I connected a light bulb to the circuit. I tried to wire it in any possible way but the light has the same brightness.
I still cant measure ac current ( i have to buy a good enough meter ).
There is one thing i noticed.
My primary coil is at the bottom and the extension is sitting on the top.
Connecting L and N either pushes the coil up or pulls it down depending on how i connect them together. That would be the magnetic flux i assume. Is there a right and wrong way of connecting it? Does the flux has to flow in one direction or it doesn't matter at all?!
View attachment 99134

View attachment 99135

View attachment 99136

If it is getting hot while under test, I suggest you remove the kindling and rags from under it. Get a piece of ceramic time or a clay pot for it.

 

And after 5 min the transformer turns off as it gets too hot!!
Im starting to think this wont work as power supply...
Anyone has any ideas? I would need something that could power about 5-6 LED each rated 100w ( would use it only on 75w each ) 32v and about 2.5amps.
I do not want to buy one i want to make my own!! But it has to be relatively simple.
Anything i could salvage from a tv or dvd player or something???

 

Bolt Rectifier to a heatsink with thermal paste...

 

In the absence of a proper AC ammeter, you can do this test, which is appropriate anyway since it's the excessive heating that you care about.

Wire the extra turns in series with the primary in either possible way. Starting with the transformer at room temperature, connect grid voltage to the setup and see how hot it gets in some fixed period of time.

Now rewire the extra turns in the other configuration and do the heating test again. Does it get less or more hot in the same time? You want the configuration where it gets less hot.

I pulled a 50 VA Transformer out of my junk box. It's a 120 VAC in, and 12.6 VAC @ 4A out. I measured the primary current when it's powered up but with no load. I then connected the 12 volt secondary in series with the primary in both possible configurations and measured the primary current with no load. Here are the results:

Config 1 .064 amps
Normal .0914 amps
Config2 .142 amps

The two cases, Config 1 and Config 2 would correspond to your two configurations. Notice that the current is about double with Config 2 compared to Config 1. Of course, of these two possible configurations of your extra winding, one of them is worse than the original transformer without the extra winding turns. That is the one you don't want!

Looking at one of your pictures, it looks like you might have around 100 turns on the primary. Is that about right, and did you wind about 10 turns on that extra winding?

I suspect you don't have an oscilloscope, but just for grins, here's what the primary voltage and current in my transformer look like on the scope, with power analysis software showing the true power and reactive power. You can see the current is highly distorted by the saturation of the core. The green waveform is the grid voltage, which is more or less a sine wave. The purple waveform is the primary current, which would also be a sine wave if the core didn't saturate. This first image shows the case where the extra winding is connected in such a way as to reduce the saturation. The power dissipation in the core is 4.17 watts:



The next image shows the primary when the extra winding is connected in such a way as to increase the core saturation. The core dissipation is now 7.82 watts:



It wouldn't be unreasonable to expect that your transformer's core dissipation would be substantially less with the proper connection of the extra winding.

You can use even more turns on the extra winding to increase this effect--lowering the core loss with no load (and with load also). It's just a question of whether you can get the extra primary turns in the secondary window along with the actual secondary turns you need.

 

In the absence of a proper AC ammeter, you can do this test, which is appropriate anyway since it's the excessive heating that you care about.

Wire the extra turns in series with the primary in either possible way. Starting with the transformer at room temperature, connect grid voltage to the setup and see how hot it gets in some fixed period of time.

Now rewire the extra turns in the other configuration and do the heating test again. Does it get less or more hot in the same time? You want the configuration where it gets less hot.

I pulled a 50 VA Transformer out of my junk box. It's a 120 VAC in, and 12.6 VAC @ 4A out. I measured the primary current when it's powered up but with no load. I then connected the 12 volt secondary in series with the primary in both possible configurations and measured the primary current with no load. Here are the results:

Config 1 .064 amps
Normal .0914 amps
Config2 .142 amps

The two cases, Config 1 and Config 2 would correspond to your two configurations. Notice that the current is about double with Config 2 compared to Config 1. Of course, of these two possible configurations of your extra winding, one of them is worse than the original transformer without the extra winding turns. That is the one you don't want!

