On Tuesday 14 May 2013 20:38:32 John Kasunich did opine: > On Tue, May 14, 2013, at 03:08 PM, Gene Heskett wrote: > > So it looks like I need to design a 10 amp constant current load, > > switch mode of course. > > Does it really have to be "switch mode of course"? > > My favorite way to make a constant current load is just a > bunch of paralleled bipolars with emitter ballast resistors. > One extra transistor makes it a giant darlington to keep > the base drive requirement down. > > http://www.ebay.com/itm/TIP147-DARLINGTON-SILICON-POWER-TRANSISTORS-/380 > 590518156 > http://www.ebay.com/itm/10-x-Resistor-1-Ohm-5W-Cement-USA-Seller-Free-S > hipping-/221136085431 > > Mount the transistors to a chunk of aluminum scrap. > > Attached is a sketch of a similar circuit I drew up for a different > application. In that case, we wanted a constant current pulse > through a coil whose resistance varied as it heated up. The > op-amp allows for the pulse, and if the input divider is a pot > you can adjust the current. > > For motor braking you don't need precision and can really > simplify things. The 1K resistors are for current feedback, > they can go away. The op-amp goes away. Put four diodes > between the first transistor base and the "ground" bus. Two > of the diodes compensate the Vbe drops of the transistors. > The other two diode drops wind up across the ballast resistors. > For your application, I'd use 1 ohm resistors, and it would draw > about 1.2 amps per section. Eight or ten sections would give > you the current you want. > > A suitable resisitor from collector to the first base would bias > the diode string using the motor CEMF, so you don't need > any power supply at all.
Humm, I have some honking big copper heat sinks, with some big round bugs on them, but I don't think the bugs are rated for the expected voltage. I'm beat, ran the rider till the carb fell off (bolt came out) then finished the place with a weed eater I had to re-thread the spool on about 3 times, So I'm wasted. But I'll look the bugs up tomorrow & see if they'll stand the music. They should, on those heat sinks, be able to gobble up a 250 watt surge each for 10 seconds. ISTR they were either head wheel drivers or reel servo drivers in a VR1200 2" Ampex videotape machine, 30 years ago. Thanks John. Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> is up! My views <http://www.armchairpatriot.com/What%20Has%20America%20Become.shtml> He who enters his wife's dressing room is a philosopher or a fool. -- Balzac A pen in the hand of this president is far more dangerous than 200 million guns in the hands of law-abiding citizens. ------------------------------------------------------------------------------ AlienVault Unified Security Management (USM) platform delivers complete security visibility with the essential security capabilities. Easily and efficiently configure, manage, and operate all of your security controls from a single console and one unified framework. Download a free trial. http://p.sf.net/sfu/alienvault_d2d _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
