Will: I have learned much from it! That's why I like this list.
Gary, wa6fgi
----- Original Message -----
From: Will Matney
To: amps@contesting.com
Sent: Monday, April 18, 2005 9:08 PM
Subject: Re: [Amps] Hipersil, the myth and the truth. (Updated)
Norm,
Really, using the trade name Hipersil is a sales gimmik IMHO. When selling an
amp, one wants the customer to know it has quality construction to sell it. In
a way, it is technically correct to use Hipersil for the name, but if they're
not actually buying the core from the Hipersil owner, I would think it should
be just termed a C-core with M6 material. I cant say who Dahl buys from, but I
would think a U.S. supplier over the price due to freight. However, I know
several other transformer companies who make C-core transformers and dont call
them Hipersil but using the same materials. Actually, if I remember, Alpha, and
Henry, used other vendors for C-cores besides Dahl. Dahl is the only one who
touts using Hipersil, but Hipersil itself is no more as Westinghouse sold that
trade name years ago. I traced this down a few years back and found that a
European manufacturer bought the name and steel line out, I just wish I could
remember their name. I knew I probably wouldn't be bu
yi
ng it so I didn't consider it any further as I buy from Magnetc Metals who
have the same alloy. I was trying to think of another vendor in a previous post
besides Core Tran and it was Arnold Engineering I think who makes steel C-cores
too. I also know a guy down in Elizabethtown, Kentucky who makes them and has
done some work for some ARRL projects. They may be listed in the new ARRL
Handbook now, I'm not sure. Ed is the guys name but cant remember the company
right off, some of you might reading this. A friend of mine here was using him
to wind transformers for equipment they build for the transit and mining
industries. I spoke to him a few times and we talked about the ARRL project I
seen they did. It was a plate transformer for someone. You'll know his or
almost anyone elses work because it's not black. Dahl buys a varnish that has a
black dye in it. This supposedly helps take away heat. If it didn't run hot,
why would one need this? It will also hide a bunch of knicks
an
d bangs too! I looked at a large C-core dahl made that wasn't dipped and it
was made like everyone elses right down to the bluish fish paper wrapper. I
have a pic of it here I was just looking at today. On his website, he even
mentions adding the black dye to the varnish in some text. I had heard of doing
this before to help the core, etc. absorb heat from the coil. However, a
transformer for amateur service like used in most amps now should only be warm
to the touch and is the way every EI core transformer I wound ever acted, never
being hot enough to damage anything or burn you to the touch.
About mid way in the coil is where the heat builds up the worst. If it gets
too hot, where the wire makes the bends at the corners, it can make the
insulation crack and eventually fail. This was especially true in the older
transformers where the wire didn't have todays coatings. They actually make an
insulation paper with small sticks glued too it evrry so often to use just for
this. It allows an air gap for the heat to escape out of the windings. Large
transformers use sticks placed around the coil layers circumference for this
reason even if its oil cooled. That's one reason I prefer an open type
transformer without endbells, so the heat can come out. To me, endbells ought
not to be used unless for safety purposes. If a transformer gets overloaded a
good bit, it can just flat melt the wire in any place and a short takes place.
However, a lot of time this is the fault of the designer not using big enough
wire to handle the load.
I'm rattling on way too much about this, but figure some may get some benefit
from this discussion. Sorry about all the blabbing on.
Best,
Will
*********** REPLY SEPARATOR ***********
On 4/18/05 at 9:14 PM Norman Hockler wrote:
>Will Matney has exposed the hype about Hipersil.
>
>Very well presented Will.
>
>Norm N8NH
>
>
>
>At 11:01 PM 4/17/05 -0400, you wrote:
>>Hipersil, the myth and the truth.
>>
>>I was asked about a transformer using nothing but a Hipersil transformer.
>>I offered an EI type, M6 material transformer of the same specs, but it
>>wouldn't do. Well folks, this gave way to me writing this for all on what
>>exactly is a Hipersil transformer.
>>
>>Hipersil is a trademark owned by Westinghouse Electric for a type of
>>transformer core and material they manufactured at one time. Hipersil,
>the
>>material, is mearly a cold rolled, grain oriented, silicon steel with
>>about 3.5% silicon added. That's it, nothing more. M6 material is the
>same
>>material offered by several steel manufacturers, and is what Westinghouse
>>bought in large coils. M6 is the AISI (American Iron and Steel Institute)
>>number for 3.5% silicon steel which has been cold rolled, with the grain
>>oriented in the rolling direction.
>>
>>
>>What is cold rolled, grain oriented (CRGO)?
>>
>>This is a type of steel, which after being rolled out to a strip, or
>>sheet, is cold rolled again to where the grain of the steel orients
>itself
>>in a certain direction. What this does is drop the reluctance of the
>steel
>>to the magnetic flux, which in turn lowers its losses, nothing more.
>>
>>
>>Why add silicon?
>>
>>Silicon is added to control residual magnetism (core staying magnetized
>).
