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Toroid Surgery

Posted: Tue Jan 16, 2018 11:08 am
by DICKEYBIRD
Got a little extra time today due to snow/late start time at the day job so I decided to commit mayhem with the toroid. Like mentioned before, the secondary resistance across the red/white was zero. When the insulation was stripped back enough to access the 2 output pairs, they were a dead short until I de-soldered & seperated them. They read continuity between the outer 2 wires and between the inner 2. I think they were incorrectly paired when originally built, hence the dead short. Now I need some help determining the correct way to pair them. Anybody care to instruct this ol' electrically challenged fellow?

Re: Toroid Surgery

Posted: Tue Jan 16, 2018 12:23 pm
by martyscncgarage
DICKEYBIRD wrote: Tue Jan 16, 2018 11:08 am Got a little extra time today due to snow/late start time at the day job so I decided to commit mayhem with the toroid. Like mentioned before, the secondary resistance across the red/white was zero. When the insulation was stripped back enough to access the 2 output pairs, they were a dead short until I de-soldered & seperated them. They read continuity between the outer 2 wires and between the inner 2. I think they were incorrectly paired when originally built, hence the dead short. Now I need some help determining the correct way to pair them. Anybody care to instruct this ol' electrically challenged fellow?
There was a phone number for CUI on the lable. Call them. What's the worst that can happen?

Re: Inrush current limiter?

Posted: Tue Jan 16, 2018 1:30 pm
by Dave_C
secondary resistance across the red/white was zero
I think when we first read your post we read this as an [open circuit] instead of a dead short! :oops:

Zero resistance verses OL (open LIne) on the ohm meter.

So zero resistance would be a "dead short" or a very good circuit path.

You should be able to ohm out the four sets of wires and come up with two pair that have similar resistance.

Or not..

Dave C.

Re: Inrush current limiter?

Posted: Tue Jan 16, 2018 2:05 pm
by DICKEYBIRD
There's also my lack of knowledge of precision electrical measuring. :( Would I be correct in assuming that the resistance in my meter & leads when the two leads are pressed firmly together at the lowest scale (.3 ohms)should be subtracted from the total resistance of the circuit being tested? If so, there's no combination of the 4 primary leads that shows more than .6 ohms on the meter (.3 ohms). Very close to a dead short. That may be what a normal toroid secondary's supposed to read?? :?

Re: Inrush current limiter?

Posted: Tue Jan 16, 2018 2:23 pm
by RayL
Which two wires correspond to a single winding is easy - each will show near zero resistance to each other. Your problem will be in figuring out the correct polarity. From the photo, I would guess the two wires on the left are each one end of each winding, and the two wires to the right are the other ends of the two windings, likely with the first winding being the left wire of the left pair, and the left wire of the right pair. From the way it appears to be wound, I would guess the two left wires are also the same polarity. So, to put the two windings in series, I would be tempted to connect the two wires in the middle to each other. To connect them in parallel, I would connect the two left wires together, and the two right wires together. In thee series configuration, if I've guessed wrong, you'll see 0V output when you apply power. In the parallel configuration, if I've guessed wrong, you'll blow the fuse as soon as you apply power. I would connect them in series to confirm the wiring, then you'll KNOW the polarity, and can connect them in parallel (if that's what you need) with no risk.

Regards,
Ray L.

Re: Inrush current limiter?

Posted: Tue Jan 16, 2018 2:34 pm
by DICKEYBIRD
Thanks Ray! This needs to output 36V so does that mean the secondary wires should be in parallel or series? Treat me like I'm challenged when it comes to AC circuits because it's true! I know that's dangerous when combined with frugality. :roll:

Re: Inrush current limiter?

Posted: Tue Jan 16, 2018 5:11 pm
by RayL
There's no way to know what without either measuring, or having a spec sheet. It's either two 18V/16A outputs, or two 36V/8A outputs. I would power it up with the secondary wires not connected at all, and measure both windings, and you'll have your answer.

Regards,
Ray L.

Re: Inrush current limiter?

Posted: Tue Jan 16, 2018 6:22 pm
by mikes
@DICKEYBIRD if you are still a bit confused about multi winding transformers, here is a nice write up: http://www.electronics-tutorials.ws/tra ... rmers.html The key as you probably know, is getting the phase (or polarity) of two windings correct when combining them.

Re: Inrush current limiter?

Posted: Wed Jan 17, 2018 8:50 pm
by DICKEYBIRD
Woo Hoo, it works! Turns out my knowledge re: DC ohms law vs AC ohms law & transformer inductance sucks. The problem was the primary wiring sequence I used was flat wrong. The secondary was correct as built and once some smart people on another forum sorted me out on how to determine which primary wires were correct & in-phase has it working perfectly!

Image

Re: Inrush current limiter?

Posted: Wed Jan 17, 2018 9:17 pm
by martyscncgarage
DICKEYBIRD wrote: Wed Jan 17, 2018 8:50 pm Woo Hoo, it works! Turns out my knowledge re: DC ohms law vs AC ohms law & transformer inductance sucks. The problem was the primary wiring sequence I used was flat wrong. The secondary was correct as built and once some smart people on another forum sorted me out on how to determine which primary wires were correct & in-phase has it working perfectly!

Image
Good, now get back to work! :D