Looking at one of your pictures, it looks like you might have around 100 turns on the primary. Is that about right, and did you wind about 10 turns on that extra winding?

I suspect you don't have an oscilloscope, but just for grins, here's what the primary voltage and current in my transformer look like on the scope, with power analysis software showing the true power and reactive power. You can see the current is highly distorted by the saturation of the core. The green waveform is the grid voltage, which is more or less a sine wave. The purple waveform is the primary current, which would also be a sine wave if the core didn't saturate. This first image shows the case where the extra winding is connected in such a way as to reduce the saturation. The power dissipation in the core is 4.17 watts:

View attachment 99145

The next image shows the primary when the extra winding is connected in such a way as to increase the core saturation. The core dissipation is now 7.82 watts:

View attachment 99147

It wouldn't be unreasonable to expect that your transformer's core dissipation would be substantially less with the proper connection of the extra winding.

You can use even more turns on the extra winding to increase this effect--lowering the core loss with no load (and with load also). It's just a question of whether you can get the extra primary turns in the secondary window along with the actual secondary turns you need.

Wow thanks. That was a very detailed message.
My primary has about 120 turns so i added an extra 15. I tried to wire it in both directions but there is not much difference.
Do ypu have overheating issues as well? Or its just me?
I will get back to it tomorrow and redo the whole lot just in case i missed something.
You said i should wire the extension in a single layer. I could add more with a double layer! Would that help? Extra 20-25 turns?

 

Wow thanks. That was a very detailed message.
My primary has about 120 turns so i added an extra 15. I tried to wire it in both directions but there is not much difference.
Do ypu have overheating issues as well? Or its just me?
I will get back to it tomorrow and redo the whole lot just in case i missed something.
You said i should wire the extension in a single layer. I could add more with a double layer! Would that help? Extra 20-25 turns?

The transformer I tested with is not a MOT; just a standard transformer. It hardly gets warm when there's no load, but MOTs are known to get hot even when not loaded. It's because they run the core well into saturation.

The only reason for winding the extension in a single layer is to leave as much room as possible for your real secondary. If you have the room, you can certainly add more turns to the extension.

What the extension is doing is either increasing or decreasing how far into saturation the transformer is pushed. Further into saturation means more core loss and hotter operation; less far into saturation means cooler operation.

Of the two ways to wire the extension in series, the behavior you will get is this. Wired one way, the transformer will get hotter when powered up unloaded. Wired the other way, it will get less hot than without the extension at all.

The more turns in the extension, those two behaviors will be increased. The "wrong" way of connecting the extension will cause the transformer to get even hotter. The "right" way will cause it to get even less hot.

Without an AC ammeter you can determine the "right" way to wire with a heat test as I described in the previous post.

 

The transformer I tested with is not a MOT; just a standard transformer. It hardly gets warm when there's no load, but MOTs are known to get hot even when not loaded. It's because they run the core well into saturation.

The only reason for winding the extension in a single layer is to leave as much room as possible for your real secondary. If you have the room, you can certainly add more turns to the extension.

What the extension is doing is either increasing or decreasing how far into saturation the transformer is pushed. Further into saturation means more core loss and hotter operation; less far into saturation means cooler operation.

Of the two ways to wire the extension in series, the behavior you will get is this. Wired one way, the transformer will get hotter when powered up unloaded. Wired the other way, it will get less hot than without the extension at all.

The more turns in the extension, those two behaviors will be increased. The "wrong" way of connecting the extension will cause the transformer to get even hotter. The "right" way will cause it to get even less hot.

Without an AC ammeter you can determine the "right" way to wire with a heat test as I described in the previous post.

