Not big enough? Oh... damn. Well, we tried, right?

 

Here is a bright idea !
I can take the copper coil OUT from an already built transformer and re-wind new coil to meet your specifications.
This way, we are using the free ferrite core, repurpose it for our designs.
We can use a stack , one on top of another transformers, to get the VA needed.
My imagination is a bit wild, you tell me in the end what is possible or not.

 

I would think they should either be synchronous motors or controllable in some way.
They do not appear to be PM rotor.
If PM, shorting the wires together and trying to spin would result in some resistance to spinning.

Those two motors are probably the reel drive motors. I have an AMPEX tape machine from the similar era. The motors turned the tape reels to hold a fairly constant torque so that the tape tension would be the correct low value. The motors served as torque motors while playing or recording, and delivered more torque for fast forward or reverse functions. Both of the motors are split-phase induction motors, and use a capacitor for phase shifting.
The constant speed motor driving the tape capstan was quite different, possibly with an electronic speed control.
So the destruction of a quite expensive tape machine certainly would upset an individual who knew what it was worth.
At that time the AMPEX tape machines sold for quite a few hundred dollars. A used one similar to what I have was offered for sale for $700 back in 1982. The one I own cost me less because it required some repairs.

 

Well, history is history and I am divulging too much. I upset @MisterBill2 here. That particular magnetophone was expensive but not THAT expensive, it might have been like a month salary or so. But not something you will have to make a bank return for 30 years. It was in the 90's, not today. Now I do know the value of things, for example I can not buy a 70V transformer and I have to build one... hopefully. And even if I can not afford to make a SMPS with you guys here, well, I am happy that I could test and actually make every motor work, and also confirm they are not burned or damaged. Which is more than I expected. If we can make a power supply for each(or at least one) , that will be more than awesome, but I control my hopes and dreams, because I understand is a hard thing to make.

 

The motors turned the tape reels to hold a fairly constant torque so that the tape tension would be the correct low value. The motors served as torque motors while playing or recording, and delivered more torque for fast forward or reverse functions. Both of the motors are split-phase induction motors, and use a capacitor for phase shifting.
The constant speed motor driving the tape capstan was quite different, possibly with an electronic speed control.

come up with that on your own? Or did you see it in post #13? I believe the second, knowing you.

 

I have another bright idea...
How much it will cost for the components of a transformer to buy? Comparative to a ready made transformer? It should be cheaper to get the components rather the transformer itself, right?
By components of a transformer, I mean the metal sheets (E and I) and the 2 copper coil diameters.

 

Depending on the intended application of the motors, it might even work to run the two of them in series.
But to get 70 volts using a standard transformer, it should work to use a 48 volt transformer connected as an autotransformer, with the 48 volts subtracting from the 120 volt mains to provide about 72 volts, close enough to 70 volts to serve well..
And as for the comment from shorty, it seems that I neglected to read post #13 last night.

 

... from the 120 volt mains ...

Thank you @MisterBill2
Romania is an EU country and we have, like the rest of European countries, 240VAC on the mains,(we used to have until 2010, a 220VAC mains) with about 30A per household wire diameter in the wall.
My request is to build 3 dedicated Power Supply Units for each motor. I know, is a nice idea to link 2 motors to 1 PSU but, I want independent motors.
It is suffice to make only a single, one PSU - if possible or permitable ofcourse. I will learn enough from it to make the rest of the other 2. That is my plan. But I remember that you have rules here, especially for high power electronics (maniacs), like this case I am coming with, and I think you will retreat from strategical reasons. And I respect and understand that. My agenda is to make my stuff work, but I must keep an eye on your website or country or individual politics, because I understand very well, there are crazy people out there, who knows what they can do and then come back and throw with shit. As they usually do.
I will not insist on this matter because, as much as I want to learn this thing, I will have to step back.
I can always erase all this entire forum thread that I started, as a very easy measure of precaution.... just thinking on alternatives.
Anyway, I am very-very pleased with the progress so far ! And all thanks to you guys here.

