On Friday, 6 March 2020 10:13:11 UTC, Michael Terrell wrote:> On Friday, March 6, 2020 at 2:36:11 AM UTC-5, Jeroen Belleman wrote: > > Michael Terrell wrote: > > > On Thursday, March 5, 2020 at 9:06:20 PM UTC-5, NT wrote: > > > > > >> Long ago I learnt that mains power was far more reliable than any > > >> battery. The ability to manually open & close will also be far more > > >> rleiable than any battery. > > >> > > >> I've not measured anything but suspect the motor is likely drawing way > > >> above 4A for tiny fractions of time. A 2.4v screwdriver motor that > > >> self limited to 4A on 5v wouldn't be a lot of use. > > > > > > Yes. That motor is an inductive load that takes more than the measured > > > stall current to start. > > > > I see DC motors as a big lossy *capacitive* load. Think about > > it: Initially, it draws a large starting current, which then > > progressively drops to more modest values when the motor > > comes up to speed and develops a back-EMF. The EMF persists > > when you disconnect, dropping exponentially as the loss > > consumes the stored energy until the motor is stopped. > > > I've never seen a wire wound, Permanent Magnet capacitor.Motors have long been run purely for their capacitive loading, though I don't recall them being pm. NT
Adapter fails to power DC motor
Started by ●March 3, 2020
Reply by ●March 14, 20202020-03-14
Reply by ●March 14, 20202020-03-14
On 2020-03-14 19:52, tabbypurr@gmail.com wrote:> On Friday, 6 March 2020 10:13:11 UTC, Michael Terrell wrote: >> On Friday, March 6, 2020 at 2:36:11 AM UTC-5, Jeroen Belleman wrote: >>> Michael Terrell wrote: >>>> On Thursday, March 5, 2020 at 9:06:20 PM UTC-5, NT wrote: >>>> >>>>> Long ago I learnt that mains power was far more reliable than any >>>>> battery. The ability to manually open & close will also be far more >>>>> rleiable than any battery. >>>>> >>>>> I've not measured anything but suspect the motor is likely drawing way >>>>> above 4A for tiny fractions of time. A 2.4v screwdriver motor that >>>>> self limited to 4A on 5v wouldn't be a lot of use. >>>> >>>> Yes. That motor is an inductive load that takes more than the measured >>>> stall current to start. >>> >>> I see DC motors as a big lossy *capacitive* load. Think about >>> it: Initially, it draws a large starting current, which then >>> progressively drops to more modest values when the motor >>> comes up to speed and develops a back-EMF. The EMF persists >>> when you disconnect, dropping exponentially as the loss >>> consumes the stored energy until the motor is stopped. >> >> >> I've never seen a wire wound, Permanent Magnet capacitor. > > Motors have long been run purely for their capacitive loading, though I don't recall them being pm. > > > NT >Free running synchronous AC motors can be made to appear capacitive or inductive, depending on the field excitation. That feature was used to provide power factor correction for certain industrial installations. These days they are largely obsolete. Jeroen Belleman
