You are using thick vinyl insulated wire as your secondary and it appears to be losely wrapped on the core. You should be using enabled magnet wire wrapped reasonably close to the core in a nice orderly fashion. The copper is also a heat sink to the core - and the rest of the magnet wire. The vinyl insulation is thermally insulating the core and, the loose wrapping means you have poor magnetic coupling and, therefore, low efficiency and heat. At least that is where I would look.The diodes have about a 1 volt forward drop per leg. At 4 amps DC thats about 8 watts. You have it on thermally insulating cloth. It can run pretty hot, but it wants a heat sink. If you builld this into metal chassis, bolting it to that will be plenty.
So i took out my secondary coil and and the primary gets hot when i apply voltage.What happens if you have the secondary of the transformer disconnected from any load an apply power to the primary? Does the transformer still get hot?
You are using thick vinyl insulated wire as your secondary and it appears to be losely wrapped on the core. You should be using enabled magnet wire wrapped reasonably close to the core in a nice orderly fashion. The copper is also a heat sink to the core - and the rest of the magnet wire. The vinyl insulation is thermally insulating the core and, the loose wrapping means you have poor magnetic coupling and, therefore, low efficiency and heat. At least that is where I would look.
The core it self does not heat up its the primary coil that gets hot and then trasferes the heat to the core. I was checking the core and it gets warmer only after my primary is hot.@Gabriell
The each of the silicon-steel plates need to be electrically insulated. Once they all start conducting with each other, you will get Eddie currents and heating of the transformer's core (known as magnetic losses). Note, this only concerns the conduction between plates (they were insulated with an oxide coating or laquer at the factory). Scratches, rust or even just age can cause the conductivity. Eddie currents can heat the core even with no short from a winding to the core.
So, the primary copper is heating before the plates near the primary? Then you must have a problem with the copper or it's insulation on the primary.The core it self does not heat up its the primary coil that gets hot and then trasferes the heat to the core. I was checking the core and it gets warmer only after my primary is hot.
Yes its definitely not the core. And the primary looks good. No cracks or scratches. I was very carful when i removed it from the core.So, the primary copper is heating before the plates near the primary? Then you must have a problem with the copper or it's insulation on the primary.
The Eddie currents are most intense on the plates close to the winding.
Ok, now I see the vice. Tell us exactly how you deconstructed the old one and built the new one. Sketches would be helpful.Yes its definitely not the core. And the primary looks good. No cracks or scratches. I was very carful when i removed it from the core.
Does it matter where i put the primary? Top or bottom of the core and upside down or not?
Sorry but i cant upload a video. I do have some pictures hope it helps.Ok, now I see the vice. Tell us exactly how you deconstructed the old one and built the new one. Sketches would be helpful.
If you cut the steel plates, you have conductivity between plates.
Or,If you simply placed an iron core within the core of another transformer, and rely on induction to couple the magnetic flux in the primary to the core of the secondary - you likely have an issue.
Please explain your experiment. A video of you taking it apart would be highly informative.
I know this is what people say. But in reality it doesn't make sense to me. Any of the MOT's I've seen have the I and E lamination's welded together. And most induction motors do the same to the stator lamination's, a line of weld down one side. Wouldn't that short one all lamination's together?@Gabriell
The each of the silicon-steel plates need to be electrically insulated. Once they all start conducting with each other, you will get Eddie currents and heating of the transformer's core (known as magnetic losses). Note, this only concerns the conduction between plates (they were insulated with an oxide coating or laquer at the factory). Scratches, rust or even just age can cause the conductivity. Eddie currents can heat the core even with no short from a winding to the core.
Yes, I guess it would. I hope the manufacturing guys are talking to the design team. It may be that the magnetic flux closest to the core is key? Doesn't make sense to me why they would bother insulating the plates. They spend a good deal of time and money on the oxide costings. 30 to 60 cycles of (magnesium alkoxide/alcohol dip, dry, steam, dry, repeat). I guess the lack of conductivity closest to the core is key? No idea why they would weld it other than, as you said, losses are ok since the usage cycle is low and nobody wants the transformer hum noise of the unwelded plates? Who knows.I know this is what people say. But in reality it doesn't make sense to me. Any of the MOT's I've seen have the I and E lamination's welded together. And most induction motors do the same to the stator lamination's, a line of weld down one side. Wouldn't that short one all lamination's together?
MOTs are designed for intermittent duty. Low cost design for that purpose results in a transformer that is running its core well into saturation. This means that the core will heat up a lot even when the transformer is not supplying a secondary load.So i just salvaged 2 more transformers. Both really good condition. I have not touched the coils nor the core. No scratches or cracks. I connected it to the power and again it gets hot. I left both on for about 5 min. The core and the primary coil is hot but i can touch it. But just barely.
Are they supposed to run hot? Can i keep using it?
I want to make power supply out of them and they should stay on for about 10-12 hours per day. Will that damage the transformer?
MOTs are designed for intermittent duty. Low cost design for that purpose results in a transformer that is running its core well into saturation. This means that the core will heat up a lot even when the transformer is not supplying a secondary load.
It looks to me like you have extra room on the secondary for more copper. The primary is wound with well defined layers; count the turns in one layer and multiply by the number of layers to get the total primary turns. If you add about 10% more turns to the primary the maximum flux density will decrease and the core and primary won't get so hot. Wind that many turns in the secondary space (in a single layer if possible), with magnet wire (the kind you're using in the latest secondary) of the same diameter (or nearly so) as the existing primary. Wire those extra turns in series with the existing primary with the proper phase. The heating of the core and primary winding should decrease substantially.
To determine the proper phasing (there are two different ways you can connect the additional winding in series with the existing primary) connect an incandescent light bulb in series with the grid voltage before connecting to this new arrangement. The light bulb will light up brighter with the incorrect connection of the additional primary turns. Leave it connected such that the light bulb is least bright. Then remove the light bulb from the circuit and run the unloaded transformer for a while to see if it heats up substantially less.
It would be good to measure the unloaded primary current before and after you add extra turns in series with the primary. If you do this, report to the forum the before and after values.
Before you add a secondary to this new arrangement, wrap some tape around the extra primary turns to insulate them from the secondary. This will work out best if you wind those extra primary turns carefully in a nice single layer.
You're measuring AC current on a DC range. I can't see the connetions to the meter very well. Back off with the camera so I can see the whole meter and where the leads are connected.So i added about 15 turns to primary from a spare coil i had ( both the same size ) but the heating issues remains. I didnt put in the secondary this time.
One thing i dont understand!
I was trying to measure the current and it keeps going up and down between -0.06amps and +0.06amps
How is that possible?
I didnt do the light bulb trick as i dont have one around me but i will hint one down.You're measuring AC current on a DC range. I can't see the connetions to the meter very well. Back off with the camera so I can see the whole meter and where the leads are connected.
Did you do the trick with the light bulb? Can you measure the current (and it must be the AC current) with both possible ways to connect the extra turns in series with the primary?
I'm returning to the big city, so I'll be on the road for a few hours. I'll check in later.
You're measuring AC current on a DC range. I can't see the connetions to the meter very well. Back off with the camera so I can see the whole meter and where the leads are connected.
Did you do the trick with the light bulb? Can you measure the current (and it must be the AC current) with both possible ways to connect the extra turns in series with the primary?
I'm returning to the big city, so I'll be on the road for a few hours. I'll check in later.
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by Jake Hertz
by Jake Hertz
by Jake Hertz
by Jake Hertz