloy, or mu-metal in the hope of reducing any stray fields further.
Is it a possibility that this could somehow mess up the magnetic circuit of the transformer and thus cause problems on start-up?
Any inteligent advice would be much appreciated, I'm really at loose ends here!!
Desperate regards.
I have a 600 VA Toroid (Antek) wired for 220V on the primaries (I'm in Europe).
I have buildt a soft-start circuit that's supposed to be good for up to 1kVA.
I've decreased the shunt resistance from 40 Ohm to 33 Ohm and beefed up the wattage rating quite well. (from 5 to 17W resistors, four off)
Now, this is what happens:
I throw the switch and when the relay closes and bypasses the resistors after approx 1 second, the 10A glass fuses go with a spectacular green flash.
The resistors get quite nice and hot, so current is being drawn before the relay closes.
To the best of my understanding, this shouldn't rerally happen. What is wrong??
One thing though, I have wrapped the outer diameter of the toroid with a strip of permalloy, or mu-metal in the hope of reducing any stray fields further.
Is it a possibility that this could somehow mess up the magnetic circuit of the transformer and thus cause problems on start-up?
Any inteligent advice would be much appreciated, I'm really at loose ends here!!
Desperate regards.
Wrapped.. well, how to clarify this better... I'll take a picture.. just to make sure everybody is on the same page.
It is not as if the entire toroid is wrapped up completely, I just made a flat strip which I then looped round the outer diameter of the Toroid.
Would this cause a shorted turn?? If so, would I brake the turn if the loop is not making a closed electric/ mechanical contact??
Yes, from the frantic reading up I've done, it seems that 1 second is more than needed, but I figured that this was OK after all provided the resistors didn't thermally overload. This is a design i found in an ELEKTOR magazine, and I guess their stuff is mostly sound..
It is not as if the entire toroid is wrapped up completely, I just made a flat strip which I then looped round the outer diameter of the Toroid.
Would this cause a shorted turn?? If so, would I brake the turn if the loop is not making a closed electric/ mechanical contact??
Yes, from the frantic reading up I've done, it seems that 1 second is more than needed, but I figured that this was OK after all provided the resistors didn't thermally overload. This is a design i found in an ELEKTOR magazine, and I guess their stuff is mostly sound..
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As I did some snooping around on Toroids and shielding, I came across this on the Plitron home page:
Magnetic Shield
Toroidal transformers radiate about 1/10 the magnetic field of standard EI transformers, but to further attenuate stray magnetic fields in very sensitive applications, such as in close proximity to a CRT, an additional magnetic shield may be called for. Magnetic shields consist of multiple layers of grain oriented silicon steel, or a high nickel content alloy, such as MU-Metal, Magnifier 79, etc.., laminated between insulation. Wrapped around circumference of transformer. Disks are also available for use within potted assemblies.
As far as I can see, this is what I've atempted, but perhaps there was some critical detail I got wrong??
Magnetic Shield
Toroidal transformers radiate about 1/10 the magnetic field of standard EI transformers, but to further attenuate stray magnetic fields in very sensitive applications, such as in close proximity to a CRT, an additional magnetic shield may be called for. Magnetic shields consist of multiple layers of grain oriented silicon steel, or a high nickel content alloy, such as MU-Metal, Magnifier 79, etc.., laminated between insulation. Wrapped around circumference of transformer. Disks are also available for use within potted assemblies.
As far as I can see, this is what I've atempted, but perhaps there was some critical detail I got wrong??
Well,
The area of uncertainty here is wether or not I've actually made a shorted turn and the effects thereof.. could be that this sort of shielding requires that the ends of the metal strip which is wrapped arround the toroid circumference, are insulated..
I could of course verify this by removing the permalloy from my Transformer, but it would be a bit messy, not to mention getting it back in place if no difference was made, hence some second opinions are welcome!
The area of uncertainty here is wether or not I've actually made a shorted turn and the effects thereof.. could be that this sort of shielding requires that the ends of the metal strip which is wrapped arround the toroid circumference, are insulated..