 

OK, and thanks for the response. I had forgotten that the local power in that area is 240 volts.
Probably the motors will run on 48 volts AC, and so that could be an option if less torque would be acceptable. Another option, far from ideal, but one way to use standard parts, would be the use of three 24 volt transformers, with the 24 volt outputs in series aiding. Each transformer would only need to provide a third of the power, so they could be smaller. That would be simple and it would not require any transformer winding at all, but it is just one option if nothing else can be available.

 

To @MisterBill2 yes, that was my first thought as well, to wire in series 3*24V small transformers and that gives me 72V for a 24V@3W traf.
And I already look for one 24V transformer and the cheapest one I could find on ebay is around 9$ USD:

I didnt check out, but I did step into the order to show you additional taxes that makes the price go up another 1/3.
"Bollocks" - I say.
And 12$*3 = 36$ USD. And that is for ONE motor. I have 2 at 70V and it means 36*2= 72$USD
and I have the 3rd motor at 80V, and it means 36$*3 = 108$ - ohohoaaa...
NeeeHeHe, hose !
Im not even sure I will even use these motors. I only want to have them ready when I will have an idea to use them.
And also the power is not right either. These transformers are rated at 3W/24V=125mA ....
while my 70V motor needs (and I did this calculation already in my original post)
" I=V/R=70V/90R=0.7A@54W for 1 coil and I=V/R=70V/115R=0.6A@42W for the second coil. And then summed up 0.7A+0.6A=1.3A drawn from the power supply to drive both coils of a single motor. "
The transformer outputs 125mA , motor needs 1.3A, the transformer will transform itself into a pile of ash -instantaneously- like in the cartoons movies when I connect this motor as its Load. I will be lucky if it will burst into fire. Haha.
I definitely need something more powerful and definitely much more cheaper as well. The cheapest way I can think of is to make something from components I already have. Since I cant have money, but I have time and curiosity to learn and to build.
And I've always wanted to built a SMPS, for learning purposes and for practical reasons as well.
Eh well... put more ideas on the table, because I strongly believe "where are more brains, more chances to happen".

 

I definitely need something more powerful and definitely much more cheaper as well. The cheapest way I can think of is to make something from components I already have. Since I cant have money, but I have time and curiosity to learn and to build.
And I've always wanted to built a SMPS, for learning purposes and for practical reasons as well.

If your thinking of reusing the cores from the transformers you showed earlier to make your transformer, I don't think it will work. None of those transformers were big enough to do it, they didn't look to have enough VA value. Buying core lamination's, wire and bobbins to wind you own transformer will cost more than buying the correct ready made one.

That said you MIGHT get away with using a microwave oven trans for the core and primary and jus making a new secondary. But still a ready made one will be better and less work.

Then we come to the SMPS you keep mentioning to run these motors. You do know a SMPS has DC output don't you? Your motors are AC.

 

There do exist inverter power supplies, but if the frequency is similar to the mains frequency the transformers will be similar and there will not be much benefit to using them.
For the motors in question the current will not be determined by the winding resistance along, but rather than the winding impedance, the vector sum of the resistance and the winding reactance. The total of 96 watts is much more than a tape reel drive motor would actually consume, although it undoubtedly will be more than the 9 watts from the three watt transformers.
One very inefficient scheme would be to use a series resistor to simply drop the voltage to the motors. Wasted power but cheap and effective.
And now one suggestion is that you determine for yourself just how much torque and what speed these motors can deliver. That will aid you in deciding what to use them for.
And certainly the value provided by the use will help decide what cost of the adaption is worth.

