ETD29 Winding Advice Needed

[Sandy]

Ok, just about to start my first coil job I have seen various ways of winding the coils on these cores, and looking for some hints why one way or the other. The Core is a TDK ETD-29 core with matching coil form.

The coil is for a 50kHz-60kHz dc to dc inverter (push pull topology) with 4 turns for each of the primary and 160 Turns of on the secondary.

Primary wire bundle is a twist of 6x22awg wires
Secondary wire is a single 28awg wire.

For this I think I'm winding the primary bifilar, and I think it will just fit across one layer on the coil form.

So the question is... Primary first, then secondary, or the reverse. And of course why so I might learn something at the same time.

Thanks for any tips!

Sandy

 

[Silvio]

Ok, just about to start my first coil job I have seen various ways of winding the coils on these cores, and looking for some hints why one way or the other. The Core is a TDK ETD-29 core with matching coil form.

The coil is for a 50kHz-60kHz dc to dc inverter (push pull topology) with 4 turns for each of the primary and 160 Turns of on the secondary.

Primary wire bundle is a twist of 6x22awg wires
Secondary wire is a single 28awg wire.

For this I think I'm winding the primary bifilar, and I think it will just fit across one layer on the coil form.

So the question is... Primary first, then secondary, or the reverse. And of course why so I might learn something at the same time.

Thanks for any tips!

Sandy

In your case due to the primary being a bit bulky I would rather put secondary windings first on the bobbin as it would sit neatly. The primary will come next and any bulges left will not matter as no more windings are going on the bobbin.

 

[Sandy]

Thanks Silvio,

I was hoping that was going to be the suggestion since it will be much easier to wind that way. I will give it a go and see how many tries it takes

Sandy
P.S. Video's are very helpful!

 

[Silvio]

You can take a look at some blogs that I posted on this site and take a good idea what to do and not to do. winding small transformers for smps is available on Youtube

 

[Sandy]

First coil done. The winder was really easy to use and the 30 rpm gear motor showed no signs of stalling even with heavy tension.

Need to figure out a better way to strip the insulation on the bundle of wires, it's pretty tough, not so happy about my solder job.

Questions coming as soon as I get off the phone with tiny screen

 

[MicrosiM]

You should have used Litz wire

 

[Silvio]

First coil done. The winder was really easy to use and the 30 rpm gear motor showed no signs of stalling even with heavy tension.

Need to figure out a better way to strip the insulation on the bundle of wires, it's pretty tough, not so happy about my solder job.

Questions coming as soon as I get off the phone with tiny screen

1) You could distribute your ends on more pins so windings will fit better or otherwise do not use the pins at all and leave the wire longer then fitting it directly to the pcb.

2) I suggest you put some sleeve at the ends

3) Stripping copper wire can be done by burning first with a lighter or small torch and then stripping with a sharp knife. It is best to unwind the bundle and heat strands separately. Some steel wool will help as well. You need to use some resin during soldering. Through cleaning of the copper is necessary for a good solder joint.
You can use also a solder pot for this job but not all hobbyists own one.
There are types of insulation on enameled copper wire. There is the type of enamel that with a hot soldering iron will burn off and one manage to solder it. The other type will have to be stripped physically.

4) Twisting more than 4 wires at a time tends to make an uneven bundle, see if 2 bundles with 3 wires each will fit better.

Regards Silvio

 

[Sandy]

You should have used Litz wire

Don't have any and it's a bit expensive. Will try some at some point but messing with the stuff I have on hand. The thinner strands would be much easier to deal with.

 

[Sandy]

1) You could distribute your ends on more pins so windings will fit better or otherwise do not use the pins at all and leave the wire longer then fitting it directly to the pcb.

2) I suggest you put some sleeve at the ends

3) Stripping copper wire can be done by burning first with a lighter or small torch and then stripping with a sharp knife. It is best to unwind the bundle and heat strands separately. Some steel wool will help as well. You need to use some resin during soldering. Through cleaning of the copper is necessary for a good solder joint.
You can use also a solder pot for this job but not all hobbyists own one.
There are types of insulation on enameled copper wire. There is the type of enamel that with a hot soldering iron will burn off and one manage to solder it. The other type will have to be stripped physically.

4) Twisting more than 4 wires at a time tends to make an uneven bundle, see if 2 bundles with 3 wires each will fit better.