I could of course verify this by removing the permalloy from my Transformer, but it would be a bit messy, not to mention getting it back in place if no difference was made, hence some second opinions are welcome!
Elbert, it could be that the fuse blows because you have a (near) short on the secondary. With the series resistor, the current is limited so a secondary short isn't 'seen'.
Try with the secondary disconnected. If the fuse holds, try with only the rectifier and caps, without the amp. At some point it will be clear where the problem is. It's very unlikely that the inrush current circuit is the cause.
jd
Try with the secondary disconnected. If the fuse holds, try with only the rectifier and caps, without the amp. At some point it will be clear where the problem is. It's very unlikely that the inrush current circuit is the cause.
jd
A few things. First, Janneman is correct, never test everything at once, do it in stages. Second, you should be using a bulb tester and then you won't be blowing fuses as often, and risking your equipment, etc. Lastly, the toroid in the photo is not mounted. Is that how you are testing? The reason I ask is mounting mistakes can lead to a shorted turn. A shorted turn is not when you wrap a conductor around the outside of the transformer, it's when you wrap a conductor through the middle and around the outside, connecting the ends to make a loop.
Janneman,
I've allready worked through that route, so unfortunately, I am running out of options here, hence my slight desperation.
I have allso ran and checked the soft-start circuit and it doesnt do anything it is not supposed to, ie cause a short circuit in stead of bypassing the resistors etc..
Redshift,
The picture doesn't show the transformer as it is installed, but close to, the only thing effectively missing, is the mounting bolt and the steel plate holding it in place.
That was allso my understanding, that a shorted turn would have to be something going through the centre of the Toroid, i.e. I've reads that the bolt must not contact the chassis in both ends, etc.. There arehowever no such conditions like that present in my set-up..
I've allready worked through that route, so unfortunately, I am running out of options here, hence my slight desperation.
I have allso ran and checked the soft-start circuit and it doesnt do anything it is not supposed to, ie cause a short circuit in stead of bypassing the resistors etc..
Redshift,
The picture doesn't show the transformer as it is installed, but close to, the only thing effectively missing, is the mounting bolt and the steel plate holding it in place.
That was allso my understanding, that a shorted turn would have to be something going through the centre of the Toroid, i.e. I've reads that the bolt must not contact the chassis in both ends, etc.. There arehowever no such conditions like that present in my set-up..
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Do you mean that the fuse blows without anything connected to the secondary?
BTW Does the mounting plate touch the screen winding & the screen winding touch the chassis bottom...?
jd
Yepp, the fues blows just as happily with the secondaries disconnected or connected.
With respect to screen winding, I'm not quite sure what that is, What I can confirm is that there are no windings on the transformers which are unisulated and/ or in electrical contact with anything if that's what you mean..
There is no contact either with the permalloy shielding I added and the steel mounting plate either.
With respect to screen winding, I'm not quite sure what that is, What I can confirm is that there are no windings on the transformers which are unisulated and/ or in electrical contact with anything if that's what you mean..
There is no contact either with the permalloy shielding I added and the steel mounting plate either.
Check the DCR of the primary and the secondary windings...
Also check to see that the edge of the chassis is not cutting into the windings and shorting something... I'd put some washers or other spacer material between the epoxy of the center of the toroid and the chassis so that the xfmr "flies" a little above the aluminum... or steel... you said this is ok.
A shorted turn would consist of anything that goes completely around the transformer and through the center (or connected to the bolt).
Removing the MuMetal shield and retesting would not be a bad idea.
I don't think it OUGHT to cause excessive current draw, but perhaps it is causing some sort of inter-turn coupling that is undesirable...
The other thing is you can run it for a while WITH the resistor in series and try to see what the current draw works out to be... with nothing on the secondary it should be rather low...
_-_-bear
Also check to see that the edge of the chassis is not cutting into the windings and shorting something... I'd put some washers or other spacer material between the epoxy of the center of the toroid and the chassis so that the xfmr "flies" a little above the aluminum... or steel... you said this is ok.
