coils

[fanman]

hey guys and gals

 fanman here, my guestion today is about coils and heat, lets assume all the coils are wound and in place and connected, in delta(3 ins 3 outs) could i hook up a large variac transformer and start pumping the amps to the coils, of course they will start to heat up. could i place a temp probe in the center of the coil and watch the temputer rise, and could i use that heat rise to estimate the output of the machine, once it gets to a certain temp with out overheating, you could set your tail to furl at that temp point, does this sound too easy. of course you have to take into account the resin that is not around the coils yet but i suppose you could do the test after the resin was in and that would be more accurite

[Opera House]

If you have a good ohm meter, the temperature can be calculated.  Just sticking a probe in is not as accurate and may create a hot spot in other sections of wire.  Knowing the start resistance at room temperature, final resistance, temperature constant of copper, it is easy to calculate the temperature.  This is how I calculate the temperature of a relay at a stable operating condition when I do UL submissions. You would need a good voltmeter that gave you a valid reading of at least 2 1/2 digits or a constant current source of at least 100ma.

[Flux]

I think you will have to do the test after you have potted the coils.

It is difficult to judge how closely this relates to the real case. You will get a low figure by this method, temperature will climb for a long time before stabilising.

You will never get a constant full output in real life and you will also have more cooling from the wind.

If you measure with a probe it should be in the centre of the winding where the maximum heat is. If you measure temperature by rise of resistance it will give you a mean figure and the centre may be rather hotter than the outside so limit yourself to less than 100 deg C rise to make sure you don't exceed the wire rating at the centre.

This is certainly a good starting point but really someone needs to check this against a real life rating. Room for scientific experiment that would benefit us all.

flux

[SmoggyTurnip]

Can you do an example problem for us?

.

[DanB]

theyll cool a lot better in the wind.  The same alternator that happily produces 700 watts continuously on a tower can burn up fairly quickly on the ground.