From: jl@glen--canyon.com   
      
   On Fri, 19 Dec 2025 22:48:02 +0000, liz@poppyrecords.invalid.invalid   
   (Liz Tuddenham) wrote:   
      
   >john larkin  wrote:   
   >   
   >[...]   
   >>   
   >> Resistors are the best way to dump power.   
   >   
   >I once had to make a set of replacement resistors for the starter unit   
   >of a 5 kW blower motor that took quite a while to run up to speed   
   >because of its high-inertia load.  I had some slate bars about 2" x 2.5"   
   >and 18" long cut to order by a slate quarry; then hand-wound them with   
   >resistance wire .   
   >   
   >The original wire had broken into short pieces when the unit was   
   >destroyed by arcing but there was one piece long enough for me to   
   >calculate its resistance using a four-terminal measurement.  When I   
   >contacted the wire manufacturers, they supplied the exact replacement   
   >which was still in production despite the unit having been made in 1919.   
   >   
   >The windings were interesting, with several tappings and one section   
   >wound two-in-hand to handle a higher current.  The control gear was   
   >connected to the air outlet of the blower and, as the motor speed   
   >increased, a cast-iron chamber was pressurised.  This caused a leather   
   >bellows inside the chamber to collapse at a rate controlled by lead   
   >weights hung on a lavatory chain.  The belows pushed a rod which slid a   
   >set of brushes over some brass contacts on an ebonite panel and   
   >progressively cut out the resistors.   
   >   
   >The motor was interesting too.  It was a repulsion-start, induction-run   
   >motor, which is quite rare nowadays but was popular in 1919, before   
   >reliable starting capacitors were available.  It needed a major rebuild,   
   >including skimming the face commutator.  The shaft was so long it   
   >overhung the tailstock end of my lathe, so we had to support it on   
   >wooden 'V' block bearings and feed it with a constant supply of oil.   
   >   
   >A very challenging and satisfying job.   
      
   Sounds like fun.   
      
   I had to dump about 8 KW once. We used a garbage can full of water and   
   a coil of copper wire. Had to refill it now and then when it boiled.   
      
   Plastic garbage cans get wobbly when they are full of boiling water.   
      
   A PCB with etched or dremeled traces might be a good dummy load, with   
   forced air or water cooling.   
      
   There are HVAC things, nichrome duct heaters with fans, that are about   
   the cheapest dummy load you can buy.   
      
      
   John Larkin   
   Highland Tech Glen Canyon Design Center   
   Lunatic Fringe Electronics   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)