Stators and heat? - Page 1
Forum section: electronics / beginners

author: Dave Wave
author_rank: Contributor
timestamp: September 19, 2018, 12:32:01 am
content: A theory question here:In boats and motorcycles, a stator coil and permanent magnet are used to generate an AC voltage (rectified to DC) for lights etc.....Does the load (or lack there of) have any effect on the temperature of the windings of the stator? Is the output of the stator a function of its design? That is to say the out put is just a function of design and RPM, so that you cannot get more than the rated output, so long as you stay within rated RPM. That is to say, one cannot burn out a stator by putting a load on it?Thanks,-Dave

author: Brumby
author_rank: Unknown
timestamp: September 19, 2018, 02:46:04 am
content: Quote from: Dave Wave on September 19, 2018, 12:32:01 amUnless the stator windings are made of superconducting material - the answer is very much Yes.Temperature rise will be dependent on the current drawn by the load and the resistance of the stator windings. No load means no current, so there should be no power lost and, therefore, no temperature rise in the stator. As load current increases, so do the stator losses and the stator temperature will rise.QuoteAbsolutely. However, like a great many electrical and electronic devices, heat is the limiting factor. One question is: How much headroom has the manufacturer allowed in giving the specifications for the design? Some manufacturers will cut it close and skimp on such margins to save a few pennies. The end result is that temperatures will rise to uncomfortable levels when high loads are presented - even when these loads are within the "specifications". Better made units will have heavier gauge wire with lower loss and, hence, lower temperature rise under the same load conditions.QuoteWell, not really. You certainly can get more than the rated output - but the amount of the extra you can get and the time over which you can do this without destroying the unit will depend on a couple of factors - the main one being heat.QuoteYes you can. By putting an excessive load on the unit, you can certainly burn out the windings. On some of the cheaper built units, you can do this even when operating within the specifications. They just design it well enough to (hopefully) survive the warranty period.

author: Gregg
author_rank: Super Contributor
timestamp: September 19, 2018, 05:46:14 am
content: The rules of thermodynamics have a way of always being in force in spite of a few claims otherwise. More power produced results in more heat produced because nothing is 100% efficient.In the real world of motorcycle and outboard applications that use a permanent magnet rotor and fixed coils in the stator, the available power varies with the engine rpm and the magnetic coupling. In a proper system, to keep the voltage within tolerances, the excess power is shorted out, dumped to ground or whatever way you want to visualize it. So in reality adding load to the system so long as it doesn’t pull the voltage down will only ease the burden on the voltage regulator. Too much load at a given rpm will pull the voltage down below the regulation threshold and put more load on the engine. While the regulator is regulating, overall power will be approximately the same.Without the voltage regulator, there may not be enough power to run lights and ignition at a low idle. Some systems have a separate set of coils for ignition separate from lights and battery charging functions while other badly designed systems merely boil the lead acid batteries.

author: Dave Wave
author_rank: Contributor
timestamp: September 19, 2018, 11:59:03 pm
content: So would it be correct to say that as the voltage drops (as the load increases)(rpm constant), the heat will increase?Thanks,-Dave

author: Brumby
author_rank: Unknown
timestamp: September 20, 2018, 03:07:26 am
content: Depends on the specific parameters of the unit. P=V.I is the way to work it out.But my general feeling is - yes.