1/ See #1
2/ I also wouldn't advice anyone without the appropriate experience and knowlege to attemp to wind a mains powered transformer. Experience and knowledge can be gained.
3/ Correct 12V is not enough.
C.
Winding transformer
- Thread starter camerart
- Start date
1/ See #1
2/ I also wouldn't advice anyone without the appropriate experience and knowlege to attemp to wind a mains powered transformer. Experience and knowledge can be gained.
3/ Correct 12V is not enough.
C.
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Knowledge can certainly be gained if one is prepared to devote enough time and effort. Only you know what your time is worth in terms of £s. Experience is more difficult, and can only really be gained safely by doing things under expert supervision.
As I said, that's what I assumed. However, I'm still not clear as to what voltage you actually need for your purpose, and you would need to know that before you could even think about any winding of transformers. Feeding that charger with an unnecessarily high voltage may well not be a very good idea. If you Google the issue, you will find a lot of people talking about how to create a 24V high current power supply using two (cheap) ATX computer PSUs, but I would advise you not to follow their example since, without a lot of knowledge and understanding (and maybe even with it), it is not at all safe.
Kind Regards, John
If you want a high power DC charging system of say 24 volts why not simply use a couple of high capacity lead acid semi-traction batteries which will act as a stable high amperage DC source for a couple of hours or so. In simple numbers, a couple of 100AH batteries offer a theoretical 2.4kWh of capacity - a bit less to prevent over-discharge.
Then you can use a much smaller capacity readily available standard 24 volt battery charger to recharge the lead acid batteries at your leisure over a much longer period of time.
Then you can use a much smaller capacity readily available standard 24 volt battery charger to recharge the lead acid batteries at your leisure over a much longer period of time.
This was suggested a few pages back and, judging by his silence about it, I can but presume that it's an approach which doesn't appeal to the OP.
Kind Regards, John
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Well, when taken together with that which charges the LA batteries, it is really a 'power supply', but one which offers the significant (cost) advantage that the LA batteries can be charged at a much lower current (hence much cheaper) than the in-use peak current being supplied by those LA batteries. If we are talking about a 'fixed' (rather than 'portable') set-up, you wouldn't really "notice the difference". If it were in a 'black box', you wouldn't know (other than by weight and size!) whether the box contained a big transformer-driven PSU, a big SMPSU or some LA batteries and a relative small charge - all you would know would be that mains power went into the box, and 24V at potentially high current came out of the box.
Kind Regards, John
Many, many, years ago as an inquisitive apprentice I got my grubby paws on an old transformer winding machine which I decided could be of use for "homer type" projects.
I researched how to create custom transformers by re-using old iron-cored units as a basis of the build.
I found an article which gave a simple formula (that has long since left my memory) relating wattage to core cross sectional area.
The article also advised (I think) that a copper carrying capacity of 1000A/inch² would also prevent problems with winding temperatures. Copper loading at 1000A/inch² equates to around 1.6A/mm². Bear in mind that transformer windings have no cooling due to surface radiation so current capacities have to be conservative. That said, 1.6A seems a ludicrously low number but at least you won't be bothered by heat.
Many a successful transformer was made, not only for myself but also for the rest of the guys at the site where I worked.
Anyways, a quick google brought up the following article that gives a method of determining wattage capacity based on core size which may be of use for those thinking of doing rewinds.
http://www.smoke.com.au/~ic/ham/transformers/used_transformers.html
Note that this article also quotes 1000A/in², amongst others
I researched how to create custom transformers by re-using old iron-cored units as a basis of the build.
I found an article which gave a simple formula (that has long since left my memory) relating wattage to core cross sectional area.
The article also advised (I think) that a copper carrying capacity of 1000A/inch² would also prevent problems with winding temperatures. Copper loading at 1000A/inch² equates to around 1.6A/mm². Bear in mind that transformer windings have no cooling due to surface radiation so current capacities have to be conservative. That said, 1.6A seems a ludicrously low number but at least you won't be bothered by heat.
Many a successful transformer was made, not only for myself but also for the rest of the guys at the site where I worked.
Anyways, a quick google brought up the following article that gives a method of determining wattage capacity based on core size which may be of use for those thinking of doing rewinds.
http://www.smoke.com.au/~ic/ham/transformers/used_transformers.html
Note that this article also quotes 1000A/in², amongst others
I presume that a re-winding machine can only be used if one can take the transformer apart and get the bobbin(s) out (and then re-assemble the transformer satisfactorily). If that is not possible, then I presume one is stuck with manually 'pushing the wire through' the available gaps the necessary number of times! Mind you, in terms of what the OP would like to do, rewinding a transformer designed to have an output of ~2000V to give an output ≤24V would probably require only a very small number of turns on the re-wound secondary, hence not too tedious.
Kind Regards, John
JW2
Indeed that was the case.
Saw the old windings apart and then endeavour to separate the Es and Is if they were alternatively inserted - which is the better design. Once you'd got the first one or two out (sometimes destructively) the rest split apart fairly easily.
