Re: Toroid transformer temperature

Most if not all modern winding wire is safe at a minimum 100C so the 80C quoted is a safe conservative estimate. Caudlet and I both used a reasonable approxiamation of 80C to avoid highly technical discussions that are heading off list.

Dave is absolutely correct about the technical procedure to establish mean temperatures of motors and transformers. The same procedures can be used to determine safe operating parameters for stepper (and other) motors if data sheets are not available.

When I have a little more free time I will do a post on how to accurately determine detent torque, holding torque and volts and amps for unknown stepper motors

Regards
Bob Thomas

--- In CAD_CAM_EDM_DRO@y..., Dave Martindale <dave.martindale@s...> wrote:
>
> > From: Chris L <datac@l...>
> >Subject: Re: Re: Torroid Question
> >
> >
> >Thanks Bob,
> >You make sense here.... Sure couldn't determine much without a long term
> >test. Obviously, If I ran it for a full day at moderate temps, that
> >would be pretty good.
> >I assume that we don't want to rely on "Fan Cooling" for a little more
> >ooomph.......
> >Do you have an opinion on what is a good target temp ?? Caudlet
> >mentioned 80C I believe....
>
> If you really want to know how hot the windings are getting, there is a
> standard test used with motors and transformers based on the change of
> resistance with temperature. You measure the winding resistance cold, then
> run the motor or transformer under some specified load (probably full load
> in your case) for many hours to get the temperature to stabilize, then
> measure the resistance again. Since the temperature coefficient of copper
> is known, you can calculate the average winding temperature.
>
> The Leeson Motors page at
> <http://www.iprocessmart.com/leeson/leeson_motor_temperature_article.htm>
> contains the formula and a bunch of other useful info. Although it's
> oriented to motors, I believe it applies to transformers too. Transformers
> are also built with different insulation classes and thus different ability
> to withstand heat. A transformer may be operating normally when it is too
> hot to touch.
>
> Dave