A shorted turn would consist of anything that goes completely around the transformer and through the center (or connected to the bolt).
Removing the MuMetal shield and retesting would not be a bad idea.
I don't think it OUGHT to cause excessive current draw, but perhaps it is causing some sort of inter-turn coupling that is undesirable...
The other thing is you can run it for a while WITH the resistor in series and try to see what the current draw works out to be... with nothing on the secondary it should be rather low...
_-_-bear
DCR of the secondary windings is pretty low, 0,8 Ohm according to my digital multimeter.. but then I don't know if this is the correct value or not. I get the same value on both secondary windings by the way.
Considering how hot the soft-start resistors got, I'm not sure that its a good idea to have a resistor connected to the primary for too long..
On the chassis aluminium sheet profile where the toroid is bolted, I allso stuck some permallloy for good measures..
Heck, the only option left now is to remove the permalloy strip and remove the transformer completely from the chassis just to elliminate this as factors...
but if that doesn't help???!
Considering how hot the soft-start resistors got, I'm not sure that its a good idea to have a resistor connected to the primary for too long..
On the chassis aluminium sheet profile where the toroid is bolted, I allso stuck some permallloy for good measures..
Heck, the only option left now is to remove the permalloy strip and remove the transformer completely from the chassis just to elliminate this as factors...
but if that doesn't help???!
Show us the entire set up that fails, its ok if its just a test setup and is messy, we will understand. We need to see the toroid and center bolt etc...
If you have a mounting bolt and metallic circular disc, and the disc touches the metallic shielding around the outer edge, you have a shorted turn. The bolt through the middle in conjunction with the shielding and case form 1 turn that is shorted.
Did you try it without the metallic shielding? without the center bolt?
I don't think its the soft start, I think you have a shorted turn or the primaries/ secondaries are connected to cause a short.
Are the voltage on the secondaries correct right before it blows up?
Once this happened to me, turned out that there was a small burr on the bottom of the chassis that rubbed off the lacquor insulation on one of the transformer turns, shorting it to the case. I repaired it by coating the wire with epoxy and covering the xformer with black electrical tape.
Do you measure short circuit between the case and any primaries or secondaries?
If you have a mounting bolt and metallic circular disc, and the disc touches the metallic shielding around the outer edge, you have a shorted turn. The bolt through the middle in conjunction with the shielding and case form 1 turn that is shorted.
Did you try it without the metallic shielding? without the center bolt?
I don't think its the soft start, I think you have a shorted turn or the primaries/ secondaries are connected to cause a short.
Are the voltage on the secondaries correct right before it blows up?
Once this happened to me, turned out that there was a small burr on the bottom of the chassis that rubbed off the lacquor insulation on one of the transformer turns, shorting it to the case. I repaired it by coating the wire with epoxy and covering the xformer with black electrical tape.
Do you measure short circuit between the case and any primaries or secondaries?
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Well, I tried again, removed all the shielding, lifted the trafo off the chassis and placed it on a wooden table (no short to chassis possible), just the bare trafo hooked up to the soft start circuit.. BANG!
This time the fuse blew because the relay on the soft start was stuck in the bypass position, so now I have to fix that damn thing as well before I can get any further testing done...
This is really getting on my nerves...
This time the fuse blew because the relay on the soft start was stuck in the bypass position, so now I have to fix that damn thing as well before I can get any further testing done...
This is really getting on my nerves...
Did you connect red primary to black primary, and then send AC to the other red/black?
Data Sheet
Looks like you have one of their older models with multiple secondaries so not quite the right data sheet/ looks like your yellow/brown wires are shorted but I cannot really see.
Its probably something that is easy to figure out if you post a complete birds-eye pic of everything with the relay pin outs shown.
Data Sheet
Looks like you have one of their older models with multiple secondaries so not quite the right data sheet/ looks like your yellow/brown wires are shorted but I cannot really see.
Its probably something that is easy to figure out if you post a complete birds-eye pic of everything with the relay pin outs shown.
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