As you say, a high current low voltage rewind can be done without splitting the core if there is enough space to work in. The problem with using pvc (or whatever) wire for the windings is that most of the space is occupied by insulation, whereas shellac coated wire (and some of it was amazingly thick) allows almost 100% of the volume to be occupied by copper. The inter-turn voltages are very low so insulation between wraps doesn't have to experience much voltage stress. You just have to ensure the primary coil and the secondary have good insulation separating them.
Toroid transformers were good for temporary lash-ups as you could simply loop heavy turns through the torus. I once made a low voltage/high current one using welding cable, with the thought that it might be useful to heat solder-ring plumbing fittings. Fantastic output, and the solder ring joints did fuse correctly but the smoking rubber of the welding cable was a bit off-putting !!
Indeed that was the case.
Saw the old windings apart and then endeavour to separate the Es and Is if they were alternatively inserted - which is the better design. Once you'd got the first one or two out (sometimes destructively) the rest split apart fairly easily.
As you say, a high current low voltage rewind can be done without splitting the core if there is enough space to work in. The problem with using pvc (or whatever) wire for the windings is that most of the space is occupied by insulation, whereas shellac coated wire (and some of it was amazingly thick) allows almost 100% of the volume to be occupied by copper. The inter-turn voltages are very low so insulation between wraps doesn't have to experience much voltage stress. You just have to ensure the primary coil and the secondary have good insulation separating them.
Toroid transformers were good for temporary lash-ups as you could simply loop heavy turns through the torus. I once made a low voltage/high current one using welding cable, with the thought that it might be useful to heat solder-ring plumbing fittings. Fantastic output, and the solder ring joints did fuse correctly but the smoking rubber of the welding cable was a bit off-putting !!
I cut out the secondary coil today, and was surprised to find it was copper coated silver coloured wire. The spaces in the 'E' are appr 17mmX25mm inside the insulation. It might have been a good idea to cut the 'E' from the 'I' but I chose to punch the windings out, and re-lace them.
Inside the microwave is a temp protection breaker circuit, with two heat sensors. One screwed onto the transformer, and one in the 'box'
There is a suppression capacitor for the secondary (high voltage) will this be ok for this project? Also a toroid on the secondary leads, and a cooling fan.
For this project, I will keep it all inside the microwave, as it will double up as a charging case, for fire prevention.
Now I need to look at Jackrae's article. Thanks.
C.
Inside the microwave is a temp protection breaker circuit, with two heat sensors. One screwed onto the transformer, and one in the 'box'
There is a suppression capacitor for the secondary (high voltage) will this be ok for this project? Also a toroid on the secondary leads, and a cooling fan.
For this project, I will keep it all inside the microwave, as it will double up as a charging case, for fire prevention.
Now I need to look at Jackrae's article. Thanks.
C.
I trust you are aware that it is possible to exceed the magnetic capability of the core if you demand too many watts (or the core area is too small for your power demand) Under these conditions magnetic saturation occurs and the transformer core effectively limits the power transfer between the input and output coils. A microwave transformer may be designed to operate near the saturation point so that the system power capability reaches a plateau at the rating of the magnetron. In other words what may look like a simple piece of engineering construction might well be a clever piece of electrical design.
Yes, I am aware, and need to check. Bearing in mind that the original microwave was 800W, does this give a guide? If too much current is drawn, can it be monitored by temperature? In which case, I could limit the current, to a safe level.
C.
That is probably not a 'suppression capacitor' but, rather, part of the voltage doubler. As I said before, you will need to get rid of the existing (inappropriate for your purpose) capacitor and high voltage rectifier/diode and replace them with an appropriate (probably bridge) high-current appropriate-voltage rectifier and a large (probably very large) value of (appropriate voltage) capacitor, wired to give full-wave rectification. Note that the required connections of those items to the transformer would be different from the connection of the voltage doubler components in the microwave.
Kind Regards, John
I have a few 'large' capacitors, one being 29,000uF, but the voltage is 25V so not quite big enough. ( I have a pair of 25V 13,000uF that could be in series, if they suit) I will need to find the correct size, for me to price it up. I've probably got the rectifiers.
C.
I've just bought a second hand 24V 1000W power supply £100 delivered. There may be taxes on top?
As we've gone this far with the transformer, I'll carry on, with a lesser project. I'll make a variable one instead. If I use what's in my junk boxes! What is the safe voltage for 25V rated capacitors?
I've got a quite a bit of 22SWG and loads of cotton insulated 21SWG copper wire (shows how long I've been hoarding it) as mentioned before it could be doubled up.
C.
As we've gone this far with the transformer, I'll carry on, with a lesser project. I'll make a variable one instead. If I use what's in my junk boxes! What is the safe voltage for 25V rated capacitors?
I've got a quite a bit of 22SWG and loads of cotton insulated 21SWG copper wire (shows how long I've been hoarding it) as mentioned before it could be doubled up.
C.
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