Regards Silvio

Thanks for the helpful advice. I did hit up the starting end with a torch, but I didn't do a good enough job cleaning things up as you can see I think the thickness of the primary may be overkill for my application, and on the next transformer will see about going down to the next smaller wire size. Good idea on splitting the wires across 2 pins!

The windings were not all that bad from the thick primary, it looks worse due to the not so smooth tape job, and since it was the outer most layer it might be ok, and a thinner gauge bundle will also help that I'm thinking.

Now need to get some time on the PCB software and draw up the schematic and a test board.

Thanks for all the feedback!

Sandy

 

[Silvio]

One thing you did not mention was the total power of the inverter you are building, perhaps we can help you in the wire size you need. You can tell us if its for intermittent or continuous rating as this makes quite a difference in the wire size. There is also an option to use copper foil for the primary turns. This can take a lot of current for example for a 0.2mm foil with a width of 29mm can easily take around 18 amps for continuous rating and 25 to 30 amps intermittent rating.
Just to calculate current handling you have to find the cross sectional area of the wires or copper foil and multiply that by 3 for continuous rating and by 4 for 50-60% duty cycle. more than that you you have to add forced cooling to the trafo.

I hope that helps Silvio

 

[Sandy]

Silvio -

It's going to be used for an automotive ignition system (multi-spark CDI). The basic use of the the transformer will be for a DC-DC inverter to generate 350-500 volts (depending on transformer and a few other bits) to charge an approx 1-2uF capacitor that will be charged by the inverter. I don't know exactly how to compute power usage of the system but given the commercial systems (MSD) claims about 1 Amp / 1000 rpm typical. So at full till the inverter would be around 100 watts or less depending on how fast the engine is operating. In seeing the guts of one of the store bought units the transformer looked similar size or smaller then the ETD29 core. It's continuous duty but pulsed to charge the discharged capacitor. Hope that all makes sense. I'm likely to favor an ETD34 or ETD39 just because, but probably way over kill.

The parts list of how I'm thinking of doing it is a SG3525 driving an IX4340 driving a pair of ST6N60's. I have not yet had time to draw up the inverter part of the circuit as I'm very rusty on my PCB software, every year it gets more complex to use . Going to target the operating frequency at 50-60kHz depending on how the simple components work out on the SG3525, likely favor a bit higher frequency since common part values end up being in the 60kHz range. Trying to keep the inverter section pretty conventional. The transformer core material I used was for the first one was N97 as I recall.

Sandy

 

[Silvio]

Hi Sandy.
Regarding the transformer primary if using 60Khz then 0,5mm wire is suitable for your trafo as this can go to a maximum of 68Khz. Your current demand in the primary for 100w and using 12v will be around 8 amps. This will be divided between you two windings being a push pull topology. I hope I understood well when you mentioned the 1A value that I assumed in the secondary. I think that the wire being a bundle of six is just right for the primary.

If I where you I would make some measurements with a unit bought off the shelf and see the proper ratings. An ETD 29 can give around 240 watts at 100kHz in a forward converter mode, so at 60Khz will be somewhat less but will still cover easily 190 watts.

I once bought an electronic ignition from sparkright and was a DIY kit. It used to give around 360v in the coil primary. It had 2 x 180 volt zeners to stabilize the output. The output device was simply an SCR as the trigger was contact assisted. I had this electronic ignition fitted to my Fiat uno and it used to give a 2.5 inch spark with 2 or 3 sparks simultaneously having a violet color. It could give a good spark even with a pooped battery.

I suggest you try out a prototype first before designing the pcb as changes with components and values may not fit. Why not try things on a piece of matrix board first?

Regards Silvio

 

[Sandy]

Thanks Silvio,

Yes will likely proto up the inverter to see how it will work, but will create the schematic so I can at something to build from, then PCB maybe

Yes, the CDI type of ignitions can create a large spark, I have a MSD marketing/test display that has one of their ignitions on it, and it's pretty scary. The MSD (Multi-Spark-Discharge) fires the spark many times during the ignition cycle vs the more traditional CDI. I could just buy one but what fun would that be

As to the capability of the ETD 29 core I guessed that at 50-60kHz that max wattage would be in the 125w range, but hard to find information on it.

All helpful info, now to draw up the schematic...

Sandy