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Re: [TCML] quench times again
Hi Chris,
I confused myself, there "is" a relationship with frequency and the
transfer rate. I'll explain later.
Chris Swinson wrote:
Ok... So the coil was half the inductance, which halved the mutual
inductance which doubled the trasnfer rate which as a result frequency
was increases....
If the secondary is wound with very large wire, it's physical size will
really lower the secondary inductance due to the very few turns allowed.
Changing the wire size changes the geometry even if the h/d aspect ratio
remains the same. When I went from 24awg to 18awg in my example, I
changed the geometry of the wire a little which caused less turns and
reduced Ls. The fact that Ls changed was the major factor for the sight
change in the transfer rate.
The relationship with coupling and mutual inductance is
M12=k*sqrt(L1*L2). So if we change either inductance, mutual inductance
will change and we would then need to adjust k to get back to the
original mutual inductance. Javatc equates the mutual inductance and
then uses K=M12/sqrt.
To quickly verify, just run my default coil and look at the transfer
time and number of 1/2 cycles. Then, change the secondary wire size
to 18 awg at 516 turns (this will keep the geometry the same and
raise the frequency). You'll find the transfer time will change from
17.16us to 17.29us (hardly a change). Look how much L changes and yet
transfer time barely changes. You will find secQ increases and ACR
decreases (that big 18 awg wire wound in that geometry is why).
Then if you want, use the 24 awg wire and reduce the turns to hit the
same frequency as the 18 awg wire size case above (use 291 turns with
the 24 awg size and secondary change "height2" to 29.55). This will
be a geometric change at near the same frequency. Transfer time will
now decrease to 10.65us. Note what I did here was change the geometry
to cause a transfer time reduction and simply set it for near the
same frequency as the 18 awg frequency using 24 awg wire. In order to
do that, the secondary geometry needed to change (less wire, get
smaller).
In my testing I kept the coil geometry the same, by using thicker wire
and less turns, but physically the coil was the same size...
Repeating my self a little here.....
200khz DCR 0.010 L=61uH ML=134uH 27.5uS
400khz DCR 0.005 L=15uH ML=33uH 13.7uS
Ok, the large wire size has done two things which affect the transfer rate.
1) L is greatly reduced and this will change k affecting the transfer rate.
2) Frequency is increased and this will decrease the transfer rate.
Here is where I was wrong. Yes, frequency affects the transfer rate. As
the number of cycles increases, the transfer rate will increase. Here is
the relationship.
Total Energy Transfer = (0.5/((1/(1-k)^.5)-(1/(1+k)^.5)))*(1/fr)
So 2 things are altering coupling (K factor) then ? one the physcial
aspects of the coils, but also the mutual inducation. such as you
could have a 8" dia secondary and 12" primary and just assume this
has a K=0.1 , Though are you saying if the secodnary is kept the same
size, but reduced in turns and thicker wire, that the mutual
inductance would be lower and K would increase ?
Lower k will increase transfer time and lower frequency will increase
transfer rate. You can affect transfer rate either way. Of course, in
reality, changing one aspect is going to change more than just the one
aspect. An example is your own coil with the large wire. Due to the
larger wire, you have fewer turns, you have big changes in L and C and
so frequency follows. Frequency is certainly going to affect the
transfer time as is the coupling which has changed due to the changes in L.
I just wanted to clarify this situation between geometry (coupling)
and transfer time. Frequency is simply a result of the LC changes.
Note that coupling has increased! Geometry and position is why, not
the frequency.
Right, so I think frequency is related, but its the actual mutual
inductance which is the casue of the decrease in mutual coupling....
It's the change in the secondary inductance which changed the mutual
inductance.
It's the mutual inductance which changed the coupling.
It's the change in the secondary inductance which changed the frequency.
It's the frequency and coupling which changed the transfer rate.
It's all intertwined.
It is confusing..... as you can also reduce coupling by physically
making the primary larger which decreses coupling again, but makes the
transfer time longer ?!
Yes. Reduce k and transfer time is longer. Increase k, and it's shorter.
This can be done without changing frequency and usually is.
But if you decrease the secondary turns and use larger wire, it also
decreases coupling but energy takes less time
*confuzzled look*
Yes, it does. Inductance is the reason.
The larger wire decreases M, decreases k, and decreases the transfer rate.
Also,
The larger wire decreases L, increases Fr, and increases the transfer rate.
So, both will affect the transfer rate and depending on the "degree" of
the change, one will affect it more than the other.
I think I see your point to a point... higher frequency really is just
a by-product of altering all other factors... all those other factors
such as mutual inductance are the real "engine" behind the transfer
rate change...
No, I was wrong. I got caught up in terminology of coupling which is a
product of geometry and inductances and ignored the frequency. In most
cases we don't make a large enough change to greatly affect the transfer
rate as much as we do adjusting the coupling. In the case of your large
wire coil, there is ample change to make a difference and frequency does
affect the transfer rate quite a bit.
I'm sorry to confuse you on that one. This morning I had to take a
second look. Glad I did.
Take care,
Bart
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