[Patrick_M]

Hi Folks,

Okay, so I've spent the last couple of days asking tons of questions about
transformers, and reading as much as I can find on the subject that I can
understand at this point.

So yesterday morning, I felt I had a brake-through in my understanding of
how transformers and electricity works, at least for the cnc system I'm building.
(HobbyCNC Pro kit)

I was pretty nervous about using a transformer with more than the called
for amperage (10A) until I finally understood that the amperage would not
be a factor as the stepper motors would only require so much, their rated
at 3A each, and that a transformer would not deliver a continuous amperage
unless it was called on to do so.

So I make this post in the group forum to verify that I am totally understanding
how all of this stuff works, and that it would be ok to use a transformer that's
rated at a higher amperage than the 10A's the kit calls for, because as stated
above.

I got two or three replies that I had finally got it, and was thinking along the
proper lines.

Then, later in the day, the owner posts that if I were to use a transformer that
a buddy of mine has that's rated at something like 35 volts and 50A's, that it
would smoke the board!

After this, another poster comments on some details that I was not aware
of, such as that the transformer, although only puts out or is rated at 35 volts,
would actually produce much more than that, and that would fry the board.

So, now here I am lost again, and trying to figure this stuff out...

OK, the HobbyCNC board says that you can use a power supply up to
42 volts. Yet the 35 or 40 volt transformer would go beyond this and fry
the board. I don't get it.

Also, it was made very clear to me, that I was not to exceed the 10A
limit or again, smoke would roll.

With all of that said, am I to understand that the recommended
transformer of 24 volts and 10A's will actually exceed that 24 volts, and
shoot upwards of 32+ volts at any given time during operation?

And, the amperage that a transformer puts out, although will not be there
unless the system starts calling for it (pulling it?) , will still burn up the system
anyway because there's to much power (or push)?

I thought I had a grasp on this transformer stuff, but I'm feeling as lost as
ever after this day.

Any insight or input is welcome.

I also have two microwave transformers that I was holding onto for a future
build of a cnc machine (one I have already rewound at 19.2 volts) and what
must be 40 or 50 amps I would think. But after getting the responses I've
gotten, those are probably useless for anything more than boat anchors now.

Thanks,
Patrick

[HobbyCNC]

Hi Folks,

Okay, so I've spent the last couple of days asking tons of questions about
transformers, and reading as much as I can find on the subject that I can
understand at this point.

So yesterday morning, I felt I had a brake-through in my understanding of
how transformers and electricity works, at least for the cnc system I'm building.
(HobbyCNC Pro kit)

I was pretty nervous about using a transformer with more than the called
for amperage (10A) until I finally understood that the amperage would not
be a factor as the stepper motors would only require so much, their rated
at 3A each, and that a transformer would not deliver a continuous amperage
unless it was called on to do so.

So I make this post in the group forum to verify that I am totally understanding
how all of this stuff works, and that it would be ok to use a transformer that's
rated at a higher amperage than the 10A's the kit calls for, because as stated
above.

I got two or three replies that I had finally got it, and was thinking along the
proper lines.

Then, later in the day, the owner posts that if I were to use a transformer that
a buddy of mine has that's rated at something like 35 volts and 50A's, that it
would smoke the board!

After this, another poster comments on some details that I was not aware
of, such as that the transformer, although only puts out or is rated at 35 volts,
would actually produce much more than that, and that would fry the board.

So, now here I am lost again, and trying to figure this stuff out...

OK, the HobbyCNC board says that you can use a power supply up to
42 volts. Yet the 35 or 40 volt transformer would go beyond this and fry
the board. I don't get it.

Also, it was made very clear to me, that I was not to exceed the 10A
limit or again, smoke would roll.

With all of that said, am I to understand that the recommended
transformer of 24 volts and 10A's will actually exceed that 24 volts, and
shoot upwards of 32+ volts at any given time during operation?

And, the amperage that a transformer puts out, although will not be there
unless the system starts calling for it (pulling it?) , will still burn up the system
anyway because there's to much power (or push)?

I thought I had a grasp on this transformer stuff, but I'm feeling as lost as
ever after this day.

Any insight or input is welcome.

I also have two microwave transformers that I was holding onto for a future
build of a cnc machine (one I have already rewound at 19.2 volts) and what
must be 40 or 50 amps I would think. But after getting the responses I've
gotten, those are probably useless for anything more than boat anchors now.

Thanks,
Patrick

Patrick,
Not quite accurate. Also, it was made very clear to me, that I was not to exceed the 10A
limit or again, smoke would roll. The transformer voltage you intended to use will smoke the board. The RECOMMENDED transformer is 24VAC 10A. No one said additional AMPS will smoke it. As suggested, www.mpja.com has a 24VAC 10A tranny for @$20. Simple and cheap.

