"Radio Shack Current Sense Resistor"

[jtsuttle]

Can anybody here give me a little more detail on the "Radio Shack Current Sense Resistor" described on the last page of the Caswell anodizing manual?

My questions about it are:

Does this install inline on the positive side or parallel to + and - ?
Where do you attach the multimeter?
How many amps is it good for?
Is it left installed during the entire anodizing process?

Thanks in advance.

[NeoMoses]

I'll take a stab at this but since I don't actually use one, some of this information might be incorrect.

1. Place it inline with the + side

2. You attach your multimeter across the terminals of the resistor. Doing this, you will be measuring the voltage drop across the resistor and can calculate the current flowing through it by using Ohm's law, V=I*R. Since resistance is known and you are measuring the voltage across it, I=V/R. Using a 0.1 ohm resistor makes this a simple I=10*V. Other size resistors can be used, but you would ideally like to use a small one to minimize the voltage drop.

3. Buy a resistor based on the maximum current you plan on using. Since you buy resistors based on wattage, I would over-estimate the maximum voltage you plan on running a bit. 15Volts for LCD, 18 volts for standard. Use the formula P=I*I*R to calculate the power you will be passing through the resistor. For example, if anodizing at 10 amps with a 0.1 ohm resistor, P = 10*10*0.1 = 10 watts.

4. Yes, it's installed during the entire process.

Fibergeek, care to double-check my answers to ensure they're correct?

[Fibergeek]

NeoMoses, you have it right.

I would add that you should now be able to purchase a 0.1 Ohm, 10W 5% resistor directly from Caswell, its the one now included in LCD kits. 5% tolerance is OK for LCD measurements.

But if you are a geek like me, or you need more power:

0.1 Ohm 50W 1% from Mouser (www.mouser.com) or Digikey (www.digikey.com) for about $7.50 ea.

[jtsuttle]

Thanks for all the info guys! I think the amp meter on my supply is flaking out so I wanted to give it a checkup. This info will help greatly.