Sorry for so much posting, but I was wondering how durable solid wires are when bent. I used my rapid-start ballast for testing my fluorescent tubes, and I put it back, but I had to bend the wires to power the tubes. So is the ballast still worth using? Are the wires going to break if I try to use it again? How many times can I expect to reliably bend the solid wires?

Avoid bending wires over and over in 1 spot, especially next to a place where they come out of something - Any wires, out of anything. This applies to solid wires on ballast as well as stranded cable of a laptop AC adapter, only difference is, hoe many times it can bend untill it fails

If its random bends along the wires there is probably no problem

If its bending where the wires enter the ballast you are in trouble after some bending - It takes more than a few single times to damage the wires, but not much more

The sharpness (radius) of the bend have bi effect on the amount of damage. Sharper bends are way more damaging

In this case, if the wires dont feel funny (more flexible than normal, so the copper allready filled with micro cracks internally) then they are probably ok for now. It does not mean that you can keep abusing them like that forever



In short, do things with sense, dont go hard on them and they will last

Same applies to posting in the forums too.... Post as you want. If for some reasdon you think you cross the line, stop crossing it, dont say sorry and keep going...But meh you hae not crossed any line, so keep posting

Thanks, So I should be OK for now. I should likely preserve the ballast until it has a use and get another one.

It is nothing else than the metal fatigue. So slight bends, with diameter of many 1000's times the wire diameter, may be tolerated till nearly infinity, because they do not exceed the slip point even in the micro crack points.
But sharper bends do exceed that, so these microcracks propagate and join each other.
That is the main reason, why the Litz wire style was ever invented - the individual wires have so small diameter, the normal cable bending remains in the "infinite" part.

The exact figures very strongly depend on the exact metal structure, so mainly all the dopants and mainly the heat treatment. So it can not be generalized for any wire you meet.

I don't get what you mean by bend diameter, it seems like the opposite should be true.

I don't get what you mean by bend diameter, it seems like the opposite should be true.

I mean a diameter of a circle matching the bending of the wire.

It is true, for such things the "radius" is more appropriate to use...

The ratio between the wire diameter to the bending radius then dictates, how much the material has to stretch on the outer side and compress on the inner. This causes a mechanical stresses in the material. Because there are defects along the wire, thesepoints gets way greater stress levels, so exceed the slip point of the metal and by that the shape change becomes irreversible. Because these are mostly the cracks, such shape change in fact means propagation of that crack.
And larger the crack is, more stress gets concentrated in it's end, so it propagates faster the next time.
These cracks then tend to join each other, then propagating through the complete cross section (it goes faster and faster as it propagates), till it goes completely through and that means the moment the wire breaks.

Now it depend on the internal crystallographic structure, how the cracks propagate. Plus when there is a crystal border, it uses to be a place, where such crack uses to stop. ANd because foreign materials tend to prevent large crystals from forming, when the material is doped and/or when it is really an alloy, there are more such "crack stopping traps", so the material becomes more resilient.

But such crystal borders also present a place, where the electrons can not move that freely, so for good electrical properties you need the crystals to be as large as possible, so need very clean metal. And that goes straight against the mechanical strength, so usually the wire materuial designs is a result of a compromise: If the wire is well supported and the electrical resistance is the top priority, the best purity the money allows copper/aluminum is used for the wires (that is most of the wiring in use). When an extra strength and fatigue resistance is necessary, the low resistance is sacrificed and so alloys are used instead (brass for structural parts, bronze for springs or so). And when it goes to really high vibration resistance wires, either some support cords are used (the power lines - a steel core provides the mechanical strength, the aluminum around conducts the electricity and provides corrosion protection for the steel) or if the wire resistance is of not that big issue, the wire cores may be made from the bronze or so as well (old military field portable telephone wires tend to use that concept; today replaced by the radio communication)

Quote from: wattMaster on June 25, 2016, 09:34:33 AM

I don't get what you mean by bend diameter, it seems like the opposite should be true.

I mean a diameter of a circle matching the bending of the wire.

It is true, for such things the "radius" is more appropriate to use...

The ratio between the wire diameter to the bending radius then dictates, how much the material has to stretch on the outer side and compress on the inner. This causes a mechanical stresses in the material. Because there are defects along the wire, thesepoints gets way greater stress levels, so exceed the slip point of the metal and by that the shape change becomes irreversible. Because these are mostly the cracks, such shape change in fact means propagation of that crack.
And larger the crack is, more stress gets concentrated in it's end, so it propagates faster the next time.
These cracks then tend to join each other, then propagating through the complete cross section (it goes faster and faster as it propagates), till it goes completely through and that means the moment the wire breaks.

So it's about defects. I would expect the wires on this ballast to be of reasonable quality.

Unless it is a true clean monocrystal, there are always defects in the crystal structure.
In fact the wire drawing process breaks the larger crystals and forms more defects in the structure, therefore the wire hardens.
So it has to undergo a heat treatment (annealing), where by applying heat, the crystal fragments rearrange to form something closer to larger crystals, so the material weakens and become malleable again for the next processing steps (include the winding - the hardened form is brittle, so more likely cracks).
The thing with old transformer is, the copper tends to harden over time and by that becomes brittle, so less resistant to any movements. This is the main reason, why old transformers are not any good source for magnet wire - it breaks way more easily...
And of course, it needs way more care, when you have to mess up with such device to not break any of the wires - they by far can not tolerate anymore, what they did at the time of the thing manufacture...

By the way the cheapest clean monocrystals on the Earth are the silicon ingots and/or wafers. Although the silicon processing for that is more difficult than other elements, the spread of the semiconductor industry made their manufacturing volumes so high, it is still the cheapest material of that purity and crystal quality on the Earth. Yet the cheapest quality 8" wafer costs nearly $100 and we are talking about few grams of the material...

And this ballast is new, which likely means the transformer is new, which means the wires are more durable. 

And this ballast is new, which likely means the transformer is new, which means the wires are more durable. 

With the bending you should be careful anyway...
When the ballast is new, there are two possibilities:
Either the wire maker neglected the heat treatment after the last wire drawing step, so the wire remained brittle. But that is strange with a magnet wire, because this usually happens with the insulation coat hardening step...
Or the ballast maker used very old stock of wires (maybe some cheap surplus,...), so they have deteriorated before even put on the ballast.
Or someone was rough to the wires before, so the cracks were already propagated.

Quote from: wattMaster on June 25, 2016, 11:12:05 AM

And this ballast is new, which likely means the transformer is new, which means the wires are more durable.  

With the bending you should be careful anyway...
When the ballast is new, there are two possibilities:
Either the wire maker neglected the heat treatment after the last wire drawing step, so the wire remained brittle. But that is strange with a magnet wire, because this usually happens with the insulation coat hardening step...
Or the ballast maker used very old stock of wires (maybe some cheap surplus,...), so they have deteriorated before even put on the ballast.
Or someone was rough to the wires before, so the cracks were already propagated.

Hmmm... I guess I will stick to my plan, the ballast maker could have used wires form anywhere.

The wires coming out of a ballast are not magnet wire, they are ordinary wire isolated with some composite material (high temp so probably not PVC). The magnet wire is only inside

Whoops, didn't realize that.  
And what could I do if the wires do break?