Ideas for shunting current with minimal heat generation
Ideas for shunting current with minimal heat generation
(OP)
I would like some ideas/suggestions on how to shunt current in a PWM circuit. The load on the circuit is not sufficient to shunt the amount of current necessary.
I need to shunt about 1.0 additional amps during the "on" cycle of the pulse. The duty cycle could be 40 - 60% and the frequency is approx 5 to 20 Hz. I could use a five ohm, 10 watt resistor but I don't have the space or the heat capacity.
It is hard to get around the physics of heat disappation, but I would like to know your suggestions. I need to fool the driver circuit into thinking that the load is drawing the current.
I am considering a peltier heater, but I'm not sure how reliable these are.
Criteria:
-Minimal heat gain (<1 watt)
-Minimal size (e.g. I can't use a 10 watt resistor due to size and heat constraints)
I need to shunt about 1.0 additional amps during the "on" cycle of the pulse. The duty cycle could be 40 - 60% and the frequency is approx 5 to 20 Hz. I could use a five ohm, 10 watt resistor but I don't have the space or the heat capacity.
It is hard to get around the physics of heat disappation, but I would like to know your suggestions. I need to fool the driver circuit into thinking that the load is drawing the current.
I am considering a peltier heater, but I'm not sure how reliable these are.
Criteria:
-Minimal heat gain (<1 watt)
-Minimal size (e.g. I can't use a 10 watt resistor due to size and heat constraints)





RE: Ideas for shunting current with minimal heat generation
I hope you're not considering a Peltier cooler as a load (as an alternative to the power resistor) because 'it makes cold...' In the context of your post, that's what it seems like...
Back to your question. Can you find the current measuring device (such as the 0.1 ohm resistor), and insert the false signal there?
...or do you need to really sink the actual current? Why?
RE: Ideas for shunting current with minimal heat generation
I don't have access to the measuring device, so I really do need to sink actual current.
RE: Ideas for shunting current with minimal heat generation
If you build it, please report back to us.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Ideas for shunting current with minimal heat generation
So how does this work? A Peltier cooler doesn't dispose of heat it just moves it an inch or two. They cost a lot. They are dimensionally constrained and they need a specific voltage. How's this help the project?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Ideas for shunting current with minimal heat generation
You say you need to dump 1 amp at, apparently, 5V ("I could use a five ohm, 10 watt resistor"). That means you need to dump 5W, period, end of statement.
Is this for school?
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
Chinese prisoner wins Nobel Peace Prize
RE: Ideas for shunting current with minimal heat generation
To 'shunt' current means to divert, create an alternate/parallel path and that sort of things. Does that mean that you want to connect something that loads the output with an extra ampere?
In power supplies, 'shunt' immediately makes you think current measurement device. And that is where I get lost. Which one are you talking about?
You say that "I need to fool the driver circuit into thinking that the load is drawing the current." That could be done without any heat generated simply by adding an offset to the current actual value. That is what VBL says when mentioning a 0.1 ohm resistor (the shunt).
Re the Peltier cooler. Do you plan to use the cooler as the extra load needed and at the same time use the cooler to move heat from circuit to ambient? Killing to birds (or is it flies?). Interesting thought.
Not knowing what your circuit looks like and still not sure what you mean by 'shunt', it is difficult to have any ideas on how to do this.
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Ideas for shunting current with minimal heat generation
Peltier coolers can be used to provide local cooling (like on a CPU), but they simply pumped the heat from one side to the other. And the power dissipated on the hot side is precisely equal (in the steady state) to the heat removed from the cold side PLUS the electrical power used in the process.
They're certainly not a load that doesn't "generate any more heat". That should be obviouse due to the fundamental rules learned in high school Physics.
RE: Ideas for shunting current with minimal heat generation
RE: Ideas for shunting current with minimal heat generation
Why do you need to shunt excess current with a PWM? Is the load needed to provide IC power from a bias winding? There are ways around this without having to put a load on the output.