Toroid ReWinding ?

[DJB282000]

I am curently working on rewinding a toroid and i do not have acces to heavyer wire. What i would like to do is use the wire that i am removing and do a set of windings in parallel.

The question that i have is how close does the length need to be so that i do not have any problems with the transformer.

Should i try and go by the length, the resistance, of the final output voltage of each winding that will be placed in series.

I am taking pictures as i am doing this and will be posting them once I finish the transformer.

An help will be greatly appreciated.

Daniel

[Al_The_Man]

It helps if you can determine the turns/volt and this way you can wind the correct number off the bat, throw an extra couple on, you can always take them off if too high.
The number of turns is independant to the gauge. Measure first, take say 10 turns off and remeasure to get the T/V.
If you have them already removed, put 10 temporary turns on and to the same.
If connecting windings in parallel, make sure they are both wound together, not one after the other in order to get good balance.
Al.

[DJB282000]

Al
I am happy to see you respond. I have read alot of posts by you feel confident in the info you give.

The coil that i am working on has 2 secondarys. each is wound on its own layer and then covered with a wrap. I have most of the first layer off as i was unwinding it i check the volts per turn several time and am getting about 2.2 turns/volt.

The wire that is curently on the transformer is .053 thick (16 ga +??).

My steppers are 2.8v and 5.5 amps.

I am going to rap the transformer for 70vdc (2.8 x 25), 49VAC (70 x .7) and 11 (5.5 x 3 /(2/3)) amps.

Am I working this out correctly.

I am also considering just leaving the first layer of the secondary in place and not removing it. Would this be a bad idea?

Next question is should i just wait and try and get my hands on some larger wire from a motor shop or ebay.

tks
Daniel

[Al_The_Man]

Do you know the VA (power) rating of the transformer? Do you know the current rating of the existing winding you want to leave on?
I would allow for 51vac if you want to end up with 70vdc to allow for the bridge drop.
With those motors, allowing for a mean current level, I would think 16g will work.
If you go this way you can leave the first winding on, cover the splice connection with heatshrink tube, make sure it is a tightly soldered splice.
Al.

[DJB282000]

The transformer has a primary of 2*115 850VA and a secondary of 2*115 800VA.
I am thinking that it was just used for isolation.

The secondary that i would like to leave on the transformer is one of the 115 vac secondarys (i just dont want to unwind it).

do you think that the original windings will be ok for 11 amps with just one winding of .053 wire wound for 51 vac.

[DJB282000]

i am also going to ad a winding to get my 5 volts for the geckos.

[Al_The_Man]

As you are no really going to any great lengths like rewinding, you will be just removing turns, so I would go that route first and monitor the performance and heating of the transformer when running, the worst case scenario is you just take the small 5v secondary off and re-wind larger secondary with larger wire, If you were starting from scratch it would be different, then it might pay to go larger.
With servo situations, the current is rarely at max for extended periods.
Al.

[DJB282000]

thanks Al
I am going to unwind until i get 51VAC as you have sugested and see what happens.

tks
I will be getting up pics asap.

[DJB282000]

I would like to thank everyone on the zone for helping out.

I am hoping that the following pics may be of some help to some else that is thinking of trying to rewind a toroid.

Here are a few pics that I took while I was reworking my toroid.

1. Picture #1. This is a pic of the toroid as I received it (cheep thanks ebay)
2. Picture #2. As I started to unwrap the plastic covering.
4. Picture #8. As I removed the copper I would carefully fold it and tap it ever few to keep them in a pack small enough to pass thru the center. I also counted the number of turns that I would remove.
3. Picture #11. WARNING: I DO NOT RECOMEND THIS. IT IS NOT WORTH GETTING ELECTRICUTED. After removing a number of turns I would stop hook the power up and test the voltage to see how much of a change I had made. After Doing this a few times and then doing a little math I found that the toroid was just over 2 turns per volt. (As I had seen on the zone). I then disconnected the power and removed more of the copper.

I decided to completely remove both of the secondarys (one on top of the other with a layer of plastic in between) and rewrap with a heavier transformer wire.

The length of the new wire was determined by measuring the length that it would take to make one wrap (around the transformer thru the center). I then multiplied that distance (7.5") by 2 (2 turns per volt) and then by my final voltage. I then added a few feet to make sure that I would have enough.

4. Picture 13. This picture shows how I held the toroid and the loop of wire that I started with.

5. Picture 14. This is just a close up of picture 13 above.

6. Picture 15. WARNING: ONCE AGAIN I DO NOT RECOMEND THIS. IT IS NOT WORTH GETTING ELECTRICUTED.
This is the last picture that I took as I was testing the voltage. After having wrapped what I thought was the proper amount of turns (calculated). I removed the excess wire that I had started out with, cleaned the end and checked the voltage before I cut it.

After having checked for the correct voltage I cut the wire back leaving about 10" sticking out.

I then added heat shrink to the wires and then tapped them in place and finished of the first secondary by rewrapping it with the plastic that I had removed in the beginning.

The final step was to add a small secondary to power my inrush limiter and then wrap that on in plastic.

I would just like to say that I would do this again without hesitation. It was not bad to do and worked out perfectly but if I do need to do it in the future I will just cut off the secondarys if I am going to rewrap.

If anyone has any questions, I will help if I can.

Thanks to all on the Zone that Helped.

[2muchstuff]

I like the particular method of looping the wire while rewinding. I have been putting off winding a power choke using #10 enameled wire. I was thinking of winding my wire onto a stick of sorts and then passing it through the torroid every wrap. I was concerened about the enamel coming off as it was wound and then unwound off of the stick. Thank you for posting the picture and solving a concern of mine.