AC volts is quite different than DC volts. An easy mistake for a newbie to make.

[Al_The_Man]

After this, another poster comments on some details that I was not aware
of, such as that the transformer, although only puts out or is rated at 35 volts,
would actually produce much more than that, and that would fry the board.


And, the amperage that a transformer puts out, although will not be there
unless the system starts calling for it (pulling it?) , will still burn up the system
anyway because there's to much power (or push)?

You need to use the rated voltage, but a transformer only supplies the current demanded of it, IOW if you had a 100a transformer and the load demanded 10amps, then that is all that will flow.
But the TXFR is CAPABLE of 100amps if it was required. It would just be overkill in sizing.
Al.

[Patrick_M]

OK, so, if the transformer is rated at or below 24 volts for the HobbyCNC system,
then the amperage is a null subject?

Please remember that I am new to this stuff, so I am likely to misunderstand
peoples responses to me until I gain the knowledge and experience needed.

With that being said, one of the reasons I purchased a kit instead of a turnkey
solution, was because I wanted the experience of learning this electrical stuff,
and even though it may be less expensive and faster to just go out and buy
xx product, rather than build it myself, I am a do it yourself'er, and part of
feeling I have a reason to exist is figuring out things like this.

It reminds me of something my Dad used to say to me all of the time...

For example, back when I started to drag race years ago, I purchased a
car where I needed to build everything myself, such as the roll cage, engine,
and all of that stuff, and my Dad would say: "Why didn't you just buy one that's
ready to go so you could save some money in the long run?". My response
was always: "But what's the fun in that?"

Not only did I want to drag race, I also wanted to know every nut, bolt, and
wire in that car, I wanted to feel as though a part of me was invested into it.

Had I known at that time that I could have ripped apart a couple of microwaves
and built my own arc welder for pennies, I would have built that too instead of
buying one. Not only would I learn how to weld, but learn how to build the darn
welder to boot!

Same goes for everything I do. I did purchase the recommended transformer
for the HobbyCNC kit, and am using it, but I still want to learn how it all works,
and I want to know enough in that manner, that I can eventually do whatever
I want, and can do it because I've gained the knowledge to be able to do that.

For example, I have a ton of digital displays from microwave's I've taken apart,
along with a pile of other electronics that I know nothing about, but am looking at
and have ideas of what I might use them for in the future.

I was thinking that someday I might add a couple of digital displays that would
show me in real time what the current voltage is from the transformer, as well
as current amperage being drawn. Sure, for the average person like my Dad
who just wants to get the job done in the fastest amount of time, that's a waist
in effort and energy, but for me, it's all in the art of learning what's going on
in life.

So, I apologize if I misunderstood what someone stated, I'm a newbie and
learning as I go. But it also warms my heart to know that I am in fact getting
a grasp on understanding the whole amperage deal as well.

So I am right in thinking that amperage is likened to a muscle builder, although
he may have all of that muscle, it doesn't necessarily mean that he uses it in
everything he does, but it is available if he needs to pick up my new big block
540 Chevy and stuff it in-between the fender rails of my race car for me.

Thanks,
Patrick

[Al_The_Man]

So I am right in thinking that amperage is likened to a muscle builder, although
he may have all of that muscle, it doesn't necessarily mean that he uses it in
everything he does, but it is available if he needs to pick up my new big block
540 Chevy and stuff it in-between the fender rails of my race car for me.
Thanks,
Patrick

Not quite a good analogy but close, often the one used is a water analogy where voltage is likened to pressure and current to flow.
If you want to brush up on fundamental Electrical/Electronics, there are many web sites that offer basic instruction.
Al.

[ger21]

OK, the HobbyCNC board says that you can use a power supply up to
42 volts. Yet the 35 or 40 volt transformer would go beyond this and fry
the board. I don't get it.

I don't know how to explain it, but when the AC voltage is converted to DC at the bridge rectifier, it's multiplied by 1.4 times (I think). So your 40V transformer will give you 56V DC.

[Patrick_M]

Hi Gerry,

Does that apply to all bridge rectifiers in curcuits such as these? I mean,
is that a calculation that I can use to figure out how things are going
to work in any given cnc system I might build in the future, regardless
of what bridge the kit might be supplied with? (110AC Std. Wall Current)

If so, I will remember and use that in the future.

Thanks,
Patrick

[ger21]

If you build a DC power supply using a transformer, bridge rectifier and capacitor, than yes.

[Patrick_M]

OK, thanks. that's good info to remember.

[ger21]

This might help you out.
http://campbelldesigns.net/files/pow...ply-part-1.pdf

[Patrick_M]

OK, I tested my 19.2 volt transformer, and after it goes through
the bridge and cap., it's up to 28.3 volts! That's a 1.4739
increase in voltage.

It's strange that it would actually boost the voltage, although
pretty cool at the same. Now I will have to study to learn why
this happens.