First of all a BIG thank you for your help! I managed to pull out another primary from a mot that was pretty much the same size as the other one so i wired them together and i put a new secondary in. So far no heating issues at all!! In fack it stays ice cold.
Im getting all the voltage i want but im getting very close and i think if i start to unwind the second primary i should reach my target voltage.

I do have one question! With two primary does it become less efficient or not?
The primary goal is to power my led lights. All together it would need about 400-450w power.
I will use a bridge rectifier and dc-dc boost converters.
This power supply should run 3 boost converters in parallel.
Is there any flaws in my plan???

 

Almost forgot the pictures

 

Wait, you are hoping for 350 - 400 watts of power out of a MOT with a 35V secondary? Assuming an RMS voltage that is 10-13 amps. What gauge wire is on that secondary? Google awg ampacity and check

What size power supply filter capacitors do you plan to use with that setup?

This is all on one MOT, correct?

 

Wait, you are hoping for 350 - 400 watts of power out of a MOT with a 35V secondary? Assuming an RMS voltage that is 10-13 amps. What gauge wire is on that secondary? Google awg ampacity and check

What size power supply filter capacitors do you plan to use with that setup?

This is all on one MOT, correct?

Well yes and no. Im hoping for around 400w. Im using 3mm wire and its rated 10amps.
The way i want to do this is connect 3 boost converters to the power supply and each converter to 2 led lights wired in series.
Capacitor is something i have to look at but the converter it self has capacitors as well.

 

If i run into overheating issues in the secondary again coupd i just use a bigger wire and weld two mot together something like this:

 

First of all a BIG thank you for your help! I managed to pull out another primary from a mot that was pretty much the same size as the other one so i wired them together and i put a new secondary in. So far no heating issues at all!! In fack it stays ice cold.
Im getting all the voltage i want but im getting very close and i think if i start to unwind the second primary i should reach my target voltage.

I do have one question! With two primary does it become less efficient or not?
The primary goal is to power my led lights. All together it would need about 400-450w power.
I will use a bridge rectifier and dc-dc boost converters.
This power supply should run 3 boost converters in parallel.
Is there any flaws in my plan???

Grid frequency transformers have two main sources of loss; core loss and copper loss. Increasing the resistance of the primary, which is what happens with two primaries, increases the copper loss, BUT, in your case, it greatly decreases the core loss. I suspect that the tradeoff is in favor of slightly more copper loss.

I would think you should be able to remove about half the turns from the extra primary without seeing much increase in how hot the core gets when unloaded. You should certainly be able to start removing turns from the second primary as a way to increase the seondary voltage.

 

I noticed someone gave you a schematic. That's great. Just a couple things I would say regarding that schematic, the + and - are backwards on the FWR (Full Wave Rectifier), but that's not highly important, from your photographs it appears you know which is the positive out and which are the AC in. The other thing about that schematic - and it's perfectly good the way it's drawn, but the artist shows the resistors between the LED's and ground. Like I said, that's perfectly fine. However, I'd put them on the positive input side just in case of a stray short circuit during testing. The resistors will help protect your power supply. And with a shorted supply, the LED's are in no danger.

As far as Ohm's Law goes, yeah, I could give you even more numbers. You don't need any of that. So I decided I'd draw a more picto-graphic representation of what I think you may want to build as far as the circuitry goes. Remember, in my drawing, the red lines are the positive leg. And notice the capacitors are in parallel. Two caps in parallel adds their values together. Two caps in series (assuming the same value) cuts the value in half.

Also, I neglected to represent the 240 VAC input side of the transformer; just the 32 volt output side.

Hope this helps.

 

First, let me say this to EVERYBODY who may disagree with me, but when you took the MOT apart in the first place, weren't there shunt bars in between the original primary and original secondary? I DO NOT KNOW TRANSFORMERS as well as others obviously do, but don't those shunts limit the amount of current passing from one coil to the other (current in the form of magnetic coupling)? Maybe you need to install the shunts. Keep in mind, I'm guessing here, and I'm sure that there's a lot of others who may be incensed that I'd be here GUESSING, but I think it's worth a consider.

