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Current Sensing Resistors - Newb Help Needed.

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Jack.Straw

Member
Hello. I'm trying to build a battery charging circuit that calls for a current sensing resistor. I've purchased what I think is the correct resistance for my needs, but i've never seen one of these little buggers before. I've built my circuit on perfboard. Do i just glue this little guy to the perfboard and solder leads to either side? Or, am i supposed to use some sort of socket?

Here is the spec-sheet on the resistor in question:
http://www.koaspeer.com/pdfs/res7.pdf

Thanks for your time,
-Jack
 

smanches

New Member
Yes, they are just a simple surface mount package. Attach as you see fit, and glue the wires to either side of the resistor.
 

Jack.Straw

Member
Will heat from soldering damage the resistor? Is that why i use glue instead? Should i use some sort of conductive glue?

Thanks again!
-Jack
 

smanches

New Member
It's going to be harder to damage by soldering than many other components. It's just an accurate resistor, nothing really special about it. Just solder it like every other component.
 

MikeMl

Well-Known Member
Most Helpful Member
You need to do a Power Dissipation calculation: P = E^2/R.

Surface-mount resistors like this one rely on heat being conducted away from it through the copper traces that it is usually soldered to. If you are not using it on a PC board, you will have to solder it to a hunk of copper large enough to conduct the heat out of it otherwise it will over heat.

If you are quick, you can solder it to something without damaging it.
 

Jack.Straw

Member
So i should glue it to a piece of copper, then glue the copper to the perfboard, then solder my leads to the resistor?
 

MikeMl

Well-Known Member
Most Helpful Member
No, solder one end of the surface mount resistor to a piece of copper about the size of a US penny. Solder one wire to the penny, and the other to the floating end of the resistor.
 

zoodlewurdle

New Member
Another way is to make two close rails of heavy short wire from a mains cable and solder it so it bridges them. The rails can be soldered onto a fibreglass PCB first. And you might best solder two thin wires to it at the same solder points too, so the heavy ones carry the current but the voltage sensing is done through the thin ones so that changes in current don't affect the sense resistance itself as well as the voltage across it.

EDIT:
What I mean is, if you have a very low sense resistance, the heavy copper wires become part of it, so for accuracy, take thin ones to the business end to do the actual sensing.
 
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