So, it is a good thing I didn't hook up that 35-40 volt transformer,
or there surely would have been smoke. 8-O

Thanks,
Patrick

[Patrick_M]

Nice ebook, thanks.

The one thing that he doesn't explain in there is way the
amperage "should never exceed" about 67% of the total
of the stepper motors?

This is where it gets back to having to much amperage
is a bad thing, and what makes it confusing to me.

In one place, people will say that you don't have to worry
about the amperage if you're over what the system calls
for, then in another place we're told to never exceed a
certain amount.

For example, one of my microwave transformers I've rewired
that delivers 19 or 20 volts, has got to be pushing the upper
limits of 40 or 50 amps I would think? In this case, these
transformers would not work with a CNC driver board.

Yet, I read where there are people using these very types of
transformers to power their CNC systems. So what gives here?
Are we looking at a case where these people are basically living
on borrowed time and it's just a matter of the right circumstance
and they're going to fry their boards or something?

Thanks for any feedback,
Patrick

[ger21]

Nice ebook, thanks.

The one thing that he doesn't explain in there is way the
amperage "should never exceed" about 67% of the total
of the stepper motors?

He means the amps that the steppers draw won't exceed 66%. The drives only draw what they need, and if the power supply can supply more, it won't hurt anything.

[Al_The_Man]

This is where it gets back to having to much amperage
is a bad thing, and what makes it confusing to me.

In one place, people will say that you don't have to worry
about the amperage if you're over what the system calls
for, then in another place we're told to never exceed a
certain amount.

Read post #3 again, also I think you are misunderstanding the reference to 67%.
It is in fact poorly worded.
What this is actually saying, is that you can take the combined stepper load and calculate the TXFR VA on 67% of this to calculate the transformer power rating.
IOW if your combined calculated load was 10amps, then use 6.7amps to calculate the VA or the value to size the transformer.
To put it another way, this is a derating value, to avoid oversizing the transformer, if you want to use a larger VA, this will not be a problem, as long as the VOLTAGE is within limits.
Al.

[Patrick_M]

Gosh darn it... You see, there I go misunderstanding again.

This is almost the very same misunderstanding I had the other
day and I started thinking that all of this amperage was a bad
thing again.

Thanks very much Gerry for setting me straight once again.

Patrick

[keebler303]

About the voltage:

AC voltage is measured as RMS (root mean square) voltage. This is a type of averaged value of the AC voltage as it is constantly changing. (sine wave). The peak value of the AC waveform is actually the square root of 2 (about 1.4) times bigger than the RMS value. When you rectify the AC voltage and add a capacitor, the capacitor stores this peak value and spreads it over the time when the voltage is less. In this way, the DC voltage is much closer to the peak AC voltage and not the RMS AC voltage.

http://hyperphysics.phy-astr.gsu.edu...ic/rectbr.html

For the amps ordeal, just imagine your car battery. When you need to start your big block racing motor, it provides the 500 amps needed to turn the starter. But when you plug in your cell phone charger to the cigarette lighter, it doesn't burst into flames. It only draws the current necessary, maybe 100 milliamps. All of this follows Ohm's Law. V=I*R. This relation lets you calculate how much current a device will draw based on the voltage of the supply and the resistance of the load. Your starter has a low resistance and your cell phone charger has a relatively high resistance. The voltage is the same for both devices, so the current much be greater for the starter to make the equation true.

Clear as mud?

Matt

[Patrick_M]

Hello Matt,

Excellent reply, I can totally understand that!

And, I just started reading/learing about Ohm's law, so although I do not
totally understand that yet, it's in there kind of mushing around trying to
take hold of those old gray matter (or is it grey matter) cells.

I finally got a chance to go out and purchase a couple of books for
beginners on electronics, and I'm loving it already. I wish there where
more time in life, I will never get to learn all I would like to before, well,
you know...

Thanks for the reply,
Patrick

[neilw20]

Just cover the term you wish to calculate. (based on (a/b x c) equals 1.)

E = Volts. I = Current(amps). R=Resistance(ohms). P= Power(watts)

1.
_E__ so cover E and that gives I * R
I x R

2.
_P__ so cover P and that gives E * I
E x I


3. Because E = I * R, substituting I * R for E in the above formula 2 gives..

__P __
I*I x R

giving
I = Sqrt(P / R)


4. Because I = E / R, substituting E / R for I in the above formula 2 gives.. (you figure out why)

_E*E_
P x R

giving
E = Sqrt(P * R)

Formatting text in this screen sucks like a vacuum cleaner.

[Wolfesmetalfab]

Ive been searching, and the cambell power supply link was just what I wanted. Does anyone have any good sources to purchase the parts from?

[Al_The_Man]

There is a ebay'er that makes Toroidal transformers, his on line store is Antek.
Al.