I have a JamMan Solo XT loop pedal that is rated at 9V DC, 200mA. I want to make a really simple altoid tin battery pack. I'm checking with you guys because I don't want to damage the foot pedal with incompetence.
So if Pmax occurs at R1 = Rload, and Vload = Iload*Rload, then R1 = Vload / Iload which is 45 ohms. Is the circuit really as simple as this to make everything operate correctly and not damage the foot pedal?
Is it advisable to find an LED with 45 ohm resistance as a substitute for a standard resistor. Are there any resistor types that you might recommend?
Theoretical Schematic
simulate this circuit – Schematic created using CircuitLab
Practical Picture
Thanks guys!
Best Answer
I think that you are making things more difficult than they need to be. If I understand correctly you are trying to make a battery power supply that is capable of supplying 200 mA at 9 volts.
If this is the case, then you don't need to worry about adding resistors or LEDs to "force" the battery to supply 200 mA. Your pedal will draw the amperage that it needs (and no more) if your battery pack is capable of supplying it. By adding the 45 ohm resistor, you will actually cause a voltage drop across the resistor and as a result will not be supplying the needed 9 volts to the pedal.
You could imagine it is your pedal being the resistor with 45 ohms resistance - no need to add another. So you should be able to directly connect the battery to the pedal and your good to go - theoretically.
However, an alkaline 9 volt battery only has a capacity of 300-400 mAh. Your pedal draws 200 mA so you would only get 1.5 to 2 hours at most. In addition to this, as you draw current from the 9 volt battery, it's voltage will drop relatively quickly. The voltage might drop below a usable level even before the 1.5 to 2 hours.
I suggest that you consider 6 AA ( or C or D) in series which will give you the 9 volts and at least 2000 mAh capacity.