Not the Usual 18v Question (9v series)

[mdame]

I have been thinking about a switch to toggle a 9v battery in series with the 9vdc jack for 18v instead of using 2 batteries.  That way i can still use just one battery at 9 or 18v.  Would this be bad for the 9v power supply?  Also, if I were using 2 9v batteries in series for 18v, and had the 9v adapter plugged in, would it damage the adapter?  Thank you.

[R.G.]

I have been thinking about a switch to toggle a 9v battery in series with the 9vdc jack for 18v instead of using 2 batteries.  That way i can still use just one battery at 9 or 18v.  Would this be bad for the 9v power supply? 

No. No problem for the adapter. The battery will still run down, but hey, it's a battery.

Also, if I were using 2 9v batteries in series for 18v, and had the 9v adapter plugged in, would it damage the adapter? 

Probably not. It may not be good for the battery that's connected across the adapter though. In effect, the adapter is charging the 9V battery. That may have various ugly effects depending on the battery chemistry.

[mdame]

Right, the switch would need to move back to the 9v position to preserve the battery when disconnecting the input.  Thank you.

[R.G.]

I think it may be simpler to just put in a charge pump doubler and switch it on when you want more voltage. One 8-pin DIP, three caps and some diodes.

And the switching.