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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

schematic

simulate this circuit – Schematic created using CircuitLab

Practical Picture

Potential 9VBattery Circuit

Thanks guys!

chazalex
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  • You're going to be very, very unhappy if you try to pull 200mA from a 9V battery. Even more so if you use the resistor, since you won't even be getting 9V from it anymore. – Ignacio Vazquez-Abrams Mar 14 '15 at 19:18
  • If the thing is designed to operate from 9 volts, you should connect it directly to the battery - no resistor needed. However, as Ignacio indicates, a common 9 volt battery won't supply 200 mA for long. – Peter Bennett Mar 14 '15 at 19:35
  • Lets stop overanalyzing the current. Guitar peddles last alot longer than 2 hours on a 9V. Very common. – Passerby Mar 15 '15 at 06:07
  • Of course they last longer than 2 hr. It's not going to pull 200mA the entire time it's on. – DLS3141 Sep 24 '15 at 13:24
  • If you want an LED indicator, put it in parallel with the supply to the pedal and use a current limiting resistor. You'll increase your current draw by a few mA powering the LED though. – DLS3141 Sep 24 '15 at 13:30

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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.

Filek
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