Need to discipate 1A. - Materials Question
Need to discipate 1A. - Materials Question
(OP)
This is pretty simple actually. I have a PLC that has a "light out" (LO) circuit that checks the filament of an incandescent bulb by intermittently pulsing the output. If there is no current draw, it sets a LO bit in the program.
I simulate the LO condition with an LED and a switch. I use a 15W 8ohm resistor to draw the required current.
My question is this...is there a discrete component that I can use to draw an amp (1A) that is smaller than a 15w resistor and/or produces less heat?
Any feedback is greatly appreciated.
I simulate the LO condition with an LED and a switch. I use a 15W 8ohm resistor to draw the required current.
My question is this...is there a discrete component that I can use to draw an amp (1A) that is smaller than a 15w resistor and/or produces less heat?
Any feedback is greatly appreciated.





RE: Need to discipate 1A. - Materials Question
TTFN
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RE: Need to discipate 1A. - Materials Question
The only other suggestions would be make the load something different.
A motor with a fan? The fan will help disperse the heat.
An LED - then some of the power will leave as light.
A buzzer - then a wee bit will leave as noise.
A battery charger - as then more than half will go into storage, at least until the battery is charged.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Need to discipate 1A. - Materials Question
If the load is present, 10 mA would be enough to tell that it's still there. And you don't really need to pulse it much longer than a millisecond.
TTFN
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RE: Need to discipate 1A. - Materials Question
RE: Need to discipate 1A. - Materials Question
My issue is that my simulator is heavy as hell and has a piece of aluminum that is covered with about 50 of these 15W resistors. In an effort to reduce the overall weight, I was trying to figure a way to reduce the physical size of the resistors while maintaining my 1A current draw. I know I am limited by physics here, but was hoping for some insight into some different components/materials that could perform the same task.
Thanks for all your help!
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James W. Hudgins, III
Southwest Signal Engineering Co.
www.swsignal.com
RE: Need to discipate 1A. - Materials Question
Bigger fins and fan. Component size is about heat removal.
TTFN
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RE: Need to discipate 1A. - Materials Question
You could shift to some terminal strips with resistors between screws.
Other info desired would be frequency of the "cold tests".
Duration of each test.
Current peak of each test.
This could all be found by using a scope across one of the existing resistors. (careful of your grounds!)
Keith Cress
kcress - http://www.flaminsystems.com
RE: Need to discipate 1A. - Materials Question
Thanks.
RE: Need to discipate 1A. - Materials Question
Alternately, since this is an emulator, there's no reason to actually run an amp through the resistors; you just have to fudge the PLC output to drive a lower current, and the feedback to the PLC to report the current current.
TTFN
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RE: Need to discipate 1A. - Materials Question
Some areas where you have not provided data:
1) Is the normal output voltage for the lamps 8V (hence 8 ohm resistor) or is that a test voltage?
2) Is the output current limited at 1A /does the PLC check for a short circuit?
Depending on the exact test conditions you may be able to reduce the real load resistors to small electronic loads.
RE: Need to discipate 1A. - Materials Question
If you really wanted, you could have a PC fake the inputs to your PLC.
TTFN
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RE: Need to discipate 1A. - Materials Question
RE: Need to discipate 1A. - Materials Question
He's running the resistors as the lamps. That means if a lamp happens to be ON the resistor will be getting a steady state ON and so needs to dump the X watts for a while. It's not just the brief "cold test". The "cold test" is just the part of the requirement that forces the actual current demand of the actual lamp loads. Otherwise he could use some 10mA LED stand-ins to just show the lamp activity.
There are no easy work-arounds that I can see. He was just hoping to cheat thermodynamics somehow. IR's use a fan/s and crowd the resistors together is about the only way to shrink this mess. I think the best solution for this test stand is to just mount it on a 19" vertical, single bay, rack mount and roll it around not carry it around. Then its weight wouldn't be an issue.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Need to discipate 1A. - Materials Question
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James W. Hudgins, III
Union Switch & Signal
RE: Need to discipate 1A. - Materials Question
RE: Need to discipate 1A. - Materials Question
RE: Need to discipate 1A. - Materials Question
But tell me what is the typical way you would mount these to a heatsink?
How would you connect to them??
Keith Cress
kcress - http://www.flaminsystems.com
RE: Need to discipate 1A. - Materials Question
RE: Need to discipate 1A. - Materials Question
The PLC can only receive voltages representing the behavior of the loads; it doesn't know where they come from or how they're generated. All you need to do is to program another PLC to generate the appropriate voltages at the appropriate times. This has the added advantage of being programmable for other scenarios or changes in the system.
TTFN
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RE: Need to discipate 1A. - Materials Question
Actually, duplication of the physical behavior is absolutely necessary. Testing of the program in the PLC is only part of the process. Simulating real-life characteristics of the bulb outputs is also imperative. The voltage levels for the bulbs are not dictated by the PLC but rather a driver card that reports health information back to the PLC.
I think Biff44 might have something there worth investigating with the real question being how to effectively sink all that heat.
Here are some pictures of my existing rig. Keep in mind the front plate is screen printed aluminum with LEDs/switches followed by a layer of Plexiglas for insulation and then the resistor network on an aluminum plate. Push/pull fan setup to remove heat from bottom to top. Kinda crude, but works very well.
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James W. Hudgins, III
Union Switch & Signal
RE: Need to discipate 1A. - Materials Question
Why do you want to make it lighter?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Need to discipate 1A. - Materials Question
Rich
www.MaguffinMicrowave.com
Microwave and wireless design consulting