>>The thinness of the laminations controls eddy currents. There is
>different
>>grades of silicon steel, with varying amounts of silicon. On the lower
>end
>>is non oriented silicon steel (CRNO) which wasn't cold rolled for the
>>grain to line up like M50. On the upper end is M6 which is about the top
>>of the heap for CRGO steel without other alloying agents being added such
>>as cobalt ot nickel.
>>
>>
>>What is a Hipersil core?
>>
>>Well, there are many "Hipersil" cores if you want to call them that,
>>including EI cores, but the steel manufacturers just use the "M" numbers
>>to designate the steel. The proper question is what is a "cut core" or a
>>"C-core"? A C-core is made by winding a thin strip of CRGO or CRNO steel
>>around a rectangular or square mandrel in a lathe. The steel strip has an
>>adhesive on it so it will bond together after it is rolled to a certain
>>thickness. This strip can be several thicknesses where 14 mils is a very
>>common one. The very thin ones like 2 mils is for higher frequency work
>in
>>the audio frequency range. 14 mils is commonly used in power transformers
>>for 50 and 60 Hz.
>>
>>After the core has been wound to the proper thickness, it is generally
>>annealed to improve its properties, or some are pre-annealed. It is then
>>bonded so it cant come apart. Next, the core is transfered to a band saw
>>and cut in half. Each half is marked and then the cut faces are either
>>machined or ground for a close fit when put back together. This helps
>>eliminate the air gap if any.
>>
>>
>>Why is a Hipersil core touted to be better than an EI core?
>>
>>Well, there's a lot of myth and mis-information here. The only difference
>>between a cut core and an EI core using the same material is weight. This
>>weight savings is due simply to the corners being rounded off where an EI
>>core is rectanglar overall, that's it, nothing more. The weight savings
>>you'll get is from 15% to 20% just because the corners are rounded off.
>No
>>matter what, each type core has to have the same core area (A) in each
>type.
>>
>>A cores power handling ability (in watts or volt amperes) comes from its
>>ability to cram all the magnetic lines of force (flux) into a small core
>>area (flux density). Every core has a maximum flux density (Bmax) which
>is
>>determined by the cross sectional area of the core (A) and the material
>>the core is made from, nothing more. If this limit is exceeded, the core
>>goes into saturation. This means that any more increase in current does
>>not cause any more flux in the core. It also means that the cores
>>permeability drops off sharply at this point. The waveform becomes
>>distorted at the point of saturation and beyond too. A core is designed
>to
>>not saturate when maximum power is drawn from the transformer (this is
>not
>>the case in an inverter). Generally, a flux density is selected which is
>>just below Bmax at design time. Lets say the material gives a Bmax of
>>14,500 gauss. A working flux density of maybe 14,000, or 13,500 might be
>>used. However, this increases the weight of the core
>> because more iron has to be added to it to keep the flux density down.
>> This is why when selecting a transformer, you should figure the maximum
>> current in amperes to be drawn for each winding including losses. Losses
>> in most filtered power supplies run around 5% or so. The reason for this
>> is the designer trys to make the transformer as light as possible and
>> this in turn means they design the transformer to run as close to
>> saturation as possible without going over. On designing power chokes,
>the
>> DC portion has to be considered along with the AC to keep away from
>> saturation. The core can be gapped to correct some of this, but that is
>> more than what can be covered here at this time.
>>
>>What are the disadvantages to a C-Core?
>>
>>First and foremost is cost. The cost of pre-made cores is expensive
>unless
>>buying a large quantuty of each size. The mounting hardware costs more
>>than does on an EI core of the same size. The last, and an important one
>>is that a C-core runs hotter than an EI core of the same size. This is
>due
>>to the mass of iron being smaller than on an EI core, plus the fit of the
>>bobbin to the core. The only plus to a C-core is labor savings, and a
>>minor weight savings. It doesn't take as long to put together a C-core as
>>it does to stack an EI core. However, an experienced builder can go
>pretty
>>darn fast stacking the lams of an EI core, even being interleaved.
>>Actually, a tigther fit can be achieved of the coil to the core on an EI
>>core than a C-core, because of adding the lams, one at a time to the
>exact
>>thickness needed. With a C-core, you get the one thickness, that's it. To
>>make it fit, extra paper or wedges is used a lot. This also makes one
>heat
>>up more if the bobbin doesn't have a ti
>> ght fit to the core. This raises the cost of the mandrel used to wind
>> the coil as it's tolerances are tighter.
>>
>>
>>Is an EI core better than a C-core?
>>
>>In my opinion, Yes! The reason being is the heat. Heat is the killer of
>>all electrical and electronic components. I wouldn't care if the core
>>weighed 20% more as long as it lasted longer.
>>
>>
>>The above is just my opinion on the subject, and hope more have been
>>brought into the light on the differences between these two types of
>>transformers.
>>
>>Best,
>>
>>Will
>>
>>If you would like a PDF copy, please e-mail me.
>>
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>
>
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