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Needing to make a suitable current transformer

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nzoomed

Sat Sept 05 2015, 10:21PM

Registered Member #54503 Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288

For my DRSSTC, im using the UD 2.7C in my system.

I see these transformers here

But i know most people make them easily enough, but finding the suitable toroids is the hard issue, but i see in the link provided that they sell the same toroids that i believe loneoceans uses for his coils.

But i cant find these on mouser, is anyone aware of the part numbers to look for on mouser? As im planning to place my order for the UD components soon, and would like to get everything in one go.

Also, what is the purpose of the second current transformer? It doesnt look like many people are using two of them.

TIA

Alex Yuan

Sun Sept 06 2015, 02:27AM

Registered Member #9614 Joined: Mon Jan 14 2013, 10:00PM
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Posts: 44

I've used these ferrite toroids with success, and they're only 81 cents each! Or 69.5 cents if you get 10 or more.

(DigiKey part number 495-3865-ND)

I've used these up to 900A.

Two current transformers are used for the current feedback and over current detection.

nzoomed

Sun Sept 06 2015, 03:26AM

Registered Member #54503 Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288

OK, they look good, and mouser stock them too, do you use two of these per transformer in a figure 8 pattern?

I would like to know more about winding and assembling these as i cant find much info and i see so many different configurations, some people add another two smaller toroids to one large toroid, but if i can get away with using just these, it would be great.

And im unsure what wire people use, is solid core wire like from cat5 cable the best to use?

Alex Yuan

Mon Sept 07 2015, 01:06AM

Registered Member #9614 Joined: Mon Jan 14 2013, 10:00PM
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for <1000A you can just use two of them. Wind 32 turns on each of the toroids with any wire gauge around 22-24. It's not important what you wind it with, as long as it fits well. Ethernet cable works great. When you've wound both toroids with 32 turns, take one and loop it once through the other toroid, and that gives you a turns ratio of 1:32:32 which is 1:1024. Then just feed the wires from the second toroid to your driver.

nzoomed

Mon Sept 07 2015, 10:20PM

Registered Member #54503 Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288

Alex Yuan wrote ...

for <1000A you can just use two of them. Wind 32 turns on each of the toroids with any wire gauge around 22-24. It's not important what you wind it with, as long as it fits well. Ethernet cable works great. When you've wound both toroids with 32 turns, take one and loop it once through the other toroid, and that gives you a turns ratio of 1:32:32 which is 1:1024. Then just feed the wires from the second toroid to your driver.

OK, that seems simple enough, i never realised they had two separate windings, i would have never thought that one turn around the second transformer would do anything!
I guess you have to solder the loop closed and keep the joint well insulated from touching the toroid.

Anyway its possible my coil will exceed 1000A, but i wont know until i have it running.

My main problem is now i may be expecting it to draw up to 20A from the mains!

Alex Yuan

Tue Sept 08 2015, 01:00AM

Registered Member #9614 Joined: Mon Jan 14 2013, 10:00PM
Location:
Posts: 44

yeah sorry for not clarifying, you loop it through once and solder it. I haven't had a problem with isolation, I just leave it open :P

My coils draw about 15A and I've been meaning to research a good PFC boost converter design to try out.

nzoomed

Tue Sept 08 2015, 07:23AM

Registered Member #54503 Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288

Thanks for your help.

I dont think my coil will exceed 1000A, but i could hit 800.
It will possibly draw 20A at the wall so i may need an electrician to wire up a 20A socket at the wall for this thing.

Getting excited, ive never built one of these before and im going for large!

Alex Yuan

Tue Sept 08 2015, 03:40PM

Registered Member #9614 Joined: Mon Jan 14 2013, 10:00PM
Location:
Posts: 44

in no way 1000A is a hard limit, just saying I'd use bigger current transformers in a larger coil

nzoomed

Tue Sept 08 2015, 09:39PM

Registered Member #54503 Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288

Alex Yuan wrote ...

in no way 1000A is a hard limit, just saying I'd use bigger current transformers in a larger coil

OK, i also believe that the comparator chip for the OCD on the universal driver board has a limit of 8-9v, so with larger coils this could be an issue, although Loneoceans talks about adding another resistor to address this.

Alex Yuan

Wed Sept 09 2015, 12:03AM

Registered Member #9614 Joined: Mon Jan 14 2013, 10:00PM
Location:
Posts: 44

You pick your burden resistor to make sure it will be in that range.

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