MWasko posted:I have a musical boxcar (6-26815) that pays off a 9v battery. It would be nice to have it play without having to remove it from the track since the on/off switch is under the boxcar. Would this second item(eBay: 253412786388) work at 9v?
Mark
As GRJ says, that receiver uses a 12V relay. The way that eBay receiver board is designed, you can replace the 12V relay with a 9V relay so that it would work with a 9V battery. You can buy the 9V relay for about $1 on eBay (search for "SRD-09VDC-SL-C"). But this does involve soldering rework of 5 terminals which may not be in your comfort zone. I suppose you could get lucky and find a receiver board with a 9V relay already installed...but I figure the 12V version (automotive applications and such) might be the only readily available variant.
A 2nd consideration for your intended application is the so-called stand-by power required by the receiver. In other words, it consumes 9V battery power 24/7 just listening for the radio control signal to turn on. As stated in the eBay listing, the standby power is somewhere in the 5 mA range. There's some tedious math that I'll skip over, but this basically means a 9V alkaline battery would deplete in a matter of days (less than a week) just sitting there doing "nothing"! But wait! There's more! Then, even if you're in the zone where the battery is still good, when you remotely activate the receiver relay to play the music, the active relay itself draws about as much battery power as the music player! So you'll be changing batteries that much more often. 