 

- To mister @shortbus, I think I failed to mention that all the scrap transformers I shown in #78, I keep them in the idea of making a SMPS. Thats the hole reason I keep them. I want to believe im not a hoarder. Haha. And the majority of them, are scrapped from other SMPS, on board or stand alone. And I didnt pay attention that SMPS is DC only. I had the impression is AC OR DC. I have little experience building one, I have some idea of its structure and how is functioning, as principle, but Im a beginner at this subject. If they are DC only, then Im screwed, especially using one for this motors project. Aaaah. I believe it is a way of converting DC to AC.. but it will be a monster circuit. If it is possible with components I have in stock, then ... I say YES, lets DO IT. Haha.
- And to respond to @MisterBill2 , I do want full power and full speed out of these motors, and also the possibility to variate them down to 0 speed. But.... it turns out it is a very expensive project after all. Its interesting your idea with the series resistors, though. As ineficient as it is (due to a lot of heat loss), do show me what you think of, Im very curious. I imagine you are thinking on a voltage divider with some power resistors.... I do have 10W resistors and I have a bit of range of them. I mentioned in one of my earlier posts: #43, the diac-triac circuit method. Isn't that a viable option? Or the power is too much for a triac to handle?

 

One very inefficient scheme would be to use a series resistor to simply drop the voltage to the motors. Wasted power but cheap and effective.

Going to be one h3ll of a resistor to drop from 240VAC to 70VAC.

 

@post #93. NO!! NOT a voltage divider with two resistors, just simply a series resistor. And it may indeed be a bit large. But for a motor with a constant load it can provide a constant voltage drop. BUT, because the motor impedance is greater tha the resistance it will not waste as much power as the calculations would predict.

and those recoder reel drive motors are not very powerful, really.

 

I had the impression is AC OR DC

The input can be either AC or DC, but the output is DC.

 

@post #93. NO!! NOT a voltage divider with two resistors, just simply a series resistor. And it may indeed be a bit large. But for a motor with a constant load it can provide a constant voltage drop.
...and those ... reel drive motors are not very powerful, really.

Aaah, you put me on the drawing tablet again.
But you deserve a nice drawing because I think you have a true genius idea. I really like it. It is truly out of the box thinking!!!
Also, dont take for granted the calculations I did there, please calculate yourself and do confirm or correct my logic there. Im not doing this calculations every day, so im a rookie at them.

 

and those recoder reel drive motors are not very powerful, really.

Well, at maximum speed and torque, I can slow down the speed of the rotor axis, but my skin is smelling like grilled chicken. I can slow it down more than half of its speed. With all my power I can press and squeeze on the axis.
So it is not THAT strong, but it is strong enough to spin a pulley and do some practical work as a grinder or a drilling motor. Potentially ! In essence, YES, they are weak motors and I always keep in mind they are (all 3 of them).
- The exceptional thing I like about them is they are absolutly quiet when at full speed. Yes you can hear a very faint bzzz but you have to put your ear close to its chassis. And I like this very silent running motors because I live in an apartment, and I have very sensitive neighbors with extremely sensitive ears, and also my sensitive father ears as well. You can imagine them as donkeys. So quiet and ninja is a very appealing option for me. Until I will move from here and then it will be another story.

 

The input can be either AC or DC, but the output is DC.

Excelent clarification and I totally confirm and approve. I didnt stay and think too much about it to be sincere. But Im glad you pointed it out. I'll try to remember it from now on.

 

OK, I was comparing the size of those motors to the size of the motor on even my smallest bench grinder. It is only a tiny fraction of the size of the motor on my regular style bench grinder, thus my evaluation. Certainly other applications will be able to use the power of those motors.
So at this point I am going to suggest rewinding a larger transformer, possibly from a scrapped appliance, or maybe from an obsolete mercury vapor, or other, lighting device. Now that LED lighting has become so common and less expensive, some of the much less efficient luminairs may become available. The main power transformer from a discarded CRT and tubes type of television would be a very good candidate for rewinding. Or even the power transformer from discarded meduim to high powered audio equipment.
And, for use in a shop environment, one power transformer could be shared among three or even more different machines. Drilling and grinding are seldom done at the same time.