Re: ampacity question

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-uswest-dot-net>" <jimlux-at-earthlink-dot-net>

under oil, it is hard to say what the max current is.  What you are really
concerned about is melting the insulation off the windings.  As such, the
transformer design has a lot to do with it.  If it is designed so that oil
can flow in and around the windings, then you can put quite a bit of energy
into I^2*R losses and the temp won't come up all that much (think of those
oil filled 1500W heaters...)

Common design guidelines are 500 circular mil/amp and 750 circular mil/amp,
but those are for air cooled, standard winding (paper inbetween layers,
close wound, etc.).

The best way to answer the question is to do a small experiment.  Take a
small spool of the wire (which will likely be very tightly wound).  Stick it
in the bucket of oil. Run DC through it and measure the voltage and current,
from which you can calculate resistance (from which you can measure the
temperature of the wire).  Jack the current up and keep track of the
temperature (allow an hour or so for thermal equilibrium between changes.)
Ideally, you should wind a test winding in the same form that you intend to
use (it doesn't have to be full scale, just enough so that the thermal
properties are similar), put it on a core (wood is ok, iron is better, but
it's not a transformer, just a thing to make the oil flow characteristics
similar)


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, February 10, 2001 6:17 AM
Subject: ampacity question


> Original poster: "bob golding by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<yubba-at-clara-dot-net>
>
> Hi all,
>     I have a question about current carrying capacity of magnet wire for
> a transformer secondary. I get different ratings from different web
> sites. Father toms table says the following.
> 28 awg=0.319A
> 30 awg=0.200A
> 32 awg=0.124A
> 34awg=0.0795A
>
> Allen's home brew pig web site says
>
> 28awg=761mA
> 30awg=477ma
> 32awg=304ma
> 34awg=187ma
>
> anybody got any definitive numbers for a transformer secondary running
> under oil.?
>
> cheers
> bob golding
>
>
>
>