[elogicca]

Ok i will be setting up some 90volt servo's to some g320's I was thinking of rewinding a microwave xformer, basically i'd like to do 80 volt 30 amp lotta va lol......

My question is this what gauge should i use to rewind and what output voltage do i want on the transformer to hit lets say 79.9 volts dc after caps? i'm going to parallel a bunch of caps what final cap value should i be looking at? going to use 100v rated caps and a 100v rectifier, is that too low should i be rating caps and rectifier higher?

thanks

[Bubba]

elogicca,
The gage of wire will depend not only on the current rating, but also on the allowable temp. rating of the wire and what you expect to have when in service. I used to have a bookmark on an excellent site for wire sizing, but haven't been able to find it yet.(will report back here when I find it:})
Please realize that as wire size goes up, so does the cost --drastically and the bigger the wire, the harder it is to work. For output voltage of the transformer you would be looking at 61-62VAC and I personally would use at least 200V rated bridge and for caps IIRC, you need at least 150% rated for them. When I make my transformers, I wind to what I think I need and then carefully hook it up and measure the voltage. If to high, remove a turn or so and if to low, add untill I achieve the desired results.
My first question is, "Do you REALLY need 30 amps?" . Based on formulas provded by MR GECKO, Watts = IPM * Lbs / 531 and on my mill/drill, it works out that I am using less than 3 amps per servo at a 500# load! Even if I am running all 4 axis at max simutaneously, that is still only 12 amps! As for size of the Cap, again from MR GECKO, Size µF=80000*I/V where I is maximum current and V is the DC voltage. So in your case of 80V and 30 amp it would be about 30,000µF! Thats a lot of cap!!!!!!

I guess what I am saying, is be sure of the values you NEED, and not guess at them. As Volts and Amps go up, so does the cost---exponetially:})

[elogicca]

The servo's i'm looking at have a terminal voltage of 90volts and a continious current of 7.6 amp with a peak current of 38 amp, so i figured if all 3 axis are going i need 22.8 amps, add some overhead and thats how i got 30 amps...
these were the servo's i was looking at

http://www.kelinginc.net/KL34-150-90.pdf

am i corrent on my thoughts, persoanlly less amps would be better as the wire thinkness and cap ratings......

Thanks

[Bubba]

Again I refer to Mr. Gecko who indicated a good design parameter was to design to 66% of your total demand or about 20 Amps in this case.

If you use geckos, you can't exceed the limits of 20 amps per drive anyhow. Also, I don't think your application will be running at anywhere max all the time anyhow! Again, I relate to the forces needed to do the job. Think about the fact that your car has an engine that will develop several hundred horsepower, but I doubt that you run it at max all the time.

Look at the watts required to drive the load. IF you are running 80V at a current of 7.6 amps, that is = to about 600 Watts. OK, IF you are running at say 20 IPM that is a cutting force of over 16,000 lbs!!!! if I have done the math correctly.
I THINK that if you try to apply 16,000 lbs of force on any of our "hobby" machines, then something is going to BREAK (hope you don't get hurt)

Just some food for thought!

[elogicca]

Lol, thanks actully my cas is at max most of the time

[elogicca]

Thankis Bubba I think i wrapped my head around it all, also saw some of your posts where you can include different windings for other voltages, cool

I'm going to try and locate some enamel winding wire tomorrow i guess 8awg for @20 amps?


Thanks

[Bubba]

Depending on which refrence you look at, you will be looking at 750 - 1000 CM (Circular Mills) per amp.
I have a couple of sources that I use depending on wire size.

For up to 12 AWG, I generally use WWW.mpja.com or www.surplussales.com as they also have large sizes. Depends on how much you need!

Sorry, I have no Canadian suppliers.

[elogicca]

Yep Canada sucks for getting stuff, lol do you think i could braid 2x16awg for a total of 20 amps??? found it locally. I guess i could use 21 for my 5/12 volt coils now just gotta convert lb's into feet cause it's sold by the pound.

[Al_The_Man]

Yep Canada sucks for getting stuff, lol do you think i could braid 2x16awg for a total of 20 amps???

If you are in a large city, you are bound to have more than a few motor rewind shops, they all use Enameled wire, often they will sell you the end of a spool, or cut it to length.
Once you get into the larger sizes it is easier if you can come by the square section wire, but harder to get.
Alternatively, wind bifilar, this is winding two smaller conductors together side by side, and paralleling them.
Al.

[Firebird0095]

Let me know if you need some big caps - I have a few lying around that you may be able to use. I am not sure of their rating right now, but they are big and I have three. I was going to use them to build a power supply, but I ended up finding drives with a built in supply.

Mark

[elogicca]

Called a few winding shops this morning, and the largest wire i can get is 16 awg for a 20 amp transformer i'd need 6 in paralell or could i use less?

[elogicca]

I also asked about insulating paper, the guy said what type lol apparently there are quite a few.. anyone have any ideas on what to use as insulating paper?

[Al_The_Man]

He was probabally referering to the Fibre or paper for lining the winding slots, it comes in various thicknesses, but for what you want, I would ask them for winding tape. A common one is impregnated linen tape, it is much easier to use.
You can use many alternatives, because you won't be shellacing and oven-baking like a motor winder would.
Just explain what you are doing and they should be able to steer you in the right direction.
In a pinch I have used a couple of layer of Electricians Tape.
Al.

[elogicca]

Well they guy looked like i was interrumpting his nap ans wasn't very helpfull, is glass tape / insulating paper necisary for a mot cnc rewind?

[Al_The_Man]

Generally with transformers or any winding, you need some protection from sharp metal edges and some insulation between primary/secondary etc.
You can usually find a source of thin hard plastic sheet as in the cover of some soft cover binders etc, a search around the average home comes up with some kind of improvised solution.
This together with insulating tape, usually works for the one-off project.
Al.

[kreutz]

What was the original rating of the transformer?

You are talking about 2.4KVA on the output (80V x 30 A) assuming a 80% efficiency 3KVA at the input. Was it rated for more than 3KVA? Once you disassemble it you will never put it together with the same stacking factor, so your transformer will probably lose efficiency.

The thickness of the tape is not hat important here because of the amount of wires in parallel you need in order to get the effective wire area equivalent to a AWG 12, so you will have to wind many layers and the potential difference between layers is low (=> no arching). What is important is the maximum temperature allowed for that material, minimum 90 degrees Celsius, and the mechanical characteristics (there is a relationship between proper tape thickness and wire diameter, you can find that figure in the manufacturer's data-sheets).

At that level of power your transformer will get hot for sure. If your original transformer was rated under 3.5KVA your re-winded transformer is going to get even hotter due to increased losses in the core and possible saturation. If you don't apply varnish and cure it in the oven it will make a lot of noise too.

[elogicca]

The target has been changed to 15-20amps 63v out of the xformer, so figuring 3x16 gauge

[Al_The_Man]

I think you will find they are not separating the laminations , in any case on most EI laminated type, they are not only shellac'd and baked but in the case of many of the MicroWave tfmr's used, there is weld bead across the lamination's, for this reason, lamination buzz is not generally a problem.
Also many of the MicroWave origin types, have a magnetic shunt that requires punching out between pri. and sec.
I still think the easiest to rewind and modify is the Toroidal type
Al.