I remember many years ago I was installing a replacement transformer in an emergency lighting system. The transformers we were installing kept burning out FAST. They did not have shunts between the primary and secondary. At least I think I remember it that way; that was back in 1982. So it's been a while.

 

One last comment: Did you say you're running this from a 240 VAC source? Is that the same rating as the transformer was originally intended to operate on? If you're using a transformer who's primary was designed to operate on 120 VAC and you're powering it from 240 VAC - Forgive me if I'm wrong, but could that be the reason why you're experiencing such overheating issues?

Also, did I read that you installed a second "Primary" (in effect doubling the number of primary turns) into your system? And you have to (probably) double the number of turns in your home made secondary; NO?

Check the resistance of a single primary. Divide the voltage by the resistance you measure. That will give you SOME idea of how much current you're drawing. I'm not good with inductance, so I can't be sure, but if you have low resistance and high voltage then you have high amperage. Amps times Volts equal Watts. If your primary is running around 300 watts, I'd imagine that's got to get pretty darn hot. WITH or WITHOUT a load. Has anyone asked your primary voltage? Has anyone asked what your primary was originally designed for? If you're using a 120 primary on a 240 line - I'd be surprised you haven't burned the house down yet.

Like I said, I'm not the expert on this subject. Sometimes the dumbest question can lead to a bright solution.

 

Yep, correct the transformer was originally on 120V ac, now its 240V, so the primary needs twice as many turns....Try 240 turns...

 

Yep, correct the transformer was originally on 120V ac, now its 240V, so the primary needs twice as many turns....Try 240 turns...

I looked back through the entire thread, and I don't see anywhere Gabriell told us that. If so, this is not good.

Gabriell, you're in Australia. Aren't you getting your MOTs from ovens sold in Australia?

 

I looked back through the entire thread, and I don't see anywhere Gabriell told us that. If so, this is not good.

Gabriell, you're in Australia. Aren't you getting your MOTs from ovens sold in Australia?

So first of all yes im in Australia. The mot ( obviously ) is 240v as we dont have 120v! With two primary i dont have overheating issues anymore. I just need a thicker wire for my secondary now to handle all the amps.
I really dont think i need the shunt in the mot but i could be wrong.

As for the leds, i prefer to connect them in series so i darw less current through them. I noticed in my previous tests if i apply full amps (32v and around 4-5amps ) the first led strats to smoke. If i use them in series i can apply full amps and full voltage ( 64v ) and nonproblem at all!

I will rewire the secondary today and post some pictures of the pricess!!

 

Ok so i replaced my secondary with 2.5mm earth wire. I think its rated something like 50amps. Did a testrun and it only gets a bit warm so that great. And i still have some more room if i want to add more.
As you see on the picture i put two E cores together. So far its working fine but im waiting for my watt meter and ac current meter to arrive so i can test everything.
Here is a pic


Now the only thing is my original issue! That bloody rectifier gets really hot even on the heatsink


This the backup one but i tried both and there is no difference.

At this stage im not using resistors around the leds cause im using a boost converter which regulates volt and amps.
Do i need to use resistors or the converter is enough?
And why would my rectifier overheat again? Am i shorting something out?
Some pictures of my setup!

The rectifier is connected to 4 capacitors each 50v 2200uF in parallel. Then 2 boost converters in parallel as well. Each converter is connected to 2 led wired in series.
Im pulling about 16amps at the moment. I think its beacuse of the converters. I may need to leave them out of the game and go through resistors straight to the led and that should pull down my amps to about 5-6.

 

Ok, could you explain how these capacitors are connected? It appears to me that all leads of all caps are soldered together in one mass. Are my eyes seeing correctly?