Using 2.1mm DC and Battery power

[T1bbles]

Hey guys,

Quick question about powering effects. I use DC plugs which have two lugs, not three (like all of the diagrams I've seen). If I want to use a circuit with a battery aswell as DC, should I just wire it up as usual but connect the battery clip wires (+ and -) to the two (+ and -) lugs of the DC jack?

This makes sense to me as it would work with DC or with a battery, however, what if both were used at once? Would that make any difference? Would it be like using an 18V power supply? Am I being dim?

Thanks 

[Mark Hammer]

Any pedal which is intended for use with either battery or external power needs to use a jack for external power which selects between power sources and never permits them to sum.  A 2-lug jack will assume that no selection between takes place.

[GroovyMan]

I guess the hackers answer would be as long as you don't put the battery in when the power to the DC socket and vice-versa, you'll be fine. I'm not sure what would happen if you had both connected at the some time? I would imagine something bad would happen to the battery.

[T1bbles]

I understand what you're saying, but does anyone know exactly what would happen? I mean I've opened up my little big muff and that takes DC and battery and that DC jack is a 2-pin PCB mount one, no switched contacts. Unless the switch is an electrical one somewhere along the line.

[earthtonesaudio]

If your battery and adapter put out exactly the same voltage, the currents will simply sum and no problems.  However, since batteries drain, this is extremely unlikely to be the case at any particular time.  With 2 different voltages, they will fight each other, the result being something probably getting hot and possibly exploding.

There are ways around it with extra circuitry (resistors, diodes, even full logic circuits) but the easy simple way is just to use a switching jack, or not have battery as an option.

[T1bbles]

Ive come up with a fail-safe solution! Which is mostly common sense, but I thought I'd share anyways.

[puretube]

Those BA2RY-snaps love to carry the voltage anywhere, when not connected to the housing...
(e.g.: shorting to the chassis)

[MoltenVoltage]

Use a SPDT switch so you MUST select between either battery or adapter. 

[T1bbles]

Yea I'm gonna put somewhere to stuff the BA2RY clip, besides when using a battery it's not connected to anything.

I'd like to do the switch thing, but I don't have a switch to hand. The BA2RY clip and housing however I have got! Lazy