cascading ct, different cores vs. double secondaries / Tesla Coils / Forums

Forums

4hv.org :: Forums :: Tesla Coils

« Previous topic | Next topic »

cascading ct, different cores vs. double secondaries

Move Thread

LAN_403

lightlinked

Tue Sept 15 2009, 02:11PM

Registered Member #2087 Joined: Tue Apr 21 2009, 08:32AM
Location:
Posts: 115

Is it okay to use two different toroids in a cascaded current transformer? Or perhaps use two of the same but on the second ct, have two secondaries wound. ie. one is going to the feedback and the other to the current limiter.

How does the single turn work out? Do I just pass the primary wire through the center or do I need to form a loop once or a U shape?

One more

I was thinking of using these yellow toroids I have on hand which I think were by Magnetics and are supposed to be for 10 - 50 mhz with a permeability of 8. is that fine?

you might call these shortcuts

GeordieBoy

Tue Sept 15 2009, 07:02PM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

A Current Transformer for what frequency?

> Is it okay to use two different toroids in a cascaded current transformer?

Yes. Provided they are both suitable materials.

> Or perhaps use two of the same but on the second ct, have two secondaries wound. ie. one is going to the feedback and the other to the current limiter.

No. Only one secondary is allowed in a CT.

> How does the single turn work out? Do I just pass the primary wire through the center or do I need to form a loop once or a U shape?

Once through the hole, that's all that is required to make a "turn".

> One more I was thinking of using these yellow toroids I have on hand which I think were by Magnetics and are supposed to be for 10 - 50 mhz with a permeability of 8. is that fine?

Probably no. They sound like they are either Type -26 Iron powder or Type -6 Iron powder. Both of which are unsuitable for current transformers. You want a high permeability Mn/Zn ferrite toroid for CTs.

-Richie,

Wolfram

Thu Sept 17 2009, 08:02AM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

If this is for the Steve Ward DRSSTC driver, there is a simple way to use it with a single CT for both feedback and overcurrent sensing. I will make a thread about it in some time, but if you're interested in some schematics, just send me a PM.

Anders M.

lightlinked

Thu Sept 17 2009, 09:48AM

Registered Member #2087 Joined: Tue Apr 21 2009, 08:32AM
Location:
Posts: 115

yeah i'm pretty much using Steve Ward's design, at least the logic part. could i just have a diode separating the signal from the OCD bridge to the feedback input? like so (cue schematic)

Wolfram

Thu Sept 17 2009, 01:35PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

Not going to work very well I think, with low primary currents, like at the start of the burst, there will hardly be any voltage developed across R2, certainly not enough to make IC2E switch. I'll try to get a good writeup of my scheme within the next few days.

Anders M.

lightlinked

Thu Sept 17 2009, 07:38PM

Registered Member #2087 Joined: Tue Apr 21 2009, 08:32AM
Location:
Posts: 115

cool, i'm looking forward to reading it
since we are on the subject of current transformers i'm trying to use a commercial ct, CSE187-L , to measure line current, random stuff you plug into the wall, how do i rectify the AC so i can use it with a DC panel meter? i've tried putting the burden after a bridge rectifier but it looks like it is still subject to the diode drop.
anyways it's 1:500 with a 50 ohm burden for 100 mv/amp
i've tried it with just the burden, no diodes and it outputs accurately

Steve Ward

Sun Sept 20 2009, 03:32PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

If you want to save on cores, you could use 1 CT to feed the other 2 "cascaded" ones.

As to your other low frequency CT: I think DC volt meters read the AVERAGE DC signal and not the RMS. So im not sure what you are after, but your method should have shown the average value, not peak or RMS.

lightlinked

Sun Sept 20 2009, 04:55PM

Registered Member #2087 Joined: Tue Apr 21 2009, 08:32AM
Location:
Posts: 115

when i tried the CT with the rectifier it only output around 7 mv for a 60 watt light bulb. i was trying it with a phase angle dimmer (uc controlled type, not analog) and when i took it to 50% the output was around 10 mv which seemed weird. then when i tried it with just the burden (ac output) it read much closer to 100 mv/amp with a "true rms" multimeter. what could be the issue? i thought that if the burden is after the rectifier the voltage is supposed to rise untill it overcomes the diode drop negating it. ideally i would like a nice fullwave rectified signal that i could sample with a micro controller without doing any half ADC reference voltage dc bias stuff. i should just get a kill a watt thingy

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob