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Old May 23, 2001, 01:28 PM
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Ralph Weaver's Avatar
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The circuit is easy, but you'll need some way to dissipate a lot of heat. That means multiple transistors and/or a large heat sink with a fan.

I have a schematic at home I'll try to dig up.
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Old May 23, 2001, 03:24 PM
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Rhode Island
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Yeah, I kinda figured something like this would need lots of big heat sinks. Not a problem.

As long as I don't need to install an HVAC system for it

Thanks!
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Old May 24, 2001, 12:32 AM
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Constant current load

Can anyone point me to a schematic for a constant current load? I'm mostly interested in something that draws ten amps with a source voltage of between 6 volts and 12 volts, and 20 amps with perhaps a bit wider voltage range.

TIA!
-Bob
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Old May 24, 2001, 08:44 AM
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I'd be curious about this too..
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Old May 24, 2001, 10:16 AM
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heat dissipation is not a problem. I drop my resistor bank in a bucket of water and when the battery discharging is done, I can make tea!! Also big heat sink with a fan. I made one(not constant current) for discharging 27 cells, I have a 5V fan on the heatsink with a 5V regulator fed off the discharging pack. WHen the fan stop, it is done. Also great for warming the shop in winter.

Brian
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Old May 24, 2001, 01:34 PM
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I was just kidding about making tea, I use about 2-3 gallons of water in a bucket and it probably raised the temp from 65 degF to about 80 degF when it is done.


Brian
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Old May 24, 2001, 06:19 PM
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Austin, Texas USA
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I came across a supply of 1.5 amp 12 volt automotive bulbs. Just wire them in parallel. Or, better yet, use the bases and you can add/delete bulbs to change the current draw.

Shawn
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Old May 24, 2001, 06:20 PM
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I came across a cheap supply of 1.5 amp 12 volt automotive bulbs. Just wire them in parallel. Or, better yet, use the bases and you can add/delete bulbs to change the current draw.
Problem is that no, it is not a constant current as voltage drops.

Shawn
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Old May 25, 2001, 12:01 AM
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Wilsonville, OR, USA
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Bob Kopski talked about one he has in his MAN column several months ago. He sent me a copy of his schematic but it wasn't finalized at the time. I don't understand electronics so can't complete it myself. Electrons still fall in the category of "magic" to me. The dissipation components are put in cold water. And he cautions don't let the water boil because the heat transfer stops!

Keith
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Old May 25, 2001, 06:15 AM
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Why not pulse the load?: say one second on nine seconds off. You can stress the battery in a realistic way at high current, without producing too much heat to dissipate.

Steve
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Old May 25, 2001, 07:43 AM
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Marietta, GA
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Voltage drop under constant load, as in flight, is the whole idea.. Pulsing it on and off will not be of much use (except when measuring battery performance for F5B-style flying, where the motor is only run for a few seconds at a time).
..a
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Old May 25, 2001, 08:29 AM
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Light bulbs, resistors etc. work OK to cycle the cells, but don't give repeatable results for serious testing. If you have the $$ you might check out the Competition Electronics Turbo 35+. It's what I use. 1, 6 and 7 cells up to 35A. http://www.competitionelectronics.com/trbothty.html

Building your own 10-40A will cost maybe $100-200 unless you can get a lot of the stuff surplus.
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